CANADA'S NEW ELECTRONICS MAGAZINE ectronics today

CANADA'S NEW ELECTRONICS MAGAZINE

ectronics todayMAY 1977 incorporating

51electronicworkshop

741 COOKBOOKMAIL ORDER

CATALOGUESREVIEWED

BUILD ETI'S

ETI'S QUICK PROJECTS

SHORT CIRCUITSFUZZ BOX, BENCH POWER SUPPLY

CHOOSING A

BURGLAR ALARM REIFROCOMPUTERPROJECT

EQUIPMENT

REPLACEMENT FOR

0 MONEYEARUNCONDITIONALGUARANTEE

/111111111.

This is a partial list. Write for full tube listing catalogueTYPE EACH TYPE EACH TYPE EACH TYPE EACH

1B3GT 1.25 6BK4C 3.35 6HS8 1.90 10GF7A 2.501K3 1.35 6BL8 1.50 6HZ6 1.50 10GK6 1.801S2A ....... ... 1.35 6BM8 1.55 1OGN8 1.851X2B 1.35 6JC6A 1.80 10JY8 1.85

6BN6 1.80 6JD6 1.85 10KR8 1.852AV2 1.25 61305 1.20 6JF6 3.902GK5 1.55 61307A 1.50 11HM7 2.803A3A 1.95 6BU8A 1.90 6JS6C 3.45 11MS8 3.503AT2 1.90 6JT8 3.95

66Z6 1.20 6JU6 3.50 12AT7 1.353AW2 1.75 6C4 1.25 6JU8A 1.90 12AU7A 1.003BW2 2.80 6CA7 3.40 6JW8 1.50 12AV6 1.003BZ6 1.00 6CB6A .95 6JZ8 1.90 12AX4GTB 1.503CB6 .90 6KA8 2.00 12AX7A 1.35

6CG3 2.25 6KD6 3.953CU3A 2.90 6CG7 .95 6KE8 2.25 12BA6 1.053DB3 2.00 6CG8A 1.50 128E6 1.05

3DC3 2.60 6CL8A 1.60 6KG6 3.95 12BY7A 1.20

3DF3 2.80 6CM7 1.30 6KT8 2.50 12C5 1.553DJ3 2.10 6KZ8 1.80

6CS6 1.35 6L6GC 2.60 12D06B 2.253GK5 1.55 6CW4 6.25 6LB6 3.75 12DW4A 1.90

3HA5 1.85 6106 5.95 12GN7 2.003H05 1.90 6DJ8 2.10 6LE8 3.404AU6 1.55 6006B 2.50 14GW8 2.00

6LF6 3.95 15008 1.604BZ6 1.35 6DT5 1.60 SLF8 1.854DT6A4EH74EJ7

1.551.551.55

6DT6A6DW4B6DX86EA8

1.201.851.601.50

6U86LN861066LT8

1.851.253.351.80

17AY3A1713E317BF11

1.601.552.50

4HA55A05

1.551.25

6EC46EH76EJ7

3.401.501.55

6LU86LX8

2.755.85 17DQ6B

17JN62.102.85

5CG8501i8A5GJ7

1.551.851.95

6EM76ES8

3.002.80

6SN7GTB

6U8A

1.90

1.25

17JZ817KV6A17KW6

1.853.955.60

5GS7 1.85 6EW6 1.35 6U10 2.505GX7 2.70 6FM7 2.00 6V6GT 1.95 18GV8 1.95

6W6GT 2.25 19CG3 2.505LJ85U4GB5U8

1.801.601.60

6GB56GE56GF7A

3.502.252.15

6X9

6Z10

2.95

3.25

21GY521JZ6

3.153.20

6AF96AJ86A L36A L5

3.502.001.85.90

6GH8A6GJ76GK56GK66GM6

1.351.901.501.601.50

8AW8A8138813108BM11

1.851.902.903.75

23Z924L06

27GB5

2.653.50

3.35

6A05A 8CG7 .90 30AE3 1.706A08

.901.55 6GU7 1.35 8DX8 2.55 30KD6 4.50

6AU6A 6GV8 1.95 6GJ7 2.25 31JS6C 3.956AV6

.956GW8 1.80 8JV8 1.85 33GY7A 3.25.956GX7 2.80 8LT8 1.85

6AW86AX36AX4GTB

1.601.701.60

6GY56GY66HA5

3.451.251.85

8U98X9

3.453.45

35W438HE738HK7

.903.503.50

6AY3B 1.60 9A08 3.25 40KD6 3.806BA6 1.25 6HE5 2.70 9GV8 2.90 40KG6 3.956BA11 2.50 6H05 1.80 9JW8 1.60 42EC4 3.856BE6 1.20 6HS5 4.45 10DE7 1.85 5005A 1.35

U

..111111.

All1111116

o

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GAMASONIC CANADA LTD./LTEEOUR PRODUCTS

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HALIFAX TORONTO

WINNIPEG EDMONTON VANCOUVER

ETI CANADA - MAY 1977 3

15 240 Wa t tsHY5Preamplifier

HY3015 Watts into 80


HY1 2060 Watts into 80



The HY5 is a mono hybrid amplifier ideally suited for all applications All common input functionsImag Cartridge tuner etc 1 are catered for internally the desired function is achieved either by amulti -way switch or direct connection to the appropriate pins The internal volume and tone crrcuitsmerely require connecting to external potentiometers (not included) The HY5 is compatible with allI l P power amplifiers and power supplies To ease construction and mounting a P C connector issupplied with each pre -amplifierFEATURES: Complete pre -amplifier in single pack -- Multi -function equalization - Low noise - Lowdistortion High overload - two simply combined for stereoAPPLICATIONS: Hi-Fi Mixers - Disco -- Guitar and Organ -- Public addressSPECIFICATIONS:INPUTS Magnetic Pick-up 3mV Ceramic Pick-up 30mV Tuner 10OrnV Microphone 10mVAuxiliary 3100rnV input impedance 47k:) at lkHzOUTPUTS Tape 100mV Main output 500mV R M S

ACTIVE TONE CONTROLS Treble 12dB at 10kHz Bass - at 100HzDISTORTION 0.05% at 1 kHz. Signal/Noise Ratio 68d8OVERLOAD 38d8 on Magnetic Pick-up SUPPLY VOLTAGE 16 50V

The HY30 is an exciting New kit from I L P it features a virtually indestructible I C with short circuitand thermal protection The kit consists of I C heatsink P C board 4 resistors 6 capacitorsmounting kit together with easy to follow construction and operating instructions This amplifier isideally suited to the beginner in audio who wishes to use the most up-to-date technology availableFEATURES: Complete kit - Low Distortion L- Short Open and Thermal Protection -- Easy to BuildAPPLICATIONS: Updating audio equipment - Guitar practice amplifier - Test amplifier - Audio

sr isiitgrSPECIFICATIONS:OUTPUT POWER 15W R M S into Bt) DISTORTION 0 1", at 15WINPUT SENSITIVITY 500mV FREQUENCY RESPONSE 10H,16kHz - 3dBSUPPLY VOLTAGE LIL 18V

The HY50 leads I L P s total integration approach to power amplifier design The amplifie features anintegral heatsInk together with the simplicity of no external components During the past three yearsthe amplifier has been refined to the extent that it must be one of the most reliable and robust HighFidelity modules in the WorldFEATURES: Low Distortion - Integral Ideatsink - Only five connections - 7 Amp output transistors- No external components

APPLICATIONS: Medium Power Hi-Fi systems -- Low power disco - Guitar amplifierSPECIFICATIONS: INPUT SENSITIVITY 500mVOUTPUT POWER 25W RMS in BO LOAD IMPEDANCE 4 16.7 DISTORTION 004s.at 25W at1 kHzSIGNAL 'NOISE RATIO 75d8 FREQUENCY RESPONSE 10Hz-45kHz - 3dBSUPPLY VOLTAGE 25V SIZE 10S SO 25mm

The HY120 is the baby of I L P s new high power range designed to meet the most exactingrequirements including load line and thermal protection this amplifier sets a new standard in modulardesignFEATURES. Very low distortion - Integral Heatsink - Load line protection - Thermal protection -I Li nn rei cons - No external componentsAPPLICATIONS- Hi Fr - High quality disco -- Public address - Monitor amplifier - Guitar androw

SPECIFICATIONS:INPUT SENSITIVITY 500mVOUTPUT POWER 60W RMS into 8.1 LOAD IMPEDANCE 4-16'.) DISTORTION 0 04 / at 60W at

1 kHzSIGNAL NOISE RATIO 9046 FREQUENCY RESPONSE 10Hz 45kFlz - 3 dB SUPPLY VOLTAGE35VSIZE 1141,50x/35mm

The HY200 now improved TO give an output of 120 Watts has been designed to stand the mostrugged conditions such as disco or group while still retaining true Hi -Fr r,erf ormancpFEATURES: Thermal shutdown - very low distortion - Load line protection - Integra Heatsink -

No external componentsAPPLICATIONS: Hi -Fr - Disco - Monitor - Power Slave - Industrial - Public addressSPECIFICATIONS:INPUT SENSITIVITY 500mVOUTPUT POWER 120W RMS into Elf) LOAD IMPEDANCE 4-16-) DISTORTION 0 OS at 100% at1 kHzSIGNAL NOISE RATIO 96dB FREQUENCY RESPONSE 10H; 45kElz - 3dB SUPPLY VOLTAGE 45VSIZE 114 101185mm

The JY400 is I I P s Big Daddy of the range producing 240W into 4, I, It has been rtesrgned forhigh pow, disco or public address applications II the amplifier is to be used at continuous high powerlevels a cooling fan is recommended The amplifier includes all the qualities of the rest of the family tolead the market as a true high power hi fidelity power moduleFEATURES: Thermal shutdown - Very low cbstormion - Load line protection - No externalcomponentsAPPLICATIONS: Public address - Disco - Power slave - IndustrialSPECIFICATIONS:OUTPUT POWER 240W RMS into 4L) LOAD IMPEDANCE 4-16'.) DISTORTION 0 1 at 240W at

1 kHzSIGNAL NOISE RATIO 94dB FREQUENCY RESPONSE 10Hz 45kHz 3dB SUPPLY VOLTAGE- 45VINPUT SENSITIVITY 500mV SIZE 114 x ion. frlrunnt

TWO YEARS' GUARANTEE ON ALL OF OUR PRODUCTS

NowAvailable

1LPMY 50

Available in Ontario from:DOMINION ELECTRONICS GLADSTONE ELECTRONICS MULTI MARK AGENTS LTD.

Dealer inquiries invited

ELECTRA ELECTRONICS CO.UNIT 12, 7222 TORBRAM RD, MISSISSAUGA, ONTARIO L4T 3V2 - TELEX 06-968653 - TELEPHONE: (416) 678-0562

4 ETI CANADA - APRIL 1977

electronics taglayFeatures

PROJECTION TV 20The big silver screen in your home

741 COOKBOOK 28A thorough look at the Op Amp

CATALOGUE SURVEY 51

A look at what s available from whom by mail order

EASIER WAY TO MAKE PCB's 57How to copy out ETI s patterns

CHOOSING A MICROCOMPUTER 60The choice now in Canada is pretty wide

ProjectsBURGLAR ALARM 13Follow-on project from last month's feature

CERAMIC CARTRIDGE PREAMP 17Circuits for superior performance

NI -CAD BATTERY CHARGER 43Top up your own with this circuit

SHORT CIRCUITS:

BENCH POWER SUPPLY 47FUZZ BOX 48

STEREO RUMBLE FILTER 54Eliminate turntable noise

InformationNEWS DIGEST 6

CIRCUITS BOOK NO. 1 6

DATA SHEET 24

JUNE ISSUE PREVIEW 42PUBLICATIONS FROM ETI 46

TOP PROJECTS NO. 3 65

TECH -TIPS 66

SUBSCRIPTIONS 68

OPEN CIRCUIT 71

READER SERVICES & INFORMATION 71

Second Class Mail registration number3955. Return postage guaranteed. FostOffice returns to Unit 6, 25 OverleaBoulevard, Toronto. Ontario. M4H 181.

Vol. 1 No. 4 May 1977

EDIITORIAL AND ADVERTISINGOFIzICES:Unit 6, 25 Overlea Boulevard,Toronto, Ontario, M4H 1B1Telephone (416) 423-3262EditorMIKE KENWARDAssistant EditorGRAHAM WIDEMANCirculation Dept.SENGA HARRISON

Marketing Manager and AdvertisingPETER PRIEST

Editorial DirectorTOM GRAHAMPublished by:Electronics Today International(Canada) Ltd.Printed by:Heritage Press, Mississauga, OntarioNews Stand Distribution:Gordon & Gotch, TorontoSubscription Rates:$12.00 per year, $20.00 for two yearsSend to Subscription Dept, ETIMagazine, Unit 6, 25 Overlea Blvd.,Toronto, Ontario, M4H 1B1.

International EditionsBritain:Electronics Today International25-27 Oxford St., London W1R 1RFEditor: Halvor MoorsheadAustralia:Electronics Today International,Ryrie House, 15 Boundary St.,Rushcutters Bay, Sydney, AustraliaEditor: Collyn RiversHolland:Electronica Top Internationaal,Postbus 260, Emmen, HollandEditor: Denis LoosFrance:Electroniques Pour Vous International42 rue Jacob, ParisEditor: Denis Jacob

Copyright. All material is subject toworld-wide Copyright protection.All reasonable care is taken to ensurethe accuracy of the information,


NEWS DIGEST

`DO-IT'YOURSELF"DPMA 31/2 -digit panel meter which caninternally accommodate 12 squareinches of user -build signal conditioningcircuitry for measurement and display ofa wide variety of electrical and physicalfunctions has been introduced by theInstruments and Systems Group ofAnalog Devices.

Using either a 334" x 4", or a smaller1.1" x 1.43", printed circuit board whichis connected internally to the basic DPM,the new AD2022 allows the user to buildin circuitry that will measure and displaysuch variables as temperature, pressure,flow, pH, capacitance, resistance, ordecibels. The self-contained "functionalDPM" requires about the same amountof space as a typical 31/2 -digit DPM anduses the industry standard panel cutoutsize (3.9"W x 1.67"H x 4.5"D).

Available from stock, the AD2022 isunit -priced at $218 inc. duty and FSTwith its companion AC26I5 breadboard-ing card priced at $25.50 includingconnector. Tracan Electronics Cor-poration, 558 Champagne Drive,Downsview, Ontario M3J 2T9.

The AC26 15 PC card is pre -drilledwith 0.100" spacing to accommodatestandard components. When populated,the function board connects to theconverter board via a 10 -conductorribbon. The flexibility of the connectionallows the function board to be "folded"onto the converter board, and the result-ing "sandwich" slid back into theAD2022 case.

Al Pollens, Product Marketing Man-ager, said the extensive use of MOS /LSIcircuitry in the "second generation"design of the AD2022 provides the extraspace which gives the AD2022 its broad,functional design flexibility. He said thatin addition to using Analog Devices'functional breadboard, users could con-

nect their own printed circuit boards upto the capacity of the AD2022.

In addition to providing extra circuitspace, the AD2022 offers ± 12 (it 201nAto power analog circuitry and + 5V100mA of logic power in its standardcharacter serial BCD outputconfiguration. with + 5V output ((-t30mA if the parallel BCD output optionis specified.

Other advantages of the "secondgeneration" design include large lighi-emitting-diode (LED) displays, 0.5"high; greater reliability because of thelower components count; lower powerrequirements, less heat build-up andlower cost.

The AD2022 has a ± I .999V DC fellscale range and features auto zerocorrectiion. Limited differential input isstandard on the new DPM, and fullfloating isolation is optional. TheAD2022 can be operated ratiometrically.

With 1975 sales of $30 million,Analog Devices is a leading supplier ofelectronic components and devices usedin measurement and control instrumenta-tion and industrial computer systems.

TUBES BEAT ANYTHING IN THE AIR

A Russian MiG-25 I-oxbat flownto Japan by a defecting pilot hasrevealed the use of vacuum tubetechnology in the Fox Fine radar.The radar has a peak output of600kW which makes it the mostpowerful airborne fire -control radarknown. USAF experts haveconcluded that the MiG-25 isunsurpassed as an extremely fasthigh -altitude intercepter. Onewonders what the Russians can dowith advanced semiconductortechnology!

INJECTEDIntegrated Injection Logic has takenoff and looks set ultimately todisplay TTL and CMOS. Specialfrequency control chips for CB usewith both analog and digitalcircuitry on one chip have alreadybeen developed and will soon be inproduction. I2L is also being lookedat by watch manufacturers becauseof its ability to source high currentsfrom an otherwise micropower chip.If someone introduces a 4000 -typeseries of logic functions in 12L, we'dbetter be ready!

1984In Britain. the Dataskil software subsid-iary of ICL is offering an analysis tosoccer clubs of their performance. A clubcan find out what results they need basedon other teams' performances, and theeffects of variables such as the absence ofa key player can be predicted. Since theresults can be predicted, why bother toplay the games at all? Players would bespared the time-consuming chore ofpractice sessions and could devote moretime to important activities like appear-ing on TV chat shows. opening bou-tiques etc.

POWER BARA 15 amp circuit breaker is a standardfeature on the "Power Bar" by Ham-mond Manufacturing. CSA industriallycertified, this quality unit comes in4, 6, and 8 receptacle models, with anoptional on-off switch, pilot light andchoice of 6 or 15 foot U -ground cords.A contemporary beige in colour, it iseasily mounted and ideal for residentialor industrial use. Hammond Manu-facturing Company Ltd., 394 Edin-burgh Road North, Guelph, OntarioNIH 1E5.

6 ETI CANADA - MAY 1977

2K -BYTE STATIC RAM MODULEMotorola's Microsystems group hasintroduced Micromodule 6, memory subsystem targeted for microcomputer -based OEM products. This provides theuser with 2048 bytes of static RAM (typeP2IO2-1 or MK4102 RAMs are used asthe memory elements), organized intotwo groups of eight 1024 x I bit RAMs.Typical memory cycle time is 500nanoseconds.

During manufacture, Micromodule 6is assigned to base address 7800 (hex) to7FFF (hex). The user, however, canchange this base address by means ofjumper wires on the module. The baseaddress can be re -assigned throughoutthe range of 0000 to F800, in 2K byteincrements. The micromodule's address,data and control busses have TTL-compatible buffered inputs; the data bushas three -state TTL outputs. M68MM06is bus compatible with both the Micro -module Familty and the EXORciser.This adaptability permits the user toutilize the hardware and software fea-tures of the EXORciser and its options toaid in system development and produc-tion line troubleshooting.

Power requirement for Micromodule 6is 1.5 A (max) at + t Vdc ( ± 5%). Theunit price is $280.00; the 2 to 9 price is$274.00. Availability from the factoryand authorized Motorola distributors, isnow.

Also new from Motorola is a modulardata acquisition system to the line. Thesystem consists of an 8 -channel,differential -input module called Micro -module 5A (MM5A) and a 4 -channelanalog output module (MM5C).

The analog input voltage range of theMM5A&B is ± 10 mV to ± 10V; theinput current range is 4 to 20 mA or 10 to50 mA (resistor programmable). Inputimpedance is 100 M; amplifier gainrange is Ito 1000 V/V (resistorprogrammable).

The MM5A&B both contain an inputmultiplexer, a high gain instrumentationamplifier, sample/hold circuit, 12 bitA/D converter, timing/control /addressdecode logic and a + 5 V to ± 15 V dc-dcconverter.

Like the MM5A&B, the MM5C is buscompatible with an EXORciser orMicromodule system. The analog outputrange is strap selectable for ± 10 V. 0 to10 V. ± 5 V or ± 2.5 V (at 5 mA).

The MM5C contains four 12 -bit,hybrid DiA converters, a 12 -bit latch,address decode/write control logic and a+ 5 V to ± 15 V dc-dc converter. Theinputs of the D/A converters are double -buffered to minimize output glitches.

Unit price of each module is $725.00;availability, from the factory and author-ized Motorola distributors, is now. For

further information on any of theseproducts contact Motorola Microsystemsat (602) 244-6815 or the TechnicalInformation Center, Motorola Semi -conduct Products, Inc., P.O. Box20294, Phoenix, Arizona 85036. U.S.A.

COMPUTERS HAVE EARSEMI Thrshold have introduced a low costvoice -input terminal based on the DECLSI-1 I Microprocessor. This means thatdata can be input to a computer by speech-a 'hands-off' approach, if you like.The Threshold 500 performs spectralanalysis of each spoken word into 32speech parameters - aspirants, vowels,long and short pauses and other charac-teristics, and compares these with pre -stored reference patterns. If they match,an output string is generated. With theaddition of a speech synthesizer yourcomputer could even mutter to itselfunder its breath!

MICROCHESS

Microchess, an intelligent chessplaying program which will run onany 8080 or Z-80 system with 4K ofcontiguous memory and an ASCIIinput; output device has beenannounced by Micro -Ware Ltd.

The Microchess documentationincludes a Player's Manual with adescription of the program, and acomprehensive appendix with detailsfor conversion of the I/O routines,or customization programs.

Features include automatic boarddisplay, multiple levels of playingskill, castling, and the ability toreverse the board at any time.

Microchess will be available at aprice of $15.00 from most majorcomputer stores or direct from:

Microchess (8080), Micro -WareLimited, 27 Firstbrooke Rd.,Toronto, Ont., Canada, M4E 2L2.

SPACE SHUTTLE ON THE TILES

Extremely pure silica glass has beenmanufactured for at least 40 years -longer than jet aircraft have beenaround. Now it is to aid and abet the

ultimate aircraft - the U.S. SpaceShuttle. Made into tiles (composed of96% silica glass) of which 34,000 areused, the material covers well over70% of the surface of the Shuttle.

These tiles are incredible heat`shedding' devices (see photo) and willbe expected to withstand temperaturesof up to 12600C for 100 re-entriesinto the atmosphere. Previous heatshields were destroyed on re-entry.

Each tile is precisely milled to fitexactly against the curvature of theShuttle body, thus making thecomposite craft as light as possible,and as aerodynamic as is feasible. Thisdoes however mean that no two ofthose 34,000 tiles are alike! Imaginethe little man in a white coat with theJob of fitting them to the aircraft - ahuge 3-D jigsaw puzzle with only onesolution out of 34,000 (i.e. 34,000 x33,999 x 33,998...x 1) possibilities!Rather him than me.


NEWS DIGEST

3-1/2 DIGIT PORTABLE DMMA 31/2 digit portable DMM costingonly U.S. $99.95 has just beenannounced by the B&K-PRECISION product group ofDynascan Corporation. The newDMM, Model 2800, is a full -featureinstrument that provides a widerange of accurate voltage, currentand resistance measurements.

The 2800 features 22 ranges thatmeasure as high as 1000 volts, DCor AC, or up to 40,000 VDC withoptional PR -28 probe. Resolution isto ImV, 1 uA or 0.1 ohm. TypicalDC accuracy is 1% with an inputimpedance of 10 megohm. The 2800also features auto -zeroing and 100%overrange reading on all ranges.

All ranges are well protectedagainst overloads. Ohms circuitryprotection ranges from +100V and -450VDC or 300VAC continuously,

to momentary overloads up to 1000volts DC or AC. All DC and ACvoltage ranges are protected up to+1000 VDC or AC RMS. Decimalpoint polarity and out -of -rangeindications are all automatic. The2800 can be powered by ordinary"C" cells, optional rechargeablebatteries, or the optional ACadapter/charger (when rechargeablebatteries are used).

The 2800 comes complete withtest leads, detailed operating manualand spare fuse. A full range ofoptional accessories are alsoavailable.

The B&K-PRECISION Model2800 is sold through electronicdistributors and will be available inApril. For additional informationcontact: B&K-PRECISION, Dynas-can Corporation, 6460 W. CortlandAvenue, Chicago, Illinois 60635.

MECO A WORLD OF ELECTRONICS

RCA MODEL 1800 MICROPROCESSOR

G. $409.950 ICE: $269.95

THE LARGEST ASSORTMENT OF MICROPROCESSORS IN CANADA FROM $9995 UP

MOTOROLA SIGNETICS AMI RCA TEXAS INSTRUMENTS

electronics ltd.

The COSMAC Microtutor is a complete small computer systemdesigned for minimum cost experiments and educational train-ing. Inputs are entered from eight binary switches and outputsare displayed on two LED hex displays.

The Microtutor is designed for quick and easy hands-on experi-ence and is an ideal introduction to computers for everyone. TheMicrotutor comes with an easy -to -follow 47 page manual de-signed to develop an increasingly intimate knowledge and abilityfor those having only basic electronics knowledge.

The Microtutor comes completely assembled and following thestep by step procedure of the manual the user will be enteringand using computer programs in a matter of minutes.

MONTREAL 4050 JEAN TALON W. H4P 1W1 (5141 735-5511 TELEX 05-25590

QUEBEC 98 OUEST ST-VALLIER ; G1K 6W8 (418) 524-4641 TELEX 011-285

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TORONTO 24 MARTIN ROSS AVE. M3J 2K9 (416) 661-0220 TELEX 02-29697


°TOP QUALITY°ETI CIRCUIT BOARDS

444 5W Stereo Amp 6.00570 React ion Tester 5.85

PARTS FOR ETI PROJECTS

LM379S 6.50 LM380N 1.80

LM382N 1.80 LM3O1A .557490 .95 7447 1.05

PN2222 .25 2N2926G .304017 1.55 555 .65741 .49 2N5088 .25

1N4001 6/1.00 1N4148 12/1.00

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THIS MC:MTH'S SPECIALS

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10uf 50v 8/1.00220uf 50v 4/1.001000uf 63v 2/1.002200uf 40v 3/2.00

Boards postpaid in Canada. IC's, etc.add 50c to total for P&P. Ont. residentsadd 7% provincial sales tax. No COD'sWRITE FOR LATEST CATALOGUE

cAn ELECTROnicsMOS BOHI690,

PETERBOROUGH,ont H91 7S4

COLOUR CAMERASony of Canada Ltd.'s newDXC-1610 Trinicon colour videocamera was designed to complementthe VO-3800 portable videocassetterecorder/ player and the newly -introduced BVU-100.introduced BVU-I00. Available fromSony video products dealers acrossCanada, the self-contained cameraunit has a four-way power capabilitymaking it ideal for field or mobileoperation. In field operations, theDXC-1610 may be powered byeither the portable videocassetterecorder or for up to three hoursusing the optional BP -60 batterypack which may be attached to thehack of the camera head. Sony'sDCC-3000 car battery adaptor orthe CMA-5 AC operated cameraadaptor are available for mobile use.

Features include: adjustableelectronic detachable viewfinder,F2:1, 17-102mm one touch zoomand focus lens, built-in electretcondenser mic and colourtemperature compensation filters,flip -open side panels to facilitatemaintenance, Sony's registered MF(mixed field) Trinicon tube system inwhich the chrominance andluminance information is sensed bya single pick-up tube, external micinput.

This lightweight camera (inc.batteries, lens, viewfinder) providesfaithful colour reproduction, reliableperformance and high resolutionwith no misregistration problems. Itis packaged in an easy -to -carryaluminum case. Sony of CanadaI.td., Industrial Products Div., 88Horner Ave., Toronto, Ontario.

SINCLAIR STRIKES AGAINThe original Sinclair Programmablecalculator was a bit quirky inoperation and limited as a scientificcalculator; this was often acharacteristic of Sinclair's calculatoradvances. Some readers may recallthe original Sinclair Scientific, whichused to cause users headachesthrough its lack of 1/x key. Thesecalculators were great value formoney though, and now Sinclair hasdone it again, but this time, thecalculator appears to beidiosyncracy-free.

The new Sinclair CambridgeProgrammable is only 4'/2" x 2" andweighs 2 oz. (HP67 is 11 oz.), yet ithas 36 steps of program memory,parentheses, line numbering andeven conditional and unconditionalbranching. Programs may besingle -stepped and edited, with stepand line number being displayed.Available for this calculator is alibrary of 294 programs for only$10. It looks like Sinclair havedefinitely got it right this timeespecially at only U.S. $29.95.

IGNITION TRANSISTORA new monolithic Darlingtontransistor circuit - type numberMJ10012 - designed specifically forthe high -voltage, high -current andharsh environmental requirementsencountered in automotive ignitionsystems has been introduced byMotorola.

Despite their improved specifica-tions, the new automotiveDarlingtoniced competitively, atU.S. $2.75 in quantities of 100 to999. The devices are available inquantity from factory anddistributor stock.

For further information, contactthe Technical Information Center,Motorola Semiconductor Products,Inc., P.O. Box 20924, Phoenix,Arizona 85036.


ALARMS

Contents

Basic AlarmPhoto Intruder AlarmIntruder AlarmPhoto Electric RelayLow Temperature/Lights outTemperature SensorCoolant levelWater LevelElectronic LockCar Battery WatchdogSimple Car AlarmSimple Lock

AMPLIFIERS &PREAMPLIFIERSHigh Input ImpedanceHigh Impedance BufferLow Output ImpedanceHigh Input ImpedanceLow Frequency ExtenderVirtual Earth PreampIC Tape Head PreampSimple Stereo Tape Player2.5 Watt20 Watt Slave10 WattLoudspeaker MicrophoneVoltage Controlled AmpWide Band AmplifierVideo Power AmpBroadband Amp

SIGNAL PROCESSORS

Fuzz BoxGuitar FuzzFuzz BoxWaa WaaDisco AutofadeSimple AutofadeInformation TransferOptical Pulse ConditionerTV Sound PickoffCracklefree PotentiometerVoltage to FrequencySine to Square WavePrecision AC to DCVoltage ProcessorUniversal MeterDouble PrecisionFast Half WaveSimple ChopperNoise Rejecting SCR TriggerPhase Shifter

SIGNAL GENERATORS

SimpleVariable Duty cycleFast EdgeFETImproved MultivibratorVariable Duty cycleStable R.C.Cheap (CMOS)Simple TTL XTALUncritical XTALPulseZero CrossingSimple PulseNeedle PulseStable Linear SawtoothZenerNoisePink

The first in a new seriesof `ideas books' for the experimenter

Simple RelaxationTriangle with independent slopeExponentialWiderange MultivibratorMultiple WaveformLinear SweepStep FrequencyBeeper7400 SirenSimple SirenShip SirenTwo ToneToy SirenKolak, Startrek, Z CarsSound EffectsSound Effects

FILTERS

BandpassLow & High PassRejection NotchBandpassCartridge E0 BcRumbleHum StopperTape Hiss ReductionSimple Crossover

DIGITALThermometerHeads or TailsBinary CalculatorVoltmeterSeven Segment to DecimalDieRandom BinaryCMOS DieMultiplexer HintsLearning MemoryCMOS Clock

POWER SUPPLIES

ConstantTemperature StableConstantVoltage ControlledPrecision Voltage DividerDual PolaritySimple BalancedVoltage DividerLow RegulatedShort Circuit ProtectedSimple TTL SupplyZN414 SupplyStable ReferenceTransformerless InvertorDC to DC ACVoltage MultiplierAutomobile ConvertorShaver AdaptorDC -DCHigh Voltage From BatteryVariable + ire or -ire outputSimple12V from Battery ChargerBucket RegulatorAdjusting Zener VoltageVariable ZenerZener Boosting of RegulatorsHigh PowerElectronic FuseBetter FuseRegulator & FuseFast ActingSCR CrowbarVoltage PolarityNi CAD DischargeCurrent Limiting

TEST

Diode CheckerGO/NO GO Diode TesterZener CheckGO/NO GO Transistor TesterQuick JFET TestCurrent Gain TesterBasic Transistor TesterSimple Transistor/SCRSCR TesterCrystal CheckCrystal CheckerGood/Bad Battery TesterBattery TesterOp -Amp TesterOp -Amp Checker:heap Logic Probekudible TTL ProbeAudible Slow PulsesLogic ProbeLogic AnalyserI and 0 Display ProbeSimple High ImpedanceVoltmeterAudio/RF TracerThermocouple ThermometerMetering Stabilised suppliesSimple Frequency Meter

TIMERS & DELAYS

Low Standby Drain741 TimerSelf Triggering TimerPulse TimerPulse DelayVoltage Controlled MonostableSequential RelaysDoor Chime Delay

SWITCHING

Touch Triggered &stableTouch Sensitive SwitchElectronic SwitchSound Operated 2 WaySPST Switch Flip FlopTwo Signals on one Wire

INDICATORS

Line -o -Light3 Step LevelLight LevelBargraph DisplayFuse FailureBlown FuseBack Up LampDC Lamp FailureFM Tuner StationCurrent FlowDisco Cue

FLASHERS

Dancing LightsLow Frequency Strobe

FlasherUltra Simple

POWER CONTROL

LDR Mains ControlFloodlamp ControlZero Crossing SyncTrain ControllerLow Differential ThermostatSimple Temperature ControlFull Wave SCR Control

AUTOMOBILE

Brake Lamp FailureCourtesy Light DelaySimple Hazard LightLight Extender & ReminderFour Way FlasherHeadlamp DipperWiper DelaySuppressed Zero VoltmeterRev Counter/TachometerAuxiliary Battery

DETECTORS &COMPARATORS

Peak Detect & HoldWindow DetectorPeak ProgramPositive PeakReaction Comparator

RADIO FREQUENCY

Crystal Marker100 kHz MarkerRF VoltmeterRF DetectorLED RF IndicatorRF Amplifier ProtectionFET-RadioOp -Amp Radio

MISCELLANEA

Phase Locked LoopTouch DoorbellPhase Lock ControlAudio MixerVirtual Earth MixerPlop EliminatorLoudspeaker ProtectionDigital Capacitance ProbeDigital Tape Recorder AdaptorBreakdown Diode SubstitutionDual Function ChargerDual Mode Amp

Capacitor SubstitutionElectronic CapacitorSpeeding Up DarlingtonsShutter SaverThyristor SensitivitySound Operated FlashStrength TesterLogic Noise Immunity

TIPS

Identifying 74 SeriesSupply PinsSoldering IC'sTinning With Solder WickPCB StencilsFront Panel FinishDIL DrillingFluorescent StartingAvoiding Insulated Heat SinksTTL Mains InterlaceBoost Your MainsHigh Resistance on Low MetersHigh Voltage ElectrolyticsTransistor IdentificationTemplate & Heat Sink forPower TransistorsTransistor SocketSolder Flow ProblemsOdd Resistor ValuesResistors in parallelCMOS DIL HandlingIdentifying Surplus ICSExtending Battery LifeBattery SnapsPower Supply or BatteryBattery CheckingMuck RemoverTransformers in reverseLoudspeaker CheckingImproving UJT LinearitySignal TracerCrystal EarpiecesCheap VaricapsZener Lifts Capacitor Rating

DATA

741 Op -Amp DataBC 107-109 DataBC 177.179 DataCMOS & TTL Data2N3055 DataMJ2955 DataBipolar Data TablesBipolar FETs RectifiersDiodes Pinouts Zener Misc


NEWS DIGESTMICROCOMPUTER KIT

An 8 -bit microcomputer system inkit form, has been introduced byMotorola's HEP/ MRO OperationsGroup. Called the Educator II, thekit contains an NMOS 8 -bit, MPU,PIA, 128x8 -bit static RAM; twoTTL 512 -4 -bit ROMs and a TTLclock circuit. The NMOScomponents are the HEP versions ofthe popular M6800 microcomputerproducts. Educator II utilizes thefull instruction set and addressmodes of the MC6800 MPU. Theclock frequency is approximately625KHz.

An executive program, residing inthe ROMs, contains routines forexamining and modifying memoslocations and MPU registers,servicing interrupts, transferringprograms to and from cassette tapes,searching tapes for specific programsand a routine to test the finished kit.The executive uses 14 bytes of RAMfor a scratchpad; the remaining 114bytes are for user programs. Anoptional 128x8 -bit RAM can beadded to the p.c. board for largeruser programs.

The p.c. board layout is quitesimple; kit construction could beaccomplished in one evening. Allcomponents necessary to get themicrocomputer "up and running"are supplied, even the solder. Aseparate power supply is required,for which a kit is available. ATest -As -You -Build feature providesfor accurate, minimum errorconstruction.

A comprehensive construction/instruction manual is included withthe kit. Nothing is left to chance inthe manual, construction steps areexplicitly detailed. Theory ofoperation of the kit's NMOSmicrocomputer components aredescribed in an articulate manrer.The user is "stepped through"increasingly complex demonstrationprograms, shown the basics ofdebugging and how to use the

:assette operation. Applicationsprograms are described and listed,along with a listing of the residentfirmware.

Educator II retails for $169.95 andis available from selected Motorola

and MRO distributors andother distributors, nationally. Theadditional 128x8 -bit RAM is alsoavailable at the same locations; theretail price is $19.04.

®KTRONThe one complete line of speakers

SPEAKERS with a very important difference

The aluminum voice coil form. The low -mass, high -efficiency, moisture -proof, heat -resistant, high -capacity, long-lasting, gua-ranteed, aluminum voice coil form. Oak-tron perfected it, and only Oaktron puts

the aluminum voice coil form in all itsspeakers: from 1%" to 15", for almostevery application imaginable. Order fromour inventory of over 170 models, or sendus your specs.

Send for your copy of the latest Oakum,' catalogue today!

s . s1. It. nit Km. 1-111)1 omnitronix ltd. 2056 SOUTH SERVICE RD. TRANS CANADA HWY. - DORVAL QUE. H9P 2N4 PHONE: 5 4 6831993

ETI CANADA MAY 1977 11

CLASSIFIED

J & J ELECTRONICS LTD.,P.O. Box 1437 E,Winnipeg, Manitoba R3C 2Z4

Semiconductor SpecialistsDo you get our bargain flyers? Send$1.00 to receive the current literatureand specials and to be placed on themailing list for the future publications.

FREE! New 64 page electronicsparts and surplus catalog jam

packed with exciting items andhard to find bargains for

hobbyist, industry and schools.Thousands of super buys in;

Electronic parts, motors, hardware,microphones, semis, fans, assembliestimers, knobs, connectors,CB accessories, speakers, trans-formers, telephones, leds,ICs, opticswire alarm parts, meters, amplifiers,kits, photocells, TV parts, audioaccessories, computer parts, powersupplies, bulbs, transmitters, fuses,switches, tape, heaters, crystals, etc.etc. Over 100 top name stereo brand.discounted. Amazing values foreveryone. We are big buyers offactory clearouts, distress merchan-dise and government surplus.Largest inventory of surplus inCanadaETCO ELECTRONICS, Dept.ETI, 183G Hymus Blvd., PointeClaire, Quebec. F1911 1E9

For SaleForty Years of Service Data120 Rcc TV manuals #1 to #12434 Rcc Radio manuals #20 to #54plus binders of radiofrom 1927 to #20 manual.Over 100 Service manuals of all kindssufficient to fill 18 foot shelf.$500.00 or best offer by June 1st.Hundreds of old type tubes,new and used - make offer.Ken's Radio & Music348 Colborne St.,BRANTFORD (519) 752-3797

PHOTOGRAPHY BUFFSBuild 8 digit timer for less

than $50.00. Auto on -off safe--light and enlarger. Accuracy

0.01%. Range: 1/2 sec to 10 millionminutes !! Complete plans and

schematic. $3.00 CAN. To:B. Lapointe, 10431 -139th St.,

Surrey, B.C. V3T 4K3. AIRMAILED

Here are professional HP qualityelectronic counters at prices that arereally affordable. Choose the one that bestfits your needs.

HP's low priced "frequency only"units use the highly desirable directcounting method for 1 Hz resolution in1 sec. Models 5381A to 80 MHz, 5382A to225 MHz and 5383A to 520 MHz.

Modular capability is yours in the5300B/5305B counter to 1300 MHz.By simply replacing the lowermodule, it can become any of 7 othermodels including a DMM or batteryoperated model.20708A

Higher sensitivity? Add Model 10855APreamplifier and get 22 dB gain, 2 to1300 MHz, $266.

They all offer high accuracy, high inputsensitivity, input attenuator, rugged metalcases. They're built to the same highquality standards as our most sophisti-cated $9000 counter, and tested andcalibrated to the industry's finest fre-quency standards. The 5383A and 5305Bhave fused inputs, too. All this is backedby HP's extensive world-wide sales andservice network.

Contact your nearby HP field engineer,or write.* Duty and taxes extra where applicable.

HEWLETT 11 PACKARD

Sales and service from 172 offices in 65 countries.Canada 6887 Goreway Drive, Mississauga, Ontario L4V 1 L9

Other offices: Dartmouth, Montreal, Ottawa, Winnipeg,Calgary, Edmonton & Vancouver.

17 ETI CANADA MAY 1977

ETI Project

BuIKLAn ALARM

ETIBURGLAR

ALARM

a

A simple and versatile control unit,with internal siren and battery.

FOLLOWING ON from lastmonth's Burglarproof Your Homearticle, we present the ETI burglaralarm. The circuit is simple,reliable and versatile. Based on asingle CMOS chip, the standbycurrent is very low, making aline power supply non essen-tial. Several versions are possible,depending on the particularcircumstances where it will beused. We built the simplestversion, and will describe it fully,with details of possible modifica-tions and additions.

BASIC UNIT

The basic unit is self-contain-ed, apart from sensor switches. A12V battery is used as thepower supply, this battery is

capable of powering the systemfor about a year, if the siren is notETI CANADA - MAY 1977

[..,

BATTERYTEST

ALARmFUJI!

activated! When in the alarmcondition the battery will powerthesiren for about 6 hours conti-nously. A battery test facility is

included in the design, whichdisplays the on load voltage. Weused a 12V siren similar to the wellknown "Sonalert", mounted insidethe case. Our siren has a soundoutput of about 93dB meters -quite loud!

Other features of the basic unitare, on /off keyswitch on frontpanel, bell test button and LEDfault indication. The box itself isfitted with anti -tamper micro -switches, so that it can only beopened in the off position,without sounding the alarm.

Another important feature is

the 30 second delay facility. Thisensures that when you switch theunit on the alarm will notsound for 30 seconds but any

ON

TEST

fault will light the front panelLED. Also if you have to walkover a pressure mat or open analarmed door, to leave, you havethe delay to do it in.

SENSORS AND SIRENS

Three types of sensor can beused with the system. Normallyopen circuit types, such aspressure mats; and normallyclosed types such as reedswitches biased by magnets.Changeover contacts can also beused, wired to break the normallyclosed circuit and short the opencircuit when operated, this ispossible as one wire is common toboth circuits. Connection to theunit is via a standard 180 5 pinDIN plug and socket, all the pinsare not used, and external bell

13

ETI BUriGLAri ALARM

SECURITYSWITCHES(DOORSWINDOWSetc.)

FRONTDOOR

BY-PASSSWITCH

r -

!PRESSi"1ATSWITCH

L O

(111k

B12

13

R210M

5,6,7

14

IC1 /14001

IA D1

R41M

01

141N4148

2,42222

Z.

1131k

021N4148

031N4148

OGOFF i!)

l4716V

NOTE Rx is selected to glue 10mA throughSCR1 270R was used in the prototype. Ifexternal unit relay is used. Rx can be omitted.

IC1/2R5 40012k7 1 10k

9.

047R

IC1/34001 R6

R71k rRx(SEETEXT)

R91008

O

ON

A D4 SIREN1N4001.-'\

OPENICLOSED

SW2a.b/

022N2222

R81k

Circuit diagram of basic alarm

units can be wired via thisconnector if required.

As shown the unit is suitablefor shop display protection,trailer protection or even as atent alarm -- a pressure matunder your ground sheet! Forsome homes the internal siren willbe all that is needed, however,the only way to find out is to try it.If you get lots of complaints fromyour neighbours or a rapid visit bymen dressed in blue -- it's loudenough! Obviously it is best to tryit out at a civilised time -- not 4am. If the internal siren is not loudenough, you will need an externalalarm. This will be describedfurther on.

INSTALLATIONBearing in mind the general

guide lines given last month, theinstallation can be worked out.Points to remember are, cover allexternal doors, and if unecono-mical to protect all windows -- tocover the internal doors as well,with the odd pressure mat -inhallways and on stairs to comple-te the protection.

Even though single core wirecan be used for the closed circuitwiring, we prefer to use 3 or 4core throughout, as this givesmore flexibility in sensors andalso creates uncertainty in themind of a would be by -passer. Italso looks like telephone wiring ifinstalled neatly.

C

If a shunt switch is not fitted tothe main exit, the alarm willsound on entry, this can beunpopular with neighbours. So ashunt switch is strongly recom-mended.

OPERATIONIn operation the unit is turned

on, by the front panel keyswitch.If the LED lights it means thatpart of the circuit is either openor closed incorrectly, if thishappens switch off and find theopen door, or chair on pressuremat etc. To check if you havefound the fault switch on again

OK aSCR1 v3A

MO

B

L

OP

R11120[1

ON

OFF0 SW1b

12v11 IT

II

-- the LED should remain unlit. Apoint to note is that you can onlytest the battery with the unitswitched off - this is to prevent thebattery being flattened by aburglar keeping the test buttondepressed (if he managed to getup to the box without setting offthe alarm).

Assuming that you have fitteda shunt switch to the exit, you cannow leave and lock the doorbehind you. This is why a shuntswitch inside the main lock ispreferred to a separate shuntswitch; if you forget to operate aseparate switch the door isunprotected.

Close-up of board and wiring, this was an earlier version - hence slightly differentto overlay shown.


-11oW it works-The circuit is based around a 4001

CMOS quad NOR gate, with the gatesconnected as invertors (cheaper thanusing invertors!). The input to ICla isderived from the closed circuit sensorsand the open circuit sensors. In thenormal state the output is low and Q1 isoff. When either R2 is shorted or thepositive supply from RI is interruptedthe gate changes state. QI is turnedhard on and LED 1 illuminates. R4 andCl form a timing circuit, which preventsICIb from giving a low output for 30seconds from switch on. After thisperiod, if LED1 is on ICI b and ICI ccharge state switching on Q2, whichtriggers SCR1 which self latches. Rx isto make sure SCR1 passes at least 10mAif a bell is used which breaks its owncircuit. RI 1 is selected to draw 100mA tosimulate a load for the battery. RIOmakes sure that Cl is fully dischargedwhen the alarm is switched off, in orderto get consistent timing periods.

Parts listQ1,2D1,2.3

2N2222 or similarIN4148 or similar

Resistors all 596 1/2W D4 IN4001 or similarR1 3 7 8 1k SCR1 100V 3A thyristorR2 10M LED1 TIL 209 or similarR4 1M SW1 (a,b) LockswitchR5 2k7R6 10k SW2 (a,b) MicroswitchR9 100R !normally open)R10 47R PB1,2 Push to make.R11 120R release to breakRX (see text)

Sensor switches see textCapacitorsC1 47 F 16V tantalum

Miscellaneous

General view of the basic unit, note anti -tamper microsmtches (SW2 a,b)

SemiconductorsIC1 CD4001A Meter Panel type 0-15V

Case 111/2 x 5 x 7 inches

Battery 12V + connector

Siren 12V type

PCB, nuts, bolts, wire, 5 pin Din plugand socket. Insulating kit for SCR 1 etc

+Ve VIASW1b

SCR1

-Ve

SCR1

SVV2a,b

SIREN+Ve

MSIAJ

SECURITYSWITCHESDOORSWINDOWS etc.

Overlay and PCBlayout (both full size).

PRESSUREMAT

ETI CANADA - MAY 1977

KEYSINITC1-1SW1a

1!)

ETI BunGLAn ALArimOn returning open the main

door and then switch the unit off.

CONSTRUCTIONConstruction is quite straight-

forward, most of the componentsare mounted on a PCB. The mainpoint to watch is that CMOS isinvolved, the usual precautionsshould be taken. Make sure your.iron is earthed and fit the IC last.All bolts must be fitted with twonuts to prevent external removal.The front panel mounted partsshould be epoxyed into place,also to prevent external tamper-ing. The two microswitchesSW2a + b should be fitted so thatthe front panel keeps themdepressed when in place. Generallayout is easily seen from thephotographs.

The unit should be screwed inposition through the back panelwhen complete.

EXTERNAL UNITSIf an external siren or bell is

needed there are three ways thiscan be done. The simplest, butleast secure is to run it in parallelto the internal siren via twinwires. A 1 A fuse should be placedin each of the leads - so that ashort circuit will not flatten thebattery. Obviously the battery lifewill be reduced when poweringtwo alarm sirens.

The second method is to run arelay in parallel with the internalsiren, the external unit then needsits own power supply. The relayshould be mounted at the mainunit. The external power supplycan be another battery or a linepower supply.

The disadvantage of boththese methods, is that if the wiresare cut the external alarm will notsound. If the cable is run insidemetal tubing this is not so much ofa problem.

BEST METHOD

The best method is to use asensor circuit with a relay output.This can be obtained fromanother CMOS circuit similar tothe main unit - only simpler.Again a relay is connected acrossthe siren but if the wires to it arecut the external siren will sound.The standby current is about1.:A so the battery can be leftconnected permanently. A sug-gested interwiring diagram isshown.

1A

RLA1

-1\ SIREN

SIREN

sisr N

EXTERNALUNIT

EXTBOARD

--IT EN12V

TO ALARMCIRCUIT

L _ _

TAMPERSWITCH

T

Top: Simplest external siren circuit.Middle: Addition of a 12 volt relay (RLA 1) gives another simple external siren circuit.Bottom: Most secure method, involves the use of a CMOS chip, circuit below.

RLA1

CONTROLBOX

TAMPERSWITCH *Pins 7,5,6,9,8,12,13

are connected to ground

UP AND DOWN

Another possible modificationis to add an upstairs/downstairsfacility to the main unit. This canbe done by duplicating the mainboard and adding an extrakeyswitch to the front panel,together with a second LED. Theinterconnection for this is alsoshown.

The batteries should be check-ed at least once a month, andreplaced when on load theyregister below 11 volts.

HC: 1

Method for interconnectingfor up/down circuits.

two modules


CERAMIC CARTRIDGEPREAMPLIFIERUse of charge amplifier improves performance of ceramic cartridges.

MOST amplifiers of commercialdesign, including our own ETI designs,omit facilities for ceramic cartridgesand allow only for the use of magneticcartridges. This is because magneticcartridges are capable of much betterperformance than ceramic althoughtop line magnetics are much moreexpensive.

Magnetic cartridges are expensive tobuild whereas ceramic cartridges arerelatively cheap to build so there is acrossover point, and many top lineceramic cartridges are much bettervalue -for -money than are magneticcartridges in the same price range.Hence many people with limited fundshave asked for details of a preamplifierinput stage specifically tailored for usewith ceramic cartridges.

The two types of cartridge, ceramicand magnetic are entirely different interms of electrical qualities. Theceramic cartridge has a much higheroutput, the working load impedancesof the 'i.wo are entirely different andthe magnetic type requiresequalization whereas the ceramic typedoes not (or does it?). The magneticprovides an output which is

proportional to stylus velocity whilstthe ceramic provides an outputproportional to acceleration. Thismeans that where a record is recordedwith constant accelerationcharacteristic the output from a

ceramic cartridge would be flat withfrequency whereas the output from amagnetic cartridge would be a

response rising with frequency at 6dB/octave. Conversely if a constantvelocity record characteristic wereused the ceramic output would fallwith frequency at 6 dB/octave.

Today all records are recorded to theRIAA standard of equalization. Tnisattenuates bass and boosts treble toprovide a characteristic very close toconstant acceleration. This proceduregives best compromise between theconflicting requirements ofsignal-to-noise ratio and of pickuptrackability. To replay an RIAAequalized record with a magneticcartridge we must use a preamplifierhaving the reverse characteristic, i.e,bass must be boosted and treble mustbe cut in order to obtain a flatfrequency response. This process is

used on all preamplifiers for magneticcartridges and is loosely just known asequalization.

However a perfect ceramic cartridge,when replaying RIAA equalizedmaterial would give an unequalizedresponse as shown in Fig. 1. In orderto make ceramic cartridges easier touse manufacturers build in a broadmechanical resonance at the nighfrequency end to boost the response.At the low end, the rise in responsebelow 50 Hz is cured by selecting aterminating impedance which causes aroll off at about 130 Hz. The responseof such a cartridge would be as shownin Fig. 2. If the bass end were not

corrected rumble of the turntablewould be accentuated and this is

clearly not desirable.Thus clearly, the impedance into

which a ceramic cartridge works is ofgreat importance and with this in mindwe investigated different methods ofmatching the cartridge to the amplifierwith a view to obtaining the utmostfrom ceramic cartridges.

DESIGN APPROACHThe ceramic pickup may be

simulated by a voltage source and aseries capacitor.

The value of the capacitor and themagnitude of the voltage source vary

30

25

20

dB

15

10

5

0

ALE

20 50 100 200 500 1000

FREQUENCY

2000 5000

Fig. 1. Typical response of a ceramic pickup without mechanical equalization.

10k 20k

30

25

20

dB

15

10

5

0

k50 Meg LOAD

d .4-I

2 Meg LOAD

1

20 50 100 200 500 1000FREQUENCY

2000 5000

Fig. 2. Response of Decca Deram showing effect of terminating impedance at lowend and of mechanical equalization at top end.

10k 20k


30

25

R2

20

1B

15

10

5

020 50 100 200 500 000

FREQUENCY2000

Fig. 3. Overall response of a Decca Deram into a charge amplifier.

1B

30

20

15

10

020

5000 10k 20k

margEminimain.rinuko

111118111411111.11111.50 100 200 500 1000

FREQUENCY2000 5000 10k

Fig. 4. Response of charge amplifier. Roll off at low end is designed to compensate forrising response of cartridge in this area.

from manufacturer to manufacturerbut lie in the range 200-900 pF and100 to 1000 mV at 1 kHz and5cms/second.

One of the most popular and readilyavailable cartridges is the Decca Deramand we performed all our tests withthis cartridge. The unit has an outputof about 150 mV and a capacitance of600 pF. The recommended loadimpedance is 2 megohms and this givesthe response as shown in Fig. 2. Thebass response can be improved butonly at the expense of greatlyincreasing the rumble. The dip at 2kHz can readily be compensated forbut we have not experimented in thisarea.

Another system commonly used is toload the unit with a low impedance(e.g. 75 k ohm) which causes a loss ofbass below 3 kHz, and then boost the

20k

bass again electronically. Thisovercomes the need for a very highimpedance. Such a techniquecombined with a rumble filter to cutthe rising response below 50 Hz cangive good results. However due to thelarge differences between variousmakes a different network needs to bedesigned to suit the bass roll -offcharacteristic of each cartridge type.

A third system which we propose,is to use a "charge" amplifier.

CHARGE AMPLIFIERWith the charge amplifier the input

impedance is zero - how then does itwork? A conventional inve-tingamplifier is shown in Fig. 5. and, asanyone familiar with amplifiers willknow, the output voltage will be:-

TABLE 1

GAIN (600 pFcartridge) C2 C3 R4

unity 560 pF 0.0082µF 390 k

6 dB 330 pF 0.015µF 180 k

12 dB 150 pF 0.039µF 47 k

R1 HIGH GAININVERTINGAMPLIFIER

OUTPUT

Fig. 5. Conventional inverting amplifierstage.

R2Vow = - Vin

R1

What is not always realized bybeginners is that R1 and R2 need notbe resistive - they may be capacitors,inductors or combination ofimpedances. It is only the impedancethat is important. Since the output ofthe ceramic pickup is a capacitor wemay connect it directly to the input ofan inverting amplifier and use a

capacitor as the feedback element. Thegain of the stage now becomes theratio of the two capacitor impedances.Although the impedance of thecapacitor drops with increasingfrequency the ratio remains constant.Therefore, with a 'perfect' amplifier,the frequency response is flat at allfrequencies.

In real circuits we generally need abias resistor across the feedbackcapacitor. This causes a roll -off at thelow end similar to that obtained whenusing a FET amplifier.

If a response down to 10 Hz is

required a resistance of 50 megohmminimum is required. However this is

C1

c2

HIGH GAININVERTINGAMPLIFIER

R1

R2

C3 "'L

BIASNETWORK

Fig. 6. Basic charge amplifier with bias andfilter network. Gain control elements arecapacitors. Bias network R1, 2, 3 and C3are required for dc stability and to roll ofbass response.

+V(10 -18V)

2N5459

INPUT

0C10.47uF

tat

OUTPUT

R3470k

OV

Fig. 7. Circuit of FET follower used toobtain the responses shown in Fig. 2.

18 FTI CANADA - MAY 1977

much too high for correct biassing anda different technique is called for.

With the arrangement illustrated inFig. 6, the effective resistance is: -

R2 + R3Reff R2

R1

provided R2 << R1, 3 andXc3 << R2

If the value of Xc 3 approaches R2the effective resistance drops and, ifthe value of R2 and C3 are properlychosen, a 12 dB/octave cut-off at thelow end can be obtained whicheffectively removes the rising low -endresponse due to the recordingcharacteristic.

Other advantages of the chargeamplifier are firstly that it is easy toobtain gain (unlike the source -follower FET approach) and secondlythat cable capacitance does not affectthe performance in any way. Onedisadvantage is that the cables areslightly microphonic and movement ofthe leads can cause an output - thishowever is not an insurmountableproblem.

The overall response of the DeccaDeram Cartridge into a chargeamplifier is given in Fig. 3, and as canbe seen the response at the low end isgreatly improved. As said before thedrop around 2 kHz could readily be

compensated for but this was notconsidered necessary.

If a pickup having a differentcapacitance were to be used the orlychange would be in the gain of theamplifier - the frequency response (ofthe amplifier) remains the same. f thegain is too high then simply changingthe feedback capacitor to a highervalue will restore it. However, if thelow frequency cut-off is to bemaintained both R4 and C3 must alsobe altered. Table 1 illustrates thevalues required.

CONCLUSIONCost for cost the ceramic cartridge is

better value for money than themagnetic type. The use of a properlydesigned preamplifier can produce asubstantially flat response.

However whilst an almost perfectfrequency response can be obtained byproperly processing the output from acartridge like the Decca Deram it cannever sound like the Shure V15 MK 3!Other factors such as transientresponse and channel separation aregenerally not as good as those of amagnetic cartridge. Whether theinbuilt mechanical resonance isactually responsible for the poortransient response is probably knownonly to the cartridge manufacturers -

INPUT

O

C

+V(10 -18V)

R710k

c40.47uFCl 2N2222

0.01uF

OV

C2'

Fig, 8. Circuit of practical chargeamplifier for ceramic cartridges whichgave the overall response as in Fig. 4.For values of C2, 3 and R4 see table 1.

one feels that if it were doneelectronically it may well be better.

This has not been presented as anormal project but rather as a basis forexperimentation. The circuit describedhas been built up and does give theresponse expected. Try it. The resultsmay be surprising.

WEST

333 QUEEN STREET WEST,

HOURS

10 a.m. to 6 p.m. -Mon. to Fri.

9 a.m. to 4 I, in. Sat.

868 1638

CALCULATOR KEYBOARD

0 9, 4 . K, C,On Off. Multiplexed each

key brought out separatelyto common. Ideal as a loxkeyboard or forlion lock

199

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ALL PRICED TO SELL QUICKLY.

Charge It,

COME AND SEE US71 10 111,1,1Wit

NS MA 1002 Electronic Clock Module 1295The MA1(102 L1.1 1110111 (.1111 k Minion is ,}1.111111,1i amt111,1.1.11 111111i111, VVilii II ,,1111,1, 11,1,)111,

hillIC MOS LSI integrated i.kick ciri.mt, 4 digit LED display, power simply and other associated discretecomponents on a single printed circuit board to form a complete election, cluck movement. The user

need add only a transformer and switches to construct a digital cluck for application in dock radars,alarm or instrument panel clocks. Direct LED drive eliminates RF interference. Tune setting is madeeasy through use of "Fast" and "Slow" scanning controls.

Features include alarm "on" and "PM- indicators. "sleep- arid '"smote" timers arid variable brightness control capability. The modules are extremely compact, the MA1002 measuring 1'375" by 3.05''This small site is achieved by bonding the I.C.to the bark ut the count board.

It is highly recommended that the transformer be obtained with the i hick module IS .3 S111.11,1

dual secondary type nut otherwise readily available.

Cheque, Money OrderOr

C O.D.

0.5"High LED 091"

..4_,VFinik7A'1:-1-'."w-..

1 2 3 rh:.

T r ainu.ToCr rnredrS5.95

EAST

91 QUEEN STREET EAST,

HOURS

10 a.m. to 8 p.m. - Mon. to Fri.9:30 a.m. to 6 p.m. - Sat.

868-1315

COPPER CLAD1 side 51.00 Per square loot

2 side 51.25 Per square foot

SOCKETSStandard Solder Tail

14 Pin S.2516 Pin 30

24 Pin S 4540 Pin 1 00

REGULATORSLM 309K +5V S1.50LM340 T +5, +12,

+15, +24V(Specify) S1.50

LM320 T -5, 5.2,-12, 15,-24V(Specify) 52.00

LM723 +3 30V 51.25

TRANSFORMERS

1 12V 2A . S2.50 4. 13V 1 2A ....S-2 6.3V 1 2A 82VCT 3 4A

22V 3,4A S2.50 or3 13V 1 2A 41V 1 1 i'2A . S3.00

62VCT 1 2A 5. 62VCT 1,2Aor or

31V 1A . S2.50 31V 1A S2.50

CODE OSCILLATOR KITPOWERFUL 1 WATT AUDIO OSCILLATOROF APPROX. 1 kHz, GOOD FOR MANYUSES. GREAT FOR WARNING ALARM,BATTERY CHECKER, VOLTAGE ;`:RICATOR AND CODE OSCILLATOR

S 95

Phone Orders Welcome,Satisfaction Guaranteed or Money Refunded.

Orders Under 51.00add 510.00 postage and handling.

Ontario Residents add 7". sales tax.

OUTPUT

R8470k

O


ProjectionPROJECTION TV started around 40

years ago using the Kerr Cell. Briefly,the Kerr Cell was a device which, withthe passage of current, changed itslight -passing characteristics. Thus, ahigh intensity light source could beused to project an otherwise weakimage onto a large screen. This offeredhopes for the then fledgling pre-war TVindustry to get around the problem ofnecessarily small pictures from thesmall picture tubes then available -some as small as 6 inches. However,war breaking out in 1939 stopped all TVwork and the miniscule production ofcathode-ray tubes was diverted to warto fill the voracious appetite of radar.

The Kerr Cell never did make it andwas forgotten, never to return. But themass production of Cathode-ray tubelearned in war, launched TV as we knowit today. It's remained essentially thesame since, with the only real changecoming with colour. Not until HenryKloss's projection TV emerged in apractical form, has any real changeoccurred. Doubtless the Ediphorsystem comes to mind, - the one we'reall familiar with from its wide use inprojection of boxing fights in largeauditoriums. But its price tag runs into$130,000 and therefore is only oflimited appeal. GE has a system for

By Jim Essex

classrooms and small auditoriums,but, again, the cost is too high, -around $39,000. Henry Kloss dec idedhe'd do better, using material readilyavailable from regular TV sets.

No, it's not done with mirrors (as inthe early TV's) which used a mirror -backed lid which, when raised,reflected the image to the viewer.Methods to enlarge this image werevirtually exhausted when the industrysaved the day producing first the 17 -inch pix tube, followed by the 21 inchwhich remained the standard of thetrade for many years. In most of us,there was always that gnawing thoughtof - "why couldn't the best of the °Edbe wed to the new to produce auseable, practical image brightenough to fill a screen similar to thoseused for home movies?" Well, itremained for Henry Kloss to do this.

Perhaps a word about him might bein order, here. He was an MIT drop -out,who, to fill his craving for develop-mental research, turned to audio. TVwasn't his cake, watching it only a fewhours a week, - more out of curiosity,the screen being far too small to excitehis interest. He developed a loud-speaker when sound demandedsomething better than was currentlyavailable for the new breed of long-

playing records now appearing in theearly 50s.

In the best traditions of people wholike to work on electronics in theirbasements, spare room or what -have -you, he put together what he thoughtthe industry lacked in an audiospeaker, sold it and AR (AcousticalResearch) was formed to produce it.He was in business. It was only a matterof time before the inevitable happened;if you could do it for sound, why notTV? Now president of a high qualityaudio products firm making, alongwith the speaker, - steareo cassettedecks - among other things, thequestion of TV and why it couldn't bemade more enjoyable, returned.

GREAT OAKSAbout eight years ago he began like

most experimenters, - from thebottom. He bought a TV kit, built it fromscratch, then convinced himself it wastechnically possible to produce animage 10 times the size and still have"an interesting brightness" as NewYorker magazine put it. Down the'street were other interesting peopledoing other interesting things withpictures. Like Edwin Land who hit it bigwith the Polaroid Land Camera. The"Brain Mafia" - as most of his age


group and usually MIT grads werecalled, - were hitting their stride!

His claim of having never inventedanything, - "I just put . . . togetherseemingly unrelated ideas in intel-ligible packages and make them work,"as Mark Jacobson put it describingKloss in his story, may be over-simplifying it. But when you realize it isan ordinary TV chassis that powers hisrevolutionary system, you may just sayto yourself, - "why didn't I think ofthat?" Of course, he put his moneywhere his mouth was, - which may bethe only real difference, like two milliondollars!

Within a half -dozen years, he had themodel 1000-A ready. Now, they areseen throughout the U.S. - andrecently in Canada.

FIRST SIGHTI first saw one at Arnie's Restaurant,

- a medium sized, rather dimly -litdining house located near theUniversity of Waterloo, an ideal placefor students to judge its merits. At onetime in my career, I had worked at theUniversity, and my scientific curiositywas somehow re -kindled at this hugescreen - at the moment, showing the 6pm news. From where I sat, I couldclearly see three lenses, brightlyflooded with light in the now familiarred, green, blue triad simulating the 3guns of a colour pix tube. But, I

reasoned, you can't achieve an imagethat big (it looked almost 7 ft.) by justmagnifying an image of a CRT, even ifthey'd provided three separate CRT'sto accomodate the three primarycolours. No. And as I learned later,there's certainly more to it than that,although I understand Sony, forexample, do just that; magnify a highintensity image - but from only oneCRT, - and project it on a somewhatsmaller screen. It is not too bright, andhas obvious limitations. How did Henrydo it?

The manager of Communicationsfor the Advent Corporation and who Isubsequently came to know, - Mr.Joseph B. Hull, Jr., - described HenryKloss's system and the company Klossheads, now not only making high -quality audio products, but projectionTV as well.

The heart of the system, heexplained, is the patented "LightguideProjection Tube" and the Schmidtoptical system, a lens originallydesigned for wide -angled telescopesfor observatories. But first, considerthe Lightguide tube, designed andmanufactured by Advent, called theAdvent "VideoBeam" Tube. You recallhow the three guns in a colour tuberespond . . . individually, to the three

colour signals transmitted. There'sone red, one blue and a green gun.When properly combined on a

corresponding "triad" pattern on theCRT's face (after passing the hurdle ofa shadow mask, incidentally, andthereby reducing the brilliance on thetube's face) we achieve white and anycolour in the spectrum between thatand black. Or, in other words, a fullrange of visible colour can bereproduced.

Two limitations are evident; - thediscrete three -dot arrangement toproduce one tiny segment of picturewith the obvious inherent fuzzinesswhich results, and the tremendousangle (90 degrees at maximum) thebeams must sweep to fill a raster. Thisis not to mention the near -impossibletask of making each beam fall on itsown corresponding dot on the tubeface after "ramming through" theshadow mask, - all of which has adeteriorating effect on the ultimatebrilliance and clarity which can beachieved. In the video beam tube - ofwhich there are three, remember, notthree separate guns within one tube asin conventional Color TV - only oneelectron gun is present. The electrongun's output is made to sweep backand forth across a 3 inch phosphor.properly coated to provide one of thethree required guns or tubes needed toform the triad. Since this light -emitting"target" need provide only one colour,it can be uniformly coated with thesingle desired colour phosphor:4C(refer to fig. 1) The efficiency thusobtained leads to a linearity (un-iformity) across the screen notpossible with the clusters of "colour

The business end of the Advent Consoleshowing the three lens system. each lensbeing fed by its own CRT.

dots" characteristic of present colourtubes. Brightness uniformity is alsoenhanced by the beam having tosweep over a mere 15 degrees insteadof the 90 degrees in conventionalCRT's. You may now ask how thispicture on the relatively small screen -actually about 21/2" wide, - is gatheredand focused onto a large, externalscreen almost 6 ft. across?

THEY DO IT WITHReferring back to fig. 1, the light

given off the small screen - or target- is directed towards the rear of the

PHOSPHOR COATED /NT E IINAI SCREENLIED BLUE OR GREEN'

ADVENT LIGHT GUIDE PROJECTION TIME c 1914 ADVENT CORPORATION

Fig. 1. The basic Advent Light guide projection !ube and connector lens. A single tube isused for each of the three basic colours.


tube where it strikes a highly polishedmirror located at the end. There it isreflected outward along the axis of thetube where it is gathered by the lens.The mirror focuses the light from eachpoint on the target to the corres-ponding area of the big screen acrossthe room.

Thus, the colour dots or lattices ofconventional TV's are not required, noris the shadow mask - making forhigher efficiency than is possible in adirect -view pix tube. This is the "key"to getting bright projection results.And of course, the optics being"inside" the tube, there's no way they'llcome out of adjustment. Before, ontheatre projection systems, a trainedtechnician was needed to do the job.All critical optical adjustments are thusmade at time of manufacture, andvulnerable optics are out of the way ofdust or damage. The front of thecorrector lens only is exposed and thiscan be dusted occasionally, of course.

Voltages and control circuitfunctions are identical with con-ventional TV's, but instead of drivingthree guns within one tube envelope,the TV circuitry is used to driveindividual guns in three separate, high -intensity small -screen tubes which areextremely bright. In addition, coupledwith this system, is a special screen -designed to reflect the maximum lightand detail from a surface made ofhighly reflective aluminum with a rigidfoam backing. Manufactured underlicense from Kodak, it is five timesmore reflective than a regularlenticular or beaded screen as used inmost home movies. Besides this, it isspecially curved in both the horizontaland vertical to exactly match the sweepof the light travelling in a huge arc fromthe "TV set" 7 feet away.

This, of course, produces "critical"viewing areas - or seating, wherein

The Videoheam receiver -projector in use. An idea of the size of the screen can be gainedfrom the viewers.

optimum viewing is enjoyed -although this is quite large and reallyoffers no restriction. (see diagrams 2and 3 for seating detail and screendimmensions). The screen surface isunderstandably somewhat delicate, toprevent smudge marks from fingerswhen handled, for example.

SET-UPWhen the "Videobeam" TV is set up,

the three tubes form a Triad, - greenon right, red on left, blue at bottom -viewed from rear. Now, if a "dot" oflight from each was aimed on thescreen, properly converged so the lightfrom each over -lapped the other, you'dget a clear, sharp corresponding

THE VIDEOBEAM RECEIVER -PROJECTOR

WHITE "dot" on the reflective screen.When swept, you obtain a raster about3 times the size of a regular 26" TV tube- or approximately 85" corner tocorner.

The screen's distance from the"control'box" type TV is critical -about the only thing that is - and astring cord is provided so this exactdistance can be checked at any time -especially after moving furniture whenthe Advent cabinet just might getpushed inadvertantly out of place byan over -enthusiastic housewife. Withinthe set itself, a cross -hatch pattern isavailable at the push of a switch so thatcorrect convergence is alwaysassured. Minute adjustments can be


Projection TV

0 PRIME

18. TO 20'

ACCEPTABLE UNACCEPTABLE

HORIZONTAL VIEWING AREA

NOTE. THE QUALITY OF THE PICTURE IN THE AREALABELLED ACCEPTABLE HAS LOWER BRIGHTNESSAND LESS COLOR INTENSITY, BUT NEVERTHELESSREMAINS ENJOYABLE TO VIEW.

FIG

Fig. 2 (a) and (b) Showing the vertical and horizontal viewingarea.

made by anyone at any time, althoughonce set, there should be no need tochange them.

LIGHT BEAMSIt is this "physical distance" which

achieves what's accomplished withinthe smaller dimmensions of a regularCRT (and which contributes to the archaving to be only 15 degrees within aVideobeam tube as compared with theconventional color TV tube's 90degrees). Thus, light beams replaceelectron beams once leaving theSchmidt optics and a whole newmethod of re -structuring light is nowpossible. And, of course, the resultsare nothing short of breath -taking.Perhaps the best definition of this isHenry Kloss's exclamation whendemonstrating the system and acommercial appeared. "Look", saidKloss. "Look, there's a fly in thatcommercial. A fly flying around one ofthe babies. You'd never see that on aconventional set."

The process has been proven byhaving the first 100 manufactured sold

VERTICAL VIEWING AREA

FIG 3 TYE VIDEOBEAM SCREEN

close to the plant in Cambridge,Massachusetts. This way, closemonitoring could be done and minorflaws corrected. Now, they are nation-wide and making over 100 Model1000A's per week*. Conventional typeTV circuitry can be used to power thethree tubes, which operate direct fromthe chroma output normally used todrive the red, green and blue guns. Thevoltage requirements for the threetubes are paralleled with the HT beingactually about 28kV. All otheradjustments are the same, like vertical,horizontal, focus, etc and the completeunit operates on 110V, 60 Hz,consuming about 160 watts. Thecomplete unit (including screen) sellsfor $3,995.00 FOB Cambridge for themodel 1000A with the Schmidt Lenssystem. A less expensive model - themodel 750 using a refractive lenssystem - sells for something less. I

asked Joe Hull the difference betweenthe two and he said it was in themethod of light -gathering that diff-erentiates the one from the other. "TheSchmidt system has a very wideaperature - f0.7 to be specific. Thismeans that about 35% of the light

DIMENSIONS ARE APPROXIMATE

emitted by the phosphors survives theprojection process, which, if you arefamiliar with optics, you will recognizeas being remarkably efficient. Therefractive system is not as "fast", withan aperature of f1.3, or about half theefficiency of the 1000A's Schmidtsystem. However, be sure not tomisinterpret that factor of about 2; theeye can barely recognize a 50%difference in brightness . . . ." In otherwords, the difference in picturebrightness is comparable to an audiolevel difference of 3 db, which is barelydiscernible. The refractive system isless expensive than the Schmidt, andthis may be an indication of things tocome; the same - or nearly the sameresult - at lower cost. Certainly, whenHenry Kloss started out, he envisageda relatively low-cost home entertain-ment medium that'd be readilyavailable to most everyone.

*The Electrohome Company inKitchener, Ontario, are manufacturingthe Model 750 under special licencefrom Advent Corporation, marketing itunder the name "ELECTROHOME-ADVENT".


-ETI DATA SHEEMK 50361-50362 ALARM CLOCK MOSTEK

THESE ARE MOS CIRCUITS, using deple-tion -load ion implantation process. Bothchips work in 12 or 24 hr mode and willdrive displays directly. Features included are10mA/segment LED drive; low voltagebackup (9v); forward or reverse timesetting; intensity control; non-MPX display;24hr alarm in three modes - tone, radio ortone plus radio; variable 'snooze' (1-59mins); count hold; summer/winter timeswitch; clear on switch on; leading zerosuppression in 12hr mode. ON 50362ONLY. Four Year Calendar; choice of datedisplay format; second alarm time.

The snooze inhibits an activated alarm for10min periods. The 'sleep' will activate theradio for between 1-59 mins (adjustable).

POWER FAILUREAt the occurrence of power failure, the

digits will flash at 1 Hz to indicate incorrecttime displayed. Set 2 (forward) switch shouldbe closed (once power is restored). Thismode is triggered when the colon outputgoes to Vss and may occur at initialpower -on.

DISPLAY MODEThe input is three state. Operation is as

follows

Display InputVssOpenVDD

ModeAlarm time displayedTime displayedSeconds displayed

When in alarm mode, the time displayedis that to which the alarm is set. It may bealtered by use of the time set procedure,given below.

SETTINGThe setting mode allows either a forward

setting or reverse setting of the display. Thesetting inputs are

Set 1 orSet 2 Input Mode

Vss Forward SetOpenVDD Reverse Set

When either the set 1 input or set 2 input isconnected to Vss the display will increment.Connecting the input to VDD will decrementthe display. When the display is not beingset, the inputs should be left open. The set 1input changes the hours digits at two countsper second. The set 2 input changes theminute digits at two counts per second.Carrys or borrows are not allowed duringtime setting.

DISPLAY FORMATThe display format is used to select a 12

hour display, 24 hour display or to blank thedisplay. The connections are.

Display Format Input Mode12 HourBlank Display24 Hour

VssOpenV00

In the 12 hour mode, the hours digits willdisplay time in 12 hour format with a PMoutput. When the input is connected to VDD,the format will be 24 hour time. In the blankmode the segment outputs will float,allowing wire -or conditions.

24

COLONIn normal operation, the colon flashes at

one Hertz rate for an activity indicator. Thecolon output conducts to Vss with a 50%duty cycle in the 60Hz mode and 40% dutycycle in the 50Hz mode. The colon is offwhen displaying calendar, seconds or sleeptime.

V..

SG 3

TH 3/PM

TH

TH 2

COLON

SNOOZE/SLEEP

SET I

SET 2

TIME SELECT

50/6C HE

DISPLAY FORMAT

TIME BASE SELECT

NC

DISPLAY MODE

WAKE SELECT

ALARM ENABLE

voo

TONE SILT

RADIO OUT

V"SG 3

TH3, PM

TH

TN 2

COLON

SNOOZE/SLEEP

SET

SET 2

TIME SELECT

50/60 Hz

DISPLAY FORMAT

TIME BASE SELECT

AUXILIARY

DISPLAY MODE

WAKE SELECT

ALARM ENABLE

V00

TONE OUT

RADIO OUT

MK 50361 N

MK 50362 N

SF 3

SE 3

SD 3

SC 3

INTENSITY

SB 3

SA 3

SG 2

SF 2

SE 2

SC 2

SB 2

SAD2

SG

SF

SE

SD

SC

SO

SA

SF 3

SE 3

SD 3

SC 3

INTENSITY

SB 3

5A 3

SG 2

Sr 2

SE 2

SC 2

58 2

SAD2

SG

SF

SE

SD

SC

513

SA

INTENSITYThe intensity input regulates the current of

the segment outputs and colon output.The intensity input regulates the current of

the segment outputs and colon output. Overa range from 3K0 to 30K0 for theintensity resistor (RSENSE), the followingequation may be used to predict segmentcurrent (IsEG);

I

VFWD LED On volts)mAsEG

RSENSE (in Kohms)

Segment current is relatively independent ofthe voltage on the segment pins, thereforethe LED display voltage supply need not bewell filtered. For minimum value of RSENSE(intensity control resistor), care should betaken to insure total circuit power dissipationdoes not exceed safe operating limits.

AM/PM OUTPUTWhen in the 12 hour operating mode, the

TH3/PM output conducts to Vss whenactive. The indicator will change states whenthe hours change from 11 to 12. When inthe 24 hour mode this output drivessegments A, D & G on the most significantdigit. Consideration must be given to wiringthe display to accommodate both 12 hourand 24 hour operation using the samedisplay.

TIME SELECT (Daylight saving time)Connection of the time select pin to Vss

will advance the time by one hour. Byopening the connection, the time will returnto the original time. Connecting this input toVDD will reset the clock to the Power Upmode.

ALARM ENABLE/WAKE SELECTThe alarm can operate in three modes

according to the voltage on the wake selectpin. The states are defined as

Wake InputVssOpenVDD

ModeToneRadioRadio followedby Tone

The Alarm enable pin enables alarm 1 whenconnected to Vss. If it is left open it willdisable the alarm due to an internal resistor.When the alarm occurs it may be disabledand immediately re -enabled and will activate24 hours later at the alarm time. The alarmwill self -disable after one hour of operation.The output tone will be in the range of 200 to1000Hz and conducts to Vss 8.3% of thetime at a 1Hz rate.

Radio out, when activated by either thealarm or sleep function, will conduct to Vss.

When the radio followed by tone mode isselected, radio out conducts to Vss at alarmtime. Eight minutes later the tone output willbe enabled. Both remain on until inhibited bythe alarm enable control, snooze, or theautomatic alarm reset which occurs after onehour.

SNOOZE/SLEEP INPUTThe snooze and sleep inputs use a single

pin to select snooze or sleep. The connec-tions are

Snooze/ Sleep ModeVss SnoozeOpen No ChangeVDD Sleep

The Snooze feature will temporarily turn offan activated radio and tone outputs to allowan additional 10 minutes' sleep. Momentar-ily connecting snooze to Vss will activate thesnooze. If left open an internal pull -downresistor will maintain the snooze featureinoperative.

Connection of the pin to VDD will displaythe sleep time in minutes in the minutesdigits. The time will start at 10 minutes, andthe set 2 input is used to set the sleep time.Radio out will conduct to Vss for the amountof time set. After the time decrements to zeroradio out will turn off, provided that theSnooze/Sleep input is not being held at VDD.

If the snooze is active, the sleep input willreset the snooze function. The snooze inputwill reset an active sleep time.


GENERALIZED CIRCUIT 112 HR. DISPLAY FORMAT)

SET FORWARD

VT43

04 It

MIR 40.44033

"4T REvERSE

A IKn

440024

MIL

ET

SE

;NOOZE /SLEEP

ENABLE

WAKE SELECT

".^ ,DISPLAYSRLAY FORMAT

12 rouP-mws,

30,

SUIENER T

RESET

R.

CURRENT 7413031CONOS.

RATE.Miff ZONA

30/60N, INPUT

0 BASE SELECT13

EC

0

DISPLAY MODE

5

/PM

T02

SG3

SE 3 40

SE 3 39

SD 3 38

SC3 3T

SB 3 35

5A3 34

COLON 6

552 3

5I2 32

5E2

5C2 30

502 29

SA 2/502 28

MK 5036INMK50362N

AUXILIARY INPUT150362 ONCE

561 27

5E1 26

SE1 25

SDI 24

ss SC1 2

18V,Sal 22

0 SOMONT INTONE OUT

ALARM

5, 21

INTENSITYRADIO OUT 3

L _ J

EN.

D

L

E

t

RADIO

0NT ENSJ

DISPLAY FONT

RECOMMENDED OPERATING CONDITIONS

PARAMETER

10 'C

Min

to 45'Cl

Max Units

Operating Voltage, VDD -12 -16 Volts

Standby Voltage. VDD -8.0 -12 Volts

Input Logic Levels:Set 1, Set 2, Display Mode,Snooze/Sleep, 50/601 -Ix, DisplayFormat, Alarm Enable, WakeSelect, Time Select, Time BaseSelect, Auxiliary VSS -1.0

VDD

VSS

VDD + 1.0

Volts

Volts

Intensity Control 3 30 K-OHMS

Segments, Colon -26 Volts

SELECTABLE 12 HR. OR24 HR. DISPLAY

TH I

DAY/MONTH

TH 2

12 HR

24HR

PM INDICATOR

VL ED

TH 3

I n 'I r rwL4 I L4 Om

FUNCTION SETTING

The displayed function is set using the setinputs while the appropriate function isdisplayed using the display mode input andauxiliary input. The set 1 input changes thehours or month digits at two counts persecond. The set 2 input changes the minuteor date digits. at two counts per second.Carrys or borrows are not allowed duringsetting except for an illegal month datecombination.

The MK 50362N contains an auxiliaryinput which allows the selection of additionalfeatures. All other functions operate like theMK 50361N.

The additional features are selected byusing the Display Mode Input and theAuxiliary Input. The selection is

FunctionAlarm 1 SetCurrent TimeSecondsMonth DateDate MonthAlarm 2 SetTime Zone

DisplayModeInputVssOpenVDDOpenOpenVssVDD

AuxiliaryInput

OpenOpenOpenVssVD0VssVDD

MONTH -DATE CALENDARThe calendar is a four year calendar.

Connecting the Auxiliary input to Vss willdisplay a Month -Date format. A Date -Monthformat can be selected by connecting theAuxiliary input to VDD. The display modeinput must remain open.

SECOND ALARM TIME .

The second alarm time can be displayedby connecting the Display Mode input andthe auxiliary input to Vss. To enable thealarm, the Alarm Enable pin should beconnected to VDD. Alarm 2 will not have anautomatic shutoff. Disabling either alarm willreset snooze.


HD 0165 KEYBOARD ENCODER HARRIS

The HD -0615 Keyboard Encoder is a 16 line to four -bit parallel encoder intended for use with manual data entry devices such ascalculator or typewriter keyboards. In addition to the encoding function, there isa Strobe output and a Key Rollover output which energiseswhenever two or more inputs are energised simultaneously. Any four -bit code can be implemented by proper wiring of the input lines.Inputs are normally wired through the key switches to the +5.0V power supply. Full typewriter encoding up to eight bits can beaccomplished with two Encoder circuits by the use of double pole key switches or single pole switches with two isolation diodes per key.Outputs will interface with all popular DTL and TTL logic families. The circuit is packaged in a hermetic 24 -pin dual in -line package andoperates over the temperature range of 0' C to + 75'C.

TRUTH TABLE

I 2 3 4 5 6 1

INPUTS

9 10 11 12 13 le IS 16

OU

I 2 3

PUTS

5 nlLILLLIITILLILLLIIILILLLLHILLILEL 11 I LLILLLMILlit. I I. 14 I.ILLILLIIILLILLIILLLILLLIT I. I. I. I.LLTILLECILLILLILLLILLLLILILLlit-LILLLILLILLANY MOOR MORE HIGH

L L L I L L L I.ILLILILLIIHNILLILLILLIIIIILLILLILHINLLLLLLLLLLLILLILLITHMLILLILLILLILLILLILMILLCILLELLCILRILLILIIIIIIIII 71 I. I. IILLIMMLINTILLIflI I L H I I L IILLLMILIMMLL L I. I. L II I. II L I L I I H LILLLTILI4

H NH

II I.

I II

C C M

I 11 I14 LLl LCX X X

5.0 V

PARALLEL2 I BINARY

OUTPUTS

AUXILIARYOUTPUTS

Figure 1. GENERAL CONFIGURATION =ORENCODING TWO TO SIXTEEN KEYS

ELECTRICAL CHARACTERISTICS

PARAMETER SUM__LIMIS_

MIN TYP MAXUNITS TEST CONDITIONS

Input Current "I'1,,, 17 mA V11.46.0V

IFOutput %o.n.o.

"1'TV0H

V01

.24

0.2

.4.0

AA.04 V

VIII''RiV 101.'")"vin3.50 10,4 3.2711A

v,L = OPenCircult.1017.-241)../1

06.14119 'CC

Power Supply Current

N.Fl^m. 'Um

52

88

mA

mA

Onelnputat5.25V

AllInpuism525V

AC Skew TimalNotell 11.00 60 200 nu

TC474'29CVcc4VII.5.0VCL<SOFF

OTL OR OPENCOLLECTOR

GATE

DUAL MONOSTABLE[1602 OR EQUIVALENTJ

2 tiF

5.0V

a

IO

Figure 2. SWITCH BOUNCE ELIMINATION

51

+5 OV SUPPLY DOUBLE POLEKEY SWITCHES

INPUTS OUTPUTS

HO 0165

M S B

STROBE

HD 0165

KR3

LSB

STROBE

NRO

1,1

OUTPUTS

OPEN CO) LECTORGATE

TO CIRCUITOF FIGURE 2

Figure 3. ENCODING UP TO 256 KEYS


TTL 7400N5974008 .19 SN74126t4 .46SN7401N .19 58741288 .55SN7402N .19 SN74132N .89SN7403N .19 SN74136N .48SN7404N .23 007414114 1.09SN7405N .23 SN74142N 2.5009740614 .49 0874143N 2.60SN7407N .49 SN74144N 2.605974080 .22 SN741459 .89SN74090 .22 09741478 2.50SN7410N .19 SN74148N 1.49SN7411N .29 514741509 1.50SN7412N .19 58741518 .98SN7413N .45 SN74152N 4.50SN74140 1.25 SN74153N .89SN7416N .39 SN7415414 1.50SN7417N .39 SN7415511 .98SN74209 .19 SN74156N .690074210 .29 SN74157N .69SN7422N .19 SN74159N 2.25SN7423N .29 SN74160N .99SN7425N .29 SN741618 .99SN7426N .32 59741620 .99SN7427N .30 514741638 .99SN7428N .30 SN74164N 1.10SA24300 .19 SN74165N 1.10SN74320 .29 SN74166N 1.35097433N .30 SN741679 2.98SN7437N .36 SN741709 2.60007438N .36 09741728 6.98SN7440N .19 SN74173N 1.55SN7442N .59 SN74174N 1.15SN7443N 1.29 SN74175N .99SN744414 1.30 59741769 .8551474450 .99 SN74177N .85SN7446AN .99 SN741788 1.25SN7447AN .89 SN741799 1.25SN74480 .95 SN74180N .99SN7450N .19 SN741819 2.75SN74510 .19 SN74182N .79SN74530 .19 097418414 1.95SN74548 .19 SN74185A 1.85S974600087470N

.19

.34SN74186NSN741900

9.951.33

SN7472N .27 SN74191N 1.33SN7473NSN74748SN7475NSN747661

.33

.33

.47

.36

097419214SN74193NSN74194N0074195N

1.101.10.99.59

SN7480N0147481AN

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SN74196NSN74197N

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SU7495AN :69 SN74273N 1.74

097496N .04 SN74276N .89

SN7497N 2.85 SN74278N 1.99

SN741008SN741040

1.9560

SN74279N09742839

.59

.99

087410514 SN74284N 4.00

SN74107N .33 SN742850 4.00

$8741090 .48 SN74290N .69

SN74110N .35 SN74293N .69

SN741119 .49 SN7429819 1.49

SN741169 1.99 SN74351N 1.79

SN741188 1.50 SN74365N .59

01474119N 2.50 SN74366N .59

SN74120N 1.19 SN74367N .59

0104121N .39 SN743689 .59

SN74122N .44 SN74390N 1.24

09741239 .69 59743939 1.24

SN74125N .46 0874490N 1.59

TTL LOW POWER SCHOTTKY0974 LSOONW41.0011.4SN74LSO2NSN74LS0319507410 049SN74LSO5NSN74LSO8NSN74LSO9N0974LS1ONSN74LS11NSN74 1.012808741-S13N09741.014NSN74 1.015N09741.020N09741.02IN597410229SN74LS26NSN741.0278SN74LS28NSN74 1.030NSN74LS 32NSN74LS 33NSN74 LS 379014741538NSN74LS4ONSN74 L0420SN74LS47ASN74LS48NSN74LS49NSN74LS51NSN74LS 54NSN741.555N00741.063NSN74 LS738SN74LS i414SN74LS75NSN74LS7614SN741.078N

.25

.25

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.25

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.29

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.25

.25

.25

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.35

.35

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1.49.39.44.64.39.39

SN74LS83AN 1.29SN741.0058SN74 LS 86NSN74 LS901SN74LS91NSN74 LS 92N

1.35.49.74.99.74

SN74LS93BN .74SN74L595AN 1.501074109580 1.3508741.39614 1.49SN74L5107N .44SN74LS 1 09N .44SN74LS112N .44SN74LS113N .44SN74LS114N .44SN74LS122N .69SN74LS123N .84

SN74LS124N 1.50SN74L0125N .64

SN74LS126N .64

SN74LS132N 1.10SN74LS133N .29

.49SN74LS138N 1.100874LS1390 1.10SN74LS145N 1.05SN74LS151N 1.05SN74LS153N 1.05

SN74LS155N 1.350874151560 1.350,04LS157N 1.05SN74LS158N .99SN74LS 160N 1.50SN74LS161N 1.50SN74LS162N 1.500874LS1638 1.50SN74LS164N 1.50SN74L016514 1.75SN74LS166N 1.75SN74LS16861 1.75SN74LS169N 1.75SN74LSI7ON 2.95SN74LS174N 1.10SN74LS175N 1.10SN74LS181N 3.25014741519014 1.59SN74LS19114 1.5908741S1920 1.59SN74LS193N 1.59SN741S194AN 1.25SN741.0195AN 1.25SN74LS196N 1.35SN74LS197N 1.35SN74LS221N 1.29SN74LS240N 1.95SN74LS241N 1.95SN74 LS 242N 1.90SN74LS243N 1.90SN74102449SN74LS247NSN74LS248NSN74LS249NSN74 LS2510SN74 LS 25380974 LS 2578SN74LS 258N044741.0259NS9741.026095074102618SN74 LS 266NSN74LS273NSN74 LS2798SN74LS280NSN74LS283N08741.529014SN74LS293NSN74LS295ANSN74LS298NSN74 IS 324NSN74L0325N0074 LS 326NSN74 LS 327N0N/741.0352NSN74 LS 3538SN74 LS 365NSN74LS366NSN74 LS 3678SN74LS3680SN74 IS 375N0874LS37705974103780010410386NSN741.039390974LS395NSN74L0670N

1.951.151.151..15

1.251.251.251.251.59.29

2.25.49

1.80.64

1.951.251.051.051.551.55.99

2.752.802.701.201.35.64.64.64.64.641.801.35.49

2.251.553.25

LED'SMorkIL1

1L5

102IL74

PL2

991.00

.60

.70

.27.

Temp IriOnta

TIL111 .80

TIL112 .80

TIL113 1.20

111114 1.10

TIL116 1.05

11017 1.20

TIL119 .90

TIL138 2.25

TIL139 2.25

TIL209A A7TIL211 .42

11L220 .18

TIL221 .21

TIL222 .36

TIL302 3.95

TI L303 3.95

TIL304 4.50

TIL305 4.50

TIL306 7.95

111_307 7.95

TI L308 7.95

TIL309 7.95

TIL311 8.95TIL312 1.60

11L313 1.60

11L31 1.45

T1L32 .85

TIL66 .95

11L78 .55

TIL81 1.15

LS800 1.85

Fairchild

FCD802 .59

FCD806 .59

FCD810 .68

FCD820A .75FLV117 .18

MV5054-1 .21

FM:4357 1.45

FND500 1.50

Fh113507 1.50

Fh4D807 2.95

FNS700 .70

CD4000BECD4001BECD4002BECD4006BECD4007BEC DO 008BE

CD4009BECD4010BECD4011BECD4012BECD4013BECD4014BECD4015BECD4016BECD4017BECD4018BECD4019BECD4020BECD4021BCCD4022BECD4023BECD4024BECD4025BECD4026BECD4027BECD4028BECD4029BECD4030BECD4033BECD4034BECD4035BECD4040BECD4041BECD4042BECD4043BECD4044BECD4046BECD4049BECD4050BECD4051BE704052BECD4053BECD4060BECD4066BECD4068BECD4069BECD4070BECD4071BECD4072BE

C / MOS LINEARS.15.19.191.19.19.99.49.49.19.19.47.79.89.47.89.89.491.15.79.99.19.89.19

1.75.44.85.99.491.752.501.151.15.84.84.79.79

1.55.47.47.89.89.891.35.74

.29

.29

.39.29.29

CD4073BEC84075BECD40768ECD4077BECD4078BEC04081BEC04082BECD4085BECD4086BECD4301BECD4502BECD4507BECD451 OBECD4511BECD4512BEcD4514BECD4515BECD4516 BECD4517BECD4518BECD4519BECD45208ECD4522BECD4526BECD4527BECD452813ECD4531BECD453913ECD4543BECD4555BECD4556BECD4581BECD4582BECD4585BE40014PC40085PC4C097 PC40099PC40160PC40161PC40162PC40163PC40174PC40175PC40192PC40193PC40194PC40195PC

I.29 Lmaol AH .45

.19 LM101AN-8 (mini dip) .39

1.50 LM3O4H h .95

.29 LM105H .95

.29 LN1307H .40

.29 LM107h1-8 (mini dip) .39

.29LM308H .99

.69

.69 L6430191t1 .99

.65 LM309K 1.79

1.25 LM311H .99

.60 LM318H t501.35 LM323K 6.951.45

1M324N .99.95

2.50 LM339N .99

2. 50 Lhol555N-8 .49

.95 LM556N-14 .89

4.00 LM70904-14 .29

1.05 001711CH 60

.69 LM723CH .551.19

L M 723iChl- 14 491.301.30 L M7331C Isl- 14 1.10

1.75 LM739N-14 1.25

1.15 LM740CH 9.951.20 LM741CH .45.99 LM741Ch1-8 (mini dip) .34

1.95 LM741CN-14 .35.69

L M747Chl- 14 .55.69

LM748CN-8 (mini dip) .383.251.25 LM748CH .39

1.49 LM776CH 3.75

.79 LM1437N-14 .49

1.10 LM 1458H .79

.89 LM1458N-8 (mini dip) .59

.89 L M 1488D 1.501.351.35 L M 1489D 1.50

1.35 L M3046N- 14 .58

1.35 LM3302N-14 .79

1.25 LM4136N-14 1.451.251.351.351.251.25

We offer the largest variety of current

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LINEAR VOLTAGE REGULATORSTL497CN 2.50 Switching Voltage Regulator 500 mA

Adjustable Output78H05KC 7.95 5 Amp 5 Volt Positive Regulator T037800 Series 1.79 Positive Voltage Regulator 1 AmpTO -3 /LM340K 5, 6. 8. 12. 15. 18, 24 Volts7800 Series 1.35 Positive Voltage Regulators (Plastic) 1 AmpTO -220434340T 5, 6. 8, 12, 15, 18. 24 Volts78M00 Series 1.59 Positive Voltage Regulator 9, AmpTO -5 /1..M340H 5, 6, 8, 12, 15, 18, 24 Volts781_00 AWC .49 Positive Voltage Regulator 100 MASeries TO -92 2.6, 5, 6.2. 8.2. 12. 15 Volts7900 Series 2.50 Negative Voltage Regulator 1 ampTO -3 /LM320K 5. 6. 8. 12, 15. 18. 24 Volts7900 Series TO- 1.59 Negative Voltage Regulator 1 amp220/1.M320T 5, 6, 8, 12. 15. 18, 24 Volts79M00 Series 1.59 Negative Voltage Regulator ampTO -5/11.4320H 5, 6, 8, 12. 15, 20. 24 Volts78M0T2C 1.35 Dual In Line Adjustable 4 Terminal Positive

Voltage Regulator79MOT2C 1.35 Dual In Line Adjustable 4 Terminal Negative

Voltage Regulator78GU1 TO -220 1.60 1 Amp Adjustable Positive Voltage Regulator79GU1 TO -220 1.50 I Amp Adjustable Negative Voltage Regulator78GKC TO -3 2.00 1 Amp Adjustable Positive Voltage Regulator79GKC TO -3 2.50 1 Amp Adjustable Negative Voltage Regulator

MOS AND BI -POLAR MEMORIESC1702A (1 Microsecond)

256 x 8 EPROM 11.65

C1702A (1.5 Microsecond)256 x 8 EPROM 7.75

C2708 1K x 8 EPROM (450 NS) 63.008080A 8 Bit MOS Cpu (2 Microseconds) 19.452102-1P 1K Static Ram 1024 x 1 (450 NS) 3.253342PC Ouad 64 Bit Static Shift Register 5.853347PC Quad 80 Bit Static Shift Register 5.85

3341APC 4 x64 MOS Filo 1 Mhz ShiftRegister 5.85

TMS0117NC Decimal Arithmetic Processor 13.00

LCM1001 Microprocessor Learning Module 180.00TMS4024NC 64 x 9 Fifo 8.95TMS4050NL 4K Dynamic Ram Plastic 300NS 9.25

118 Pin)TMS4060NL 4K Dynamic Ram Plastic 30014S 925

(22 Pin)AY5-1013P 8 Bit Uart 6.95Semi4804A 4K Static Ram 1024 x 4 (450 NS)

Single 5V Supply 19.4593415PC 1K Ram 4ONS Open Collector 14.3093425PC 1K Ram 40 NS Tri-State 14.30AM2901DC 4 Bit Bi-Polar Microprocessor

Slice 40.95AM2902PC Carry Look Ahead Circuit 4.15AM2905PC Quad 2 Input Bus Transceiver 10.55AM2907PC Quad Bus Transceiver with Tri-

State Receiver and Parity 9.10AM2909PC 4 Bit Cascadable Microprogram

Sequencer 9.30AM2918PC Quad Deregister with Standard

and Tri-State Outputs 5.65F8 Kit 8 Bit Microprocessor Evaluation

Kit With Software 225.00

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MR. rlIESTOITS

741 COORBOOR

OPERATIONAL AMPLIFIERS (OP -AMPS) CAN besimply described as high -gain direct -coupled voltageamplifier 'blocks' that have a single output terminal buthave both inverting and non -inverting input terminals.Op -amps can readily be used as inverting, non -invert-ing, and differential amplifiers in both a.c. and d.c.applications, and can easily be made to act asoscillators, tone filters, and level switches, etc.

Op -amps are readily available in integrated circuitform, and as such act as one of the most versatilebuilding blocks available in electronics today. One ofthe most popular op -amps presently available is thedevice that is universally known as the "741" op -ampIn this article we shall describe the basic features of thisdevice, and show a wide variety of practical circuits inwhich it can be used.

BASIC OP -AMP CHARACTERISTICS AND CIR-CUITS

In its simplest form, an op -amp consists of adifferential amplifier followed by offset compensationand output stages, as shown in Fig. 1 a. The differentialamplifier has inverting and non -inverting inputterminals, a high -impedance (constant current) tail to

OFFSETCOMPENSATION

STAGE

INVERTINGINPUT

NON INVERTINGINPUT

COMMONLINE

Fig. la Simplified op -amp equivalent circuit.

000

give a high input impedance and a high degree ofcommon mode signal rejection. It also has ahigh -impedance (constant current) load to give a highdegree of signal voltage stage gain.

The output of the differential amplifier is fed to adirect -coupled offset compensation stage, which

effectively reduces the output offset voltage of thedifferential amplifier to zero volts under quiescentconditions, and the output of the compensation stage isfed to a simple complementary emitter follower outputstage, which gives a low output impedance.

LINES OF SUPPLYOp -amps are normally powered from split power

supplies, providing +ve, -ve, and common (zero volt)supply rails, so that the output of the op -amp can swingeither side of the zero volts value, and can be set at atrue zero volts (when zero differential voltage is appliedto the circuits input terminals.)

The input terminals can be used independently (withthe unused terminal grounded) or simultaneously,enabling the device to function as an inverting,non -inverting, or differential amplifier. Since the deviceis direct -coupled throughout, it can be used to amplifyboth a.c. and d.c. input signals. Typically, they givebasic low -frequency voltage gains of about 100 000between input and output, and have input impedancesof 1M or greater at each input terminal.

Fig. 1 b shows the symbol that is commonly used torepresent an op -amp, and 1 c shows the basic supplyconnections that are used with the device. Note thatboth input and output signals of the op -amp arereferenced to the ground or zero volt line.

SIGNAL BOXThe output signal voltage of the op -amp is

proportional to the DIFFERENTIAL signal between itstwo input terminals, and is given by

eo,= Ao(e 1-e2)where Ao=the open -loop voltage gain of the op -amp(typically 100 000).


OP -AMP

0 V

4OUT

TB1

TB2

Fig. lc Basic supply connections of an op -amp.

e, =signal voltage at the non -inverting inputterminal.

e,=signal voltage at the inverting input terminal.Thus, if identical signals are simultaneously applied

to both input terminals, the circuit will (ideally) give zerosignal output If a signal is applied to the invertingterminal only, the circuit gives an amplified andinverted output If a signal is applied to thenon -inverting terminal only, the circuit gives an

amplified but non -inverted output.By using external negative feedback components,

the stage gain of the op -amp circuit can be veryprecisely controlled.

REFERENCEVOLTAGE

(e2) SAMPLEVOLTAGE

(el)

SUPPLYVe

SUPPLYOUTPUT

Fig. 2a Simple differential voltage comparatorcircuit.

TRANSFER REQUESTFig. 2a shows a very simple application of the

op -amp. This particular circuit is known as a differentialvoltage comparator, and has a fixed reference voltageapplied to the inverting input terminal, and a variabletest or sample voltage applied to the non -invertingterminal. When thq sample voltage is more than a fewhundred microvolts above the reference voltage theop -amp output is driven to saturation in a positivedirection, and when the sample is more than a fewhundred microvolts below the reference voltage theoutput is driven to saturation in the negative direction.

Fig. 2b shows the voltage transfer characteristics ofthe above circuit. Note that it is the magnitude of thedifferential input voltage that dictates the magnitude ofthe output voltage, and that the absolute values of inputvoltage are of little importance. Thus, if a 1V referenceis used and a differential voltage of only 200uV isETI CANADA - MAY 1977

needed to switch the output from a negative to apositive saturation level, this change can be caused by ashift of only 0.02% on a 1V signal applied to thesample input. The circuit thus functions as a precisionvoltage comparator or balance detector.

SUPPLY+Ve

eVe SATURATION

3

mV2 1.1

1

Ve SATURATION-Ve

SUPPLY

.1

mV

DIFFERENTIAL(e1- e2) INPUT

Fig. 2b Transfer characteristics of the differentialvoltage comparator circuit.

GOING TO GROUNDThe op -amp can be made to function as a low-level

inverting d.c. amplifier by simply grounding thenon -inverting terminal and feeding the input signal to

INPUT

VeSUPPLY

VeSUPPLY

OV

Fig. 3a Simple open -loop invertingd.c. amplifier.

OUTPUT

the inverting terminal, as shown in Fig. 3a. The op -ampis used 'open -loop' (without feedback) in thisconfiguration, and thus gives a voltage gain of about100 000 and has an input impedance of about 1 M.The disadvantage of this circuit is that its parametersare dictated by the actual op -amp, and are subject toconsiderable variation between individual devices.

CLOSING LOOPSA far more useful way of employing the op -amp is to

use it in the closed -loop mode, i.e., with negativefeedback. Fig. 3b shows the method of applyingnegative feedbac< to make a fixed -gain inverting d.c.amplifier. Here, the parameters of the circuit arecontrolled by feedback resistors R, and R2. The gain, Aof the circuit is dictated by the ratios of R, and R2, andequals 132/R,.

The gain is virtually independent of the op -ampcharacteristics, provided that the open -loop gain (A0) islarge relative to the closed -loop gain (A). The inputimpedance of the circuit is equal to R,, and again isvirtually independent of the op -amp characteristics.

29

R1

INPUT

VIRTUALGROUNDPOINT

SUPPLY+Ve

OP AMP

SUPPLY-Ve

OUTPUT

oV

Fig. 3b Basic closed -loop inverting d.c. amplifier.

It should be noted at this point that although RI andR2 control the gain of the complete circuit, they haveno effect on the parameters of the actual op -amp, andthe full open -loop gain of the op -amp is still availablebetween its inverting input terminal and the output.Similarly, the inverting terminal continues to have avery high input impedance, and negligible signalcurrent flows into the inverting terminal. Consquently,virtually all of the R1 signal current also flows in R2, andsignal currents i, and i2 can be regarded as beingequal, as indicated in the diagram.

Since the signal voltage appearing at the outputterminal end of R2 is A times greater than thatappearing at the inverting terminal end, the currentflowing in R2 is A times greater than that caused by theinverting terminal signal only. Consequently, R2 has anapparent value of R2/A when looked at from itsinverting terminal end, and the R1-R2 junction thusappears as a low -impedance VIRTUAL GROUND point.

Fig. 4a Basic non -inverting d.c. amplifier

INVERT OR NOT TO INVERT ...It can be seen from the above description that the

Fig. 3b circuit is very versatile. Its gain and inputimpedance can be very precisely controlled by suitablechoice of R, and R2, and are unaffected by variations inthe op -amp characteristics. A similar thing is true of thenon -inverting d.c. amplifier circuit shown in Fig. 4a. Inthis case the voltage gain is equal to (R,+ R2)/ R2 andthe input impedance is approximately equal to30

(Ao/A)Zin where Zin is the open -loop input impedancwof the op -amp. A great advantage of this circuit is that ithas a very high input impedance.

FOLLOW THAT VOLTAGEThe op -amp can be made to function as a precision

voltage follower by connecting it as a unity -gainnon -inverting d.c. amplifier, as shown in Fig. 4b. In thiscase the input and output voltages of the circuit areidentical, but the input impedance is very high and isroughly equal to Ao X Z,,.

The basic op -amp circuits of Figs. 2a to 4b areshown as d.c. amplifiers, but can readily be adapted fora.c. use. Op -amps also have many applications otherthan as simple amplifiers. They can easily be made tofunction as precision phase splitters, as adders orsubtractors, as active filters or selective amplifiers, asprecision half -wave or full -wave rectifiers, and asoscillators or multivibrators, etc.

Fig. 4b Basic unity -gain d.c. voltage follower

OP -AMP PARAMETERSAn ideal op -amp would have an infinite input

impedance, ze-o output impedance, infinite gain andinfinite bandwidth, and would give perfect trackingbetween input and output. Practical op -amps fall farshort of this ideal, and have finite gain, bandwidth, etc.,and give tracking errors between the input and outputsignals. Consequently, various performance parametersare detailed on op -amp data sheets, and indicate themeasure of "goodness" of the particular device. Themost important of these parameters are detailed below.

OPEN -LOOP VOLTAGE GAIN, A0. This is thelow -frequency voltage gain occuring directly betweenthe input and output terminals of the op -amp, and maybe expressed in direct terms or in terms of dB.Typically, d.c. gain figures of modern op -amps are100 000, or 100dB.

INPUT IMPEDANCE, Z.,. This is the impedancelooking directly into the input terminals of the op -ampwhen it is used open -loop, and is usually expressed interms of resistance only. Values of 1M are typical ofmodern op -amps with bi-polar input stages, whileF.E.T. input types have impedances of a million Meg orgreater.


OUTPUT IMPEDANCE, Z0. This is the outputimpedance of the basic op -amp when it is usedopen -loop, and is usually expressed in terms ofresistance only. Values of a few hundred ohms aretypical of modern op -amps.

INPUT BIAS CURRENT, I. Many op -amps use bipolartransistor input stages, and draw a small bias currentfrom the input terminals. The magnitude of this currentis denoted by lb, and is typically only a fraction of amicroamp.

SUPPLY VOLTAGE RANGE, V, Op -amps are usuallyoperated from two sets of supply rails, and thesesupplies must be within maximum and minimumlimits. If the supply voltages are too high the op -ampmay be damaged, and if the supply voltages are too lowthe op -amp will not function correctly. Typical supplylimits are ±3V to ± 1 5V.

INPUT VOLTAGE RANGE, Vior The input voltage tothe op -amp must never be allowed to exceed the supplyline voltages, or the op -amp may be damaged. Vwbss) isusually specified as being one or two volts less than vs.

OUTPUT VOLTAGE RANGE, If the op -

amp is over driven its output will saturate and belimited by the available supply voltages, so Von.) isusually specified as being one or two volts less than Vs.

DIFFERENTIAL INPUT OFFSET VOLTAGE,Vi In the ideal op -amp perfect tracking wouldexist between the input and output terminals of thedevice, and the output would register zero when bothinputs were grounded. Actual op -amps are not perfectdevices, however, and in practice slight imbalancesexist within their input circuitry and effectively cause asmall offset or bias potential to be applied to the inputterminals of the op -amp. Typically, this DIFFERENTIALINPUT OFFSET VOLTAGE has a value of only a fewmillivolts, but when this voltage is amplified by the gainof the circuit in which the op -amp is used it may besufficient to drive the op -amp output to saturation.Because of this, most op -amps have some facility forexternally nulling out the offset voltage.

COMMON MODE REJECTION RATION, c.m.r.r. Theideal op -amp produces an output that is proportional tothe difference between the two signals applied to itsinput terminals, and produces zero output whenidentical signals are applied to both inputs simultan-eously, i.e., in common mode. In practical op -amps,common mode signals do not entirely cancel out, andproduce a small signal at the op -amps output terminal.The ability of the op -amp to reject common modesignals is usually expressed in terms of common moderejection ratio, which is the ratio of the op -amp's gainwith differential signals to the op -amp's gain withcommon mode signals. C.m.r.r. values of 90dB aretypical of modern op -amps.

TRANSITION FREQUENCY, fT. An op -amp typicallygives a low -frequency voltage gain of about 100dB,and in the interest of stability its open -loop frequencyresponse is tailored so that the gain falls off as thefrequency rises, and falls to unity at a transitionfrequency denoted fr. Usually, the response falls off at arate of 6dB per octave or 20dB per decade. Fig. 5ETI CANADA - MAY 1977

+120 - DASHED LINES = CLOSED -LOOPRESPONSE

+100

+80-----+60 +- OPEN -LOOP

RESPONSE

+40--------+20------ ------

0

-2010 100 1k 10k 100k 1M

FREQUENCY-HzFig. 5 Typical frequency response curveof the 741 op -amp.

10M

shows the typical response curve of the type 741op -amp, which has an fT of 1 MHz and a low frequencygain of 100dB.

Note that, when the op -amp is used in a closed -loopamplifier circuit, the bandwidth of the circuit dependson the closed -loop gain If the amplifier is used to give again of 60dB its bandwidth is only 1 kHz, and if it is

used to give a gain of 20dB its bandwidth is 100kHz.The fT figure can thus be used to represent a

gain -bandwidth product.

PARAMETER 741 VALUE

Ao OPEN -LOOP VOLTAGE GAIN 100dB

Zit, INPUT IMPEDANCE 1M

Zo OUTPUT IMPEDANCE 150R

I, INPUT BIAS CURRENT 200nA

Vs !MAXI MAXIMUM SUPPLY VOLTAGE ±-18V

Vo ,MAX) MAXIMUM INPUT VOLTAGE 31/

Vu (MAXI MAXIMUM OUTPUT VOLTAGE ±14V

V,. DIFFERENTIAL INPUT OFFSET VOLTAGE 2mV

COMMON MODE REJECTION RATIO 90dB

FT TRANSITION FREQUENCY 1MHZ

S SLEW RATE 1V/uS

Table 1 Typical characteristics of the 741 op -amp.

SLEW RATE. As well as being subject to normalbandwidth limitations, op -amps are also subject to aphenomenon known as slew rate limiting, which hasthe effect of limiting the maximum rate of change ofvoltage at the output of the device. Slew rate isnormally specified in terms of volts per microsecond,and values in the range 1V/us to 10V/us are commonwith most popular types of op -amp. One effect of slewrate limiting is to make a greater bandwidth available tosmall output signals than is available to large outputsignals.

THE 741 OP -AMP.Early types of 1.c. op -amp, such as the well known

709 type, suffered from a number of designweaknesses. In particular, they were prone to a

phenomenon known as INPUT LATCH -UP, in which31

741 (001t150011the input circuitry tended to switch into a locked state ifspecial precautions were not taken when con-necting the input signals to the input terminals, anctended to self-destruct if a short circuit wereinadvertently placed across the op -amp outputterminals. In addition, the op -amps were prone tobursting into unwanted oscillations when used in thelinear amplifier mode, and required the use of externalfrequency compensation components for stabilitycontrol.

NCrn

1

OFFSETV+ OUT NULL

OFFSE TNULL

INPUT

INPUT

TAP

OFFSET - V- V -NULL INPUT INPUT (AND CASE)

8 pin Minidip or DIP 741(Top View)

Fig. 6 Outlines and pin connections of the twomost popular 741 packages.

T05 741(TOP VIEW)

OUTPUT

OFFSETNULL

These weaknesses have been eliminated in the type741 op -amp. This device is immune to input latch -upproblems, has built-in output short circuit protection,and does not require the use of external frequencycompensation components. The typical performancecharacteristics of the device are listed in Table 1.

The type 741 op -amp is marketed by most i.cmanufacturers, and is very readily available. Fig. 6shows the two most commonly used forms ofpackaging of the device Throughout this chapter, allpractical circuits are based on the standard 8 -pindual -in -line (D.I.L. or DIP) version of the 741 op -amp.

OUT

10k(OFFSET NULL)

TO SUPPLY-Ve

Fig. 7 Method of applying offset nulling to the741 op -amp.

The 741 op -amp can be provided with externaloffset nulling by wiring a 10k pot between its two nullterminals and taking the pot slider to the negativesupply rail, as shown in Fig. 7.

Having cleared up these basic points, let's now goon and look at a range of practical applications of the741 op -amp.32

Fig. 8a x 190 inverting d. C. amplifier.

Fig. 8b Variable gain (xl to x 100) invertingd.c. amplifier.

BASIC LINEAR AMPLIFIER PROJECTS. (Figs. 8 to11).

Figs. 8 to 11 show a variety of ways of using the741 in basic linear amplifier applications.

The 741 can be made to function as an invertingamplifier by grounding the non -inverting input terminaland feeding the input signal to the inverting terminal.The voltage gain of the circuit can be preciselycontrolled by selecting suitable values of externalfeedback resistance. Fig. 8a shows the practicalconnections of an inverting d.c. amplifier with a pre-setgain of x100. The voltage gain is determined by theratios of R, and R2, as shown in the diagram.

The gain can be readily altered by using alternativeR, and/or R2 values. If required, the gain can be madevariable by using a series combination of a fixed and avariable resistor in place of R2, as shown in the circuit ofFig. 8b, in which the gain can be varied over the rangex1 to x100 via R2.

VARIATIONSA variation of the basic inverting d.c. amplifier is

shown in Fig. 9a. Here, the feedback connection to R,is taken from the output of the R3-R4 output potentialdivider, rather than directly from the output of theop -amp, and the voltage gain is determined by theratios of this divider as well as by the values of R, and


741 CO011130011

R11M

INPUT

R310k

OUTPUT

R410OR

OV

Fig. 9a High impedance x 100 inverting d.c. amplifier.

R2. The important feature of this circuit is that it enablesR,, which determines the input impedance of thecircuit, to be given a high value if required, while at thesame time enabling high voltage gain to be achieved.

The basic inverting d.c. amplifier can be adapted fora.c. use by simply wiring blocking capacitors in serieswith its input and output terminals, as shown in thex100 inverting a.c. amplifier circuit of Fig. 9b.

Fig. 9b x100 inverting a.c. amplifier.

NON -INVERTING ...The amp can be made to function as a non -inverting

amplifier by feeding the input signal to its non -invertingterminal and applying negative feedback to theinverting terminal via a resistive potential divider that isconnected across the op -amp output. Fig. 10a showsthe connections for making a fixed gain (x100) d.c.amplifier.

The voltage gain of the Fig. 10a circuit is determinedby the ratios of R, and R2 If R2 is given a value of zerothe gain falls to unity, and if R, is given a value of zerothe gain rises towards infinity (but in practice is limitedto the open -loop gain of the op -amp). If required, thegain can be made variable by replacing R2 with aETI CANADA - MAY 1977

0

INPUT

Fig. 10a Non -inverting x 100 d.c. amplifier.

potentiometer and connecting the pot slider to theinverting terminal of the op -amp, as shown in the circuitof Fig. 10b The gain of this circuit can be varied overthe range x1 to x100 via R,.

... AND RESISTANCE TO INPUTSA major advantage of the non -inverting d.c. amplifier

is that it has a very high input resistance. In theory, theinput resistance is equal to the open -loop inputresistance (typically 1 M) multiplied by the open -loopvoltage gain (typically 100 000) divided by the actualcircuit voltage gain. In practice, input resistance valuesof hundreds of megohms can readily be obtained.

Fig. 10b Non -inverting variable gain (xl to x100) d.c. amplifier.

BLOCKING OUTThe basic non -inverting d.c. circuit of Fig. 10 can be

modified to operate as a.c. amplifiers in a variety ofways. The most obvious approach here is to simply wireblocking capacitors in series with the inputs andoutputs, but in such cases the input terminal must bed.c. grounded via a suitable resistor, as shown by R3 inthe non -inverting x100 a.c. amplifier of Fig. 11a. If thisresistor is not used the op -amp will have no d.c.stability, and its output will rapidly drift into saturation.

33

741 COOKBOOKClearly, the input resistance of the Fig. 11a circuit isequal to R3, and R3 must have a relatively low value inthe interest of d.c. stability. This circuit thus loses thenon -inverting amplifier's basic advantage of high inputresistance.

OUTPUT

R11k01

ov

Fig. 11b Non -inverting, high input -impedance,x 100 a.c. amplifier.

DRIFTING INTO STABILITYA useful development of the Fig. 11a circuit is

shown in Fig. 11b. Here, the values of R and R, areincreased and a blocking capacitor is interposedbetween them. At practical operating frequencies thiscapacitor has a negligible impedance, so the voltagegain is still determined by the ratios of the two resistors.Because of the inclusion of the blocking capacitor,however, the inverting terminal of the op -amp issubjected to virtually 100% d.c. negative feedbackfrom the output terminal of the op -amp, and the circuitthus has excellent d.c. stability. The low end of R3 isconnected to the C3-R1 junction, rather than directly tothe ground line, and the signal voltage appearing at thispoint is virtually identical with that appearing at thenon -inverting terminal of the op -amp'

Fig. 1 la Non -inverting x 100 a.c. amplifier.

34

Consequently, identical signal voltages appear atboth ends of R3, and the apparent impedance of thisresistor is increased close to infinity by bootstrap action.

This circuit thus has good d.c. stability and a veryhigh input impedance In practice, this circuit gives atypical input impedance of about 50M

VOLTAGE FOLLOWER PROJECTS (Figs. 12 to 13).A 741 can be made to function as a precision

voltage follower by connecting it as a unity -gainnon -inverting amplifier. Fig. 12a shows the practicalconnections for making a d.c. voltage follower. Here,the input signal is applied directly to the non -invertingterminal of the op -amp, and the inverting terminal isconnected directly to the output, so the circuit has100% d.c. negative feedback and acts as a unity -gainnon -inverting d.c. amplifier.

The output signal voltage of the circuit is virtuallyidentical to that of the input, so the output is said to'follow' the input voltage. The great advantage of thiscircuit is that it has a very high input impedance (ashigh as hundreds of megohms) and a very low outputimpedance (as low as a few ohms). The circuit actseffectively as an impedance transformer.

PRACTICE, AND ITS LIMITSIn practice the output of the basic Fig. 12a circuit

will follow the input to within a couple of millivolts up tomagnitudes within a volt or so of the supply linepotentials. If required, the circuit can be made to followto within a few microvolts by adding the offset nullfacility to the op -amp.

The d.c. voltage follower can be adapted for a.c. useby wiring blocking capacitors in series with its input andoutput terminals and by d.c.-coupling the non -invertingterminal of the op -amp to the zero volts line via asuitable resistor, as shown by R, in Fig. 1 2b. R, shouldhave a value less than a couple of megohms, andrestricts the available input impedance of the voltagefollower.

LACED UP OHMSIf a very high input -impedance a.c. voltage follower

is needed, the circuit of Fig. 12c can be used. Here,is boostrapped from the output of the op-amp, and itsapparent impedance is greatly increased. This circuithas a typical impedance of hundreds of megohms.


741 COON130011

C1

0-11

INPUT

0

R1100k

741

+9V

7

4

-9V

C20,.1

11--0

(NONPOLARISED)

OUTPUT

C32p2

R210k

OV

Fig. 12c Very high input -impedance a.c. voltagefollower.

DRIVING CIRCUITS AMP-LYThe 741 op -amp is capable of providing output

currents up to about 5mA, and this is consequently thecurrent -driving limit of the three voltage followercircuits that we have looked at so far. Thecurrent -driving capabilities of the circuits can readily beincreased by wiring simple or complementary emitter

Fig. 13a Unidirectional d.c. voltage follower with boostedoutput (variable from OV to +8V at 50mA.)

A

follower booster stages between the op -amp outputterminals and the outputs of the actual circuits, asshown in Figs. 1 3a and 1 3b respectively.

Note in each case that the base -emitter junction(s) ofthe output transistor(s) are included in the negativefeedback loop of the circuit Consequently, the 600mVknee voltage of each junction is effectively reduced by afactor equal to the open -loop gain of the op -amp, so thejunctions do not adversely effect the voltage -followingcharacteristics of either circuit.

The Fig. 13a circuit is able to source current only,and can be regarded as a unidirectional, positive -going,d.c. voltage follower. The Fig. 13b circuit can bothsource and sink output currents, and thus givesbidirectional follower action. Each circuit has a

current -driving capacity of about 50mA This figure isdictated by the limited power rating of the specifiedoutput transistors. The drive capability can be increasedby using alternative transistors.

0

INPUT

0

74

+9V

7

4

-9V

012N3704

2N3702

OUTPUT

R110k

OV 0

Fig. 13b Bidirectional d.c. voltage follower with boostedoutput (variable from CV to± -±81/ at 50mA).

MISC AMP PROJECTS (Figs. 14 to 22)Figs. 14 to 22 show a miscellaneous assortment of

741 amplifier projects, ranging from d.c. adding circuitsto frequency -selective amplifiers.

Fig 14 shows the circuit of a unity -gain inverting d.c.adder, which gives an output voltage that is equal to thesum of the three input voltages. Here, input resistors R,to R3 and feedback resistor R4 each have the samevalue, and the circuit thus acts as a unity -gain invertingd.c. amplifier between each input terminal and theoutput. Since the current flowing in each input resistoralso flows in feedback resistor R4, the total currentflowing in R, is equal to the sum of the input currents,and the output voltage is equal to the negative sum of theinput voltages. The circuit is shown with only three inputconnections, but in fact can be provided with anynumber of input terminals. The circuit can be made tofunction as a s -d; -called 'audio mixer' by wiring blockingcapacitors in series with each input terminal and withthe output terminal.


741 CO011130011

R1100k

R2100k

R3

INPUT 100k

INPUT2

INPUT 1.53 27k

134

100k

119V

9V

OUTPUT

OV

Fig. 14 Unity -gain inverting d.c. adder, or 'audio mixer'.

FIG. 15 shows how two unity -gain inverting d.c.amplifiers can be wired in series to make a precisionunity -gain balanced phase-splitter. The output ofthe first amplifier is an inverted version of the inputsignal, and the output of the second amplifier is a

non -inverted version.

OUTPUT

ONVERTED)

INPUTOUTPUT

2(NON

INVERTEDI

Fig.15 Unity -gain balanced d.c. phase-splitter.

FIG. 16 shows how a 741 can be used as aunity -gain differential d.c. amplifier. The output of thiscircuit is equal to the difference between the two inputsignals or voltages, or to ere,. Thus, the circuit can alsobe used as a subtractor. In this type of circuit thecomponent values are chosen such that RI/ R 2 = R4/ R3,in which case the voltage gain ,A =R2/ R, The circuitcan thus be made to give voltage gain if required.

.R1

100k

INPUT2

INPUT1

OUTPUT

FIG. 17 shows the amp can be made to act as anon-linear (semi -log) a.c. voltage amplifier by using acouple of ordinary silicon diodes as feedback elements.The voltage gain of the circuit depends on themagnitude of applied input signal, and is high wheninput signals are low, and low when input signals arehigh. The measured performance of the circuit is shownin the table, and can be varied by using alternative R,values.

INPUT VOLTSfi, = 160 R, = 1060

NHS) V0.412.141 S) GAIN 'WRNS) GAIN

I NV 110.4V XII0 21.41/ X21

10.4V 330NV X33 170.V X 17

1004! 450 NV X45 360..V X 3 6

IV 560 .. V 0056 470,.V 0047

10V 600NV 00 07 560NV X0056

Fig. 17 Circuit and performance table of non-hnear(semi -log) a.c. voltage amplifier.

Al

10k TO 10M(SENSITIVITY)

3

0-

DI

R4100k

OUTPUT

C118

(SEE TEXT)

VIN V v k11(1IR! = (R, = 1011KS2) (R1 = Ih112) = 1081S2)

50 mV 500 mV 5 V 50 V 2.85 V20 mV 200 mV 2 V 20 V 2.81 V10 mV 100 mV IV 10 V 2.79V

5 mV 50 niV 500 tnV 5 V 2.60 V

2 mV 20 niV 200 mV 2 V 2.03 VI TIN 10 n15/ 100 mV 1 V 1.45 V

500 9V 5 mV 50 mV 500 mV ONN V

200 5V 2 mV 20 mV 200 mV 0.4(1 V

100 AV I ntV 10 mV 100 mV 0.20 V50 9V 500 NV 5 inV SO titV 010 V

Fig. 16 Unity -gain differential d.c. amplifier, or subtractor

36

Fig. 18 Circuit and performance details of constant -volumeamplifier.

ETI CANADA - MAY 197/

741 COORBOOKFIG. 18 shows how the 741 can be used together

with a junction -type field-effect transistor (JFET) tomake a so-called constant -volume amplifier. The actionof this type of circuit is such that its peak output voltageis held sensibly constant, without distortion, over awide range of input signal levels, and this particularcircuit gives a sensibly constant output over a 30dBrange of input signal levels.

The measured performance of the circuit is shown inthe table. C, determines the response time of theamplifier, and may be altered to satisfy individualneeds.

ACTION TAKENThe action of the Fig. 18 circuit relies on the fact that

the JFET can act as a voltage -controlled resistance whichappears as a low value when zero bias is applied to itsgate and as a high resistance when its gate is negativelybiased. The JFET and R3 act as a gain -determining a.c.voltage divider (via C2), and the bias to the JFET gate isderived from the circuits output via the D, -C, network.When the circuit output is low the JFET appears as alow resistance, and the op -amp gives high voltage gain.

When the circuit output is high the JFET appears asa high resistance, and the op -amp gives low voltagegain. The output level of the circuit is thus held sensiblyconstant by negative feedback.

Cl20n

INPUT

0

R1 9V10k

-9VR3

15k 15k

C2 C310n iOn

I-OUTPUT

6k8

C4 R4

I2On

820R

OV

Fig. 19 1 kHz tuned (acceptor) amplifier (twin -T).

CHOOSE YOUR FREQUENCYThe 741 op -amp can be made to function as a

frequency -selective amplifier by connectingfrequency -sensitive networks into its feedback loops.Fig. 19 shows how a twin -T network can be connected tothe op -amp so that it acts as a tuned (acceptor) amplifier,and Fig. 20 shows how the same twin -T network can beconnected so that the op -amp acts as a notch (rejector)filter. The values of the twin -T network are chosen suchthat R2= R3=2 x 134, and C2= C4/ 2, in which case itscentre (tuned) frequency =1/6.28 R2.C2. With thecomponent values shown, both circuits are tuned toapproximately 1 kHz.ETI CANADA - MAY 1977

Finally, to complete this section, Figs. 21 and 22show the circuits of a couple of variable -frequencyaudio filters. The Fig. 21 circuit is that of a low-passfilter which covers the range 2.2kHz to 24kHz, and theFig. 22 circuit is that of a high-pass filter which coversthe range 235Hz to 2.8kHz. In each case, the circuitgives unity gain to signals beyond its cut-off frequency,and gives a 2nd order response (a change of 1 2dB peroctave) to signals within its range.

RI RV110k 100k

Fig. 21 Variable low-pass filter, covering 2.2kHz to 24kHz.

1

100k

L

RV2100k

R210k

9V

OUTPUT

OV

Fig. 22 Variable high-pass filter, covering 235Hz to 2.8kHz.

37

741 COORBOORINSTRUMENTATION PROJECTS (Figs. 23 to 31)

Figs. 23 to 31 show a variety of instrumentationprojects in which the 741 can be used. The circuitsrange from a simple voltage regulator to a linear -scaleohmmeter.

OUTPUT0-12V0-50mA

F -g. 23 Simple variable -voltage supply.

FIG. 23 shows the circuit of a simple variable -vol-tage power supply, which gives a stable output that isfully adjustable from OV to 12V at currents up to amaximum of about 50mA. The operation of the circuit isquite simple. ZD, is a zener diode, and is energised fromthe positive supply line via R,. A constant referencepotential of 12V is developed across the zener diode,and is fed to variable potential divider RV,.

The output of this divider is fully variable from OV to12V, and is fed to the non -inverting input of theop -amp. The op -amp is wired as a unity -gain voltagefollower, with Q, connected as an emitter followercurrent -booster stage in series with its output.

Thus, the output voltage of the circuit follows thevoltage set at the op -amp input via RV,, and is fullyvariable from OV to 12V. Note that the circuit uses an18V positive supply and a 9V negative supply.

Also note that the voltage range of the above circuitcan be increased by using higher zener and unregulatedsupply voltages, and that its current capacity can beincreased by using one or more power transistors inplace of Q,.

-(40V TO 4W (UNREGULATED)

F11

022N3055

Fig. 24 3V - 30V, 0-1 amp stabilised p.s.u.

OUTPUT- 3 30V

0 -1A

38

FIG. 24 shows how a 741 op -amp can be used asthe basis of a stabilised power supply unit (P.S.U.) thatcovers the range 3V to 30V at currents up to 1A. Here,the voltage supply to the op -amp is stabilized at 33V viaZD,, and a highly temperature -stable reference of 3V isfed to the input of the op -amp via ZD2.

The op -amp and output transistors Q, -Q2 are wiredas a variable -gain non -inverting d.c. amplifier, with gainvariable from unity to x10 via RV,, and the outputvoltage is thus fully variable from 3V to 30V via RV1. Theoutput voltage is fully stabilized by negative feedback.

+ OUTPUT3 --30V0 -1A

Fig. 25 3V - 30V stabilised p.s.u. with overload protection.

FIG. 25 shows how overload protection can beapplied to the above circuit. Here, current -sensingresistor R is wired in series with the output of theregulator, and cut-out transistor 03 is driven from thisresistor and is wired so that its base -collector junction isable to short the base -emitter junction of the Q1 -Q2output transistor stage.

Normally, 03 Is inoperative, and has no effect on thecircuit, but when P.S.U. output currents exceed 1A apotential in excess of 600mV is developed across R,and biases 03 on, thus causing 03 to shunt thebase -emitter junction of the Q1-02 output stage andhence reducing the output current Heavy negativefeedback takes place in this action, and the outputcurrent is automatically limited to 1A, even undershort-circuit conditions.

FIG. 26a shows how a 741 can be used inconjunction with a couple of silicon diodes as aprecision half -wave rectifier. Conventional diodes act asimperfect rectifiers of low-level a.c. signals, becausethey do not begin to conduct significantly until theapplied signal voltage exceeds a 'knee' value of about600mV.

When diodes are wired into the negative feedbackloop of the circuit as shown the 'knee' voltage iseffectively reduced by a factor equal to the open -loopgain of the op -amp, and the circuit thus acts like anear -perfect rectifier.

The overall voltage gain of the Fig. 26a circuit isdictated by the ratios of R, and R2 to R3, as in the caseof a conventional inverting amplifier, and this circuitthus gives a gain of unity. The circuit can be made to


741 COOKBO011

R310k

ACINPUT

Fig. 26a Precision unity -gain half -wave rectifier.

HALF -WAVE(+Ve)OUTPUT

act as a precision half -wave a.c. /d.c. converter bydesigning it to give a voltage gain of 2.22 to giveform -factor correction, and by integrating its rectifieroutput, as shown in Fig. 26b.

Note that each of the Fig. 26 circuits has a highoutput impedance, and the outputs must both be fed intoloads having impedances less than about 1M.

R110k

o -I

ACINPUT(0-2V RMS)

-9V

DCOUTPUT(0-2V)

OV

Fig. 26b Precision half -wave a.c./d.c. converter.

VI s610V

IV10O

10mV

16AV

10M0I MO

100k 010k0IN 0

R1SEETABLE

Fig. 27 High-performance d.c. voltmeter converter.

FIG. 27 shows how op -amp can be used as ahigh-performance d.c. voltmeter converter, which canbe used to convert any 1V f.s.d. meter with a sensitivitybetter than lk /V into a voltmeter that can read anyvalue in the range 1 mV to 10V f.s.d. at a sensitivity of1M /V- The voltage range is determined by the R,value, and the table shows some suitable values forcommon voltage ranges.

FIG. 28 shows a simple circuit that can be used toconvert a ,1mA f.s.d. meter into a d.c. voltmeter withany f.s.d value in the range 100mV to 1000V, or intoa d.c. current meter with any f.s.d. value in the range1 uA to 1 A. Suitable component values for differentranges are shown in the tables.

R1

SEE TABLE

INPUTSEE

TABLER2

+9V

9V

RV110kISET ZERO)

OV

VOLTMETER CURRENT METERIka Rd f R0

'000V 1090 I kC) 1 A 00 010

100V 10P40 10140 100A1A 00 Inrov WHO 100k0 10mA 00 100

IV 900k0 1000 IkM 00 1000

1100k4V 00 700k0 10094 00 1 k C)

10AA 00 I0k019A 0)) 100kC/

Fig. 28 Simple d.c. voltage or current meter.

FIG. 29 shows the circuit of a precision d.c.millivoltmeter, which uses a 1 mA f.s.d. meter to readf.s.d. voltages from 1mV to 1000mV in sevenswitch -selected ranges.

FIG. 30 shows the basic circuit of a precision a.c.volt or millivolt meter. This circuit can be used with anymoving -coil meter with a full scale current value in therange 100uA to 5mA, and can be made to give any fullscale a.c. voltage reading in the range 1 mV to1000mV. The tables show the alternative values of R,and R, that must be used to satisfy different basic metersensitivities, and the values of R3 and R4 that must beused for different f.s d. voltage sensitivities.

HOME OHMFinally, to conclude, Fig. 31 shows how the 741

op -amp can be used in conjuncton with a 1 mA f.s.d.meter to make a linear -scale ohmmeter that has fivedecade ranges from 1 k to 10M.

The circuit is divided into two parts, and consists of avoltage generator that is used to generate a standard test


T41 (0011130011

Fig. 29 Precision d.c. millivoltmeter.

C1

ACINPUT

9.0

L 9000 lnnSS= 3600 I 300

leap 000ve,eSS 01, USE WinsPUS E 141 METER MONS

MEN,

tpN

131. E. NEW I se YEN INOSLNSilis0ES

Fig. 30 Precision a.c. volt/millivolt meter.

Fig. 31 Linear -scale ohmmeter.

voltage, and a readout unit which indicates the value ofthe resistor under test.

The voltage generator section of the circuit compriseszener diode ZD,, transistor (11, and resistors R, to R,.The action of these components is such that a stablereference potential of 1V is developed across R4, but isadjustable over a limited range via RV,. This voltage isfed to the input of the op -amp readout unit. The op -ampis wired as an inverting d.c. amplifier, with the 1 mAmeter and RV3 forming a 1V f.s.d. meter across itsoutput, and with the op -amp gain determined by the40

values of ranging resistors R5 to R9 and by negativefeedback resistor Fix.

Since the input to the amplifier is fixed at 1V, theoutput voltage reading of the meter is directlyproportional to the value of R, and equals full scalewhen R and the ranging resistor values are equal.Consequently, the circuit functions as a linear -scaleohmmeter.

CALIBRATIONThe procedure for initially calibrating the Fig. 31

circuit is as follows: First, switch the unit to 10krange and fix an accurate 1 OkS2 resistor in the Fix

position. Now adjust RV, to give an accurate 1V acrossR4, and then adjust RV 2 to give a precise full scalereading on the meter. All adjustments are thencomplete, and .the circuit is ready for use.

MISCELLANEOUS 741 PROJECTSThe 741 op -amp can be used as the basis of

a vast range of miscellaneous projects, includingoscillators and sensing circuits. Four such projects aredescribed in this final section.

FIG. 32 shows how the 741 op -amp can beconnected as a variable -frequency wien-bridge oscilla-tor, which covers the basic range 1 50Hz to 1 .5kHz, anduses a low -current lamp for amplitude stabilisation. Theoutput amplitude of the oscillator is variable via RV, andhas a typical maximum value of 2.5V r.m.s. and a t.h.d.value of 0.1%. The frequency range of the circuit isinversely proportional to the CI -C, values The circuitcan give a useful performance up to a maximumfrequency of about 25kHz

LP1ANY 12-28VLOW CURRENT(<50mA)LAP1P

Fig. 32 150Hz - 1.5kHz Wien -bridge oscillator.

Fig. 33 shows how either a 741 or a 709 op -ampcan be connected as a simple variable -frequencysquare -wave generator that covers the range 500Hz to5kHz via a single variable resistor. (The circuit producesa good symmetrical waveform.)

The frequency of oscillation is inversely proportionalto the C, value, and can be reduced by increasing theC, value, or vice -versa. The amplitude of the squarewave output signal can be made variable, if required,by wiring a 1 OkS2 variable potential divider across theoutput terminals of the circuit and taking the outputfrom between the pot slider and the zero volts line.


741 COORBOOR

Fig. 33 Simple 500Hz - 5k Hz square wave generator.

FIGS. 34 and 35 show a couple of useful ways ofusing the 741 op -amp in the open -loop differentialvoltage comparator mode. In each case, the circuits arepowered from single -ended 1 2V supplies, and have afixed half -supply reference voltage applied to thenon -inverting op -amp terminal via the R1 -R2 potentialdivider and have a variable voltage applied to theinverting op -amp terminal via a variable potentialdivider.

The circuit action is such that the op -amp output isdriven to negative saturation (and the relay is driven on)when the variable input voltage is greater than thereference voltage. Conversely, the op -amp output isdriven to positive saturation (and the relay is cut off) whenthe variable input voltage is less than the referencevoltage.

R LA12V RELAYCOIL 180ROR GREATER

Fig. 34 Precision frost or under temperature switch canbe made to act as a fire or over temperature switch by transposingR1 and TH 7 positions.

FROSTY RECEPTIONThe Fig. 34 circuit is that of a precision frost or

under -temperature switch, which drives the relay onwhen the temperature sensed by thermistor TH, fallsbelow a value pre-set via RV,. The circuit action can bereversed, so that it operates as a fire or over -tempera-ture switch, by simply transposing the RV, and the TH,positions. In either case, TH, can be any negative -tem-perature -coefficient thermistor that presents a resis-tance in the range 9000 to 91dt at the required triptemperature.

RLA12V RELAYCOIL 180ROR GREATER

Fig. 35 Precision light -activated switch can be made to act as adark -activated switch by transposing R 1 and L DR positions.

LIGHT WORKThe Fig. 35 circuit is that of a precision light -activated

switch, which turns the relay on when the illuminationlevel sensed by light -dependent resistor LDR exceeds avalue pre-set by RV,. The circuit action can be reversedso that the relay turns on when the illumination fallsbelow a pre-set level by simply transposing the RV, andLDR positions. In either case, the LDR can be anycadmium -sulphide photocell that presents a resistancein the range 9005 to 9k0 at the desired switch -on level.

ELECTRONICS

Go0 PRIX S CIRC T

00...........0 0,,07711:11 EIJIMMENTIJI WIESTHEE leaSSE11 10 ME

111010 0000 OEM NEM Mgr MEM.....- .....

0 4

11111111111

MARE TOIN OWN PRIMOCINCOIT MARIS

INJECTORALL - from Fingers to Doughnuts a verycomplete line of quality circuit board materials.

omnitronix ltd. L -I. A/2056 SOUTH SERVICE RD. TRANS CANADA HWY. - DORVAL. QUE. H9P 2N4 PHONE 15141 683-6993


electronics todayWhat to look for in the June issue:

G.S.R.

MONITORBack in April we explained what biofeedback was and just

how it can be used to control some of the internal bodyprocesses.

Perhaps the best way to start experimenting with this fasci-nating subject is to use a galvanic skin response monitor. TheG.S.R. Monitor we describe is simple to build and use- one ofthe fascinations of biofeedback being the speed and ease withwhich control can be learnt.

MultimeterGuide

There's more to meters thanmeets the eye - and the pocket.Knowing which one to buy canbe a problem with so manyavailable. We set out to guideyou in your choice and showyou what to look for.

SIGNALINJECTOR/

TRACER

No excuses for this all toofamiliar project it's short andeasy to build but it is also verygood and what's more, useful.

+25A generation

awayElectronic systems and dis-

coveries that we take for grantedwere not even dreamed of a

generation ago. Will the samething happen in the next generation? What will our childrentake for granted in 25 yearstime?

We take a look at the systemsof the future and try to forseejust how electronics willdevelop. Evalution or Revolu-tion; part one starts in June.

The articles described here are in anadvanced state of preparation, but circum-stances may necessitate changes in the issuethat appears.

DIGITAL

SOUND

SYNTHESISThe music synthesiser has

now been around for sometime-too long some may say-and its abilities have been amplydemonstrated by various rockgroups. The main limitationon the use of a synthesiser asa live instrument being thatit is monophonic (only onenote at a time). Next monthwe suggest various digital tech-niques that may be employedin the design of a basic MULTI -PHONIC system, which wouldovercome most of the inherentmonophonic limitations withoutthe size and complexity of a fullpolyphonic system.

SoundOperatedFlash

Dramatic pictures and seq-uences, even shots for researchpurposes can easily be takenwith our Sound Operated Flash.Another down to earth projectwhich can be cheaply built toproduce some amazing pictures.

42 ETI CANADA -- MAY 197_/

NICKEL CADMIUMBATTERY CHARGERUniversal unit will charge practically any nickell-cadmium battery currently in use.

THERE is an increasing proliferationof portable equipment, such as flashguns and calculators, which could, oralready do, use rechargeable batteriesof the nickel -cadmium type.

If the equipment was originally fittedwith rechargeable batteries, a chargermay well have been provided. Butwhen replacing ordinary dry cells withrechargeable types a charger will berequired. Unfortunately,nickel -cadmium battery packs come ina variety of voltages and ampere -hourratings and a charger supplied for onepiece of equipment leg, an electronicflash) will seldom, if ever, be suitablefor other equipment such as anelectronic calculator.

The ETI 519 battery charger willcharge almost any nickel -cadmiumbattery in use today. The charging rateis switch -selectable for batteries from50 mA/h to 2500 mA/h capacity.

Any battery voltage up to 20 volts isautomatically accommodated. Novoltage selection is required.

T1

RANGES

O 2500 mA/H

O 1000 mA/H

O 500 mA/H

O 250 mA/H

O 100 mA/H

O 50 mA 'H

mAihr

250-,r 500

1001A ,,-M00

2500

CHARGE FOR 14HOURS- AT CORRECT

BATTERY RATINt,

DO NOT CHARGEAl HIGHER RATE THAN SPECIFIED

OR FOR MOM THAN IR HOURS

Charging time is approximately 14hours for a flat battery andproportionally less for one that is

partially diischarged.Overcharging at the correct

ampere/hour rate will not damage anickel -cadmium battery. Thus an

overnight charge for a partiallydischarged battery may be safelygiven. In fact, provided the correct

Fig. 1. Circuit diagram of the Nickel -Cadmium Battery Charger.

ampere/hour charging rate has beenselected no damage will occur if lefton charge for 48 hours.

CONSTRUCTIONThe circuit is a very simple one.

Practically any method ofconstruction may be used providedcare is taken with the insulation of 120Vac wiring.

In our prototype unit we assembledall components on tag strips, with theexception of the range resistors whichwere mounted directly on the rangeswitch itself.

If only a single range is required, a

BATTERYVOLTAGE'1.25-3.755-1011.25-2021-30'

TABLE 1

TRANSFORMER -12.6 V CT24 V CT40 C CT60 V CT

R11.8k2.2k3.9k5.6k

' Capacitor C1 voltage rating shouldbe 50V.

Current rating of the transformer, inmA, should be greater than themaximum mA/h battery rating dividedby 10. A single winding transformerof half voltage may be used if a bridgerectifier is employed.


TO TRANSSECONDARY

TO BASEOF Q1

How it worksCurrent regulators operate in

opposite fashion to voltageregulators. In a current regulator, thecurrent remains constant regardlessof changes in load impedance - theoutput voltage varies, to maintainconstant load current.

In this circuit, the 120 Vac lineis reduced by T1 to 40 Vac. This isthen rectified by DI, D2 and filteredby Cl to provide approximately 28Vdc.

This dc supply is then regulated byQ1 and its associated components toproduce a current level selected bySW2.

Transistor Q1 is biased by D3 andD4 such that there is about 1.2 Vbetween the base of 01 and thenegative side of Cl. As there is 0.6 Vbetween base and emitter of Q1,there will be 0.6 V developed acrossthe resistor network R2 -R7.Therefore the emitter current of Q1must be 0.6 V divided by the resistorvalue selected by SW2.

The emitter current generated asabove will produce an approximatelyequal collector current which chargesthe battery and remains constantprovided there is at least one voltbetween the collector and emitter ofQl

R1R2R3R4

w0. 2< 01-

0wucc v)

Zz<w Cc

I-0l-0

Fig. 2. Layout of com-ponents on the tag -strip.

PARTS LIST

ResistorETI 519

3k9 Y2W 5%2R23R 95R6

R5 12RR6 39RR7 56RD1 -D4 Diodes 1N4001 or similarC1 Capacitor 1000mF 35V electrolytic01 Transistor 2N3055T1 Transformer 120V pri 4OVct sec

500mASW1 Two -pole on -off switchSW2 Six -position single -pole rotary switchMetal box, bracket for 2N3055, line cordand plug.

II

single resistor may be used. Its value inohms should be 6000 divided by themA/h rating of the battery. Thenearest 5% nominal value to thatcalculated as above will be adequate.

By virtue of the nature of theconstant current supply any battery,or bank of batteries up to 20 voltsmay be charged. If the 20 voltcapability is not required a differenttransformer may be used as detailed inTable 1.

The transistor dissipates a fairamount of heat and hence should bemounted on a piece of aluminium toact as a heatsink. This piece ofaluminium should be insulated fromthe case, or if not, the transistorshould be mounted on the 3!uminiumvia a mica washer and insulatingbushes.

These Philips DeForest Distributorshave the book"Building Hi-Fi Speaker Systems"

BRITISH COLUMBIAVancouver Cam Gard SupplyVictoria Queale ElectronicsKamloops Cam Gard Supply

ALBERTACalgaryRed DeerEdmonton

Cam Gard SupplyCam Gard SupplyCam Gard Supply

SASKATCHEWANRegina Cam Gard SupplySaskatoon Cam Gard Supply

MANITOBAWinnipeg Cam Gard Supply

Sperling Sales

ONTARIOThunder Bay C & F Electronics

Inter Comm SupplySault Ste. Marie Carsall IndustriesSudbury Sonic Northern

Westbume Industrial EnterprisesJohnson Electrical SupplyJohnson Electrical SupplyWestbume Industrial EnterprisesWaterloo ElectronicsC.M. PetersonC.M. PetersonC.M. PetersonProvincial ElectronicsC.M. PetersonWestbume Industrial Enterprises

St. Catharines Hunson SupplyHamilton Care Electronics

C.M. PetersonP.B. ElectronicsWestburne Industrial EnterprisesArcade Sound SystemsDavies and PetersonDominion RadioElectro Sonic SupplyFairview ElectronicsGladstone ElectronicsTeltronicsWestburne Industrial Enterprises

Oshawa Davies and PetersonWestbume Industrial EnterprisesWestbume Industrial EnterprisesBleeker RadioWackid Radio

TimminsNorth BayBarrieWaterlooWindsorSarniaLondon

Kitchener

OakvilleToronto

KingstonOttawa

QUEBECMontreal Addison TV

Payette Radio

NEW BRUNSWICKSaint John Cam Gard SupplyFredericton Cam Gard SupplyMoncton Cam Gard Supply

NOVA SCOTIAHalifax Cam Gard Supply

PHILIPS

talk PHILIPS44 ETI CANADA - MAY 1977

6th Edition, 232 PagesSuggested Retail Price $695

New from PhilipsThe definitive work on speaker enclosure design and constructionSince its first publication in1969, "Building Hi-Fi SpeakerSystems" has become a classicin its field.

And now in a completely updatedsixth edition, it includes seventeennew enclosure designs and the

theories behind them.These enclo-sures -which are designed forPhilips DeForest quality speakers -can be built by anyone who hasbasic cabinetry skills.

Also included are curve chartsdefining frequency response and

distortion, energy response, livingroom response, impedance andcrossover characteristics for eachenclosure.

This book is a definite must foranyone who wants a superior soundsystem at less cost.

Available only from Philips DeForest distributors and dealers (see list on opposite page).

PHILIPS ElectronPHILIPS Electron

Division PHILIPS

PUBLICATIONSrFROM EllinFROM THE PUBLISHERS OF

ELECTRONICS TODAY INTERNATIONAL

ETI

CIRCUITS

Not

$5.00 £1.50 $2.50

from the pahshers o1 electronics today international

Take the mysteryout of electronics withthis straightforwardlogical course

CIRCUITS No.1:A brand new concept from the house of ETImore than 100 pages packed with a widerange of experimenters circuits. Based onthe 'Tech Tips' section carried in the over-seas editions of ETI, Circuits 1 is the first ofa series of specials - produced for the enthu-siasts who know what they want, but lotwhere to get it! Circuits 1 will also act as acatalyst for further development of ideas,ideal for the experimenter. The collection ofmore than 200 circuits is complemented bya comprehensive index, making searches fora particular circuit quick qnd simple. Also,similar circuits can be compared easily, dueto the logical layout and grouping usedthroughout. Last and by no means least, Cir-cuits 1 has no distracting advertisements inthe main section!

TOP PROJECTS No. 4:A collection of 28 constructional projectsreprinted from ETI. This is the fourth in aseries published by the British edition (Nos.1,2, and 3 are not available). Projects arecomplete and include: Sweet Sixteen SteeoAmp, Waa-Waa, Audio Level Meter, Expa id-er/Compressor, Car Anti -Theft Alarm, Head-light Reminder, Dual -Tracking Power Sip -ply, Audio Millivoltmeter, ThermocoupleMeter, Intruder Alarm, Touch Switch, Push -Button Dimmer, Exposure Meter, PhotoTimer, Electronic Dice, High Power Beacon,Temperature Controller, Electronic One -Armed Bandit plus many more.

$5.00 FOR CIRCUITS No. 1$2.50 FOR TOP PROJECTS No. 4

ELECTRONICS - IT'S EASY:Volumes 1 and two of the best introductoryseries to electronics ever published in a mag-azine. Volume three, completing the series,will be available in a few months.

Electronics - It's Easy! takes a fresh lookat electronics: it avoids the usual introd.jc-tions to the subject which mostly seem des-igned to frighten you away before you reachpage 10!

Volume one leads the raw beginner froma gentle introduction, explaining circuits in'black -box' form up to the use of operation-al amplifiers.

Volume two deals with more advancedtechniques, and deals with digital and logiccircuits.

These books have sold extremely well inAustralia and in Britain. In Holland theyform the basis for a correspondence course.

$6.00 FOR BOTH,$3.50 INDIVIDUALLY

WA A WAA. SIMPLE CMOS MYERHI Fl AMP 8W 8W, CAR ALARMDICE. AUDIO MILLIVOLTPUSH BUTTONE

TRACKING P.S.U.RUDER ALARM, PHOTO TIMER

CAR AMP. EMERGENCY BEACONARM BANDIT. LOGIC PROBE

URTESY LIGHT EXTENDERD4..IGHT REMINDER. TOUCHTCH. FLASH TRIGGER, BASIC

ER SUPPLY CAR FLASHERURE METER. TEMPERATURE

LLERS. THERMOCOUPLECERAMIC CARTRI

electronicsVokane 2 .4t's easyfrom the ottitshers or electronics today internatmal

THESE PUBLICATIONS ARE AT PRESENT ONLY AVAILABLE FROM ETI

Send your orders. with payment (not cash), toETI PUBLICATIONS

Electronics Today InternationalUnit Six

25 Overlea BoulevardToronto, Ontario

M4H 181Please specify which publications you require. and print your name and aidress clearly.


SHORT CIRCUITS-

BENCH SUPPLYA NEW COMPONENT from Fairchildmakes this power supply much simplerthan other designs of similar capa-bility. The 78MGT2C is a long title, infact written in our type, the name islonger than the device!

The meter should be looked uponas an optional 'luxury' extra. Thedesign will function perfectly withoutit, and will be very much cheaper toconstruct. Use a decent pot, and cali-brate it.

CONSTRUCTIONPhysically the most difficult part ofconstruction will undoubtedly proveto be drilling the case. Mount all thecomponents to the PCB as shown inthe overlay, noting that BR1 and C1are mounted onto T1, not the board.

The short circuit protection resistorR2 is specified as OR5 (1/2 ohm) at 5W.You could use two 1R in parallel(at 2.5W each) if you have troubleobtaining the component.

Q2, the output series pass trans-istor, must be isolated from the casewhich functions as its heatsink. Alsoensure the connections to C1 do notshort to the case while you're at it!The heatsinks for IC1 can be bent toany convenient shape or size, the mini-mum size for which may be taken tobe that which we used! There is no DC(output) fuse, as the IC can look afteritself better than any fuse!

\\\ D C VOLTS

CONTROL

ETI PSU

111111

Y'Vfaof 011

lioW it worksWhat can we say? ICI does all the work.Cl is provided to smooth out the fullwave rectified DC from BR1. The volt-age at the output pin 2 of ICI is variedby varying the control voltage applied topin 3.

Q2 is used to enable more current tobe drawn than IC1 could provide.Unaided, it could supply 500mA. In thiscircuit loads can draw in ecess of 1.5A

max

without the supply shutting down.Should the dissipation of the chipexceed safe limits, the output will belimited.

Short circuit protection for the seriespass transistor is prcvided by R2 and Ql.C2 and C3 provide input and output by-passing, and their retention is recom-mended to ensure stability in all possiblecorditions.

Circuit diagram of the Bench Sipply


-Short Circuits02 'I)"

R1

T

Ve (+VeIOUTPUT

TO M1 ANDOUTPUT

SOCKETS

Q2 'e'

-4 R2,i 1-

+R2I) I-*SEE TEXT

HEAT SINK(SEE DETAIL 'X')

021 I

R3

RV1 CHASSIS

+Ve INPUTFROM

-Ve T1, BR1,C1

Component Overlay

rn

Oilpik)4rit. 0

0: Le 0

PCB Foil Pattern (full size)

78MGT2C

0 02 3

1) IN2) OUT3) CONTROL4) COMM

ALSO HEAT SINKTABS ARE COMM.

Parts List

RESISTORSR1 5R6 1WR2 OR5 5W (SEE TEXT)R3 4k7 YAN

CAPACITORSC1 2,200u 50V electrolyticC2 220n polyesterC3 100n polyester

SEMICONDUCTORSQ1 2N2905 or similarQ2 TIP 32A or similarIC1 uA78MG T2C

(positive voltage regulator)BR 1 200V 1.6A Bridge Rectifier

POTENTIOMETERRV1 25k Lin. rotary

SWITCHSW1 Off/On rocker type 3A 120V

METERM1 0-25V DC panel type

TRANSFORMERT1 117V - 24V 2A type

MISCELLANEOUSKnob, insulating kit for Q2, fuse holder,fuse, 4mm. red and black sockets, grommet,P.C.B. pillars, nuts, bolts, etc, neon.

FUZZ BOXSTRANGE AS IT SOUNDS, by far themost popular and sought after effectthese days is distortion. More fuzzboxes have been constructed andpurchased than any other of themyriad types of guitar 'modifiers' onthe market.

Although the aim is basically verysimple, some very high prices arebeing asked, which would tend tomake one think (or hope!) that thereis more to the principle than meets thesoldering -iron. We've kept ourssimple: the total cost including boardand case should be approximately$13.00.

CONSTRUCTIONThe stereo jack SK2 is used to

switch the unit on and off; when amono jack is inserted it shorts twocontacts, and completes the supplycircuit. The battery specified48

Care has been taken inthe mechanical designThe bypass switch andboth level and fuzz controls can be foot -oper-ated whilst playing. RV2can be set so level atfuzz and bypass areequal, however it can beused with RV1 to extendthe range of effectspossible.

LEVEL

OUT

FUZZ

Transistors Q1 and Q2 amplify theincoming signal, and the gain is such thatthe input will 'overload' when used withan electric guitar. RVI adjusts theamount of feedback present, and hencevoltage gain.

The output is therefore a 'squared'version of the input signal, the amountof 'squaring' being variable by RV1.

Parts ListRESISTORSR1

R2R3R4R5

All %W 5%39k100k680R5k656R

CAPACITORSC1 10u 16V electrolyticC2 100u 16V electrolyticC3 47n ceramicC4 47u 16V electrolytic

SEMICONDUCTORSQ1,2 2N2222

POTENTIOMETERSRV1 1k Lin. rotaryRV2 100k Log. rotary

SWITCHSW1a,b

SOCKETSSK1SK2

Double pole, doublethrow, push on/push off,footswitch .

Mono Y." jack socketStereo '4" jack socket

CASE6" x 4" x 2" approx. Metal type

MISCELLANEOUS2 large knobs, battery, battery clip,screened wire, P.C. board pillars, nuts,bolts, etc., P.C. board as shown.

noloV TO BATTERY 91

RV2LEVEL

Ikei 4

CT oe-rt

2)01 CI

Cornpotient Overlay

Ar

4

01c 1 2N222210

INPUT11-101/.'0111

101.

4.16

R556T

R4

100k

C347,,

1)02100k

CF

022N2222

11V1k

E1177

61,0

C2100

IV?

3

2

3 S,

1011 TPI1T

TOOK

son rcliEn ON clY SK2 CONTACTSISEE TEXT)

Circuit Diagram

should last a long, long time, ascurrent drain is quite small. Usescreened wire where shown on thecircuit; to link SW1 and the output,and the 'bypass' signal with theoutput.

This switch, SW1, not only switchesthe signal through the circuit, but alsotakes the output from RV2 to ground

when in the 'non -fuzz' position,preventing breakthrough of thedistorted signal onto the line.

Assemble the PCB in the usualmanner; watch the orientation of thetransistors lest you get a 'fuzzed' junc-tion. Take the case of RV2 to the'ground' side of the pot.


A favorite pastime of Canadian electronics enthusiasts is todrool over the American magazines, lapping up the ads forjust about anything, for just about nothing. An initial burstof enthusiasm to get started on a pet project is oftentempered by caution at the thought of buying from so faraway, and the hobbyist is discouraged before reaching thepost office for a money order.

There are, unbeknownst to many, quite a fewCanadian distributors and mail order operations of varioussizes. Their advertisements, in the past, have not had amedium through which to reach a wide market, but wehope that ETI will change this situation.

When checking component availability, we at ETImake use of a number of catalogues from these mail ordercompanies, and as a service to all concerned we present herea review of those we have. We feel that as an aid to projectcompletion, a well stocked library of catalogues is just asuseful as a soldering iron or screwdriver. Whether one livesin a major city, with handy distributors, or far from a partssource, a catalogue is a guide to what parts are available, atwhat cost, and frequently provides needed data and specs.

Some companies make a charge for their catalogue, butthey are far from making a profit on it, and for the timesaved, the reader is making a good investment. Also, somecatalogues contain coupons applicable to purchases,encouraging the reader to save money.

Our review indicates what each catalogue contains, arough idea of how much, and some out of the ordinaryfeatures we have found useful. It should be noted that whatis in a catalogue is not necessarily the complete stock ofthat company. This is especially true in the case of ICs andother semiconductors, where the market changes so rapidlythat catalogues have difficulty keeping up. We try toindicate this where possible.

Different styles of catalogues are published withdifferent readers in mind. The first three catalogues arechiefly for industrial use, providing extensive data, includ-ing mechanical and electrical specs on an enormous varietyof items. They are useful for weight lifting practice andsubmarine ballast also. At the other end of the scale are"pocket portables" that are little more than price lists,for the reader who knows exactly what to buy.

A SURVEY OFCATALOGUES FROM

MAIL ORDERCOMPONENT

SUPPLIERS

[i]

Electro Sonic Inc.,1100 Gordon Baker Rd.,

Willowdale, OntarioM2H 3B3

electricalelects'

!echoelectroelectronicale nic

lo tr onicle trosonic

electro sonicElectro Sonic's most recent catalogue at the time of writingis five years old, and is reportedly about to be replaced by anew version. The old one is no longer available from thedistributor, but is reviewed as it is still used by manycompanies, and may be held at a local library. The exten-sive data includes mechanical and electrical specs, plusapplications information, formulae, and illustrative photosand line drawings. Electro Sonic also carries a large stock ofsemiconductors (including ICs) and tubes not listed. Thiscatalogue has been updated periodically with 'Educational'and 'Industrial' newsletters, announcing new items, andrevising the pricing.

CESCO Electronics Ltd.,Head Office:

4050 Jean Talon St. W.,Montreal, P.Q.

Also Toronto, Ottawa, Quebec A WORLD Of

[ETHNICS

CESCO's catalogue contains the most comprehensivecollection of data on ICs and other semiconductors, makingit an invaluable reference. Again the style is similar to thatdescribed for Electro Sonic. Coverage of other areas is alsoquite extensive, as would be expected of an industrialcatalogue. It is up-to-date, both with respect to specs, andalso prices. Thus gives the reader a good idea of all designparameters.

Saynor Electronics Limited,99 Scarsdale Rd.,

Don Mills, OntarioM3B 2R4

SAYMOR ELECTROMICSUMITED

Saynor has avoided ICs but has a large selection of ICsockets and PC board supplies, and components in almostevery other field in connection (no pun) with electronics.Much the same presentation as Electro Sonic's catalogue,but data and prices are more up-to-date.

J & J Electronics Ltd.,310 Notre Dame Ave.,

Winnipeg, ManitobaR3B 1P4

1976

J.& J.

The catalogue from J & J Electronics shows a definiteorientation toward the hobbyist market, both in range ofproducts and product description. Less data is provided,but this may be an asset for some, since essential data doesnot become confused with frequently unimportant details.In addition to their 76 and 77 catalogues, J & J has (have?)published other flyers and useful pamphlets such as their'An Introduction To CMOS'.

50 ETI CANADA - MAY 197/

BUYERS GUIDEGladstone Electronic Supply Co. Ltd.,

1736 Avenue Rd.,Toronto, Ontario

M3M 3Y7

Our review of Gladstone's published works is based upontheir 75 and 76-77 catalogues, plus flyers. The cataloguesare strong in the areas of stereo equipment, andcomponents oriented toward the tube TV service business.The selection includes 'bargain' parts 'paks', and also a

comprehensive line of kits from Amtron. Illustrations andtext descriptions for most items.

Future Electronics Corp.,5647 Ferrier St.,

Montreal P.Q.H4P 2K5

Also Toronto

Future's 77 pocket size catalogue provides a concise, clearlist of their large selection of semiconductors (specialty ofthe house) with one line IC descriptions, and essential dataon the discretes. An unusual section is devoted to RFWattmeters and accessories.

This company has over-the-counter facilities in Montrealand Toronto under the name Active Electronics Corp.

Radio Shack, Head Offices:3999 Philips Ave.,

Burnaby, B.C. V5A 3K4P. 0. Box 34000, Barrie,

Ontario L4M 4W58092 South Service Rd.,

Trans -Canada HWY,St -Laurent, P.O. H4S 1M5

Probably the most colourful of our assortment, the RadioShack catalogue is approximately one third audioequipment, one quarter CB and car audio, and thi:remainder components, tools and equipment for thehobbyist. The catalogue lists almost the entire contents ofmost Radio Shack stores, which includes a supply of themore popular items. One of Radio Shack's chief merits isthat with over 525 Canadian stores they are all over every-where.

Coronet Electronics Supply Ltd.,649A Notre Dame St. W.,

Montreal, P.Q.H3C 1 H8

Sorry, no front cover shot for this catalogue - we didn'tthink it would reproduce too well. Unfortunately, this isr-tpresentative of the inside as well. It is a shame that whatis probably a good collection of parts is obscured bypoor production. Perhaps Coronet could be persuaded toexpend a little more effort in this direction. As for theproducts themselves, mary of the most needed items areavailable, including Exar's line of ICs and CSC's bread-boarding and related products.

Dominion Radio & Electronics Co.,535 Yonge St.,

Toronto, OntarioM4Y 1Y5

Dominion Radio's catalogue appeared in the last Tissue ofETI, so many readers will be able to judge for themselves. Agood assortment of components is offered, though low inthe IC department. We could list numerous useful orunusual items, but see their ads in this issue instead.

ETCO,183G Hymus Blvd.,

Pointe Claire, P.Q.In9R 1E9

Also Montreal

$1,141201 ILI 1 0121111111! Int!

Here we find the most diverse assortment of new andsurplus items. The style is '20th century Poly Paks', hencethe reader has quite a time browsing through the mixture ofcomponents and equipment. The only organized sectionsare those noted in the chart. Other items include motors,power supplies, radiation survey meters, parabolic mikes,etc.. The reader may be interested in the dials and knobsoffered, often difficult to find.

Chips,P. 0. Box 1030,

Oakville, Ontario,L6J 5E9

We have just received a flyer from these people whichcovers assorted components of general interest, plus detailsof a couple of kits they are preparing. It would be difficultto call this one a catalogue, but perhaps in a few years...


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THE ABOVE CHART

shows the list of com

pany names, versus their

catalogue contents in major areas of hobbyist interest. T

he cataloguesare listed

in approximate order of decreasing w

eight, with H

eathkitlisted separately as their catalogue covers a slightly different field.

We have given a subjective rating to each section, based on how

use-ful each w

ould be, hence H=

heavy, M=

medium

, L=light use. A

section

was judged useful if

it contained a large number of item

s (good sel-ection) and also if it had a large am

ount of data (useful as a reference).A

n idea of the average volume of data presented throughout is also

shown, along w

ith an indication of whether the catalogue

lists new

and/or surplus components.

(1).;.,

,...,,,..IMt 11: II IIII li

CANMOS Electronics,Box 1690,

Peterborough, OntarioK9J 7S4

EILECTFOVICS EIECfRONI,a real,'

Trintronics Limited, MALL ORDER Ca' et -

P. 0. Box 181, SStation G,Torontot Ontario,

M4M 3G7aCIALOGOE

.......

A clean and sharply produced catalogue is this, with well -organized layout of a modest selection of most needed A modest production, but well laid out: easy to read anditems. CSC products and some Hammond cabinetry. This find what you want. A minimum description of most partscompany also provides PC boards for many ETI projects, is sufficient to avoid mistakes, but not enough data foralthough these are not listed in the catalogue. actual design and selection. Exar's ICs are included.

p MUM.Heathkit:

Supreme Electronics Inc., 1,-#,.., r am, ts: Heath Schlumberger, E..iPRODUCTP. 0. Box 327, 1480 Dundas Street E.,.al

, ,,---.

Victoria, B.C. GUIDE Mississauga, Ontario ,_

,..,

V8W 2N2 L4X 2R7 r = 6 . -. _ ,

- Also Montreal, Ottawa, Winnipeg,Edmonton, Vancouver

.

A handy assortment of ICs and semiconductors appears in This catalogue does not really cover the same field as thethis publication. Descriptions and illustrations with most others, but we felt we should include it for completeness. Itof the products. Of special interest are the CSC line, EICO is a guide to a large line of kits including quality audiohome security products, and a line of equipment coolingfans.

equipment, ham gear, radio control, test equipment, andloads more.

High Performance Dry Batteries

DRY BATTERIES

FORTrans.110r Rattan

'C'ro,7:"Pe UM.1A.ID-CELL)

18'Photoflasheshlearmg tfocls

''::ho'h'go",::E

126

UM -3A (AA -CELL)

General PureObe

UM -2A- (C -CELL)

116

006P (Flat 9 Volt)336

-4(

RECHARGEABLE BATTERIES

NICKEL CADMIUM

AP&

D Cells -

C Cells -

AA Cells -

006P -9 Volt -

006P with charger -

'8C1 Battery Charger -

57.95 per pair

57.95 per pair

57.75 per pair

513.95 each

519.95 each

$16.95

'Chargers D,C, & AA cells up to 4 at the same time

DOMINION RADIO & ELECTRONICS COMPANYTHE HOME OF RADIO & ELECTRONIC SUPPLIES

535 YONGE STREET, TORONTO, ONTARIO. M4Y-1Y5


STEREO RUMBLEFILTER

This internal view shows how the rumble filter is assembled.

Active filter designimproves clarity ofbass reproduction.

C10.1?pF

C2 C30.039p F 0.039p F

1--IR247k

INPUTR156k

IN BYGONE DAYS rumble filterswere very popular because even thebest of turntables, used then,generated considerable vibration dueto bearing and motor deficiences.These vibrations, mechanically

R3470k

Q1

2N2586

C40.47u F

R4 R51M 12k

R612k

+3V

OUTPUT

OV

transmitted to the pickup cartridge,resulted in an audible output. Hencehigh-pass filters were oftenincorporated in amplifiers to reducethis objectionable rumbling sound toan acceptable level, and as bassresponse seldom extended below. 50Hz, a simple RC filter with 6 dB peroctave roll -off below 50 Hz wasconsidered adequate.

Modern turntables have far smootherbearing and drive arrangements thantheir early counterparts - and for thisreason many ampiifier manufacturersno longer include a rumble filterfacility.Those that do are rarely satisfactory.

Their slope is generally inadequate andthe main effect of switching them in isto roll off the low -frequency responseto the detriment of programmecontent.

At first sight it would seem better toexclude the rumble filter altogetherand just make sure that our turntablesdo not generate any appreciablerumble.

Surprisingly perhaps, a rumble filteris still very much required and ifdesigned correctly can make anappreciable improvement toreproduction - even when used withturntables that generate no rumble atall!

The reason why will be clearlyapparent if you take the front grille

Fig. 1. Circuit diagram of therumble filter. Two required forstereo.

54

Fig. 2. Printed circuit boardlayout for the rumble filter40mm x 70mm.


off one of your speakers and - withthe phono-cartridge tracing a sectionof record that has no recorded content(or very low level content) - turn thevolume control up fairly high. Youwill almost certainly find that the coneof the bass driver is making wildexcursions to and fro, probably atfrequencies between 5 Hz and 15 Hz.

So it's sub -audible - why then doesit matter?

Well it really does - and we'llexplain just why later in this article-but first let us consider just where this5 Hz - 15 Hz content comes from.

Firstly, modern turntables and armshave mechanical resonances lyingwithin the 5-15 Hz region. Secondly,stereo cartridges are sensitive in thevertical as well as horizontal planesand will respond to uneveness inrecord or turntable surfaces. They willalso respond to a defect in the recordsurface known as pressing rumble.

In addition the noise finds its wayonto the record during the actualrecording process. This recorded noiseis due to LF noise and rumblesometimes being induced in therecording lathe by seismicdisturbances, and by vibration in drivegears and cutting head carriage rails.

Lastly vibration of a low frequencynature, due to people walking past theturntable or vehicles passing byoutside, may well excite the turntableand arm resonances even though theturntable is reasonably well sprung.

WHY SUB -AUDIO

NOISE MATTERSThis very low -frequency noise is

responsible for a remarkable amountof intermodulation distortion whichgenerally makes the bass soundmuddy. In extreme cases it may causethe reproduction to sound as ifspeaker cone break-up is occurring. Thereasons for this are as follows.Preamplifier stages usually have two

or three transistors around which largenegative feedback is applied forequalization and/or tone control. Atsub -audio frequencies these feedbacknetworks are not generally effective.Thus the LF signals may well receiveconsiderably more amplification in thepreamplifier than would normally beexpected. Secondly although themagnitude of the LF signal may notitself be sufficient to overload thepreamplifier, the combined LF andmusic signals may well cause thepreamplifier to clip. Even if clippingdoes not occur the LF signal will causeintermodulation distortion despite thefact that the LF signal is inaudible!

Most modern power amplifiers arequite capable of amplifying this noisesignal, presenting it to the loudspeakerat a surprisingly high power level. The

speaker itself has very little acousticloading at these low frequencies andthe cone will thus move considerablyand may even be driven beyond itslinear excursion region. Even if notactually overdriven, the preserce ofsuch large cone excursions willproduce a high level ofintermodulation distortion.Whilst elimination of factors causing

the noise is by far the best procedure,a lot of these factors are completelybeyond the control of the average hi-fiowner. Hence a rumble filter would,seem to be the obvious answer. But,we do not want to sacrifice any lowfrequency response and we wantsignals in the offending 5-15 -Iz regionto be attenuated as far as possible -two apparently conflictingrequirements. In addition, as LF noisecannot be allowed to enter theequalization stages of the preamplifier,

PARTS LISTR1 Resistor 56k 1/4W 5%R2 47kR3 470kR4 1MR5,6 12k

Capacitor 0.12mF polyesterC2,3 " 0.039mF "

" 0.47mFQ1 Transistor 2N2586 or similar

for stereo 2 of each of the above

PC Board2 dual phono sockets2 dual battery holders or one 4 wayholder.4 1.5V batteries.2 8mm long spacers1 small aluminium box.

HOW IT WORKS

The filter consists of three separatesections: -

A passive RC filter consisting ofR 1 and Cl.

2. An active filter comprising C2.3, R2, 3, 4 & 5 and Ql.

3. A passive filter cornpriing. C4and R6.

The active filter (from input of C2to output to C41 is a standard designwith the exception that values havebeen selected to give a peak in theresponse at the cut-off frequency.The maximum lift is about 2 dB andthis characteristic, combined withthose of the two RC filters. gives asharp knee to the rolloff. Thecomposite filter has a. lift of 0.2 dBbefore turning over sharply.

Thus low frequency response ismaintained substantially flat down to50' Hz and is only 2 dB down at 40Hz. Thereafter the response dropsyeti, rapidly and is in excess of 30 dB-down below 15 Hz where most LFnoise occurs.Current drain of the two filters is

only 100 µA and the batteries willlast their normal shelf life of about12 months, thus no power switch isrequired. Batteries should be replaced

1IN U 'LI IN


STEREO RUMBLEFILTER

+2

+1

0

-1

-23

4

-5

-10

-15

-20

FREQUENCY IN HERTZ

20 30 40 50 60 80 100 200 300 400 500

F

S

RST R.

COND

.NETWORK

R.C. NETWORK

r

/OVERALL RES ONSE

-25

ACTIVE FILTER ECTION

NPUT IMPEDANCE

the filter must be situated before thepreamplifier. This also poses problemsas the signals at this point are verylow-level, and there is a danger ofintroducing hum which would be

merely replacing one fault by another.

THE SOLUTIONTo maintain response down to at

least 50 Hz, whilst obtaining 30 dB ormore attenuation to LF noise, wemust use a filter which has a sharpknee and an ultimate attenuation slopeof 24 dB per octave. The mostsatisfactory (and cheapest) method ofdoing this is to use an active high-passfilter - and this is the approach wehave used. To obviate the possibility

200k

190k

180k

170k

160k

150k

140k

130k

120k

110k

100k

90k

80k

70k

60k

50k

40k

30k

20k

10k

20

Fig. 4. Characteristicsof the rumble filter.

of hum -pickup, the unit uses a batterypower supply, one each for left andright channel filters. The use ofseparate batteries prevents ground loopsand ensures that channel separation ismaintained. As current drain is verylow the batteries may be expected tolast their shelf life (12 months or so)and for that reason an on/off switchhas not been included.The unit fits between the turntable

and the amplifier, cuts any frequencybelow 35 Hz and has a totalattenuation of 37 dB at 10 Hzincreasing at 24 dB/octave below that.

CONSTRUCTIONWe built our unit onto a small

SPECIFICATIONInput Impedance

(rises below 50 Hz) 47kOutput ImpedanceInput voltage

(maximum)x i mu m)Cut-off Frequency

(-3dB)Cut-off Slope

(maximum)

at 10 HzGain

at 1 KHz

<5k

250mV

36 Hz

24dB/octave

37 dB

-0.2 dB.

printed circuit board, but layout is notcritical and other alternative methods,such as matrix or Veroboard, may beused successfully.

The signal levels involved areextremely small (about 100 µV at 50Hz) and for this reason a metal box isa must if hum pickup is to beminimized. And, as said before, twoseparate battery supplies should beused in order to avoid earth loops. Weused a conventional four-way batteryholder to hold the two sets ofbatteries. These holders normallyconnect all four_ batteries in series.However it is a simple matter to snipthe connection between the two setsof two cells.

The phono sockets for both input andoutput should be insulated from themetal case. When connecting the unitwe found minimum hum wasintroduced by grounding the turntableto the metal box and then, by taking aseparate ground from the metal box tothe amplifier. However experimentationin the positioning of grounds may wellshow that some other configuration isbest for your particular setup.


Fig. 1. Place the Letrafilm over the diagram.

Easier wayto makeyour ownP. C.

Now you can do away with all thefuss and bother of conventional

printed circuit preparation, says A. J. Lowe

Fig. 2. Trace around the copper areas on the diagram. Mark hole positions and corlers also.

7 It 19 1

7 T

A, last! Here's a quick, cleanmethod of preparing printedcircuit boards for etching - and

it's or the home constructor.Photographic methods are fine if you

want to produce a large number ofidentical boards, but far too slow,expensive and involved for the'one-off' man who simply wants tomake one board - usually from adiagram in a magazine.

The standard method, for theexperimenter, involves the use oftracing paper, carbon paper, and aresist paint. Sure, it works - but thosewho have used it know how hard it isto get narrow clean -edged lines withpaint. Sometimes the paint is thin andporous and lets the etchant through,and sometimes it runs across narrowgaps, leaving short circuits to becleaned up later. Sometimes the paintis thick and hard to manage. Besides, ittakes ages for the paint to dry.

This new method requires no tracingpaper, no carbon paper, no paint, nobrushes, no solvents - and you canhave a printed circuit board ready inan hour or so.

It depends on the use of a cut-outcolour film used in the graphic artsfield, called LETRAFILM. Made bythe manufacturers of the widely -usedLetraset stick -on letters, it isobtainable from artists' shops anddrawing office supply houses.

Letrafilm is a thin sheet of filmavailable in a range of 50 colours,sticky' on one side and matte onthe other. The sticky side is backedwith a translucent paper support. Thematte side can be written or drawnon with ease. The film is quite im-pervious to etchants and so makes


Fig. 3. Separate the Letrafilm from its backing support.

Fig. 4. Place the film down on the copper side of the p.c. board.

Fig. 5. Press the film down gently.

Fig. 6. Cut around the copper areas with a sharp craft knife.

Fig. 7. Remove the unwanted film, leaving film over the areas where copper is to remain

an ideal resist. It is available in sheets10" x 15" and is quite inexpensive.Only a few pence worth will cover thetypical printed circuit board. A lightcolour, such as pale yellow, is ideal forthis application.

Here's how to use it:1) Cut a piece of Letrafilm, complete

with its backing, about 3/8" or solarger all round than the printedcircuit board.

2) Place a sheet of aluminum, orphenolic board, or even printed circuitboard, below the diagram of theprinted circuit. This gives a hardsupport for the next few operations.

3) Lay the Letrafilm over thediagram (see Fig. 1) and hold it downat one side with sticky tape. It will befound that the diagram can be seenquite clearly through the Letrafilm.

4) Trace around the copper (i.e.black) areas in the diagram with apencil. (Fig. 2), making sure that thecorners of the board are marked aswell. The position of holes for thecomponent leads should be markedwith a pencil dot. This is anotheradvantage of this method over the

have to be gauged later.Many diagrams prepared

professionally, using stick -down circlesand lines, have lots of fine curves andindentations where none is reallyrequired. There's no need to followunnecessary detail and it may beeliminated as tracing proceeds.

5) Remove the Letrafilm from thediagram and carefully separate the filmfrom its backing sheet (Fig. 3).

6) Lay the film, sticky side down, onto the thoroughly cleaned coppersurface of the printed circuit board,using the corner marks as a guide (Fig.4).

7) Press the Letrafilm gently downon to the printed circuit board. (Fig.5). Do not press too hard, as this willmake later removal of the unwantedfilm portions unnecessarily difficult.Small air bubbles need not besqueezed out.

8) Cut around the pencilled outlinesof the copper areas with a sharp craftknife (Fig. 6). This process is mucheasier than painting, and quicker -and clean sharp lines are automatic.

Do not, at this stage, do anythingabout the dots marking componentlead hole positions.

9) When cutting is complete,carefully peel away the unwanted film


from the board - that is, the filmwhich does not cover areas wherecopper is required. This is done bygently lifting the film at one cornerand easing it back. It will break as youprogress, but that's no disadvantage(Fig. 7). Watch that none of the'islands' lifts, due to bad cutting alongthe pencil lines. If one does lift, pressit back and cut around it once again.

10) When all the unwanted film hasbeen lifted, lay a sheet of paper overthe board and press down firmly allover it. This bonds the film to thewanted copper so that it acts as aneffective resist (Fig. 8). Make sure thatno air bubbles are near the edge of anisland. In the middle they don'tmatter.

11) Etch the board. This can be donein your usual etching bath. For thosewho have never made a printed circuitboard before, an effective etchingsolution is 4oz. of ferric chloridedissolved in 10oz. of hot water. Thiswill etch a typical board in 20 to 30minutes. Protect your eyes and hands- the solution is corrosive.

12) When etching is complete,remove the board from the etchingbath and wash it clear of etchingsolution under running water. Dry theboard by dabbing it with a rag.

13) With a scriber, mark thepositions of the holes for componentleads by pressing through the film intothe copper (Fig. 9). The pencil dotsalready made (see introduction 4above) give the positions.

14) Remove the remaining Letrafilm.This can be peeled and rubbed off(Fig. 10).

15) Clean away any residual adhesivefrom the film by cleaning the boardwith an abrasive domestic cleaningpowder and, if needed, some steelwool. The board is now clean andready marked for drilling (Fig. 11).

16) To prevent the copper oxidising,it should be sprayed with a specialprinted circuit board lacquer.Alternatively - and much morecheaply - it can be brushed with a

Fig. 8. Press down hard, to bond the remaining film to the board.

Fig. 9. After etching away all unwanted copper, mark hole positions with a scriber.

rosin solution (one lump of rosindissolved in a little methylated spirit).This makes a first-class flux andmaintains the shiny look of the board.Well, there it is - a simple, clean,

efficient and quick method ofdoing -it -yourself and, at the sametime, saving money.

Fig. 10. Remove remaining film from theboard.

Fig. 11. The board, cleaned and ready fordrilling.


eta microfile

Choosing a

MicrocomputerTHE WHOLE HOBBY of micro -computing, or "personal computing" isnow entering a terrific expansionperiod. Over the past year, newmagazines have started, stores haveopened, clubs have been formed andmany people have been introduced tothe idea of owning your owncomputer. These people have beenreading books and magazines, tryingto absorb as much information as theycan in order to select which micro-computer they'll buy to suit their ownneeds.

The trouble is that a computer is afairly expensive item for leisure use.While a family can easily lay out severalthousand dollars on a camper or boat,the benefits are enjoyed by severalpeople for years. On the other hand, acomputer plus peripherals can easilycost as much, but is generally a purelypersonal investment.

This means that if you're planningbuying a computer, and you're new tocomputers, you want to get it right.Here's a few hints:

PSYCHOLOGYThe problem of convincing the family(ie, usually your wife), that a computeris useful for doing householdaccounting, that it's great for teachingthe kids arithmetic, and that these TVgames pale into insignificance besideStar Trek or Wumpus is a tricky oneand is best left to you (you know yourwife better than I do, honest!). Try tokeep the conversation off yourprevious attempts at ham radio, beermaking, astronomy, woodworking etc,the remains of which almost fill thebasement. Read all the magazines, andpoint out all the articles on domesticand useful applications of computers.Don't get enthusiastic about them all;

By Rick Smith

111

(Computermaster Systems, Toronto)

The Microkit 816 can incorporate either an 8080 or 6800 processor. Available softwareincludes an excellent text editor.

she knows perfectly well that you'llnever manage more than a few.

If you're lucky she may be one ofthose people (like you) who aremesmerized by computers; if so, a jointvisit to your friendly neighbourhoodcomputer store to see a few demosystems may do the trick, after pre -warning the proprietor not to discussprices of course.

If you are a youngster, and anticipateparental opposition, use the"computers as a career" trick. Visityour book store and buy someacademic -looking volumes of com-puter science and also investigatecollege courses. Leave books andcollege syllabuses (syllabi?) scatteredaround and see what happens. (Thechances are that if you're keen enough


to want to own your own computer,you ought seriously to consider it as acareer anyway.) Avoid references toprevious large investments in motor-bikes, hockey gear etc.

Once you have your computerworking, your first job is to make it dosomething impressive or useful andmake sure everyone knows about it -like teaching the kids arithmetic. Thisis the first step towards breaking downopposition to that new floppy disk -i.e. if you don't live up to at least someof your earlier promises you have nochance later.

Finally, after reading this, tear outthe page and burn it in case your dearlady mistakes it for a real cookbook.We'll both feel a lot safer that way!

BACKGROUNDAssuming that you've gotten over thathurdle and also that you've got thenecessary pieces of paper, i.e. dollars,what do you do now? That depends onhow much you know and what youwant to do. Let's deal with both thesepoints in turn.

If you're a complete novice, thendefer buying a computer for a whileuntil you know enough to make a wisechoice of machine. The only exceptionI would make to this is if you areabsolutely loaded with money, inwhich case I would say; Buy everythingthe salesman shows you and then learnby doing. Seriously, if you are in thisfortunate position an lmsai/Altair with1K memory will let you learn the basicsof microprocessor/computer oper-ation and provide the basis of almostany application -tailored system.

Unfortunately most of us have towatch those pennies to a greater orlesser extent, and so we trade offpotential against cost. The general rulewith all things is that you get what youpay for, and microcomputers are noexception. Unfortunately, micropro-cessors being as complex and versatileas they are, the ingenuity of the

The Cromemco "Bytesaver- is used to store programs in the form of EPROMs. It includes

a PROM programmer and software for driving it.

designer can make small, low-costsystems do things that larger moreexpensive systems can't do. But this isoften at the expense of some otherfacility, or more often expandability inthe sense of freedom to configure thesystem the way you need. Many singleboard computers fall into this category- they were designed with the ideathat most applications would use thatone board plus perhaps some interfaceelectronics; unfortunately hobbyistsdon't work that way. They usually wantto keep adding memory and peri-pherals, and with the single boardcomputer this usually means rippingmemory and peripheral interfaces offthis card to reduce it to only a basicCPU. It may be cheaper to buy anordinary CPU board in the first place.

We've said that you don't want toblow your cash on some nine -daywonder that will be obsolete by thetime you've built it. This is not a greatproblem in practice. Most manu-facturers realize that this thoughtoccurs to potential purchasers, and sothey endeavour to provide options fortheir own systems such as high levellanguages (usually BASIC), peri-

The MicroCyber 1000 above is an expanded version of thepopular 6502 Kim single board computer. The Z-80 based CPUcard by Cromemco on the right will instantly upgrade any 8080system (almost). Advantages include a vastly expandedinstruction set and higher speed.

pherals such as printers, videoterminals and cassette interfaces. Ifyou have sufficient memory and a fewperipherals plus BASIC, you can havean awful lot of fun even with the mostnon-standard system in the world.

FLEXIBILITYThis is a very important point for thebeginner who may not know exactlywhat he wants to do with his system. Ifyou want to try various applicationsand especially if you're not very hot onhardware, then the Altair/Imsai/S100bus is the way to go, almost certainly. Agreat number of companies areoffering plug-in boards and peri-pherals for computers using thissystem. Examples are: plug-in videodisplay terminals, floppy disk con-trollers, various cassette interfaces,serial and/or parallel interfaces,floating-point arithmetic boards,colour graphics boards, videodigitizers, PROM programmers,speech synthesizers, music synthe-sizers, front panels, upgraded CPU's,AC power controllers, blank wire -wrapcards - the list goes on and on. Thesecards will, in theory, work with any


S100 system; in practice there may beminor problems with some of the morespecialized boards, but only minormods are usually needed.

Bear in mind that S100 -basedsystems are often more expensive -the basic price quoted for mostcomputers in this class is for the case,PSU, CPU card and front panel only.You still have to buy some memory toget it to work at all and in order to doanything interesting you'll need a lot ofmemory, a video display terminal and acassette interface plus BASIC. AtCanadian prices, you are now in theregion of $1,500 - an Imsai 8080 is$900.00 basic.

If you know your interests lie in thesoftware domain only, then theproblem is simpler - slightly. You'remain requirement is for memory bothin RAM form, and also backup storagein the form of cassettes or, in thefuture, perhaps floppy disk. You mayalso want a line printer in addition to avideo display terminal. Many systemsoffer these in addition to the S100setups. Southwest Technical ProductsCo., for instance, have a nice 6800based system which satisfies theserequirements and many other systemswhich are comparatively new, anddon't have many hardware -compatibleextras, are able to support a lot ofmemory and the basic peripherals aprogramming type needs.

The best way to gain knowledge ofthis thorny topic is to read every articleyou can get your hands on and betterstill, to talk to other computer users atclub meetings. For a variety of reasonsmagazine writers always avoid bothlavishing praise on a system and moreimportantly, making harshly criticalstatements about a particular model,since mistakes do happen and a

company's reputation could beunjustly ruined. An individual at a club,however, can talk individually abouthis own experiences with his system

The Matrox ALT -256 is a 256 X 256 high resolution graphics generator for the S-100 bus.S395.00 and a 2-4 week wait will bring you this machine from Matrox Electronic Systems.P.O. Box 56. Ahuntsic Stn., Montreal, Quebec, H3L 3N5.

The E & L MMD-1 is shown here with its optional "piggy -back" board which incorporates acassette interface and extra memory.

Matrox's MT X-1632 4K video RAM (above) is specially designedfor incorporation into video display terminals. Cromemco'sDazzler colour TV interface on the right is excellent forexperimenting with computer art.


The Infinite UC1800 kit in exploded form.

Cromemco's D -7A I 0 board simplifies games applications enormously.

E & L Micro Designer is used in the "Bugbooks".

and usually knows the pitfalls involved.Store operators are usually helpful aswell bearing in mind of course thatthey want to sell their products.

In short, if you forsee expandingyour system in various directions in thefuture, the S100 bus of Altair/lmsai/Polymorphic and the rest is the bestand will be around for a long time. Ifyou are sure of your requirements,then you may be able to cut costs andcome up with a better system, bychoosing a different machine such asSWTPC, Wavemate, OSI, etc.

SOFTWAREHere's another thorny subject. Again,the 8080 based machines such as theImsai and Altair are out in frontbecause there's just so much softwareavalable. The only machine -specificparts of any program are theInput/Output routines which are for aspecific interface device at a particularaddress. However, most I/O boardsuse the same serial interface chips, andcan be located at any address, so thatthe I/O routines will work. If there arespecific problems, the I/O routines canoften be patched or re -written to suityour system.

The major piece of softwaredesirable for your system is a BASICinterpreter. BASIC is a high-levellanguage (Beginner's All-purposeSymbolic whichenables you to write programs quicklyand simply in something like theEnglish language. It has statementslike FOR N = 1 TO 20, I = I+N*N, NEXTN, PRINT I which are easy to learn.Computer games are almost alwayswritten and published (hint, hint!) inBASIC. A BASIC interpreter is theprogram which generates the machinecode instructions that actually executethe BASIC statements. A typicalBASIC interpreter is 6-8K bytes inlength and you always buy it from yourcomputer store, never write oneyourself unless a) you think you canmake money from it (it has to be good)and b) you don't mind being acandidate for the funny farm after-wards. People who write interpreterslive in a strange world of linear hashes,symbol tables and thunks (?) wayabove us lesser mortals who can barelywrite programs to add two and two.

COMMERCIAL SOFTWARESoftware holds the key to the successof many systems. Processor Tech-nology for example, appear to bechasing after the high-level softwareand games fans with their Sol -20system. The Sol is backed up withseveral versions of BASIC, plusFOCAL (a calculator -type languageoriginally developed for DEC's PDP8)as well as math programs and games.


Other high level languages can beexpected to appear; in fact FORTRANand COBOL are rumoured to beavailable, though as they are intendedfor commercial uses, they areexpensive.

An interesting variation used byprofessionals developing micro-computer based products is PL/M,Intel's special implementation of PL/1for microprocessor development. BothMotorola and National Semiconductorhave similar languages for theirmicroprocessors while RCA useFORTH, a language specially suited totake advantage of their CDP 1802'smultiple stacks. These special versionsof PL/1 have special capabilities toenable the programmer to writesections of assembly language andembed these into the PL/M program.Unfortunately, these languages are a)too expensive and b) not practical inmemory requirements for thehobbyist.

If your interests lie in electroniccontrol systems or you have specialinterface and I/O requirements beprepared to write some assemblylanguage. This is a convenient form ofmachine code in which each statementis a direct instruction to the processor,compared with BASIC's LET Z1 =

5*N+SIN x /5 type of statement whichmay invoke several hundred bytes ofmachine code in its execution. Mostcomputers are supplied withassembler programs which convertassembly language to machine codewhich x.:an then be run. Check thiscarefully - assembly language is avery useful capability.

GOING IT ALONEAs we have said, various S100compatible cards are available,including processors, memory andI/O, and now you can buy completefront panels and the mother boardsthat they all plug into. So what's to stopyou buying these separately, in kitform, building a power supply andputting your own design together?Nothing, if you have the skills andexperience to do it. But really youcouldn't have acquired that experiencewithout first building a similar 8080,S100 based computer. The advantagesof a home-brew computer are: 1) youknow the design intimately 2) you'llprobably save money 3) you canmodify it greatly without knocking theresale value down. Disadvantages: 1)You'll find no-one able to help directlywhen the going gets tough. 2)Documentation standards will be low,3) you'll miss out on software support,user groups etc. 4) Cosmetics andmechanical design will probably be

ropey.If you know you can do it, go ahead

- if you think you can, hold fire untilyou know you can. Of course, we don'twant to discourage you, but thinkabout what you're letting yourself infor. If you stick with well-known kitsand select wisely without modifying,you shouldn't have too much trouble,but as soon as you try anything likealtering the bus definition slightly, thenyou could be in it up to your neck.

KIT BUILDINGAssuming that you decide to buy anlmsai or Sol or Polymorphic orwhatever, should you buy it assembledor in kit form? The answer, for mostreaders of this magazine, is to buy a kit.If you're reading ETI you've probablybuilt a few projects before, some ofthem at least as complex as theindividual boards of a computer kit.Besides, the difference in price on abasic lmsai 8080 is $300.00! If you haveproblems when building your kit, thestore you bought it from can usuallyhelp out.

On the subject or prices, and buying,don't, whatever you do, delay buying a

Don't be fooled by the prices in USpublications. Import duty and taxesadd considerably to these and if you tryto buy from the States to save you willbe paying all kinds of shipping andhandling charges, charges for filling inCustoms forms, as well as en-countering delays and skirmishes withthat delightful band of Civil Servants,"Customs Canada", who will delight ininspecting your computer piece bypiece, and charging you anything from23.2% to over 50% duty and FederalSales Tax on identical items. It's a lotsimpler to deal with your local store,who will take care of these hassles foryou.

YOU'RE ON YOUR OWNThat's really as much as we can tell youabout buying a microcomputer. Wepurposely haven't done a step-by-stepcomparison of Imsai vs Altair vsSWTPC, simply because a lot of theinformation is available in adver-tisements or from stores, and the restcan be got by asking a few people.Most of the information is probablyirrelevant to your application anyway,and we'd have missed out the vital data

Infinites "UC1800" is the only kit computer using RCA's CDP1802.

computer because of the trends incalculator and watch prices. While it istrue that microprocessor and memorychip prices have fallen dramatically,and will continue to do so, this does notmean that computer prices will fall. Onthe contrary, the silicon in a typicalcomputer is only a small part of thecost - the case, printed circuit boardsand connectors, switches and powersupply account for the bulk of it. Theprices of these components will not godown; they will go up, and this isreflected in recent price hikes by lmsaiand Polymorphic, which the rest of theindustry are expected to follow.

you really needed.Don't get tied up in questions of

processor speed and instruction set.Virtually all of the popular processors(Z-80, 8080, 6800, 6502 etc) are morethan adequate in both areas. Sinceyou're using the system for your ownpleasure only, neither of these is aproblem - doubling processor speedmay halve system reaction time from1/4s to 'As - big deal! The only problemmay be in applications such as high-speed reactive games.

Soak up all the information you can- it's your decision and it's one that'sfun to make.


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tech -tipsTech -Tips is an ideas forum and is not aimed at the beginner.

ETI is prepared to consider circuits or ideas submitted byreaders for this page. All items used will be paid for. Draw-ings should be as clear as possible and the text should prefer.ably be typed. Circuits must not be subject to copyright.Items for consideration should be sent to ETI TECH -TIPS,Electronics. Today International, Unit 6, 25 Overlea Blvd.,Toronto, Ontario, M4H 1B1.

DICl1p

D1

SW2

C21p

A B

C31p

B

C41p

4 CS1p

A 13 -1 +-A- B

C61p

6

A

Cf********0-0SVV1 .9V

SW30

R2390R

3 ID4 ID5

R1 (SEE TEXT)

'FREEZING' SEDUENTIALOSCILLATOR

After switch on, SW3 (a dpdt)is operated and then returned to itsnormal position. This switches off thefirst module, and switches on all theothers via the diodes. A biased switchmay be used.

On the closure of SW2, a number ofLEDs will flash in sequence. On theopening of SW2, the circuit will'freeze' in whatever state it was in, theLED remaining on.

The basic circuit consists of a num-ber of transistor pairs, one for eachLED. They are connected in a 'ring' bycapacitors from the emitter of one pairto the base of the next. The LEDassociated with each pair is driven bythe inverter -driver transistor Q3.

The rate of oscillation is dependenton 81, a value of 10 k gives a rate justfaster than the eye can perceive.

OVO

Q1 is a 2N2604. 02, 03 are 2N2222s. All diodes are 1N4148s.

RANDOM PULSE GENERATOR

The 7413 provides a means of 'squa-ring up' waveforms before applyingthem to logic circuits. A reverse biasedgermanium diode is used to providerandom 'sine -wave' type pulses, i.e.white noise. The output from thewhite noise generator is fed into theinput of the 7413. When the outputfrom the generator attains the value of1.8V, the output goes low and the out-put from the hex inverter goes high.This output is then fed to the counter.By making the output from the whitenoise generator variable, via a potenti-ometer, some degree of control overthe 'randomness' may be obtained.

WHITENOISEGENERATOR

DECADECOUNTER


tech -tips'SNOOZE' DELAY UNIT

I 700 OHMRELAY

imo-- LINE

EQUIPMENT LINE

e

This unit is intended to turn off a pieceof equipment after a predetermined time.The supply voltage is taken from theequipment to be switched and the relaycontacts are wired in parallel with thepower switch on the equipment.

When the equipment is turned on byis own power switch and the 'set' switchis activated, the large electrolyticcapacitor C1 in the delay unit is chargedup via limiting resistor R1. C1 dischargesslowly through R2 and RV1 but whilethe charge is retained above a sufficientlevel, this charge keeps the two transistorsturned on and the relay activated. Theequipment power switch may now beturned off, power being maintainedthrough the relay. When the capacitor isdischarged the relay is released, turningoff the equipment. Delay times areproportional to C1 and R2 + RV1. Timedelays in the order of an hour are possible.

C11 0 On

R11M

PROBE

RV150k

D1

R210k

D2

AUDIBLE LOGIC STATEINDICATOR

7

R41N!

The indicator will work with eitherTTL or CMOS circuits. A useful fea-ture is that the unit can be powered bythe same supply as the one supplying

D4

IC1b

4 / On

D5

D1 -D5 IN4148

ICI is CD4011IC2 is uA746

01, 2 are 2N222203 2N5367

IC1c IC1d

R62M2

the circuit under test. Logic state 1 atthe probe will produce an audible toneon the loudspeaker. A switching signalat the probe also activates the loud-speaker.

RV1 sets the threshoild level atwhich IC2 will switch on. This is

01

R710k

ZD15V1 RV2

50k

02

R84k7 03

SPEAKER1W8 OHMS

OV0

+5V

normally set at maximum (wiper atthe R2 end). RV2 sets the volume ofthe audible tone, and can be adjustedas required.

IC2 can be substituted by theequivalent LM741 but R3 must beremoved first.

TOUCH -SWITCH FOR LOGIC

An n -channel field-effect transistor isthe basis of this simple tr gger. In itsquiescent state the voltage at the out-put is about 3V. When the plate is

briefly touched with a finger, theminute currents between the body andthe plate alter the electric field at thegate of the transistor. The effect is tocause a drop in output voltage. It fallsalmost to zero and can be used to

trigger a TTL flip-flop. This can beconstructed in the usual way, usingtwo NAND gates from a 7400 IC. Ifseveral triggering circuits are required,it is more convenient to use the 74118sextuple bistable latch.

The value of the capacitor is notcritical, but 10uF is convenient. Thetouch -plate can be an area of copperetched an a circuit -board, a square ofaluminum foil, or simply a thumb -tackpressed into an insulating support.


Subscriptions will com-mence with the next avail-able issue, but please allowup to 6 weeks for process-ing of order.

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p N(01

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Make sure of your issue, fillout the card (or coupon if thecard's already gone) and mail itto us.

Use this coupon if somebody's already used the cardTo: 5nELECTRONICS TODAY INTERNATIONAL, Unit 6, 25 Overlea Blvd, Toronto, Ont. M4H 1B1 Send me ETI for one year (12 issues) for $12.00 Send me ETI for two years (24 issues) for $20.00

For U.S. add $3.00 per year for postage, outside U.S. and Canada add $5.00 per year.

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tech -tips

A0

0B

O

C

A

C

D

oa Ob Oc Od

(6)

e Of og

DCBA a bc de f g

0 0 0 0 0 0 0 0 0 0 0

0 0 0 1 0 0 0 0 0 0 0

0 0 1 0 0 0 0 0 0 0 0

0 0 1 1 0 0 0 0 0 0 0

0 1 0 0 0 0 0 0 0 0 0

0 1 0 1 0 0 0 0 0 0 0

0 1 1 0 1 0 0 0 0 0 0

0 1 1 1 0 0 0 0 0 0 0

1 0 0 0 1 1 1 1 1 1 1

1 0 0 1 1 1 1 1 0 1 1

1 0 t 0 1 1 1 0 1 1 1

1 0 1 1 0 0 1 1 1 1 1

1 1 0 0 1 0 0 1 1 1 0

1 1 0 1 0 1 1 1 1 0 1

1 1 1 0 1 0 0 1 1 1 1

1 1 1 1 1 0 0 0 1 1 1

TRUTH TABLE for the 'add-on'decoder. Note that when the input is01102 (610) a logical one is inserted inthe 'a' column to provide the resultingseven -segment '6' with a cap, thus diff-erentiating it from a 'b'.

HEXADECIMAL TO 7 -SEGMENTDECODER.

The circuit described below providesan extension to the 7448 BCD toseven -segment decoder, converting itinto a hexadecimal to seven -segmentdecoder which will give the nJmerals0-9 and the characters A, b,C,d,E, andF as output for a four bit binary input.

(Inputs of A,T,B,T3,C,7,D are neededwith an inverting buffer - fan out 30 -on the D input.)

The 7448 is disabled by bringingthe blanking input low when the inputis greater than 01112 (i.e. D is con-nected to Bl/R BO on the 7448.) Out-puts from the 7448 and the add-ondecoder are OR-ed together creating asingle seven -segment output.

0

10k

2 555

TIMER

/ORP 12or equivalent

0Vcc 12V

12V relay

SCHMITT TRIGGER

A very useful schmitt trigger can bemade by utlising a single 555 timerwith its trigger and threshold inputsconnected together. The schmitt has avery low input current (1.5uA) andcan directly drive a relay taking up to200mA of current.

The circuit shows a 555 schmittbeing used to energise a relay wren the

0light level on a photoconductive cellfalls below a preset value; the relayenergises when the voltage on pins 2and 6 is greater than 2/3Vcc andde -energises when the voltage fallsbelow I/3Vcc. This gives a hysteresisof 1/3Vcc. The circuit can be used inmany other similar applications wherea high input impedance and low out-put imaedance are required with theminimum component count.


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110 watts RMS7.5 ohms

170 watts RMS7.5ohms

kHz -0.5d8 10-30 kHz 0.5c18 10-30 kHz -0.5d87.3V per microsec. By par microsec. 8.4V per m crosec0.05% @ 1kHz 0.05% @ 1kHz 0.05% @ 1kHz

Dampvng Factor 200 400 400Hum---Input

8 Noise 115d8 below 70Watts

115d8 below 110Watts

115 dB below 170eeil_

Sensitivity Od810.775V) 70watts

00E1(0.775W 110watts

Od810.775V1170watts

Input Impedance 47k 47k 47kPower Requirement a 35Volts 45V It '' 55 VoltsOverall Pitmans. 5.8" Long a 3"

Widea 1" High.5.8" Long a 3"Wide it 1" High

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'OPEN

by Tom GrahamYOUR RESPONSE to Electronics Today (whichincorporates Electronic Workshop) has, to put it mildly.been fantastic.

The letters, personal comments and phone callsindicate that we're doing something right, and we hopethat, as we gain experience, we can provide the kind offeatures and projects that you want. The projects that wehave run so far appear to have been popular - we hopethat the articles we are planning will be as successful.

We have received a few comments on the Europeanterminology that occasionally crops up in the magazine -most of the comments are not unfavourable. We mustadmit to being a little idiosyncratic in this area - but for avery good reason. Electronics Today International is notone magazine; it is five, operating independently aroundthe world. This means that we are able to invest a lot oftime and money in each project, in order to develop it to avery high quality.

It is so easy for mistakes to be made in the preparationof articles, and we minimise these by cutting down thenumber of stages an article goes through before printing.Once we have our final prototype completed and workingperfectly, the circuit diagram is drawn once, so that errorsthat may occur in re -drawing are avoided. This is why ourcircuit diagrams are different from the North Americanstyle you may be used to. If other editions around theworld decide to use the same project, their circuit diagramwill be identical, although there may be variations in thecomponent types and even the method of construction.Our internationalism also enables us to bring you articleson electronics from around the world - we know thereare a lot of interesting things happening outside SiliconValley, U.S.A.!

Finally, the Canadian scene is the important one to us.We are striving to bring you news and events fromCanada, but we need information input from you. If yourcompany is releasing a new product, make sure youMarketing or Advertising Department let us know with apress release. Since there isn't another magazine like ETIin Canada, they're probably not in the habit of doing this.Similarly, if your radio, or computer, or electronoc club aredoing something interesting, or even if you've comeacross something new or unusual, let us know.

A magazine is, in one sense, a data processing machine- if you help us with the input, we can work wonders onthe output.

electronics NayINFORMATION

COMPONENT NOTATIONS AND UNITSWe normally specify components using the recentlyagreed International Standard. Many readers will be un-familiar with this but it's simple, less likely to lead to errorand will be used by everyone sooner or later. ETI hasopted for sooner!

Firstly decimal points are dropped and substituted withthe mu,tiplier, thus 4.7uF is written 4u7. Capacitors alsouse the multiplier nano (one nanofarad is 1000pF). Thus0.1uF is 100n, 5600pF is 5n6. Other examples are 5.6pF= 5p6, 0.5pF = Op5.

Resistors are treated similarly: 1.8M ohms is 1 M8,56k ohms is 56k, 4.7k ohms is 4k7, 100 ohms is 100R,5.6ohms is 5R6.

BACK NUMBERSPrevious ssues of ETI-Canada are available direct fromour office for $2.00 each. Please specify issue by themonth, not by the features you require.

SUBSCRIPTIONSThe annual subscription to ETI for Canadian readers is$12.00, a two year subscription is $20.00. For U.S. sub-scribers, one year is $15.00, two years is $26.00. Pleasesend orders to ETI Subscriptions Dept.

PUBLICATIONSAt the moment we have five special publications available- Circuits No. 1 ($5.00), Top Projects Nos. 3 and 4,($2.50 each) and Electronics - It's Easy, Vols 1 and 2($3.50 each or $6.00 the pair). Orders to ETI SpecialsDept. please.

EDITORIAL QUERIESWritten queries can only be answered when accompaniedby a self-addressed, stamped envelope, and the reply cantake up to three weeks. These must relate to recentarticles and not involve ETI staff in any research. Markyour letter ETI Query.

NON-FUNCTIONING PROJECTSWe cannot solve the problems faced by individual readersbuilding our projects unless they are concerning inter-pretation of our articles. When we know of any error weshall print a correction as soon as possible at the end ofNews Digest. Any useful addenda to a project will besimilarly dealt with. We cannot advise readers on modifi-cations to our proects.

COMPONENT STORESETI is available for resale by component stores. We canoffer a good discount and quite a big bonus, the chancesare customers buying the magazine will come back to youto buy their components.

PRICESAll prices quoted in the editorial of ETI are in Canadiandollars, except where stated. Advertisers in U.S. may giveU.S. dollar prices. Where we only know an overseas price,e.g. in U.K. pounds, we convert approximately to Cana-dian dollars, erring on the conservative side, where possi-ble.


WHO IS THE ONLY SUPPLIER WITH 8 TYPES OF 'LYTIC0 REPLACEMENT CAPACITORS FOR RADIO -TV SERVICE?

SPRAGUE. Don't waste valuable service timechasing down capacitor replacements . . . Seeyour Sprague Distributor for all your 'lytic needsand you'll be able to put more time into actualservice work ... that's where the profit dollars are!

TYPE TVL TWIST-LOK® CAN -TYPE ELECTROLYTICSLock in place with twist

of tabs. Sealed aluminumcases for long life. With-

stand high surge voltages,high ripple currents, hightemperatures. Single, dual,triple, and quadruple sec-tion units. Capacitancevalues from 2 to 5000 µF.Voltage ratings from 6 to600 WVDC.

TYPE PCL PRINT-LOK® CAN -TYPE ELECTROLYTICSUniversal printed wiring

board mounting base.Sealed aluminum cases forlong life. Withstand high

surge voltages, high ripplecurrents, high temperatures.Etched cathode construc-tion. Ideal for selenium rec-tifier circuits. Single, dual,triple, and quadruple sec-tion units. Capacitancevalues from 2 to 3000 µ F .Voltage ratings from 3 to500 WVDC.

TYPE EV VERTI-LYTIC® SINGLE -ENDED ELECTROLYTICSFor vertical installation

on high -density printed wir-ing boards. Used for cou-

OK° -4 I

pling, decoupling, bypass,filtering. Excellent capac-itance stability. Low leakagecurrent, low ESR. Metal -encased, with plastic insu-lating sleeve. Capacitancevalues from .47 to 3300 µF.Voltage ratings from 6.3 to63 WVDC.

TYPE TVA ATOM® STANDARD TUBULAR 'LYTICSDependable metal case

construction with plastic in-sulating sleeve. Withstandhigh temperatures, high rip -

ple currents, high surgevoltages. Low leakage cur-rents. Long shelf life. De-signed for operation attemperatures to 85°C. Sin-gle, dual, triple, quadruple,and quintuple units. Capac-itance values from 1 to50,000 µ F . Voltage ratingsfrom 1 to 600 WVDC.

For complete listings of more than SMITH-PATTERSON5600 replacement components get & ASSOCIATESCatalog CC -621 from your Sprague 1120 Hamilton St.distributor, or write to: Vancouver, B.C. R3E 2T1

TYPE EE MINILYTIC® MINIATURE ELECTROLYTICSCompetitively priced, yet

substantially higher qualitythan most imported capac-

itors. Low leakage currentsassure minimum drain andlonger battery life in bypa3sapplications. Also ideal ascoupling capacitors. Capac-itance values from 1 to 2500µ F . Voltage ratings from 3to 150 WVDC.

TYPE WH13D ECONOMY ULTRA -SMALL ELECTROLYTICSExcellent replacements

for capacitors of this typein miniaturized solid-state

circuitry, especially wherehigh volumetric efficiency,low cost, and dependableperformance are importantconsiderations. Metal -encased, with plastic insu-lating sleeve. Capacitancevalues from 1.5 to 3300 /LF.Voltage ratings from 3 to100 WVDC.

TYPE TE L1TTL-LYTIC®Withstand 2000 hr. life

test at rated voltage andmax. temperature of 105°C.

105° ELECTROLYTICSMost other low-cost minified'lytics of this type designedfor shorter test at lowertemperature. High capac-itance stability, even afterdrastic temperature change.Capacitance values from 1to 800 µ F . Voltage ratingsfrom 3 to 150 WVDC.

TYPE AM ANTENNA ROTATOR ELECTROLYTICSAluminum electrolytic

capacitors of correct sizeand rating for all popular

or JOHN R. TILTON, LTD.1900A Eglinton Ave. EastScarborough, OntarioM1L 2M1

makes of antenna rotators.Metal -encased with plasticinsulating sleeve. Single -ended design, with longflexible insulated leads.Choice of four different ca-pacitors to provide exactreplacement.

5S-11001,1

SPRAGUE,1411111111111=11rito

THE BROAD -LINE PRODUCER OF ELECTRONIC PARTSTHE MARK OF RELIABILITY

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