counts up and down;presets and latches;drives any 7 -segmentdisplay - LED, LCD;common cathode orcommon anode

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Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CT1 1PE,Kent, U.K_Tel.: Canterbury (0227) 454439.Telex: 965504.Office hours: 8.30 - 12.30 and 13.30 - 16.30.

Editor: P.V. HolmesAssistant editor: E.J.A. KrempelsauerUK editorial staff:L. SeymourOverseas editorial staff:P.H.M. Baggers. A. Dahmen, I. Gombos,P.E.L. Kersemakers, R.P. Krings,P. v.d. Linden, D.R.S. Meyer,G.C.P. Raedersdorf, J.F. van Rooij,G.O.H. Scheil,Editorial secretariat:C.H. Smeets, G.W.P. WijnenHead of design:K.S.M. WalravenLaboratory staff:J. Barendrecht, G.H.K. Dam, K. Diedrich,G.H. Nachbar, A. Nachtmann,R.A.F.M. Salden, A.P.A. Sevriens,J.P.M. Steeman, P.I.A. TheunissenPublishing manager:A.J. BrialeyAdvertising manager:S. Brooks

The circuits are for domestic use only. Thesubmission of designs or articles to Elektorimplies permission to the publishers to alterand translate the text and design, and touse the contents in other Elektor publi-cations and activities. The publishers cannotguarantee to return any material submittedto them. All drawings, photographs, printedcircuit boards and articles published inElektor are copyright and may not bereproduced or transmitted in any form or byany means, including photocopying andrecording, in whole or in part without priorwritten permission of the publishem. Suchwritten permission must also be obtainedbefore any part of these publications isstored in a retrieval system of any nature.

Patent protection may exist in respect of cir-cuits, devices, components etc. described inthis magazine. The publishers do not acceptresponsibility for failing to identify suchpatent or other protection.

Elektor is also published in Dutch, French,German, Greek, Italian, Portuguese,Spanish, Turkish and (in part) Swedish inassociation with AlIt om Elektronik.

Distribution in UK.:Seymour Press Ltd., 334 Brixton Road,London SW9 7AG.

Copyright -f 1985 Elektor Publishers Ltd.,Canterbury.

Printed in the Netherlands. ]ABC

Volume 11 - Number 3 ISSN 0308-308X

news, vieuws, people 3-18

selektor 3-22Grand unification: for and against

K.I.T.T. scanner 3-24A special -effect unit as seen on TV

AXL amplifier 3-27Reliable, robust, and inexpensive to build, this power amplifier is suitable for manyapplications.

pH meter 3-32Measuring the degree of acidity or alkalinity in aqueous solutions, this meter will beof particular interest to aquarium owners.

missing link 3-41

how to make your own PCB3 3-42

turnout (points) control 3-45This electronic drive for model railway turnouts can prevent the burning out of theirsolenoids.

new keyboard for Spectrum 3-48We have designed our own keyboard to replace that fitted to the Spectrum.

19 kHz precision calibrator 3-52.A simple -to -build and accurate unit for use wherever a precise 19 kHz signal isrequired.

versatile counter circuit 3-54In response to many requests, we have developed a counter that will meet most ofyour requirements.

darkness -sensitive light switch 3-58A simple aid for all householders in their fight against the growing menace of beingburgled.

mini active loudspeaker 3-61A good -quality speaker that can be connected direct to the headphone output ofcassette players and FM receivers.

transistor unitester 3-64This unit enables you to find out which pins correspond to base, emitter, and collec-tor of any transistor.

market

switchboard

appointments

readers' services

index of advertisers

Versatile module ^ "1!...14. .

laaAarctr-An MA

-c-Annao SZ ractive mini

3-65

3-73

3-74

3.80

3-82

A selection from our April issue:

III the first cuckoo in spring... real -time -clock for micros X -Y plotter solar cell receiver rev counter with power curveIN 10 A power supply

We regret that owing to circumstancesbeyond our control it has been necessaryto shift the 'X -Y plotter' from March tothe April issue.

This month's cover depicts an example ofthe 'versatile counter' module which isdescribed on pages 3-54/57 in this issue.

3-03

elektor march 1985 advertisement

lkaz kaix e4/-_446wv£34. February 1978Infrared Light Gate/ThrowingSome Light on LEDs:Formant- the Elektor Music Synthesiser181iSlcnv onion/CMOS FunctionGenetator/Zener Tester/Develop-ment Taner:Experimenung withthe SC//1P (4L

£38, June 19781/4 GHz Counter:Constant Am-plitude Squarewave to Saw.tooth Converter/Seryo PolarityChanger/ Monopoly Dice MiniCounter: Digital Clock. Using theSC/MP/Programmable Call Gen-erator/TV Sound Modulator!Automatic Stereo Swatch/TrafficLight ControllersEasy Music.

£54. October 1979Touch Tuning/Battery Serer/Im-pedance Bridge/New ProgramsIca the SC/MP/Digital R ev Court.ter,DogifaractShon.interval Lightgyirehipcg for Variable fuzzBox IGate.dspper /Strain Gauge/IPlayed TV GamesoProgrammalateSequencer.

E55, November 1979Topamp:Flash Sequencer:Elecironies the Easiest WaylRe-mote Control Motor Switch/Home Trainer/Fuel Economiser:I Played TV Games 121,Shon-waae converter/Ionosphere/LowVoltage Dimmer/1 See yourPo int:5mo vont+ ratted Motor_

E58. February 1980Aerial BoosterlFet Oparnps rnthe Formant 'TV InterferenceSuppression I Elektor Vocoder121/Aerial AmptiliessiDegisptayiAnalogue Delay Technology/Ex-tending the 114 GHz Counter:Digital Thermometer_

£65, September 1980Sc RAM .4.8 or 161C. EPROMon aSinole Card/Precision PowerUnit:Electronic Linear Ther-mometer/The Josephson Com-outer /VOX Printed CircuitEbardiEjektor Measuring Multi..pathiHogh Speed Readout forElekterminaliMusical Box/Elec.trolytologys Curve Tracer:Usingthe Vococter.

£66. October 1980Programmable Shde Fader -TouchDoorbell:Switched Capacitors,more TV Games/The JuniorComputer %Serrsory Card.RernoteControl Shoe Projectors VineoPattern Generator:LCD TuningSrate.Dual Slide Faders

E67, November 1980An rpm Indicator as anEconomy GusseDraught Deter.tors How to Recycle Dry CellBatteries:Energy Saving KnownowSSimPle Fuel Economymeter Automatio Pump Control:Long Life Technique in LightBulbs'Automatic Curtain Con.trol.Fridge Aterm:Know the ins.or.d Oils of your Central Hearin;

System Energy Saving MotorControl/CO/fee Machine Switch!Operational Hours Counter.

=

E58, December 1980Canned Circuits. 23 of the bestentries which incluiss MidnightRaid Detector/A Flash in theCan / Can-smeter Canine De-fence.£70. February 1981Audio Power Meter/Noise Reduction Process Timer / Ht&voltage from 723 JuniorsGrooving Up/The Voiced.Unvoiced Detector EmergencyBrake for the Power Supply.150 W DC to DC Convener forthe Car/Low Noise 2 MetrePre.Amp.:2"i Digit DVMsWxyre-phon.

E72. April 1981Transistor blatchniaker:Unwer-sal Power Supply:Intelektitior.middy Sensor/Logic Analyser II.Crystal controlled Stroboscope;Junior Cookbook.

E73, May 1981Camping Clock / FrequencyDoubler/The Fully FledgedJunior Computer:Tans to Com-puters:Choke Alarm/Bar CodesLogs AnatyserAVaveform Generator,Sophisticated Softwarefor the Junior Computer/ Read.I no Bar Codes.E77, September 1981DFM DVM/Revolution Counter/Digital Barrameter(dB Con-verter/TV Games Extended:Disco Lights Controtter;OUADESL63/Analogue LED Disotay1Volt:Ammeter for Power Sup-plies.Chat tering Chips:TransistorIgnition Update/Soldering Alu-minium.£89, September 1982Gas Detector :Rapid LoadingGames/The Elektor Connection!Inductive Sensor DarkroomComputer Part 1 ; ApplikatorlHome Telephone SysterniSyn.thesised Sourxt Animation/TimeReceiver for the Rugby MSS=Three Phase Tester_

E90. October 1982DSB Demodulator/LC D. ther-morreter, ultra Sonic DistanceMeasarement.Electrolytics RunDry:Darkroom Computer Parr2/Short Wave Band Shifting forSSB Recever:16 Channels withonly Five ICs. Pre -amp for theSSB Receiver Active AeriesTranssstor and IC Data.£91. November 1982Drum interface/Talking DoeModes Train LightinoG altarTurer:Cerberus:Floppy Disc In-terface for the JunioriCubsolar Bell:Mini-Organ ExtensionKitchen Timer£93, January 1983P.filliohmrneter/accessores forthe Crescendo power amplifier/Darkroom computer tipslChipsfor digital aucko13 A compute,

supply/Traffic-light control sys-tem / Tomorrow's music / Upperand lower case on the Elekterminal.

E94, February 1983Prelude part 1 NAM - video!audio modulator / Main teamdimmer/Prelude class A head-phone amplifier/Fuse protector!Acoustic telephone modem/Double dice/Chips for digitalarch part 2.596. April 1983Low poser digital thermometer/MCIMM phony preamplMem-brane switches/Interlude/RCequalizer/7-day timer/control-ler/Junior program tester/Pre-lade Wart 311Prograrrunabledarkroom timer/Talking clockextension.

E97. May 1983Wattmeter/ASCII keyboardiPrelude pc iltultitesteriMaestro/part 11/What is powernPeral les.serial keyboard cornerrer;Morsecomer ter/78L voltage I non

. and 79L/Morse decoding withthe zsoa599/100. July/August 1983Summer Circuits Double Issuecontaining over 100 projects.

E101. September 1983Video Graphics ! Autotest64k on the 1 ek Dynamic RAMCard / highspeed CMOS / VDUCard / Personal FM / PrecisionVoltage Divider Alarm Eaten-sron / Junior Synthesizer /Simple MOSFET Test.

£102 October 1983Basicode-2 / Music Cluantisizer /Solid-nate Darkroom Lighting IHigh -voltage Regulator / Anem-ometer / Programmable PowerSupply / Basistocke2 Interfacefor the Junior Computer / Elec-tronic Voltage Regulator - Bat-tery Eliminator 1 TransistorSelector i FSKleaner I EPROM-mer using the Junior Computer.

E103, November 1983Doorbell - or telephone -operated flashlight:Power Con-troller for Model Railways!Decoupling in Digital Circuits?CPU Card/Decimal to BinaryConverter/Movement Detector:Electronic two-tone Metronome!Pseudo Stereo/Universal Ter-minal/Uhresonic/Infrared Bar-rier/Trick Battery/Crescendo re-visited.5104, December 198364 -way 2-chmensional Bus BoardOAF / HF USB Marine Receiver/LED Ornaments/SymmetricalPower Supply/Video Amplifier/Locomotive HeadIntip Reverser!Frost Warning Device/DiscoPhaser/Banking Program/NOV-RAM Data Storage without Illin-nriessfitus Extension! Cumu-lative index 1953.

E105, January 1984Gy rot:Mane/How accurate isyour watch? /Digital CassetteRecorder/Audio Signal Embel.InheriUniversal Active Filter/from Thermometer to Thermo-stat/Audio Sleuth at work/PfindDirection I neficato 0280 EPROMprogrammer/Home-made towscost Wiring Probe/Address de -ding.

5106. February 19846502 Tracer/Diesel Tarnorneter!Programmable Disco DisplayLights/Video CarrabinerlDigi-tsster with a differenceiRevers-ing Buzzer/Memory timing/Mating Logic FamilissICapaci-tanoeMeteriSasscode 2 for Juniorplus VDU Card/Constant Volt-age Source/CS Chip Selekt/Video Sync Box.

E107, March 1984Petrol Sauer:Trrac Control Elcerd/UHF Video and Audio Modu-lator/ GET & GO/Elabyrinth/Varistor Protection Circuits/Real -Time Analyser (part 1)/Applicator/Tape Timer.5108. April 1984Opbcal Memones:Convotting theFlavin -rusk Once Motor/RaseGenerator/Usag the Pulse Gene,atorlIntedgenr EPROM Eraser/280 &maw t OS/ Metronome Essenvon/Real-time Analyser. partVarntrie AC Power SjOptytototiChip Sew/kr/tape ContentsDetector_

E109. May 1984Noise SqueSchi&tortwave PocketFL4ctio 'Fleecy Tester:SwitchingPoorer Supply/Analytical VideoDisplay/AviaryIllumination! Howmany Watunlaini CressendoWlook or EXOR and E MICR Gates;EPROSt Copier:Digitai CassetteRecorder revisited/Rea:to/me Arta.rylir. part 3:R5423 Interface.

5110. June 1984Portatre Distress SonaliZX Eaten.sionssDisco DrumDailywheetTypewriter Printer Interface.Maxi.imam and Minimum Memory/Lead kid Battery Clinger/Woe-sets Microphoreillaerging BASICProorarrissEcho Sounder:VersatileAucko Peak Mere,

5111/112. July/August 1984Surrle,W C,rcults Douala. IssueCOntaimrn mer 100 projects

£113. September 1984Data Communication by Tele-phone 'Acrne cross -over Firer/Digital Cassette Recorder withthe Z)031/Flash Meter/DigitaltachometerlDIRPUT:SCART.Adapter/Anodizing Alu-minium/Lamp Saved Double-sil,K1 Printed Circuit Boards

E114. October 1984The Sinclair CIL - first ewes -sons/ Raiirwle-2/Tuning ForkBalancing Transformers/VideoColour (menet/Programmingthe 6845/ZX81 Cassette PulseCleaner/Direct-coupledModem/Battery Tester; RS232Centronics Converter; DynamicPre-amplrfier_

A. GiektOTelectrorftsvideocolourinverter

E115. November 1984The Story of Valves:Autochm/Mini Printer/Burglar Deterrent/How to make your com PCBs;RS232'V24: the Signals/Useyour TV Receiver as a Moni-tor/ TelephaseNalve Amish.fier; Bectronic Gas Meter.

E116, December 1984Electronic Cancll&The XP2206in the Function Generatot1Shor-thand BASIC!Function Gener-al/is/Time Switch/Cumulativelode. 1984, Musical GreetingCan Soklering lip afor _ , 2:rnputer-contmeedSI s= Sot -car Controller/

:-==.:sessor-controlled Fre-qui== Meter (part Of.

017. January 1965Commodore Cassette Inter-face:VHF/UHF Mockdator/Post.able Guitar Amplifier/30 watta.f. Output Stage sneolRumble Deter-tor!uP-contrcraKIFrequency Meter/SwitchingRadio Control Channels.

elektorelectronics

E118. February 1985GnolLashi 12 GHz InputSmne Microphone Preamplifier:Remote Model Control byMicrocomputer/DIY COnn.ec-tortProgrammaW RhythmBox/EPROM Selector,RecverPower front Engine Battery:RIXMeterlFrograrron.able KeyboardEncoder.

Back numbers of Elektor currently available are detailed above, with a brief description of their contents.Send for your copies now, using the pre -paid Order Card inside the back cover of this issue.Prices are as follows: any one issue (except July/August) £ 1.50

additional issues, each £ 1.30July/August (Summer Circuits) £ 3.00

Prices include postage and packing. Overseas orders requiring airmail postage add £ 1.50 per issue (£ 2.00 for July/Augustissue) (Prices subject to change without notice)

3-04

advertisement elektor march 1935

The prices quoted in my Catalogue arebelow normal trade price - some at onlyone tenth of manufacturers quantity trade.Just send large 24p stamped addressedenvelope for free copy.

Millions of components: thousands of different linesRechargeable Nickel Cadmium batteries (ex unused equipment)AA(HP7) 1.25 volt 500 mA. Set of four E2I.T.T. Mercury Wetted relay 20-60 VDC Coil. SPCo. 2 A. 79p or 10 for E7Clear L.E.D. illuminates Red, Green or Yellow depending upon polarity/current.Oblong 5 x mm Face 25p or5 mm Red Flashing L.E.D.

Watch/Calculator/Lighter etc.RW52 (PX675) RW54RW56 1DH323, WH8)RW57, RW58IN4004 or IN4006 Diodes

100 for E23 or 1000 for E20025p or 10 for E2.25

Mercury BatteriesMade by Ray -O -VAC

30p each or10 for £2.60. 100 for E21

300 for E6.50T05 or 1018 Heatsinks 10 for 75p, 100 for £6.50, 1000 for E55Clipover Heatsink for I/C or T0202 device 21 x 18 mm

20p or 10 for £1.80, 100 for £16.50 or 1000 for E155Heatsink for TO3 or Plastic Power 19p. 10/E17.50, 1000/E165KE1S005/01/02 3 amp 50 V/100 V;200 V/ bridge rectifiers 3513136pi4Op.10 off 0.20/E3.40/E3.70. 100 off E30/01/E34.Plessey SL403 3 Watt amp. From Bankrupt source, hence sold asuntested. 4 for 60p or 10 for E1.20p.

SEND PAYMENT PLUS 17p SAE OR LABELPostal orders. cash - prompt dispatch.Cheques require 9 days from a Tuesday banking to clear.Crossed postal orders and cheques - add 20p handling due to Bank'sincreasing 'commission' on business accounts.Cheques drawn on Barclay's Bank not accepted.

Prices you would not believe before inflation!

BRIAN J. REEDTRADE COMPONENTSESTABLISHED 28 YEARS

161 St. Johns Hill. Clapham Junction, London SWil 1TQ.Open 11 am 1. c 30 pm Tues. to Sat. Telephone 01-223 5016

F O R UB Ay Lull TATLC0ORMDPEORN E N T

/CVA LIU LE\ELECT

FREE44 PAGEPRICED ANDILLUSTRATEDCATALOGUEON REQUEST

FREE POSTAGEGOOD DISCOUNTS

GOOD SERVICETHOUSANDS OF

STOCK ITEMSPHONE YOUR ORDER

ACCESS ORBARCLAYCARD

ELECTROVALUE LTD 28 St Jude's Roao. Engietield Green. Egham.Surrey TW20 OHB Phone Egham (0784) 33603. Telex 264475

North Branch. 680 Bumage Lane. Manchester M19 1NAPhone 061 432 4945

Tenlion this publication when replying

xmorefbaifasMaia637-FONTHNON17"

!.:ore than 10 taskssimultaneously and, in somecases, up to 300 times faster!That's what replacing the basicROM with the new Forth doesfor the ZX81 - and more!

The brains behind thebreakthrough belong to DavidHusband, and he's buildingSkywave Software on the strengthof it. Already orders are floodingin and it's easy to see why.

The ZX81-FORTH ROM givesyou a totally new system. Inaddition to multi -tasking and splitscreen window capability, youcan also edit a program whilethree or four others are executing,schedule tasks to run from 50times a second to once a year, andwith a further modification switchbetween FORTH and BASIC

_never you like.

The ZX81-FORTH ROM givesyou a normal keyboard with a 64character buffer and repeat, itsupports most 16k, 32k, 64k RAMpacks, it is fig -FORTH compatibleand it supports the ZX printer.

The price, too, is almostunbelievable. As a "fit it yourselfEprom", complete with manual,it's just E25+VAT. Add E3 p&p UK(£6 Europe, £12 outside Europe)and send your order to theaddress below.

SksiviiatipSOFTWARE

Davd Hustind73 Curzon Road, Bournemouth.4P+N. ENGLAND -Tel, (0202)302385International +44202 302385

ewraINSTRUMENT CASES LTD.

UNIT 19 WICK INDUSTRIALESTATE GORE ROAD NEWMILTON HANTS BH25 6SJTelephone:NEW MILTON 621195

We manufacture beautiful enclosures. Ask for cata-logue (which includes £5 in vouchers). You won'tbelieve the prices.

19" Rack mounted,Free Standing andPlug-in Module framesusing high quality ex-trusions.Prices from.... £15.00

+ VATHigh quality Pack -flatenclosures with sepa-rate Chassis.Prices from £9.60

VAT

2 Part enclosures plusChassis. Hammer Bluefinish.Prices from £3.04

- VAT

Keyboard and ConsoleUnits.Prices from £4.90

TRADE AND EXPORT ENQUIRIES WELCOME.over 12 years in the enclosure business.

3-,

elektor march 1985

Forecasting Europe'selectronic futureThe European electronics market isset to expand by around 7.5 per centin real terms in 1985, compared with1984, according to the 12th editionof Benn's Yearbook of West Euro-pean Electronics Data, the industry'sleading handbook.In 1985 the total West Europeanelectronics market for equipment andcomponents will reach $96 billion(109) at constant 1983 values, com-pared with $89.3 billion (109) in 1984,and is forecast to reach $114 billionin constant terms by 1988, an annualaverage growth rate 1985-88 of 5.75per cent in real terms (figure 1).

Europese ElectronicsMarket By Sects

1364 Ex...^.arce Rrres)

St.00

twanows Nea LosINS

100.661w

1046CC

1.66104.11.

26%26%

20%

19%1 13:til 1-c13%

11% 'car13% 15%

12% Cal12% 12%

9% 9% CUJI

0 3%4%- OEWs- MAI

The yearbook cites a slowdown inWest European economic growthbeyond 1985 as the reason for therelatively low growth rates 1985-88,as Europe follows the USA into aneconomic downturn (on preset con-sensus forecasts) in 1986.Particularly slow moving sectors inthe 1985-88 period will be the OfficeElectronic Equipment market, pro-jected to grow at an annual averagegrowth rate of 2.5 per cent 1985-88,and the Consumer Electronicsmarket, where only 1.5 per cent perannum real growth is expected1985-88.Fastest growing sector will be Elec-tronic Data Processing (includingcomputers, personal computers,word processing systems, and com-puter peripherals) which can enjoy amarket growth rate of 8.25 per centper annum in real terms 1985-88,taking the total European EDPmarket to $32 billion in 1988.The second largest European equip-ment market, for Telecommuni-cations equipment, will reach some$15.3 billion by 1988, assuminggrowth in the order of 6 per cent perannum over the period 1985-88.The overall component market,including active, passive and audiocomponents is also projected toexpand at 6 per cent per annum1985-88, taking the combined total to

$22.3 billion in 1988. Within thecomponent sector, integrated circuitsand other microcircuits are expectedto maintain a growth rate of littlemore than 9.5 per cent per annum inreal terms for the 1985-88 period,taking the total IC market (includinghybrids) to approximately $4.9 billionin 1988, after $3.8 billion in 1985, forEurope as a whole. The IC market(including hybrids) is projected togrow by almost 15.5 per cent in 1985compared with 1984, when themarket is estimated at $3.27 billion.Other major sectors covered in theyearbook include Control andInstrumentation, expected to expandat some 5.9 per cent per annum1985-88, Communications andMilitary equipment, growing at a rateof 5.75 per cent in real terms1985-88, and Medical and Industrial

Electronic Equipment, a sector whichis forecast to increase at a rate ofapproximately 5 per cent per annumover 1985-88 period.In national terms, the most surpris-ing feature is the rise of the UnitedKingdom market to vie with that ofWest Germany in size as the largestelectronics market in Europe, by1988, when the UK market will beapproximately $25.5 billion in totaland West Germany $25.6 billion,each market representing some 22.5per cent of the European total (figure2).A prime factor in the faster growthof the UK market at 6 per cent perannum over the period 1985-88,compared with 5.25 per cent perannum in the FRG, will be the surgein the UK EDP market, which is pro-jected to overtake the Germanmarket in size in real terms by 1988,when the UK EDP market will be$6.8 billion, compared with $6.6billion in the FRG; in 1984 therespective totals are estimated as$4.5 billion in the UK and $4.9 billionin FRG.However there are strong indications

European Importsof Electronics Productslarro-e. A, Prces & Excharcie Rtes)

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3-18

elektor march 1985

European Exportsof Electronics Products(Curer.-. P e Rates)

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that British manufacturers may notbenefit from this UK market grovithto the same extent as importers. Ananalysis of data from the new andprevious editions of the yearbookseries shows that imports of elec-tronics equipment and componentshave grown at a much faster ratethan output in the UK over the fiveyear period 1979-83 and reveals analarming increase in the UK tradedeficit in electronics goods comparedwith other European countries.At current annual prices andexchange rates UK imports in theElectronics sector represented 17 percent of total European imports ofelectronics goods in 1979, but hadincreased to 21 per cent of totalEuropean electronics imports by 1983(figure 3). In contrast, the UK's shareof European Exports of electronicsproducts remained static over the

1979-83 period, at approximately 16per cent of European total Exports(figure 4), valued at $6.1 billion in1979 and $7.0 billion in 1983.Even more alarmingly, the UK tradedeficit in the Electronics sectorincreased from $1 billion in 1979representing 25 per cent of the totalEuropean electronics trade deficit, to$4.1 billion in 1983 (the latestavailable complete year) representingover 45 per cent of the total Euro-pean trade deficit in electronics of$9.1 billion in 1983 (figure 5).Comparative data for other majorEuropean countries shows that WestGermany reduced its import pen-etration as a percentage of the Euro-pean electronics total from 22 percent in 1979 to 21.3 per cent in 1983and has run a trade surplus in elec-

European Balance ofTrade in Electronics Products(Exports Minus Imports)

Rates)

5.7vr, It 5

tronics products throughout thewhole period 1979-83 inclusive,although this reduced from a surplusof $1.5 billion in 1979 to a surplus of$0.7 billion in 1983.France reduced its electronics tradingdeficit from 20.7 per cent of theEuropean total in 1979 to 19.6 percent of the European total in 1983,although in value terms the deficitmore than doubled from $0.8 billionin 1979 to $1.8 billion in 1983, at cur-rent prices and exchange rates.The most improved trading perform-ance was achieved by Italy, however,which reduced its electronics tradingdeficit from over 28 per cent of theEuropean total electronics tradingdeficit in 1979 (at $1.2 billion) tounder 15 per cent of the Europeantotal electronics deficit in 1983 (at$1.3 billion deficit in 1983).In output terms (figure 6), the UKfared slightly better over the 1979-83period, improving its production ofelectronics equipment and com-ponents from 17.7 per cent of theEuropean total in 1979 to 19.2 percent in 1983. The FRG share of totalEuropean electronics production fellfrom 28.2 per cent in 1979 to 26.2

European Outputof Ekoctronice Products(Cis-r-rit Arrxia' s Rtes)

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per cent in 1983 and the Frenchshare fell from 19.8 per cent in 1979to 18.5 per cent in 1983; Italy main-tained its share of European elec-tronics output at approximately 10per cent of the total in 1979 and1983 (all values at current prices andexchange rates per annum).

This is the end of ourbroadcasts...A milestone in the history of Britishbroadcasting was reached lastJanuary when all of the remainingBBC 405 -line (vhf) transmitters wereswitched off.When the 405 -line service started in1936 it was described as "Theworld's first regular public service ofhigh -definition television pro-grammes". The number of viewershad been dwindling since the intro-duction of the duplicate 625 -lineultra -high frequency (uhf) colour ser-vice in 1969. In its hey -day, the405 -line network comprised one hun-dred and seven transmitters.After the formal opening by thePostmaster General, Major G.C.Tryon on 2nd November 1936, theservice grew in popularity when theBBC screened the first major outsidebroadcast in May 1937, the Coron-ation of King George VI. Over 23000receivers were in use in September1939 when the Alexandra Palacetransmitter was closed for the waryears. The service re -opened afterthe war in 1946, screening the Vic-tory Parade on the 8th June.Television spread throughout the UKwith stations at Sutton Coldfieldserving Birmingham and theMidlands opening in 1949, HolmeMoss serving Yorkshire and Lan-cashire in 1951, and Kirk O'Shottsand Wenvoe serving parts ofScotland and Wales in 1952. TheLondon transmitter moved to CrystalPalace in 1956 to provide a bettersignal to London and the HomeCounties.

3-19

elektor march 1985

Software availabilityslammed...Although one in every four homes inBritain has a computer, the Con-sumers' Association reports that theready availability of software isdeplorable. In a guide to software,the association says that most com-puter retailers, on average, stock onlythe twelve best-selling softwarepackages. Over 3000 programs havebeen produced for the Spectrum,but even the largest stores have onlyabout one hundred of these on theshelf.

...and hardware in declineThis year may well prove to be awatershed for many computercompanies. Sales of home com-puters last December did not reachthe expected figures and were evenslightly below those for the corre-sponding period in 1983. Only win-ners were Sinclair, with theSpectrum outselling almost all othercomputers together. It is reported,however, that the QL is doing badly.Towards the end of last year, Sinclairwere shipping 100 000 Spectrums amonth, while total output of QLs forthe year is claimed to be 40 000.It is also reported that Acorn aredoing badly, with the BBC microtaking a nosedive. The Acorn Elec-tron is still number three in the UKbut well behind Sinclair and Com-modore.A British company that did well in1984 is Amstrad whose hi-fi stylemicro comes complete with tapedrive and monitor.Oric, however, found the ground toohot in the UK and has all but leftthese shores, hoping to do better inFrance where its Atmos was votedthe best micro in 1983.The big losers are undoubtedly theJapanese whose much heraldedidentikit MSX machines have so farfailed to get off the ground. Toshiba,for instance, imported 40 000 MSXmachines and estimated in Januaryto have sold about 20 000. The prob-lems with the MSX seem to be four-fold: they look obsolescent; theysuffer from a serious shortage ofsoftware; there is a distinct lack ofmarket awareness; they are tooexpensive (at an average price of£280 they are no bargain comparedto the £180 Spectrum+ or the £190Commodore 64).

Marconi enters cellularradio marketMarconi Mobile Radio, a division ofMarconi Communication SystemsLimited, has announced its entry intothe Cellular Radiophone market.The new Marconiphone Cellularproducts include a choice of twovehicle mounted sets, and a modern

cordless personal radiophone thathas battery charging facilities. Thisnew equipment meets all thedemands of modern CellularRadiophones, including a wide rangeof standard telephone facilities, anelectronic memory that stores thethirty most often called numbers,hand -free dialling, conferencing, anda call redirect facility. Other optionsare to follow.To satisfy the growing cellularradiophone market, Marconi arefurther expanding their nationalradiophone sales and service centres,particularly in London, where theirWembley centre will be able tohandle over one hundred car instal-lations per week.

Optical mouseDisk drive manufacturer Shugart Cor-poration has introduced an opticalmouse, a palm -sized device used toposition a cursor on a microcom-puter screen.The optical mouse offers severaladvantages over mechanical devices.Since the optical mouse has nomoving parts, it is more reliable, doesnot require periodic maintenance,and is lighter and quieter thanmechanical units. The Shugart pro-duct is also more reliable than mostother optical mice since it has nointernal mirrors to adjust.The Shugart mouse can be movedup to twenty-five inches per secondwithout affecting cursor positioningaccuracy. It also features 200 pulseedges per inch to accommodate highresolution graphics. It is availablewith parallel, serial, or RS232Cinterfaces.

\ECIE

PE2PLE

A sound conferenceThe International TelecommunicationUnion's (ITU) regional administrativeradio conference to plan the use ofthe 87.5...108 MHz VHF soundbroadcasting band, which ended lastDecember, involved about 100countries in Western and EasternEurope (including the whole of theUSSR) plus Iran and Afghanistan,and the whole of Africa. Is hasestablished a broadcasting plan forthe entire area: the Final Acts willcome into force on 1 July 1987.The UK delegation was led byofficials from the DTI's RadioRegulatory Division, and includedrepresentatives from the Home OfficeBroadcasting Department, the BBC,the IBA, and the Civil AviationAuthority.The UK's objectives for the con-ference were:I to secure a further two national

VHF networks, one to enableBBC Radio 1 and Radio 2 to haveseparate frequencies, and the otherfor the introduction of a newindependent national radio service;II the provision of additional fre-

quencies for the development ofBBC and independent local radio;I the maintenance of the existing

VHF networks and improvementsto their coverage.These objectives were accepted withonly very minor modifications, andthe plan thus establishes theregulatory framework within whichpresent and future VHF sound broad-casting in the UK can be developed.

SERT twenty years oldThe Society of Electronic Ft RadioTechnicians, SERT, celebrated itstwentieth anniversary last month. Itwas established in 1965 to provideprofessional services both for Tech-nician Engineers and for EngineeringTechnicians. Today, the society hasover 8500 members in the UK andmany countries overseas, while itsactivities range from local andregional meetings for members tothe organizing of major electronicsrelated symposia that attracted par-ticipants from Europe and the USA.One of the prime objectives of theSERT has always been to gainrecognition of the standards of itscorporate members by industry andthe general public. As a nominatingbody of the Engineering Council, itshares with the Council the desire toestablish standards of competencefor all engineering staff.

Exit for silicon?The end may be in sight for silicon,the semiconductor material thatmade the computer boom possibleand gave its name to California's'Silicon Valley'. Use of galliumarsenide (GaAs) in semiconductors, a

3-20

elektor march 19E5

faster, harder substance, will multiplynearly tenfold by 1992, according toa new study by Frost Er Sullivan.The Gallium Arsenide SemiconductorMarket (# 1352) notes that in manyfields GaAs semiconductors are in anexcellent position to challenge siliconones, and the technology is headedin that direction. Integrated circuitswill be the major market because ofseveral material factors: in lower field intensities, the

greater electron mobility of GaAscould translate into (processing)speeds ranging from three to tentimes as fast as silicon at similarpower; GaAs can be operated at much

higher temperatures than silicon- an important reliabilitycharacteristic; GaAs has superior radiation resist-

ance, important for hazardous andharsh radiating environments: this isof particular note for satellite appli-cations.The main applications for GaAssemiconductors lie in communi-cations: satellite broadcastingsystems, cellular radio, digital audio,and television.

World databaseComprehensive and up-to-date infor-mation on products, skills,knowledge, and facilities provided bythe UK's universities, colleges, andresearch establishments will beavailable throughout the world froma computer database being set up inthe Scottish Development Agency'snewly -completed technology centreon the St Andrews Universitycampus.Financial backing for the project,which will be marketed by CatermillPublishing, has come from the SDA,Electra Investment Trust, and theLonaman Group.Among the subjects to be coveredare the life and physical sciences,medicine, biotechnology, electronics,and engineering. The database isexpected to be available to industrialusers within a year, but work ongathering data has already started.ILPS)

MIQAL to the aidPaisley College of Technology hasbeen given Government approval toset up a unique education and train-ing centre for Scotland's electronicsindustry.The £0.5 million Microelectronics andQuality Assurance Laboratory(MIQAL - pronounced Michael) willbe based in the college's Departmentof Electrical and Electronic Engineer-ing, and will be funded jointly by theScottish Education Department, the

SDA, and by the electronics industryitself.Several leading companies - Ferran-ti, IBM, Barr Et Stroud, BurroughsMachines, Hughes Microelectronics,Hewlett Packard, and Digital Equip-ment Corporation - as well as theEngineering Industry Training Board,have already committed a total of£75 000 to the project, with othercompanies expected to follow in thenear future.MIQAL offers an extensive range ofeducation and training coursesspecifically designed to meet theneeds of Scotland's fastest growingindustrial sector. With microelec-tronics scheduled to undergo stillfurther expansion in Scotland by1990, the Centre will play an increas-ingly important role, according to itscreator, Professor Lionel Davis, Headof Paisley's Department of Electricaland Electronic Engineering.

Decision time...The London -based InternationalMaritime Satellite Organization(INMARSAT) expects to make adecision early this year on who willbuild its next generation of maritimecommunication satellites.Two international consortia have bidto provide the organization with upto nine satellites. One is headed byBritish Aerospace in partnership withthe Hughes Aircraft Company of theUS and Satcom International ofFrance. The other is headed byBritain's Marconi group and made upof the Ford Aerospace and Com-munications Corporation of the USand Aerospatiale of France.INMARSAT's first generation satellitesystem is now linked with more than3000 earth stations mounted onocean-going vessels, off -shore oilrigs,seismic survey ships, fishing boats,ice breaker, cable laying ships, andshipping company offices. (LPS)

The roll -up, fold -up batteryRechargeable batteries of the future,big enough to drive a car, and yetsmall enough for ordinary home use,are likely to be completely solid andcapable of being rolled up like stick-ing tape or made in flat sheets andfolded.This is the prospect held out by ane..., project just launched by scien-tists at the UK Atomic EnergyAuthority's Harwell researchlaboratory. Their work to find theright materials and technology toenable solid batteries to be offered inany shape or size is being sponsoredby battery users, manufacturers, andmaterials specialists.According to a UKAEA spokesman,the project will provide the basictechnology for the manufacture ofall -solid batteries. These are likely to

-OPT

be made from lithium and vanadiumoxide instead of the lead and nickel -iron of conventional batteries.Harwell's applied electrochemistrycentre has already shown that itsnew type of battery cells do work.Using foil -thin strips for the com-ponents, a complete cell need beonly 0.22 mm thick, and this is likelyto be reduced further still.Harwell has been working on solidbatteries for some time. With helpfrom Denmark, the EEC, and severaluniversities, is has been studying thepossible use of lithium batteries todrive cars. (LPS)

PeopleGordon Parker, BSc, C Eng, MIEE,Head of BBC's Engineering DesignsDepartment, retired on 11 Januaryand was succeeded by Ian Millar,MA, until then Head of StudioGroup.

New show for electronics inretailingThe new electronic retailing anddistribution exhibition, Retail '85,covering innovations in electronicretailing and all the equipment rel-evant to modern competitive trading,is to be held at the KensingtonExhibition Centre, London, from 16TO 18 April 1985.The equipment on display is alsoexpected to be of interest to otherbusinesses where cash and stockcontrol, display and security areimportant considerations. Theseinclude the catering and hotelindustry, cash and carry outlets, themotor trade, and petrol fillingstations. (LPS)

3-21

Grand Unification: for andagainstDuring the past few years twoimportant events in fundamental par-ticle physics have provided evidenceon the one hand for and on theother against grand unified theories,known as GUTs for short, whichseek to explain all the fundamentalparticles of matter and all the forcesof nature in the same mathematicalterms. The -first event is really a non-event: it is the failure of physicists sofar to detect proton decay. Thesecond is the production and identi-fication of particles called W and Zbosons, findings which strengthenthe case for GUTs perhaps morethan it is weakened by the failure tofind protons decaying.

Protons, the positively -charged par-ticles in atomic nuclei, certainly havevery long lives. They last for billionsof years before they decay, losingmass as energy and changing intoother particles. In fact it is stilluncertain whether protons do decay.Scientists in India, Europe andAmerica have set up experimentsdeep underground with sensitivedetectors to search for proton decay.The reason for siting the experimentsunderground, in a disused gold -minein India, in the Mont Blanc tunnel inEurope and in a salt mine in NorthAmerica, is that it prevents thedetectors being confused by thearrival of highly energetic particles incosmic rays from outer space. Noevent generally accepted byphysicists as being due to protondecay has yet been detected by anyof the scientific teams.The failure to detect proton decay isimportant to grand unification theory.There are several reasons for wishingto observe it, among them the factthat it probably happened a lot inthe first fraction of a second afterthe 'big bang' in which the universebegan. Observing proton decaywould provide a replay of one of themore important events of that all-important earliest epoch.Equally important is the evidencethat proton decay would provide forsymmetry and unity in nature. If pro-tons decay, then the particles ofwhich protons themselves are madeup, namely quarks, have to betransformed into others called lep-tons, the generic name for particlessuch as electrons. Quarks and lep-tons are now believed to be the onlytwo truly fundamental types of par-ticles, and groupings of various typesof quarks on the one hand and lep-tons on the other are beginning tolook very similar. If proton decay

shows that quarks can be trans-formed into leptons, then the unifica-tion of all forms of matter is in sight.For proton decay to mean thatquarks and leptons are inter-changeable, however, implies anaverage lifetime for protons beforethey decay of about 1031 years. Themore the observed lifetime of theproton exceeds this span, the lesslikely it is that quarks and leptons areinterchangeable and the further theunification of matter which dependsupon it recedes.So, the failure of physicists to agreethat they have found decaying pro-tons in any experiment so far, andthe consequent implication that thelifetime of the proton is longer thanhad been thought (statistics showthat they should have found severaldecaying by now if the lifetime wasas predicted) does not encourageGUTs. But while the physicistsinvolved have been taking one stepback from GUTs, other groups maybe said to have taken two steps for-ward with their identification of theW and Z bosons.To understand why this is so import-ant, you need first to understandhow far unification of the forces ofnature has proceeded. Matter is heldtogether by four forces: gravitation,electromagnetism, and the strongand weak nuclear forces. The greatphysicist James Clerk Maxwellunified the hitherto separate elec-trical and magnetic forces into one inthe 19th century. Just over ten yearsago particle physicists Abdus Salemin the UK and Steven Weinburg andSheldon Glashow in the USA con-structed a theory which unified theelectromagnetic and weak nuclearforces. To prove it meant that par-ticles, the so-called W and Z bosons

elektor march 1985

which the theory predicted mustexist, had to be found.The electromagnetic force betweenparticles is carried by other particles,photons. If, as Salem, Weinberg andGlashow predicted, weak and elec-tromagnetic forces are really just twomanifestations of the same thing,the weak nuclear force should alsobe mediated by particles, the W andZ bosons.W bosons must be very heavy andso operate over very short distances.It requires very high energies tocreate W bosons that are not lockedup inside atomic nuclei and that flyabout freely enough and for longenough to be observed. Suchenergies were not available at thetime when Salem, Weinberg andGlashow put forward their theory.But the energies needed to liberatedetectable W and Z bosons havenow been produced at the EuropeanLaboratory for Particle Physics,CERN, near Geneva.The experiments involved colliding abeam of protons circulating insidethe Super Proton Synchroton (SPS)with a beam of anti -protons cir-culating in the opposite direction.Each proton is made of three quarksand each anti -proton of three anti -quarks. When quark and anti -quarkcollide they annihilate each other andrelease enough energy to create par-ticles as heavy as the W and Zbosons.On 20th January 1983 CERNannounced that, among some 109collisions of particles observed intheir proton -anti -proton collidingexperiments, they had seen thecharacteristic signature of W bosonsin just five. These observations weremade by one of the two teams ofscientists working with the SPS

The forces in nature

Type Intensity of forces(decreasing order)

Binding particle(field quantum)

Occurs in:

Strong nuclear force

Electromagnetic force

Weak nuclear force

Gravitation

-1

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-,07'1:02

-1 0-1,

Gluons (no mass)

Photon (no mass)

Bosons Z°, W-, W-(heavy)

Graviton?

Atomic nucleus

Atomic shell

Radioactive betadisintegration

Heavenly bodies

rj. I

Exchange of particles is responsible for the forces

3-22

elektor march 1985

proton -anti -proton collider, the teamknown as UA1. Soon after, four moresuch events were reported by thesecond team, UA2. Some 80 Wbosons have now been seen andvery recently five Z bosons havebeen identified.The remarkable discovery rewardedsix years of intense activity at CERNand on the part of the British par-ticipators in the CERN experiment,from the Rutherford -Appletonlaboratory near Oxford, Queen MaryCollege in the University of London,and Birmingham University.Altogether, 120 internationalphysicists, including 22 from the UKare involved in UA1. Their experimentuses a chamber that records thetracks of all the charged particlesfrom the collisions of protons andanti -protons. Surrounding it are twoarrays of counters to measure theenergies of all the particles producedby the collision. One array measuresthe energies of leptons, the other theenergies of strongly -interactingnuclear particles such as protons andneutrons.This second array, called a Hadroniccalorimeter, was built by the threeUK scientific groups. It consists ofseven thousand sheets of scin-tillators, detectors that scintillatewhen struck by the particles, withinstrumentation to record andmeasure the energy of the impacts.The UK scientists also produced anelectronic processor to measure theenergy of impacts and to decideelectronically whether or not theyshould be recorded. This vital part ofthe apparatus enables theexperimenters to select, from thethousands of events produced everysecond by the colliding beams, justthose that merit study.The W boson is so heavy, about80 times the mass of a proton, thatit is created in a state of rest out ofthe energy of quark -anti -quark collis-ion. It is unstable and decays almostimmediately to lighter particles. Oneway in which it decays, which canbe detected, is to form two particles- an electron and an anti -neutrino.Only the electron is discerned whenthis happens, because neutrinos can-not be detected by conventionalmeans. So what should be discern-able in this mode of decay is a high-energy electron track going off inone direction with, most unusually,nothing complementing it in theother direction. What has really hap-pened is that while the high-energyelectron has gone off in one direc-tion carrying a momentum of 40 GeV(giga-electronvolts), half the energyof the W boson it came from, an

Electricity

Unknownforce?

Magnetism

Electromagnetism

Light

Maxwell's theory ofelectromagneticwaves

QuantumelectrodynamicsPhoton

Weak forceRadioactivebeta decay

Field theoryof weak force

W',

Unified electroweak forcePhoton W', Z°

Strong forceAtomic nuclei

QuantumchromodynamicsGluon

Unification of quantumfield theory

GravitationMovementsof planets

So far noquantum effect

Possible uniquebasic force?

anti -neutrino has gone off, undetec-tably, in exactly the opposite direc-tion with a balancing momentum of40 GeV. In the UA1 group's firstexperiments 800 000 events wererecorded on magnetic tape; com-puter selection picked out 40 ofthem, and careful scanning of thoseproduced just five that showedexactly the right characteristics, withhigh-energy electrons going off inone direction and a large amount ofmomentum clearly missing in theopposite direction.Discovery of the W particle wasfollowed in May by four events to dowith Z particles. The Z particle issimilar to the W but carries nocharge and is slightly heavier. It isexpected to be produced ten timesless frequently by collisions betweenprotons and anti -protons than is theW particle, which explains why the Ztook longer to find, although itssignature is equally distinctive.Most physicists agree that the identi-fication of the W boson cements thebond between the electromagneticand weak nuclear forces. The nextstep in grand unification is to try todemonstrate that the strong nuclearforce and the weak/electromagneticforces are mediated by particles inthe same way. A theory of theaction of the strong force involvingits mediation by particles, calledgluons, already exists and it may bepossible to confirm their existenceexperimentally. So far, however,physicists have made little progresstowards assimilating the fourth force,gravitation, into a grand unifiedscheme of things.Stan/forth Webb (938 S)

IT training for UK andoverseas studentsBritish industry has already pledgedmore than £10 million to set up anInstitute of Information Technologycapable of training 6000 people eachyear in IT skills. The proposedinstitute will train students fromhome and abroad.Sir Henry Chilver, principal of theCranfield Institute of Technology,which runs courses for the govern-ment and the private sector inscience, technology, and manage-ment studies, said recently that planswere now at an advanced stage. Theinstitute would be set up in MiltonKeynes where a wide range of ITservices are already being developedfor offices, homes, commerce, andindustry.The institute will be a whollyindependent body but linked withnearby Cranfield in the field of pro-duction technology.The first students will begin studieson short courses while on leave fromtheir regular employment towards theend of this year.By 1990 the aim is to have an annualoutput of 800 undergraduates, 500postgraduate doctoral and master -degree students, and up to 5000students on in -career short courses.Among the British IT manufacturersand user companies now concernedin the institute's planning stage areBICC, Thorn -EMI, Racal Electronics,Plessey, STC, Ferranti, BritishTelecom, Cable and Wireless, AcornComputers, and Longman Publishers.(LPS)

3-23

KATT. scannerelektor march 1985

we let you inon the secretbehind one ofTV's specialeffects of themoment

Science fiction writers are hampered only by their own imaginations,which generally means that they are very little hampered indeed.Movie -makers, on the other hand, are often forced to take reality intoconsideration and do the best possible job with the tools that areavailable. Most of them, fortunately, succeed in making their filmssufficiently 'unearthly' with special effects. Special effects also serveto enhance more ordinary films or TV shows, one of the mostpopular at the moment being a computer that thinks it is a car.Inspired by certain science fiction movies and our automotive friendwe came up with a special effect unit of our own.

Movie makers and TV show producersfeel justified in doing almost anything todraw a big audience or improve theirratings. One of the more popular of these'special effects' shows at the moment hasa fully -computerised car as its hero. Thiscar (we will refrain from telling you that itis called K.I.T.T. as that would be advertis-ing) has a series of lights running acrossits bonnet to simulate a 'scanner'. We allknow. of course, that it is nothing of thesort but that does not detract from theeffect.Many special effects are very simplewhen the 'trick' is known. The 'KIT -T scan-ner', for instance, is simply a row of lightsflashing in sequence one after another. Asthe photograph shows, this does notinvolve anything very complicated. Muchof the circuit is lepeated eight times. Butbefore we get ahead of ourselves let ushave a look at the actual circuit diagram.

The circuitThe operation of the circuit is easy tofollow. When the power is applied theswitch -on reset circuit, consisting of C4and RI9, takes pin 1 (Preset Enable) ofcounter IC3 high for a short time. The datapresented to the parallel inputs, I1...14, isloaded into the counter. All four of theseinputs are grounded so IC3 is reset tozero. This has the effect that the circuit

always starts from the same condition.except for the state of flip-flop N2/N3.As long as the circuit is powered theoscillator based on N4 provides a clocksignal for the 4029. with the frequencybeing preset by means of P1. The count in1C3 is incremented by each clock pulseand is continually output via QA. QB andQC. Each of these outputs is connected toa corresponding input in IC2. This binaryinformation is decoded by the 4028 so oneof its outputs is continually high. The 4029always starts from a count of zero so thismeans that the first output of IC2 to behigh will be pin 3 ('0'). Each successiveclock pulse from N4 then causes the nextof the 4028's outputs to ao high. and theprevious one to return low, of course.When output '7' of IC2 goes high thissignal is fed via NI to flip-flop N2/N3causing it to toggle. As a result pin 10 ofIC3 is taken low so the 4029 starts tocount down. When it reaches zero the COoutput causes N2/N3 to flip again so IC3starts counting up.Each of IC2's outputs ('0'..:7') is con-nected to the exact same sort of circuit.When an output goes high the appro-priate switching transistor, T9...T16,causes the corresponding driver transistor,TI...T8, to conduct so one of the lampslights. The result is that each of Lal...La8lights, one after the other, first in risingsequence, then falling, then rising again,

3-24

1

El

+0 IAO

51

12 V

PI

... T8 = 80 139T9 ... 716 = BC 5476

NI ... N4 = ICI = 4093

Lal La8 = 12 V.< 10 W

5V

0

1N4148

21 r, A

RIT

78L05

5V

CI9

76 ,0 F.14;4;

n

<1 12 13! 3 5),

ale

PEIC3

4029cLX

I=1ZIP

scannerelektor march 1985

Figure 1. The circuitdiagram and the photo-graph attest to thesimplicity of the circuit.The electronics itself usesvery little power, most ofit being consumed by theeight lamps. The tran-sistors will be overloadedif the lamps used have ahigher power rating thanthe one stated in thedrawing.

3-25

2KITT scannerelektor march 1985

Parts list

Resistors:

RI...R8,R17 = 470 0R9...R16 = 15 kR18 = 47 k -

R19 = 100 kR20 = 100P1 = 250 k preset

Capacitors:

Cl = 100 µ/25 VC2,C4 = 100 nC3 = 2.2 p/16 V

Semiconductors:D1 = 1N4148T1...T8 = BD 139T9...TI6 = BC 5478IC1 = 4093IC2 = 4028IC3 = 4029IC4 = 781_05

Miscellaneous:

F1 = fuse, 1 A slow blow,with PCB -mounting fuseholder

Lal ...La8 = light bulb,12 V/10 W max.

Si = singlepole singlethrow switch

Figure 2. The scanner canbe assembled on thisprinted circuit board (EPSNo. 85025). Do not forgetto insert the short wirelink between IC1 and IC2.

and so on. The speed at which this occursis determined by the position of Pl.The circuit requires a power source of12 V d.c., such as a car battery, and its cur-rent consumption will be about 25 mA.The regulated 5 V needed for IC1...IC3is provided by IC4. Incidentally, theswitching transistors (T9...T16) need onlya single common collector resistor as onlyone of them conducts at any one time.

Construction and calibrationAssembling the circuit for the KITT scan-ner is simply a matter of soldering all thecomponents onto the printed circuit boardwhose design is shown in figure 2. Themechanical section is no more difficult.The photograph shows how our prototypewas put together. Each lamp is mountedin its own section in the reflector. Thereflector is made of a number of pieces oftin soldered together. The wall betweentwo lamps is not vertical; it consists of twopieces of tin soldered together in a 'V'shape with the free ends soldered to the

floor of the reflector. Do not make thesewalls finish flush with the top of the reflec-tor as we have done. The lamps will seemto run into each other better if the wallsonly extend about 2/3 to 3/4 of thisheight. A sheet of perspex was fitted infront of the reflector and this was coveredwith red tape.The only variable component in the scan-ner is preset Pl. This is 'calibrated' byadjusting it until the lamps flash at aspeed that you find pleasing.

A final point......about using the circuit. As anypoliceman will tell you, not just anybodyis legally permitted to fit flashing lights totheir car, even if they are not blue. Thatmeans that the 'scanner' as shown on theTV show is illegal in most pans of theworld. Elelctor readers are imaginative,however, and we are sure you can comeup with an even more innovative use forthis KITT scanner.

3-26

AXL amplifierelektor march 1985

This photographof two AXLs forming astereo amplifier showshow the printed circuitboards, the MOSFETs, thealuminium bracket, andthe heat sink are con-nected together.

AXL amplifierThe AXL amplifier described here is intended for operation in class A,AB, or B. Its design specification stipulated that it should bereasonably compact, reliable, robust, and relatively inexpensive tobuild. It is suitable for use as a power amplifier for electrostaticheadphones, in an active loudspeaker system, or in a small hi-fiinstallation.

The classification of an amplifier dependson the portion of the input current cycleduring which output current flows. Inclass A amplifiers, output current flowsover the whole of the input current cycle.These amplifiers have low distortion andlow efficiency. In class B amplifiers theoutput current is cut off at zero inputsignal, so that a half -wave rectified outputis produced. Such amplifiers are very effi-cient but suffer from cross -over distortion.In class AB amplifiers the output currentflows for more than half but less than thewhole of the input cycle. At low input -signal levels class AB amplifiers tend tooperate in class A, and at high input -signal levels as class B amplifiers.Power amplifiers commonly work in push-pull, that is, they use two matched devicesin such a way that they operate with a180' phase difference. The output circuitscombine the separate outputs in phase.When complementary transistors are usedin the two halves, no phase shift isrequired in the inputs. If both halves ofthe stage are active simultaneously, they

Technical data

Input sensitivity

Input impedancePower gainOutput power

Dissipation(no signalcondition)

Frequency res

Harmonic distortion(primarily 2ndharmonic)

Damping factor

790 mV for 25 W into 8700 for 40 W into 4

class A, B orAB

5 k425 dB15 W into 8 4 1 class A- full drive7 W into 4 41 quiescent current: 1 A2 W into 8 Q class A- reduced drive1 W into 4 Q1 quiescent current: 350 mA

25 W into 8 ) class AB - full drive40 W into 450 W into 8 Q ), class B70 W into 4 4 J quiescent current: 100 mA65 W - class A with quiescent current of 1 A

and supply voltage of + 32 V23 W - class A with quiescent current of 350 mA

and supply voltage of i 32 V9 W - class B with quiescent current of 100 mA

and supply voltage of 2 x 45.. _50 V13 Hz...65 kHz at -3 dB class A 600 Q source20 Hz...20 kHz at -3 dB class B impedance

40.02 per cent in frequency range20 Hz...20 kHz

100 (at 1 W output at 100 Hz)

3-27

AXL amplifierelektor march 1985

Figure 1. The circuitdiagram of the AXLamplifier.

T15.716 71 TIO

till__ 0

52C,

a

CaAIM

provide equal contributions to the outputcurrent: this is the case in class A oper-ation. In class B operation only one half ofthe stage is active at any one time, andthis depends on the polarity of the outputcurrent.A predetermined mode of operation, A, B,or AB, is effected by suitably adjusting thequiescent current (that is, the currentunder no signal conditions) through theoutput stage. The quiescent current flowsthrough both halves of the output stage.Each change in the current with respectto the quiescent current in each half ofthe stage contributes to the output cur-rent. In class A operation, the quiescentcurrent is so high, and the output currentso low, that both halves of the outputstage are on all the time. In class B oper-ation, the quiescent current is, in theory atleast, zero. In class AB operation, thequiescent current is set to a level which isappreciably higher than in class B, butmuch lower than in class A.Because of the heavy demands on thepower supply and cooling, a class Aamplifier is considerably dearer per wattoutput power than a class B amplifier. But,since the reproduction in class A is betterthan in class B, it seems logical to opt fora compromise: that is, class AB! Thisbecomes even more attractive when yourealize that during the reproduction ofboth music and speech full output is

required during very short periods only.With a well-chosen quiescent current, theamplifier therefore sometimes works inclass A (low inputs) and sometimes inclass AB (high inputs). The consequentincrease in distortion as compared withthat in class A operation is measurable,but not audible.As to the question of rated power output,bOth the Crescendo (Elektor December1982) and the Mini Crescendo (Elektor -May 1984) appear to meet a need, at leastaccording to many readers' letters. Butbearing in mind the design specificationmentioned before, we modelled the AXLamplifier on the Mini Crescendo, resultingin a symmetrical circuit with two com-plementary MOSFETs in the output stage.Both as regards costs and dimensions, thecase. the power supply, and the heat sinksare comparable to those in the MiniCrescendo.

CircuitAs most amplifiers, the AXL may be splitinto an input stage, voltage amplifiers, andan output stage. As shown in figure 1, theinput stage consists of a dual symmetricaldifferential amplifier. The two transistorsnormally constituting a differential ampli-fier are formed by cascodes T1 T8, T2 -T6,and T3 -T7, T4 -T8 respectively. A cascodeis a super -transistor in which there is only

1Ttt TUI,

Til

BF 470

BC 550C

Tt

BF 469

7t2 R2

ED3

1N4148

®L 1o

ell30 V

O. -"Pr22_ 722,

63Yi

715

2SK134

R27LI

R23

11.

26449

-7T-ja.13

220aisd v 30 V

&WI] 1

lk 3-28

negligible feedback from collector tobase. Furthermore, the collector of such atransistor is an almost ideal currentsource.The output voltages of the differentialamplifiers are present across resistors R13and R14 from where they are applied todriver stages Tll and T12 via emitterfollowers T9 and T10. Note that the collec-tors of the emitter followers are con-veniently connected to zener diodes DIand D2 which are required to ensureproper balance between the two sectionsof the dual input circuit.In contrast to the two Crescendos, driversTll and T12 are not connected in acascode circuit, because the output stagehere is voltage -controlled via complemen-tary emitter follower T13-FT14. This dualstage can draw a sufficiently high currentvia R22. This arrangement obviates theneed of using the input capacitance of theMOSFETs for frequency compensation.This compensation is now obtained viaMiller capacitors C7 and C8, which inessence are connected between base andcollector of TI1 and T12 respectively.There is, therefore, a deliberate feedbackfrom output to input of the drivers, andthe aim of a cascode circuit is precisely toprevent such feedback. Current amplifi-cation in this arrangement is low, and thisis the reason that emitter followers T9 andT10 have been added.The collectors of the drivers are intercon-nected via network P1 -C9 -D7 -D8, whichserves to adjust the quiescent current tothe required level. The diodes providetemperature compensation for the currentset by P1; they derive their temperatureessentially from the heat sinks of T13 andT14. The stability with temperature of thequiescent current is not of paramountimportance in view of the excellentthermo-electronic properties of theMOSFETs.The parallel combination of R20 and R21forms the load of the driver stages. Thevalues of these resistors have beenchosen such that on the one hand thevoltage amplification of the drivers isreasonably high, and on the other that thecontribution of these resistors (via the cur-rent amplification mechanism of T13+T14)to the gate control impedances of T15 andT16 is negligible (that is, with respect toR23-FR25 and R24-FR26 respectively).As already mentioned, the output stagesof the AXL amplifier are voltage con-trolled, because that gives an even betterlinearity than current drive. It also keepsthe output impedance, without feedback,lower. The improved linearity and loweroutput impedance result in very goodoverall performance with a low feedbackfactor. And that is desirable, becausefeedback is and remains a necessary evil.Diodes D3...D6 provide simple, but ef-ficient current limiting of the MOSFETs.Network R29/C14 improves the stabilityunder no-load conditions. Resistors R27and R28 act as stabilizers of the direct cur-rent setting of the output stages. Network

central

earthingpain!

131= 880C10000

b 1 A MI

B1.62= 1381)C10000

centralearthingpoint

B1= 380C10000

85027-2a

85027-2c

85027-211

AXL amplifierelektor march 1985

Figure 2. Various powersupplies for the AXL:common -or -garden (2a):de luxe (2b); and for usein class B operation (2c).

C)1_

10000_UM 40 V

40 V

L

LsL

et.

OR

10000ow 40 V

R

LsR

=104:7,'

ToR

3-29

AXL amplifierelektor march 1985 3

Figure 3. The printed cir-cuit board of the AXLamplifier.

Ll/R30 reduces to some extent thecapacitive load at the negative -feedbacktake -off point. The feedback is applied tothe input stages via R4. CapacitorsC10...C13 provide decoupling of thesupply lines.The parallel combination Cl-C2-C3, inconjunction with RI, provides a filter ford.c. and very low frequency signals. FilterR2/C4 prevents signals above about60 kHz from reaching the input stages.

ConstructionThe AXL amplifier is constructed alongsimilar lines as the two Crescendos, and itmay therefore be useful to reread the tworelevant articles. Note that the output tran-sistors are mounted on the printed circuitboard: thermal coupling with the heat sinkis effected via a right-angled aluminiumbracket as shown in the photograph onpage 3-27. This arrangement obviates anycritical wiring and results in a very com-pact construction.As regards the power supply, figure 2gives you a choice of three. Figure 2ashows one that is common to the left-handand right-hand channel; figure 2b gives adesign for separate supply to the twochannels; and figure 2c is intended foruse when the AXL amplifier is operated inclass B.

The circuit of figure 2a is a single -transformer design. The large -valuesmoothing capacitors are necessary tokeep the ripple voltage on the supplylines low; with smaller capacitances thisvoltage might easily become unaccept-ably large in view of the high quiescentcurrent. The ripple voltage does not somuch affect the audio signals as reducethe dynamic range.Note that there are two earth returns perchannel: one to the pcb, and one to theloudspeaker. The central earthing pointshould be the only connection to theamplifier case. This means that the phono(or jack) sockets must be mountedinsulated from the case. The connectionsbetween these sockets and the pcbshould be made in screened cable withthe screen connected as appropriate atboth ends of the short cable.The design in figure 2b provides separatesupplies for the left-hand and right-handchannels, which are normally only foundin very expensive amplifiers. The arrange-ment ensures that there is guaranteed nointeraction between the two channels viathe supply lines. The great advantage ofusing this power supply is that a stereoamplifier can be built from two absolutelysymmetrical mono amplifiers which onlyhave the mains switch in common!

3-30

AXL amplifierelektor march 1985

If it is required to operate the AXL perma-nently in class B, higher supply voltagesare needed. A suitable power supply isshown in figure 2c. Note that the rating ofcapacitors CIO and C12 in the amplifiershould also be increased to 64 V.Construction of the amplifier on theprinted circuit board is straightforward;note, however, that diodes D7 and D8should be mounted vertically.The mounting of the MOSFETs, the alu-minium bracket, the heat sink, and allother practical constructional details havebeen described in the previous crescen-do articles (Elektor - December 1982 andMay 1984) and is further illustrated in thephotograph on page 3-27.Before the amplifier can be taken into use,it is necessary to check and, if necessary,to correct the off -set direct voltage at theamplifier output, and to set the quiescentcurrent.Ideally, the direct voltage at the outputshould be zero, but in practice a valueof not more than ± 50 mV is perfectlyacceptable. First, measure the directvoltage under no-load and no -drive condi-tions. If it is negative, T2/T6 and T3/T7should be made to conduct harder, andTl/T5 and T4/T8 less so. This may bedone by reducing R6 and R7 by a certainamount, and increasing R5 and R8 by the

same amount. The total values of R5+R6and R7+R8 therefore remain unchanged.For instance,R6 = R7 = 120 Q; R5 = R8 = 180 Q.If the direct voltage has risen to less than-50 mV, no further action is required; ifnot, the resistance values should bechanged further, e.g.,R6 = R7 = 100 Q; R5 = R8 = 220 Q.If the direct output voltage is too high andpositive, R6 and R7 should be increased,and R5 and R8 reduced, in a similar wayto that described for negative values.The quiescent current is measured byconnecting a d.c. milliammeter in thepositive or negative supply line, or by ad.c. millivoltmeter across R27 or R28(about 25 mV per 100 mA). The quiescentcurrent may be set with PI between100 mA and 1 A. The lower value pertainsto class B operation, the higher to class A.We have found that a value of 350 mAgives the best compromise between per-formance and dissipation, but the finalchoice is, of course, yours! 14

Parts list (each channel)

Resistors:

R1 = 10 kR2 = 1k8R3 = 8k2R4 = 180 kR5,R6,R7,R8,R22 = 150R9,R11 = 3k3R10,R12 = 12 kR13,R14 = 2k7R15,R16 = 1 kR17,R18 = 82R19 = 18 kR20,R21 = 22 kR23,R24 = 100R25,R26 = 220 Q (mounton trackside of pcb)

R27,R28 = 0027 5 WR29 = 10 Q/1 W carbonR30 = 1 4r1 W carbonP1 = 1 k preset (turn fullyanti -clockwise beforemounting)

Capacitors:

C1,C2,C3,C15 = 820 n(preferably MKM =metallized plastic poly -carbonate)

C4 = 1 n polystyreneC5,C6 = 47 p!2.5 VC7,C8 = 47 p polystyreneC9 = 220 y/10 VC10,C12 = 100 y (ratedvoltage> single supplyvoltage)

C11,C13 = 220 nC14 = 22 n

Semiconductors:T1,T2,75,T6,T10 =

BC 550CT3,T4,T7,T8,T9 = BC 560CT11,T14 = BF 470T12,T13 = BF 469T15 = 2SK134 (Hitachi-

MOSFET)T16 = 2SJ49 (Hitachi-MOSFET)

D1,D2 = zener 15 V/400 mW

D3,06,137,08 = 1N4148(mount D7 and (38vertically)

04,05 = zener 12 V/400 mW

Miscellaneous:

Lt = about 2 pH: 20 turnsin 2 layers of 1 mm dia.enamelled copper wire(SWG19) on R30; see de-

tail in figure 1heat sink for T15 116;minimum height 100 mm;e.g. SK85; 0.6°C/W

aluminium bracket, right-angled, minimum dimen-sions: 125 mm long. 6 mmthick, each side 60 mmwide

two heat sinks for T13 andT14, 8.5°C/W, e.g. SK09

mounting and insulatinghardware and silicongrease substitute for thetransistors to be cooled

3-31

pH meterelektor march 1985

acidity/alkalinitymeasurement byLCD

Determining the pH value of an aqueous solution is one of the moreimportant measurements in inorganic chemistry. Any connection withelectronics seems remote, and yet chemists have made use ofelectronics in pH measurements for years. They do this with a specialsensor which enables the degree of acidity or alkalinity to bedisplayed analogously or digitally. Until recently these sensors wereprohibitively expensive for hobbyists, but as prices have been comingdown, we decided to design a pH meter which will be particularlyappreciated by aquarium owners.

pH meterAs most electronic hobbyists are nochemists, we will keep 'chemistry' to anabsolute minimum.Each aqueous solution has a certainmeasure of acidity or alkalinity, which isdependent on the concentration ofhydrogen -ions in it. The higher the con-centration, the higher the acidity, and thelower the pH. When the concentration islow (very few hydrogen -ions), the pH ishigh and the solution is alkaline. A pHbelow 7 indicates acidity and a pH inexcess of 7 indicates alkalinity.The pH is defined as the logarithm of thereciprocal of the hydrogen -ion concen-tration, (11+), i.e. pH = log:,1/(H+)Table 1 gives the pH scale with corre-sponding numbers of grams of hydrogen -ions per litre of solution, the relativestrength of the solution, and typicalexamples.A neutral value does not correspond to aconcentration of zero ions, but to onewhich lies at the division between acidityand alkalinity: that is a pH of 7. The con -

pH

Table 1.

hydrogen -ionsin g/1

relativestrength

0i.5

:'

01

23

1.00.1vinegar0.010.001

10 000 000

10 0004 0.0001 1 0005 0.000 01 1006 0.000 001 10

T27 = 0.000 000 1 0

2 c

8 0.000 000 01 10

9 0.000 000 001 10010 0.000 000 000 1 1 00011 0.000 000 000 01 10 00012 2 0.000 000 000 001 100 00013 t 0.000 000 000 000 1 1 000 00014 -7, 0.000 000 COO 000 01 10 000 000

typicalexample

5% hydrochloric acid

gastriclsulphuriceon

juice,ijuice

fruit juice, winebeerblack coffeemineral water.rain waterpurified water,fresh milksolution of washingsodaborax solutionsoapy waterfilm developerammonia solutionlime water10% caustic sodasolution

centration is also dependent to someextent on the temperature of the solution.Depending on the nature of the solution,the pH/temperature relation is eitherdirect or inverse. Measurement of the pHis normally related to a temperature of25°C_There are two methods for determiningthe number of H+ ions in an aqueoussolution: colorimetry and electrometry.In the first, an acid -base indicator is used,which has a different colour in acid orbase solutions. The colour change is dueto a marked difference in colour betweenthe undissociated and ionic forms. Suchindicators are accurate only to about 30per cent.The electrometric method is based oncomparing the voltage measured by asensor and a reference potential. Adetailed description of this sensor is givenlater in this article.The output potential of the sensorchanges by about 59 mV per pH unit; thisis a reasonable value which may bemeasured direct with a d.c. voltmeter.Because of the temperature -dependentbehaviour of the pH sensor, a temperaturesensor was thought to be no luxury. OurpH meter therefore includes a pH sensorand a temperature sensor, with the tem-perature correction for the pH sensorbeing made automatically. Moreover, thetemperature can be displayedindependently.

Electronic partThe circuit of the pH meter uses a specialvoltmeter IC and is therefore quitestraightforward as figure 1 shows. Thischip, IC1, contains a dual -slopeanalogue/digital converter and a completeLCD drive stage.Capacitor C2 is a memory for the auto -zero function in the IC. Capacitor C3 is anintegrator which is charged via Rl. Refer-ence capacitor Cl is also part of the dual -slope integrator. The battery is connectedto the IC (pins 1 and 26) via switching tran-

3-32

sistor T1. This transistor is controlled by amicro -switch in the stereo socket for thetemperature sensor; it conducts only if theplug of that sensor has been inserted intothe socket. This makes an on/off switchsuperfluous.The POL(arity) output, pin 20, switches onthe minus sign on the display via gate N3when the input signal is negative. TheTEST output, pin 32, arranges a low -batterysignal on the display if the battery voltagedrops below 7.8 V.The LCD display is controlled via outputsAl...01, A2...G2, and A3...G3. Thedecimal point is set according to thechosen function by N1 and N2.The reference voltage is connected toREF HI and REF LO (pins 36 and 35respectively), while the potential differ-ence from the pH sensor is applied toIN LO and IN HI (pins 30 and 31respectively).When the reference voltage is suited tothe quantity to be measured (temperatureor pH) and the starting voltage of themeasuring range (IN LO) is presetappropriately, the display will give a directreading of the temperature or the pHvalue.Input REF LO is connected to COM(pin 32), which is not the earth connectionof the IC, but provides a stabilized poten-tial which is about 3 V below the 9 Vsupply voltage. The reference voltage fortemperature measurements is set simplyby R13/P1; that for pH determination isprovided by voltage divider R22/P4/R21

and opamp A2. Switching between thetwo reference voltages is carried out byelectronic switches ES1...ES4. The start-ing voltage for measuring temperature andpH is preset by R19/P2/R17 andR20/P3/R16/A3 respectively.With switch Sl in position R/V, the tem-perature sensor is connected between A(1.69 V reference voltage proyided byopamp A4) and B. In this way, the sensorforms a temperature -dependent voltagedivider with R23. At 0°C the resistance ofthe sensor is about 1650 P.- and the poten-tial at B (with respect to earth) is thenaround 1.3 V. The level at IN LO is set tothe same value by P2, so that the displayreads 00.0 at 0°C. At higher temperatures,the resistance of the sensor decreases,the voltage at B rises, and the display willthen read a positive value. Similarly, attemperatures below 0°C, the display willindicate a negative value. The referencevoltage is preset with P1.Opamp Al at the pH input provides therequired high input impedance of 10' Q.It would be possible to connect the pHinput direct to the relevant inputs of ICI(also 10- Q) but switch Si would then haveto be of very high quality to provide sucha high isolation resistance between itscontacts. As there was a spare opampavailable in IC2 anyway, we opted forusing that and a cheap switch. The outputvoltage of the pH sensor drifts about200 µV/°C. This means that the referencevoltage must drift 200 µV/°C in theopposite direction to compensate for the

1

9 9.

33H4.9343

0.

9V

p1 Al _ A4 = /C2 - %D84NI ... N4 = IC3 = 4070ESI ES4 = IC4 - 4066

mt. 07

I/44148

pH meterelektor march 1985

Figure 1. The circuitdiagram of the pH meteris based on a special ICwhich processes thevoltages provided by a pHsensor and a temperaturesensor: the results areshown on a 31/2 digit LCDdisplay.

32.caKTY ID A

IEl

Al

V

Otipsr

IC2 IC4

T

"L-t

c

t1

tna

A3

.32

k,.a

w

TI

3,3

1

E,4

O

T9411

LCD,'092 1391.

0

0Dos

Min34.

3.

ESI

pTr

-a JJ11:14=1.,LI-i,v6s7,;;;z2aa:va22,1s:1-4

IC 1ps 7106

01C

C091 I C REF

Er

ii C:1 CT

.12//

TES,

G BC55DC9/01. 13.9

NCSTi A Cl

A2213..

--- -;_%Urn TF)0(l'A

el.r71.1.1:0A1

LCD

22.

.99991

3-33

pH meterelektor march 1985

Figure 4. Construction ofthe pH sensor used forthis article.

sensor drift. This correction is providedautomatically by opamp A2. The invertinginput of this opamp is therefore con-nected to the temperature sensor via aresistor. The ratio RI1:RI2 determines thedrift per 'C.A separate setting by P3 arranges for asuitable level at the IN LO input. AtpH = 7, the pH sensor provides a voltageof around 0 V, but it is preferable andmuch more convenient for the display toread 7.00. This is achieved by voltagedivider R20/P3/R16 and A3, which com-bine to provide a voltage of 413 mV(7 x 59 mV) at the IN LO input. This setting

is also temperature dependent: compen-sation is provided automatically byR14/R15.

ConstructionThe printed circuit shown in figure 2 con-tains relatively few components, whichmakes construction a fairly simple matter.However, the choice of those componentsis pretty important. Many resistors (thosemarked with an asterisk in the parts listand a triangle in the circuit diagram) MUSTBE metal film types. This is not so muchbecause of high tolerance. but rather to

The pH sensorIn pH measurements use is made of thepotential difference that exists between ametal electrode and the electrolyte intowhich it is immersed. Such a potential dif-ference also exists between two differentelectrolytes. Electrolytes may be acids.bases, or salts.In electrometrical pH measurements agalvanic chain is used which consists oftwo electrodes that are electrically con-nected by one or more electrolytes. Exter-nally, the two electrodes are intercon-nected by a measuring device of veryhigh internal resistance. As this devicedraws virtually no current, the chemicalconstitution of the electrolyte is notaffected.Several galvanic voltages are produced inthe chain which cannot be measuredindependently. In the sensor used here,there are therefore a reference electrodeand a measuring electrode: figure 4 showsa sketch of the construction.As the name implies, the reference elec-trode provides a fixed galvanic voltagebetween it and the electrolyte to bemeasured. It consists of a rod of silvercompound which is surrounded by abuffer solution, potassium chloride, KCI.The potassium chloride is connected withthe electrolyte via a diaphragm whichensures minimal liquid transfer and very

4

85024-4

low electrical resistance. In the sensorused here, the diaphragm is made of aporous ceramic.The measuring electrode consists of asilver rod which is bonded to a glassmembrane and surrounded by apotassium chloride solution. A potentialdifference will arise across the membranewhich is dependent upon the differencein acidity/alkalinity between the buffersolution inside the sensor and the elec-trolyte into which the sensor is immersed.The potential difference is probablycaused by an exchange of sodium andhydrogen ions between the glass and thesolutions.The potential difference between the twoelectrodes is directly proportional to thedifference in pH of the buffer solution andthe electrolyte. AU other galvanic voltagescancel one another. Because of the hightransfer resistance of the measuring elec-trode, and to prevent chemical changes inthe solutions, the measuring device inter-connecting the two electrodes externallymust have a very high impedance input -of the order of 1012 Q.

Using the sensorIt should be evident that because of theglass membrane the sensor should beused with care.The sensor used contains a maintenance -free buffer solution. In other words, thesolution around the two electrodes cannotbe replenished. To prevent drying out ofthe solution, the sensor should thereforealways be kept in a potassium chloridesolution when it is not in use.Some golden rules for using the sensorare: Never leave the sensor unguarded. A

protective cap is supplied which shouldalways be placed over the membraneside. This cap is filled with potassiumchloride and may need replenishing oncein a while with a KCI solution of 3 mol/litre (this is available as a standardsolution). Never touch the glass membrane - not

even with a cloth, because this willalmost certainly destroy the electrode. Before every measurement rinse the

sensor thoroughly in distilled water.

3-34

ensure good stability. All presets MUST BE10 -turn cermet types. ICI MUST BE a type7106 and not a type 7106R, because thathas all connecting pins reversed w.r.t. the7106.After all components have been mountedon the component side, the display shouldbe fitted at the track side. Use a 40 -way ICsocket which has been cut lengthways asholder. Note that some types of display donot have an arrow for battery indication,but LOW BAT or some other sign. In suchcases it may be that the battery indicationis terminated in another than pin 38.Then, place the printed circuit in the box,

but do not yet secure it. Just see wherethe packing density at the edge of theboard is least and on that basis determinethe location for switch SI and the BNCsocket at the underside of the box. Screenthe BNC socket with a piece of tinsoldered in position.File some slots in the box for the presetsso that these can be operated even whenthe box is closed.Locate the stereo socket for the tempera-ture sensor beside the battery com-partment.The wiring between the BNC socket andthe board is fairly critical: use double -

Never use tap water! Before every measurement, take the

temperature of the electrolyte to bemeasured. This is necessary because ofthe temperature -dependent behaviour ofthe sensor. The pH meter automaticallycompensates for temperature differencesw.r.t. 25°C. Some electrolytes may discolour the

glass membrane or the diaphragm. Thesuppliers of the sensor have available avariety of cleaning liquids for specificcases. At the extremes of the measuring range

(around 0...2 and 12...14) a smallmetering error occurs which cannot becorrected. Over the remainder of therange, an accuracy of two per cent isattainable provided the calibration hasbeen carried out correctly.

p'

Finally, a few words about the life of thesensor. Filled with a gel as used here, ithas a life of 1...3 years, depending onthe number and type of measurements.The great advantage of this type of sensorlies in its ease of use: it only needs to beimmersed in the electrolyte to bemeasured. There are, however, alsoseparate measuring and reference elec-trodes available (which therefore makereplacement of the buffer solutions poss-ible), but these are much more cumber-some to use. although they have anappreciably longer life. They can also begiven a new lease of life by being treatedwith special aqueous solutions. Againstthat, they are also considerably moreexpensive, so that in practice most hob-byists will invariably opt for the sensorused in this article.

pH meterelektor march 1985

It should notbe done likethat...

But like this...

3-35

pH meterelektor march 1985 2

Parts list

Resistors:

RI = 270 k'R2 = 100 kR3 = 1MR4J15,R7...R9 = 1 MR6 = 180 k -

RIO,R16 = 39 leR11,R12,R14 = 130 kR13.R15 = 91 k'R17 = 47 kR18 = 470 k'R19,R21 = 75 kR20 = 150 kR22 = 180 it'R23 = 6103*P1...P5 = 50 k ten -turn

preset' = 1% metal film

Capacitors:

Cl-..C3 = 220 nC4 = 100 p polystyreneC5 = 4;17/16 VC6.C7 = 22 JA/16 Vtantalum

Semiconductors:D1 = 1N4148T1,T2 = BC 550 CICI = 7106IC2 = 11084IC3 = 4070IC4 = 4066

Miscellaneous:S1 = double -polechangeover switch

1 off pH sensor type U455:order no. 104553001BNC termination - (LifeScience Lab,Saruni Road,Luton LU3 2RA,Bedfordshire. Telephone:0582 597676)

1 off temperature sensor,type KTY-10-6 (old codeKTY-10-A): KTY-81-210;KTY-81-220

1 off 3 r. digit LCD display1 off stereo 3.5 mm socketwith built-in switch

1 off BNC socket1 off 9 V power packbattery

1 off Verobox 65-2996Hhandheld box with switchcut-off, dimensions145 x80x36rnm

PCB 85024

Figure 2. The printed cir-cuit board of the pHmeter_ The LCD display ismounted at the trackside. DO Nur use a 7106Rfor IC1 - only a 7106!

3-36

3 pH meterelektor march 1985

screened teflon cable and keep it as shortas possible. This is vital because of thehigh isolation resistance required. Allother connections may simply be madefrom flexible equipment wire.If the pH sensor has not yet been fittedwith a BNC plug, do so now. Fittingshould be done with great care: the cableis of a special type with a very high iso-lation resistance.The temperature sensor should be fittedwith a length of standard single screenedcable and then inserted into an emptyballpen holder which is subsequentlyfilled with two -component araldite (anexample of this may be seen in the photoof figure 3). The cable should then be fit-ted with a 3.5 mm stereo jack: screen tothe housing and the conductor to theforemost section. The rear section is usedfor switching the supply voltage on andoff.

CalibrationBuffer solutions with a pH of 4, 7, and 9respectively are required for calibratingthe meter; they are normally availablefrom the suppliers of the sensor.Set switch Sl to position 'temp' (V/R infigure 1). Place the temperature sensor ina mixture of water and crushed ice (stirwell!), wait a few minutes and then adjustP2 to obtain a reading of exactly 1.69 Vd.c. between the output of opamp A4(pin 7) and earth. The display should thenread 00.0. Next, place the sensor, togetherwith a clinical thermometer, in a largebowl of water at about 37°C. Again wait afew minutes and then adjust PI so that the

display shows the same value as the ther-mometer.Next, set Si to position 'pH' (U/S infigure 1). Remove the protective cap fromthe pH sensor and thoroughly rinse thesensor in distilled water.Place the pHsensor and the temperature sensor in thebuffer solution with a pH of 7, whichshould be at 25°C. Wait a few minutes andthen adjust P3 to give a reading on thedisplay of 7.00. Remove both sensors fromthe solution, rinse them thoroughly indistilled water, and then place them in thebuffer solution with a pH of 4, which againshould be at 25°C. Wait a few minutes,and then adjust P4 to give a displayreading of 4.00. Remove both sensors fromthe solution, rinse them thoroughly indistilled water, and then place them in thebuffer solution with a pH of 9. The displayshould then read 9.00; if not, slightlyadjust P4, and repeat the pH 4 test. Finally,remove the sensors from the solution,rinse them thoroughly in distilled water,and then place them again in the solutionwith a pH of 7. The display should thenread 7.00; if not, carefully repeat the abovecalibration.The meter is now ready for use. It isadvisable to calibrate it at regular intervalsbecause of the ageing of the pH sensor.Calibration is also recommended beforemeasurement when the meter has notbeen used for some time.This concludes the description of the pHmeter, but for those of you who areinterested there follows a detailed accountof the pH sensor. 14

Figure 3. This photographshows clearly how themeter is assembled in thecase.

3-37

speech formicrocomputersphonemesynthesizer withCentronics input

A phoneme (Greek: 'speechsound') is a basic soundunit in a language. E.g. inEnglish 't' and areseparate phonemes; 'c' and'k' may be the same or dif-ferent (cider; caulk; kirk);and 's' may be the same ordifferent (sirup; cork; civet);'ph' and 'f' are the same.

Speech processing with personal computers is still a very costly andrestricted affair. Fairly simple methods using your own spoken textneed large memories and even then the results are modest. Industrial,and therefore much more expensive, computers don't do all thatmuch better, although they sound better. The phoneme generatorsuggested in this article is relatively inexpensive and can be operatedwith a medium-sized memory.

The proposed phoneme generator isbased on the type SPO 256 speech pro-cessor IC. We set out to produce a com-prehensive construction plan, completewith pcb and application notes. But prac-tical work with the circuit soon showed(as we should have known) that it's not assimple as all that: a pity, but on the otherhand the SPO 256 is by far the cheapestIC of its kind on the market. If you wantquick results ("Hurray, my computer can

talk!"), you'll have to think again. Thisarticle is rather for those who areinterested in experimenting with speech.It can teach you a lot about the structureof spoken language and the programmingof a phoneme synthesizer. A littleexperience in the art of phoneme arrang-ing can give much enjoyment in comingto grips with the principle of speechdeliverance.

3-38

Phonemes and soundsFrom the definition of a phoneme it is evi-dent that any word in a language can bebroken down into a number of phonemes.The word 'man', for instance, consists ofthe phonemes 'm', 'a', and 'n'. But hereagain, difficulties arise, particularly inEnglish, for there are twenty-six basic let-ters in the English alphabet, but over fortybasic sounds. The English language getsaround this problem by using the sameletter or letters for different sounds, as in

Table 1.

phoneme represen-tativesound

(bold letters)decimal

codeallophone duration

(ms)

00 10 pause01 20 pause02 50 pause03 100 pause04 200 pause05 OY 290 boy06 AY 170 five07 EH 50 left08 KK3 80 count09 PP 150 peak10 JH 100 jump11 NN1 170 none12 IH 50 it13 TT2 100 to14 RR1 130 right15 AX 50 trouble16 MM 180 magnet17 TT1 80 part18 DH1 140 they19 IY 170 see20 EY 200 stay21 DD1 50 card22 UVVI 60 computer23 AO 70 long24 AA 60 hot25 YY2 130 yard26 AE 80 man27 HH1 90 he28 BB1 40 trouble29 TH 130 thin30 UH 70 push-pull31 UW2 170 food32 AW 250 south33 002 250 do34 GG3 120 jig35 VV 130 very36 GG1 80 go37 SH 120 shift38 ZH 130 measure39 RR2 80 bring40 FF 110 for41 KK2 140 skip42 KK1 120 ask43 ZZ 150 zero44 NG 200 talking45 LL 80 look46 WW 140 wire47 XR 250 dear48 WH 150 where49 YY1 90 yes50 CH 150 chip51 ER1 110 counter52 ER2 210 turn53 OW 170 slow54 DH2 180 lathe55 SS 60 stop56 NN2 140 no57 HH2 130 hertz58 OR 240 store59 AR 200 arm60 YR 250 clear61 GG2 80 glue62 EL 140 angle63 BB2 60 bit

the many ways in which the ough combi-nation can be pronounced; and it givesthe same sound all sorts of different mean-ings and spellings: the same vowel<i>appears in sit, women, village, busy andenough, for instance. Then there are pear,pair; and pare; site sight, and cite; so,sew, and sow; caught and court; fatherand farther. German has the same in, forinstance, sein and sein ('to be' and 'his');Wetter and Wetter ('punter' and 'weather');and French in perk pair, paire ('father','peer', 'pair'); stir and stir ('sure' and 'on'),and sot and seau ("foolish' and 'bucket').If a word can be broken down intophonemes, it should be possible to buildup words from phonemes and it is thisconsideration, of course, that lead to theconcept of speech production bymicroprocessor. From the above examplesit is evident that speech production bymicroprocessor is immeasurably easierthan speech recognition. We must bear inmind, however, that if a computer uttersthe word rain, it could actually meanreign; which of the two can only beassessed by the context in which it isused. The human brain can cope; butthen it has a memory besides which eventhe most powerful computer memoriespale into absolute insignificance. You willalso see the enormous problems still tobe resolved before we can hope to pro-duce a computer that can differentiatebetween taut and taught or between Monaand moaner. None the less, in theory atleast, if the memory of a computer isloaded with the forty -odd phonemes ofthe English language, it should be able toproduce all the words contained in ourlanguage - given a suitable speech pro-cessor, of course.

The SP0256 as phoneme syn-thesizerThe prototype of the SP0256 introducedsome years ago was not really a phonemesythesizer, but rather a speech cardshrunk onto a chip with a word store inROM. The later version, the SP0256-AL2,is, however, since its internal ROM con -

Table 2.

hello 27-07-45-53.02this 18-12-55-04is 12-55-04the 18-19.04elektor 19.45-07-08-13-58.04speech 55-09-19-50.04card 08-59-21-02

10 for K = 1 0 35 step 120 restore 6030 read I40 LPrint CHM!)50 next K: end60 data 27, 07. 45, 53, 0270 data 18, 12, 55, 0480 data 12, 55, 0490 data 18, 19, 04

100 data 19, 45, 07, 08, 13, 58, 04110 data 55, 09. 19, 50, 04120 data 08, 59, 21, 02

speech for microcomputerselektor march 1985

Table 1. Correlationbetween phoneme code.allophone, phoneme dura-tion, and respresentativesound.

An allophone (Greek: 'othersound') is one of the variantsounds forming a phoneme.

Table 2. Example of asimple sentence, the cor-responding phonemes,and the relevant BASICprogram.

3-39

speech for microcomputerselektor march 1985 .-- .7.-APCi-k1 1:4*

.-3,3.--.7.3.3

3.....4

rV S7vv3.e

+-CA'S"

LATC-_=

vv2t.C.. mt.:3 2E,;COE,CviraS:

ra2r: max..01.i

4 - 4P,LSE 6,37,1

HUHU 111 1

Figure 1. Block diagramof the single -chip NMOSspeech processor typeSP0256-AL2. The 2 KROM of this new versioncontains information forthe generation of sixty-four different phonemes.

Figure 2. Circuit diagramof the completeexperimental phonemesynthesizer.

3T.311,tak

No.

22

2,2

t I

'1

05C2CSCSC233 0.003.60 RESET

INGITN_OLIT

TEST

40

AZA3

7 la

85008-3

Figure 3. The pin con-figuration of theSP0258-AL2.

-S,S95008-1

given in figure 1. The data for thephonemes are stored in a 2 K ROM. Thesynthesizer, which consists of a twelve -pole digital filter and a five -register gener-ator, is controlled by addressed data. Thephoneme data determine on the one handwhich raw sound material is required fromthe generator, and on the other withwhich filter coefficient this sound must beprocessed. The digital, filtered signal isconverted externally into a pulse -widthmodulated analogue signal.

Example of applicationAll necessary hardware is shownschematically in figure 2. The input of thesmall circuit can be connected to anystandard Centronics interface. As only thephoneme data are transferred, the totaldata flow is very small. On average, eightbytes are sufficient for one second's

2

C11

=On

2

16 20STRO

000 4 16 18ict

5 14 17010020 74

LS244

12 la

030 11 g laI 13 7 '4010

05 L1A. 130

BLISTO 17 9

3A 4

23 7 19

R5

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..L0

AO IC2

SP 0256-AL2

OUT 24

LRO taw RR 2.mAS-

1-n A7 osc

3.4;14rtz

2 TST

X1 [I

C2 C1I

R9

0 RIO Ca

lOy16V

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lotC10 C3 Cc-772n 72n

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1051 16V

6 a

L.1385

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220y16V

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664X,92

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MPLS

1W

tains data for phonemes instead of for acertain number of words. This is also avery economical chip, because it is usedin vast quantities in many industrial appli-cations - with a different ROM content.Integrated circuits developed specially foruse as phoneme generators, e.g. the SCOTproduced by Votrax, are considerablymore expensive, although to our ears thisIC produces a clearer, albeit Americanrather than English, sound. This Americaninfluence is also evident in theSP0256-AL2 which stores fifty-ninephonemes, listed in table 1, althoughEnglish linguistics and phoneticsrecognize only forty -odd phonemes in theReceived Standard. This is a pronunci-ation of English which gives little or noclue to the speaker's regional affiliations.The synthesis of words from phonemes iscomparable to a jigsaw puzzle. Particularlyin the beginning it seems almost imposs-ible to get the correct phoneme, but aftera while your ear will become attuned andword formation is then feasible.The block diagram of the SP0256-AL2 is

speech. The phonemes (speech signal)generated by IC2 are available at pin 24 asa digital signal. A small external low-passfilter converts this into an acceptableanalogue signal. The required soundvolume is provided by IC3, a simple audioamplifier of the well-known type LM 386.Programming is relatively simple: all youhave to do is to write in the appropriatephoneme code from the list in table 1.These data are then transferred to theprint interface by LPrint. As an example,the sentence 'this is the elektor speechcard' and the relevant phonemes aregiven in the upper half of table 2, whilethe corresponding BASIC program islisted in the lower half.This is only a small example, but we hopethat you will soon progress to biggerthings! Have fun! 14

Literaturetalk to computers by H P Baumann,Elektor, May 1981, p. 5-17talking board, Elektor, December 1981, p.12-04

3-40

elektor march 1985

tuning fork(October 1984, page 10-26)On page 10-28, secondlumn, lines 10...13C12/C13iR40 shouldC12/C13/R37C14/C15/R41 shouldC14/C15/ R38D36 should read D2D37 should read D3

I

co -

read

read

digital band-passfilter(July/August 1984,page 7-48)

Resistor R19 should be con-nected in series with additio-nal capacitor of 1 ;IF betweenpin 13 of IC1 ( - input of A4)and earth: this will raise the Qfactor to its required value_the times stated at the outputwaveforms of the two mono -stables are the periods of theinput pulses and not of theoutput signals.

flash meter(September 1984,Page 9-36) .

There are some stubbom ca-ses defying our previous solu-tion to problems caused byleakage currents. If you areexperiencing these, removepin 3 of IC6 from its socket,unsolder all connections tothis point on the pcb and re-make them 'in the air' direct

to pin 3. Use short lengths ofinsulated wire. The other sideof DIL switches S5...S8 andthe corresponding terminalsof C8...C11 should also beunsoldered from the pcb andremade 'in the air' with shortlengths of insulated wire.

3-41

elektor march 1985

How to make your own PCBsYou require an aerosol of 'ISOdraft'transparentizer (distributors for the UK:Cannon & Wrin, 68 High St., Chislehurst,Kent, 01 467 0935, who will supply thename and address of your local stockist onrequest), a mercury vapour lamp, sodiumhydroxide (caustic soda), ferric chloride,positive photo -sensitive board material(which can be either bought or homemade by applying a film of photo -copyinglacquer to normal board material). Wet the photo -sensitive (track) side of

the board thoroughly with thetransparant spray. Lay the layout cut from the relevant

85021 - darkness -sensitive light switch

DANGER! Ultra -violet light is harmful to your eyes, so when working witha mercury vapour lamp, wear some form of effective eye protection.

page of this magazine with its printedside onto the wet board. Remove any airbubbles by carefully 'ironing' the cut-outwith some tissue paper. The whole can now be exposed to ultra-

violet light. The exposure time is dependent upon

the ultra -violet lamp used, the distanceof the lamp from the board, and the photo-sensitive board. If you use a 300 watt UVlamp at a distance of about 40 cm from theboard and a sheet of perspex, an exposuretime of 4 ... 8 minutes should normally besufficient. After exposure, remove the layout sheet

(which can be used again), and rinse

85025 - KITT scanner

the board thoroughly under running water. After the photo -sensitive film has been

developed in a sodium hydroxide solu-tion (about 9 grammes of caustic soda toone litre of water) for no more than21/2 ... 3 mins at 20°C, the board can beetched in ferric chloride (500 grammes ofFeC13 to one litre of water). Then rinse theboard (and your hands!) thoroughly underrunning water. It is advisable to wear rub-ber or plastic gloves when working withcaustic soda or ferric chloride solutions. Remove the photo -sensitive film from

the copper tracks with wire wool anddrill the holes.

3-42

85019 - versatile counter module

EnenMN.us.ENLii_lilia IMMO

;SCIirp-ku fur4.=

/Mk

3-43

elektor march 1855

PC board pages

3-44

turnout (points)

turnout Ipoints) controlelektor march 1985

with or withouta computer

controlTurnouts (points) are usually controlled remotely by the use ofelectro-magnetic drives (solenoids) which are operated by shortpulses of current. In practice things sometimes go wrong and thepulses of current will cause the solenoids to go literally up in smoke.The electronic drive and power supply described in this article canprevent such disasters.

As long as the turnouts in a model railwayare remotely controlled by hand, the riskof damage to the solenoid is small: youwill note almost immediately whether thecoil goes on humming when the voltagehas not been switched off in time.Nowadays, it is not too difficult toautomate any model railway by amicroprocessor. This implies immediately,however, that much more stringentrequirements must be met by the turnoutcontrol circuits, because the computercannot hear, see, or smell. This seems anexcellent reason to have a critical look atthe control of electric turnouts. At the endof this article we will give our imaginationfree rein and see what a computer-controlled model railway would look likeand, particularly, how such a model couldbe realized.

TurnoutsManufacturers of electro-magnetic drivesassume that the solenoid will only get a

short pulse of current, sufficient to changeover the turnout: no current is required tokeep it in its new position. Relativelyspeaking, the change -over of a turnoutrequires considerable power and becauseof that a large current flows through thesolenoid. If that current continues to flowfor some time, the resulting heat willcause the insulation of the coil to melt.The change -over of turnouts is thereforeoften effected by switches with spring -loaded contacts, which cannot, however,guarantee that the pulse of current is shortenough, because it is possible that theswitch is pressed too long or that theswitch contacts stick owing to a defect. Toprevent such mishaps, most turnouts areprovided with a micro -switch that cuts offthe current to the solenoid as soon as theturnout has changed over. This is the sumtotal of safety precautions provided bymost manufacturers.There are, however, other causes formishaps. The most common is that owingto insufficient current the drive does not

3-45

turnout (points) controlelektor march 1985 1

Figure 1. To prevent theburning out of a turnoutsolenoid that is driven bya power supply as shownin figure la, simple pro-tection circuits as shownin figures lb and lcshould be added. Thecurrent to the solenoid isthen limited by R1 or R2:during switching theenergy from C2 or C3 isused. The extension in lcaffords more protectionthan that in lb. When thepower supply so extendedis loaded with a solenoid.T1 is off and only thecharge of C3 is used forchanging over the turn-out. Only after thesolenoid has beenswitched off can C3recharge (rapidly) via Ti.

Figure 2. This electronicswitch is intended forswitching turnouts. WhenS1 is changed over, T1and T2 (or T1' and -r2., asthe case may be) areturned on briefly. Thiscauses the solenoid to beenergized and the turnoutchanges over.

7812

:C;

tf

20 V25 mAtent.

470070V

63017-1c °

reach the other side or clatters against it.In either case, the micro -switch does notcome into operation and the conse-quences may be disastrous. More safetyprecautions are therefore necessary andthese can be provided by electronics.

Power supply for turnoutsA suitable power supply of conventionalconfiguration is shown in figure la. To limitthe current through the solenoids, aresistor may be connected in series withthe +20 V line as shown in figure lb. Thepower supply solves the problem of short-circuits (and the consequent very highcurrents) in a simple way. To ensure that asufficiently high current is fed to thesolenoid, an electrolytic capacitor, C2, isconnected after the series resistor, RI. Byexperimenting with the value of thecapacitor (the value shown was right forour purposes), it is possible to match thepulse energy with the requirement of theparticular type (brand) of solenoid.But even this circuit has drawbacks. Theshort-circuit current of 50 mA may still betoo high, and it takes a relatively longtime after a pulse of current before C2 hasrecharged sufficiently to enable turnoutsto be operated. The value of the short-circuit current cannot be reduced byincreasing the value of RI because this

will lengthen the recovery time of C2. Norcan the recovery time be shortened byreducing the value of RI, because thenthe value of the short-circuit currentbecomes too high.There are two solutions to this problem.The simpler is connecting a series resistorand buffer capacitor in the supply to eachturnout (one transformer can power manyturnouts because energy is only requiredin short bursts). The recovery time is thenstill too long to enable quick successiveoperations of one turnout, but all otherturnouts can be operated (alomost) simul-taneously. This solution is best suited tothose systems where further automation isplanned, because only one particular turn-out is normally changed over between twotrains.The second solution is of particular usewhere manual control of turnouts isintended to be retained. It consists ofextending the power supply by the circuitof figure lc instead of that in figure lb. Therecovery time is then much shorter, aboutone second, so that only one seriesresistor and buffer capacitor need to beused to control all turnouts. This solutionis not suitable for automation because itdoes not allow the simultaneous operationof a number of turnouts (as the pulse ofcurrent becomes too weak).

2 20 V

3-46

Control electronicsThe use of push-button switches withspring -loaded contacts for the control ofturnouts is now no longer necessary.Instead, a simple change -over (toggle)switch is used: Si in figure 2. The circuitin this figure generates a pulse of currentin one of the two turnout coils every timeSi is changed over and the input is conse-quently switched between 0 and 12 V. Theposition of the turnouts is indicated byLEDs DI and Dl'.Although no precaution is one hundredper cent reliable, it is highly unlikely thatthe solenoids will burn out. After all, thereare three safety precautions: the supplycurrent is limited by RI and Cl; R6 and C2ensure that transistors TI and T2 are onfor only a brief moment, and there is stillthe turnout's own safety switch.The stabilizer circuit shown in figure 2aneeds to be built only once: it is capableof driving some ten turnouts; and evenfifty if a I A transformer is used and Cl isgiven a value of 2000 ,F!

AutomationThe circuit has already become very use-ful because manual control of the turnoutshas become much more reliable. Byadding a further extension, it becomespossible to switch between manual andautomatic control, as shown in figure 3.There is now an 'auto/man' input which isshown for 'automatic' operation.The turnout signal 'auto W' is passed onand if the output of N4 is connected withthe input (terminal A) of figure 2, the pos-ition of the turnout is determined by the'auto W' signal. Note that switch Si infigure 2 is now located at the 'man W' ter-minal of figure 3. The 'auto W' signal isgenerated by the computer that controlsthe model railway. Note that the computeris powered by +5 V and the circuit infigure 3 by +12 V. This requires levelmatching which can, for instance. beeffected with an open -collector gate.

Computer controlThe last paragraph dealt with computercontrol, but here we must disappoint you:it is not (yet) possible to present a fullycomputer -controlled model railway in afew pages. We have, however, decided, aswith the junior computer, the TV gamescomputer, and the Formant, to publish allthe required information in a book to bepublished this spring: 'Automate yourmodel railway'. You may well ask yourself:"For whom is that book intended? Doesone have to be a computer specialist or isit suitable for the interested layman?"To answer those questions, it is sensibleto ruminate on what is involved inautomating a model railway.In the first place, trains must be able totravel. This requires a power controller,preferably a good one that allows slowstarts and pull-ups. Such a controller is

3

N1 ... N4 = IC4= 4011

turnout (points) controlelektor march 1985

630173

and remains indispensable, whether therailway is controlled by hand or bycomputer.Reliable turnout control, as we have seenabove, is of prime importance.A further requirement is the division ofthe railway into blocks and sections andthe addition of colour light signals. At thisstage it is also sensible to incorporate pro-tection circuits, irrespective of whetherthe movement of the trains is determinedby man or by machine. If the protectioncircuits are electronic rather thanmechanical (i.e. relays as recommendedby many manufacturers), the reliability fac-tor is further increased appreciably.Only when the above points have beenattended to does it become sensible toconsider the addition of a microprocessorto control the entire system. The result ofthat addition will be a railway on whichtrains, in some mysterious fashion, movealong the tracks without mishap and(apparently) without needing human help.In that sense, it is possible to build themodel railway in steps. Each step in itselfis sensible, irrespective of whether furtherautomation is contemplated or not. Thisapproach makes it possible to go as far aspersonal taste or bank account or bothallow.To be honest, the book starts with apower controller which has been kept suf-ficiently simple to allow anyone building itsuccessfully. On the other hand, the lastchapter dealing with how the Junior com-puter can control the system takes a littlelonger to digest But, of course, by thetime you get there, you have that muchmore knowledge and experience!The final question may well be whether itis a good thing to automate a modelrailway. Unfortunately, this cannot beanswered with a simple yes or no. Thereare hobbyists who immediately upon com-pleting a project dismantle it to startafresh. Others do nothing but write newtimetables. In the same way, there are pro-ponents and opponents of computer con-trol of a model railway. 14

Figure 3. This circuitmakes turnout controlreally interesting. Itmakes it possible tochoose between manualcontrol or automatic con-trol by computer.

3-47

new keyboard forSpectrum...elektor march 1985

When Sinclair introduced a new Spectrum last autumn, they at lastacknowledged that the poor keyboard on the old Spectrum wasallowing the competition to take over slices of what had been a safeSinclair market for some time. It is gratifying to see that they havefinally decided to right this abomination.The new machine is type -coded Spectrum+ and is a much moreuser-friendly unit that can stand comparison with any other computerin its price class. Its faint resemblance with its bigger brother, theQL, gives it an impression of solidity. Inside it has remained verymuch the same. And why not? Apart from its miserable keyboard,the old Spectrum, with its wide-ranging BASIC and its really usefulgraphics, was one of the best -value -for -money home computersaround.

newkeyboard

forSpectrum . . ....makesprogrammingeasier

The noteworthy aspects of the newkeyboard are not just the much easier tooperate keys, but also a large number ofsingle -key operations. which on the oldSpectrum were only available by pressingmore than one key at the same time. Thismakes programming and particularlyediting a lot easier.If you have an old Spectrum and wouldlike the facilities of the Spectrum+,without buying the new version, the cir-cuit suggested here is for you.

The new keyboardThe layout of the new keyboard is shownin figure 1. All keys of the old keyboardhave been retained, and new ones havebeen added as follows:Top row: TRUE VIDEO; INVERT VIDEO;BREAKSecond row: DELETE; GRAPHICThird row: EXTEND MODE; EDITFourth row: FULL STOPBottom row: SEMICOLON; DOUBLEQUOTATION MARKS; four CURSOR keys;COMMAOther novelties are that the CAPS SHIFTand SYMBOL SHIFT have been duplicatedat the left-hand and right-hand side, andthat the SPACE bar has been centred andmade wider.

OperationHow Sinclair has solved the problem ofthe additional keys is of little interest here,

as we had designed the present circuitbefore the Spectrum+ had beenannounced.Figure 2 shows what the Spectrum lookslike when the keyboard cover and theconductive silicone rubber sheet directlyunderneath it have been removed. Thecircuit diagram of the 8 by 5 scannermatrix that has become visible is shown infigure 3. Each switch shown in thediagram represents a key contact. Thenumbering is arbitrary and has no specialsignificance. This matrix is also present inour proposed new keyboard, with the dif-ference, however, that the touch -keys havebeen replaced by full-size keys: this givesa feel that is similar to that of a typewriterand entry speed is, therefore, muchhigher and much more reliable. The sec-ond CAPS SHIFT and SYMBOL SHIFT keyshave simply been wired in parallel withthe original ones.The old keys that need no additional ornew electronic circuitry are called 'A' keysin figure 4.The key contacts in figure 3 are controlledwithout any problem by CMOS switches.These switches are at the heart of ourdesign: any of the additional keys operatestwo or more CMOS switches simul-taneously. If we now consider the 'B' keysin figure 3, we see that all functions con-trolled by contacts S41...S51 have this incommon: the CAPS SHIFT key must bepressed at the same time as another key.It is therefore necessary that each keycontact is connected to a CMOS switch

3-48

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(ES) that is connected in parallel with theCAPS SHIFT contact on the 8 by 5 matrix.and to a switch that is connected in paral-lel with the relevant original key contact.For example, to carry out the operation'edit'. it is necessary to actuate the '1' andthe CAPS SHIFT keys. The former iseffected by ES2, and the latter by ES1(which interconnects the Al and B1 buslines). All CMOS switches, except those

that operate the CAPS SHIFT and SYMBOLSHIFT keys, are controlled via delay net-works. This is necessary to ensure that atall times the CAPS SHIFT or SYMBOLSHIFT contact is operated first. Thediodes are decoupling devices andshould not be omitted. otherwiseerroneous operation may ensue.Keys S52...S55. the 'C' keys, operatesimilary to S41...S51, except that here the

new keyboard forSpectrum...elektor march 1985

Figure 1. Layout of theproposed new Spectrumkeyboard, with all the oldkeys retained in theiroriginal position. Thenewly added keys do notrepresent new instruc-tions or functions, butenable single -key oper-ation where before morethan one key had to bepressed. Note theenlarged ENTER key, theduplication of the CAPSSHIFT and SYMBOLSHIFT keys, and themuch better location ofthe SPACE bar.

Figure 2. Once the lid andconductive silicone rub-ber sheet have been liftedoff the keyboard. thescanner matrix becomesvisible. ConnectionsAl...A5 and 81...88 areidentical to those on thecircuit diagram. The newkeyboard is connected inexactly the same way asthe old one: this is bestdone with ribbon cablewhich is soldered at theunderside of the com-puter board in place ofthe obsolescent socket.

3-49

new keyboard forSpectrum...elektor march 1985

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SYMBOL SHIFT key instead of the CAPSSHIFT key is actuated (by ES13). With thehelp of figures 1 and 3 it is possible torealize any function you want by usingfurther keys and CMOS switches. The pro-posed circuit follows the keyboard of theSpectrum+, however, although many ofyou may find the VIDEO keys rather anunnecessary luxury which are betterreplaced by COLON (:) and SOLIDUS (/)respectively.

Extend mode keyThe EXTEND MODE key, the 'D' key, issomewhat different from those describedsolar. To jog your memory: if you want touse instructions printed in green (oldkeyboard), it is necessary to press theCAPS SHIFT and SYMBOL SHIFT keys sim-ultaneously, release them, and then pressthe appropriate command key. If you wantto use red instructions, the situation iseven worse: you then have to press theSYMBOL SHIFT key, holds this down, andthen press the instruction key. Theseproblems are resolved by the EXTENDMODE key, S56. This switch is connectedto ES1 (CAPS SHIFT) via monostableN1/N2, and to ES13 (SYMBOL SHIFT) viaD22. When S56 is held down when theinstruction key is pressed, the monostableformed by NI and N2 opens the CAPSSHIFT key contacts after a very short time:the 'lower case' (red) instructions are thenavailable. If, however. S56 is pressed andthen released before the instruction key ispressed, the upper case (green) instruc-tions become available.

Power supplyThe keyboard may be operated from theSpectrum power supply. It is, however,recommended to use an 8 -volt regulator,because a level of 5 V is pretty close tothe lower limit of the CMOS ICs. It isfurther recommended to solder a capaci-tor of about 220 nF between the supplypins of each IC. The circuit has beenworking faultlessly in our laboratories for

some months, so that we cannot foreseeany problems.

ConstructionAs keytops with the original Sinclairinscriptions do not appear to be commer-cially available, it is best to use keyboardswitches with transparent keytops. Thesetops snap on to the switch and consist oftwo pans. The lower part may beengraved, marked with Letraset, or apiece of printed card may be placed on it,so that when the transparent top part issnapped on, the key -top appears to have aprinted legend. Character set transparen-cies are available from many retailers.The keyboard may be constructed on aprinted circuit board (we do not offer onewith this project, so it will have to bemade by yourself) or on veroboard.Dimensions are about 400 x 150 mm, sounless your retailer stocks this size board,you may have to make one from two.Because of the pressures exerted on akeyboard, mechanical strength of theboards is, of course, vital.

Finally......a tip for all d.i.y. programmers. In manygames, it is possible to interrupt with theaid of the cursor keys. On the old Spec-trum keyboard, the cursor arrows werelocated above the figures 5...8, and itwas, therefore, simple to interrupt thegame or other program by writing thesefigures in conjunction with the INKEY S -function. For instance,IF INKEY S = "8" THEN...Because the cursor keys on the newkeyboard are separate, and have no sym-bol, but only a function character, it isnecessary to use the code of the cursorfunction if you want to control the com-puter with the cursor keys. This can beascertained from the handbook. The cor-responding instruction will now besomething likeIF CODE INKEY $ = 10 THEN... 14

new keyboard forSpectrum...elektor march 1985

Figure 4. Identifying thesingle key switches byA... D makes it clear thatfrom a purely electronicspoint the keyboard maybe considered in fourparts: (1) keys A, whichare unaltered; (21 keys B,which control functionsfor which on the oldkeyboard the CAPS SHIFTkey had to be operated atthe same time; (3) keys C,which control functionsfor which on the oldkeyboard the SYMBOLSHIFT key had to bepressed at the same time;(4) key D, which actuateseither the lower case(red) functions or theupper case (green) ones.

3-51

19 kHz precision calibratorelektor march 1985

a simple test -instrumentcalibration aid

19 kHz precisioncalibrator

Test instruments are essential for any serious laboratory, be it'professional' or a hobbyist's workshop. Bad test equipment, on theother hand, can be worse than no equipment at all as it gives wrongimpressions that are likely to be taken as 'truths', Accuracy is alwaysa point of doubt with home-made test instruments and for thisreason we were very careful to give a detailed test procedure for ourrecently -published frequency counter. In hindsight, however, itoccurred to us that one point could be considered as an example of'Catch 22': a good frequency counter was needed to calibrate thecrystal oscillator. To remove this difficulty we came up with a simple,but accurate, circuit.

A test instrument must be reliable andaccurate and, in general, the more you areprepared to pay the more of these twoqualities you can expect Home-madeequipment is somewhat of an unknownquantity in this respect and must in somecases be referenced to other proven testinstruments. This is the case with the fre-quency counter circuit, whose crystaloscillator must be calibrated with refer-ence to a frequency meter that is knownto be accurate. Fortunately, there is a wayout of this 'Catch 22' situation, and all thatis needed is the small circuit shown hereand a cheap FM transistor radio.

19 kHz from the radioThe frequency of 19 kHz was not simplychosen at random for this circuit. This is,

in fact, the frequency of the pilot tonetransmitted in FM radio signals. In thecase of good quality or hi-fi tuners,however, this frequency is very effectivelysuppressed after the stereo decoder sothey are unsuitable for our purposes.The loudspeaker or earphone output of amono FM radio is connected directly tothe input of our circuit. Band-pass filterRI/Cl/L1/C2 removes all unnecessarypans of the signal and this is thenamplified by TI and fed into pin 3 (INPUT)of IC1.The 567 (ICI) is a phase locked loop (PLL)used as a tone decoder. The functions ofeach of its pins are indicated in thediagram of figure 1. The PLL is tuned to aparticular frequency by means of theexternal timing components connected topins 5 and 6. The values indicated set IC1

3-52

1 19 kHz precision calibratorelektor march 1985

R3

LOOP . OUTPUTFILTER FILTER

CS

1070V

C5

700n 7. 70n

R9

D3

55041

5V

19kHz

to a frequency of 19 kHz, of course. Theband -width of this lock frequency' isdetermined by C5, while C4 serves tosuppress the effects at the output ofspurious input signals outside the lockrange.When ICI detects an input signal withinthe frequency range selected it locks ontoit. The 567's output then goes low so theyellow LED lights. If the PLL is not prop-erly locked onto the input signal, or if theinput signal does not remain within thelock range for a while, capacitor C8 ispartly charged so the green LED cannotturn on. As soon as the PLL is properlylocked onto the 19 kHz signal T2 is turnedoff and the two LEDs light together. Thesignal output from pin 5 of ICI is then asquare wave with a frequency of exactly19 kHz.

Construction, calibration and useThe circuit should be constructed care-fully bearing a few points in mind. Keepall wiring as short as possible and makesure to use thick cable for the ground andpositive voltage supply lines. It is alsovery important to connect capacitor C6 asclose as possible across IC1's VCC andground pins (4 and 7).Connect the input of the circuit to theloudspeaker (or earphone) output of anFM mono radio and tune into a strongtransmitter broadcasting in stereo. Care-fully set preset P1 so that the green LEDjust lights at the input signal's minimumamplitude.To use the circuit increase the radio'svolume control slightly and tune into a dif-ferent transmitter. The yellow LED lightswhen ICl locks. The green LED will onlylight if there is not too much noise on thesignal. Increase the volume setting or/andtune to a different transmitter until thegreen LED lights continuously. If thegreen LED lights when the radio is tuned

to a number of different transmitters thecircuit is working correctly and the outputsignal then has a frequency of 19 kHz.There are a few final points regardingusing this circuit. First of all, it isadvisable to tune the radio to a 'quiet'transmitter such as a classical musicprogram. There is less chance of noise orinterference on such a signal than wouldbe the case with a contemporary musicprogram. The second point concerns theaccuracy of the 19 kHz pilot tone. The EBU(European Broadcasting Union) normstates that this must be 19 kHz + 2 Hz. Thisis quite a tight tolerance but in most casesthe signal will be even closer to 19 kHz.The measurements we made showed thatthe signal was, in fact, accurate to within+ 0.001%.This test circuit was designed as an aid tosetting up the microprocessor -controlledfrequency counter described in theJanuary 1985 issue of Elektor but it canalso be used to test and calibrate otherlaboratory equipment. In the case of thefrequency meter simply let it warm upfirst and then measure the 19 kHz with theA input. Trim the preset in the oscillatoruntil the display shows '19.0000 KHZ: Bythe same token this circuit need not onlybe used for calibration purposes. It couldbe used in any application where a veryaccurate 19 kHz signal is required butbecause a radio has to be connected toits input it cannot be considered as a per-manent fixture.

Figure 1. With a cheapradio connected to itsinput this circuit is a veryeffective 19 kHzcalibrator. Depending onthe actual radio used itmay be possible to drawthe power supply of 9 Vd.c. from the radio's bat-teries or power source.The circuit's current con-sumption is about 40 mAwith both LEDs lit. If theradio cannot supply it the9 V can be provided byseparate batteries.A different value ofinductor can be used forL1 but the capacitance ofC1 will then have to bere -calculated from theformula: C1 = 114,tzeL.where f = 19 kHz, ofcourse.

3-53

versatile counter circuitelektor march 1985

Counter circuits have long been a tradition in Elektor. It started withone of the very first issues way back in 1975 and has continued eversince. In spite of this we still get regular requests for counters to dothis and counters to do that. To satisfy all these, we have developed acounter circuit that can: count upwards and downwards; be used with a variety of displays: LED, LCD, FD, and others; store the counter contents; preset the counter position.

versatile counter circuitupwards ordownwards, forLED or LCD, forcommon -cathode orcommon -anode

The circuit diagram in figure I showsnothing really surprising: decoder, ICI;counter, IC2; and seven -segment LD1. Thesurprises are contained within the ICs!IC2 is a synchronous BCD upwards anddownwards counter whose content maybe preset. The presetting function is asyn-chronous.BCD counter ICs generally contain fourbistables and a number of gates withwhich the required function can bearranged. Asynchronous operation means

that one of the bistables toggles when theclock at its input changes. In other words,each bistable is clocked by itspredecessor. Operation is synchronouswhen the output level of a bistablechanges when the output level of thepreceding bistable goes logic high and afresh clock pulse arrives at its input. Thispulse is provided simultaneously to theclock inputs of all the bistables. With thisarrangement the result does not have towait for the clock to be provided to the

3-54

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last in a long line of bistables.For instance. in an eight -stage counteroperating in the asynchronous mode. 32bistables have to be clocked before theresult is indicated. In synchronous mode,the result is known immediately.There are therefore seven terminalsneeded: two for the supply voltage, Ub(3...18 V), four for the outputs of thebistables (01...Q4), and one for the clockinput (Clk) which is internally connectedin parallel to all bistables. Then there is artinput for signal U/D. which gives thecommand to count upwards or down-wards. And, of course. there is a reset (R)input.Preselection of the counter position is car-ried out via inputs P1... P4. The lowestvalue bit accords with P1 (and subse-quently with output Q1!). Preselection isevaluated when input PE is logic 1,independent of the clock signal; this

mode of operation is therefore asyn-chronous.The two remaining terminals of thecounter IC are CI (carry in) and CO (carryout). It is these terminals that make thecircuit of figure 1 into a proper functionalelement, for they make the connectionbetween the previous and the followingcounter elements. The counter elementscan thus be connected in cascade by con-necting the CO of the previous element to.the CI of the next.The other IC, a BCD -to -seven -segmentdecoder with latch and display driver. issimilar. A glance at the pin -out shows thatseven outputs are available for displaysegments a...g. Then it has four inputsfor the BCD information. A... D. and twoterminals for the supply voltage of3...18 V.The interesting pins here are Ph. B1, andLD. Pin LD is normally logic high; ."hen it

2 CPct

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P1

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versatile counter circuitelektor march 1985

Figure 1. A counterelement consists of acounter IC (synchronousBCD upwards anddownwards counter withasynchronous preset), adecoder IC (BCD -to -seven -segment decoderwith latch and displaydriver), and the LEDdisplay.

Figure 2. Operation of thecounter IC is more easilyunderstood with the aidof this timing diagram.

85019.2

3-55

versatile counter circuitelektor march 1985

Figure 3. Connections tovarious display readouts.When a liquid crystaldisplay is used, thedecimal point should beconnected via an XORgate: the inputs of thegate to Ph and Dp, andthe output to Dp.

Table 1R = resetCI = carry inputCO = carry outputPL = parallel loadU/ D = upidownCIk = clackPE = pulse enableOp = decimal paintPh/Com = common anode/common cathode

LD = latch disable

Parts list

Resistors:

Fi1...R8 = 220 Q./118 W

Semiconductors:LD1 = MAN4410A gr;MAN4610A o; MAN4910Ar; MAN4810A y (allGeneral Instrument)for Siemens or HewlettPackard types see text

ICI = MC14543B(Motorola)

IC2 = MC14510B(Motorola)

Printed circuit board 85019

Figure 4. The printed cir-cuit board can house twocounter elements; itshould be cut into two,with one part containingthe display section. orinto three if only oneelement land display) isrequired.

3LIQUID CRYSTAL ILCI READOUT INCANDESCENT READOUT

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goes low, the information at the BCDinputs is stored in the IC, and the memorycontent is subsequently fed to pins a...g.Pin B1 is normally logic low. When it goeshigh, all pins a...g are low. The segmentoutputs are also logic 0 when a number

greater than 9 (in BCD code) is present atthe input pins.The junction of pin Ph is best seen withreference to figure 3, which shows thevarious connections to the displayreadouts. We have opted for the LED

3-56

5 versatile counter circuitelektor march 1985

12 V250 mA

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display, because this is not only the mosteconomical but is also the most suitablefor use with this particular IC.

ConstructionA printed circuit for two counter elementsis shown in figure 4. The board should becut into two, with one part containing thedisplay, or into three if only one element(and the display) is required.The boards are put together as shown inthe photograph: that containing IC1 andIC2 is at right angles to the display board.The earth planes of the boards must besoldered together; this makes it impera-tive that the boards are cut absolutelystraight. Additional stability is provided byresistors R1...R8 being soldered to twoboards!Most terminals are located at the shortedge of the board(s); only Dp, +, and LDare at the long side. This was arranged sothat when several boards are in cascade.they can be placed side by side on aprototyping (vero) board. To ensure suf-ficient stability, the terminals at the longside, and possibly also the Clk terminal,must be soldered to the vero board. Ourprototype which was assembled in thismanner proved more than adequatelystable. Do not forget to connect the COterminal on one board to the CI terminalon the next.

A final word about the LED display. SinceIC1 can provide a segment current of only10 mA, it is advisable to use the General -

Instrument type given in the parts list.Siemens and Hewlett Packard types drawrather more current, about 15..25 mA, forthe same light intensity. When these typesare used, it is therefore advisable to buffereach of the segment outputs as, for in-stance, in figure 3 (incandescent or gasdischarge readout).Take care to solder the Ph/Com terminalwith correct polarity.

ApplicationsOne of many possible applications of thecounter element is shown in figure 5,which is an adaptation of the 'revolutioncounter' described in the September 1981issue of Elektor. As is shown, the specialIC type MK50398 then used is replacedby six of the present counter elements (ofwhich only two are shown in figure 5).As we said in the beginning, there is nocounter requirement that cannot be solvedby the element presented here!

12V

0

0135019-5

Figure 5. Example of anadaptation of the revol-ution counter describedin the September 1981issue of Elektor. Notethat only two of the sixrequired counter elementsare shown.

3-57

darkness -sensitive lightswitchelektor march 1985

As can be read almost daily in any newspaper, the number ofburglaries in private residences continues to increase. The police areoverworked, and the courts, as usual when it concerns crimesagaints the private citizen, far too lenient, so that manufacturers ofsecurity equipment are, understandably, doing good business in spiteof the hefty prices they charge for their products. The philosophyappears to be that if you have something worth protecting, you'renormally quite prepared to pay for it. But does it really have to be soexpensive? Since it is a fact that most burglaries occur during thehours of darkness, we feel that even a relatively simple, andinexpensive, switch as suggested here will deter most would-beintruders. And don't forget, no security system, however expensive,gives one hundred per cent protection!

darkness -sensitivelight switchto frighten offwould-beburglars

Figure 1. The circuitdiagram of the darkness -sensitive light switchwhich automatically turnsthe outside lightls) onand off depending on theambient outside light.The sensor used is anLOR (R81. The integratedmains -synchronized trig-ger circuit type TDA 1024enables the practicalrealization of the switchto be small. One of theadvantages of mains -synchronized triggering isan appreciable increase inthe life of the light bulbsused.

The great advantage of the proposed elec-tronic switch, compared with itsmechanical counterpart, is that it is fullyautomatic in operation. When it gets darkaround your house, the lights at the frontand back doors are automaticallyswitched on and turned off again atdaybreak. The degree of darkness or lightat which this happens can be preset. Thedarkness -sensitive switch is based on alight -dependent resistor (LDR).The circuit diagram of the complete elec-tronic switch is given in figure 1, fromwhich it will be noted that the number ofcomponents has been kept to an absoluteminimum. This was made possible by theuse of a mains -synchronized trigger IC forsilicon -controlled rectifiers, the typeTDA 1024. This can conveniently be fedfrom the mains via a simple series RC net-work, R9/C2, so that a separate supply isnot necessary. Capacitor C3 also serves asa current -limiting component, whileresistor R3 limits the current caused by

the closing of mechanical switch Si andby high -frequency mains noise.Basically. the electronic switch proper istriac Tril. Every time the mains passesthrough zero, the triac is fed by a triggerpulse from IC1, but only when it is darkoutside. Triggering at the zero crossingpoint has the advantaae that high -frequency noise generated at the on or offswitching of the load is kept very low. Ifthe triac were triggered at any arbitrarymoment, sharp pulses of current, whichare rich in hamonics, might contaminatethe mains supply. Another advantage ofswitching at the zero crossing point is thatthe initial current through the coldlightbulb(s) is limited which increases theuseful life of the bulb appreciably (seealso 'lamp saver' in the September 1984issue of Elektor).The trigger pulses generated by theTDA 1024 are very short. A constant gatecurrent would cause too much heat gener-ation in the IC itself and in resistors R3and R4, that is, the components that drawthe reauired trigger energy from themains. Resistor R3 largely determines thepulse duration and, together with the on -chip zero crossing detector, ensures cor-rect synchronization of the pulses with themains. The value of this resistor iscalculated so that at the end of the triggerpulse the momentary current through theload, that is, light bulb La, is definitelygreater than the holding current of thetriac. If that were not the case, the triacwould turn off immediately the gate pulsedecays, and, if a bulb of low power wereused, this would either not light at all or,at best, flicker. The latter of the twoeffects is caused by the asymmetry inholding currents and occurs when themomentary load current after the decayingof the pulse is larger than only one of thetwo holding currents. This is the reasonthat the diagram in figure 1 does not only

3-58

state a maximum, but also a minimumpower rating for the lightbulb(s). If a triactype TAG 226 is used, of which thepositive (from A2 to Al) as well as thenegative (from Al to A2) holding current is10 mA at 25°C maximum, the circuit willfunction correctly even at temperaturesround freezing point and bulb ratings of25 W. Higher bulb ratings (up to 200 W) ora more sensitive triac allow even lowertemperatures, which is important if theelectronics are placed outside; we willcome back to this later in the article.Network RUC1 in parallel with the triachas the task of preventing the triac tocommence conducting on high -frequencynoise pulses generated by otherappliances.When a light -dependent resistor, such asR8 in figure 1, absorbs light, its resistancedecreases. The LDR is here connected ina Wheatstone bridge, one arm of which isformed by resistor R7 and the LDR, andthe other by preset P1. The preset enablesthe bridge being set so that the light bulbis turned on when it gets dark outside.The voltage balance across the bridge isdetermined by a comparator in IC1 (pins 4and 5). Network C4/R6 delays the bridgebeing unbalanced by flashes of lighting orohter short changes in light intensity.Capacitor C3 decouples the comparatorinput. Capacitor C5 smoothes the controlvoltage generated by the IC.To prevent erratic operation of the circuitduring slow changes in outside light, as atdawn or dusk, the IC has inherentswitching hysteresis, which may be fixedexternally between two limits by R5. Thehysteresis varies between 10 and 300 mVfor values of R5 between co and zero; apractical average value has been chosenin the present circuit.

Practical aspectsDue to the use of an integrated trigger cir-cuit, the printed circuit board of the lightswitch could be kept small enough (65 x50 mm) to fit in a single junction box. Thismay, of course, be one that is already partof your electrical system, provided this is

on the circuit (i.e. same fuse) to whichyour outside light is, or will be, connectedand that there is space for the board.In the following it is assumed that youhave to fit outside lights. From a con-venient take -off point in the electricalsystem, run 5/8 in. conduit to the positionwhere the junction box with PCB will belocated. Also fit a mains on/off switch (S1in figure 1) near the box or in any otherconvenient position in the new run. Thejunction box should preferable be fittedindoors, because low temperatures makethe triac less sensitive and it is less likelyto be damaged by intruders.If, however, you have no choice but toplace it outside, use a more sensitive triac,such as the TAG 206 or TAG 207, lightbulbs of not less than 40 W, and fit thebox out of easy reach.From the junction box run a 3 -core cableto the outside light(s) and a 2 -core cableto the sensor (LDR) as shown in figure 4.These cables should be run in conduit or

2

darkness -sensitive lightswitchelektor march 1985

Parts list

Resistors:

R1 = 68QR2 = 47QR3 = 680 kR4 = 390R5 = 470R6 = 22 kR7 = 47 kR8 = light -dependentresistor, 50...100 k

P1 = preset 100 k

Capacitors:

Cl = 100 n/400 VC2 = 220 n/400 VC3 = 100 nC4 = 100 fill0 VC5 = 470 y/25 V

Semiconductors:IC1 = TDA 1024Tril = triac, min. 4 A/400 V; max. holdingcurrent -i- 10 mA; max.positive trigger current10 mA; suggested typesTAG 226 or TAG 227 -more sensitive types areTAG 206 or TAG 207

Miscellaneous:

2 -way terminal block forPCB fitting

3 -way terminal block forPCB fitting

PCB 85021

Figure 2. The printed cir-cuit of the light switch iseasily fitted inside asingle junction box. Thetriacs suggested need notbe cooled with bulbratings up to 200 W.Higher ratings are notrecommended, even withcooling of the triac: heatdissipation in a watertightjunction box is not verygood.

3-59

darkness -sensitive lightswitchelektor march 1985

Figure 3. Photographshowing the light switchfitted in a junction box.

Figure 4. Suggestedinstallation diagram. Thecolours in brackets referto obsolete wire colourcodes.

4

brown Iradl2.5 won'

Si

Woven (radl2.5 root.

o-

hive (black)2.5 mm'

518" condwtytllow and groan(yellow) 2_5 ism'

NOTE: colour coda for thalble cabta ir. sfs-=,du.,_.Urn) = brown

ontrail=blue=Elk/1111.'0010w and omen

that for condo itad eabl ty.Lbw) = redN(autrail = blackEt arthl = non-frau:axed

1:1VrValjointnt

red1_5 m'

1

indoors I outside r>

!in

Woven fre2d)2.5 mm -

3 -coremains cable

I

1= b!iie 'black]2_5 own.

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black15 ennt

550214

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LDRRe

be suitable, preferably armoured, for out-door use. The green and yellow wireshown near the bulb La is intended forearthing the metal parts of the lamp -holder.The most convenient way of fitting thesensor is to cut the conduit containing the2 -core cable flush with the outside wall,connect the cable to the LDR, and then fixthe resistor to the conduit with araldite(make sure that this is transparent!).Needless to say, there are various otherways of fixing the resistor, but it is, ofcourse, important that whatever youchoose ensures watertightness.Only incandescent light bulbs with a totalrating of not more than 200 W should beused. Neon or similar tubes should not beused because their inductive propertieswould upset the triggering of the triac.Rest the calibration of the light switch.

Wait till you find it's dark enough outsideand then, using an insulated screwdriver(called a mains tester or electricians'screwdriver), adjust preset PI so that thelight just comes on. That's all!Remember to keep switch S1 turned on;this switch is not superfluous, however,because it should be possible to removethe mains from the circuit.If you already have outside light(s), simplyfit the electronic light switch between theexisting mechanical switch and thelight(s). The sensor should, of course, stillbe fitted as described above.Obviously, you cannot expect automaticoutside lights to be a guarantee againstintruders. But, coupled with security lockson outside doors and windows, they offergood additional, yet inexpensive, protec-tion measures against would-be intruders.

3-60

As the title implies, this project is not intended to make hi-fi buffs situp, but rather to meet the many requests for a simple activeloudspeaker that can be connected direct to the headphone output ofsmall cassette players and FM receivers.

mini active loudspeakerelektor march 1985

mini active loudspeakerThe main requirements our designerswere asked to meet were: reasonablysmall dimensions, not too expensive tobuild, active operation, and good qualitysound reproduction. Furthermore, it had tobe a loudspeaker system that could beconstructed by anyone, which also meantthat the integral amplifier had to be keptsimple. The result is a perfectly accept-able concept which leaves room for somevariation, dependig on personalpreferences and available materials.Purely from a quality point of view, anenclosure of about 7 x 45/s x 31/8 in.(18 x 12 x 8 cm) cannot be claimed tohave more than a modest specificationand yet it is surprising how well this smallunit behaves, particularly if it is fitted withthe recommended two-way system.

LoudspeakersThe choice of loudspeaker unit(s) is, ofcourse, of paramount importance. For-tunately, there are quite a number ofsuitable loudspeakers on the market.Those we tested varied in quality fromreasonably good to excellent.Of the loudspeaker units we tested for aone-way system we found the 8 -cmVisaton type FRS8 and the Audax typeHIF78BiSM best value for money. In thefinal analysis the Audex wins on pointsbecause it has slightly better bassresponse and power handling (15 W com-pared with the 10 W of the FRS8). Of the10 -cm types, the Isophone BPSL100/7(10 W) and the Audax HD10P19BSM (15 W)gave the best results. One-way systemsusing these loudspeakers axe eminentlysuitable for use in bedrooms, hobby-rooms, and teenagers' bedsitters.Our own preference, however, is a two-way system that uses two Audax speakerswhich fit nicely in the proposedenclosure. The woofer is a typeHD10P25FSC (which can also be used as asingle unit in a one-way system) and thetweeter a type TW60A (which is alsoavailable in different constructions andthen type -coded TW51A, TW74A, orTW80A).The HD10P25FSC has a resonance fre-quency of 52 Hz and power handling of30 W. It has reasonable mid -frequencyperformance which starts tapering off atabout 5...6 kHz. As the TWA60A's rangegoes down to well below those fre-quencies, these two speakers, togetherwith a simple crossover network, form aperfect combination for our purposes. The

TW60A has a power handling of 40 W andmeasures 6 x6 cm.

ElectronicsThe electronic part of the system is keptquite simple as shown in figure 1, andconsists of a power supply, an integrated15 W power amplifier, and a passive cross-over network.The power supply could not be simpler atransformer, a bridge rectifier, and twoelectrolytic capacitors - that's all.The power amplifier is just as simple, con-sisting of just an amplifier module typeHY-30 and a volume control, Pl. Even theheat -sink is integral with the IC! The HY-30has only five pins so that mistakes in con-necting up are virtually impossible. Thevolume control will in many cases not berequired, because the output level of mostcassette players or FM receivers is alreadyadjustable.The crossover network, R1 -R2 -C3 -C4 -L1,has a slope of 6 dB/octave which is notparticularly steep, but that is not requiredwith these loudspeakers anyway. It has,however, the advantages over higher -order

1

Fl

S1

100 mA

B = 1340C2200/3500;4xTtl 1N5401

2: 12V 22005

C2

22005

25V

5V

good sound

reproduction at

low cost

Figure 1. The completeelectronics of the miniactive loudspeaker unit: asimple power supply; anamplifier module; and apassive crossover filterfor the two-way system.

1.1 e 02 mN, we textc3 2r7 mrtallited plattie foilC4 = 5,$ *iRI = 5f18/5111R2 e snail a

85034.1

3-61

mini active loudspeakerelektor march 1985

Figure 2. The 30 W a.f.output stage published inthe January 1985 issue ofElektor is a suitablealternative to the HY-30 ICshown in figure 1.

networks that the phase shift it introducesis very small and its response to pulses isbetter.Note that LI is not a miniature choke, buta coil specially made of 0.75...1 mm dia.wire for crossover networks.

Alternative power amplifiersIt is, of course, possible to use a poweramplifier other than the HY-30 IC. In fact,any reasonably good 15...20 W amplifiermay be used, provided it fits in the box.A suitable alternative is the 30 W a.f. out-put stage published in the January 1985issue of Elektor. That amplifier provides20 W into 8 ohms and has the advantagethat, together with the required powersupply, it may be cronstructed on our85001 pcb. A schematic of the ensuinglayout is given in figure 2.

EnclosureThe main requirements for the enclosureaxe that it must be fairly robust, relativelyfree of resonances, and as small as thechosen loudspeakers and the electronicpart allow. Our prototype was constructedin a cast aluminium alloy box df18 x 12 x8 cm which is available frommany retailers. Because of its high rigidity,cast aluminium alloy is eminently suitablematerial for a loudspeaker enclosure.Although the sides of the box are notparticularly thick, there is virtually notendency to resonate. Normal damping isachieved by covering the side and rearpanels internally with one -inch thick glasswool or rock wool.

ConstructionMost of the constructional details will beclear from figure 3. The power transformeris suspended from the top panel; the elec-

trolytics and bridge rectifier are fitted tothe rear panel. Cut a rectangular hole of55 x 40 mm centrally in the rear panelunderneath the rectifier, to which theHY-30 module is fitted. The sides of thismodule have special slots into which thefixing bolts fit. Any gaps between themodule and the enclosure should besealed with two -component epoxy resin.The crossover filter is mounted at the bot-tom of the box. Mains input (with strainrelief sleeve), fuse holder, signal inputsocket, and, where appropriate, thevolume control are fitted in the left-handside panel.The loudspeakers are mounted inside thelid of the enclogure. The woofer requiresa circular cut-out of 92 mm diameter andthe tweeter one of 50 mm diameter. Takecare to connect the speakers with correctpolarity: the + is indicated by a red dotnear the relevant speaker terminal.Once the unit has been wired up andtested - there is no calibration - thestrips of glass wool or rock wool shouldbe pressed against the side and rearwalls. For the sake of clarity, these stripsare not shown in figure 3. Finally, fit apressure sensitive adhesive sealing stripat the inside outer edges of the lid, whichcart then be screwed into place.Finally, figure 4 shows what the enclosureinside looks like when the alternative30 W a.f. output stage is used instead ofthe HY-30 module. This set-up requiresrather more space, so that you may haveproblems if you opt for the two-wayspeaker system and your mains trans-former is on the large side. However, ifyou use a single speaker, there should beno problem as is clear from figure 4. Noteanother advantage of using a metalenclosure: there is no heat sink requiredfor the power output IC! 14

3-62

3 mini active loudspeakerelektor march 1985

Figure 3. Loudspeakers,crossover network, ampli-fier module, and mainspower supply fit neatly ina commercially availablecast aluminium alloyenclosure. Some strips ofglass wool or rock wool(not shown) provide therequired damping.

Parts list

Trl = mains transformer,2 x 12 V/1 A

B = rectifier B40C2200/500or 4 off 1N5401

C1,C2 = 2200 µF/25 VFl = fuse 100 mA (T)S1 = DPDT mains switch

Amplifier:ICI = ILP module type

HY-30P1 = 100 k tog poten-tiometer

Crossover network:

Ll = 0.2 mH (wire dia.1 mm)

C3 = 2y7, metallized plasticfoil

C4 = 5;46, non -polarizedelectrolytic

RI = 6Q8/5 WR2 = 6Q8/5 W

Loudspeakers:

woofer: AudaxHDIOP25FSC (8 Q)

tweeter: Audax TW60A(8 Q)

Miscellaneous:cast aluminium alloy enclo-sure, about 18 x12 x 8 cm

fuse holderstrain relief sleeve or bushfor mains lead

25 mm thick glass wool orrock wool as required

phone socket or jack socketfor chassis mounting

Figure 4. The sameenclosure as shown infigure 3 but here fittedwith the 30 W a.f. outputstage shown in figure 2.The aluminium box is anexcellent heat sink for theamplifier IC.

3-63

transistor unitesterelektor march 1985

G. Fossa n

Many electronic components may only be fitted into a circuit in oneway: the polarity must be correct in other words. Diodes, electrolyticcapacitors, ICs (to name but a few) are marked to show what is theircorrect polarity but transistors do not have any such indication.Knowing the type of the transistor in question it is, of course, asimple matter to look at the data sheet and find out which pinscorrespond to emitter, collector and base. If you do not have the datasheet to hand, however, this makes matters somewhat more difficult.

transistor unitestera universalall -in -onetransistorconnectiontester

Figure 1. The transistor tobe tested is fitted to the'TT position. Its polarity(b, c and e), correct oper-ation and gender (PNP orNPN) are determined withP1 and Si.

ecbecbe

Two things are of vital importance when atransistor is to be used in a circuit, namelywhich pins correspond to emitter, collec-tor and base and whether it is an NPN orPNP transistor. The transistor's data sheetgives this information but the chances arethat you will not have the appropriate datasheet when you need it. A collection ofdata sheets would seem to be the answerbut a much better solution is to make atransistor connection tester like the oneshown here.

A switching transistorThe most striking thing about the unitestercircuit shown in figure 1 is its simplicity.The component under test, TT, is used asa switching transistor. The base current isvaried with PI until the transistor switcheson and causes two of the LEDs to light.Which LEDs light (D1/D2 or D3/D4)depends on whether TT is NPN or PNP.(This is defined by the position of Sl.) Theintensity of the LEDs at a particular pos-ition of PI gives an indication of the tran-sistor's current gain.

The test procedureIn our prototype we fed the 'b', 'c' and 'e'terminals from the circuit to an IC socket,as the diagram indicates. We found thatthis simplified using the circuit as all poss-

8.331

ible connection orders are catered for. Totry a different bce layout the transistor'spins are each moved one hole further. Atransistor is tested as follows: Plug the pins of TT into the IC socket

in any order but making sure that eachfits into a different hole - one into 'b', oneinto 'c' and one into 'e'. Turn PI com-pletely around and back, then switch Slover. If one of these two operationscauses two of the LEDs to light simul-taneously the pin stuck into the 'b' pos-ition is the transistor's base. In this caseboth LEDs will light when PI is at one endof its travel and both will be off at theother end of the travel. Any other indi-cation on the LEDs indicates an incorrectconnection so TT's pins should bechanged around until the right indicationis found. If none of the possible combi-nations gives the correct indication eitherthe transistor is faulty or the component inquestion is not a transistor. Having found the base, the emitter and

collector must now be determined. Thebase current is Set with the potentiometerso that moving PI slightly gives a clearlyvisible change in the light intensity of theLEDs. The LEDs are set to 'medium'brightness and the collector and emitterconnections are then swapped. If theLEDs burn more brightly than before the'c' and `e' connections are now correct. If,on the other hand, the LEDs become dim-mer the previous arrangement wascorrect.

Final pointsThe circuit is easily constructed on apiece of Veroboard and can be connectedto a suitable d.c. power source (batterieswill be sufficient). The voltage supplyshould be about 4.5 V, but must never begreater than 6 V. There is no actual needto use an IC socket for the 'b, 'c' and `e'connections but this does simplify matters.The operation of the unitester can beverified by taking a transistor whose con-nections are known. Select PNP or NPN asappropriate and plug the transistor cor-rectly into the TT socket. When PI ismoved fully around two of the LEDs willlight or go out, depending on whetherthey were on or off.

3-64

elektor march 1985

Mixed -contact dinconnectorsA new range of mixed -contact DIN connectorsis now in stock at Dage (GB) Limited. Made bySiemens, these connectors offer mixes ofstandard pins with up to eight cavities foreither r.f. or high -power contacts; for instance,to take power on to back panels.The r.f. contacts are available either for cable -end or for pcb mounting. For power connec-tion, there is a choice from 10 A, 20 A, or 40 Aratings.

Standard commercial DIN connectors, alsomade by Siemens, are also stocked.The ordinary DIN contacts are electrolytic goldover nickel. The single -row types B, C, and Mhave a contact current rating of 1.5 A and con-tact resistance of not more than 20 milliohms.Types D, F, and G have a contact current ratingof 5.5 A and contact resistance of not morethan 15 milliohms.Dage (GB) LimitedEurosem DivisionRabans LaneAylesburyBucks HP79 3RG102967 33200telex: 83518 (3161M)

Yearbook of West EuropeanElectronics Data12th editionThe new edition of this famous handbookdetails markets 1983-88 and production1982-85 for seven major electronics equipmentsectors and three electronics component sec-tors for 14 European countries. Sectorscovered are Electronic Data Processing (Com-puters), Electronic Office Equipment, Controland Instrumentation, Medical and IndustrialElectronics Equipment, Communications andMilitary Electronics, Telecommunications,Consumer Electronics Equipment, and Active,Passive and Audio Components.Additional data include the output of Vehiclesand Domestic Appliances in Europe, forecastsof Leading Economic Indicators such as GrossDomestic Product, Inflation, Industrial Out-put, Balance of Payments, Unemployment to1985 for each European country, ExchangeRates against the US dollar, a four languageglossary, and a complete explanation of theInterpretation and Classification of thestatistics and a guide to the Electronic Productheadings.

Benn Electronics Publications LtdPO Box 28Luton LU2 OBD(05821 417438telex: 827648 (3153M)

New catalogues from ImhofA new leaflet giving full details of their reviseddesign Impak and Elbox instrument cases.An eight -page brochure giving details of theirlatest major product innovation - the Eliterange of lightweight all aluminium racks.The Express Service Catalogue.

Imhof -Sect° Standard Product LimitedAshley worksAshley RoadUxbridge UB8 2S0(08951 37123 (3154M)

Surface Mounted PackagingSurface mounted components are revol-utionizing the electronics manufacturingindustry claims Texas instruments in a free28 -page booklet published to explain thebenefits and methods of this new technology.The Customer Response CentreTexas Instruments LimitedManton LaneBedford MK 41 7PA/0234167466 (3156M)

Revolutionary new in -linefuse holderA recently announced new fuse holder incor-porates several innovations that make it moreversatile, economical, and safer than currentlyavailable units. For instance, the Safeguard

osARGilminHigh Temp, Low Resistance

u FUSE HOLDERHeat shield Head spring

7.2.111C _.......:=\High temp. High performancematerial spring

20mm - V. fuse range '1Designed for both-continental end glass fuses

W/TH SIX

WINNING FEATURES

fuse holder has a unique heat reflecting shieldto improve the fusing factor. Under overloadconditions, heat is reflected back onto thefuse, causing it to fail sooner, thereby improv-ing its safety performance.The new unit will accommodate a range offuse lenghts from 20 to 32 mm and will alsohandle quarter inch caps or continental points.

Safeguard Fuse Company Ltd63 Woodham LaneNew Hats'WeybridgeSurrey K775 3ND(0942145300 (3162M)

Macintosh Buyers GuideMore than 200 software, peripheral, and add-on products are contained in this new publica-tion launched by Apple Computer (UK) Ltd.Representing the universe of Macintosh soft-ware and hardware, the new guide is availablefrom all Apple authorized dealers in the UK ata maximum suggested retail price of £5.95.Apple Computer (UK/ LtdEastman WayHemel HempsteadAlerts HP2 7HO(04421 60244telex: 825834 (3158M)

Hotmelt glue gunThe Hotfix 180 hotmelt glue gun developed byPower Adhesives Ltd has been selected by theDesign Centre. The gun which incorporates

.the latest technology is designed around asolid-state self-regulating heater. The heater,called PTC (positive temperature control)ensures that the gun reaches proper operatingtemperatures in 3...4 minutes and that it canoperate on any voltage between 100 and240 V. Another advantage of the heater is thatno thermostat is required because it regulatesitself intemally to the correct temperature,ensuring complete accuracy and reliability.The gun takes standard 12 mm diameter Flofixglue sticks.Amongst further design features are a clip -onstand; a power warning light; a fully enclosed,doubly insulated heater housing; and a rangeof optional nozzles and adhesives. The gunwill bond, seal, assemble, insulate, repair, re-inforce, encapsulate, and fill.Power Adhesives Ltd103 Wentz RoadDagenhamEssex RM10 8PS(015931 7228/9 (3133 Ml

Subminiature trimmerpotentiometersA complete designer's guide to the wide rangeof newly -developed trimmer potentiometersfrom Murata is now available in a 24 -pagemanual.

Murata Erie Electronics UK Ltd100-102 Albert StreetFleetHants(02514128585 (3157M)

New mains filtersA new range of mains filters, the FN380 series,is now available from Schaffner EMC Ltd.Developed for use in electrical and electronicequipment, the FN380 incorporates a poweron/off switch and fuse, and is suitable for awide range of applications, including officemachines, electronics instruments, and mosttypes of industrial and professional electronicequipment.

The FN380, which can be supplied with fuseholders for US (6.3 x 32 mm) or IEC(5 x 20 mml fuses and either a single or atwo -pole rocker switch, has been approved tothe relevant VDE, UL, and SEV standards,with CSA pending. The fitters are available inline current ratings of between 2 A and 6 A at250 VAC (50...400 Hz) and operate over thetemperature range -25°C... -85°C. Overalldimensions are 58 x 32 x56.5 mm.

Schaffner EMC LtdOne Ashville MyMolly Millar's LaneWoktiighamBerks RG11 2PL(0734) 784669 (3163M)

3-65

You ain't heard nothing yet!The power supply section of very high-fidelityamplifiers can match the improvements inrecord pressing, low -noise tape materials, andcompact discs, etcetera, by the use of a type40/3488 ultra -low -noise toroidal transformerfrom Avel-Lindberg Limited.Designed to provide 1200 VA continuously andover 2000 VA intermittent operation with full -wave rectifier and capacitive input loads, the40/3488 has available a d.c. output power of750 W (twice 75 V d.c. at 5 A d.c.), which

means it can drive a high -quality stereo ampli-fier under 'music power' conditions at 250 Wper channel where the percent efficient. At this power level, the radiatedfield and acoustical hum from the toroid is onlyten per cent of that experienced from a normalstacked lamination type.Toroidal transformers are generally half theweight and volume of equivalent stackedlamination types and in the 1200 VA ratingcompetitive in price.Avel-Lindberg LimitedSouth OckendonEssex RM15 5W107081 853444telex: 897106 (3159M)

Step-by-step keyboarding onthe personal computerby Steven RadlauerISBN 0 8120 2628 4256 pages: paperback £5.95Computer users require more than powerfulmemory and a fast printer to get maximumproduction from their machines. They alsoneed to be proficient at typing, getting infor-mation and instructions into the computerquickly and efficiently. Barron's new self -instruction book, step-by-step keyboarding onme personal computer; teaches how toincrease typing output and thereby increasecomputer output.All typing skills and special computer oper-ations are taught one step at a time, thenimmediately strengthened through practiceexercises and drills. Topics include word pro-cessing techniques, preparation of all types ofbusiness correspondence, editing and proof-reading a text, and other essential skills.Numerous business applications are included,making the book particularly useful forupgrading office production. A special 'WordProcessing Workbook' section contains 25lessons with abundant instruction, practice,and drill material. In addition, the book

includes en introduction to the importantwords and symbols of BASIC.Esther Elven Barron's33 Sacktille StreetLondon W1X 1DB(011734 7282 (3152M).

Amstrad CPC464 exploredby John BragaSeduced by glossy advertisements andfavourable reviews you splash out on aCPC464 computer from Amstrad. By allreports, that would be a very sensible thing todo as the manufacturers seem to have gotalmost all their sums right with their first forayinto the personal/small business computermarket. Even the Amstrad manual is moreinformative than most. There comes a point,however, when you know the manual inside -out and start to think 'What next?'. You coulddo a lot worse than buy this recent publicationfrom Kuma. The author assumes a reasonableknowledge of the computer's basic featuresand takes up where the manual ends. Thebook starts by looking at the machine'sfeatures but this is simply as an introduction tothe remaining four parts of the book. Thesedeal with the musical capabilities, graphicsfeatures, assembly language programmingand a home accounting program as a

demonstration of a serious application.The hook is written in a clear, readable style,with numerous examples to illustrate thefeatures. Each section is dealt with in a

o .1-,

27.1Z..EP C.Pc 4 64 &-XPZ.0.21/9.13- P. I

TICILD4.EJA-1-zoxtzt.

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methodical manner and some of the ac-companying examples are very long. Insteadof keying them in laboriously, however, youcan buy two cassettes from Kuma and simplyinput the programs from them. The acid test ofa book (or any review product for that matter)is the question of 'Would we buy it?'. Theanswer, in this case, is 'Probably!'.Kuma Computers Limited12 Horseshoe PathHorseshoe RoadPangbourneBerkshire RG8 7JW107 3571 4335 (3151 MI

Iron stand leaves bothhands free!Tele-Production Tools are now manufacturinga stand for their `stiron' range of heavy-dutysoldering irons.This all -metal stand has fixing holes in itsheavy base so that it can be mounted firmly onthe work -bench.Any 'stiron' 875 series soldering iron in therange 60.. _200 W will fit into the stand: the

eIektor march 198.5

operator can then use both hands in offeringthe work -piece to the iron for soldering.Tele-Production Tools LimitedStiron HouseElectric AvenueWestcliff-on-Sea

SSO 9NW107021 352719 (3160M)

Miniature encapsulatedtransformersWith the introduction of twin voltage Low Pro-file Transformers and a range of miniaturecentre tapped 1.2 VA devices, Clairtronic nowhas the widest range of Encapsulated MainsTransformers in the UK. These designs areintended to avoid the most frequent cause ofminiature transformer failings... handlingdamage to the exposed winding wire termin-ations. Encapsulation in polyurethene resinprotects these fine wires and ensures reliabilitywith good thermal conductivity.The standard types are potted in square boxeswith power outputs ranging from 1.2 VA to50 VA in ten sizes. The Low Profile rangecovers 4 VA to 45 VA also in ten sizes withmounting heights from 17 mm to 49 mm.The latest Low Profile Transformers have twoprimaries and dual outputs which meet thedemand for multiple voltage devices for use inboth North America and Europe. The twinprimaries may be connected in series or paral-lel for use on 240 V or 120 V supplies.

All transformers are proof voltage tested to4 kV r.m.s. (Low Profile units at 5 kV) and aredesigned to meet 1EC742 (BS 35351 andCEE 15.

Clairtronic LtdChurchfiefd RoadChalfont St PeterBucks SL9 9EP(0753) 887227 (3164M)

3-66

an

CIRCUITMATEM 15)mpact full -function keter8% Vdc accuracy/A lac + dc)parate diode test

10agece: £12.00

M20DM 15, plus:

Transistor gainMeasurement

Ponductancemeasurement;High or low power for

-

'resistancemeasurement

`Price:C47.00

111

il)1125Like DM 15, plus:Capacitance

Measurementeasurement

measurementHigh or low power forresistancemeasurementContinuity buzzer

i Price: £58.00

nyu.1411.444

-12-41trzz=v3=2

-

maw -Feature -packed digital

multimeters at very low prices

.14.7 .11

From Beckman Industrial comes a new range of eightlow-cost 31/2 digit multimeters - the Circuitmate series.

All are readily available from your local BeckmanIndustrial distributor.

Send for full details of a new range which cuts cost withoutcutting quality.

Beckman IndustrialBeckmanIndrial Ltd

Electronic Technologies Division, (.71i Sales 5:: Nlarketing OrganisationMyle_n Hrgu. 11 Wagon Lane. Sheldon. Birmingham B26 3DU

Tel: 021-7427921 Telex: 336659

DM 77Autoranging

handheld meter0.5% Vdc accuracy.High or low power

for resistancemeasurement

10A (ac+ dc)Continuity buzzer

Price: £46.00

DM 73Autoranging probe

meter0.5% Vdc accuracyisplay-hold button,Continuity buzzer

Price: £39.75

DM 40Robust handheld

meter0.8% Vdc accuracy

2A lac+ dc)Tilt bail and antiskid

padsPrice: £49.00

DM 45Like D.M -10, plus:0.5 Vdc accuracy

10A (ac+dc)Continuity buzzer

Price: £65.00

From a gentle purr to a mighty roar.the tightly controlled power of thebeast is yours to command!

PROFESSIONAL QUALITYHIGH POWER LOuDSPEAKIRS

A new range of superb qualify loudspeakers.* Virtually indestructible high temperature

voice -coil reinforced with glass -fibre* 100', heat overload tolerancer Advanced technology magnet system* Rigid cast alloy chassis* Linen or Plastiflex elastomer surrounds* 5 -year guarantee (in addition to statutory rights)

Avaiiab!e. in 5.8. 10.12. 5 aria 18 inch mcdeis ...;;In 811 and some 1611impedances and with input powers ranging from 50W to 300W e.g.5in. 50W 95dB 80: XG39N 1611: XG40T £17.95§Bin.100W 98dB 811: XG43W129.95§

10in. 100W 100dB 811: XG46A £29.95§12in. 100W 101dB 811: XG49D £29.95§12in. Twin Cone 100W 100dB 80: XG50E 1611: XG51F £31.95§Note - the output power doubles for each 3dB increase (ref 11V oi 1m).

PRECISION GOMMULTIIVI

A new range of very high quality multimeters offering truly amazingquality at the price.

Pocket Multimeter. 16 ranges. 200011V DC AC £6.95§(YJO6G)M-102BZ with Continuity buzzer, battery tester and 10A DC range. 23 ranges,20,00011 V DC £14.95§ (YJO7H)M -2020S with Transistor. Diode & LED tester and 10A DC range. 27 ranges20.00011V DC £19.95§ (Y.108J)M -5050E Electronic Multimeter with very high impedance. FET input. 53ranges including peak -to -peak AC. centre -zero and 12A AC DC ranges£34.95§ (YJO9K)

M.5010 Digital Multimeter with 31 ranges including 2011 and 20mA DC AC FSDranges. continuity buzzer, diode test. and gdd-plated PCB for long-termreliability and consistent high accuracy (0.25c:. 1 digit DCV) £42.50§ (YJ1014

N B. Al our prices include VAT and Carnage. A 50p handkng charge must beadded if your total order u less than £5 on mat order (except catalogue).

MAPUN ELECTRONIC SUPPLIES LTD.Mal Order: P.O. Box 3. Rayieo. Essex SS6 8LR. Tel: Scutnend (0702155291.SHOPS

BIRMINGHAM Lynton Square. Perry Barr. Tel: 021-356 7292

SOUTHEND 282-284 London Rd. Westdifl-on-Sea. Essex. Tel: 0702-5541X.:Shahs dosed ail day Monday.

LONDON 159-161 King Street. Harnmersoutl). W6. Tel: 01-748 0926. MANCHESTER 8 Oxford Road. Tel: 051-236 0281. SOUTHAMPTON 46-48 Bevis Valley Road. Tel: 0703 25831.

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Our huge range of top quality electronic components at very competitiveprices are all detailed in our catalogue. and with well over 600 new linesin our 1985 edition and many design improvements. it's well worthgetting a copy. Here are just a few examples from the catalogue.(The items below are NOT kits).* Most phono and jack plugs now with integral strain relief sleeve - gold-platedtypes also available from 14p (gold from 70p)* Stereo Disco Mixer with cross -fade, talk -over. cue monitoring. aux input,slide controls. Only £58.95 (AF99H)

IL1111111111 I IIIIIIIMt LI I- f T i-ET I- f 1 f ti 4 44 4 +4

* 10 -Channel Stereo Graphic Equalisers -3 models - basic; with peak levelmeter: and with spectrum analyser - from £77.95 . * Digital Delay Line permits Slap -back. Doubting. Flanging, Chorus and Echo.11 controls. Only £195.00 (AF98G)* Video Enhancer improves picture quality when recording from one VTR toanother, and with TV's with monitor input. Only 28.95 (XG59P)* Detailed descriptions of the exciting new 74HC range of IC's which combinethe advantages of CMOS and TTL. From 46p* Keyboards: sloping keys. two-tone grey, mounted in steel frame, very smartcases (extra) available. 61 keys, only £33.95 (YJ12N)

79 keys, only £37.95 (YJ13P)* Resistors now 50ppm 'C. 0.4% only 2p each!* Auto transformers 120 240V 50VA. £10.75§ (YJ56L). 100VA £14.95§(YJ57M). 150VA £16.95§ (YJ58N). 250VA £21.95§(YJ59P).* Digital Clinical Thermometer. Only £13.95 (FK51F)

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Check our 1985 Cataloguefor all our other fascinatingnew lines. '

Pick up a copy now at any branch of W.H.

Phone before 2pm for Smith or in one of our shops. The price is

same day despatch. still just £1.35. or £1.75 by post from ourRayleigh address (quote CAO2C).

Post this coupon now for your copy of the 1985 catalogue.Price £1.35 + 40p post and packing. If you live outside the U.K.send £2.40 or 11 International Reply Coupons. I enclose £1.75.

Name

Address

355

§ Indicates that a lower price is available in our shops. All offers subject to availability. Prices firm until May 11th 1985.