ctor meYr"ERNATIONAL AUGUST 1981

INFRA -REDALARM

Wired SoundBench Power Supply

ecording Tapes &Tape RecordinAnatomy of a Micro

ein Bridge Oscillator

THE TAPSHOWN

HERE IS AHOLOGRAM

BUT BO1HHANDS AND

THE CUPARE REAL

electronics ltd

Send Certified cheque, Mastercard, Visa, American Express...include expiry date, card number and signature.We process C.OD.'s for Canpar or Canada Post.Minimum order $10.00.Add 5% (minimum $2.00) for shipping and handling.Ontario residents add 7% Sales Tax.ARKON ELECTRONICS LTD.409 Queen St. West, Toronto, Ontario M5V 2A5(416-868-1315)

Three good reasons to buy ahandheld DMM from Fluke.MODE D804:THE INVESTIGATOR Nine functions

dc voltageac voltagedc currentac currentresistancediode testconductance (1/R)logic level and

continuity detecttemperature (K -type

thermocouple) Peak hold on voltage and current functions Selectable audible indicator for continuity

or level detection 3 'Is -digit resolution 0.1% basic accuracy LCD display Overload protection Safety designed test leads Full year parts & labor warranty

FLU -D804 $339.95

MODEL D802:THE ANALYST Seven functions

dc voltageac voltagedc currentac currentresistancediode testconductance (1/R)

3'12 -digit resolution 0.1% basic dc accuracy Overload protection Safety -designed test leads Full year parts & labor warranty

FLU -D802 $258.95

MODEL D800:THE TROUBLESHOOTER

Six functionsdc voltageac voltagedc currentac currentresistancediode test

3'12 -digit resolution 05% basic dc accuracy LCD display Overload protection Safety -designed test leads Full year parts & labor warranty

FLU -D800 $172.95

1..FLUKE

LOW COST DMM'SFOR BENCH OR FIELDThe D810 and D811 are general purpose,bench/portable digital multimeters that are identi-cal except for power sources. The D810 operates online voltage, while the D811 is also equipped withrechargeable batteries that provide 15 to 40 hoursof operation depending on functions used.

Because these DMM's measure the true rms valueof ac signals, even complex inputs such as squarewaves and peaked waveforms can be measuredwith accuracy and confidence to 50 kHz ( *3 dB to200 kHz typical).

The wideband, low -noise measurement accuracyin these two benchtop multimeters is madepossible by a Fluke -manufactured hybrid rmsconverter.

31/2 LCD display Auto zero, auto polarity AC or battery operated models One year warranty Many other features not found

in other DMM'S!FLU -D810 $365.95FLU -D811 $418.95

(with Ni Cad batteries)

r

FLUKE DMM ACCESSORIESFLU -Y8205 Carrying case (FLU -D810, D811). 51.95FLU -C90 Carrying case (FLU -D800, D802, 0804) 15.95FLU -A81 AC adaptor (FLU -D800, D802, 0804) 29.95FLU -80J10 10 Amp current shunt 44.95FLU -Y8133 Deluxe test lead set 27.95FLU -Y8134 Deluxe test lead set with safety connectors 27.95FLU -Y8140 Slim test lead set 27.95FLU-80TI50C Temp. probe (C) 176.95FLU-80T150F Temp. probe ( F) 176.95FLU -Y8102 Sheath thermocouple (D804) 74.95FLU -Y8103 Bead thermocouple (D804) 34.95FLU -Y8104 Thermocouple termination (D804) 14.95FLU -Y8008 Touch and hold probe (D810, D811) 65.95FLU -80K40 40KV high voltage probe 115.95FLU-81RF 100 MHz rf probe 65.95FLU -801600 Clamp -on AC current probe 600A 136.95FLU -Y8100 200A AC/DC current probe 262.95FLU -Y8101 150A AC current xformer 108.95

Send $2.50 for ArkonElectronics 100 Page

Catalogue or pick it up inour store when you're in

our area. We have thelargest computer and

electronic hobbiest storein Canada.

Add 35¢ postage.

COME AND SEE US AT THE CNE!- We are exhibiting the newest productsIS xcei t ron i x from Multiflex Technology in the Better Living Centre at the Canadian National Exhibi

Component/ & Computing Inc. tion in Toronto, August 24 to September 7,1981. See you there!

319 COLLEGE STREET, TORONTO, ONTARIO, CANADA, M5T 1S2 (416) 921.5295

SVERSAFLOPPYDisk Controllerdvr

8 wngiety. 8 dousely and 5,

D SYSTEMSII VDB 8024 Video

Board_ 80 characlers by 24 lines- 7 by 10 metro

sided/double dens. - Upper/lower case. sette!.std./smote den. and user -programmablesmolt, sKled/songle characters

SBC200 Single -Board Computer

- Es ElaHOM an, is RAM_,,,,,,,.,..... PO POr ts- echannel counterbrner us

Z80 Starter Kit ing 280.CTC- Programmable baud rate

- ,iiei On general°, for ser ai port

,,.,,,,,,,,,,,,,,,,,,,- PROM OI.VA."'.- Kansas City standard $445cassette miertace- Prcors.on tor two S 100 caw EXPANDOPROMsires- Wire wrap are. EPROM Board

Memory Specials 45101 CMOS $4.49*

116-200nS $3.30*4116-300nS $1.95*

2708 EPROM $4.50** 2114L-200nS $4.25*2716 EPROM $7.25°° 2114L-450nS $3.49*2732 EPROM $16.9580 2102LFPC $1.69*

*10% off 8 or more piecesI

**10% off 16 or more piecesdens.ly may be used in any -Full cursor control - Monitor ROM provides

On board 280.CPU - is sockets. DP seoch seu1

cOmbinallon - and 26 memory/port exanune and- Comm! Ironware FAOM RAM table tor 2706 or 2716 EPROM-ay.lablechange CPU reV...A... ,1 lo 32K/Keyboard power and oter. and change. breakpointslace - 280CTC ana 280.PiO allow - Cen.... sesh SD$498 parallel 110 and vectored inter.

rusSystems Imsal. altaa. SOL 21,or Crornemco Z80 CPU cards

$539 -°;ll an board ',no .candable ;:'." 6g65'',',.a,°,.., 1'A:'::,', a°. 'to 21,

MPC4 4 -Channel $485MPB100 CPU $197Serial I/0 BoardBoard PROM 100 EPROM

-r wriaauAla:.,nd, - 5.100 compatobie Z80 Programmer EXPANDORAM II280.CPU rolcroprOceSSor board Memory Board- Real.orne does - 2 or 4 MHz opera., - Programs 2706. 2716 2732

and 2516 EPROMs 1,-. al I, or 4164 RAM cnips- Programmable baud rates tor - 4.1ou'et. 077Kee,m-18.9 to lo up t 15. on one 5100all ports y..,,, any 1K block , ,flee,,,,,, - 25V poprarnmIng pulseboard- 11, RAM on board - Socket lor 2K EPROM generaled o.boara- Bank select laature allows up-. control EPROM - Optional wait slates - Automatic yeolocation of pro to, boa,d, on Inc ,...n. po,

- FIFO Pullers on an 1,,,,, - Can be used wall many S-109 Warnrrao0 ..n,, erasure - Operates .1, Nal CPU, .1.- E59400400 RAM computers

-! SPECIALSON T.T.L

741500 19 7415123 75. 7415241 1 I.,74E501 19 7415125 .57 7416242 1 ,o741502 .25 7415126 .57 7415243 1 10741503 :iis 7415132 A9 7415244 1.10741504 25 7415133 .95 7416245 2 05741005 .25 7415136 57 7415248 1 39741608 19 7415138 73 7415249 1 25.

741509 .25 7415139 .62 7415251 67741510 .22 7415145 1.38 7415253 6974E511 25 74E5147 2.50 7415257 69741512 .25 7415148 1.59 7415258 72741513 28 7415151 .55 7415259 1 65741514 .50 7415153 .45 7415260 .95741520 7415154 225 7415266 45741521 2 7415155 85. 7415273 1 73

HamegOscilloscopes- The specials continue onGerman -made Hameg 'scopes

model reg. sale priceHM307 1550.00 $495.00HM312 S555.00 $789.00HM412 $1277.00 $1149.00HM512 52000.00 51795.00

A00res5$685 $348122

741526 50 7415156 9' 7415275 4 95r

$279 $319 741527 58 7415157 59 7415279 59741530 22 7415158 7415280 1 95741532 29 7415160 89 7415283 9971L537 35 7415161 75 7415290 92741538 .35 7415163 .75 7415293 48

MU LTI FLEXMultiflex Z80A Computer System- Sales of the multiflex Z80A system have been going so well that we are ableto offer the original kit price of $375 once again. We suggest that you get yoursystem quickly, however as our cost will soon force us to permanently in-crease the price.

$375 kit $475 assembled

741542 84 7415164 .75 7415298 1.48741547 .85 7415165 1.14 7415299 2.8974L548 .89 7415166 2.10 7415323 6.25741551 .25 741-5170 2.05 7415324 2.90741573 .39 7415173 15 7415365 .6774LS/4 .42 7415174 .49 7415366 .67741575 A3 7415175 .49 7115367 .65741578 .35 7415181 245 7415368 .65741583 le 7415190 .92 7415373 1.59741585 .95 7415191 .92 7415374 1.59741_586 AO 7415192 .62 7415375 .83741590 ,18 7415193 .82 7415377 1.59741591 le 7415194 .83 74153713 1.27741592 .59 7415195 .89 7415390 1.25741595 .59 7415196 1.09 7415393 1.25741596 .9 7415197 .09 7415395 1.497415109 .45 7415221 1.057415112 45 7415240 1.15

ASCII Keyboards- 106 keys: Typewriter -stylekeyboard plus numeric and cur.sor control keypads- Several control keys, user.definable through two PROMs- ASCII encoded- Power LED and remote pro -cessor reset switch included

$124.95

Multiflex Video/Graphics Board- Colour video graphics and character board based on the Motorola 6847. ThisS-100 board will work with many computer systems, adding several I/O func-Lions as well as video. But here's the clincher: A complete colour RF modulatoris included on -board! Price not yet available; please check with Exceltronix

,

IC Sockets: a penny a pin!- high quality low -profile solder -tail DIP sockets.

Available in 14, 16, 20, 24, 28, and 40 pin types.staff.

Multiflex 64K Memory Boards- S-100 memory boards, based on the 8202 memory controller from Intel. On-board refresh and bank select. Boards may be purchased with as little as 16K ofRAM and may be upgraded at any time to 32K, 48K, or 64K configuration.

$599 for assembled and tested 64K board. Please call for other pricingdetails.

Multiflex Logic State Analyzer- 16 bits, 1024 -word memory- 5 MHz operation- Equals or outperforms competitive analyzers costing 5 to 10 times its price.- Come in for a demonstration

$395 in kit form; $475 assembled and tested

Shugart Disk Drives- Single sided, single or double density 51/1"SA400 floppy drive- Soft or hard sectored $390SA450 - All the features of the SA400 (above) exceptdouble sided $580

SA801 R - Single sided, single or double density 8" flop-py drive- Hard or soft -sectored- Designed for side -by side mounting of two $685drives in a standard 19 -inch rack

SA85OR -All the features of the SA801R (above) but double sided $950_

Mail OrdersSEND A CERTIFIED CHEQUE ORMONEY ORDER (DO NOT SENDCASH). MINIMUM ORDER IS $10PLUS $3 FOR SHIPPING. ON-TARIO RESIDENTS MUST ADD7% PROVINCIAL SALES TAX.VISA AND MASTERCARD AC-CEPTED: SEND CARD NO.,SIGNATURE, EXPIRY DATE ANDNAME OF BANK.

Price PolicyREMEMBER THAT AT EX-CELTRONIX, ALL PRICES ARENEGOTIABLE FOR QUANTITYPURCHASES. IF YOU CANNOTAFFORD LARGE QUANTITIESON YOUR OWN, HOW ABOUTSTARTING A CO.OP.

Microprocessors and Support 4.358226 9498228 68251 6 4390

1802 10.99 8253 10.951822 9.95 2804.1)M4 . 138, J 39 8255 53931824 4.55 Z804510/0 5 '35 6821 3 39 8257 10.35

1852 1.95 2804,51011 35.95 6845 33.29 8259 10351853 1 85 211104.51012 3.39

Z804.510/935 95 685027 00 6852 3 39 6502 8.95

1771 19.95 2804.0ART 18.95130804 0.39

6506505 4 9.891791 79.95

8.35 65209 95

6800 5.99 8085 7452804 -CPU 9.49 6802 1155 8212 2.53 6522 10.252804-P10 9 89 6809 25.05 8214 4 39 6532 14 COZBOA.CTC 9 75 6810 173 8216 2 49 6551 14.05

ALL PRICES ARE IN CANADIAN FUNDS, 9% FEDERAL SALES TAX INCLUDEDCircle No. 22 on Reader Service Card.

ETI-AUGUST 1981

Electronics Today InternationalEditorial and Advertising Offices

Unit 6, 25 Overlea Boulevard,Toronto, Ontario, M4H 1B1

Telephone (416) 423-3262

Publisher and EditorHALVOR W. MOORSHEAD

Assistant EditorJOHN VAN LIERDE

Editorial AssistantSTEVE RIMMER

Advertising ManagerSENGA HARRISON

Advertising RepresentativeJIM O'BRIEN

Advertising ServicesCAROLYN WYATT

Subscription DepartmentBEBE LALL

NADIA HIJAZI

Accounts DepartmentNANCY ALLEN

Production ManagerTERRY FLETCHER

ProductionSARAH -JANE NEWMAN

CINDY BAKER

Contributing EditorWALLACE PARSONS

INTERNATIONAL EDITIONSElectronics Today International,

145 Charing Cross Road,London WC2H OEE, UK

Electronics Today International,Ryrie House, 15 Boundary Street,

Rushcutters Bay, Sydney, AustraliaElrad

Kommanditgesellschaft, BissendorferStrasse 8, 3000 Hannover 61, Germany

Electronica Top InternationaalPostbus 93, Bilthoven, Holland

ETI Magazine is Published by:Electronics Today International (Canada) LimitedNewsstand Distribution: Master Media, Oakville,

Ontario

SUBSCRIPTIONS$16.95 (one year), $29.95 (two years). For USadd $3/yr., other countries add $5/yr. Please

specify if subscription is new or a renewal.BACK ISSUES AND PHOTOCOPIES

Previous issues of ETI Canada areavailable direct from our offices for

$3.00 each; please specify by month, not byfeature you require. See order card

for issues available.We can supply photocopies of any article

published in ETI Canada; the charge is$2.00 per article, regardless of length. Please

specify both issue and article.

POSTAL INFORMATIONSecond Class Mail Registration No.3955.

Mailing address for subscription orders, undeliverablecopies and change

of address notice is:Electronics Today International, Unit 6,

25 Overlea Blvd., Toronto,Ontario, M4H 1B1.

COPYRIGHTAll material is subject to worldwide copyright protec-tion. All PCB patterns are copyright and no companycan sell boards to our design without our permission.

LIABILITYWhile every effort has been made to enaure that allconstructional projects referred to in thra-magazinewill operate as indicated efficiently and properly and

that all necessary components are available, noresponsibility whatsoever is accepted in respect of thefailure for any reason at all of the project to operateefficiently or at all whether due to any fault in the

design or otherwise and no responsibility is acceptedfor the failure to obtain component parts in respect ofany such project. Further no responsibility is acceptedin respect of any Injury or damage caused by any fault

in design of any such project as aforesaid.

ElectINTERNATIONAL

FeaturesRecording Tape andTape Recording 18There's more to tape recording than meetsthe eye, writhing magnetic fields leapingacross tape head gaps desparately tryingto impress sound on stubborn magneticoxide particles. We look at the ins andouts of tape recording and how they makea non-linear medium, linear.

Anatomy Of a Micro 25Everyone knows that the microprocessor

the heart of any microcomputer. ButMPUs have their own innards too andunderstanding the workings helps a pro-grammer to make them work better.Henry Budgett leads the tour.

L

5 40

5k0

I St

loP

12V

555 Astables On p 39

0OV

Holograms 31

Making seemingly solid objects out ofnothing is a pretty neat trick, but that'swhat holograms do. Anne Sullivan looksat lasers, interference patterns and othergood things.

0OUT

AUG UST 1981 Vol. 5. No. 8.

Tape ... Piles Of It. See p 18

Wein Bridge Oscillator 35Although they're somewhat difficult toimplement, Wein Bridge oscillators haveenjoyed great popularity. If you wantpure sine waves, you'll want to turn topage 35.

555 Astable Circuits 39By now, our readers have seen countlessarticles on the 555 timer IC. Undaunted,however, Ray Marston has taken bread-board in hand to describe some exoticways and means of extracting top perfor-mance from this versatile chip.

Into Electronics 55It's Part II now and Ian Sinclair discussesaudio signal processing including recordsand tape recording.

The ghastly, deformed creature on our covercould be a burglar, possibly invading the

home of some innocent victim to plunder ... the family jewels, the good silver ...

maybe even the holographic water faucets.Insidious cad! Actually, it's just one of the

editorial guys holding a flashlight. Find outhow to keep our editors out of your house

with the ETI infra -red burglar alarm, on page11.

ProjectsInfra Red Alarm 11More than just yer average electric eye,our Infra Red Alarm is designed to avoidfalse triggering from high flying moths orlow flying Concordes. Infra Red radiationmakes it invisible, dual emitters and detec-tors make it invincible!

Bench PSU 41Powering projects with batteries can bepricey at best, and unreliable at its worst.Plug into your local utility with our BenchPower Supply project featuring steppedoutput from 1V5 to 20 V at 1 amp.

Wired Sound 49If you thought that only 120 VAC comesout your wall outlets, you're dead wrong.With our Wired Sound unit, you canmake your own Muzak, listen to the babyin the East Wing or make a wireless inter-com.

ERNATION AI 1UGUS1 1981

INFRA -REDALARM

Wired SoundBench Power Supply Recordiug rapes &lope Recondinfkoatorny of Nlit to,Veot hr dgt, r ),,I1,gor

Electric Music On p 46

Cat Door, p66

ColumnsFun Of Electronics 28

What's New 46Steve Rimmer

Audio TodayWally Parsons

60

Tech Tips 67Our Readers

News & InfoNews 7Babani Books 16Tab Books 24Next Month 38ETI Specials 44Reader Service Card 44Alas! 53Subscriptions 54Classifieds 62ETI Binders 66

ADVERTISERS' INDEX

Active Component SalesCorp 10,72Amitron 66Arkon Electronics 2Audiovision 37Avalon Audio 34BCS Electronics 30,54,68Bryan Electronics 59,68Classified 62Dominion Radio andElectronics 6,7Duncan Instruments Ltd 8,48Dynamic Sound andComponents 65Electronic PackagingSystems 8,48Exceltronix 3HammondManufacturing 48,67,68Len Finkler Limited 71McGraw-Hill 29Newtronics 37,69Nu West Video Systems Ltd 8Orion Electronic Supplies 3413 -A -E Industrial ElectronicsLtd 66Se co Electronique 37,69Sheppard Agencies 37

Editorial QueriesWritten queries can only be answered when accom-panied by a self-addressed, stamped envelope.These must relate to recent articles and not involvethe staff in any research. Mark such letters ETI-Query. We cannot answer telephone queries.

BindersBinders made especially for ETI are available for$6.75 including postage and handling. Ontarioresidents please add provincial sales tax.

Sell Ell and ETI Special PublicationsETI is available for resale by component stores. Wecan offer a good discount when the minimum orderof 15 copies is placed. Readers having trouble in ob-taining the magazine could ask their local elec-tronics store to stock the magazine.

Component Notation and UnitsWe normally specify components using an interna-tional standard. Many readers will be unfamiliarwith this but it's simple, less likely to lead to errorand will be widely used everywhere sooner or later.ETI has opted for sooner!Firstly decimal points are dropped and substitutedwith the multiplier: thus 4.7uF is written 4u7.Capacitors also use the multiplier nano (onenanofarad is 1000pF). Thus 0.1uF is 100nF, 5600pFis 5n6. Other examples are 5.6pF = 5p6 and 0.5pF= Op5.

Resistors are treated similarly: 1.8Mohms is 1M8,56kohms is the same, f7kohms is 4k7, 100ohms is100R and 5.60hms is 5R6.

PCB SuppliersETI magazine does NOT supply PCBs or kits but wedo issue manufacturing permits for companies tomanufacture boards and kits to our designs, Con-tact the following companies when ordering boards.

Please note we do not keep track of what isavailable from who so please don't contact us for in-formation on PCBs and kits. Similarly do not askPCB suppliers for help with projects.

K.S.K. Associates, P.O. Box 54, Morriston, Ont. NOB2C0.B&R Electronics, P.O. Box 6326F, Hamilton, Ont.,L9C 6L9.WentwortMElectronics, R.R.No.1, Waterdown,OnL,LOR 2H0.Danocinths Inc., P.O. Box 261, Westland MI 48185,USA.Arkon Electronics Ltd., 409 Queen Street W., Toron-to, Ont., M5V 2A5.A-1 Electronics, 5062 Dundas Street W., Islington,Ont., M9A 1B9.Beyer & Martin Electronic Ltd., 2 Jodi Ave., Unit C,Downsview, Ontario M3N 1H1.Spectrum Electronics, Box 4166, Stn 'D', Hamilton,Ontario L8V 4L5.

535 Yonge Street,Toronto, Ont. M4Y 1Y5Phone (416) 922-1818No collect calls please

POTENTIOMETERSA huge selection available.Slider controls from 99c to$2.95; Single pots 49c (withswitch 59e) Dual pots 69c(with switch 79c). See ourcatalogue for full range andother types.

ETCHANT16 oz32 oz140 oz

$ 2.25$ 4.25

$14.95

eF00W001200150018002200680082010

CAPACITORSNISSEI POLYESTER FILM

Price2020202020202020

uF012015047056061308210

Poce20203030303030

0F0270033003900470056018022

Price20202020202525

uF021 25033 25039 2512 3515 4018 4522 50

CAPACITORSAXIAL LEAD TANTALUMS

DIPPED SOLID TANTALUMCAPACITANCE TOLERANCE - 20.,

WV% WV25 WV50 WV16 WV25 WV35uF SV20 SV32 SV63 uF SV20 SV32 SV46

1 25 0 2222 25 0333.3 25 047 354.7 25 0 68 35

10 .25 25 30 1.0 3522 30 30 35 15 3533 30 35 35 2 2 35

47 35 35 35 3 3 35100 35 40 50 4 7 35 35

220 35 40 55 6 8 35 35330 40 50 65 10 45 50 55470 45 55 75 15 50 55 851000 60 70 1 00 22 55 65 1352200 75 1.05 33 65 1.20 2 253300 1 05 1 35 47 1.95 2 754700 1 65 1 95 68 2 75

100 3 50

ZENERSTYPE itBZX61-C 751N4623IN751A1N4733AIN473414-515-04

114574IN753A

IN754AIN752A17-515-35HZ7B

N755A

IN74738A

N757AN4 739A

BZX61-C9V1IN757A

TTL7400 ... .45 7423 ... .55 7472 ... .55 74123..-1.107401 ... .45 7425 ... .65 7473 ... .70 74125 ... .987402 ....45 7426 ... .65 7474 ... .70 74141 ...1.157403 ... .40 7427 ... .55 7475 ... .98 74150 ...2.507405 ... .75 7430 ... .45 7476 ... .70 74151 ... .987406 ... .85 7440 ... .45 7485 ...1.40 74154 ...2.507407 ... .95 7441 ...1.35 7486 ...1.50 74160 .1.757408 ... .75 7442 ...1.35 7490..,1.15 74164 ...1.257409 ... .45 7446..-1.45 7491 ...1.15 74177.,,1.457410 ....39 7447 ...1.65 7492 ... .85 74190 ...1.657411 ... .55 7448..-1.75 7493 ... .85 74191 ...1.607412 ... .55 7454 ... .65 74121... .65 74192 ...1.557413 ... .85 7460 ....40 74122 90 74193 2 957420 .45

4000 SERIES4000 ... .50 4015 ... 1.50 4026 ... 2.35 4044 ... 1.054001 ... .45 4016 ... .50 4027 ... .85 4045 ... 1.784002 ... .45 4017 ... 1.50 4028 ... 1.50 4047 ... 1.094006 ... 1.25 4018 ... .75 4029 ... 1.25 4049 ... .454007 ... .20 4019 ... 1.65 4030 ... .40 4050 ... 1.504008 ... 1.15 4020 ... 1.25 4033 ... 1.95 4069 ... .45

4010 ... .75 4021 ... 1.95 4040 ... 1.29 4510 ... 1.954011 ... .65 4024 ... 1.25 4041 ... 2.05 4511 ... 1.954013 ... .65 4025 ... .40 4043 ... 1.30 4516 ... 1 354014 ... .90

MICROPROCESSOR

74LS00... .85 74LS32... .80 74LS109... .80 8080 ...8.9574LS04... .60 74LS33... .60 74LS125...1.00 8212 ...3.0074LS08... .65 74LS38... .80 74LS132...1.40 8216 ...3.5074LS10...1.50 74LS74... .70 74LS151...1.60 8224 ...8.9574LS11... .75 74LS75...1.10 74LS155.. 1.10 8228 ...6.2574LS20... .70 74LS86... .70 74LS247.. 1 18 8255 ...8.9574LS30... .65 74LS90.. 95 280..14.95 4116 ...7.95

14001600220025001000Can

4700Elec

4700Corn6800RPE

PC BOARD SPECIALSEpoxy Base PC6" x 61/2" 25(C ea.

13" x 4" 35c ea.13" x 6" 50c ea.

VOLTAGE WATTAGE3.3V 1W 1N758A 10 1W

4.3 1W IN759A 12V 1W

5.1 1W IN964B 13 .5

5.1 1W 3E216D5 14 1W

5.6 1W IN966 16 1W

6.2 1W BIX61-C18 18 1W

6.2 .5 HZ20C 20 1W

6,2 1W BIX61-C20 20 1W

6.8 1W GE5028 20 .1W

5.6 1W 14-515-31 22 .5

6.8 1W IN4751A 30 1W

7 1W BZX61-C30 30 1W

7.5 1W BZX 79-C36 36 1/2w

7.5 1W BIX61-C56 56 1W

9.1 1/2W IN5045 56 5W9.1 .5 BZX61-

C68 68 1W

9.1 1W IN4764A 100 1W

9.1 1W IN559313 183 1W

POWER SUPPLY16 65 6800 Com 2516 65 15000 RPE1016 .75 12000 Corn 4010 65 14000 Com 40

16 1.50 15000 RPE 1015000 Can 16

40 1.75 15000 Can 2515000 Com 50

100 8.95 44000 Corn 35

25 6.95 80000 Corn 20

6.954 506957 50

4.504.90

5.5011.95

14.95

14.95

LOGIC TRAINER . ....574.95MODEL DLT01A new development package for aBASIC DIGITAL LOGIC COURSE.Four gates and a counter. Circuit isincluded along with an in-depthmanual. Protoboard included.

STEREO PHONOPREAMP KIT $11.25MODEL EK8OSP001Anyone with a ceramic input receivercan enjoy the quality of a magneticcartridge with this simple but very ef.fective Stereo Phono Preamp.Specification, Standard RIAA, Fre-quency Response, 20Hz to 2KHz1.5dB. Input Sensitivity: 5rny inputfor 500mv output. Maximum Output:700my rms. Input Overload: 100myrms. SIN Ratio Greater than 60dB.

16 CHANNEL MULTI -MODE LEDCHASER KIT $32.95MODEL EK8OLCM16We're proud to add this to our line.it's similar to our 15 channel LEDchaser but with many extra features.There are over 60 selectable modes.A few: Up. Down, Skip. Pulse. Scram-ble. Single Pulse. Multi Pulse andmany more. An optional 120 vacboard is available (Extra)

RADIAL LEADOF

2.23.347

1022334710022033047010002200

WV16 WV25 WV50SV20 SV32 SV63

.2525

.25 2525 .25 2525 .25 2',.25 .25 30.25 .30.30 .30 3'i30 .35 4535 00 6040 .50

1..0060

75

STROBE LITE KIT . ....$21.95MODEL EK8OSLOO1Fantastic for special effects.Variable speed Xenon flash gives youa "STILL MOTION" effect. A realattention getter.

CRYSTAL RADIO KIT $8.95MODEL EK8OCR001A self powered radio which uses aresonant circuit and detector for AMradio reception. An ideal project forthe beginners.

1.5 to 24v POWERSUPPLY KIT 524.95MODEL EK8OPS024A variable Power Supply suitable formany digital and linear applications.Delivers an output current of 100ma.from 1.5v to 15v and 500ma. from 16vto 290.

0.24 VOLT POWERSUPPLY KIT $39.95MODEL EK8OPS028A trueO to 28 volts capable of deliver-ing ) amp continuous. Full wave rec-tification, filtering and capacitancemultiplication provides a clean dosource for sensitive audio and digitalwork. An ideal supply for the ex-perimenter.

TRANSISTORSPART No.2N2906 -BF -245

-

BF -199 -TIS 92 -BD136 -

BD135 -2SC1505-2SC1520-2SC1507-2SC1446-MJE2370-

AD161

2SC1304-2SC1104-2SD24Y -AD162 -

AD139

2N3614

8D182 -BU205 -

BU108 -

2SC940-

BF245A2SC945

2SC839

2N1613 -AC -187 -

REPLACEECG -159ECG -133ECG -199ECG -161ECG -128ECG -185ECG -184ECG -198ECG -198ECG -198ECG -198ECG -242

ECG -155ECG -175ECG -124ECG -124ECG -124ECG -131ECG -104ECG -175ECG -121ECG -162ECG -130ECG -165ECG -165

ECG -283ECG -163A

-133ECG -199EGG -199ECG -289ECG -123AECG -191ECG -289ECG -102AECG -128ECG -103A

1.791.991.151.592.402.992.792.953.002.952.953.59

4.952.952.592.592.593.991.893.503.959.954.799.959.95

11.9512.95

2.25.89.89

1.591.594.251.491.991.992.30

STEREO AUDIOMIXER KIT $49.95MODEL EK80AM001Inputs 2 phono, 1 aux. Master con-trol. Expandable. Frequencyresponse 20Hz-20kHz 5v output,0.01% distortion.

16 CHANNEL LEDCHASER KIT $22.95MODEL EK8OLC016A very familiar sight seen at discos.department stores, and on neonsigns. 16 LED's flash in sequence up -down or alternate. Adaptable to 120vac. (Extra)

POWER SUPPORT 120 524.95MODEL EK8OPLC120A 120 volt power board which allowsyou to connect regular lamps to ourLED Chaser Kits. 8 channels are sup-plied per board with 150 watts perchannel. They can be easily inter-faced for 16 channels.

5 WATT IC AUDIOAMPLIFIER KIT $19.95MODEL EK80A0OSA general purpose 5 watt amplifierwith Thermal Overload and Short Cir-cuit Protection.

DOMINION RADK): The Home of Radio and Electronics Supply

Circle No. 12 on Reader Service Card.

TRANSFORMERS8801S $8.95Primary 110V. Secondaries 700V r 150mA, 250V 0 50mA, 13.5V(-,/ 1.5A (Specifically designed for the 7984 transmitting compac-tron tube.)

2826500 $3.95Primary 110V. Secondaries 28V (it 2A, 6V a 500mA

24-10182.1 $14.95Primary 110V Secondaries 56 V (CT) qi 8A, 2V 0 2A. 6.3V (4 4A

24-101822 $14.95Primary 110V Secondaries 58V (CT) at 10A. 24V (a 2A. 6.3 (a 4A

321 TK $3.95Primary 1 120V: Secondaries 10V (CT) 500mA, 14V 0 500mAPrimary 2 120V Secondaries 20V (CT) 500mA. 28V ar 500mA

PHILIPSPHILIPS

tieSo'

ElectronDevicesDivision

DeForestQuality'

'Loudspeakers

Combi Plates (Squawker &Tweeter on Aluminum Plate)

AD21160ST8 Dram°. ColAD21161518 Flat Dash

Full Range40506108407062089710MC4012100MB

PassiveCones")

NS no

10 NI 530 W 720 W 825 Yv

Radiators ("Drone

Tweeters - Dome

Tweeters - Dome - FerroFluid

Tweeters - Cone

Squawkers (Mid Range) Dome

Squawkers (Mid Range) Cone

Woofers408000408001 Rubber Surround 12 00408002401000

Foarn SurroundRubber Surround

14 2534 50

4010900/W4012000

Foam 5urroundFoam Surround

15 0018 75 0001312.3310 6

401201 Rubber Surround 35 90 4000100W8 WOW 4013/

Cross-Overs AD80C3010/13AD110651353,4 6

ADF1500/8,4 2 way 9 754D8065216/8.4408067/1.301 4

ADF 1660/8,4ADF200033

2 way2 way

9 159 15

A06240033ADF3000014

2 way2 way

508 85

4D3W8SPADF6 55P

3 way hi Powery ..,e, 6. Power

31 5032 00

ADF 7 3SPADF500,4500i8ADF7002600,8/4

y way 6, Power3 wet,3 way

4101)40 4012240W0 WOW

ADF700 3000,8/4AD1SUBW

3 waySub Wooly.?

RESISTORSValues from 1 ohm to 10 meg. V. or1/2 watt Still Only 31/2,z each.

MINIMUM ORDER$10.00. All merchan-dise subject to priorsale. Prices subject tochange withoutnotice.

SHIPPING.Add 5% extra to covershipping, excess re-funded. Orders over$75 shipped pre -paid.Ontario residents add7% P.S.T.

NEW'

Computer PhoneRauland-Borg (Canada) Inc. hasannounced the Rauland TelecenterIll, a new microcomputer -controlled internal communica-tions system.

The RT 2002 AdministrativeTelephone System is all solid-state,has instant direct dialing bypushbutton handsets and requiresno central operator. A total of 110lines (10 administrative and 100staff stations) are available in thebasic system and this number maybe increased to 200 with a TAC 100Expander.

The system features a digitalreadout at each station and canstore and display up to 100 'call -ins'. Further enhancements of theRT 2002 are personnel tracking,conference call capability, zonepaging and a system -wide alarmcapability.

The Rauland Telecenter IIIRT 2002 administrative telephonesystem is available across Canadafrom authorized Rauland-Bord(Canada) dealers.

For more information, con-tact Rauland-Borg (Canada) Inc.,1361 Huntingwood Drive, Scar-borough, Ont. MIS 3J1

New Diecast Boxes

Hammond Manufacturing an-nounces a new line of improveddiecast aluminum alloy boxes.Good R. F. shielding makessmaller sizes excellent for R. F.connectors. The countersunk lidhas an interlocking flange and thebox is drilled and tapped forscrews provided.

The boxes have an attractiveground and tumbled finish whichmay by painted if required. Quan-tity discounts are provided whenthe ground and tumbled surface isnot required.

These boxes are available atall Hammond distributors.

Looking Back DoubleDice, June 81Inputs of IC2c and lC4c should bepins 11, 12 and 13 instead of 13, 14and 15 respectively. The outputs ofboth these gates is pin 10, ratherthan pin 12.

The PCB is correct .Thanks to Ted McLeod of

London, Ontario, loyal reader andfrothing dice friend, for this one.

Sinclair's Latest, June1981The article was a bit vague onavailability of the ZX81 inCanada. It isn't. The ZX81 willprobably makes its debut heresometime this fall. When it finallydoes arrive, rest assured we'll tellyou about it. Watch this space!

High PerformancePreamplifier December1979, Projects Book No.2It took a while for this overlay er-ror to come to our attention, butthe R133 just below SW3 (HICUT) is in fact R113.

TV "On A Chip"A 12,000 square mil silicon chipthat contains all of the signal con:ditioning circuitry for a completeblack & white television receiverhas been introduced by Motorola.This single -chip TV, trademarkedMonomax, houses all but thepower stages and the sound IFstage of the receiver and replacesfour separate chips commonly us-

ed to perform the same functionsin today's state -of -the arereceivers.

The circuit is designed to ex-ceed the most demanding stan-dards of today's TV design and in-corporates five Motorola patentedcircuit improvements that providesignificant benefits towards betterTV performance.

The new circuit is now beingmade available through allMotorola distributors.

7

DUNCAN INSTRUMENTS LTD

DUAL TRACEOSCILLOSCOPESMODEL MS -6021o Bandwidth DC -20 MHzo Triggered Time Base 0.5 uSec to 0.5 Sec per division

o Variable Delay Timeo Rise Time 17.5 nSeco 5 mV to 10 V per divisiono x5 magnifiero Internal graticuleo Operating voltage 115/230 VAC, 60 Hz

OTHER MODELS:MS -6020 (as MS -6021 but without delay time) $820MS -6040 (DC -40 MHz) $1800MS -6045 (DC -45 MHz) $1930

All prices FST IncludedIn Ontario, add 7% PSTFOB Weston, Ont.

COMPLETE "IN-HOUSE" SERVICESALES - CALIBRATION - REPAIR

MODEL MS -6021$940

DUNCAN INSTRUMENTS LTD.ELECTRICAL MEASURING INSTRUMENT SPECIALISTS

122 MILLWICK DRIVE, WESTON. ONTARIO M9L 1Y6TELEPHONE (416) 742-4448 TELEX 065-27271

lero

Circle No, 21 on Reader Service Card.

PRODUCTSAVAILABLEFROM:

Dealers for VERO:Waterloo Electronic Supply219 Hartwood AvenueWaterloo, Ontario

Psionic925 Crawford AvenueWindsor, Ontario

Noramel2407 St Catherine E.Montreal, Quebec

Kingston Electronic Supply147 Joseph StreetKingston , Ontario

General Electronics Limited5511 Yonge StreetWillowdale, Ontario

Exceltronix319 College StreetToronto,Ontario

R -A -E Industrial Electronics Ltd.11680 -170th. StreetEdmonton, Alberta

Cite ElectroniqueJean Marc Emond Inc.383 CanardiereQuebec,P.Q.

Kris Electronics Limited1070 Morrison DriveUnit 1BOttawa, Ontario

Cite Electronique Inc.3185 Rue HochelagaMontreal, Quebec

Interior Electronics Limited3102 -29th. AvenueVernon, British Columbia

Interior Electronics Limited1743 Springfield RoadKelowna, British Columbia

Interior Electronics Limited1304 Battle StreetKamloops, British Columbia

Cite Electronique Inc.918 Rue King OuestSherbrooke, Quebec

Atwater Electronics Ltd.886 Dundas Street E.Mississauga, Ontario

VERO Products distributed in Canada by:

Electronic Packaging Systems Ltd.P.O. Box 481, Kingston, Ont.K7L 4W5 (613) 384-1142

See our ad elsewhere in this issue.

X99 SOof,Kes

< S."94, < (<.`

High Gain Feed $210.

24 Channel Receivercomplete withRemote. $1950.

120° LNA withspecification sheet AT425$995.

Andrews 10 Ft. highgain antenna completewith feed and mount.$2495.

nJwU pi !go II

1604) 324 3343 Nu. West Video Systems Ltd.6590 VICTORIA DRIVE, VANCOUVER B.C. V5P 3X9

8

Circle No. 15 on Reader Service Card.

ETI-AUGUST 1981

NEWS

PowermosA significant advancement inN -channel enhancement modepower MOSFETs is announced byPhilips Electronics Ltd. Known asthe Powermos, it can be drivendirectly by microcomputer orTTL/LSI outputs - typically 5Vwith negligible drive power. Swit-ching speeds are 10 to 100 timesfaster than for conventionalbipolar devices. Present types cancontrol currents as high as 14amperes. Because of a positivetemperature co -efficient of 'on'resistance, the Powermos is notsubject to secondary breakdown, isthermally stable and can easily beconnected in parallel. It is par-ticularly suitable for inductive loadswitching. Typical applicationsare switched mode power supplies,motor control, household ap-pliances, consumer andautomotive electronics, measuringequipment and data processingperipherals. For more informationcontact Herb Parkes at PhilipsElectronics Ltd., 601 MilnerAvenue, Scarborough, Ontario,M1B 1M8.

f31"7. .4~ PACK

ZX-80Gladstone Electronics announcesthe availability from stock of twonew add-on units to extend the ver-satility of the ZX80.

A 16K memory expansionunit, termed a RAM -pack, simplyplugs into the back of the ZX80and extends the memory storagecapacity 16 -fold. Suggested price is$169.95, claimed to be half that ofcomparable memory expansionunits.

Also available is an 8K BASICROM which is a user plug-inreplacement for the original equip-ment 4K chip. This adds to theZX80 functions with full floatingpoint arithmetic, log and trig func-tions, programme storage andrecall by filename and controlfunctions for the ZX80 Printer. Ata suggested price of $59.95, the 8KROM comes with 200 pagemanual.

The ZX80 Personal Computernow has a new lower price:$299.95.

ETIDOUBLEDICEjune 81

MiceMice are these small brown fuzzythings that live in one's copydepartment and eat things withouttelling anyone. At least, that'swhat they do here. In the last fewissues a band of unusually vora-cious mice have consumed no lessthan four printed circuit boardlayouts and a reader service cardnumber. Munched 'em right offthe page, leaving not so much as ascrap of paper or a tip. Now andthen you can here them runningthrough the walls, belching con-tentedly.

Anyway, if you look on pageeight of our July issue, an ad forAllan Crawford Associates, youwill notice that the bottom of thepage contains the handy work ofseveral mice; no number for thebingo card. If you are interested inreceiving some information onAllan Crawford's new next dayshipment of their extensive line oftest gear, please circle No. 30 onthis month's card.

As for the PCB's, they arepresented here in totality, com-pleteness, and without teethmarks.

If any readers have a gooddesign for a solid state mouse trap,we'd be interested in seeing it.

ET!BIKESPEEDO

ETI-AUGUST 1981 9

LCtie

OlnFOLLOW THE SAVI

ROCKWELL INTERNATIONAL AIM65As a learning aid AIM65 gives you an assembled, tested and warranted R6502 basedmicrocomputer system with a full sized keyboard, an alphanumeric 20 character dis-play and uniquely, an alphanumeric 20 column thermal printer. An on board AdvancedInterface Monitor program provides extensive control and program development func-tions. 1K RAM.

Low price of $552.50 Attractive yet durable

plastics case for the AIM65 SAE1-1Reg. $95.00 $79.95

Power supply - BRUT-35MI 5V/24VReg. $95.00 $74.95

ROCKWELL MICROFLEX 65EXPANSION BOARDS - Microflex 65 productsmay be used with Rockwell's AIM 65 AdvancedInteractive Microcomputer for product developmentand desktop microcomputer applications.Contact the addresses below for further information.' AIM 65

THE NEW 1981 IC MASTEROne book - Two volumes five updates Bigger and better 150 manufacturers Two volumes cover the latest information on 50,000 IC's Master selection guides including digital, interface, linear, memory,

microprocessor, microcomputer board, custom IC's and microprocessordevelopment systems

Comprehensive alternate source directory listing 40.000 direct replacement parts Includes a discontinued parts index"IF YOU WORK WITH ELECTRONICS, YOU CANT DO WITHOUT IT!"

"BONUS OFFER" with every purchase ofthe 1981 IC Master receive the followingdata books, Hitachi IC Memories,

NEC 1980 Catalog,and Condensed CatalogTeledyne JFET Manual

Total book package value $150.99Our super special offer 99.99You save 51.00

PeL .10 - FP pattern

.10T

VECTORBORD1VECTORBORD stands for quality. Government and industry standards are based onthis material which is now available through distributors to hobbyists, engineers andexperimenters."P" PATTERN. Boards with "P" in part number are ideal for building circuits usingintermixed DIPs and discrete components. The .1" spaced holes accommodate solder -able terminals, and wrap post terminals. DIPs and many other components may also bemounted directly to the board without terminals.64P44ELDP epoxy glass composite, 4.5' x 6.5" x 1/16" $ 3.95 ea64P44-062XXXPDP Phenolic, 4 x 5" x 6.5" x 1/16" 2.95 ea79P44ELBDP epoxy glass composite, 4.5" x Er x 1/W 4.95 ea169P44ELDP epoxy glass composite, 4.5' x 1T x 1/W 8.95 ea169P84-062DP epoxy glass composite 8.5" x 17" x 1/16" 14.95 ea

ETCHED CIRCUIT MATERIALS + positive photo resist boards:CU65/45-1RDP 6.5" x 4.5" phenolic, 1 oz. copper, 1 side. 7.95 eaCU70/45WE-1RDP T x 4.5" epoxy glass, 2 oz. copper, 1 side. 11.95 ea

DEVELOPER - Positive acting; developer must be used with + positive actingresist coated boards. 1'/. ounce (enough for at least 200 square inches). Part number0088-21-15OP. $2.95 eaR407DP RUB -ON RESIST ARTWORK - Includes DIP and other IC patterns, lines,pads, edge connector contact pad sets. Rub onto mylar film master for use with photoresist boards. Rub directly to copper for direct transfer type board. Includes four sheets5" x 5.5". $5.95 ea.

+ POSITIVE 32X-1DPPRINTED

CIRCUIT KITNo other materials needed,

except UV light source.Easy to prepare artwork with direct

positive materials - nonegative. $29.95 es

Kit contains: two copper clad (one side)boards: one + positive photo -resistcoated, one uncoated direct transfertype: four sheets of up-to-date circuitsymbols, lines pads, IC pad sheets andreference markings, plus burnishing tool;mylar film for master circuit pattern;opaque mask cutting film; glass pressureplate: developer and etchant with tray foruse: etch brush, razor knife: layoutpaper, instructions.

NGS DIRECT TO BACK COVER

SYNERTEK® SYM-1 Full Documentation - Two Manuals SY6502 NMOS 8 -Bit Microprocessor Five On -Board Programmable Interval Timers 28 Key Keypad Six Digit Display 4K Byle ROM SUPERMON Resident Monitor, User Expandable 1K Bytes of Static RAM provided, expandable to 4K Bytes On -Board with Sockets

Provided User PROM/ROM for up to 28K Bytes of Low price of $318.50

User Program Applications In

- Training - Engineering - Prototyping- Instrumentation - Testing - Experimentation

Expansion Port for Add -On Modules ......"' Requires Single +5V Supply ti-,--- 32 Character Single -Line

Oscilloscope Display Same Hardware Interface Busses

as KIM -1 (MOS Technology) Dimensions 8.25 in. x 10.72 in. Power Supply for the SYM-1 5/10 volt power SYM-1Vector 22/44 Pin Plug Boards for the experimenter. Expand your system's capabilitiesyourself! Compatible with the AIM -65 and SYM-1. 3682-2DP $ 19.95

IryAMoto=

OHIO SCIENTIFIC SUPERBOARD IIThe ideal starter computer with full expandability. A complete system on a boardincluding a full keyboard, a video monitor interface, RS232 and cassette interface,DAC, 8K BASIC -in -ROM, and 4K of static RAM. Requires regulated 5V at 3 amps and avideo monitor or TV with an RF modulator.Accessories - 610 board with 8K RAM expandable to 24K disc interface

- Floppy disc 5", 90K storage- 630 board with color and I/O capabilities- Assembler/editor in machine code in cassette with manual- Extended monitor in machine code on cassette with manual- Special graphics characters- Fully assembled and tested tr.:)1k.

Active Package - Superboard II with Extra 4K mem-ory $449.95

Accessories available:610-8K --8K expansion RAME330 Board - Expander board general purpose I/O

board with RGB colorCD -3P - Single 5" mini -floppy mounted in caseContact addresses below for further information.

SUPERBOARD II

STATE OF THE ART BOOKS FROM TEXAS INSTRUMENTSTTL data book/LCC4112 $12.19Transistor and diode data book/

LCC4131 21.85Power data book/LCC4041 14.99Voltage regulator handbook/

LCC4350 4.25Integrated circuits data book/LCC4330 11.28

MOS memory data book/LCC4782

OPTO electronics data book/LCC4231

TMS 9900 series data book/LCC4400

4.48

5.83

16.15

Texas Instrument Understanding Series. Understanding Solid State Electronics.Understanding Digital Electronics. Understanding Calculator Math, UnderstandingMircroprocessors. Understanding Communication Systems.Total package value $35.40Active Special 29.95You save 5.45

SUPER SUMMER SPECIALS

HEWLETT PACKARD 7 SEGMENT BUBBLE DISPLAYPart No. 5082-74332.79 mm (.11 inch.), seven segment GaAsP numeric indicators.Applications include hand-held calculators, portable instruments, digital thermometers,or any other product requiring low power, low cost, minimum space, and long lifetimeindicators. $6.44 ea.Super L.E.D. sale. T 1'4 RED. 100 pcs $7.95 200 pcs. 514.95 500 pcs $34.50TRIMMER POTENTIOMETER'S (Thumbwheel Adjustment). Available values inOHMS: 100, 250, 500, 1K, 2.5K, 5K, 10K, 250K and MEG.I10-90 pcs. .12 ea, 100-499 pcs, .10 ea.'I. watt and '/: watt resistors available. 5% bulk pricing. 'I. W $8.90 per thousand.

W $9.95 per thousand. Minimum 1000 per value.

MINIMUM MAIL ORDER $10 00Arkl 53.00 to cover postage and handing

PRICES ARE IN CON FUNDS FOB CANADAFederal Sales Tax Inc'Provincial Sales Tax Extra

5651 FERRIER STMONTREAL. QUEBEC114P 21(5Tel 15141 731.7441

BAXTER CENTER1050 BAXTER ROADOTTAWA. ONTARIOK2C 3P2Tel 16131 820.9471

LARGE INVENTORY AT ALL LOCATIONS

STORE HOURS'Monday to Thursday 9.00 am - 600 pmFriday 900 am - 900 pmSaturday 9 00 am -530 pm

VISA ANDMASTER CHARGEACCEPTED

4800 DUFFERIN ST 5809 MacLEOD TRAIL SDOWNSVIEW. ONTARIO UNIT 109M3H 559 CALGARY. ALBERTATel 14161 661.1115 T2F1 0J9

Tel 14031259-6437

3070 KINGSWAYVANCOUVER. BCV5F1 5J7Tel (604) 4383321

rflActiveCompotstror!

Circle No. 5 on Reader Service Card.

INFRA REALARMA project to help you sleep nights: Our IR Alarmwill warn you of intruders or of the wife raidingthe ice box.

THIS UNUSUAL infra -red beam alarmproject has a maximum useful rangeof about 10 meters and can form thebasis of a first-class domestic orcommercial security alarm system.The project comprises two units -an infra -red transmitter and an IRreceiver with a relay output. Both ofour prototype units are line powered.The receiver unit contains facilitiesfor operating the relay in either thelatch or non -latch mode and for exter-nally disabling the relay (for 20seconds) via concealed 'by-pass'switches so that authorized persons canpass through the beams without ac-tivating the alarm.

The most unusual feature of ouralarm system is the use of a dual -

beam infra -red link. The two beamsare spaced a few inches apart andboth beams must be brokensimultaneously to operate the alarm.Our system thus responds only to ob-jects greater than the dual -beam sizeand cannot normally be false -triggered by moths or other insectspassing through the beams or settl-ing on the transmitter or receiverdiodes.

IRBeam PrinciplesInfra -red beam systems present a cer-tain paradox in that the beam is notparticularly directional (the transmit-ter and receiver do not need to bepointing directly at one another) yetthe actual 'link' is highly directionaland can be broken by a matchstick -sized obstruction placed anywherealong the link. To understand theparadox, try the following simple test.

Pick out a spot -size object (aspot of paint or a screw head, etc).Now move around the room, notingthat the object is visible from manydifferent angles and that the visualcommunication beam is thus not par-ticularly directional. Now, from anyconvenient viewing position, look atthe object with one eye only andmove a finger into the line of sight.

The object is obscured - the visuallink is thus highly directional. This isa good analogy of a conventionalsingle -beam IR system, with the ob-ject acting as a single IR source andthe eye as a single IR detector. Thissystem is susceptible to false -triggering by moths or other small in-sects that stray into the beam or set-tle on the transmitter or receiverdiodes.

Make Milne A DoubleNow take the above visual test a bitfurther and pick out two spot -sizedobjects that are spaced roughly 7.5cm apart and again check that theyare visible from many differentangles. Now look at the objects withboth eyes and try to break the visuallink by moving various items into theline of sight. You'll notice that thevisual link can only be broken by asolid item with a width greater thanthe spacing of the two objects (7.5cm), but that this item can break thelink if placed anywhere a ong the lineof sight.

This latter test is a good analogyof our dual -beam alarm system, withthe two object spots acting as thetwo IR sources and the two eyes ac-ting as the two IR detectors. Oursystem can only be activated by ob-jects greater than a certain size and

cannot normally be false -triggered bymoths or other insects that stray intothe beams or settle on the transmitteror receiver diodes. The beams are notunduly directional and do not requirethe use of lenses to complete the IRlink, so installation is simply a matterof roughly pointing the transmitterand receiver towards each other.

Transmitter ConstructionThe transmitter construction shouldpresent few problems. We used twoPCBs on our prototype, one for theline power supply and the other forthe actual transmitter circuit. Takethe usual precautions over compo-nent polarity when assembling theboards and use sockets when moun-ting the two ICs.

When PCB construction is com-plete, make all necessary inter-connections, taking special care toensure that the two infra -red LEDsand LED 1 are fitted with the correctpolarity. Now switch on. If all is well,LED 1 will glimmer dimly, indicatingcorrect transmitter action. If you havea 'scope you can check that the cor-rect output waveform is generatedacross the two IR LEDs.

The completed unit can now befitted in a suitable case, with the twoIR LEDs pointing out from the boxfront. The IR LED spacing determines

ETI-AUGUST 1981 11

INFRA-RED ALARM

the minimum object size that will bedetected by the system; we used aspacing of about 4 cm on our pro-totype unit.

Receiver ConstructionThe receiver unit also uses two PCBs,one for the power supply and onelarge board for the preamp/mainreceiver. Some care is needed in theconstruction of the large board, dueto the use of a compact layout andminiature components.

When construction of the boardsis complete, fit them into a suitablecase, together with T1, and make allnecessary interconnections, takingspecial care to ensure that the twoIRDs are connected with the correctpolarity. The connections betweenthe IRDs and the large PCB should bekept as short as possible to avoid un-wanted pick-up. The IRDs should bemounted on the front of the cases,with the same spacing as used for thetransmitter IR 1LEDs.

Setting UpWhen construction is complete, setPR1 and PR2 to mid -value and enable

C3

L--

IR LED1ANODE

LED1CATHODE

the relay in the non -latching mode.Now space the Tx and Rx a meter ortwo apart, roughly facing oneanother, and turn the receiver on, butnot the transmitter. The relay (RLA)and LED 1 should turn on after adelay of about 20 seconds, indicatingthat no IR signal is being received.

Now turn on the transmitter andcheck that the relay and LED 1 turnoff. Reduce the setting of delay con-trol PR1 until relay 'chatter' starts tooccur, accompanied by flashing ofLED 1, and then turn PR1 back untilthe chatter/flashing ceases. Thispoint marks the minimum delay set-ting that can be used with the system.

Now temporarily cover (with afinger) the face of one of the IRDs,reduce the setting of sensitivity con-trol PR2 until RLA/LED 1 turn on andthen turn PR2 back slightly past thepoint at which both components turnoff. You should now find that RLA/-LED 1 turn only when both IR beamsare broken simultaneously. Theswitch -on delay can at this stage beincreased beyond the minimumestablished value if required.

T2

Fig. 1 Circuit diagram of the transmitterand its own power supply.

+9V)' LED1

4r \

IC2 iro.

ANODE

0 C2

''.... ~ 11.- OV

IR LED2CATHODE

46.

The two IR LEDs and IR detectors aremounted in the case ends.

49m1".

SS

TRANSMITTEDOUTPUT WAVEFORM

rxENAA TING

FLAT

0 °9% 91/ °....;°7W1 +LD271 CONNECTIONS

T: B1: 9V

-L-

C'Tos,BATTERYSUPPLY

0BV

NOTESD1 D2 ARE 1N414801 IS 2N2904Q2 IS MPS6566IC1 IS CD40118IC2 IS ICM7555IR LED1 2 ARE LD271

12 Fig. 2 Transmitter component overlay. ETI-AUGUST 1981

IRDt

1 C6z lor

1002A

RIO1001

R1110k

C/

AAA CB270p

1+ C9oT 72.

1,41,1

IMO

RI3171

2

P

7k

IC3

PR227kSENS

Fig. 4 Circuit diagram of the receiverpreamp.

Fig. 3 Transmitter power supply compo-nent overlay.

+9V OV

±-

A CI11n5

C) SENSITIVEFACE

K

SFH206CONNECT1OS

020618

2015V6

R2410k

02327k

NOTE04 I36 ARE 1N41401051 IRO2 ARE SF/4205CO1 -105 ARE CA3140

075417

IC

02612k

O

O

TO MAINRECEIVERUNIT

PROBLEMS? NEED PCBs? Before you write to us, please refer to 'Component Notations'and 'PCB Suppliers' in the Table Of Contents. If you srill have problems, please address yourletters to 'ET; Query, care of this magazine. A stamped, self addressed envelope will ensurefastest reply. Sorry, we cannot answer queries by telephone.

AC

HOW IT WORKSThe IR transmitter beam signal comprises 1 mSbursts of 20 kHz pulses, repeated at 50 mS inter-vals. The transmitter generates peak IR diode cur-rents of 600 mA but, because of the widemark/space ratio (1:50) of the transmitter signal,the mean transmitter current is a mere 6 mA. Thiscurrent can be provided by either a battery or aline powered supply. Both options are shown inthe circuit diagram.

The basic transmitter signal is generated byICI and 1C2. IC1b-ICIc are wired as a non -symmetrical astable multivibrator producing alter-nate periods of I mS and 49 mS. The output ofthis astable is buffered by ICId aid used to gate20 kHz astable IC2 on and off via D2. Theresulting waveform is used to gate 600 mAconstant -current generator QI-RI-LED 1 on andoff via ICI a and Q2 and thus feed high energisingcurrents to the two series -connected infra -redtransmitter diodes. The high -current transmitterpulses are derived from storage capacitor CI.

The two infra -red detector diodes are con-nected in parallel and wired in series with RIO, sothat the detected IR signal is developed acrossRIO. The signal is amplified by 105. The outputof IC4. These two amplifier stages have theirresponses centered on 20 kHz, with third orderlow -frequency roll -off provided via C7 -t I andC12 and with similar high -frequency roll -off pro-vided by C8 and the internal compensationcapacitors of the two ICs.

The amplified output of 1C4 is rectified andsmoothed by voltage -doubler D4 -D5 andassociated C -R networks and fed to voltage -comparator IC3, fed to sensivity control RV2 andthen further amplified by 105 (at point B) takesthe form of a series of repetitive positive -goingpulses when a strong IR beam signal is present, orof a logic 0 signal when the beam is broken. The Bsignal is passed to the main receiver unit.

To understand the operation of the mainreceiver unit, assume initially that the emitter ofQ1 is shorted to ground. The output signal of thepreamplifier circuit is fed to point B and rectifiedand smoothed by the DI -CI -RI PRI network andthe resulting DC signal is inverted by ICI a and fed

to one input terminal of composite AND gateICI b -ICI c. This signal takes the form of logic 0 ifthe IR beam is unbroken, or logic 1 if the beam isbroken. The response time to a break can bevaried via PRI.

The second input to the composite ICI b -IC lcAND gate is derived from the positive supply linevia the R2 -C2 -R3 switch -on delay network and isnormally high (within a few seconds of supplyswitch -on). The output of the AND gate is fed tothe base of relay driving QI via R7. SW1 can beused to connect (enable) or disconnect the relayfrom Q1 collector.

Thus, under normal circumstances, thepresence of a beam signal results in the ICla inputto the AND gate being low, in which case theAND gate output is low and QI and RLA are off.When the IR beam is broken the ICI a input to theAND gate goes high, so the AND gate output goeshigh and drives QI RLA and LED I on (assumingthat SWI is closed). An exception to this actionoccurs for a brief period following power switch -on of the receiver unit, when the relay -driving cir-cuit is effectively disable via the R2 -C2 -R3 delaynetwork. Note that the relay can be operated ineither the latching or the non -latching mode viaSW2.

In the description above we've assumed thatthe emitter of QI is shorted directly to ground. Inpractice, however, the connection to ground ismade via Q2 collector. Normally, the input toICId is low, so ICId output is high and Q2 isdriven to saturation via R9 and acts as an effectiveshort circuit, so the above action is normally ob-tained. Q2 can, however, be cut off at any time,thereby disabling the relay circuit, by momentarilyclosing PBI or PB2. This action causes C3 tocharge rapidly via R4 and cut off the Q2 base drivevia ICId. The base drive is restored roughly 20 Safter the release of PB1/PB2 as the C3 chargeleaks away via R5. This 20 S disable facility allowsan at thorised person to pass through the IR beamwithout activating the alarm by first momentarilyoperating one of the PB1/PB2 buttons.

The complete IR receiver circuit is poweredfrom the AC line via the TI -BR I -05 network andthe IC2 12 V regulator chip.

ETI-AUGUST 1981 13

INFRA-RED ALARMIRD 1

CATHODE

IRD1,IRD2ANODE

°Cr."-%1°R 5.C5/D 0,(1/4as

ETI

0 0000-0 0-0 0.0

TransmitterResistors All 1/4 W, 5%

R1 1R5R2 47RR3 4k7R4 12kR5 2k2R6 22kR7 10kR8 820kR9 470R

CapacitorsC1 1000u 16 V electrolyticC2 1n5 polycarbonateC3 100n polycarbonateC4 100u 16 V electrolytic

SemiconductorsIC1 CD4011BIC2 ICM7555Q1 2N2904Q2 M PS6566IR LED 1,2 LD271BR1 50 V, 1AD1,2 1N4148ZD1 9V1

LED1

Fig. 6 Component overlay of the combinedpreamp and receiver board.

The infra -red intruder alarm transmitterPCB (top) and the receiver 'CB (below).

ri\VcrW00-0AR-AnDLARuni

PARTS LIST

D3

COILRLA1

4-sw, com.SW1

SW2 (LATCH)

PB1,2

+12V

ALA._2

OUTPUT

MiscellaneousT1 12 V 100 mASW1 DPDT miniature toggle

RECEIVERCase for transmitter

Resistors all 1/4 W, 5%R1,5 470kR2 2M2R3,7,16,25 4k7R4,15 470RR6,13,26 12kR8 680RR9 1k2R10 100kR11,12,17,18,22,24 10kR14,19 1 MO

R20 6k8R21 47kR23 27k

C2 6u8 25 V tantalumC3 47u 16 V tantalumC5 1000u 16 V electrolyticC6 100n polycarbonateC7,11 1n5 polycarbonateC8 220p ceramicC9 22u 25 V tantalumC10 100u 16 V PCB typeC12 4n7 polycarbonateC13 47n polycarbonateC14 10n polycarbonateC15 3n3 ceramic

SemiconductorsIC1 CD4093BIC2 7812 + 12 VIC3,4,5 CA3140Q1,2 MPS6515D1,4,5 1N4148D2,3 1N4001IRD1,2 SFH2O5BR1 50 V 1A

PotentiometersPR1 2M2 miniature Miscellaneous

horizontal T1 12 V 3 VAPR2 27k miniature horizontal RLA 2 Pole N/O 12V 120R

CoilSW1,2 SPDT miniature toggle

Capacitors SW3 DPDT miniature toggleC1,4 220n polycarbonate Case for Receiver

14 ETI-AUGUST 1981

InstallationInstallation of the alarm system issimplicity itself. Merely space the Txand Rx the required distance apart(up to several meters), point themroughly towards each other and then

Fig. 5 Circuit diagram of the receiver andpower supply.

adjust sensitivity control PR2 untilthe required switching action is ob-tained. 1-hdden bypass switches (PB1and PB2) can, if required, be placedon either side of the beam to allowauthorized access.

P111 20 SDISABLE IP 2 O

RELAYOUTPUT

R72M1

R3437

CI220..

O

470k

PRI2M2DELAY

Cl8ANT

R44704

LED1

RB!MR

R A1 V

.>1.?0

Owl

RELAYENABLE

C4

OUT

CO

12V

1 1 1

BR1%et

HEATSINK

IN OUT

4- 2> 1 I -1-+12V °V

Fig. 7 Component overlay of the receiverpower supply board.

NOTE:D1 IS 1N4148D2 -D3 ARE 1N4001BR1 IS 50V 1A BRIDGERECTIFIER01-02 ARE MPS6515IC1 IS CD40938IC2 IS LM78M12 OR SIMILART1 IS 12V 3VARLA IS 2 POLE CIO RELAY12V COIL RESISTANCE120R OR GREATER

01

4/4 Bita

1NONLATCM LATCH\ 5W2

ClI

N

C51000v25V

SYI3

0 -

LINEINPUT

ETI-AUGUST 1981 15

Conuniaeeinners

BABANI BOOKSSPECIALLY IMPORTED FROM ENGLAND

BP35: HANDBOOK OF IC AUDIO PRE AMPLIFIER ANDPOWER AMPLIFIER CONSTRUCTION 55.50F.G.RAYER, T.Eng.ICEILAssoc.IEREThis book is divided into three parts. Part I. understan-ding audio IC's Part II. Pre -amplifiers. Mixers and ToneControls. Part Ill Power Amplifiers and Supplies In.cludes practical constructional details of pure IC andHybrid IC and Transistor designs from about 250mW to100W output.

BP37: 50 PROJECTS USING RELAYS. SCR's $ TRIACS$5.50

F.G.RAYER, T.Eng.(CEI),Assoc.IERERelays. silicon controlled rectifiers ISCR si and bi-directional triodes ITRIACM have a wide range of ap-plication in electronics today. This book gives tried andpractical working circuits which should present theminimum of difficulty for the enthusiast to construct Inmost of the circuits there is a wide latitude in compo-nent values and types allowing easy modification of circuits or ready adantation of them to individual needs

15P351: SO (FET) FIELD EFFECT TRANSISTOReROJECTS $5.50F.G. RAPER, T.Eng.(CESAssoc.IEREField effect transistors iFETst, I ind application in a widevariety of circuits The projects described here includeradio frequency amplifiers and converters. test equipment and receiver aids, tuners. receivers, mixers andtone controls, as well as various miscellaneous deviceswhich are useful in the home

This book contains something of particular interesttor every class of enthUsiast - short wave listener.radio amateur. experimenter or audio devotee

13P42: 50 SIMPLE L.E.D. CIRCUITS 53.55R.N. SOARThe author of this book. Mr R N Soar. has compiled 50interesting and useful circuits and applications covering many different branches of electronics using one ofthe most inexpensive and freely available components- the Light Emitting Diode IL. EDI A useful book lorthe library of both beginner and more advanced enthusiast alike.

BP44: IC 555 PROJECTS $7.55E.A. PARR. B.Sc.,C.Eng., M.I.E.E.Every so Often a device appears that is so useful thatone wonders how life went on before without it The 555timer is such a device. Included in this book are Basicand General Circuits. Motor Car and Model Railway Circurls. Alarms and Noise Makers as well as a section onthe 556. 558 and 559 timers.

B P48: RADIO CIRCUITS USING IC's $5.90J.B. DANCE, M.Sc.This book describes integrated circuits and how theycan be employed in receivers for the reception of eitheramplitude or frequency modulated signals The chapteron amplitude modulated ta.m I receivers will be of mostinterest to those who wish to receive distant stations atonly moderate audio quality, while the chapter on Ire-ClUenCy modulation lf.m.) receivers will appeal to thosewho desire high fidelity reception.

B P47: MOBILE DISCOTHEQUE HANDBOOK $5.90COLIN CARSONThe vast majority of people who start up "MobileDiscos" know very little about their equipment or evenwhat to buy. Many people have wasted a "smallfortune- on poor. unnecessary or badly matched al1.pamtus.

The CM of this book Is to give you enough inform*.lion to enable you to have a better understanding 01many aspects of "dleCO" gear.

SP411: ELECTRONIC PROJECTS FOR BEGINNERS 55.90FA. SAYER, T.Eng.(CE0, Assoc.IEREAnother book written by the very experienced author -Mr. F.G. Sayer - and in it the newcomer to electronics.will find a wide range of easily made projects. Also.there are considerable number of actual componentand wiring layouts, to aid the beginner,

Furthermore, a number of protects have been ar.ranged so that they can be constructed without anyneed fOr soldering and, thus, avoid the need for a solder-ing iron.

Also. many of the later projects can be built alongthe lines as those in the 'No Soldering' section so thismay Considerably increase the scope of projects whichthe newcomer can build and use.

BP65: SINGLE IC PROJECTS 56.55R.A.PENFOLDThere is now a vast range of ICs available to the amateurmarket. the majority of which are not necessarilydesigned for use in a single application and can offerunlimited possibilities All the projects contained in thisbook are simple to construct and are based on a singleIC. A few protects employ one or two transistors in adds.lion lo an IC but in most cases the IC is the only activedevice used

BP86: BEGINNERS GUIDE TO MICROPROCESSORSAND COMPUTING $7.55E.F. SCOTT, M.Sc., C.Eng.As indicated by the title this book is intended as an inIroduction to the basic theory and concepts of binaryarithmetic. microprocessor operation and machinelanguage programming

There are occasions in the text where somebackground !Mori -nation might be helpful and aGlossary is included at the end et the hook

BP67: COUNTER DRIVER AND NUMERAL DISPLAYPROJECTS $7.55F.G. RAVER. T.Eng.(CEI), Assoc, IERENumeral indicating devices have come very much to theforefront in recent years and will. undoubtedly, find in.creasing applications in all sorts of equipment Withpresent day integrated circuits. it is easy to count.divide and display numerically the electrical pulses ob-tained from a great range of driver circuits.

In this book many applications and projects usingvarious types of numeral displays, popular counter anddriver IC s etc are considered.

BP68 CHOOSING AND USING YOUR HI.F1 $7.25MAURICE L. JAYThe main aim of this book is to provide the reader withthe fundamental information necessary to enable him tomake a satisfactory choice from the extensive range ofhi-fi equipment now on the market

Help is given to the reader in understanding theequipment he is interested in buying and the author alsogives his own opinion of the minimum standards andspecifications one should look for The bcqk also offershelpful advice on how to use your hi-fi properly so as torealise its potential. A Glossary of terms is also included

BM: ELECTRONIC GAMES $7.55AUTHOR: R.A. PENFOLDIn this book Mr. R A. Penfold has designed anddeveloped a number of interesting electronic game pro-jects using modern integrated circuits. The text is divid-ed into two sections. the first dealing with simple gamesand the latter dealing with more complex circuits

EIP70: TRANSISTOR RADIO FAULT-FINDINGCHART 1240AUTHOR: CHAS. E. MILLERAcross the lop of the chart will be Wong Imo rectanglescontaining brief descriptions of these fauns cis -sound weak but undistorted set dead sound low ordistorted and background noises One then selects themost appropriate of these and tollowing the arrows carries Out the suggested checks in sequence until thefault is cleared

19P71: ELECTRONIC HOUSEHOLD PROJECTS 57.70AUTHOR: R. A. PENFOLDSome of the most useful and popular eiectronic con.Struction projects are those Thal can be used in oraround the home The circuits range rum such thingsas '2 Tone Door Buzzer. Intercom, through Smoke orGas Detectors to Baby and Freezer Alarms

BP72: A MICROPROCESSOR PRIMER $7.70AUTHOR: E.A. PARR. B.Sc.. C.Eng.. M.I.E.E.A newcomer to electronics tends 10 be overwhelmedwhen first confronted with articles 01 books onmicroprocessors In an attempt to give a painless approach to computing this small book will start bydesigning a simple computer and because of it simplicity and logical structure the language is hopefully easyto learn and understand In this way such ideas asRelative Addressing. Index Registers etc will bedeveloped and it is hoped that these will be seen aslogical progressions rather than arbitrary things to beaccepted but not understood

213 ELECTRONIC CIRCUITS FOR MODELRAILWAYS $4.50M.N. BABANI. B.Sc.(Eng.jThe rnader is given constructionai details of how tobuild a simple model train controller. controller withsimulated inertia and a high power controller A signalsystem and lighting for model trains is discussed as isthe suppression of RF interference !ruin model railwaysThe construction or steam whisks andmodel train c^.."^- , .ered

221: 28 TESTED TRANSISTOR PROJECTS 55 50R.TORRENSMr Richard Torre, - A well experienced ,

development engmenr ,rid has designed. developedbuilt and tested the many uselul and interesting circuitsinciuded in this book The projects themselves can beSplit down into simpler building blocks which areshown Separated by boxes in the circuits lot ease ofdescription. and also to enable any reader who wishesto combine boxes from din terent projects to realiseideas of his own

223: 50 PROJECTS USING IC CA3130 55 SO. AUTHOR: R.A.PENFOLDIn this boOli the author nas designed ,iii,: O

number of interesting and useful projects whir,divided into live general categories I - Audio Prue'. '

F Projects ill - Test Equipment IV - Household Projects V - Miscellaneous Proiects

224: 50 CMOS IC PROJECTS $4.25R.A. PENFOLDCMOS IC s are probably the most versatiledigital devices for use by the amateur enthusiast t

are suitable ior an extraordinary wide range of ap;lions and are .1150 some of the most inexpensive ai deasily available types of IC

Mr R A Penfold has designed and developed anumbei of Interesting and uselul protects which are

into four general categories I - MuitivibratorsII - Amplifiers and Oscillators ill -- Trigger Dm ices IC

Special Devices

BPI. FIRST BOOK OF TRANSISTOR EQUIVALENTSAND SUBSTITUTES S2 80B.B. BABANINis guide covets many thousands 0, trans.511, 5000"IQ possible alternatives and equivalents Covers IranSiSIMS made in Great Britain. USA. Japan GermanyFiance. Europe. Hong Kong and includes typeS orOduCed by more than 120 dilferent manufacturers

BPI4. SECOND BOOK OF TRANSISTOR EQUIVALENTSAND SUBSTITUTES 54.80B.S. BABANIThe First Book Of Transistor Equivalents has had tohe reminted 15 times The Second Book produced inthe same sty'e as the first book in no way, duplicatesany of the data presented inn The Second Book contains only additional material and the Iwo books coinpiernent each Other and make available some ot themost complete and extensive information in this heldThe interchangeability dela covers semiconductorsmanufactured in Great Britain. USA. Germany Fran' .Poland. Italy East Germany. Belgium Airs:'-,,Netherlands and many other countries

B P24: 50 PROJECTS USING IC741 S4 25RUDI a UWE REDMERThis book originally Published in Germany by TOPP hasachieved phenomenal sales on the Continent andS abani decided in view of the fact that the integratedcircuit used in this DOOk is inexpensive 10 buy lo makethis unique book available to the English speakingreader Translated horn the OrldlnS1 German withcopious notes data and Circuitry must for everyonewhatever their interest in electronics

BP33: ELECTRONIC CALCULATOR USERSHANDBOOK $4.25M.N. BABANI, B.Se.(Eng.)An invaluable book for all calculator users whatevertheir age or occupation Of whether they have thesimplest Of most sophisticated of calculators Presentsformulae. data. methods of calculation conversion lactors. etc with the calculator user especially in mindoffer, illustrated with sirnie examples inciudes the wayto catcutale using only a simple lox function calculatorTrigonometric Functions (Sin Cos. Tani HyperbolicFunctions (Sinn. Cosh. Tann, Logarithms. Square Rootsand Powers

CATCHAGOODBOOKFROME.T.I.

BP81: ELECTRONIC SYNTHESISER PROJECTS 57.30M.K. BERRYOne of the most fascinating and rewarding applications01 electronics is in electronic music and there is hardly agroup today without some sort of synthestser or effectsgenerator.

Although an electronic synthesiser is quite a com-plex piece of electronic equipment. it can be brokendown into much simpler units which may he built in,dividually and these can then be used or assembledtogether to make a complete instrument.

BP83: VMOS PROJECTS $8.20R.A. PENFOLDAlthough modern bipolar power transistor give excellentresults in a wide range of applications: they are notwithout their drawbacks or limitations. This book willprimarily be concerned with VMOS power FETsalthough power MOSFETs will be dealt with in thechapter on audio circuits. A number of varied and in.teresling projects are covered under the main headingof: Audio Circuits, Sound Generator Circuits. DC Con-trol Circuits and Signal Control Circuits

BP84: DIGITAL IC PROJECTS 88.11E.G. RAVER, T.Eng.(CEI),Assoc.IEREThis book contains both simple and more advanced pro-tects and it is hoped that these will be found of help tothe reader developing a knowledge of the workings ofcholla] circuits.

To help the newcomer to the hobby the author hasincluded a number of board layouts and wrongdiagrams. Also the more ambitious projects can be builtand tested section by section and this should help avoidor correct faults that could otherwise be troublesome.

An ideal book for both beginner and more advancedenthusiast alike

BM: INTERNATIONAL TRANSISTOREQUIVALENTS GUIDE $12.25AUTHOR: ADRIAN MICHAELSThis book will help the reader to bnd possiblesubstitutes for a popular user -orientated selection ofmodern transistors. Also shown are the material type.polarity, manufacturer selection of modern transistors.Also shown are the material type. polarity, manufacturerand use. The Equivalent are sub -derided into European.American and Japanese. The products of over 100manufacturers are included.

An essential addition to the library of all those in.!crested in electronics, be they technicians, designers.engineers or hobbyists.

Fantastic value for the amount of information itcontains.

BP86: AN INTRODUCTION TO BASICPROGRAMMING TECHNIQUES $8.25AUTHOR: S. DALYThis book is based on the authors own experience inlearning BASIC and in helping others, mostly beginners.to program and understand the language.

Also included are a program library containingvarious programs, that the author has actually writtenand run, these are for blorhythms, plotting a graph ofagainst 5, standard deviation, regression, generating amusical note sequence and a card oame.

The book is complemented by a number of appendices which include test questions and answers on eachchapter and a glossary.

BM: SIMPLE L.E.D. CIRCUITS $6.25AUTHOR: R.N. SOARSince it lirst appeared in 1977, Mr. R.N. Soar's book hasproved very popular. The author has developed a furtherrange of circuits and these are included in Book 2. Pro-jects include a Transistor Tester. Various VoltageRegulators, Testers and so on.

205: FIRST BOOK OF HI-FI LOUDSPEAKERENCLOSURES $3.55B.S. BABANIThis book gives data for building most types ofloudspeher enclosure. Includes corner reflex, bassreflex, exponential horn, folded horn, tuned port.kllpschorn labyrinth, tuned column. loaded port andmulti speaker panoramic. Many clear diagrams forevery construction showing the dimensions necessary

BPBO: POPULAR ELECTRONIC CIRCUITS -BOOK 1 $8.25R.A. PENFOLDAnother book by the very popular author, Mr. R.A. Pen-fold, who has designed and developed a large number ofvarious circuits. These are grouped under the followinggeneral headings; Audio Circuits, Radio Circuits. TestGear Circuits, Music Project Circuits, Household ProjectCircuits and Miscellaneous Circuits.

Babani Books are now available fromArkon, CESCO, Dominion Radio andGeneral Electronics.

19P49: POPULAR ELECTRONIC PROJECTS 86.25A.A. PENFOLDIncludes a collection of the most popular tveteS of cincults and protects which. we feel sure. will provide anumber of designs to interest most electronics con-structors. The ',trowels selectee. cover a very wide rangeend are divided into four basic types. Radio Protects.Audio Projects. Household Projects and Test Equipment.

BP 50: IC LM3900 PROJECTS 55.90H.KYBETT.B.Sc., C.Eng.The purpose of this book is to ntroduce the LM3900 tothe Technician. Experimenter and the Hobbyist It plovides the groundwork for both simple and more advanc-ed uses, and is more than lust a collection of simple cir-cuits or projects.

Simple basic working circuits are used to introducethis IC. The LM3900 can do much more than is shownhere. this is lust an introduction. Imagination is the onlylimitation with this useful and versatile device. But firstthe reader must know the busts and that is what thisbook is all about.

BP51: ELECTRONIC MUSIC AND CREATIVE TAPERECORDING 55.50M.K. BERRYElectronic music is the new Music 01 the Twentieth Cen-lury. It plays a large part in pop- and rock' musicand, in fact. there is scarcely a group wIthoul some sortof synthesiser or other el feels generator

This book sets out to show how electronic musiccan be made at home with the simplest and most inex-pensive of equipment. It then describes how the soundsare generated and now these nay be recorded to buildup the final composition

BABANIBOOKS

ELEMENTS OF ELECTRONICS - An on -going seriesAUTHOR: F.A. WILSON. C S I A., C.Eng..BP62: BOOK 1. The Simple E ectronic Circuit and

Components $8.95BP63: BOOK 2. Alternating Current Theory 58.95B Pb4: BOOK 3. Semiconductor Technology 8.95B P77: BOOK 4. Microprocessing Systems And

Circuits 512.30The aim of this series of books can he s taled quite simply - rt is .to provide an me rpensiye introduction tomodern electronics so Ow the reader will slat on Meright road by thoroughly understanding the fundamentalprinciples involved.

Although written especially, for readers with tomore than ordinary arithmencal skills the use olmathematics is not avoided. and all the 17 idlhemat ics recloned is taught as the reader progresses

Each book is a complete Poetise of a particularbranch of the subject and theielore, can be used on ,isown with one proviso, that the later books do notduplicate material from their predecessors thus a work-ing knowledge of the subjects coveted by the earlierbooks is assumed

BOOK 1 This book contains all the tundamentattheory necessary to lead to a lull understanding of thesimple electronic circuit and is main components

BOOK 2: This book continues with alternating cur.rent theory without which thee can be no comprehen-SIOn 01 speech, music, radio, television Or even the eiectricity mains.

BOOK 3' Follows on semiconductor technology.leading up to transistors and Integrated circuits

BOOK 4; A complete description of the internalworkings of microprocessor

InternationalTransistor

'Guide "t'

6P73: REMOTE CONTROL PROJECTS 58.56OWEN BISHOPthis book is aimed primarily at the electronics en.!nosiest who wishes to experiment with remote control.Full explanations have been given so that the reader canfully understand how the circuits work and can moreEasily see how to modify them for other purposes.cepencting on personal requirements lye r only areRadio control systems considered buy also Infrared.visible light arid Ultrasonic systems as are the use ofLogic ICs and Pulse position modulation etc

B P74: ELECTRONIC MUSIC PROJECTS 57.70PENFOLD

Alth0,1131 rif 01 the more recent branches of amateurelectIWIres electronic music has now become extreme,1, popular and there are many projects which tall intothis category

The purpose of this book is to provide the construc-tor with a number of practical circuits for the less com-plex items of -electronic music equipment. includingsuch things atun Box. Waa-Waa Pedal, Sustain Unit.Reverberation nd Phaser Units. Tremelo Generator etc

B P75: ELECTRONIC TEST EQUIPMENTCONSTRUCTION 57.30F.G. RATER, T.Eng. ICED. Assoc. IEREthis book covers In detail the construction of a widerange of test equipment for both the Electronics Hobbyists and Radio Amateur Included are protects ran,mg from an FET Amplified Voltmeter and Resistan,aridge to a Field Strength Indicator and Heterodyne Frequency Meter Not only can the horne constructor enjoybuilding the equipment but the finished protects canalso be usefully utilised in the lurtherance of his hobby

3P76: POWER SUPPLY PROJECTS $7.30PENFOLD

Line power supplies are an essential part of many elecIonics protects The purpose of this book is to give anumber of power supply designs including simpleenstabillsed types fixed voltage regulated types. andtenable voltage stabilised designs. the latter beingprimarily intended for use as bench supplies for theelectronics workshop. The designs provided are,all lowvoltage types 101 semiconductor circuits '

There are other types of power supply and a numberof these are dealt with in the final chapter including a-Cassette power supply. NI -Cad battery charger. voltage3tep up circuit and a simple inverter

BP78: PRACTICAL COMPUTER EXPERIMENTS 87.30E.A. PARR. B.Sc.. C.Eng., M.I.E.E.Curiously most published maternal on themicroprocessor lends to be of two sorts, the first treatsthe rni r.r °processor as a black box and deals at lengthwith programming and using the beast The secondtype of book deals with the social impact None of thesenooks deal with the background 10 the chip and this is ashame as the basic ideas are both interesting and sim-ple

This book aims to 1,11 in the background to themicroprocessor by constructing typical computer circurls in discrete logic and it is hoped that this will form auseful introduction to devices such as addersmemories. etc as well as a general source book of logicCircuits

8P79: RADIO CONTROL FOR BEGINNERS $7.30A.G. RATER, T.Eng.(CEI).Assoc.IERE.The aim of this book is to act as an introduction to RadioControl for beginners to the hobby The book will com-mence by dealing with the conditions that are allowablelor such things as liequenLv and pbwer 01 transmissionThis is followed by a 'block' explanation of howcontraldevice and transmitter operate and receiver andacluatortsi produce motion in a model

Detail's are then given ol actual solid state transmitling equipment which the reader can build Plain andloaded aerials are Men discussed and so is the heldstrength meter to help with proper setting up

The radio receiving equipment is then dealt wonwhich includes a simple receiver and also a crystal controlled superhel The book ends with the electromechanical means of obtaining movement of the con-trols 01 the model

These books are specially imported from England by us.All prices include handling and postage. To order, usethe order form in this publication or write to:

Unit 625 Overlea Blvd.,Toronto, Ontario

M4H 1 B1

RECORDING TAPEAND TAPE RECORDINGIf you're a newcomer to the popular pastime of tape recording and reproduction, here's a completerundown on the technicalities.ALL HI-FI reproduction is dependenton the storage of information and itsretrieval when required. Informationstored on a phonograph form of a

modulated groove, and the signalwaveform is visible under a microscopeor a powerful magnifying glass.

With tape recording, however, thesignal is stored by a magnetic oxide thatcarries an invisible, varying magneticpattern. To record and recover theinformation a series of energy con-versions is necessary: acoustic -to -electric, electric -to -magnetic, and viceversa.

As with the disc system there arelosses and technical inadequacies thathave to be compensated for by equalisa-tion. However, in tape recording,equalisation is not a single stage pro-cess with mirror image characteristicsused on record and playback. Instead,it is a complex two -stage process appliedpartly when recording and partly onplayback, to give an overall flat re-sponse. Before we discuss this in detaillet us consider the nature of tape and ofthe recorded signal.

Recording tape consists of a thin,pliable base of plastic material, such as

mylar or polyester. The base is coatedwith a magnetic oxide paste about fourmicrons thick (one micron is onemillionth of a metre), the constituentsof which are the oxide itself, a binder,a solvent, and a lubricant.

During manufacture the oxidepowder, which is in the form of minuteneedle -shaped particles (or magneticdomains), is given a type of 'grain'. Thatis, the particles have a common orienta-tion. For some computer and videosystems the grain is vertical - perpen-dicular to the direction of tape travel -but for conventional sound recordingthe grain is horizontal (Figure 1).

Aligning the particles in this wayallows a more concentrated coating tobe applied than would random applica-tion. For a given type of oxide and agiven tape width, the thickness of thecoating determines the maximum out-put possible from the tape.

The most commonly used oxide isgamma ferric oxide (Fe03) and, untilabout 1966, it was the only oxide regu-larly used in the manufacture ofmagnetic tape. Later developmentswere chromium dioxide (Cr02), ferri-chrome - a mixture of ferric andchrome coatings - and cobalt. More re-cently 'metal' tape formulations haveappeared.

Early ferric tapes were noisy, hadlow sensitivity, and poor high frequencyresponse. With improved manufactur-ing methods the tape was improvedimmensely and finer oxides, with moreregular particle structure, were de-veloped to give lower hiss, higher outputlevels, and better high frequencyresponse.

Chromium dioxide enjoyed a popularvogue in cassette recording but, while ithas a slightly superior high frequencyperformance at low speeds, it is moreprone to distortion than ferric tapes andis now being superseded by ferri-chrome. For reel to reel recording atspeeds above 95 mm/s there is no ad-vantage to be gained from the use oftapes other than ferric oxide.

Tape magnetisationWhen tape is in a so-called demag-netised state the individual particles(domains), although physically aligned,

18 ETI-AUGUST 1981

have no common magnetic sense(Figure 2). The domains may be re-garded as minute bar magnets, butwhen these are of random polarity, aswith blank tape, the only output pro-duced by the oxide is in the form ofnoise. To record a signal on the tape itis necessary to modify the distributionof polarity so that a magnetic analogyof the audio signal applied to themachine's input is written along thetape's length.

To store the input signal on tape itmust be converted into a form that thetape will recognise and retain. This con-version is carried out by the tape head(Figure 3), which is effectively a ring -shaped electromagnet. The audiosignal, in the form of a varying voltage,is applied to the head winding.

Now, if a current flows through apiece of wire a magnetic field is createdaround the wire, and if the wire is

wound into a coil this field is intensified.If a core, such as soft iron, is insertedinto the coil it will become magnetisedand remain so until the voltage appliedto the coil is removed. A tape head issimply a variation of this idea with thecoil curved to bring the two ends (poles)into close proximity.

With a constant voltage applied tothe coil, the iron core will have a Northand South pole, rather like a horseshoemagnet. If the polarity of the supplyvoltage is reversed, the two poles will bereversed. If we substitute an audiosignal, such as a sinewave, for the con-stant voltage, the poles will alternate insympathy with the positive and negativehalf -cycles of the applied signal.

The strength of the poles at anyinstant will depend on the voltage of thesignal, which in turn depends on theamplitude of the original sound. Be-cause of a shim placed at the front ofthe head, filling the gap between thepole -pieces, the magnetic flux cannoteasily pass from the North to the Southpole. In fact, the reluctance of the shim(reluctance is the magnetic analogy ofresistance) is so high that it is easier forthe flux to complete the magnetic circuitby crossing the air space in front of theshim.

If a tape is passed over this concen-trated magnetic flux the magneticcircuit is completed through the tapeoxide. The effect of the varying flux onthe moving tape is to produce a series ofbar magnets along the length of thetape. The stronger the magnetising thegreater will be the strength of the barmagnet so formed. The length of a par-ticular magnet depends on the rate atwhich the applied magnetising force ischanging polarity, and on the linear

Broadcast video tape

IlltltlIII 1 1 1

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1,1III 1;,1 I

I I I 1 1

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IL liDirection of travel

Vertical grainof domains

6.4 mm recording tape

/ Direction of travel-lihHorizontal magneticdomains

Figure 1. During manufacture themagnetic particles are given a commonorientation.

N -S N-S5 -N N-SN-S S-NN N S

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Random distribution

Figure 2. An erased so-called demagnetisedtape with a random distribution ofdomains.

Winding

Front gap shim

Rear gap

pole face

Figure 3. A typical record/playback head.

speed of the tape. (For example, at10 kHz with a tape speed of 190 mm/s,the recorded wavelength takes up 0.0190.019 mm of tape. Wavelength here istape velocity divided by frequency.)

In the case of a sinewave input - asshown in Figure 4 - a wavelength con-sists of two bar magnets of equal length.The positive going half -cycle by South -to -North field, although the oppositecould equally well be the case.

So far the concept is relatively easyto grasp. An electrical signal is convertedto a magnetic form and is effectively'written' - in the form of a varyingmagnetic flux - on the tape oxide. It isthen retained and at any time themessage may be read by the repro-ducing system. What complicates thematter is that in both recording andplayback the transfer from electrical tomagnetic, and from magnetic to elec-trical energy is non-linear.

TransferEvery tape has what is known as a tapetransfer characteristic, which shows therelationship between the applied mag-netising force (H) and the resultant tapeflux (B). This characteristic will differfrom one type of tape coating to another- a typical transfer curve is shown inFbgure 5.

The characteristic is derived from ahysteresis loop, which describes thetape flux resulting from the applicationof one cycle of magnetising force to theoxide. For the sake of simplicity we willask you to accept the derivation of thehysteresis loop, and from it the tapetransfer characteristic (TTC).

The significant thing is the shape ofthe TTC itself. There is a discontinuityat the origin of the B -H curve, with anearly linear slope in the central regionof the positive and negative sections ofthe curve. Beyond a given point an in-crease of applied magnetising forcegives no increase in the resultant tapeflux: this is the point of tape saturation.

BiasThe TTC is therefore a graph of appliedmagnetising force versus the resultantmagnetic flux induced in the tape oxide.If the input is in the form of a sinusoidalswing either side of the B axis (Figure 6)

Fig. 4. A recorded tape has areas of magnetic polarisation corresponding to the positive andnegative half cycles of the applied waveform.

ETI-AUGUST 1981 19

RECORDING TAPES AND TAPE RECORDING

then the recording will be distorted be-cause of the shape of the characteristic.

To overcome this distortion the inputsignal must be offset on to the linearpart of the TTC. This is done by super-imposing the audio signal on a highfrequency sinusoidal bias waveform(Figure 7). The shape of,the bias enverlope is thus a replica of the audio inputsignal, but this signal is now applied tothe linear part of the TTC. One of theobjects of bias adjustment is to ensurethat the bias voltage gives the requiredoffset of the audio signal on to the linearpart of the curve.

Iron oxide and chrome tapes varywidely in their bias requirements - upto 40 per cent more bias being requiredfor chrome tape, which is more con-sistent than iron and shows littlevariation between brands. Ferric tapevaries considerably from one brand toanother, and once a machine has beenoptimised for a particular brand of tapeit is advisable to stick to that brand un-less there are compelling technical oreconomic reasons for doing otherwise.When the recording bias is adjusted itwill be found that if too low an offsetvoltage is used the signal will be dis-torted: if it is too high, demagnetisationof the high frequencies will occur andthe top response will be impaired.

Tape headsIn tape recording we are concerned withtwo types of magnetic material - thatwhich is magnetically 'hard', and thatwhich is magnetically 'soft'.

A hard material will retain a largeproportion of any induced magnetism,which cannot be easily erased. Record-ing tape is magnetically hard.

A 'soft' material will react quickly tochanges in magnetic force, but whenthat force is removed will retain verylittle magnetism. This ability to reactrapidly to changing magnetic con-ditions is exactly what is required of atape head which, consequently, is madefrom soft material. In this context hard-ness and softness are magnetic, notphysical properties.

Three functions have to be performedby the tape heads, functions that are so

20

individual that, if they are of beperformed efficiently, require threeindependent heads - erase, record, andplayback.

For economic reasons manufacturersoften combine the functions of two ofthe heads, and fit machines with anerase head and a dual purpose record/playback head. Apart from the engi-neering compromises that such anarrangement necessitates, there arealso operational disadvantages, themost serious of which is that the tapecannot be monitored during recording.

The basic elements of a tape headhave already been shown in Figure 3. Inthe case of the erase and record headsthe flux due to the current through thewindings induces a varying magneticflux into the core. In the case of theplayback head, the magnetised tape in-duces a varying flux into the poles, whichproduce an electromotive force (emf) inthe windings, and hence an electricaloutput.

Of particular importance are thewidth and alignment of the gap, and theshape of the pole -pieces in contact withthe tape. The width and alignment ofthe gap largely determine the attain-able high frequency response, whilethe head contact area affects the lowfrequency playback response. In orderto maintain precise head alignmentsome manufacturers construct the headblock as a single unit with the headsrigidly fixed to a common, machinedbaseplate.

Erase headIt is a curious feature of the recordingprocess that the bias waveform, whichreduces distortion and enables a goodrecording to be made, also has thecharacteristics required to erase thetape.

The important factor for erasure is ahigh enough current to carry the tapeinto saturation at each reversal of po-

1111.11111111111

11111111111111111111111101111111110

larity. It is not possible to demagnetisethe tape - the particles are alwayspolarised in one direction or another.However, if the distribution of magne-tism is completely random, the effect isof a mutual cancellation within thetape, which thus has no external flux.

The object of using a high frequencyerase current is that it subjects the indi-vidual domains to a large number ofreversals of polarity in a short space oftime. The tape is moved through a con-centrated magnetic field, the effect ofwhich progressively reduces as the tapeleaves the head. Therefore the tape isfirstly repeatedly saturated at each re-versal of polarity as it crosses the headgap. Then the weakening field, as thetape leaves the gap, is unable to reverseall the particles in a given area, and thefinal polarity a particle adopts is notgreatly influenced by the originalsignal polarity. The tape therefore his arandom magnetic distribution and issaid to be demagnetised.

In practice it is possible for some ofthe particles to recover partially theiroriginal magnetic sense. For this reasona second pass over the erase head isoften necessary to obtain completeerasure. To increase the depth oferasure many tape recorders are nowfitted with double -gapped erase headsthat give a similar effect to two passesof the tape across the head. The erasegap may be as much as 20 micronsalthough with a double -gapped head thesecond gap is usually considerablysmaller. The erase frequency must behigh enough to produce the rapidlyreversing flux and to avoid thegeneration of spurious beat frequencies(with 19 kHz and 38 kHz signals fromstereo tuners). It is usually in the regionof 80 to 150 kHz.

Record headWhereas at the erase head a saturatingmagnetic force is used to remove anyexisting signal waveform from the tape,

ETI-AUGUST 1981

at the record head a bias current of pre-cisely controlled amplitude is mixedwith the audio signal to minimise dis-tortion of the audio waveform.

The record head gap is much smallerthan the erase head. It must be smallenough to produce a high flux density,but wide enough to allow for a numberof changes of polarity of the bias wave-form. Depending on the bias frequency,tape speed, and gap dimension, each do-main is subjected to around 10 cycles ofbias current. Again, the bias results in apolarisation of the magnetic domainsbut, because of the presence of the audiosignal, as the bias field diminishes, sothe polarity of the domains is increas-ingly influenced by this varying signal.

Thus, instead of the tape reverting toa natural state it is magnetised accord-ing to the amplitude and frequency ofthe applied audio signal. This meansthat the tape is recorded as it is leavingthe head gap, and the gap itself is not toociritical as far as the audio waveform isconcerned. A typical record head gapfor a machine running at 95 and 190mm/s would be six microns.

The relationship between the currentin the head winding, the permeability ofthe core, and the flux concentration atthe gap is not linear. To overcome thisa high reluctance rear gap is used that isanalogous to a constant current resistor.The reluctance of the rear shim is sohigh in comparison with the rest of themagnetic circuit that it swamps anyvariation in the permeability of the corematerial, and a virtually linear flux isproduced at the front gap. The rear gapis usually about 10 times that of thefront.

PlaybackA tape head is a piece of precision en-gineering. Iri the case of playback headthe tolerances are so closely definedthat there is virtually no margin forerror. Even a slight departure fromspecification can lead to a major loss ofperformance.

One of the crucial dimensions isthat of the playback head gap. Due tothe nature of the head material, the fluxcoupling with the poles, and the head -to -tape contact area, the effective gapmay be as much as twice the physicalgap. Because the playback head tole-rances are so tight, if a dual purposehead is constructed it will, to all intentsand purposes, be a playback head.

The output from the playback headdepends on the efficient coupling of thesurface induction on the tape with thehead and its associated preamplifier. Aplayback head core has extremely highpermeability - several thousand timesETI-AUGUST 1981

The advent of high energy tapes enables cassette decks to match performance with their reel toreel big brothers. The cassette format allows sophisticated and computerized control of play-back and record operations.

w

B (a)...

H

(b)

.atD -a

Applied magnetising force (arbitrary units)Fig. 5. The non-linear tape transfer characteristic (a) is derived from the hysteresis loop (seeinsert). It is a graph of induced magnetic flux versus applied magnetising force.

Saturation point

Distortedrecording

--. SI le wave Input

Saturation point

Fig. 6. Distorted recording resultsnon-linear tape transfer characteristic.

form

Linear part ofcharacteristic

H

'Ill' 1A . .. 1 HF bias envelopeor,

I modulated by%

I audio signalI. 1. /

`'I .,

- L',I

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amplitude 11°'

Fig. 7. The distortion can be minimisedby off -setting the audio signal onto a highfrequency bias voltage.

21

RECORDING TAPES AND TAPE RECORDING

Wavelengthe'<ei=head gap= 5 urn

Figure 8. When the recorded wavelengthequals the playback head gap there is noflux linkage with the head core andconsequently no output.

that of air - so that the tape flux at thepoint of intimate contact with the headwill seek the easy path through the headcore.

The changing flux pattern as the tapemoves across the head results in an emfin the head windings, a voltage that in-creases with frequency because it is pro-portional to the rate of change of flux.Hence, doubling the frequency willdouble the output from the head - inother words the output from an idealhead would rise at 6 dB per octave.

In practice a straight line graph is notrealised, and the 6 dB per octave slope isonly achieved at low and mid frequen-cies. At the upper end of the audiospectrum a point is reached (Figure 8)where the recorded wavelength is com-parable with the effective gap of theplayback head. When this point is reach-ed the variation of flux will occur withinthe gap dimension and consequentlythere will be no output from the head.The frequency at which this happens isknown as the extinction frequency, al-though the ideal slope does not suddenlyfail as the extinction frequency is

reached. As shown in Figure 9, it beginsto roll off at about half the extinctionfrequency.

Now we can see the problem in per-spective. To achieve a theoreticalextinction frequency of 20 kHz at190 mm/s the effective gap should be9.5 urn, giving a physical gap of about5 urn. The response of the head maynot be as good as the theoretical figuresgiven above, but in general the headwith the narrower gap will have thebetter high frequency response.

Playback systemWe have briefly discussed the principlesof the recording and playback processes.Let us now consider how the playbackand recording chains are interlinked andequalised so that a flat overall responsecan be obtained.

65

56

50

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100 1000Frequency (Hz)

10 000

Figure 9. Playback head responses - (a) ideal response and (b) practical response with headloses

dB

10

0

-1010 100100 1000

Frequency (Hz)

Figure 10. Theoretical response of the playback amplifier.

+5

0

10 000 100 000

a

b

100 1000 1 0 000

Figure 11. Ideal recorded tape flux (a) and typical tape flux allowing for head and otherlosses (b).

We have already referred to the ex-tinction effect, which is a major causeof high frequency loss. In addition tothis, when the recorded wavelength isvery short the individual poles are insuch close proximity that some of theflux fails to emerge from the surface ofthe tape. Instead, it completes the ma-netic circuit through the oxide and sodoes not energise the tape head. Otherlosses are due to imperfect head -to -tapecontact, and coupling losses between

the head and preamp. At the bass end,where the wavelength is long comparedwith the head gap, the output may fallat a rate greater than 6 dB per octave, aspart of the flux path is through the air.

To compensate for the response at thehead it is apparent that the playback am-plifier must have an initial slope fallingat 6 dB per octave, it must flatten out inthe mid frequency range and then add adegree of boost at the top end to compen-sate for the head losses. Figure 10 shows

22 ETI-AUGUST 1981

the theoretical response of the playbackamp.

Record systemThe signal current is fed through a re-sistor to the head winding and mixedwith the bias waveform. The value ofthe resistor is such that it is well inexcess of any change in impedance ofthe head (which increases with fre-quency). The effect is that variations ofhead impedance are minor in compari-son with the value of the feed resistor,resulting in a constant current input tothe head. Thus, for a signal of givenamplitude, the head current is constantregardless of frequency.

In theory this Would appear to give aconstant level of magnetic induction onthe tape oxide. Again the ideal is notrealised because of high frequencylosses (Figure 11). In the main these aredue to partial erasure of the signal bythe bias, the falling permeability of thetape with increasing frequency, andpoor head -to -tape contact. To compen-sate for these losses the theoreticalresponse of the record amplifier shouldbe the inverse of Figure 11. In fact it isnot quite this simple.

If sufficient pre -emphasis wereapplied during recording to give con-stant tape flux with frequency, the tapewould saturate at high frequencies.Also, as we have seen, the response ofthe playback head is not flat, and theresponse curve of Figure 10 would notproduce a flat output from a tape fluxthat held constant with frequency.dB

+20

+10

0

-10

EqualisationWhat is required is a two-part compen-sation process, part of which is appliedon recording and part on playback. Theresult should be a flat response over agiven frequency range. However, be-cause the losses vary not only withfrequency but also with tape speed, theequalisatior must be switched to givethe optimum response curve for eachtape speed.

Anyone with a turntable expects tobe able to play any phonograph recordand to achieve a consistent standard ofreproduction. Similarly it should bepossible to play a tape recorded on onemachine on any other machine. Withoutthis requirement each designer couldequalise for the various losses in anyway and, provided the mach ne had anoverall flat response, the customerwould be happy - until attempting toplay someone else's tape on thatmachine!

Obviously a standard is required, butto what does it refer?

It describes the recording charac-teristic, which is a curve of recordedtape flux level against frequency, andwhen plotted appears as in Figure 12.Tape flux is measured in nanowebersper metre (nWb/m) of track width, andrecording characteristics are commonlyreferred to in terms of the circuit time -constants that would produce animpedance curve of the same shape.

The problem is to arrive at a recordedtape flux (not frequency response) as perFigure 12, having taken account of the

318

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100 1000Frequency (Hz)

Figure 12. Recording characteristics to BS1568: 1970.

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various losses in the recording' system.To do this the designer usually beginswith the playback system, knowing thatif a calibration tape can be playbackaccurately, one of the variables is fixed- playback equalisation. A recordingamplifier can thus be devised that willproduce the tape flux levels shown inFigure 12, and a flat overall responsewill result.

To summarise this rather complexprocess: there are losses during thevarious energy conversions in the recordand playback chains. Equalisationcirucits are used during record andplayback such that an overall flat re-sponse is obatianed. Because the lossesin the system vary with tape speed, afamily of curves is required if a machinehas more than one speed.

To ensure that tapes can be inter-changed it is essential that a taperecorded on one machine shall be repro-duced satisfactorily by another. Forthis reason specific recording characteris-tics have been adopted, and provided amachine conforms to the appropriatestandard, compatibility will be achieved.*

AUDIOPHILES!SYNTH NUTS!

TAO 111.041,-... .33

oftolv Maw.. Wallow/

WV VPIWASK P. VWDOINCIM

No electronic enthusiast should be with-out one! The Active Filter Handbook dis-cusses all types of filters. The authorstarts with two fundamental filter types,Butterworth and Chebyshev, and explainsall definitions,.concepts and fundamentals.Unlike others, this book does not ignoremathematics, but rather shows the deriv-ation of all design equation.

Practical applications are included andcover such diverse areas as graphicequalisers and communications modems.

Send $9.75 /cheque or money order) toETI Book Service, Unit 6, 25 Overlea Blvd,Toronto, Ontario M4H 1B1 or use theconvenient order form elsewhere in thisissue. Order TAB No. 1133.

ETI-AUGUST 1981 23

fJ

f,

? r 1 . I 1. , , r

Master Handbook Of 1001 Practical CircuitsTAB No.800 $18.30Master Handbook of 1001 More Practical CircuitsTAB No. 804

1 $18.3,,,Vc

Here are IC and transistor rairCuits for practicallyanything and everything - with ALL the data needed

rk. The ideal schematic source -book rihnicians, engineers, experimenter .

anyone who must occasionallyt or adapt electronic circuits forver. You'll find any circuit u'rer L

13c1 in the pages of this rich vos are classified according to ge I

and the Sections hemselves appear inal r

to put tf3emtofor all active toamateurs - forregul constrpurp whatseve elyTha

list Er men acts ou Can BuildTAB No.8 5 $11.75

Here's the A to Z guide you need to build all sorts ofelectronic test equipment - from a simple signaltracer to a sophisticated modularized 50 MHz count- and virtually everything in between! Herevoltmeters and ammeters, capacitance meters,resistance and impedance measurers, testers forsolid-state components, digital volt-velers, calibratand frequency standards, signal generators, irecy counters, oscilloscopes, and a variety ofequipment. The variety is incrediple andendless ... virtually every test instrument ypossibly; ant to build for -eW

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oprocassorA Beginner's Guide- With ProjectsTAB No.1015

Here's a plain- gli i fa stingworld of the mi rocomput - it's capa es, parts,functions, and rogramming ... an you can haveone in your ow home. Num projects, using ac-tual computer parts, strate the operation of acomputer and lead to the assembly of a workingmicrocomputer capable of performing many usefulf unctions around the home and office.

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How To Design, Build & Test Complete SpeakerSystemsTAB No. 1064 $11.85

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This clear guide shows you exactly how aspeaker works, how its power and resonance are at-tained, and how speakers may differ from oneanother. It's as thorough a book as you'll find on the

'complete subject of speakers, speaker systems, andenclosures.

ciroia: deicing With An Analog WorldTAB No. 07g $12.35

Are you lo Wing for ways to really put your microcom-puter to w k? This book tells you how to go about it

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Very simply, this book is for thecroprocessor/computer user who wants to use thechine to measure certain conditions, or to controlernal devices.

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Create your own robot? All the information you needto build a walking, talking friend and companion or ahelpful servant appears in this book!

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Whether you want a robot for a experimenting, fora security application or to perform some tasksuitable for "smart" machine, all the ideas you needare packed into this book.

The Active Filter HandbookTAB No.1133 $9.75

A designer's and users' guide to the theory and ap-plications of active filter circuits.

For anyone interested in electronics, this handyone -stop guide to modern filter technology will proveinvaluable. It introduces filters and their purpose,compares different filters, and covers LC passive filteroperation, op amps, Butterworth filters, Chebyshevfilters, low-pass filters, high-pass filters, etc. This all-inclusive manual offers coverage of electronic mathand basic electronic theory also. Cannot be beat for acomplete and practical discussion and examinationof filter techniques.

if ..14!116

Electronic Music SynthesizersTAB No. 1167 $8.40

If you're fascinated by the musical possibiliies ofelec-tronic music synthesizers, this book provides allthe information you need to choose, use, adapt, oreven build a synthesizer. It's filled with data on syn-thesizers in general.. and on individual models, can-didly explaining the advantages and disadvantagesofeach one. Such musical workhorses as the Moog(Minimoog and Polymoog), ARP 2600, Oddessy, PAIA,Oberheim, RMI and EML synkey synthesizers arepresented in full detail. Also included is a Chapter onaccessories and on the various components that can,with the help of this book, produce almost any soundyou hear ... or can imagine!

But that isn't all - once yo've learned whatmakes a synthesizer work and how to produce allkinds of music and sound effects, Horn includes a fullsection on how to build your own. Ther's even a list ofuniversal patch diagrams to assist you in your tinker-ing and experimenting. If you'd like a book that givesyou solid, practical help in choosing and using - orbuilding - a synthesizer, this informative manual isyour best choice.

Towers International Op Amp Linear IC SelectorTAB No.1216 $11.40

If you deal with op amps (and linear -ICs with op ampcharacteristics) in any way, here's a wealth of prac-tical Information that will help you solve selection,design, and replacement problems. This internationalguide includes basic specifications for over 5,000 opamps and linear ICs, and contains data on ratings,characteristics, case details, terminal identifications,applications use, manufacturers, and substitutionequivalents. Here you'll readily find data on a specificop amp when you know only the type number. Plus,you'll be able to locate the manufacturer of the device.And, particularly Important with obsolete units, you'llfind guidance on a readily available substitute.

A series of Appendices includes a glossary of opamp terms, tabulation codes for manufacturers,manufacturer house numbers, tabulation codes forapplications, case outline and leadout diagrams, andcodes for leadout connections. If you want the latest,most complete details on op amp -linear -IC's availabletoday, you'll find it in this book.

How To Build Your Own Self -Programming RobotTAB No.1241 $11.75

This is a straightforward how-to book about machineintelligence - a practical guide that shows you howto build a robot capable of learning how to adapt tochanging circumstances in its environment. The uni-que little creature described in this book, namedRodney, can pick up signals and stimuli from his en-vironment and develop perceptions just like humansand higher animals do. Yet Rodney is fully trainable,and his "personality" can be altered and molded byhuman intervention. All in all, Rodney is in a class byhimself, and is a most remarkable and fascinatingmachine - he can program himself to deal with theproblems of the moment and devise theories for deal-ing with similar problems in the future. Yes, Rodney isself -programming, and as a result no two Rodneysbehave exactly the same way. In fact, if you wipe Outhis self -generated memory, he'll develop another onethat's somehow different from the first.

To get yours, fill in the form in this issue or write to ETI Magazine, Unit 6, 25 Overlea Blvd., Toronto, Ontario M4H 1B1. Please allow six weeks fordelivery. Due to sometimes uncertain supplies, some books may not be in stock, please indicate whether you wish your order held or if you wishyour money refunded.

NATOMY OF A MICROA lot happens inside a micro during program execution. We take a look.

WHILE MANY PEOPLE look upon themicroprocessor as a 'black box', a trueunderstanding of its inner workings isvital to its full exploitation. It is im-portant to understand at this early stagethat the much -vaunted micro is merelya very complex piece of electroniclogic and is totally useless on its own.Without the ranks of qualified engineers,programmers and other allied trades,the supposedly mighty micro is an incom-prehensible lump of high technology!

Architectural HeritageThe average general purpose computercan be divided into a number of dis-crete elements. One of these com-ponents is the Central Pro-cessing Unit or CPU, and this can besub -divided still further. The micro-processor is really a totally integratedcentral processing unit; it still needs allthe other bits and pieces to make itperform as a computer. Some of thelater designs do incorporate internalmemory areas and one or two even haveself-contained programs, the new SC/MP

8 BIT INTERNAL DATA BUS

from National Semi with the NIBLBASIC built in being a prime example.

The three main,sections of the CPUare the registers, the' ALU and the con-trol circuitry.

Taking them in order we find thatthe registers are a group of storage unitswithin the CPU. Some of these areavailable to the programmer, others areused solely by the processor as countersor storage locations. The most impor-tant of these is the Accumulator.This register is used to store the data tobe processed by the ALU, a typical in-struction being to add the contents ofsome memory location to the Accumu-lator and to hold the result in theAccumulator for further processing.Many of the current families have othergeneral purpose registers for datastorage - the 8080 has six for example.

Flagging Already?Closely associated with the Accumulatorare a number of special registers calledthe flags. These are used to indicate thestatus of the ALU after an operation.

07 00BI DIRECTIONAL

JVL DATA BUS

DATA BUSBUFFER/LATCH

Typical flags are 'carry' showing than anarithmetical carry has occurred, 'over-flow' which simply shows that thenumber has exceeded the word lengthof the Accumulator and a number ofbits which indicate the sign of the resultin the Accumulator. There is also oneother register connected with theAccumulator and ALU and this is theindex register. This holds any offsetsused in addressing in indexing andits inclusion is machine dependent.

The processor also requires a num-ber of special registers, the instructionregister and the program counter beingtwo typical examples. These both havea 'double word' capacity, that is theycan hold a full sixteen bit address. Thecontents of the program counter are al-ways one in front of the address cur-rently being used. This is in order toallow subroutines to rejoin the pro-gram at the right place. When multiplesubroutines are used, these addressesare held in a LIFO memory area calledthe stack. Some processors have a built-in stack which allows only a certain

Fig. 1. Block diagram of the internal areas ofan 8080. The TEMP registers (*) are used bythe CPU i ernally and cannot be accessed.Figures in to the number of bitsavailable i or latch.

ACCUMU ATOR18/

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ETI-AUGUST 1981 25

ANATOMY OF A MICRO

number of subroutines, whereas othersuse a dedicated area of memory, whichcan be, in theory, as large as you like.

All the stored information in memoryis, until decoded, garbage. The instructionregister performs two tasks in that it notonly holds the currently selectedaddress contents but also decodes themto see if they are valid instructions ordata. This is usually done by a maskprogrammed ROM (Read Only Memory)which has all the valid instructionsstored in it. The reason for coding theinstructions set into a 'microprogram' aretwofold. Firstly, it makes the controlcircuitry much simpler and, secondly,one can, in theory at least, change theinstruction set of one's processor. As anexample of this there are some 20 extracodes built into the Z80 CPU that arenot mentioned in the manuals. Appa-rently they are not all guaranteed towork on all Z80s. Manufacturers some-times use these codes to verify-theoperation of the CPU or memory chips.Usually the codes are not the same fromone manufacturer to another. (Oneperson we know found one in the 6800which he gave the mnemonic EX -CUD,or EXecute, Curl -Up and Die. Whenexecuted,the chip would cycle throughthe memory, dumping some hex codeinto each location. Upon completionthe device then went into a WAIT andwould ignore any efforts to reset orreactivate it).

Cycling AroundAll the processes of control are underthe charge of a central clock whichsynchronises the various happeningswithin the CPU. Some processors re-quire a two phase clock, others a

single phase, but in almost all cases

MEMORY TRANSFERUNIT

MEMORY ADDRESSREGISTER

the clock must be crystal controlled.The reason for the accuracy needed isthat, if one is to expand the systemfurther than the basic CPU and itsassociated support circuitry, the clockmust remain stable under variations oftemperature and varying loads. Compu-ter buses are fairly capacitive and can,over reasonable transmission distances,turn a nice square wave into a veryunpleasant object indeed. The funda-mental speed of the CPU is governed bythe clock frequency. The original 8080ran at 1 MHz and will, therefore, processat twice the speed. However, andthis is a common misconception, theactual CPU doesn't process at thesespeeds because of a number of reasons.

The most obvious reason is that theALU is a serial device, that is it takesone bit at a time rather than processingthe entire word. The second reason,which I will elaborate on in a minute,is that one has to perform a numberof discrete operations within the chipjust to get the information in a placewhere it can be processed and thistakes time. All these operations areperformed in cycles, the fundamentalunit of time taken to fetch and executea single instruction. On inspectionof a data sheet on your chosen microyou will find this time quoted in termsof the number of clock cycles taken.All other instructions are then specifiedin the number of cycles that they take.State VisitTo further explain this concept of in -

Fig. 2. Functional block diagram of a CPU.This represents the minimal configuration youwould expect to find. You could implementthis (for fun) in discrete logic elements andsee how it worked. It makes a good demon-stration piece for schools and colleges.

CONTROLUNIT

struction cycles let's take a look at thevarious types. The basic -FETCH cycle,also known as the M1 cycle, is made upof four states. During the first three,the processor fetches the instructionfrom the memory location indicated bythe program counter. The counter is atthis point showing the current locationand has not been incremented. The -fourth cycle is taken up by decodingthe instruction. An example of this isthe instruction to add the contents ofa register to the Accumulator. If wewish to access a memory locationrather than a register, we will have toperform a memory read, which requiresan extra machine cycle. Say we wishto add the contents of a given memorylocation to the contents of the Accumu-lator. The sequence of operations is

as follows: the processor extracts thesingle byte instruction from the memorylocation given in the program counter;this takes three states. This is decodedand the processor sends, as an address,the contents of its H and L registers.The data word returned during thiscycle is held in a temporary registerinside the CPU and we have now usedsix states. The final act of adding thetemporary register contents to theAccumulator takes a further statemaking seven in all, or two cycles.The longest operation of all, in 8080code, takes 16 states or five machinecycles.

The Ins & OutsThe final section of our look at theinternals of a CPU is the connnectionsyou can make with the outside world.Generally, the CPU is housed inside aDIP package with some 40 legs. Under

ARITHMETICUNIT

DMA

PROGRAMCOUNTER

MEMORY BUFFERREGISTER

INSTRUCTIONREGISTER

DECODE &CONTROL

CARRY ADDER

'INDEXREGISTER

OVER-FLOW

t tACCUMULATOR

26 ETI-AUGUST 1981

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normal circumstances, assuming thestandard eight bit CPU, we will have16 pins for the address bus, eight pinsfor the data bus and 16 pins left toplay with. Just what you do with themdepends on the kind of CPU you have,but let's take a close look at the pinson an 8080.

the synchronisation of external trans-fers. These include memory and I/Ooperations and it is the converse ofDBIN. There now follows a groupof controls, which are concerned withthings called interrupts. An interrupt isthe computer equivalent of a tap on theshoulder and is used by peripheral devices

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Having already mentioned the addressand data bus, we only need to say thatthe data bus is a bi-directional systemand is capable of tri-state operation. Itcan assume a high impedance state,which is neither a logic zero nor one andis used under some special circumstances.Four further legs can be allocated topower; the device needs ±5V, +12V andground. Yet two more legs can beallocated to the required two phaseclock, leaving us ten possible controlsignals to communicate the state of thedevice to the outside world. These areSYNC, DBIN, WAIT, HLDA, INTE,READY, HOLD, INT and RESET.Taking these in order, the SYNC indicatesthe first state of each machine cycle,thus acting as a synchronisation signal,hence the name. The DBIN signal tellsthe outside world that the CPU canaccept data. It should be used to ex-ternally enable the transfer. WAIT is anindication that the CPU has entered aWAIT state, triggered by pulling theREADY line low before the secondstate time. This causes extra states to beadded to the cycle time for as long asthe READY line is held low. Theprocess is often used in situations wherethe memory or device currently beingaccessed is slower than the processor.

Our next signal, WR, is provided for

Pin designations of the 8080. Developed byIntel, fathers of the micro, it is still regardedas the workhorse of eight bit processing. Italso spawned the Z80, probably the mostpowerful eight bit chip using current techno-logy (although it faces some stiff competitionfrom the Motorola 6809).

A10GNDD4

D5

D6

D7

D3

02DIDO

-5V

RESETHOLDINT

oft2

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WRSYNC.5V

1

2

3

4

5

6

7

8

9

10

11

12

13

1415

16

17

1920

Fig. 3. Timing diagram showing the variousstates that can make up a machine cycle:The vertical arrowed lines indicate informa-tion access states.

to tell the processor that they are readyto be looked at. The INT line must beset high to tap the computer on itsshoulder, but this will only work if theINTE line has been enabled previously.Inside the CPU, the interrupt is signalledby a status bit being set and the externaldevice must put its instruction onto thebus in order for any action to be taken.The HOLD line is concerned with directmemory access and as such we shall notdwell on this. The HILDA is merelyan indication that the CPU is in

a HOLD state. Finally we havethe RESET line which, as its nameimplies, does. The signal will restore theCPU to the first state of a machine cycleand it also clears the program counter.It is essential to start all the power upsequences with this signal I otherwiseyou never know what you may findyourself doing! It is also worth notingfor all those sceptics among you thatpressing RESET does not destroy allyour registers, it merely sets you backto the beginning witnout destroyingyour program unless the person whoprogrammed the monitor on your systemclears the memory as the first operation.Whoever said that programmers werelogical anyway?

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27

The Fun of Electronics

Hot..oGRAPHY

EXHIBITION. _

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2P100s, tIcation

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wan 1M1.1 inputI Probe resistance9M11 1°,0

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HOLOGRAMSHolography is the art of making three dimensional photographs, as Anne Sullivanexplains. If you think your collection of slides takes up a lot of space now...

At first not a very impressive shot (above); a magnifying glass (in focus) with out -of-focus bottles in the background but these two photo-graphs together demonstrate well the wonder of holograms for if we refocus the bottles appear sharp. We can also move to the left whichwould bring the bottles on the right into view - and still in focus.

Holography records light wavesreflected from an object andreconstructs them to produce a three-dimensional image. Holograms canonly be recorded using a strongcoherent light, so, to explainholography it is important to unders-tand the nature of light itself. All lighttravels in waves. White light is com-posed of all the colours of the spec-trum, each colour having its ownwavelength. Because white light iscomposed of many differentwavelengths and phase orientationstravelling together, it is known as in-coherent light. Coherent light is com-posed of waves of identical lengthand frequency travelling in phase,such as that produced by a laser.

Mirror, Mirror....All objects reflect light, the amountvarying in intensity according to theshape and nature of the object. Ahologram is recorded whenwavelengths of coherent light thatare in phase overlap to produce awavefront known as an interferencepattern. The interference pattern,which records the dimensions anddepth of the object, is recorded on aphotographic plate and when the in-terference pattern is reconstructed,we see what appears to be a three-dimensional image of the original ob-ject - a hologram.

Holography was discovered byDennis Gabor in 1948 at the BritishLaboratories in Rugby. His earlyholograms confirmed this theory, butthe images were dim and blurred.Development was hindered by a lackof a sufficiently strong source ofcoherent light and photographicemulsions of a high enough quality.In 1960 with the invention of the laser,a strong source of coherent lightbecame available and in 1964 twoAmerican scientists, Emmett Leithand Juris Upatnicks were able to fur-ther the pioneering work done byGabor. Leith and Upatnicks producedthe first bright holograms and thesystem they developed is known as'off axis transmission holography'.

Object LessonTo make a hologram the light from alaser is split into two beams using abeam splitter. One beam is directedonto the object to be recorded (thereference beam). The intensity of thelightwaves reflecting from all thepoints of the object combine withwaves of the reference beam to pro-duce an interference wavefront in theemulsion. The photographic plate(which is an extremely fine grainsilver halide emulsion) is thendeveloped and fixed in a similiar wayto conventional photographic film.The developed plate which contains

the interference pattern is ahologram.

Image MakingTo reconstruct or view the hologram,the reference beam from the laser isdirected at the holographic plate atthe same angle as in the recordingstage. When it emerges it recreatesthe light waves from the original ob-ject and reconstructs a three-dimensional object behind the holo-graphic plate. this type of hologramwhere the image is reconstructedbehind the plate is known as a 'virtualimage hologram'.

Reconstruction of a hologramwhere the image appears in front ofthe plate (a 'real image hologram) ismore complicated. If the procedure isreversed and the holographic plate islit from behind, the image that isreconstructed in front of the plate willbe back to front and with reverseperspective; that is, the objects in thebackground will appear larger thanthose in the foreground. This inside -out image is known as pseudoscopic.

In order to create a real imagehologram a second hologram is madeof the pseudoscopic image. Whenthe second generation hologram isreconstructed, the image appears infront of the plate the correct wayround ie orthoscopic, the image hav-ing been reversed twice.

ETI-AUGUST 1981 31

HOLOGRAPHY

Another type of hologram wasdeveloped in the Soviet Union in theearly sixties by Y.N. Denisyuk whicheliminated the need for a laser toreconstruct the image and so helpedto bring holography out of thelaboratory and make it more accessi-ble to the public. This type ofhologram is known as 'white lightreflection hologram' and, although alaser is required to make thehologram, the image can bereconstructed using a white lightsource.

Daylight 3-DIn white light reflection holography,Denisyuk also eliminated the need fora beam splitter. A beam of coherentlight is passed through theholographic plate and acts as boththe object and reference beam. It il-luminates the object to be recordedand is then reflected back throughthe holographic plate. The emulsionrecords the interference between thebeam and the reflection from the ob-ject. The hologram is viewed by direc-ting white light onto the holographicplate. The plate acts as a filter andselects only the coherent light toreconstruct the hologram.

Another method of making whitelight reflection holograms uses thepseudoscopic image of a lasertransmission hologram (in a similarway to making a real image transmis-sion) but with the reference beam ofthe second hologram coming fromthe opposite side of the plate.

In 1969 Dr. Stephen Benton,working for the Polaroid Corporationdeveloped a system that enabled a'real image hologram' to be viewed inwhite light. Making a so-called 'whitelight 'rainbow' transmissionhologram' is a more complicated pro-cess, but it basically involves twostages. Initially, a transmissionhologram is made. Then a secondhologram is made in the same waythat a 'real image hologram' would berecorded except that just a horizontalslit (3-5mm) of the master is il-luminated. The slit is projected in -front of the hologram and the whitelight passing through it acts as afilter. The white light passingthrough the slit is diffracted and pro-duces a rainbow effect, so, depen-ding on the viewing angle theholographic image appears in all col-ours of the spectrum. Dr. Benton has

/ /BEAM I, /

MIRROR

/ / /

since modified his process and isnow able to produce achromatic(black & white) images. Another typeof reflection hologram known as a'dichromate gelatin hologram' wasdeveloped in the USA in the sixties.These holograms are made using am-monium dichromate instead of asilver halide plate. This method pro-duces holograms with a very brightimage, but limited depth. Its majorapplication so far has been in the pro-duction of holograms in the forms ofpendants.

Life ClassIn all the methods of holographypreviously described the subject mat-ter has to be an inanimate object, asany movement, even breathing, would

LASER

Two dimensional picturessuch as this do not chargewith different viewingangles. With a hologramthe sphere would movebehind the pole, and thecube could obscure thepole if viewing angle waschanged, by moving yourhead.

disturb the interference pattern ofthe wavelengths and no image wouldresult. However, animate objects canbe recorded holographically using apulsed laser. A pulsed laser emits in-tense flashes of coherent light, ratherlike a flashgun, which freeze themovement of the subject long enoughto record the image. Using a pulsedlaser it has even been possible tomake a hologram of a bullet in flight.Pulsed lasers can also be used tomake holographic portraits of people,but when making a hologram of a per-son a large sheet of frosted glass hasto be used to diffuse the light fromthe laser for safety.

Another type of hologram, an 'in-tegral hologram' incorporates move-ment. Integral holograms are not

Fig. 1. The single beam from a common laser is split in two. One beam (reference)is taken directly to the photographic plate. The other gets there via the objectThe two beams produce an interference pattern in the emulsion.

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ETI-AUGUST 1981

strictly holograms, but a marriage ofcinematography and holography asthe subject matter is not recordedwith a laser, but with ordinary 16 or35mm black and white film. An in-tegral hologram is basically a seriesof holograms joined together tocreate movement. The process wasdeveloped by Lloyd Cross of theMultiplex Co. in 1974. An integral (ormultiplex) hologram is also made intwo stages. First the subjects is film-ed on a turntable which moves at afixed speed. Any movement to berecorded has to be slow and smoothor the resulting hologram will haveblurred or jerky movement. The blackand white film is then scanned by alaser and each frame is made into avertical strip hologram using a techni-que similar to the 'Rainbow' method.The resulting series of vertical stripholograms are contained on a flexiblephotographic sheet. To reconstructthe holograms the film is usuallyplaced in a 120° cylindrical container(360° holograms can also be made).The container is illuminated frombelow by an ordinary incandescentlight source. Integral holograms arepopular as they eliminate some of theproblem of the other types ofholography, in that they are not con-fined to same size reproduction,allow a certain degree of movement,can be copied relatively cheaply andthey can be reconstructed easily us-ing an ordinary light source.

ApplicationsThe applications of holography arenumerous - among them, storingdigital information, recording worksof art and preserving them for posteri-ty, as point of sale displays for adver-tising, in education to demonstratecomplex forms such as molecularstructures, as a completely newmedium for artists to work in and asan art form in the home.

MOVES FILMPAST WINDOW

RE ERENCEBEAM

(PULSED)

MASK

ILLUMINATINGBEAM (PULSED)

Fig. 6 One method of producing a

holographic film of a moving object. Apulsed beam illuminates the spinningcube.

RECONSTRUCTEDIMAGE

DIVERGINGBEAM

PLATE A

Fig. 2 Recovering a holographic image. Abeam of light (white or laser, dependingon the method of recording used) isdirected at the photographic plate at thesame angle as that of the reference beamduring recording.

PLATE A

CONVERGINGBEAM

pRECONSTRUCTEDIMAGE(PSEUDOSCOPICREAL)

Fig. 3 The image can be made to appear infront of the plate by illuminating it fromthe front. However, the image is reversedin all respects. Objects in the backgroundappear to be larger than those in theforeground.

PLATE B

CONVERGINGBEAM

RECONSTRUCTED

PORTHOSCOPICIMAGE

REAL)

TFig. 4 To return the perspective to normal, a second hologram must be made fromthe first.

PLATE A

PLATE B

CONVERGINGBEAM

RECONSTRUCTEDIMAGE(PSEUDOSCOPICREAL)

SUBJECT

DIVERGINGBEAM

ffiRECONSTRUCTEDIMAGE

DIVERGINGBEAM

Fig. 5. To make a white light reflection hologram, the recording reference beam and objectto be recorded are on opposite sides of the plate. The back of the plate is often coated withblack to give a dark viewing background during reconstruction.

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34 ETI-AUGUST 1981

THE WEIN BRIDGE OSCILLATORProbably the most popular type of low frequency sine wave oscillator as it is superior in virtually all respectsto phase -shift types. Unfortunately it does not seem to be all that well understood. This article sheds somelight on this most useful circuit.

Twin Wein Bridge oscillator using lamps for feedback stabilisation.

MOST STUDENTS of electronics - thatincludes hobbyists, you learn from yourhobby don't you? - would be familiarwith the "Wheatstone Bridge"; thatoften -handy technique for measuringunknown values of resistance. The WeinBridge is an outgrowth of the Wheat-stone Bridge. The basic circuit is shownin Figure 1.

This circuit has some unique pro-perties. The networks R1 -C1 and R2 -

C2 form a potential divider betweenpoints A and B. Both networks have animpedance which decreases with fre-quency. At one frequency, and one fre-quency only (depending on the valuesof R1 -C1 and R2 -C2), the bridge willbe balanced. That is, if a sinewave vol-tage is applied between A and B novoltage will appear across C and D.Another interesting, and useful propertyof this bridge is that, at the balancefrequency, the phase of the voltageacross C and B will be exactly the sameas that across A and B. The same willbe true for harmonics of the balancefrequency, but, the impedances of R1 -

C1 and R2 -C2 will not be the same as atthe balance frequency and the bridgewill be unbalanced.

Well, how are these properties of theWein Bridge used in an oscillator? Thebasic circuit of a Wein Bridge oscillatoris shown in Figure 2. The componentnumbering of the Rs and Cs is the same

as in Figure 1. We are assuming that theamplifier has good common -mode re-jection, an infinite input impedance andzero output impedance. Fortunately,an op -amp is a reasonable approxima-tion to this and the circuit as shown willwork well with a common -or -garden741 at frequencies up to 10k Hz.

The Wein Bridge components areconnected such that positive andnegative feedback is applied around theop -amp. This should be readily apparentfrom the way Figure 2 its drawn. Thenegative feedback is derived from the re-sistive potential divider R3 and R4.Positive feedback is provided by the po-

zp

Figure 1. Basic circuit of the Wein Bridge.

tential divider R1 -C1 and R2 -C2. Theamount of positive feedback throughR1 -C1 will increase with frequency asthis network has a decreasing impedanceas frequency increases. The parallel RCnetwork formed by R2 -C2 also hasdecreasing impedance with increasingfrequency, tending to shunt the amountof applied positive feedback (via R1 -C1)to ground. At the balance frequencythe applied positive feedback will be amaximum, falling at frequencies aboveand below the balance frequency. How-ever, if the bridge is balanced, the posi-tive feedback and the negative feedbackwill be equal . . and the circuit will notoscillate. But, if the amount of nega-tive feedback provided by R3 -R4 ischosen to be fractionally less than the

Cl R1

Figure 2. Basic Wein Bridge oscillator circuit.

35ETI-AUGUST 1981

WEIN BRIDGE OSCILLATOR

positive feedback at the balance fre-quency, the circuit will oscillate. Sincenegative feedback predominates at allother frequencies, and the bridgeremains unbalanced, harmonics of thebalance (or resonant) frequency are sup-pressed and the waveform produced willbe a sine wave of great purity.

In practise it is necessary to includesome means of sensing the amount ofnegative feedback so that the amplifiergain can be held at the precise amountnecessary to ensure oscillation. If theamount of negative feedback is toolittle, the waveform wilt be distorted.If too much, oscillation will not occur.Secondly, if the gain varies (for what-ever reason) the feedback needs to bestabilised to prevent distortion and

level variations.The simplest way of doing this

is to incorporate a thermistor or tung-sten filament lamp in the negativefeedback potential divider. If the latteris used for this purpose - and commonlights bulbs used for bezel lamps havetungsten filaments - it would replaceR4 so that gain increases of the ampli-fier stage cause increased currentin the lamp. This, in turn, would causethe temperature of the filament to rise,increasing its resistance, thus increasingthe amount of negative feedback. Theuse of these temperature variabledevices sets a limit on the lowest fre-quency at which the circuit can be used.When the period of oscillation is com-parable to the thermal time constant ofthe particular light bulb or thermistor,the change in resistance over each cyclewill bring about gain variations whichresult in distortion of the output

CI C2

2.2 siF R2 0.068 p F300K

021N7557.5V

Figure 4. Example of a practical Wein Bridgeoscillator with a FET in the feedback (cour-tesy National Semiconductors).

36

waveform. Also, these devices have a"settling time" that prohibits thefrequency from being changed quicklyin a variable oscillator using this circuit.

The solution to these problemsentails using a FET as part of thefeedback element. The FET becomespart of R4 - as shown in Figure 3 -driven by an RC network between theop -amp output and the gate. In thisway, the 'averaging time' of the circuitcan be tailored to suit the job required.An example of a practical circuit is

given in Figure 4.A lot of the advantages, and the uni-

que properties of the circuit, becomeapparent from a look at the mathe-matics involved; it's quite straight-forward really.

The impedance of C1, at a certainfrequency 'f', is given by:

1

ClZ - jwC

Where: ZC1 = impedance of C1

= 2 nf

j =1/-1So the total impedance Zs, of the seriesnetwork R1 -C1 is given by:

Zs = RI + jwC

Since the impedance of capacitor C2 isalso given by:

ZCl =1

jwC

Where: Z2 = impedance of C2

w = 2 id

j =\/-1and C2 is in parallel with R2, the totalimpedance of the parallel networkR2 -C2 (Zp) is given by:

1 1 1=

ZP+

R2 1

jwC1

therefore: = + j (...)C

PZ R2

Oscillation will occur when:

R3 ZsR4 ZP

since it is this condition which will re-sult in unity gain.

Figure 3. Feedback stabilisation using a FET.

If we let R3 = 2 X R4, and substitutethis in the equations for Zs and Zp, thisequation becomes:

2R4 1

= R4 (RI +1 + j 6.)C jwC

R2

and this simplifies to: w2 _1

121 R2 Cl C2

since

then

and f -

w= 2 Tr f,

2/rf =

N/121 R2 Cl C2

1

1

27r -/R1 R2 Cl C2

The major advantage of the WeinBridge oscillator is its inherent stabilityand predictable frequency output. Inother low frequency oscillators em-ploying RC networks in the feedback,the frequency of oscillation is directlyproportional to the values of the com-ponents in the network. In the WeinBridge, you can see from the lastequation that the frequency of oscilla-tion is proportional to the squareroot of the component values in thenetwork. The ease with which ampli-tude levelling and level stability can beachieved by using simple thermaldevices in the negative feedback is

another advantage. Thirdly, the low dis-tortion possible with this circuit con-tributes greatly to its popularity.

On the other hand, to vary thefrequency, two components have to bevaried simultaneously - either C1/C2or R1/R2. The fact that the one ofthese is wholly above ground' compli-cates things - but it's not an insolubleproblem as there are many Wein Bridgeoscillators around!

ETI-AUGUST 1981

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INTERNATIONAL

Ground LoopsYour twenty-first birthday comes andgoes and suddenly you have more moneythan you know what to do with. You rushout and buy a tonne of stereo equipment.Finally, late at night you get it all con-nected up, hit the power switches and waitfor glorious 100% pure sound to pourforth. Instead, however, when the relaysclick over, your ears are assaulted by thishorrendous 60Hz hum. Obviously,something is wrong.

Next month we're going to look atground loops in the context of HiFi equip-ment and how you can cure your loopywoes.

CP/MThis denizen of the disk is largelymisunderstood by neophytes in the com-puter field. More powerful than BASIC inROM, faster than a cassette interface,CP/M can make your micro a bettermachine to live with. Bruce Evans outlinesthe basics.

At thetime of go-

ing to press, thearticles mentioned

are in an advanced stageof preparation. However, cir-

cumstances may result in changesto the final contents of the magazine.

ProjectsNext month we'll be presenting four pro-jects to fill your evenings.

Our first project is aimed at the con-structor with a dim and/or dull stereo.Next month's LED VU meter willbrighten up even the most boring ofsystems and provides a meaningful indica-tion of what's happening in the wires toboot.

If you have suicidal tendencies, youcan safely slake them with our Russianroulette game. Easy to build and use, wepredict it will be a hit at parties, in bomb -shelters, and with executives.

If you've been saving up to outfityour 1971 Dodge Polara with a

tachometer (to impress your girlfriend orwhatever), don't write that cheque! Nextmonth's issue will bring a high qualitybargraph tachometer that's easier to readand can serve as landing lights for moths.

And finally, if you've ever had to putup with a power failure, you can ap-preciate how useful it is to have a workingflashlight, candle, match, even a tiredfirefly. Our emergency power unit keepsits battery permanently juiced and readyfor the utility eclipse. Great for the home,cottage or treehouse.

Flat PowerFlat batteries could probably solve all ofsociety's problems. You could use them asbookmarks, to shim up a chair leg, evenplay a mean game of solitaire. They'realso pretty decent as power sources, asJohn Van Lierde reveals.

Gm RevisitedNext month our theory corner will belooking at Gm. What's Gm you ask? Evenif you don't ask, we're telling you. It's aneat way to figure out how to make tran-sistors work properly, so stop groaning,sharpen up your wits and keep an eye onyour mailbox for the September issue.

38 ETI -AUGUST 1981

555 ASTABLESRay Marston devotes a few pages to a discussion of special applicationfor 555 or 7555 astable circuits.

THE old-fashioned 555 timer, or itsmodern CMOS counterpart, theICM7555, can readily be used as a

highly stable and cost-effective astablemultivibrator. Usually, the device ismerely used to generate simple squarewaves, but in practice it is readilycapable of performing some fairly fancytricks: it can, for example, be used togenerate useful ramp and sine wave-forms and can be gated.

Gating The 555/7555 AstableThe 555/7555 astable can be gated onand off in a variety of ways, to producea variety of output waveforms. Figure 1shows the basic connections and theequivalent circuit of the standard555/7555 astable, it is necessary tounderstand the operation of this basiccircuit in order to appreciate the actionof the various gating methods. In thefollowing discussions, a 12 V supply railis assumed in all circuits.

The first point to note about the Fig.1 equivalent circuit is that the IC con-tains a three -resistor potential divider,two voltage comparators, a flip-flop, atransistor and an output buffer. Thedivider ratios are such that one-third ofthe supply voltage (ie. 4 V) is set on thelower comparator and two-thirds of thesupply voltage (ie. 8 V) is set on theupper comparator. The circuit action issuch that, in each operating cycle, C1first charges up to 8 V through R1 -R2,at which point the upper comparatoractivates the flip-flop and turns the pin7 transistor on; the transistor then dis-charges C1 through R2 until the C1voltage falls to 4 V, at which point thelower comparator activates the flip-flop and turns the pin 7 transistor off,causing C1 to recharge through R1 -R2.The operating cycle is then completeand repeats ad infinitum. A ramp wave-form with an amplitude that swingsbetween 4 V and 8 V is generated acrossC1 and a rectangular waveform isgenerated at output pin 3.

The conventional way of gating the555/7555 astable is with the pin 4 resetterminal, as shown in Fig. 2. When thispin is pulled to ground (by a 1k0resistor), the flip-flop output is drivenhigh, thus discharging C1 through R2and the transistor and also driving thepin 3 output low. The resulting circuitwaveforms are shown in the diagram.Note that, when the astable is gated on,

Fig. la. Basic circuit of the 555 -type astablemulti vibrator.

the first half cycle is considerably longerthan the succeeding half cycles. Alsonote that, when the astable is first gatedoff, the C1 voltage takes a substantialtime to decay to zero. The pin 3 outputis zero under the off condition.Alternative MethodsOne alternative method of gating the555/7555 is shown in Fig. 3. Here,when the circuit is gated on, D1 is

reverse -biased and the astable operatesin the normal way, but when the circuitis gated off D1 shorts out C1 and pullspoint A to ground; in practice, ofcourse, SW1 can be replaced by anelectronic switching waveform (theoutput of a CMOS gate, etc.) Note inthis circuit that, when the astable isgated on, the first half cycle is againconsiderably longer than the succeedinghalf cycles, but that the Cl voltage fallsabruptly to zero at gate -off. Also notethat the pin 3 output is high in the offstate.

ON

OFF'

+12V

-OFF

B

L

+12V

Fig. lb. Equivalent circuitof the 555 -type

astable multivibrator.

ON -a. .4-OF -

8V

OV

ov

Fig.3. Basic method of gating the 555 astableusing Cl, with resultant waveforms. Note thatthe period of the first half -cycle is longer thanthat of the succeeding half -cycles.

- OFF -I.

154

OFF -

-- 4Vov

12V

ov

Fig. 2. Conventional way of gating the 555astable, with resultant waveforms.

ETI-AUGUST 1981ov

39

555 ASTABLE 12V

Figure 4 shows how the above circuitcan be modified so that the duration ofthe first half cycle is almost equal tothat of the succeeding half cycles. Thisis achieved by choosing the R3 -R4values so that the C1 voltage is only afraction below 4 V (one-third of supplyvolts) under the off condition. A sub-stantially different set of waveforms canbe obtained by choosing the R3 -R4values so that the C1 voltage is a

fraction below 8 V (two-thirds ofsupply volts) under the off condition, asshown in Fig. 5.

It should be appreciated that the555/7555 astable can only oscillate if itstiming capacitor (C1) is free to swingbetween the 4 V and 8 V switchinglevels. This simple fact makes itpossible to voltage -gate the astable byusing the circuit of Fig. 6. Here, thecircuit produces output waveforms onlywhen the input voltage exceeds 8 V.The circuit can be made to trigger at

412V

UVOF F -

- 8V

4V

ov

12V

ov

Fig. 4. Modification of the Cl gating scheme,giving constant -period half -cycles.

narrow output pulses at the 'B'terminal. This circuit is useful forgenerating variable -frequency constant -width pulses.

555/7555 Sine Wave GenerationFigure 11 shows how a sine wave signalcan be obtained from a 555/7555astable. Here, the symmetrical rampwaveform of C2 is buffered by Q1 andthen AC coupled to the R1 -R2 -D1 -D2divider/limiter netword. This networkattenuates the ramp signal and thennon -linearly removes the ramp's positiveand negative peaks, to produce a sine -shaped waveform of about 1 V peak -to -other levels by giving the op -amp anappropriate voltage gain factor.

Finally, an alternative method ofgating the 555/7555 astable is shown in

A

B

OV

- OFF ON OFF

-BV

ov

12V- ov

Fig. 5. This sight modification of the Clgating scheme produces a considerable changein the circuit output waveforms.

Fig. 7. Here, the circuit is gated off bydriving the C1 voltage above 8 V by Dl.A feature of this circuit is that its 'B'output is low under the off condition.

Asymmetrical AstablesThe basic 555/7555 astable generatesnear -symmetrical output waveforms,provided that R2 is large relative to R1(giving near -equal C1 charge and dis-charge time constants). Figures 8 to 10show alternative methods of generatingnon -symmetrical waveforms. In Fig. 8,C1 charges through R1 -F2 butdischarges through R2 in parallel withR3 -D1, to produce the waveformsshown. In Fig. 9, C1 charges throughR1 and R2 in parallel with R3 -D1, butdischarges through R2 only; this circuitis useful for providing narrow outputpulses at the 'B' terminal.

Finally, in Fig. 10, C1 chargesthrough R1 -R3 -D2 and dischargesthrough D1-RV1-R1-R2, to produce

A

-OFF .1. :4111 ON

-

ov

OFF -;

12V

- I - r - - 4V

12V

ov

peak amplitude at the output terminal.The distortion level of the resulting sinewave is typically of the order of 3% andits frequency can be varied from a fewcycles per minute to several hundredkilohertz by suitable choice of the C2value.

AM OutputFigure 12 shows how the pin 3 squarewave output of the 555/7555 astablecan be amplitude -modulated to producethe typical attack -hold -decay envelopeof a simple musical instrument or of aspecial -effects sound generator. The

.12V

OFF-wl ON.

jeV

Fig. 6. The voltage -controlled astableproduces an output only when Vin exceedstwo-thirds supply (8 V in this example).

heart of the unit is the diode AND gate,or mixer, formed by D1 -D2 -R5. Oneinput of this gate is fed from the outputof the astable via R3 -R4 and the otherfrom across R6. The basic action of thisgate is such that (ignoring the diode voltdrops) its output amplitude is equal tothe lesser of the two inputs.

Con timued on page 63.

Fig. 8. A method of producing a non -symmetrical fixed -ratio from the 555 astable.

Fig. 7. This Cl gating scheme produces a'B' output that is low in the off condition.

40 ETI-AUGUST 1981

BENCHPOWERSUPPLYUNITDesigned with the beginner inmind, this bench power supplyunit combines high performanceand quality and yet is simpleto build.

TEST AND EXPERIMENTAL equip-ment remains perhaps one of the mostpopular project areas in electronichobbyist magazines. Rightly so, ofcourse - the home constructor wouldfind it difficult to build and test hisprojects without test gear - and themost fundamental piece of equipment(bar a test meter) is arguably a powersupply. The beginner naturally uses drycells as a power supply for his first fewprojects, but eventually there comes atime when his requirements are for avoltage which is impossible to obtainwith batteries (eg 20 V) or a highercurrent than batteries can supply (e.g. 1amp).

Bear in mind that a good powersupply unit is worth its weight in gold.Consider this: you would only have to

Inside our Bench Power Supply Unit.

purchase 30 or 40 x 9V cells at today'sprices and the power supply would bepaid for!

And so the scene is set! Enter fromthe wings to rapturous applause thePSU, a power supply with six switchedoutput voltages (although you can adaptto a fully variable 1V5 to 20V supply ifyou wish). One simple, three terminalintegrated circuit, (the LM317K) doesall the hard work and it features amaximum output current of 1.5 amps,more than adequate for 99% of projects.The IC is called a voltage regulator andthis particular variety has been aroundfor three or four years now. That mustsay something for its quality andreliability in these days of rapidlychanging technology. The alternative isa voltage regulator, using relativelyexpensive discrete transistors. However,of necessity these discrete componentvoltage regulators are complicated ifthey are to be as efficient as their ICcounterparts. Because of this, there aremore things to go wrong (as we all

know, the well-known 'Murphy's Lawstates what can go wrong - will!)

Given that all connections arecorrect our PSU is virtuallyindestructible. Even a direct shortcircuit on the output will do no damage,an internal current limiter keeps thingsin order. In this way, of course, there isless likelihood of a circuit under testbeing damaged if, say, it has a shortcircuit due to a solder bridge betweentracks. A simple dry cell battery wouldcontinue to pass current at its highestrate until removed, by which timedamage may have been done. TheLM317K continually monitors its ownoutput current and if it is too high it"folds back" ie it switches the outputcurrent off. When the short circuit isremoved or repaired the regulator auto-matically switches the current back on.

ConstructionCare must be taken with the primarypart of the circuitry ie everything up toand including the power transformer T1(the left hand side of the circuit diagramof figure 1.

The first constructional step is themarking and drilling of the case.Ideally, a mild steel case should be used,in order to reduce electrical interferencewith other equipment which may bepositioned close to the power supply.Mount the transformer on the base,leaving enough room for the PCB,bearing in mind the size of the capacitorC1. Bolt the fuse holders power on/offand DC on/off switches, neon (withintegral resistor), output sockets andIC1 to the case, leaving only the six -wayrotary switch and the PCB out.

Insert a grommet in the cable hole,push through the power cable so thatenough cable is inside the case to com-plete all of the AC line side wiring(figure3). We have shown all wires to be loosein the figure but when wiring up yoursupply, form all wires around the edgeand keep them together using cable tieslacing cord or ordinary string - what-ever you have at hand. Fasten the cable

ETI-AUGUST 1981 41

BENCH POWER SUPPLY UNIT

Fig. 1. The ETI

0FS1IA COUICITBLOW

r.P."

T1

20Vt0000u 00,

5108

3305

IC

SW1

230R O2

o -oSW3 FS2IA OUIDN

BLOW

NOTES.ICI IS CM 3175SRI IS I AMP 50V BRIDGERECTIFIER01,3 ARE 1N/002

Bench PSU circuit diagram. There's not a lot in it, but what is there does the job well.

HOW IT WORKSSimply by inserting whatever value ofVout we require into the formula, weobtain the necessary value of R2.

eg R2 = 220 (13 I) = 308R25

Transformer T1 provides the necessarystep-down function from 120 VAC to 20VAC which the rest of the circuit requires.It also isolates the low voltage side fromthe high -voltage (line) side ie there is noelectrical connection from line to lowvoltage output.

The 20 V AC obtained at the trans-former secondary is rectified by bridgerectifier BR1 to DC. Filter capacitor CI"smooths out the bumps" providing afairly level input voltage of about 28 V DCto the voltage regulator IC1.

The output voltage of ICI is given bythe formula Vout =1V25 (1+R2/R1).

where R2 and RI are as in figure X byfixing the value of RI at 220R then R2can be calculated from the aboveto be

R2=220 (VV

I25

The nearest preferred value is 330R, there-fore the output voltage is slightly over 3volts DC. This resistor corresponds to R6in the circuit of the ETI PSU and position1 of the rotary switch SW2. By combiningR6 with R5 in series and by turning SW2to position 2, an overall resistance of

330 + 510 = 840R

is obtained giving a voltage of 6 VDC.Similarly the remainder of the voltagesteps ie 9 V, 12 V, 15 V and 20 V areobtained by adding further resistors intocircuit by means of SW2.

0C3

IN ADJUSTOUT

TO IC1

1

The resistor chain and SW2 could bereplaced by a potentiometer to give a con-tinuously variable output voltage but anexpensive panel meter will then berequired, to allow reading of the voltage.Switched resistors give a sufficient rangeof voltages and obviously keep the costdown considerably.

PARTS LISTRESISTORS (All %W, 5%)

OV

SW2

Fig. 2. Overlay details of the printed circuitboard. It is important that capacitor C1is polarised correctly.

R1 820RR2,4,5 510RR3 560RR6 330RR7 220R

CAPACITORSC1

C2C3

10,000u 40 V electrolytic,single ended100n polyester10u 35 V tantalum

SEMICONDUCTORSIC1 LM317K voltage regulatorBR1 1A,50 V bridge rectifierD1,2 1N4002 diode

MISCELLANEOUSSW1 Double -pole, double -

throw toggle switchSW2 6 -way rotary switchSW3 Single -pole, double throw

toggle switchFS1,2 Panel mounting fuse -

holders and 1 Amp quick -blow fuses.

Neon Panel -mounting with inte-gral resistor

T1 20V, 20VA power trans-former

Grommet, cable clip, knob, 2 x 4mm 0/Psockets, case to suit,mounting clip for C1.

42 ETI-AUGUST 1981

as it comes through the case wall using abolt -on cable clip or similar. Thisprevents the cable from being pulledout. Alternatively, you could use a plugand socket connector assembly as wedid (see photographs).

We advise the use of rubber sleevingto cover the joints where a power leadjoins external hardware eg a switch or afuse holder. This can help safeguardagainst electric shock hazards. You cantest your wiring at this point if you havea meter. Measure the output voltage ofthe transformer when switched on. Itshould be about 25-30 V AC under no-load conditions.

Once the line voltage side has beenwired in, the PCB can be completed.Mount C1 on the board using a capacitorclip and solder the tags to the boardmaking sure it is polarized correctly iethe tag close to the red dot or positivePROBLEMS? NEED PCBs? Before you writeto us, please refer to 'Component Notations'and 'PCB Suppliers' in the Table Of Contents.If you still have problems, please address yourletters to 'ETI Query', care of this magazine.A stamped, self addressed envelope will en-sure fastest reply. Sorry, we cannot answerqueries by telephone.

-VeSOCKET

GROMMET

NEUTRAL

R1

SW2

0

Fig. 4. The low voltage side of the benchPSU project.

ALTERNATIVELY YOU COULD USEPLUG/SOCKET CONNECTOR

P CLIP TO HOLD CABLE TIGHTLY

LIVE

GROUND

FUSE HOLDERHOW MAINS INPUT

LIVE CONNECTS TO THEEND OF THE HOLDER,

NEON WITHINTEGRALRESISTOR

SW1ON,OFF

1 I 'le

Fig. 3. Shows connection details of theline circuitry. Care is needed as line voltagecan be dangerous.

marking on the capacitor goes to thepositive connection on the PCB. ThenSW2 (the rotary switch and resistors)can be mounted. Note how the resistorsare mounted on SW2 and make sure youget them in the correct order. Youwon't do any damage if they are in thewrong order but the output voltages willnot be correct.

Next, wire up the PCB, the twoswitches and the output sockets as inthe connection diagram, again taking allleads neatly around the outside of the

case and tying them together. Finally,wire in IC1 to the PCB.

At this stage, the PSU is completeand should work first time. Measure theDC output using a meter and check thatall the settings are correct. If youpossess a 25 V or a 30 V panel meter, analternative suggestion is to insert a 4K7linear potentiometer in the front panelinstead of the SW2-resistor combination,with the meter across the output anduse it to give a reading of the now fullyvariable output voltage.

ETI-AUGUST 1981 43

CANADIANPROJECTSBOOK NO.1

Canadian Projects Book No.1100 pages $3.00 -25 of our most popular projects from ourearlier issues including: Audio Limiter, 5WStereo, Bass Enhancer, Modular Disco, 50W/100W Amp Modules, IB Metal Locator, TouchOrgan, Electronic Mastermind, Double Dice,Reaction Tester, Sound Operated Flash, Burglar efAlarm, Injector -Tracer, Digital Voltmeter.

IMI*8 JANUARY 1961

Projects Book No. 2100 pages $3.95Contains 25 of the best projects from re, .1

issues including the High Performance Se,4000 Amplifier (including Preamps and Pock.Supply), Rumble Filter, Dynamic Noise Filter,Logic Probe, Cable Tester, Function Generator,Rain Alarm, Digital Tacho, 1 wo Octave Organ,Light Chaser, Shutter Speed Timer, Ni-CadCharger and more. First published January 1981.

ELECTRONICCIRCUIT DESIGN

More eC giCircuitsu its$4.50

Over 150 circuits plus articles on CirctiitConstruction, Test Gear, a project on a pikitatPanel Meter, Design notes on 'SpeakerCrossovers, TTL pin -outs, Design notes onCrystal Oscillators.

Hobby Projects100 pages $3.95First published Summer 1980. Contains 25straight -forward projects most of which havenever appeared in the magazine including:Stereo Amp, Audio Mixer, Scratch and RumbleFilter, Constant Volume Amp, GraphicEqualiser, Envelope Generator, White NoiseEffects Unit, Linear Scale Ohmmeter,Intercom, Drill Speed Controller, LED Tacho,Parking Meter Timer, Electronic Organ, TouchSwitch, Electronic Dice, Siren, SimpleReceivers.

Electronic Circuit Design92 pages 53.95A collection of major articles on various aspe.t,of circuit design including CMOS, Audio Amp.lifiers, Power Supplies, SCR's, Op -Amps, Usingthe 3080 and Temperature Control. A largenumber of useful circuits are given but theemphasis is on guidance and how to tackle thedesign for yourself.

25 Electronic PITO' cts

r

ETI S ECI LSAvailable trom your local electronic parts store or direct

from ETI (please add 45c each to cover postage).Send money to:

Electronics Today Magazine,Unit 6, 25 Overlea Blvd.,

Toronto, Ont.,M4H 181

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3 Mail the card and the advertiserwill send you literature freeof charge. If the card has beenremoved, or if you want theinformation in a hurry, phoneor write direct to the advertiserand refer to the ETI issueand page number.

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the card)M. Tech Tips

THIS WEEK MARKS THE END ofwhat might have been one of themost innovative of the SouthernCalifornia fly-by-night computer sys-tem companies, a spark of pure capi-talistic evil when all around was justmediocre avarice and dirty dealing. Itbegan, as so many of these things do,in a tool shed in in a subdivision inMarina Del Vista Mar San Waldo, aprosperous suburb of greater LosAngeles. From this humble begin-ning, over eighty five different pro-ducts (eighty six, actually) emergedto blow the fuses of computer ownersaround the world, all bearing thefamiliar sabre toothed gerbil logo ofThe Flying DiMeglifestafionioliBrothers and Associates.

There are those who would saythat the closing of this promisingyoung firm, after only a year and ahalf of operation, is due to the infla-tionary economic cruelties of ourtimes. However, I think that the pro-blem was far more subtle than eitherof these. Much of it lay with the com-puter industry, which was unable toaccept the sorts of radical designconcepts the brothers were using.

Some examples of this prejudiceare easy to see. For example, therange of parts used in the designs oftheir boards was rather restricted.. .largely limited to old DTL chips whichhad had the numbers rubbed off withsand paper. It should be said in theircredit, however, that every board thatleft their premises was functional.Each one did something. . . in mostcases, smoked and/or burst intoflames. A few of the more sophisti-cated ones exploded.

Perhaps even more innovativethan the actual system architectureof the brothers' designs was thenovel approaches they took to mar-keting their equipment. Consider thead in one major computer magazinefor an eight inch disc drive for $99.00(crank optional at $12.50 extra).However, I think that the most in -

WHAT'SNEW

teresting item in the catalog had tobe the digitally controlled four voicesynthesizer.

We'll probably never know wherethe bothers found all the war surplusbugles they sent out, or what theyfigured the average user needed witha wind sock. There was, however, abeautifully designed interface cardwhich allowed the processor to drivethe four electric washing machinevalves crazy glued over themouthpieces of the instrumentscausing only moderate damage to thesystem's I/O ports, plus a really niftyplastic hand, which could be servocontrolled to handle the mute. Therewas a complete set of documentationprovided (usually either a Xerox of theinstructions for rebuilding a Buickcarburetor or the owner's manual forthe French built Piednonstenchoultrasonic foot deoderizer). Thesystem could be put together withequal ease by either an expert or acomplete amateur, and it must bestated that of the three hundred andtwelve people who bought the inter-faces, only two ever fel: moved towrite in and complain.

Of the rest, only eighty five show-ed up armed with anything larger thana .32. Many only brought knives, clubsor hot tar.

Neither of the brothers wereavailable for comment after the an-nouncement of their dissolution.Their whereabouts appears to beunknown, or, at the very least,unavailable on anything other than a'need to know' basis, and then only toofficials of the FBI and the TreasuryDepartment. I talked briefly with oneof the brothers' distributors in Carmelto inquire as to whether we mighthope to see their products on themarket again sometime in the future.Alas, the answer was... probably not.However, extradition laws can bechanged.

With the brothers no longeroperational, there are relatively few

By Steve Rimmer

workable computer music systemsaround. Well, I suppose that situationwasn't much different before theirplace was mortared. In any case,we're going to have a look at one ofthe finest ones this month. . . thecreator of which couldn't see muchuse for a windsock either.

More KomputermuzikRemember Dave McLey? . . . we

got to look at a bit of his studio a fewmonths ago. Well, in the interval bet-ween then and now, it has sproutedsome new appendages, and becomestill more surreal and karmic andgenerally mind blowing. For onethilng, all the lights now light, theparaphenalia squeaks and whistlesupon command. . . you gotta knowthe command, though, . . .andthings generally sound off in the mostfascinating ways. Thus it was that I,possessed of nothing more than abelly .full of Quarter Pounders withcheese and a slightly dinged up Pen -tax once bought late at night from apoor Swedish phosphor peddler(another story, this) dangling fromabout my neck, did once again ven-ture into the chrome plate and smokygreen plastic of Toronto's dive nuvea,Yorkville, to see what the alchemistof computer music was presently upto.

Actually, when I got there, hewasn't up to much of anything. Thesystem was down. I suggested it hadblown a fuse, which earned me a kindof sour look. We thereupon went forlunch . . .which really made meregret I'd pigged out at Mac's. Half anhour later, upon returning, thingswere again functional and cool.They'd located the burned out fuse,changed it, and all was benificientand wonderful. 'You want a score?'McLey asked, proffering me a page ofsheet music.

'Oh neat.' It looks like Bach. Ac-tually, it is Bach except that it says

ETI-AUGUST 1981 45

WHAT'S NEW`copyright 1981 by Dave McLey'.Shades of Jethro Tull.

'I haven't got around to changingthat.' He explains. 'It thinkseverything it does is by me.'

What is neat about the score,though, is that it is neither handdrawn, nor has it been printed, exact-ly. The computer did it. It wasreproduced under machine control ona Hewlett Packard plotter. It can alsobe displayed, with resolution at leastas good as the printed page, on theCRT of a terminal. When you playsomething on the music system'skeyboard, it will churn out a score foryou. 'It still thinks F-- is the same asa G natural, but we'll have that out ina day or two.'

There's this chick with blond hairand big glasses who wanders in andout from time to time carrying anarmload of printouts. McLey is stilladjusting the software.

`I'm gonna show you some ofwhat it can do,' He begins, 'But if youcome back in three days it'll be ableto do a whole new set of stuff it can'tdo now. I just got the voice boards re-done, and it sounds. .

Harpsi 3`Prelude' is the name of the file theBach piece is stored in. It's called upby telling the machine to 'PlayPrelude'. Once it's playing, it can betold exactly what to play it with.'Harpsi 3', a harpsichord voice patch,would tell it act like aharpsichord.. . it could, however,just as easily be a tuba, a log drum, ora frog. A frog?

`Ya, well, I was fooling aroundwith it the other day, and I had thisvoice, which I called 'frog'. It's still inthere.' There's also a voice thatsounds vaguely New Wave, althoughthe file name is not reproduceable ina family publication. Bach doesn'tsuit New Wave, anyway.

46

Anyway, it has a harpsichordvoice. Just like an electric piano, ex-cept this once sounds like a harp-sichord. If you didn't know you werein McLey's office listening to his com-puter you'd swear you were in theworkshop of Herz or Zuckermann,tucking your ears into the seven-teenth century. 'Does it sound fairlyreal?' He asks.

'Well, ya. You can't hear the plec-trums on the strings, or the keys bot-toming out, but other than that itsounds about right.' The harpsichordI've played had a manual and plectraof genuine authentic plastic; anyonefamiliar with a decent instrument pro-bably wouldn't be as concerned withthe lack of these sounds. Maybe'Harpsi 4' could be developed to pro-duce the sounds of bargain in-struments.

He sets the prelude to playrepetitively. 'It'll have thirty two

voices in a while; I've only got eightgoing now, 'cause we're still chang-ing them.' McLey says. Each voice is,in fact, a digitally controllable analogsynthesizer all by itself. 'Myengineers just love it when I handthem a board they've been working onfor a month and say 'it's reallynice. . . now change it to do thisand this.'

`Changing the voices is just amatter of telling the machine to playdifferently . .all the patchcords arevirtual.' He types a few characters,and in the space between two notesthe computer instantly repatchesitself and plays horn. Good horn, too.Not like me; on my best days I soundlike a moose call. The changes areglitchless, and require so little typingthat it's possible to change the pat-ches on the fly during a performance.

'It also does things like adjustingthe mix,' He can bring down the levelof one voice relative to the rest fromthe keypad on the terminal, 'and pans

from right to left, and so on.'It also handles transposition,

right there before your very ears. If it'ssitting there cranking out a piece, itcan be instructed to do it in a dif-ferent key, just by using the organkeyboard. Thus, if it started out in Cand a D- were played on the board, itwould start playing the stuff suchthat all the C's were D -'s and all theother notes were shifted accordingly.It can, in some cases, actuallytranspose up or down the full span ofthe keyboard, although, for practicalpurposes, after about three octavesthings get a bit odd.

There's something you can dowith this feature that's really quiteweird. Given that the system is play-ing a piece, it is possible, by using thetransposition thing to play the play-ing of the piece, transposing it in rela-tion to another score. Be neat with aharmony line.

OverdubdubsIf you take one voice, and putsomething on it, say a rhythm line, itis possible to add up to seven otherlines by overdubbing them, just likeon tape. As the first voice plays away,additional stuff can be played on thekeyboard, from whence it gets loadedinto memory in the conventional man-ner. However, there are a lot of thingsyou can do with this approach thatcouldn't happen on tape.

One thing, of course, is that thedata in memory, essentially pitch andrhythm, does not presuppose any par-ticular voicing. Thus, if it is easier tohear a specific track played like aHammond organ while overdubbing,that's cool, even if it's going to be asitar in the final mix. The speed caneasily be altered, as can the timesignature; both can be one thing forentering the score into the systemand quite another upon performance.There is also an adjustable degree ofresolution on the notes . . .ah ha!

Continued on page 64.

ETI-AUGUST 1981

PULLING THE PLUGA Peek At An Upcoming ProjectThese photos were shot during someof the testing of a soon to bepresented project; the ETI homebrewhelicopter. Featuring an easily ob-tainable Daimler-Benz engine,relatively simple metalwork, and com-plete microprocessor control of allvital functions, the do-it-yourselfchopper should be the ideal projectfor the advanced constructor,especially anyone who found ournuclear power plant kit an interestingchallenge. When complete, the air-craft will provide you with hours ofcarefree flying, and make you the en-vy of your neighbours (not to mentionthe DOT).

The three photos shown herewere shot during a test sequence afew weeks ago. The first shows theaircraft under manual control. The se-cond illustrates the chopper a mo-ment after engaging themicroprocessor autopilot, and thethird . . .well, we're still having a fewproblems witl the PCBs. In the sameissue as we present the first install-ment of the construction details, wealso hope to be offering all ETIreaders some low cost war surplusparachutes we picked up cheap.

Now, it should be stated that thehelicopter is not recommended forthe beginner. If you've been havingtrouble getting your electronic diceproject to work, maybe you should

get a few more under your belt beforetackling this baby. Also, readersshould be aware that a few specializ-ed tools and some test gear will be re-quired. At the very least, you'll want astorage scope, a laser refractometer,a micro-wobbulatometer, ametalurgical infra spectroscope, atitanium boring lathe, a .001 mmfinger gauge and an IBM 370 pro-cessor system for doing your initialcalculations and set up. Please donot plan to complete the project byskimping on these minimal essen-tials. . . a credit card calculator justwon't do.

The helicopter will be built onth rty seven easily made printed cir-cuit cards. In addition, a complete kitof the metalwork will be madeavailable for the nominal charge of$102,987.99.

Watch this space for more newson this groundbreaking ETI project.

'Pulling the Plug' is a forumspecifically for the disseminationof lies, falsehoods, untruths andsimilar deviations from reality. Wetake no responsibility for it shouldanything turn out to be factual.

DesignerCircuits

ONE ARMEDBANDITThis circuit is designed to give anapproximate simulation of a onearmed bandit slot machine, and isonly intended for home -entertainment purposes. The unithas three seven segment LED dis-plays, and when a pushbutton isdepressed, all display segmentsappear to light up. When the but-ton is released, a random numberis displayed. The idea of the gameis to obtain a row of three identicalnumbers in the display, with (say) 1point being scored for "000", twopoints for "Ill", etc., up to 10points for "999". The object of the

game is to score as many points aspossible in an agreed number ofattempts, say 25 or 30.

The circuit consists basically of aclock oscillator using IC1 and athree stage counter which uses IC2to IC4. The 4047 CMOS deviceused in the ICI position is amonostable /astable device whichis used here in the true gatingastable mode. Under quiescentconditions R2 takes the gatinginput (pin 5) low, ana prevents thecircuit from oscillating. DepressingSW1 takes the gating input high,and starts the circuit oscillating at afrequency which is controlled byR1 and C1. The specified valuesgive an operating frequency ofabout 10kHZ, although the exactfrequency is unimportant, it just

needs to be reasonably high.The display section uses three

CMOS 4026 decade counter/seven segment decoders, whichcan be used to directly drive highefficiency common cathode dis-plays such as the FND500,DL704, etc. The three displaycircuits are connected in series, inthe normal way, so that one thou-sand clock pulses take the displaythrough every number from"000" to "999", and then back to"000- again.

Thus, when SW1 is operatedthe display cycles through everynumber about ten times persecond, with all the display seg-ments appearing to switch on con-tinuously as the action of the dis-play is too fast for a human

O

observer to perceive. When SW1 isreleased, the display is "frozen- atwhatever number it happened tobe displaying when IC1 ceasedoscillation. There is, of course, noway of operating SW1 to definatelyobtain one of the winningnumbers, and it is purely a matterof chance whether or not one ofthese is displayed, as is the casewith a real one armed banditmachine.

IC1 to IC4 are all CMOS de-vices, and normal CMOS handlingprecautions should be observedwhen dealing with these. The cur-rent consumption of the unit can beover 50 mA when certain numbersare displayed, and a large batterysuch as a 276 should be used as apower source.

ETI-AUGUST 1981

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Circle No. 9 on Reader Service Card.

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MULTIMETERSINPUT IMPEDANCE: 10 megohmsRANGES: DCV - 200 mV, 2/20/200/1000 V

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Supplied complete with leads, battery,carrying case.

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* Either model, $89.50 FST IncludedIn Ontario, add 7% PSTFOB delivered in Canada

COMPLETE "IN-HOUSE" SERVICESALES - CALIBRATION - REPAIR

DUNCAN INSTRUMENTS LTD.ELECTRICAL MEASURING INSTRUMENT SPECIALISTS

122 MILLWICK DRIVE. WESTON. ONTARIO M9L 1Y6TELEPHONE (416) 7424448 TELEX 06527271

Circle No. 11 on Reader Service Card.

A system for distributing a Hi-Fi or other audiosignal to any number of remotely -located speakers,using the power lines as the communication link.

THIS UNUSUAL PROJECT is design-ed to distribute an audio signal to anynumber of speakers that areremotely -located throughout a houseor office building, using the powerlines as the communication link. Thesystem has an overall audio frequen-cy response that extends to 20 kHz,with typically less than 0.5% totalharmonic distortion and is designedto deliver a maximum of about 2watts to each speaker. The systemrejects all unwanted noise and has anoverall audio sensitivity of about 10mV for 2 watts output on eachspeaker.

The system comprises a singletransmitter unit and any requirednumber of remotely -locatedreceiver/amplifier units. Thetransmitter unit generates a 200 kHzcarrier signal, which is frequencymodulated by the audio input signaland which the transmitter superim-poses on the neutral line of the 120volt AC wiring. At each receiver unit,this FM signal is picked up from thelines, is amplified, demodulated andthe resulting audio signal is then fedto an external eight ohm speaker via a2 watt power amplifier IC.

The transmitter and eachreceiver unit is provided with its ownvolume control. Each receiver unit isalso provided with an automatic mutefacility, which disables its audio out-put when the transmitter is turned off.All units are line powered and simplyplug into existing wall sockets, noother interconnections being re-quired. All units incorporate a varietyof safety features, but it is essentialfor correct operation that the socketsbe wired in the correct polarity: each

socket should thus be tested with aneon indicator or similar devicebefore plugging a unit into place.

The Wired Sound system canreadily distribute an audio signalthroughout an entire house or officebuilding and has a variety of practicalapplications. In the home, it can beused to transmit the output of amusic centre or other audio source toall rooms in the building. Alternative-ly, the transmitter can be fitted with amicrophone and pre -amp and used asa baby alarm, enabling the baby to beheard from any part of the house.

n an office, the transmitter canbe coupled to a mixer unit and usedto distribute music signals and an-nouncements throughout the entirebuilding without the expense of hav-ing to fit additional wiring.

Construction: The TransmitterThe entire transmitter unit, in-

cluding the power transformer, isassembled on a single PCB. Con-struction should present few pro-blems if the usual precautions aretaken to ensure that all semiconduc-tor devices and electrolytics are fittedin the correct polarity.

When construction is complete,set the core of L2 and the slider ofRV1 to mid position. If you have a'scope, give the unit a functionalcheck by checking that a signal of afew hundred mV at about 200 kHz ispresent across the output terminalsof 12: set the frequency to precisely200 kHz via RV1 and trim the core ofT2 for maximum output.

You can, if you wish, case thecomplete unit; our own prototype isuncased, as it is intended to be built

into an existing audio amplifiersystem.

Construction: The ReceiverMost of the receiver unit (except

T1, RV2, SW1 and LED 1) is wired upon a single PCB. Constructionshould present few problems if theoverlay is followed with care. Whenconstruction is complete, fit the PCBand remaining components into asuitable case and complete the inter-connections to T1, RV2, SW1 and LED1, as indicated on the overlay and thecircuit diagram.

When construction is complete,set the core of T2 and the slider ofRV1 to their mid position, connect theoutput of the unit to an eight ohmspeaker and switch the unit on. Withmute switch SW1 on, little noiseshould come from the speaker: withSW1 off, lots of 'white' noise shouldcome from the speaker, indicatingthat the system is functional. If youhave a 'scope, monitor pins 4-5 of IC1and adjust RV1 to obtain a frequencyof about 400 kHz.

Setting Up The SystemAccess to a 'scope is needed

when initially setting up the system,as follows.

Switch on both units and apply asuitable audio (music) signal to theinput of the transmitter. Turn thetransmitter volume control to zero,

ETI-AUGUST 1981 49

WIRED SOUND

Fig. 1. Circuit diagram of the Line Transmitter.

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680

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No es:DI, D2 are 1N400103-06 are 1N414801-02 are MPS6521ICI is LM565CNIC2 is LM78L12CZIC3 is 380N12 s 455kHz IF transformer

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ETI-AUGUST 1981

PWR 12VFROMT1 12V

OVAND GROUND

k 0 RV2 RV2LED 1

SPKR RV2 SW1

Fig. 3. Component overlay for the transmitter board.

TRANSMITTERResistors All 1/4W, 5%R 1 470RR2R 3 , 4 , 7

R5R6R8R9R 1 0R 1 1

2k24k722k150k470k18k270R1k8

PotentiometersR V 1 4k7 min horiz presetR V 2 10k logCapacitorsC1 1000u 25V PCB elec-

trolyticC 2 10n 1000V disc ceramicC 3 1n0 polesterC 4 330n polycarbonateC 5 10n polyesterC 6 , 9 10u 16V tantalumC 7 1n0 ceramicC 8 220p polystyrene'C 1 0 2u2 16V electrolyticC 1 1 10u 16V electrolytic

SemiconductorsI C 1 78L12I C 2 LM566CN

PARTS LISTD 1 , 2 1N4001D 3 1N4148 1 2N2222Q 2 MPS6521LED1 0.2 in red LED

use the 'scope to monitor pin 2 of T2in the receiver and adjust T2 core formaximum signal. Next, monitor pins4-5 of 101 in the receiver and set RV1to the mid position at which lockingto the 200 kHz carrier occurs. Finally,set the receiver volume control to midvalue and adjust the transmittervolume control so that the musicsignal is heard at the receiver withoutapparent clipping. The system isthen complete and ready for usethroughout the house or office.

MiscellaneousT1 12-0-12 6VA transformer, 12V 100mAbulb. TR-103 IF Transformer, Armaco12-0-12 transformer 6VA, 12V 100 mARECEIVERResistors All 1/4W, 5%R1R2R3R4R5R6R7R8R9,10R11R12R13R14R15

1k81k2820R3k31k0560R390R3k9680R220k47k2k215k10k

PotentiometersR V 1 10k min horiz presetR V 2 220k

CapacitorsC1C2C3C4C5C6C7C8C9C 1 0C 1 1 , 1 4C 1 2C 1C 1 5C 1 6C 1 7

1000u 25V electrolytic10n 250V AC ceramic1n0 polystyrene2u2 tantalum150n polycarbonate2n2 ceramic10n polyester68n polycarbonate1n0 ceramic10u tantalum220p polystyrene2n2 polystyrene330p polystyrene220n polycarbonate100u 25V electrolytic470u electrolytic

SemiconductorsI C 1 LM565CNI C 2 LM78L12CZI C 3 LM380NQ 1 , 2 MPS6521D 1 , 2 1N4001D 3 , 4 , 5 , 6 1N4148LED1 any LED

Miscellaneous12-0-12 transformer 6VA, 12V 100 mAbulb 8 ohm loudspeaker, TR-103 IFTransformer (Armacol

ETI-AUGUST 1981Continued on page 70

51

WIRED SOUND

A fully assembled line receiver PCB. Note the polarity of the ICsand polarised components.

The system is designed to transmit an audiosignal to any number of remotely -locatedreceiver/speaker units, using the AC wiringas the communication link. The transmitterproduces a low-level 200 kHz carrier signal,frequency modulated by the audio signal,which it superimposes on the neutral side ofthe power lines. At each receiver unit, thecarrier signal is picked up from the wallplug amplified, demodulated and theresulting audio signal is passed on to aspeaker via a 2 watt audio amplifier IC.The use of an FM link ensures a good audioresponse and excellent noise rejection.

System operation relies on the fact thatthe AC wiring is highly inductive and actsas a fairly high impedance to a 200 kHzsignal. At this frequency, the wiring can beregarded as an inductive potential divider,with the power sub -station at its `low' end.This 'divider' normally produces relativelylittle signal attenuation between powerpoints that are separated by dozens or hun-dreds of metres of wiring and can be used asan excellent built-in 'data link' in anyhome.

The TransmitterIC2 is a voltage -controlled oscillator,

or VCO. Its operating frequency is deter-mined by the values of RV1-4 and C8 andby the voltage on pin 5. With the compo-nent values shown, the VCO operates at acentre frequency of 200 kHz and produces asquare wave output at pin 3. This output isused to drive common emitter amplifier Q1,which uses a standard IF transformer (T2)as its collector load; the centre frequency ofT2 is shifted to 200 kHz by C3 and its 'Q' isreduced to a fairly low value (to give abroad -band response) by R2. The outputsignal on T2 secondary (pins 4 and 5) has an

HOW IT WORKS

AUDIO I/P

V2OL UM

Fig. 4. Component overlay of the receiver.

amplitude of a few hundred mV rms.Audio input signals to the unit are fed

to volume control RV2 via C11 and thensubjected to about 20 dB of amplificationvia Q2. The output of Q2 is used to fre-quency modulate the VCO via C9 and pin5. Consequently, the output of T2 is a 200kHz 'carrier' signal frequency modulatedby the audio signal. This output is coupledinto the neutral line of the AC wiring vialow -value capacitor C2 and current -limiting`fuse' LP1. Note that one side of T2 outputis wired to the ground side of the line,thereby ensuring that standing DC potentials of only a few volts exist between theprimary and secondary windings of thetransformer. C2 and LPI ensure that thesystem will not be damaged if the outputsignal is accidentally fed to the live, ratherthan the neutral, side of the line.

Q2 and IC2 are powered from aregulated supply via ICI, a 12 voltregulator. I

The ReceiverThe 200 kHz frequency -modulated line

signal is picked up on the input of T2 via C2and current -limiting 'fuse' LP1; D3 and D4are used to limit the T2 signal amplitudes toa few hundred millivolts. T2 is tuned to 200kHz via C3 and has its 'Q' reduced to a fair-ly low value via R4, to give a broad -bandresponse. The isolated output signal of T2is fed to the base of common emitteramplifier QI via current -limiting resistorR5.

The base of QI is biased to 4V5 via theR2 -R3 divider network. Q1 is overdrivenby the input signal and has its output clip-ped at about 6 volts peak -to -peak. The out-put of QI is fed to the pin 3 input terminal

of ICI via R8 -C6 -R9. ICI is a phase lockedloop and is used to demodulate the 200 kHzFM carrier signal. This IC contains areference oscillator, which is set to the samecentre frequency as the carrier via RV I -R13and CI 1 . The demodulated audio signalappears at pin 7 of ICI. C12 -R14 -C13 -R15 -C14 are used to filter out any vestiges of thecarrier and the resulting 'clean' audio signalis passed on to volume control RV2 viaC15. The output of the volume control isfed to 2 -watt audio amplifier IC3 and isthen passed on to an external eight ohmspeaker via C17. Most of the circuit (otherthan IC3) is powered from a stabilised sup-ply via IC2, a 12 volt regulator.

The receiver unit is provided with anautomatic 'mute' facility, which kills theaudio output in the absence of a carriersignal, via Q2 and its associated network.Q2 is wired across the input to the volumecontrol and kills the audio signal when bias-ed on. Q2 is biased from two independentsources. It is positively biased (biased on)via R11 and the R2 -R3 potential divider andcan also be negatively biased (biased off)from the output of Q1 via the C7 -D5 -D6 -C8 -R12 rectifier network. The values ofR II and R12 are chosen so that the negativebias is predominant and Q2 is turned off inthe presence of a carrier signal in excess ofabout 1V5 at Q1 collector. In the absenceof a suitable carrier signal the negative biasfalls to a negligible value and Q2 is turnedon via RII.

The automatic mute circuit can bedisabled by closing SW I, in which case thephase -locked loop tries to lock on to noisesignals in the absence of a carrier and con-sequently produces very high noise levels atthe output of IC3.

52 ETI-AUGUST 1981

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INTOELECTRONICS,Part

Ian Sinclair continues his discussion of radio and also loo

Audio SystemsThe one part of a radio system we haven't dealt with yetis the audio section - the circuit that handles the audiofrequencies all the way from the detector to the loud-speaker. We've left this section so far not because of anydifficulty but because the circuits are so similar to thoseused in other audio systems, such as disc and tape

PRE- VOLUME/AMPLIFIER TONE

CONTROLS

VOLTAGE POWERAMPLIFIER AMPLIFIER

Fig. 1. Block diagram of a typical audio system.

LOUDSPEAKER

recorders. The range of frequencies that we're talkingabout, the audio range, is from around 30 Hz to about20 kHz which is the range of frequencies of sound thatcan be detected by a human ear in good condition.These sound frequencies, converted into electricalsignals by a microphone constitute the audio frequencysignals which have to be amplified and converted backinto sound. The circuits of any audio system must carryout voltage amplification, the control of gain (volumecontrol), the control of the shape of the gain/frequencygraph (tone control to you), and power amplification sothat a loudspeaker can be driven. A block diagram cf thesystem looks as in Fig.1.

SIGNALIN

RV2TREBLE

Fig. 2 Baxandall tone control circuit.

Toning UpVoltage amplifiers are familiar by now, and the idea ofamplitude control (using a potentiometer) is simple, butthe tone control stages of a Hi-Fi amplifier are a bitdaunting if you've never seen similar circuits before. Fig.2.shows one very popular type called a Baxandall circuit.

ks at disk and tape recording.

In this circuit, a network of resistors and capacitors isconnected so that it feeds two lots of signals into thebase of a transistor. One signal is the audio signal fromthe previous stage, the other is a feedback signal fromthe collector of the transistor. Now this is negativefeedback which will have the effect of reducing the gainof the amplifying stage. but the amount of signal that isfed back depends on the settings of RV1 and RV2 as wellas on the values of the resistors and the capacitors in thecircuit. For example, if the slider of RV1 is nearer end Xof the potentiometer, then the signal in through Cl andR1 can reach the base of Q1 much more easily than thesignal (feedback) through C6, R2 and most of the resist-ance of RV1 . Because of this, the easier feedback path isthrough C4 rather than through RV1 . C4 has a rathersmall value, so that it will pass high and middlefrequencies more easily than very low frequencies,causing bass boost. The bass is boosted because more ofthe higher frequencies are being fed back, so the gain ofthe transistor for high frequencies is less than it is forlow frequencies. With the slider of RV1 at end Y, onlythe higher frequencies of the signal can easily reach thebase of the transistor without passing all the waythrough RV1, so that this now acts to cut bass. RV2 hasa similar action on the high (treble) frequencies, so thatseparate control of the two ends of the audio range canbe achieved. Such elaborate control is used only for highquality sound equipment. Your 10 dollar Hong -Kongradio makes do with a 0.1u capacitor wired across thespeaker.

FEEDBACK Churning Out The Power, And Sinking ItQ1 COLLECTOR

One part of an audio system that we haven't spent muchtime on is the power output stage. Power output isneeded because loudspeakers convert electrical powerinto audio (sound) power, so that electrical power in the

TO NEXT STAGE form of a signal with enough voltage and current01 BASE amplitude must be supplied. Loudspeakers are inef-

ficient devices, converting less than 1 % of the electricalpower into sound, so that a fair amount of electricalpower is needed. A power output transistor therefore hasmuch larger current passing through it than we ever usein a voltage amplifier transistor, and because loud-speakers are damaged by direct current flowing throughthem, we have to couple the signals to the loudspeakerby a transformer or a capacitor. One exception to thatlast rule is that the DC can be balanced out in a type ofoutput circuit called a bridge circuit, but these are rare.

Fig. 7. shows a single -ended output stage which usesone transistor with a transformer as its collectorload. The term single -ended just means that the signal is

ETI-AUGUST 1981 55

INTO ELECTRONICS"

not shared with any other transistors - you'll seecircuits later which do share the signal and are notsingle -ended. The bias of the transistor is set so that acurrent of about 0.5 A flows when no signal is applied,and the full amplitude of signal at the input will cause thecollector current to swing between 1 .0 A and zero

+12V

100R

1/2w

100u

T1

r7( Lis

2N3055

IRO

Fig. 3. A single -ended output stage.

Fig. 4. A push-pull output stage.

current at the peaks. The voltage at the collector isabout supply voltage (12 V) with no signal, and theaverage voltage does not change when a signal is ap-plied, so that with a full -amplitude signal the voltageswings down to zero volts (at the peak of current) and upto 24 V (at zero current). The peak voltage signal istherefore 12 V, the peak current signal is 0.5 A, the peakpower is 12 x 0.5 = 6W, and the average power is half ofthis, 3 W.

This type of single -ended output stage (a Class Astage). is wasteful of power and is used mainly in the typeof line operated equipment where high quality soundis not important ( the TV, boy, the TV. If they'regawking at the picture, they're not listening to thesound). Most output stages make use of the push-pull, ordouble -ended principle, in which two transistors sharethe output signal between them. These push-pull circuitscan also be operated with a large steady current (Class

V

Fig. 5. A fully complementary output stage.

A), but most designs make good use of both transistorsby running each transistor with very little bias current, sosaving power. The most popular circuit of this type is thetotem -pole circuit breifly referred to in Part 5 (Fig.

11). Let's look over that circuit again. In its simplest.(and best) form, it uses one PNP and one NPN transistorconnected as a pair of emitter followers, feeding theloudspeaker through a capacitor. With no signal input,the circuit is biased so that the voltage at the emitters is

56

iii;1 equal to half of the supply voltage. When the samesignal input is taken to the bases of the two transistors,the positive half of the signal will cause Q1 to conduct(with Q2 biased off because Q2 is a PNP type). Thevoltage at the emitters will follow the shape of thepositive half of the signal waveform, since Q1 is anemitter follower. The negative half of the waveform willshut off Q1 and make Q2 (PNP, remember) conduct sothat the voltage at the emitters now follows thewaveshape of the negative half of the wave. At theloudspeaker, the complete waveform is used. Because ofthe coupling capacitor, the waveform at the loudspeakerhas an average value of zero; there is no DC level.

Fig. 6. shows a more complete output stage of thistype. RV2 along with the diodes D1 and D2 providessome bias, so that the base of Q2 is at a higher voltagethan the base of Q3. If both basses were at the samesteady bias voltage, then signal voltages betweenV/ 2 -0.5 and V/ 2 + 0.5 would not produceany output, because a transistor does notconduct until its base voltage is about 0.5 V higher thanits emitter voltage (negative to emitter voltage for thePNP type). Even when some bias is applied, thewaveform output for very small signals is never quiteperfect because the two transistors never match eachother perfectly enough. This type of distortion is called'cross -over distortion.' RV2 acts to adjust the biascurrent flowing in the output transistors, and can be setso that the cross -over distortion is as low as it can be for a

SIGNAL IN

Fig. 6. A more complete version of the 'totem pole' output stage.given in Part 5.

given pair of transistors. RV1, along with R2 providesnegative feedback of bias voltage and of signal. Becausethe output stage (which we can think of as a singleemitter follower) is directly coupled, adjusting RV 1 setsthe voltage at the emitters of the output transistors. Inuse, RV1 is set to make the DC voltage at the join of R5,R6 equal to about half supply voltage. A more accuratemethod of setting is to connect in a signal whoseamplitude is large enough to cause each peak of theoutput signal to appear flattened. RV 1 is then adjustedso that both peaks are flattened symmetrically (Fig.7c.) The amplifiers is now set so that it can handle themaximum amplitude of the input signal.

ETI-AUGUST 1981

:c)

Fig. 7. Using a large amplitude wave to set an amplifier for max.input signal.

Fig. 8. Typical transistor heat sinks.

C2 is a 'bootstrapping' capacitor whose job is to assist01 to drive the bases of the two output transistors.When a signal of near maximum amplitude is beinghandled, there would not be enough voltage across R3(which has a small value) to pass base current into Q2unless we could increase the voltage of the supply. Thepositive feedback signal through C2 does just that ateach peak, and also helps to avoid signal losses. There'sno risk of oscillation, because the voltage gain of Q2 isless than unity.

Fig. 9. Block diagram of a record player.

result is that power is dissipated in the transistors, andinevitably this means that the transistors will get hot.Unless we can pass on this heat, the temperature of theoutput transistors will increase until the collector -basejunction, which is the part that has to dissipate thepower, fails. There aren't many water-cooled transistorsaround (yet), so that the heat has to be passed on to theair, using convecting fins called heatsinks. These heat -sinks ( Fig. 8. ) are chunks of metal, finned andblackened, to which power transistors are tightly bolted,usually with a layer of heal -conducting silicone grease tohelp make good contact. The metal chassis of anamplifier is often used as the heatsink, and because thecases of power transistors are connected to their collec-tors electrically, mica washers have to be used aselectrical insulators between the transistors and themetal chassis. This prevents the transistor collectorsfrom shorting to the chassis or to each other.

DiscThe block diagram of a record player is shown in Fig.9. All of the transistor stages should now be familiarto you, but the transducer is not and a brief look at it isworthwhile. Most discs nowadays are stereo, meaningthat two separate recordings are made on the sametrack. We could, if we liked, record quite differentsounds on the two channels, as they are called, but weuse stereo recordings mainly for the pleasing effect ofhaving sound appear to be coming from a larger sourcethan one small loudspeaker. Stereo recording uses twomicrophones, and inevitably the sounds reaching thesemicrophones will not be identical. The aim of stereois finally played back though two loudspeakers. Thechannels are labelled L cleft and R (guess).

On a disc, a cycle of sound wave is recorded as a wavepattern cut into the plastic material of the disc. Whenstereo recording is used, the waves on one side of thegroove, which has a V-shape, will not be the same as thewaves on the other side, because each side of the groovecarries the recording of one of the stereo channels. The

PICKUPCARTRIDGEVIBRATION -TO-- (ELECTRICAL -TO -ELECTRICALTRANSDUCER PRE -

AMPVOLUME/TONE

VOLTAGEAMP

POWERAMP

VIBRATIONTRANSDUCER

CONTROLS

I

Frying TonightBefore we leave output stages, though, there's oneimportant point about all of them. Output stages usetransistors which can pass quite large currents at fairlyh'lh voltages, compared to most voltage amplifiers. TheETI -AUGUST 1981

groove angle is 90', so that the pickup cartridge mustinclude two transducers set at 90' if it is to convert theshape of the disc groove, into two separate electricalsignals. The use of a 90° angle makes it easy to keep thechannels separate (to avoid cross -talk, as they say).

57

INTO ELECTRONICSSTYLUS

j's DIRECTION OFR CHANNEL ONLY / \-- OSCILLATION ---/ LCHANNEL ONLY

STYLUS

STEREO GROOVE WITHDIFFERENT SIGNALS INTHE TWO CHANNELS

Fig. 10. Recovery of left and right channels form a single groovein a stereo disc.

TRANSDUCER 1

YOKE

CANTILEVERARM

STYLUSFig. 11. Transferring stylus movement to transducers using a 'yoke'

TRANSDUCER 2

Earnest students of Mechanics will tell you that a forcehas no components at 90" to its line of motion. Well, itworks, anyhow.

movement of the stylus has to be transferred tothe transducers by using a yoke ( Fig. 11.) and for highquality replay, the mass of each of these moving partsmust be very low. The stylus has to be able to return to itsnormal central position after each wave, so that somesort of return spring is needed, but for good reproduc-tion this 'spring -back' must be as low as possible. In thelanguage of the cartridge designer, the compliance mustbe high. The rms signal from most cartridges of the Hi-Fitype is around 2 mV at full belt.

TapeThe disc player as we know it just evolved out of theprimitive gramophones of the last century, and haschanged from being a purely mechanical gadget into amainly electronic system. Magnetic recording (tape orcassette) is just as ancient, and has adapted more readilyto electronic methods, because it needed electronicmethods from the start. Stereo is easier to provide ontape, because we can record several tracks on one tapeusing as a transducer for each channel a tiny elec-tromagnet, the recording head.

The principles of magnetic recording are shown inFig. 12. A signal current passes through the ele-tromagnet, so that a varying magnetic field exists at thegap in the head. The magnetic material, nowadaysalways a plastic tape coated with iron or chromiumoxides, is pulled past the,gap at a steady speed. Eachpiece of tape is left magnetised, and the amount ofmagnetisation is proportional to the amplitude of thesignal current in the head at the instant when the tapewas in the gap. When the same tape is run at the samespeed past another head (or the same head with differentconnections to the coil) the changing magnetism at thehead (caused by the combination of the magnetisationand the movement) induces voltage signals in the coil of

the replay head. These signals, a millivolt or so inamplitude, can then be amplified. Block diagrams of atape recorder system, both for recording and for replay,are shown in Fig.13.

One awkward complication is the way that magneticmaterial behaves. Small current signals through arecording head leave no magnetic signal on the tape,large signals can cause the magnetic material to 'satu-

MOVEMENT OF TAPE

TAPE

FROM RECORDING TO R PLAY

AMP AMP

Fig.12. The principle of tape recording.

rate' so that the waveform is clipped ( Fig. 14. ) Toovercome the small -signal problem, we add, whilerecording, a small signal at a high frequency, around 80to 100 kHz, which is much too high to hear on replay.This is called the bias signal, and it is the bias signalwhich ensures that the tape always has some signalbeing recorded. To avoid saturation problems, theamplitude of signals must be controlled so as not toreach the level at which the tape saturates, so thatmeters or AGC circuits are used to keep the recordinglevel below the saturation point.

What makes tape so difficult to use satisfactorily isthat the amount of bias and the saturation level isdifferent for each tape, and the amount of bias that isneeded for any particular machine varies from one brandof tape to another. Adjustments to recorders can bemade only if very specialised instruments are available,and very few laboratories have these instruments, sothat the type of tape recommended by the maker of atape recorder should adhered to.

Fig. 13. Block diagram of a record/ replay tape recorder system.

MICPRE -AMP VOLTAGE

AMP

OSCILLATOR(8k Hz)

(a)

REPLAYHEAD

PRE -AMP VOLTAGEAMP

(b)

RECORDINGHEAD

POWERAMP

L/S

58 ETI-AUGUST 1981

Two -Headed RadioOne final problem - how do we transmit stereo signalsby radio? One answer would be to use two differentfrequencies for the two channels, but that isn't verysatisfactory - it uses up too many frequencies, and theunfortunate listener with a mono radio will hear only the

Fig. 14. The use of a bias signal to overcome the small -signalproblem.

MAGNETISMN-5

SIGNAL +SIGNAL -

SATURATIONLEVEL

NO SIGNALRECORDED

SATURATION LEVEL

MAXIMUMPOSSIBLESIGNALAMPLITUDEPEAK -TO -PEAK

MAGNETISMN -S

XAMPLITUDE OFBIAS SIGNAL

L

left channel or the right channel. The way out of thisproblem, is to mix the L and R signals to form L+ R andL-R. Now the L+ R signal is the normal mono signalwhich listeners with no stereo equipment will normallyreceive, and the L-R signal, the difference signal willallow a stereo receiver to recover the two separate R andL signals. How do we transmit them? Well, the (L-R)signal is amplitude modulated on to a low frequencycarrier (called a subcarrier) at 38 kHz, and most of thecarrier signal is then filtered out, leaving only themodulated sidebands (for more on sidebands, see thenext part). The (L + R) signal, with frequencies up toabout 14 kHz is added in, and a small -amplitude 19 kHzsine wave added. We now have a signal which consistsof three parts at quite different frequencies, easy toseparate, and the whole of this signal is now frequencymodulated on to a carrier at around 90 MHz.

A mono receiver will demodulate the signal, but willfilter out all the parts whose frequencies are above 14

Fig. 15. Block diagram of a stereo radio transmitter.

MILSAMPS

MIXERS

L + R

ADDER

L -R

OSCMULTS90MHz

FMMOGUL

AmtIoui.

DOUBLER38 kHz

OSC19k Hz

FILTER

kHz, so that only the ( L+R ) signal is received. A stereoreceiver ( Fig. 16. ) is much more complicated. Themono (L+R) signal is filtered off in one circuit, the19 kHz sine wave in another, and the sidebands of the

(L-R) modulation in a third. The 19 kHz sinewave isused to generate a 38 kHz carrier (using a frequencymultiplier circuit) which is then added to the (L-R)modulation. This lot can now be demodulated using asimple diode detector, so that we have the L-R signal.Now the signals are combined. If we add the signals:(L+ R)+(L-R), we get 2L, a left channel signal. If weinvert one signal and then add: (L+ R)-(L-R), the resultis 2R, a right channel signal. This operation, calledmatricing, recovers the original L and R signals whichcan then be separately amplified. A set of filter circuits isused to remove traces of the 19 kHz and 38 kHz signalswhich would otherwise cause bother with taperecorders, since they can beat (remember) with the tapebias sinewave.

//SUPERHET

90MHzREC

FILTERL R

19 kHzAMP

I9MHzOSC

DEMOD

DOUBLER

AOD

SLBTRACT

TO AUDIOAMPS

Fig. 16. Block diagramof a stereo radio receiver.

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ETI-AUGUST 1981Circle No. 20 on Reader Service Card.

AUDIOTODAY

If your tone arm is on the dust cover of your stereo, something is wrong. Wally Parsons considers the permutations.

IF YOU WERE wandering throughthese fields last month, you may havecome away feeling confident that youcan now set up any pickup arm cor-rectly. All that is necessary is to takethe appropriate equations, plug theright numbers in, and read off theright answers on the LCD. In anycase, matters are certainly simplifiedby the fact that for any given armlength there is a single correctamount of overhang, and a single cor-rect degree of offset, right?

Well, actually, nothing is eversimple, except perhaps the mind of avoter who believes politicians' elec-tion promises. Unlike the aforemen-tioned politicians, numbers don't lie,but they are very specific as to theiranswers. Consequently, we must bevery careful to be sure that weunderstand the question to which theanswer applies.

Consider, for example, the for-mulae given last month for determin-ing the correct arm geometry forminimum tracking error. Mathemati-cians in the audience, as well asothers who get a kick out of spendingan evening pushing calculator but-tons may have discovered someshades of grey between the blacksand whites.

But, first, for the sake of newmembers of and visitors to the AudioToday Show and Tell Club, as well asthose whose pages may have fadedduring the interval, let's recapitulatethose equations.

L = arm length, from pivot tostylus tip

D = stylus overhang, as il-lustrated in fig. 1

0 = tracking angle, as illustratedin fig. 1

B = pickup offset angler = groove spiral radiusr1 = innermost groove spiral

radius of interestr2 = outermost groove spiral

radius of interest

To find tracking angle,0 =57.3[(r/2L) + (D/r)] degrees

To find overhand, D

D= r22

L[1/4(1 + r,/r2)2 + ,,/r2]

and offset angle B is

57.3r, (1 + r,/r2)B - degreesL[1/4(1 + r11r2)2 + r,/r2]

Now, if that array of alphabetsoup hasn't been chewed upsomewhere in the Twilight Zone thatlies `twix the typewriter and the prin-ting press certain facts can be glean-ed from their examination. As a mat-ter of fact, you can even draw somepretty pictures, such as fig 2. (soalright, already, Geiger it ain't; he candraw his pictures on his page, I'lldraw mine on mine.)Fig. 1. Tracking angle

It is equally obvious that thetracking angle can be cancelled byoff -setting the pickup by an amountequal to the tracking angle. However,that correction only holds at oneradius.

It is equally obvious that thetracking angle can be cancelled by of-fsetting the pickup by an amountequal to the tracking angle. However,that correction only holds at oneradius.

As a matter of fact, the only con-dition zero tracking error can beachieved with a pivoted arm is one inwhich the arm is of infinite length, inwhich case the required offset is zero.

If anyone is sceptical of theabove statement, he has only to solveEq 1, 2, and 3, using X as the value forL.

He will discover that zero error isachieved at any radius.

He will also be awarded a Nobelprize for mathematics. Or a trip to arubber room.

If the arm is overhung, the track-ing angle is increased. However, solv-ing Eq. 1 for a variety of radii yields agraph like one of the curves shown infig 2. Under these conditions, thetracking angle for the inner groovesincreases more than the angle for theouter radii. As a matter of fact, asradius increases the curve for theoverhung condition and zerooverhang condition converge, untiluntil at a radius of infinity they meet.

At the other end of absurdity, asthe groove radius becomes smallerthe tracking angle increases, until, ata radius equal to the overhang itreaches 90°.

Fortunately, no one makesrecords with such a range of grooveradii.

How Everything Works TogetherI never cease to wonder at the waynature arranges things so that theywork with each other.

Wheels, for example. Isn't it for-tunate that wheels are round. Makesit so much easier to put tires on them.

And hands. Having four fingersand a thumb makes for a nice fit withgloves, don't you think.

Another fortunate coincidence isthe fact that it is possible to obtainacceptable performance at a recordgroove radius of only 2.5" and a max-imum of 5.75". As it happens, prac-tically any arm long enough to bemounted on the outside of a record ofany diameter can be set up with suffi-cient overhang to provide almost con-stant tracking angle at any useableradius.

Take, for example, an arm with alength L =9" mounted with anoverhang of 0.73" as per Eq 2. At aradius of 5.75" the tracking angle willbe 25.6° and at 2.5" it will be 24.7°. At3.5" the tracking angle will be 23.1°.Maximum variation is 2.5°. If a pickupis mounted with an off -set of 24.35°,

60 ETI-AUGUST 1981

AUDIO TODAY

the resulting angle will be zero at ap-proximately 3.25" and 4.4". Thisamount of off -set is extrapolatedfrom the co-ordinates used to drawfig 2, and were calculated at intervalsof 0.5". They come close to agree-ment with the recommended off -setcalculated using Eq. 3, that is, 24.0 °.

Notice that, through the radiusrange of interest the curve is substan-tially horizontal. If a larger range ofradii is to be accommodated, Eq. 2will prescribe a lesser amount of off-set. As a result, the sharp upwardturn of the curve will be moved to thesmaller radii, and the curve represen-ting the outer radii will slopedownward more steeply. The overallrange of tracking angles will begreater, but will still show a substan-tially horizontal attitude throughout -the middle range of radii.

The OffsetOnce we have established the re-quired overhang, it is necessary todetermine the off -set angle of thepickup. The purpose of Eq. 1 was toallow us to examine the behaviour ofthe arm. Eq. 2 is used to establish theamount of overhang which will givethe smallest range of tracking anglesover the radii of interest. Eq. 3 cannow be used to determine what angleof offset will correspond most closelywith the tracking angles resultingfrom application of Eq. 2. If this off-set corresponds to any angle withinthe range used for calculation, otherthan the single minimum angle, therewill be another radius at which off -setand tracking angle will agree,resulting in zero error. If we were toselect the minimum radius as thepoint of agreement, we would alsofind a corresponding point near theoutermost radius. In the case of our9" arm this would result in an error ofapproximately 1.75° in the mid -band,and 0.5° at the outer radius. Use ofEq. 3 provides for zero error at twomore closely spaced points in themiddle radii and less overall error.

Whither PerfectionWe have now achieved minimumtracking error. But is this really whatwe want? Why do we want minimumtracking error in the first place? Wewant it because minimizing trackingerror minimizes distortion.

However, the amount of distor-tion generated by tracking error isdependent on many factors, one ofwhich is groove velocity. As a result,for a given level of distortion, less er-ror is allowable in the inner grooves

that the outer grooves. It would ap-pear, then, that we should aim forzero error at the innermost groovewith an increase at the outer groove.

The catcn here is that, while thelatter radius is constant the formervaries from record to record. A casualperusal of randomly selected discsfrom my own library showed that,while a great many were recordedwith inner diameters of 2.5", many didnot utilize that much of the disc area,with some having inner diameters ofover 3". It may well be, then, that it isbetter to minimize error over thoseradii which are universally en-countered, and allow some relationwith respect to extreme innergrooves.

Special ApplicationsJust because the standard range ofradii is 2.5" to 5.75" it doesn'tnecessarily follow that you have toset up an arm accordingly. If you col-lect older recordings and wist) to tapethem with maximum fidelity, it maybe worth your while to set up an armfor a specific application. For exam-ple, 45's have a range of about 2" to3", and can benefit from less offsetand overhang.

Arm LengthMany people assume that a longerarm exhibits less tracking errorbecause the tracking angle and rangeof variations is less with a long armthan with a short. While this istheoretically true, in practice it's oflittle consequence. This is illustratedin fig. 3 in which our above mentionedarm is compared with an arm of 12",both optimally overhung. Althoughthe absolute values of trackingangles are substantially different theshap of the curves show less varia-tion that a small change in overhangas shown in fig. 1.

As a matter of fact, an arm 24"long shows no more than a 20° im-provement.

Indeed, moving the pickup backand forth in the head shell, an easymatter with some components, androtating it sightly in its mount can ef-fect substantial changes in trackingerror.

Obviously, great precislion mustbe exercised in pickup and arm moun-ting. It would be kind of nice to havesome visual means of checking ac-curacy.

Many modern arms mount thepickup by means of screws whichpass through the top of the head-

35

LT, 50

ctt

f, 25

15

10

a

33

30

.aao

io

10

shell. By mounting a gauge as shownin fig. 4, it is possible to check for er-ror. The front edge of the gauge ismounted parallel to the mountingscrews, either using the screws, orwith tape or rubber cement. The frontedge is set exactly over the styluslocation, and the gauge length is atleast 6", long enough to reach thecentre spindle. At any point of zerotracking error, the front edge of thegauge will pass over the centre of thespindle.

Fig. 2.

1 55 2 2.5 3 3.5 4 t$ 5 3.2 I.0,05 .+cne.

0; 11.

.1 1 1.1 1 1.1 1 3.1 4 4.1 1 1.1 iRADIUS Inehel

Fig. 3.

If you wish to experiment withangles and overhang, try attachingthe gauge to a Dust Bug type ofrecord cleaner, and experimentingwith it.

Most educational.*Note that Eq. 1 is slightly simplifiedand is accurate for use within theradi: of interest. However, it cannotbe used to prove this statementbecause the error, introduced by theapproximations become gross. Theequation to use, which can be used inplace of Eq. 1 in all cases is:

0 = arc sin [(r2 + 2LD - D2)/2rL],radians. (Eq. 1a)

Eq. 1 ignores D2 and assumesthe sine of the angle to be equal tothe angle. Thus, it can be workedwithout a calculator or set of tableswithout significant sacrifice of ac-curacy.

Continued on page 69ETI-AUGUST 1981 61

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62 ETI--AUGUST 1981

ov

Thus, when D1 is fed with the squarewave output of the astable, the peakoutput of the unit will be zero when theR6 voltage is zero, or 5 V when the R6voltage is 5 V, etc. In our circuit, R6 isshunted by electrolytic capacitor C2.Thus, when PB1 is pressed, a large volt-age is applied to R6 and a large -amplitude square wave output is avail-able. When PB1 is released, the R6voltage and the square wave outputamplitude decay exponentially to zero

NOTE:D1 & D2 ARE 1744148

RV1 AT MAX

r

+12V

OV

RV1 AT MIN

Fig. 0. A method of producing a non-symmetirca variable -ratio output from the555 astable.

131 PB1RES RELEASE

OUTPUT WAVEFORM

- 12V

OV

R7100R

C21000

Fig. 12. A method of amplitude modulatingthe pin 3 output of the 555 astable in musicand sound generator applications.

Fig. 9. Alternative method of producing anon -symmetrical fixed -ratio output form the555 astable.

81

555R2 a OR100k 10%47555

A

1 0n

(with a time constant of R6 -C2),shown in the diagram. The R3 -R4 net-work is used to apply a slight offset biasto the rectangular input waveform, toensure a full cut-off of the output wave-form after PB1 is released.

Finally, Fig. 13 shows how the above

2

3

R34k7

R41k0

D1184148

- .0V8- YOVS

- - ov

- - OV8OUTPUT WAVEFORM

R5100k

R64k7

as

.12V

NOTE OV01& D2 ARE 1744143

Fig. 11. A 555 sine -wave generator witha range of 83 Hz to 1.4 kHz (via R1).

.102V

01BC109

R7100k

PB1

R810OR

C2100u

02BC109

OUT

/3910k

0ov

Fig. 13. A modification of the Fig. 12circuit to give extended decay times and abuffered output.circuit can be modified to give extendeddisplay times (via emitter follower Q1)and a buffered audio output (via emitterfollower Q2).

Who Do You Buy From?Buying electronic parts in Canada can be a nuisance,nobody knows this more than we do. To help some of ourmore isolated readers we are compiling a list of stores inCanada for inclusion in the magazine in a future issue.

Tell us who you shop from. By doing so. you'll be help-ing readers like yourself and the stores you patronize.

We have induced a list of the stores that appeared inthe January 1981 Directory. Please do not send us namesthat appear there. we already know about them. Pleasesend store names and addresses to:

Stores Directorydo Electronics Today

Unit 625 Overlea Blvd.Toronto. Ontario

M4H 1B1

BRITISH COLUMBIA Mackin. Mal Kitchener.Wlerloo Sarnia Zeriirn Radio Canada Si RornualdKamloops Bast 2 Consul., K W Surplus Gear Vioeoland Limited Selco ElectronicsCam Gard Supply Lim Red ,righouse Simon. Waterford Thetford MinesLimited SASKATCHEWAN Waterloo Electronic Norfolk Electronics Copeland Electronics Etektronicse EnrTrail Morse Jaw Supply Co Inc Limited OUEBEC Trots RiyieresILIS Electronics Ltd. Sonic Supplies Ltd. Computer Innovations Toronto Blainylile Malleau Electronic...Vancouver Raul. Limited A.1 Etectronics Surplus Peen° Ouebec NEW BRUNSWICKActive Component gado Supply 8 Service Landon Active component Sales Amite. Electromoue MonctonSales Carp 09711,00d R J Bucttland Company Corp. Inc Amphion Elecoon, ,Cam Gard supply Ltd Saskatoon Forest City Su plus Ltd Active Surplus Annex LOwaueull LimitedConti Electronics Cam Gard Supply Mississauga Anton Electronics Master Vox Ltd. NOVA SCOTIAGlenwood Trading Com Limded Atwater Electronics Limited Monte -Jolt Halifaxpany Limited Swift Current Limited Battems Included Distribution JNIC Amphion ElectronicsHealn Company G W Colortronics Ltd. Heath Company Cisco Electronics Ltd Dstribution Inc LimitedIntel. Electronics Ltd MANITOBA K S K. Associates Dominion Radio and Montreal Basic Computer Salesfi.A.E Industrial Elec Ottawa Electronics Active Component LtdConics LwoledWinnipeg

it rd Supply Ltd. Active Component Elstonsclence Inc Sales Corp. Cam Gard SupplyVictoria Hee,. Electronic Sales Electro Son, Inc.Addison Electronic Ltd LimitedOueete Electronics Ltd Caner Corp ElectioniCS Mt Cite Electronic.. Mini Comp SystemsALBERTA J 6 I Electronics Compumart ExcelPon. Com- Casco Etectronics Ltd LimitedCalgary Limited Computer Innovations portents & Computing Elco Electronics SydneyActive Component W ES. Electronics Limited McOrporated Hamilton Avnet Elea Fisher ElectronicsSales Corp Limited Corrals Electronics General Electronics Ponies LimitedB 8. E Electronic Sueetv ONTARIO Limited Gladstone Heath Company PRINCE EDWARDLimited Biamplon Heath Company North Amerman Elea ISLANDvisions Bryan Electronics Kris Electronics ',,eg,C'e"'L.Cm'puter Cenlie conics Co Limited CharlottetownEdmonton Georgetown Videoland Meuse of Computers Payette radio island Radio CentreGardiner Industrial Elm: Inventories Untimtled Weciod Radio Inc Radio Hovarte LimitedConics Ltd Guelph Owen Sound M & WComa.. Stores Products ElectromquesHeath Company Neutron Electronics Norte VVestern Etin Inc Lteer Electronic NEWFOUNDLANDel A.E Industrial Limeed Pon. Supply Ignited Rectic Trade Supply Wnoleselers Co Limited St. John'sElectronics North Bay Limited Standard Electronics Eiectronic CentreVideoland Videciand Super Electronic Limner,

Continued from page 47

WHAT'SNEW

It's actually possible to tell thecomputer how fussy it is to be withregards to the position of each notein regards to the meter. It can be setin increments of fraction of a note,down to 1/128 note. However, this allbut defeats the wonderful artisticsplendor of this feature for those ofus who play . . .with expression,which is to say, a bit sloppily fromtime to time. Suppose, instead, wetell it to regard the smallest incre-ment of time as a quarter note. Withthis in mind, any note playedanywhere within an eighth notebefore or after where it should havebeen will turn up right on time. Freakyfar out.

Overdubs, or over writings, orwhatever you'd call them, done on thesystem are capable of being alteredin pretty well all the ways by whichyou could change the tracks of amultitrack recording done on realmagnetic tape, plus, of course, theothers we've looked at. Thus, for ex-ample, one voice in eight, or one partof one voice, can be changed. Wholevoices can be eliminated. You don'teven have to rewind.

Oh ya, and there's even syntheticreverb, but it sounds real. First rateEuropean cathedral sound. You canalmost hear the frescos crumblingand falling off the ceiling in bits.

Play (Call Subroutine)'When I explain this thing, sometimesthere's a problem getting people tounderstand what the words mean.'McLey explains.'lf I want it to play, I

just say 'play', and it knows what I

mean. But people are so used to com-puters dealing with codes that theycan't see it as just a word. They wantto know if a musician can reasonablybe expected to deal with a computer.'

The cool thing about McLey'ssystem, the aspect of it that's gobbl-ed much of the time he's spent indeveloping it, is that it tends to berather transparant to the user. Itdoesn't behave like acomputer . . .it's more like talking toanother musician over a keyboardand CRT, instead of an intercomm.Thus, instead of going 'F69 Error inlocation 033A' and beeping in-cessantly, it just tells you to 'GuessAgain' when you tell it to 'drop dead'.That, actually, seems to be its only er-ror message; its language is sosimplified, and it is so sophisticatedin handling it, that it doesn't reallyneed a whole barrage of codes andflags.

Absolutely everything you tellthe system to do is in English, a bitmore precise than conversation, butthere isn't a 'CALL' or a 'GOSUB' tobe found. The fact that it's a com-puter quickly becomes irrelevant. It'sno more difficult to understand than anew synthesizer. A bit more tricky topay for, perhaps. . .

An example of this is in settingup the voices. The machine can be in-structed to put a 'virtual synthesizer'on the screen of its terminal, a blockdiagram of one of McLey's voiceboards, with all the parameterssetable from the keyboard. Thus, thewaveshape of the oscillators, theslope of the filter, the attack anddecay times and so on can be set. It'sa perfect analog of plugging togethermodules with patchcords. McLey'sonly used it once.

The first voice he produced waslaboriously set up using this analog.However, the system, permits theparameters to be changed withoutresorting back to this thing, so anyvoice can be modified into any othervoice by just changingcharacteristics. For example, theharpsichord voice could be changedto a horn by saying:

Use the harpsicord voice, but with asquare wave oscillator.Use a high sustain levelUse a higher filter frequency.Use a shorter decay.

and so on. Because this pro-cess is so easy to keep doing, a voicecan easily be developed by trial anderror, fiddling with one characteristicat a time until it's right. It can thereupon be renamed, and rememberedas a new voice. McLey has a library ofover a hundred voices at the moment,which he considers to be pretty bare.'I haven't really developed a lot ofsounds yet, because we're stillchanging the voice boards. It's a dragto sweat over a sound and get it rightonly to have to throw most of it outwhen the new cards come.'

EncoreUnfortunately, the really splendid

part of McLey's marvelous new in-strument doesn't reproduce well onpaper; the sound of it can blow themind clear into the next dimension.At times, it is almost too perfect babetaken for real. Every note is setflawlessly in place, and every instru-ment perfectly miked and reproduc-ed. It is, in fact, capable of doingthings beyond the scope of accousticinstruments, such as having the lutestop of the harpsichord sound as loudas a French horn, or have a flute play-ing down in the same register as acello. It's also capable, when doingscores and figuring out transposi-tions and parts for actual accousticinstruments, to indicate the im-possibilities of such things. Thus,one could use it to score a piece forgiven instruments and let it keeptrack of whether what was goingdown was actually playable by thoseparticular instruments. In a while, itwill be so sophisticated in thisrespect that it will be capable of figur-ing out chords for guitar in terms ofwhether a hand could actually fingerthem.

And everything comes outperfectly. Man, old J.S. Bach'd haveloved the thing. Except, of course, itdoesn't speak German.

Next month . . .ah, next monthwill be September, when the leavesget colourful, the kids go back toschool, and the new shows crop upon TV. Not in this particular order, ofcourse. The new shows make theleaves die, I think.

Next month, however, is also thedue date for the end of civilizationand the coming of the antimatter wi-zards, according to the Church of theEclesiastic Food Processors. Now, ifthis comes to pass, as it is written inthe sacred scriptures of this cult onpaper towels handed down to the pro-phet Roderick Melvin the Atonal fromon high, or while high, I'm not surewhich, yes, if this should transpire,friends, we're all due to betransmuted into pink plastic flam-ingos, to be placed upon the frontlawns of the wizards' in laws for timeever after. Therefore, when you getthe next copy of ETI, scurry quicklyaway from the newsstand and. . .

. . . Read this column first.ltmay be last thing you check outbefore . . .plastification sets in.

Be brave, my children, and staytuned.

64 ETI-AUGUST 1981

YNRIMIC

Sabtronics revolutionized the market with the first low cost, highperformance Digital Multimeter. Now representing Sabtronics in Canada,Inouye Enterprises Limited is featuring the complete line of outstandinginstruments and accessories available nowt and the new instruments andaccessories soon to be released. The engineers at Sabtronics have design-ed high performance into their products, but still to be built at a low cost.At Inouye Enterprises Limited, we guarantee your kit to work, or bring itback to us or any one of our Authorized Dealers. We guarantee the fac-tory assembled units for a period of one year and the kits for a period of90 days from the date of purchase.

Circle /VO. 33 on Reader Service Card.

sabtronics

Item Model Description KitA 2010A LED Ben-

ch/Portable$15953

DMM8 2015A LCD Ben-

ch/Portable$191.75

DMM8110A 100MHz Ben-

ch/Portable Fre-quency Counter

$15953

C 8610A 600MHz 8 Digit $191.75Bench/PortableFrequencyCounter

86101 600MHz 9 Digit $207117Bench Frequen-cy Counter

5020A 1Hz - 200KHz WABench FunctionGenerator

E 1100011 1GHz Bench 9 WADigit FrequencyCounter

F 2035A LCD Handheld $138.60DMM

G 2037A LCD Handheld $174.90DMAifTher-mometer & Pro-be

ACCEnOR1Ei

Assembled$207.87

$240.09

$207.87

$240.09

$272.32

$207.87

$385.11

$174.90

$213.40

Motel Description Price

PSC-65 6111MHz Prescaler: Accurately extend any $79.76601MHz Counter up to 600MHz and above.

t H1-2, Tcuch & Hold Probe: For use with Models $35.452010A, 2015A, 2035A and 2037A DMM's.

HV.-3J High Voltage Probe: Extend ass 10M $59.75impedance DVM to 30,000 VDC.

AC -126 AC Adapter/Charger: Permits AC line oper- $14.75at on of all Sabtronics Bench/Portable DMM'sand Frequency Counters.

N8-124 trard Batteries: Set of 4 "C" sue cells. Pro- $38.67vides up to 8-12 hours of continuous use.

LEP 10 ALdio Frequency Probe: Switchable for $35.45either low frequency (DC-100KHr) or high fre-quency (.1-100MHz).

RFR-16 Telescopic RF Pick-up Antenna: or use $17.72wilt any BNC input connector type frequencycounters.

DEALERS WELCOME. Please call for further information and quantitypricint. All above merchandise has Federal Sales Tax in price, just addProvincia, Sa es Tax (Ontario Residents On1,1 (a 7%. Include with allorders$6.75 per instrument for handling and shipping.Prities Subject To Change Without Notice.

3LEASE NOTE: In the event of a postal disruption, please do notlesitafe to call us wit -1 you orders. We will be happy to processjour corder C.O.D. or ducugh your VISA or Master Card via courierservice.

To speed de very enter VISA or Master Card numbers when issuing3ersonal cheques. Inzkide vpur expiry date and your signature. Thiswill er-able us to process your order in the least amount of time.

DYNAMIC SOUND AND COMPONENTS, division ofnouye Erterprises Limited, 87 Green Lane, Unit #12,

Thornhill, Ontar a L3- 2A1. (416) 886-1070/71.

ETI-AUGUST 1981

RAEKITCMOS Electronic Dice Kit

$24.95RAEKIT #3010

At last: a pair of trulyfair dice that youdon't even have tothrow! Just touchingthe contacts on theCMOS ElectronicDice will start theLED's "rolling".Within momentsthey will freeze in arandom pattern ofdice. After a fewseconds the circuitwill turn itself off toconserve itsbatteries.

MAIL ORDER INFORMATIONPayment by, VISA/Mastercard (Include signature, number and expirydate), cheque or money order. Add $2.00 for shipping, B.C. residentsadd 6% Sales Tax. Visit our new Edmonton store

R -A -E Industrial Electronics Ltd.3455 Gardner Court, Bumaby, B.C.V5G 4J7 Phone: (604) 291.8866

Mastercard

Circle No. 4 on Reader Service Card.

INTRODUCING

ammtrom °HIGH POWER CROFILTERS

pgA

Amitrong cross-overshave been designed with the audiophile

in mind. All capacitors are 100 Volt ratings havinga tolerance of ± 10%, and all coils are wound to a 1%

tolerance and encased with a protective cap. The M.I.L. specfibre -glass board has minimum copper removal to allow for

high current capacity, and incorporates 0.205" (standard)terminals for quick connect usage.

Three conventional cross -over modelsTwo sub woofer models

12 and 18 db models to 200 watts

For further information contact:McBRIDE

McBRIDE

LOUDSPEAKER SOURCE INC.Exclusive Canadian Distributor

14-440 Phillip St., Waterloo, Ont. N2L 5R9 (519) 884-3500

Circle No. 14 on Reader Service Card.

eti cat door...When was the last time you did something nice for your faithful little kitty cat. the ador-ing creature that leaves you gifts of dead mice in your underwear drawer, claws thelegs of your two hundred year old antique dining room suite and awakens you cheer-fully at four AM with a mating call that sounds like feeding time at the day care centre?You cad' You've been taking all this devotion for granted. Well. now, for the low priceof $6.75 plus 7% PST for Ontario residents, you can buy the new ETI combinationswinging cat door and magazine binder. Easily attached over any convenient hole us-ing two common railroad spikes or a lot of masking tape, it permits your pet to comeand go as it pleases. Plus, should one of your neighbours, less enamoured of kitty thanyourself, get the testy twelve gauge and blow it into next week. your new cat door willhold a whole year's worth of ETI magazines. The new ETI cat door; binder costs nomore than the old binder used to. It comes in five decorator colours, all of which areblack. Write for qtaantity prices if you want to do something nice for your llama

ETI Cat Door/BindersUnit 6, 25 Overlea Blvd.

Toronto, OntarioM4H 161 lJ

Yes, it does look like somebody stole all the wires out of it.Rather peculiar how such things can happen. They were allin there just the other day. You see, the problem here is thatthere are all sorts of possible explainations. It could be thework of carniverous cable rats. It may be the boss's idea ofa unique pink slip. Or, it could be a new wrinkle intechnology. If it were rats, there'd probably be telltalesigns, like Minnie Mouse pin-ups all over the inside of thecable. The only way to really be sure which of the other twooptions are involved is to be really up on what's happeningin the forefront of electronic technology. And the best wayto do that is to read ETI.

If you're like this fellow, a bit tied up in your work, youmight not find it altogether convenient to get out to thenewsstand to get ETI each month. You might want tosubscribe. For just $16.95 a year, or $29.95 for two, you canhave ETI delivered right to your door. . . or your cable tun-nel, if you prefere.

ETI MagazineSubscriptions Dept.

Unit6, 25 Overlea Blvd.Toronto, Ontario

M4H 1B1

ETI-AUGUST 1981 66

ON TIME R1,D1OFF TIME .7 R2,C2

CMOS MonostableBarry Wilkinson

This monostable uses a 4027B CMOSJK flip-flop. The time constant is set byR1C1, and D1 speeds the discharge ofC1.

WIPERMOTOR

CUT WIRE

ON

TO 12VVIA FUSE

- - -

*1VIA FUSE

OF 9 fill1r I=

0

,I

;

w

,0 I7V TO PULSERvIA FUSE

111

it 1 sl ;Iwo n tat positionWIPER SWITCH

'Nother Wiper DelayThomas Smith

Grant Wood's wiper delay circuit (ETI,January 1981) will not function withsome motors, especially those manu-factured by Bosch. These motors havea set of contacts that short the motorwindings to park the wipers. A DPSTrelay must be used to prevent blownfuses.

TT23

1.

a HAMMONDPOWER SUPPLY

Will let yousleep nights

Hammond Power Suppliesare designed 3 ways better formaximum reliability, long life

and your peace of mind.

QUALITY COMPONENTSOur design uses hermetically sealed IC Regulators and IntegratedDarlington Transistor output regulation stages. Reliability is increased 4:1over competitive economy units using plastic devices. The reducedcomponent count further increases efficiency by as much as 2:1. We alsouse enclosed, wire wound pots for output voltage adjustment to providemuch longer service than the open carbon types used by, some competitors.

2. CONSERVATIVE RATINGSOur smaller units use a 100 watt hermetically sealed output stage comparedto the 30 to 60 watt plastic transistors typically used. Our larger modelsfeature a TO - 3 hermetically sealed dual rectifier derated to 30% or less ofits capacity to eliminate rectifier failure.

3. BETTER CONSTRUCTIONOur transformers are electrostatically shielded isolation types which, togetherwith a high frequency by-pass capacitor filter circuit, reduce noise and H.F.transients by more than 4:1. We mount the TO - 3 can directly on the frame foroptimum heat transfer and use more dissapation material than others to ensuremuch higher output current at elevated temperature.

HOW MUCH BETTER?Enough to show a MTBF of 50,000 hours.60,000 hours for the same units at 10%derating. Enough that we don't hesitate ingiving you a full 2 year warranty.Invest in some peace of mind. Ask for us byname at distributors across Canada or circle ournumber on the reader card for catalogueand prices.

HAMMONDMANUFACTURING,.WHAMMOND MANUFACTURING COMPANY LIMITED

394 EDINBURGH RD. GUELPH ONT. NM 1E5PHONE (519) 822-2960 OR (416) 456-3770

Circle No. 8 on Reader Service Card.ETI-AUGUST 1981 67

The only portablescope with acomponent tester.

Capacitor 33 uF Transistor E -C Transistor B -E

Oscilloscope Specifications:

Y Deflection

B -E 1 uF + 68 ohms

X Deflection

Bandwidth: DC- 10 MHz( 3 dB) Timebase: 0.2s-0.2 us/cmOvershoot: Less than 1% Triggering: 2 Hz -30 MHz (3mm)Sensitivity: 5 mV - 20 V /cm Auto+ level controlInput Imp: 1 M ohm // 25pf Bandwidth: 2Hz- 1 MHz

General Information

Component Tester.Calibrator.Power Supplies:A -C. -InputWeight '

For single components and in circuit0.2V ± 1% for probe alignmentRegulated Including high voltage110, 127, 220, 237, VA.C., 50 -60 Hz8-1/4 Lbs.4-1/2"H x 8-3/8'W x 10-7/1670

We service all makes of Oscilloscopes:TEKTRONIX HEWLETT-PACKARD

GOULD ETC.From coast to coast. Call us next time.

980 Alness St., Unit 35, Downsview,Ontario (416)661-5585 M3J 2S2

Circle No. 10 on Reader Service Card

0.24V POWER SUPPI2i',--1 AMP

Buildroiectihs

with thisgi andre protectpowerall your

sup-ply kit.

"A MODE ELECTRONICS KIT"boxed kit without P.C.B. - $26.50boxed kit with P.C.B. - $29.95bagged kit without P.C.B.- $24.95

Fun, simple to build, instructions in-cluded"A MODE ELECTRONICS KIT"

boxed kit without P.C.Et - $14.50boxed kit with P.C.B. - $15.50bagged kit without P.C.B.- $12.50

- DO NOT send <4.postage.- All KIT-KING Kits

are postage prepaid.- C.O.D. orders 52.00 additional- Ontario residents add 7% sales to- Mastetcharge, VISA -Money Orders-Be sure to sign your order- DO NOT send cash

THE STARLIGHT

An exciting digital controlled audio activated light display control unit. P.C.board and all parts except case andlights included. 1500w.

A "KIT KING KIT" - $49.953. CHANNEL COLOUR ORGANA classic! Still one of the favouritesof kit builders.3.channel colour organ with mastercontrol.

"A MODE ELECTRONICS KIT"

boxed kit without P.C.B. - $16.50boxed kit with P.C.B. - $17.50bagged kit without P.C.B.- 515.50

THE STEREO SIXKIT KING'S exclusive 6 channel stereocolour organ with audio limiter. P.C.board included. 1500w.A "KIT KING KIT" - $49.95

YEARLY SUBSCRIPTION!To receive Bulletins and Flyersfor KIT-KING'S exciting new

Kits, Protoboards and our low costBread -board Kit Line, send $3.50 to:

KIT -KINGP.O. Box 2068

Bramalea, OntarioCanada, L6T 3S3

Circle No. 19 on Reader Service Card.

PLASTIC BOXES

A serviceable range of boxes complete withintegral card guides, moulded from abs flameretardant thermo plastic in orange, blue, grey andblack. Six sizes available with choice of plastic,metal or clear crystal lid. Economical styreneboxes also available in six sizes, black only withstyrene lid.

FREE CATALOGUEHAMMOND

MANUFACTURING .wHAMMOND MANUFACTURINGCOMPANY LIMITED394 Edinburgh Road N.Guelph Ontario CanadaN1H 1E5

Circle No. 7 on Reader Service Card.

Continued from page 61Only In Canada, You Say.....The experiences of people like Tom-my Hunter and Gordon Lightfootwhile in the New Knighted States forrecording sessions may go a longway towards making the safety ofCanadian cities attractive to bothAmerican and Canadian artists, andkeeping our recording studios busy.

The fact that so many of thesestudios are superbly equipped andstaffed by first class engineersdoesn't hurt either.

And now there's digital.

PARALLEL

IMTG SLOTS

SHELL (top view)

Figure 4

McClear Place Studios Ltd., ofToronto now holds the distinction ofbeing the first Canadian recordingstudio to acquire digital recordingequipment. The system is the SonyDigital Recording System, and coin-cides with the studio's planned ex-pansion to include a dual purposestereo digital and analogue mobilefacility.

The first efforts were recordedfor the independent high quality jazzlabel innovation, and recent effortsinclude Sackville records first digitalrelease, with Don Thompson and EdBickert, as well as a live club sessionwith Rob McConnell and the BossBrass for Jazz Music Productions.

In support of this and othermoves into digital, Sony has installeda fully electronic digital editing suitein a central Toronto location usingtheir DAE1100 Computer Editor. Itfeatures microsecond editing ac-curacy, digital cross -fade, fade in andout, and will be made available toanyone using Sony's new digitalrecorders.

Contact Sony Canada, Pro-fessional Products Div., 411 GordonBaker Rd., Willowdale Ont., M2H 2S6.

N DCE I- : ---

lipSuper ClassFkmilleillt-f..i2ov,

toot.,S ..-,power 11 MN i - ,: to'

lox. oitc N4907

...,t4 tkaadA''"e;5

'PRICES GOOD THRU. OCT. 1981

Kit No. Description PriceNA904 710/ I ov, 1 irr It 95

Power AmpNA905 trOW MOS II I DC -of 95

Power A,,,1,NA1106 120W MOS hl I 1X 114'15

Power AtopNA908 200W 5 2 0( 211'15

Power Atop W Ser, PowerSupply

NA9(19 75W s 2 Pure 51111 II-.

Class A DC Power ArnoW ( alnnet

NAI/211 I( Stereo PhonoPre -Amp

NA921 I( 4719 Stereo 15 'I")

lone ControlNA922 D( C Ia.. A Pro- 141 95

tesstonal Stereo Pre-AfopW Regulator

NA924 0( f f 1 Super 94 95

( la, A Stereo Pre Ang,NA925 Protessgrnal 4.:5 ) )

11 T Stereo Pre AtopNA940 10W I( Stereo 19 95

Amp

Kit No. Description PriceN 59 1 I 111155 ',Ierec, II(

( 1,,,,,. A ,I,u,{1 \\ ',pl. Pr,ter tor

N \94 , 250 \\ Stereo I-11'( LI, A \ Illp AN Spk Pt.,Ie. tor

15'14- 2-0.5 2 Mini lute .)'),gr,tled Amp V\ rah I I)Meter N (a,

'.5`11,11 I-, ',lei, III) 4,' ,

I, t'I MeterN 59, r IS step III no

\ Shaped I I'D I ooel %It u,N 501111 Sok Pron.. tor

\ 5 1111 Del.1 N

's '5`1111Pro Poolnetrg 1/1'11

I quall/erN N'1tt I I ICI tr(,,,, 181)' I

I ( Sc, And IO, erheof IonAmp

N19/9, 151 Mn IR 1

1/1'

\\ I,1,1'NI -'III 1 ' , 1111111)11 1

1 1)

( lor kN R1100 0 1,05 i ',A 21

FO'gulator

NEWTRONICS ENGINEERING INC -Send Cheque Or rsT)ile) k ndcfgliffiNM Plus 52 00 For Postage Handling208 Sparltna Are.. Suite 110. 0 \

Toronto. Ontario 1.115T 2W3 oot\ Residents Add 7%I-Ontario(416) 368-8994 15 S1 Al)( P S T

-Federal Sales Tax Included.

Circle No. 25 on Reader Service Card.

ACCESSORIES

FROM OK MACHINE TOOLBattery WrapTool-BW-2630: $27.95Bit for AWG-30-BT-30: $5.49Just -Wrap Tool-JW1: $20.95(Available in Blue -White -Yellow or Red)Manual Wrap-WSU-30: $9.95

FROM AP PRODUCTSACE 200K-SolderlessBoard: $29.95HOBBY BLOX-ModularCircuitBasic IC's Starter Kit: $8.95Basic Discrete Cornponents Kit: $9.25(Each one includes aProject Book)

ASK FOR YOUR FREE CATALOGPHONE ORDERS: (418) 839-8367Send your cheque, M.O., VISA orC.O.D., NO Shipping charge. Mini-mum order: $5.00 Quebec residentsadd 8% P.S.T.

IELCO1'0', E .

ROMUALD.,),JEEIEC. 06W 5M3

ELEMOrliOUECircle No. 24 on Reader Service Card.

ETI-AUGUST 1981

TECH TIPS

555 Voltage ControlS Draper

0

V-CONTROL2-Vcc VOLTS

O 3

- 7

IC1741

0

0 1

This circuit was developed to provide acheap, reliable and accurate voltage con-trolled oscillator. It uses readily avail-able components and the control overmark -space ratio common to other 555

WIRED SOUND Continued from page 51

R1SEE TEXT

7

CA3080

3

R247OR

R347k

Att\A/

C1

IC3555

-"<)+3-9V

R4SEE TEXT

0/PO

OV

ETI-AUGUST 1981

0-3-9V

0circuits is retained. Frequency -voltageresponse is linear over approximatelyone decade making the circuit useful intiming applications. Operation is as

follows.

IC1 buffers the input voltage andproduces the control current for IC2.IC2 is an operational transconductanceamplifier and produces an output currentmultiplied by the differential inputvoltage. This output current is used tocharge and discharge the capacitor C1 inthe normal way. The equation for out-put high and output low times are givenbelow:Output high time = R1C1 (47.5+R4)

9024V control

Output low time = R 1 C1192Vcontrol

where all resistances are in kilohms andall capacitances are in microfarads.

Current consumption is a miserly10mA from a 12V supply making theunit suitable for battery power.

N.B. - R1 should not be less than 18k

Tech -Tips is an ideas forum and as such is notaimed at the beginner; we regret that we can-not answer queries on these items. We donot build up or test these circuits prior topublication.

You can't beat The System!GLOBAL SPECIALTIES CORPORATIONSmarter tools for testing and design.

1* i 11ff111111111111111111111111111! :1ZN.iI. ...V,

Experimentor solderless breadboard

2

u.s. PAT Dag. NO. 2Z.5+5..ei

c

"we I.*1 view

111(144,&"

is

Experimentor Scratchboard workpads

41. /111111111111111111111111111113

RilM11111111111111111111111

Experimentor Matchboard pre -drilled PCBs.

When you have a circuit idea that you want tomake happen, we have a system to make it happenquicker and easier than ever before: TheExperimentor System.

You already know how big a help ourExperimentor solderless breadboards can be. Nowwe've taken our good idea two steps further.

We've added Experimentor Scratchboardworkpads, with our breadboard hole -and -connectionpattern printed in light blue ink. To let you sketch upa layout you already have working so you canreproduce it later.

With Experimentor Matchboard you can go frombreadboard to the finished product nonstop! We'vematched our breadboard pattern again, this time ona printed circuit board, finished and ready to buildon. All for about $4.25.

There's even a letter -and -number index for eachhole, so you can move from breadboard (wherethey're moulded) to Scratchboard (where they'reprinted) to Matchboard (where they're silkscreenedonto the component side) and always know whereyou are.

When you want to save time and energy, you can'tbeat the Experimentor System.

- ---------- -- 7------------------ ------------------- : ------------ Z . ----- - - _ ----- - - - -

YOU CAN'T BEAT THE SYSTEM!

1EXP-300PC which includes one itemA Matchboard pre -drilled PCB

4.25

2EXP-302, which includes three itemsThree 50 -sheet Scratchboard workpads

$ 5.20

3EXP-303 which includes three itemsTwo Matchboards and an EXP-300solderless breadboard $ 25'

4EXP-304, which includes four itemsTwo Matchboards, an EXP-300breadboard and a Scratchboard workpad $26."

For your FREE Global Catalogue, mail this coupon to:len finkler limited80 Alexdon Rd. Dovvnsview, Ontario, M3J 2B4

Please send catalogue to:

Name Position

Company Dept

Address

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Circle No. 13 on Reader Service Card.

THE EXPERIMENTOR SYSTEM Available from leading Electronic Parts DistributorsCircle No. 13 on Reader Service Card.

ri-2r-tActmPonenive tirenu ACTIVE CONTINUES TO HOLD THE LINE ON PRICES

Zilog

Z80 -CPU0804 -CPUZOO -P1028011-P10080-CTCZBOA-CTC080.0MA0504 -DMA

COMPUTER SUPPORT CENTER

MOS MEMORIESPart No.

MOS Static RAM'sPrice

2101-35 0' r 41 350NS 22 PIN 5.142102-25 - ?SONS 16 PIN 1.42P2111-451. .150NS 18 PIN 3.87P2112-3514 , :SONS 18 PIN 3.452114L Low ..., :4 11024 x 41 300NS 4.492147 41< 1411 5NS 12.942147 41< 14K ' -ONS 11.64

UART's

40 Khz Single 5V SupplySpecial 5.14AY5-10134

IK CMOS RAM5101 16 1256 x 4) 450NS 22 PIN Low Power 4.49

4K CMOS RAMP6504 4K 146 x 11 550NS 18 PIN 110MWP6514 46 ,14 x 4145ONS 18 PIN 110MW

SHIFT REGISTERS

Z80.510/0 2 5 MHz 29.19 MICROPROCESSOR EPROM'Sz8 /0 4 : MHz 36.212 5 MHz 9.04 086510 1 , MH2 29.194 0 MHz 12.29 Z8085)0 1 0 ... -1 36.21 )$10.342 5 MHz 7.09 Z80-510 2 ' '.'..: 29.19

CHIP SETS6800 CPU 6.05

---'4 0 MHz 9.95 0800.010 2 : .5, 36.21 6802 CPU 11.252 5 MHz 7.09 080-510 9 . MHz 21.91 6808 CPU 8.39

2 5 MHz 20.74 080048T 5 MHZ 15.54 4.75

S 6.184 0 MHZ 9.95 0804510 9 : : MHz 28.00 6809 CPU 25.94

68104 0 MI -12 29.84 08011.0ART 4 0 MHz 19.316820 3.45

6666888842552051

38.353.45

3.45

3.45

1403A 100.5)14044 IT0.5)3341APC FIFO 1 MHz3342PC 64 Od3347PC 80 DR

ECL RAM

8.398.39

dual 512 bit 3.87single 1024 ml 3.87

6.185.144.49

10410ADC/HM2106256 x 1 bit fully decoded 15NS 16 pin

CLOCK CHIPMSM51332RS 16.84Microprocessor Real-time Clock/Calendar

10.95

CMOSCD4001BE .23 CD4040BE .85 CD4108BE 2.20CD4002BE .23 CD4041BE 1,16 CD4510BE .75CD4006BE .77 C04042E36 .70 CD4511BE .73CD4007BE .31 CD4043BE .77 CD4512BE .94CD4008BE .87 CD4044BE .62 CD4514BE 2.18CD4009BE .51 CD40468E .99 CD4515BE 2.82CD4010BE .51 C04047BE .90 CD4516BE .98CD4011BE .23 CD4049BE .49 CD4519BE .68CD40126E .23 CD4050BE .42 CD4520BE .73CD4013BE .38 CD4051BE .99 C04522BE 1.01CD4014BE .73 C040528E 1.03 CD4526BE 1.63CD4015BE .73 C04053BE 1.03 CD4527BE 1.16CD4016BE .42 CD4060BE 1.16 C0452138E .94CD4017BE .70 CD4066BE .62 CD4531BE 2.07CD4018BE .68 CD4068BE .31 CD4532BE 1.09C04019136 .62 CD4069BE .23 CD4539BE .77CD4020BE .88 CD4070BE .31 CD4543BE 1.87CD4 1BE CD4071BE .30 CD4553BE 2.46CD4022BE 1.03 C04072E16 .25 CD4555BE .90CD4023BE .23 CD4073BE .31 CD45568E .55C04024BE .57 CD4075BE .36 CD458186 2.46CD4025BE .26 CC/4076E1E .70 CD4582BE .90CD40268E 1.89 CD40788E .31 CD4584BE .55CD4027BE .55 CD4081BE .23 CD45858E 1.03C040288E .70 CD408286 .23 CD4702BE 11.64CD4029BE .94 .CD4085BE .57 40097PC .94CD4030BE .94 CD4086BE .90 40098PC .94CD4033BE .94 CD4093BE .49 40161PC 1.56CD4034BE 3.17 CD4099BE 2.26 00174PC 1.27

,...004035136 .90 CD4104BE 3.07 40175PC 1.27

DIODES & RECTIFIERS1 AMP RECTIFIERS 3 AMP RECTIFIERS

IN4001 .05 IN4005 .09 IN5400 .16 IN5405 .25IN4002 .06 IN4006 .08 IN5401 .18 IN5406 .27IN4003 .07 044007 .09 IN5402 .20 IN5407 .29IN4004 .07 IN5403 .22 IN5408 .31

IN5404 .23SUPER SPECIAL

1N25013 37 amp 200V $2.55

2ENER DIODESIN4728A - IN4752A (1 watt) .16IN47534 - IN4754A (1 watt) .33IN7464 - IN759A (400 mW) .1211452248 - IN52528 (400 mW) .13IN5336A - IN5378A (5 watt) .62

SWITCHING DIODESIN9140 .051144148 .05

(T7P-29ATIP29BTIP29CTiP30ATIP3OBTIP30CTIP31ATIP31BTIP31CTIP32ATIP32BTIP32C

T;741 A

.48.49.51.51.55.55.49.55.59.55.59.62.70

TIP41BTIP41CTIP42ATIP4213TIP42CTIP110TIP111TIP112TIP115TIP116T110117TIP120TIP121

.74 TIP122 .94

.77 TIP125 .94

.74 T1P126 1.00

.77 TIP127 1.09

.83 TIP140 1.87

.70 TIP141 2.13

.74 TIP142 2.55

.83 T1P145 2.39

.72 TIP146 2.57

.77 TIP147 2.93

.83 TIP2955 1.0883 TIP3055 .9188 FT3055 .77

8035 CPU8039 CPU8080A CPU8085 CPU815582128214821682248226822882518253825582578259827987488755

7.7410.345.798.399.042.574.492.574.492.576.476.44

10.996.44

10.3410.3410.9946.8041.60

6502 CPU6504 CPU6505 CPU6520652265326551

9.699.959.957.44

10.3414.1114.24

PROM'S74S288 3.25 256 bit. 16 PIN745188 3.25 256 I30. 16 PIN93427/82S129 4.49 14. 16 PIN93417/825126 4.49 16. 16 PIN93446/7621 6.44 2K. 16 PIN93436/7620 6.4093453/7643 10.3493448/7641 10.9993451/82S181 25.94825185/7128 36.34745478/7132 25.79825191/7138 101.40

2K. 16 PIN46, 18 PIN4K, 24 PIN4K. 24 PIN84. 18 PIN84, 24 PIN164. 24 PIN

C1702424 +US027081K r 8 450C2716/TMS2516 ei venvoi"16K 45ONS Singe 5V SupplyTMS2532 IT I Pin Cull32K 14096 r 8) 450 nsC2732 110101 version)32K 14098 a 8) 450 nsTMS2564644 184 a 81 450 n5

$9.07

$38.94

$24.38

$182.00

16K STATIC RAM Special $29.84TMM2016-3 16K 12K 81 300NS16K MOS DYNAMIC RAM'S (16 PIN)4116.20 120ONSi $4.494116.30 1300NSI Ceramic Special 3.194K MOS DYNAMIC RAM'S0554060.30 Special 3.454K 144 x t i 30ONS 22 PIN16K CMOS STATIC RAM Special6116 16K 12v 81 15ONS 15 PIN $67.606414 MOS DYNAMIC RAM4164 64K .o4V 1. 200NS 15 PIN $46.80

$62.49

LM301AN -8LM307N-8LM308N.8LM308CHLM30911LM310HCLM311CHLM311N-8LM318N-8LM318CHLM323KLM324NLM339N

LED209LED211LE0212LED220LED222LE0224

LINEAR I.C.'s.42 LM348N14 1.29 LM748CN-8 .51'.38 M .68 LM1458N-8 .49

1.14 LM555N-8 .33 LM1488N-14 .861.24 LM556N14 .68 LM1489N74 .862.03 LM567CN-8 1.09 LM1495CN-14 2.541.94 LM709CH .77 LM1496CN-14 1.771.09 LM714CH 4.75 LM2211CN-14 3.58.68 LM723CH 1.09 LM224OPC 2.15

1.29 LM723CN14 .62 LM3081DC 2.031.48 LM725CN8 1.63 LM3403N-14 1.116.05 LM733CN'14 1.77 LM3524PC 7.711.92 LM739CN-14 2.20 LM3900N .626.44 LM741CH .82 LM4136N-14 1.14

LM741CN-8 .36 ULN20034N 1.0"LM747CN-14 .73

OPTOELECTRONICSL.E.D. LAMPS

T 1 3 mm RedT.1 3 mm GreenT.1 3 mm YellowT114 5 mm RedT11. 5 mm GreenT11. 5 nun Yellow

DISPLAYSFND357 375 Common CathodeEND500 500 Common CathodeEND507 500 Common AnodeDL14164 digit 16 segment alphanumeric display 1

ISOLATORSIL074 Dual Opto Isolator 1500V1L074 Quad Opto Isolator 1500VILCT6 Dual Opto Isolator 1500VMCT2 0010 Coupler 1500V

1.291.291.29

32.506 hl

DUAL -IN -LINELOW PROFILEI.C. SOCKETS

CONTACTS8 PIN

14 PIN16 PIN18 PIN20 PIN22 PIN24 PIN28 PIN40 PIN

-.Nor \..12 VOLTAGE REGULATORS.25

011/..iRNDY

PRICE.11.1620.27.30.33.36.42.61

.1 78XXKC (00-3) 1 amp pos

.31 78XXUC (T0-220) 1 amp pos

.21 78MXXL1C (TO -220) ": amp pos79XXKC (70.3) 1 amp neg79XXUC (00-220) 1 amp neg79MXXUC 110-220) amp nag781-105KC (T0-3) 5 amp 5V78P05KC (TO -3) 10 amp 5V78H12KC (70-3) 5 amp 12V

1.6/3 781-1154C (00.3) 5 amp 1555.14 78MXXHC (70-5) amp pos1.68 79MXXHC (70-5) 'amp neg.70 78LXXAWC )T0-92( posTIL111 Opto Coupler 1500V .70

4N26 Oplo Isolator 2500V .704N33 04t0 Isolator 1500V .65

$2.44.83.47

2.93.98.88

7.7412.557.747.742.152.41

.51

SCR's and TRIAC'sCIO6D .44 SCR 5 amp 4005 TO -220TIC44 47 SCR 0.6 amp 30V TO.92TIC47 .55 SCR 0.6 amp 200V TO -92TIC 116B 1.26 SCR 8 amp 2005 TO -220TIC 1160 1.29 SCR 8 amp 4005 TO.220TIC 126B 1.42 SCR 12 amp 2005 TO -220TIC 126D 1.53 SCR 12 amp 400V TO.220TIC216B 1.29 Triac 6 amp 2005 TO -220TIC216D 1.29 Triac 6 amp 4005 TO -220TIC226D 1.42 Tnac 8 amp 4005 TO -220TIC236D 1.81 Triac 12 amp 400V TO -220TIC246D 1.89 Triac 16 amp 4005 TO.220TIC263D 2.93 Triac 25 amp 400V TO -2202141595 1.16 SCR 1 amp 505 TO -52N6401 2.03 SCR 16 amp 100V TO 220

Bi-Fet OP AMPSTLO6ICP .94 Low PowerTL062CP 1.29 Dual Low PowerTL064CN 2.54 Quad Low PowerTL071CP .70 Low Noise71_072CP 1.25 Dual Low NoiseTL074CN 2.46 Quad Low NoiseTLO8ICP .55 J-Fet InputTL082CP 1.11 Dual J-Fet InputTL084CN 2.07 Quad J-Fet InputTL495CN 6.44 Switch. Volt Reg 25rnATL497ACN 3.87 Switch. Volt. Reg 500mATL430CLP .90 Ad) Shunt Volt Reg.TL431CLP 1.01 Ad) Pos. Vol Reg

2N4044 1.562N697 .382N706 .382N1613 .382N1711 .38

2141893 .3821422224 .2521423696 292N2484 .31

2N29054 .512N29074 252143053 .38

TRANSISTORS2N3055 .73 2N37022143440 .73 2N37042143771 1.68 2N37062143772 1.66 21437102N3773 2.46 21439042N6133 .73 2N39062146489 1.63 2N39072N6545 6.18 2N41232N3439 1.01 2N41242N6059 3.19

21441252N60551.892146079 5.01 2144126

2N4401

13 2144402 .10 2N5770 .16 MPSAtS .16.13 2N4403 .10 2145771 .17 MP50,S5A4,4,32 :2211

2145772 .18.13 2144410 .20PN2222A .12 MPS456 .16

22NN5050 .168887

.16 PN2369A .12 MP5470 .18

2145172 .16 P142907.4 .12 MPSA92 .182145220 .18 PN3565 .16 MPSA93 .16

.13 2N5221 .18 PN3567 .16 MPSA14 .1609 2145223 .18 P144249 .16 MPS2925 .1609 2N5226 .18 PN5138 .13 MPS2926 .1609

D9.10

21455512145227

.18 MPSAO5 .162N5401 .202N5550 .14

.18 MPS413 .16MPSAO6 .16

MN, pP 55 33339921 ;1162

MPS3393 .16

.13

.09

.09

TTLSCHOTTKY 8 LOW POWER SCHOTTKY

7400N

740314

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.29.31 774422457114N 1.61 .3142

77440054NN

.31 7425914 2..4996 .42

7406N

.31 74273N 2.59 74LS75N .46

7407N

7744227796NN 49

7409N

.47 7427814 3.09 74LS78N 28

741214 .49

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7413N

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74293N74283N

1:4427 7744ILZIN 1.0949

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7436614NAN ..7805 7744LL5S6923NN .60

1.16

.47 74367614

7423N

.46 74368AN 75 74LS96N

7425N

.38 74390N 1.25 74LSIO7N

.47 74393N 1.68 77441.1110912NN7422N

7426N

.47

7427N .42 74503N .49 74LS125N

.42 74SOON .47 74LS122N

.51 74502N .49 74LS123N

777444332708NNN .55 74504N .73 74LS126N.29 74505N .62 74LS132N

7437N

.51 74508N .62 74LS133N7433N

7440N

.51 74509N .77 74LS136N

.47 7451014 .62 74LS138N743814

7442N

.47 7451114 62 741_5139N

.29 74515N .62 741_5145N

7446N 1...380957

7445N 1.09

777444455307NANN .85 74537N 11166 77,4ILLsS1,5553NN

7451N

747214

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77447745NN

.38 7457414 .75 741.5158N .62

.47 74585N 2.57 741.5160N .90745414

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.47 7458614 .94 74LSI61N 7547 745112N .94 74LS162N .94.51 745114N 1.611 74LS163N 75

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.49 74612414 3.33 74LS164N .757483AN .62 745132N 1.61 74L5165N 1.167484AN 1.77 745133N .62 74LS166N 2.13748514748614

.86 745134N .70 741.5170N 2.0751 745135N 1.68 741_5173N .77

7490AN .42 74513814 1.25 74LS174N .517491AN .55 74513914 1.25 74LS175N .517492AN .49 745140N .96 741_5181N 2.577493414 .49 745151N 1.29 74LS189N 5.79

AN .88 745153N 1.25 74LS190N .947495614 .70 745157N 1.25 741.5191N .94

.77 745158N 1.25 74LS192N .837497N 2.46 745161N 3.71 74LS193N .837410014 1,79 74S16214 4.81 7415194N .837410414 .83 74S163N 4.60 74LS196N 1.1477441107414 .577 7216684 5:759 74LS197N 1.14

74LS221N 1.1674110N I9 74517414 1.25 74LS240N 1.1674111N .75 745175N 1.25 741.524114 1.1674116N 1,56 74SI9IN 5.14 74LS242N 1.1674120N 1,63 745182N 2.20 741.5243N 1.1674121N .62 745189N 5.79 74LS244N 1.167412214 .68 745194N 2.18 74LS245N 2.157412314 .48 74S195N 2.18 74LS247N .9974125N74,26AN .626 7744522205,41N 7.61 74LS248N 1.42

6.44 74LS249N 1,257412814 la 74024014 3.84 701_5251N .70744.13N362N :59 7744$S224441N 3:84 74LS253N .70

74LS257N /37744114421NN

3.871.09

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74LS259N74LS260N74LS266N

1.681.16745257N

74147N 1.61 777444S$2S2276°584NNN 20.6174LS273N 1:4474LS275N

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74547114NN 3.87 74LS32ON

13.38774416621N AN :8833 774454547742NN 11226555 74LS322N

77441163N AN :833 74S47614 7.74 74LS324N74LS348N

74165N .83 741.3009 .22 74LS352N7416614 08 74LS01N .22 74LS353N74170N 2.57 74LSO2N .29 74LS362N-417214 6,44 74LS03N .29 741_5365147417314 1.03 74LSO4N .29 74LS366N7417414 /5 74LS05N 29 74LS367N74175N ,75, 74LS0814 22 741.5368N74176N .99

74LS1ON7LSOgN

.31 74LS373N1.4225 74LS374N74179N 1.42 741.511N .31 74LS375N74180N .901 74LS12N .31 74LS377N7418214 .93 74LS13N .33 74LS378N74184N 3.07 74LS14N .51 74LS379N74185N 307 74LS20N .23 74LS390N74190N 08 74LS21N .23 74LS393N7419114 .88 74LS26N .51 741.5395N7419214 08 74L527N .38 74LS447N74193N .83 741_530N .23 741.5490N74194N .83 74LS32N .38 74LS630N 110.5077 44 11 99 5 6N 60 741_537N .38 741_5669N 1.09

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.51

.62

.75

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1.27.57.74.62

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12.94.68.68.68.68

1.631.63

831.631.291.421.271.271.551.132.46

MINIMUM MAIL ORDER 510 00Add 53 00 to cover postage and handling

PRICES ARE IN CDN FUNDS FOB CANADAFederal Sales Tax IntlProvincial Sales Tax Extra

5551 FERRIER sTMONTREAL OUEBECM4P 21(5Tel 45141 731 7441

HALTER CENTER1050 BAXTER ROADOTTAWA ONTARIOK2C 3P2Tel 16131 8209071

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Friday 9 00 am - 9 00 pmSaturday 9.00 am - 5 30Pm

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