E T AN JUST A LANDMARK ALSO INSIDE: 555 TIMER ......Can these new devices kill off the op -amp? 555...

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HY5025 Watts into 80

The HY5 is a mono hybrid amplifier ideally suited for all applications Al common input functionsnmag Cartridge tuner etc , are catered for internally the desired luncheon is achieved either by amulti -way switch or direct connection to tee appropriate pins The interns volume and tone circuitsmerely require connecting to external potentiometers (not included) The 1-1Y5 is compatible with allI L P power amplifiers and power supplies To ease construction and mourning a P C connector issupplied with each preamplifierFEATURES: Complete pre -amplifier in single pack - Multi -function equalixation - Low noise - Lowdistortion - High overload - two simply combined for stereoAPPLICATIONS: HiFi Mixers - DISC, - Guitar and Organ -- Public addressSPECIFICATIONS:INPUTS Magnetic Pick-up 3mV Ceram,. Pick-up 3OmV Tuner 100mV Microphone 1OrnVAuxiliary 3-100m1; input impedance 47k,.) at lkHzOUTPUTS Tape 100mV Main output 500mV R M S

ACTIVE TONE CONTROLS Treble 1 7di3 10kH, Bass - at 100HzDISTORTION 0.05% at 1 kHz. Signal/Noise Ratio 68dBOVERLOAD 38dB on Magnetic Pick-up ';UPPLY VOLTAGE - 16 50V

The HY30 is an exciting New kit from IL P it features a virtually indestructible I C with short circuitand thermal protection The kit consist. of I C heatsink P C board 4 resistors 6 capacitorson:liming kit together with easy to follow construction and operating inituctions This amodfier es

the beginner in audio who wishes to use the most updodate technology aallableFEATURES: Complete kit - Low Distortion - Short Open and Thermal Protection - Easy to BuildAPPLICATIONS: Updating audio equipment - Guitar practice amplifte - Test amplifier - Audio

SPECIFICATIONS:OUTPUT POWER 15W R M S into 8.1 DISTORTION 0 1 at 15WINPUT SENSITIVITY 500mV FREQUENCY RESPONSE 10Hz - 3d8SUPPLY VOLTAGE - 18V

The HY50 leads I L P s total integration ,pproach to power amplifier design The amplifier features anintegral heatsink together with the simpl,cify of no external components Diiratg the past three yearsthe amplifier has been relined to the extent that it must be one of the moat reliable and roo ist HighFidelity modules in the WorldFEATURES: Low Distortion - Integral Featsink - Only five connections - ? Amp output transistors- No external components

APPLICATIONS: Medium Power Hi -F, systems - Low power disco - ',10/onar amplifierSPECIFICATIONS: INPUT SENSITIVITY 500niVOUTPUTk, POWER 75W RMS in 8..) LOAD IMPEDANCE 4 16i) DISTORTION 0 04, at 75W at

SIGNAL 'NOISE RATIO 7548 FREQUENCY RESPONSE 10Hz-451(1-IF - 348SUPPLY VOLTAGE 75V SIZE 105 50 25rnim

I -1Y1 20'heWI 70 is the baby of I L P s new high power range designed co meet the most exacting

'cornments including load line and thermal protection this amplifier sets a new standard r modular

FEATURES: Very low distootion - Integral Heatsonk - Load line proteri.n - Thermal proection

60 Watts into 8)- No external componentsAPPLICATIONS- Hi F: - High gualit? disco - Public address - Mre10101 amplifier - ;.-moitar and

iqaSPECIFICATIONS:INPUT SENSITIVITY 500mVOUTPUT POWER 60VV RMS into fii.) LOAD IMPEDANCE 4-16.) DISTORTION 0 04 r, at 601Ar at

1 kHzSIGNA1 NOISE RATIO 90.18 FREQUI NCY RESPONSE 10Hz 45kHz - if dB SUPPLY Vet PAGE35V';7E 114.50x85rnm

El)(200 soo HY/00 now ireflreyerl m rpyr, ar 01 1 20 Watts has been designed m stand thimoor De. (I ske h as disco re- (Jr. III. while still relael.ng If .0 HIFI r,rfoornanceFEATURES: Thermal shutdown - von, oo,/ dHtnotinn - Loan Ilne piotiorhon -

integral Heatsmk. .- rellrleere,

120 Watts into 80 APPLICATIONS: H. F. Drser, - Winn -or Pnwon Slave initnstcal Puhhr addressSPECIFICATIONS:daPt,' SEYSITIVITY 500mV'70 TPuT POWER 170W RMS into tir t OAD IMPEDANCE 4 1fidt DISTORT ON 0 05 100W .

kHzSIGNAL NOISE RATIO 9648 FREQUENCY RESPONSE 1nh, 45kH? - 3,18 SUPPI d vCs

45V',LIE 114 100 85,11,1,

HY400 'he IY400 is I I P Big Daddy of th- range prodinsng 240W mti 42' it has neen leLpteil '.-dis. nor 11k101.1 address apnin atinols If the amplifier ,s in ised i rintnunn,

a r n4 -fling tan recninmended The arnplitnn int hodes all the gunman, of the rest 01 to eke. a eye high pOwe, h. fidelity novo, module

240 Watts into 4()FEATURES ': ermal shutdown - deny low distormion - Licari I 'le ;voter -1.m Fro

APPLICATIONS: Pinola- address Disco - Power slave - IndustrialSPECIFICATIONS:

,'OVVER 740W RMS into 4') LOAD IMPEDANCE 4 16') DISTORTION 0 I at 740V1i

SIGNAL NOISE RATIO 94.18 FREQUENCY RESPONSE 10Hz 45kHz - 3,113 SUPPI1 vol TAITF- 45V

INPUT SENSITIVITY 500n -1V SIZE 114 x 100 .

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1B3GT 1.25 6BK4C 3.35 6HS8 1.90 10GF7A 2.501K3 1.35 6BL8 1.50 6HZ6 1.50 10GK6 1.801S2A ....... 1.35 6BM8 1.55 10G N8 1.851X2B 1.35 6JC6A 1.80 10JY8 1.85

68N6 1.80 6J D6 1.85 10KR8 1.852AV2 1.25 6805 1.20 6JF6 3.902GK5 1.55 6B07A 1.50 11HM7 2.803A3A 1.95 6BU8A 1.90 6JS6C 3.45 11MS8 3.503AT2 1.90 6JT8 3.95

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

6CG3 2.25 6KD6 3.953CU3A 2.90 6CG7 .95 6KE8 2.25 I2BA6 1.053063 2.00 6CG8A 1.50 12BE6 1.053DC3 2.60 6C L8A 1.60 6KG6 3.95 12BY7A 1.203DF3 2.80 6CM7 1.30 6KT8 2.50 12C5 1.553DJ3 2.10 6KZ8 1.80

6CS6 1.35 6L6GC 2.60 12006B 2.253GK5 1.55 6CW4 6.25 6LB6 3.75 12DW4A 1.903HA5 1.85 6LD6 5.95 12GN7 2.003H05 1.90 6DJ8 2.10 6LE8 3.404AU6 1.55 6D06B 2.50 14GW8 2.00

6LF6 3.95 15008 1.604BZ6 1.35 6DT5 1.60 6LF8 1.854DT6A4EH74EJ7

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6U86LN86L066LT8

1.851.253.351.80

17AY3A178E317BF11

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4HA55A05

1.551.25

6EC46EH76EJ7

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5CG85GH8A5GJ7

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6EM76ES8

3.002.80

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6U8A

1.90

1.25

17JZ817KV6A17KW6

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5GS7 1.85 6EW6 1.35 6010 2.505GX7 2.70 6FM7 2.00 6V6GT 1.95 18GV8 1.95

6W6GT 2.25 19CG3 2.505L485U4GB5U8

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6GB56GE56GF7A

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6X9

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3.25

21GYS21JZ6

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2.653.50

3.35

6AQ5A 8CG7 .90 30AE3 1.706A08

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6AU6A 6GV8 1.95 8GJ7 2.25 31JS6C 3.956AV6

.95

.95 6GW8 1.80 8JV8 1.85 33GY7A 3.256GX7 2.80 8LT8 1.85

6AW86AX36AX4GTB

1.601.701.60

6GY56GY66HA5

3.451.251.85

8U98X9

3.453.45

35W438HE738H K7

.903.503.506AY3B 1.60 9A08 3.25 40KD6 3.80FBA6 1.25 6HE5 2.70 9GV8 2.90 40KG6 3.956BA11 2.50 6H05 1.80 9JW8 1.60 42EC4 ......... 3.8568E6 1.20 6HS5 4.45 I ODE7 1.85 5005A 1.35

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Celebrating our 19th yearservicing the Electronics

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/FULL FUNCTIONCALCULATORfor only $1.99(including case)

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TERMS & CONDITIONS: ABBEY pays full shippingcharges anywhere in Canada on all prepaid orders over$25.00. C.O.D. orders, send 25% deposits, balanceC.O.D. All orders shipped same day. Minimum order10 tubes.

CONIC

e a e-,ELECTRONICS LIMITED

306 Rexdale Boulevard, Rexdale, Ont. M9W 1R8 745-9555

electronics todayFeaturesTHE CN TOWER: MORE THAN JUST A LANDMARK 22The technical features in the world's tallest building

BIORYTHM CALCULATOR 24Find out your condition from a machine!

VCT 31

Can these new devices kill off the op -amp?

555 TIMER APPLICATIONS 3538 circuits using this popular IC.

YAMAHA B1 REVIEWED 49Powerful amplifier uses power FETs.

SCOPE TEST YOUR CAR 60Tune your automobile with just a scope

MICROFILE 65Microprocessors and microcomputers for the hobbyist

Projects

FIVE WATT STEREO AMPLIFIER 16Use just two ICs to make this project.

PHILIPS LOUDSPEAKER SYSTEM 27An off -the -shelf speaker!

REACTION TESTER 52Measure your reaction time against your friends'

SHORT CIRCUITS 55PATCH DETECTORHEADS OR TAILSSCR TESTER

InformationWELCOME TO ETI CANADA 7

NEWS DIGEST 9

PUBLICATIONS FROM ETI 15SUBSCRIPTIONS 61DATA SHEET 46MARCH ISSUE DETAILS 30TECH -TIPS 74

Our first cover shows two aspectsof the types of article that arecarried by ETI.One of our features describes thetechnical side of the CN Tower.

Vol.1 No.1

Our thanks to the CN Towerfor supplying the photograph.Also shown is our ultra -simplestereo amplifier project.

EDITORIAL AND ADVERTISINGOFFICES:

Unit 6, 25 Overlea Boulevard,Toronto, Ontario, M4H 1B1Telephone (416) 423 3262

Editorial DeptLES BELLPETER BERNARD

Circulation DeptSENGA HARRISON

Marketing Manager and AdvertisingPETER PRIEST

Published by:Electronics Today International(Canada) Ltd.

Printed by:Heritage Press, Mississauga, Ontario

News Stand Distribution:Gordon & Gotch, Toronto

Subscription Rates:

$12.00 per year, $20.00 for two yearsSend to Subscription Dept, ETIMagazine, Unit 6, 25 Overlea Blvd.,Toronto, Ontario, M4H 1B1.

International EditionsBritain:Electronics Today International,25-27 Oxford St., London VV1R 1RFEditor: Halvor Moorshead

Australia:Electronics Today International,Ryrie House, 15 Boundary St.,Rushcutters Bay, Sydney, AustraliaEditor: Collyn Rivers

Holland:Electronica Top Internationaal,Postbus 260, Emmen, HollandEditor -in --chief: Anton Kriegsman

France:Electroniques Pour Vous International42 rue Jacob, ParisEditor: Danis Jacob

Copyright: All material is subject toworld-wide Copyright protection.

ETI CANADA - FEBRUARY 1977 5

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HALIFAX TORONTO

WINNIPEG EDMONTON VANCOUVER

6ETI CANADA - FEBRUARY 1977

this ism CANADA

'SO WHAT?' New magazines always start with a

page of publisher's blurb (which few of you willread). It's always full of well-meaning intentionsand pledges for the future: 'It's YOUR magazine'...you know the stuff! So, let's forget it. Or shouldwe? We're proud of what we've done and whatwe plan to do and some of you may still be readingso let's tell you something about ourselves - and tryto be honest.

This is our first true Canadian edition. TheBritish edition of ETI has been shipped over heresince February 1976, just to see how it sold. It soldpretty well where it was available (in ten cities);well enough, in fact, for us to increase the ordersby 50% within six months. Reader reaction wasmonitored, advertisers were shown the figures andmost were interested: with this information theplans for ETI - Canada were formed.

What did we have? A fair number of sales, areasonable amount of encouragement but above allan overpowering feeling that Canada NEEDED aconsumer/hobby electronics magazine of its own.Until we brought out this issue, Canada was by farthe largest country in the industrialized wordwithout its own magazine covering this field.

Now starting up in virgin territory may soundgreat - you can't fail but it brings its own problems.How do you pitch the editorial balance; experienceof the existing editions of ETI doesn't help. Eachedition of ETI, in Britain, Australia, France andHolland operates independently - as we do inCanada - the balance is tailored to its own market.For example in Britain ETI has seven competitorsin the hobby -electronics field: this has obviouslyled to a degree of specialisation. ETI - Britain does

not pretend to aim at the raw beginner, nor does itcover ham radio. In Australia the range is wider;there's competitior but no tendency to specialise.

There, we've made an admission. We've pitchedthis issue at a pretty broad spectrum but we maygo even wider. We're feeling our way and we canonly hope that we aren't going to lose any of youon the way.

ETI is the second largest electronics magazine inthe world if we add together the various editions(No.1 is south of the border!) with a combinedcirculation of just under 200,000 a month. Alleditions are unique in that every member of theeditorial staff has come from the ranks of, andremains, an electronics enthusiast. It's not policy -

just a fact.We'll not explain our editorial aims too much,

this issue represents the balance that we'll start offwith. If you don't like it - well, take a look at usagain in nine months - we may have come round toyour way of thinking. If you do like it, and weobviously hope you do, we're wasting our timeoverselling ourselves.

ETI - Canada will contribute to, and receivematerial from, the other editions of ETI.

As you'll see from our cover - and from TomGraham's page at the back - we've combined withElectronic Workshop to strengthen our arm. Wehope that readers of EW find that they are stillbeing served by this edition: we plan to haveplenty of material in the servicing field.

Well, that's it. We hope we haven't bored youtoo much if you've read this far - all we ask is foryou to judge us by the contents.

e BC ronicsiiitoday international Z

£111-2

SCIENI0 IIICS SURVEYED

Pi I- I r-jr-';;TillWillin14111%ofig*IIUM

TV PAiTIM WHAMS

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ETI CANADA - FEBRUARY 19777

The SLEUTH Solves - FM Reception ProblemsRead what the December issue of FM GUIDE says about

The MAGNUM 85FMPower Antenna

And an unsolicted testimonal fromMr. P.M. of PeterboroughDear Mr. Bruenig:

I enclose the guarantee card from myFM 85 which I purchased from Minicola'shere in Peterborough. I am very happywith the unit: most stations are at least35 to 40 db stronger

'I

Most of us would like to improve our FM reception, nomatter the quality of the system we have. At last a new pro-duct manufactured by Magnum Electronics in Toronto, calledthe "Power Sleuth", has solved the problem of bringing inthose far away stations loud and clear.

Many of the antenna amplifiers that have been around foryears have had serious drawbacks. They would not only am-plify the FM signals, but would also add noise and distortion.In Toronto, the "Power Sleuth" not only brings in distantstations but also seems to eliminate interference from localstations. On the receiver and antenna used in this test we wereable to increase by 30% the number of stations clearly receiv-ed. For example, a station in Niagara Falls that previouslycame in only very weakly and was for the most part unlisten-able was with the "Power Sleuth", quite adequate and comfor-table to listen to.

Impressive!At under $100 the Magnum 85 FM would fit into most

Christmas budgets. The 85 FM is easily hooked into any stereosystem, a very complete instruction booklet is included withevery unit. Warranty is lifetime on workmanship and fiveyears on parts. For further information please contact Mag-

num Electronics Inc., 72-74 Stafford St., Toronto M6J 2R8.

MAGNUM ELECTRONICS INC.72-74 STAFFORD STREET, TORONTO, ONTARIO M4J 2R8

(416) 364-6754

No matter how much you paidfor your receiver... we guarantee

to improve FM performance.

DM2 Multimeter.PlataiLi5 111_

COMPARE the SinclairDM2 with any digital multimeter under $300.No other unit has as many features, with such a high degree ofaccuracy, at anywhere near this low price! Compare specifications.

Max DC voltsMax AC voltsMax DC currentMax AC currentResistor ranges up toAuto polarityMetal CasePush-button selectionWarranty10 Day TrialPrice FST incl.

SINCLAIDM2R Fluke HP B & K8000A 970A 283

1999V 1100V 500V1999V 1199V 500V1.999A 1.999A 1.99A1.999A 1.999A 1.99A19.99,4-2 19.99m.C2 19.99k4S2YES YES YESYES NO NOYES YES NO1 YR 1 YR 1 YRYES149.95 335.00 310.00

1500V1500V1.999A1.999A19.99k4S2YESNONO1 YRNO256.00

COMPREHENSIVE5 Functions giving 22 ranges.

ACCURATE3%. digit 8 MM LED display gives a quick clear readindicator.Dual slope integration. High stability.Protected! Separate fuses for current and resistance

PORTABLEWeighs only 3.5 lbs. with battery. Measures 2" x 6"

AND REALLY RUGGEDTough metal casing takes the roughest treatment

* on it!The Sinclair DM2 has all the capabilities of higher priced units. State-of-the-art circuitdesign, high quality components, outstanding performance and proven reliability - at arealistic price. Only $149.961 Compare it to others. You can't buy better for twice theprice. But don't believe us. Test it for yourself. Simply send your cheque, Chargex or Mas-ter Charge number, or company purchase order. And in the unlikely event that you areunsatisfied, return it within 10 days and we'll refund your money in full.

ing. Overload

circuits.

x 9"

- try standing

mansronE-11-ELECTR011ICS1736 Avenue Rd. Toronto M5M 3Y7 Ontario

O Please send more information.O Rush Sinclair DM2 to me. Enclosed is 0 Cheque 0 M.O.Chargex

0 Master Charge

NO.QTY_Sinclair DM2 & test leads $149.95@ NAME_ AC Adapter 7.95@

- 9V Battery Pack 4.50@COMPANY

- Leatherette carry case 19.95@ ADDRESS_ Rechargeable Battery Pack 24.95@

Ont. Sales Tat 7% extraTOTAL ENCLOSED $ Ell lan77


NEWS DIGESTPERTEC GETS MITSMITS, manufacturers of the Altairrange of hobby/small business com-puters have been bought by Pertec,who are primarily suppliers of disk andtape drives. Could be we'll see somenice Disk Operating Systems soon!

FCC PROPOSALThe US Federal CommunicationsCommission has drawn up a tentativelist o' proposals for submission to theWorld Administrative Radio Confer-ence in 1979. Amongst the proposalsis one that CB should share withamateur, amateur -satellite and radio-locatipn services in the 220 - 225MHzregior.. It sounds to us like a sure-firerecipe for something, probablytrouble!

WATCH THIS SPACEAt the bottom end of the LED watchmarket the giants are preparing to slugit out. Texas Instruments retailers havebeen offering plastic cased watches foras little as $12.95 and both Fairchildand National Semiconductor areexpected to follow TI's lead into thereally ow end. Meanwhile, some ofthe smaller companies, includingGruen, Bulova, and Time Computer,

ave suffered serious financial losses.somebody's going to get burntfingers ..

100MHz DUAL TRACE SCOPE

The bwd540 oscilloscope combines afull 100MHz specification with labaccuracy and versatility, and fieldportability.

The amplifier risetime of 3.5nS issuitable for all logic circuitry fromDTL to ECL. The main sweep triggerextends from DC to beyond 125MHzwith variable hold -off to greater thanone sweep length. It can trigger oncomplex digital words and on virtuallyevery waveform within the verticalamplifier's range including TV lineand frame. The delayed timebasehas its own trigger source switching,level and polarity selection. For full

digital compatibility the Z molulationis DC coupled and requires only f2Vfor full blanking.

Other specifications include: 5mVto 20V/div attenuation range; 5r6 to5S/div main sweep; 5nS to 13/iivdelayed sweep; DC to better than125MHz main timebase trigger withvariable trigger hold -off; identical X -Yoperation; 80 x 100mm screen.

Power requirements: 120 or 240VAC or 20-30\/ DC. The scope measures165 x 320 x 430mm, and weighs 9kg.

Duncan Instruments Ltd., 6E Mill-wick Drive, Weston, Ontario M9L 1 Y4

SUM THING SHARPSharp Electronics of Canada Ltd. hasintroduced a new ten -digit electronicprinting desk -top calculator, the EL -

1052, with grand total memoryregister to store grand total additions,subtractions and summations.

The EL -1052 utilizes a mechanicalten -digit impact printer which printsnegatives in red and can print up to13 digits per line. Average printingspeed is 2.6 lines per second. Otherfeatures include a one -touch percentkey for taxes and discounts, a non-add/sub-total key for printing codes,dates, etc. and for sub -totals of cal-culations in progress, and a constant/add -mode selector switch and an over-flow error check device.

The EL -1052 weighs just over 5lbs.,operates on AC current only and isavailable from Sharp Dealers acrossCanada, price $139.95.

Heathkit Modl us ...The totally flexible hi-fisystem for today...and tomorrow!Beath solves the problem of obsolescence with the incredibleModulus hi-fi system! Housed in a single unit, the AN -2016,is a superb stereo/4-channel preamplifier with the featuresand specifications of the finest separates - an advancedAM -FM tuner with digital frequency readout, and first-classAM too - complete sound control facilities and four peak -responding output level meters. With one of its matching

HEATH

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MONTREAL795 Lewsndre St. E.

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WINNIPEG OTTAWA1316 Portage Ave. 866 Merirale Rd.

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NEW 600/60 MHz Frequency CounterNow available in Canada

MODEL CTR-2X

8 Digit DisplayLarge .3" LED Readouts

Automatic Dp. PlacementResolution to 1 HzHigh Input SensitivityAutomatic Input LimitingInput Diode ProtectedSelectable Gate Times, lms and 1 sec.Provision for 10 sec.High Stability 10 MHz Crystal Time Base

Plug-in Time Base

Plug-in Prescaler

SPECIFICATIONS BASIC WITH PRESCALER

FrequencyInput Z

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60 MHz1 Meg/20pf30 my @60 MHz10 my @25 MHz1 Hz to 60 MHz120v RMS to 10 MHz

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600 MHz50 ohm150rnv @600 MHz

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Send me ModelBill my ChargexExpiry dateName

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KIT PRICESKit C7R-2X 60K $339.00Kit CTR-2X 600K 5649.96

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CIA -2X 60 5519.00C7R-2X 800 5689.95

Ontario residents add 7%UP., Tex

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ELECTRA ELECTRONICS CO.7222 TORBRAM ROAD - UNIT 12 MISSISSAUGA ONTARIO L4T 3V2 - TELEPHONE 678-0562

amplifiers, it's E superb stereo system with your choice ofpower outputs. With two matching amplifiers, it's deluxe4 -channel. With the addition of "build -in" modules, it's SQ,Dolby FM and CD -4. No waste, no replacement, no "blackbox" wiring hassles. It's all you need for a lifetime of listen-ing! Find out about Modulus and the over 400 superb elec-troni: kits from Heath in our new catalog. Send for it today!

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PROFESSIONALPOWER AMPLIFIER

MODULES 436"FEATURES :SHORT & OPEN CIRCUIT, IMPEDANCEOVERLOAD, MISMATCH AND THERMALPROTECTION. ONLY 5 EXTERNALCONNECTIONS REQUIRED.FULL 2 YEAR GUARANTEE.

NEW100w MODELPower Output 70we tt s RMS

7.5 ohms110 watts RMS

7.5 ohms170 watts RMS

7.5ohms

Frequ. Response 10-30 kHz -0.5dB 10-30 kHz -0.6dB 10-30 kHz -0.6dB

Slewing Rate 7.3V per microsec. 8V per microsec. B.4V per microsecT.H.C. 0.05% @ 1kHz 0.05% @ 1kHz 0.06% @ 1kHz

Damping Factor 200 400 400

Hum & Noise 115dB below 70watts

115dB below 110watts

115 dB below 170wett5_

Input Sensitivity OdB10.775V1 70Vil A tts

OdB (0.775V) 110watts

OdB (0.775V) 170watts

Input Impedance 47k 47k 47k

Power Requirement C 36volts / 45Volts * 55 VoltsOverall Dimens. 5.9" Long x 3"

Wide x 1" High.5.8" Long x 3"Wide x 1" High

4.8" Long x 3"Wide x 1" HighHeat sink 6- x

POWER SUPPLIES

Send me ModelBill my ChargexExpiry dateName Ontario add 7% P.S.T.AddressCity Prov

ELECTRA ELECTRONICS LTD.Unit 12, 7222 Torbram Rd, Mississauga, Ontario L4T 3V2

Tel. (416) 678-0562 Telex 06-968653

I.P.S. 60 $89.95 100 $109.50 150 $139.50

Master ChargeSignature


NEWS DIGESTHOBBY-WRAP TOOLThe new BW-630 Hobby Wrap is a re-volutionary battery powered tool forwire -wrapping 30AWG wire ontostandard DIP socket terminals (0.25"square). The tool comes complete witha built in bit and sleeve for producingthe preferred 'modified' style wrap.

A built-in device to prevent over -wrapping is standard. Carefullydesigned and developed for the seriousamateur, the tool weighs only 1 loz.and runs on any standard or recharge-able 'C' size batteries. Pistol gripdesign of rugged ABS, positive index-ing mechanism and quality construc-tion assure exceptional performance.Price: $48.75 (batteries not included).Len Finkler Ltd., 25 Toro Rd., Down-sview, Ontario, M3J 2A6.

VARIABLE PERSISTENCE/STORAGE OSCILLOSCOPEA new variable persistence/storageoscilloscope from Hewlett-Packardincludes a number of features notnormally found in instruments in thisprice range. Selling for V576.00, theModel 1223A includes a burn -resistantCRT and automatic storage control tomake it easy to capture low rep -rateand single -shot waveforms for storeddisplay. The 15MHz bandwidth and2mV sensitivity make it ideal ineducation, medical, electromechanical,and many other applications.INQUIRIES MANAGER, Hewlett-Packard (Canada) Ltd., 6877 Gore wayDrive, Mississauga, Ontario.

IMSAI UPDATEIMSAI have released a new version oftheir editor -assembler for the 8080.It's yours in the form of paper tapeand manual for $40, US price. Biggestpart of the update is multiple devicedriver routines and a larger symboltable space. Also featured is an im-proved debugger.

NEW CATALOGUEFROM UNIVERSITYIllustrating a comprehensive line ofspeakers, horns, drivers and micro-phone accessories, the new 1977University Sound 16 -page cataloguehas now been released.

Featuring sectionalized productinformaticn on University's Life -Safety Speakers, Explosion -ProofDrivers, Column Speakers, Horns,Multiduty Speakers, Underwater andWeatherproof Speakers, and a widerange of Paging/Talk-Back Speakers,the catalogue is designed to Provideboth technical and application inform-ation. Copies are now available bywriting to John R. Tilton Ltd.,1200A Eglington Avenue East,Scarborough, Ontario.

COLOUR -BAR PATTERNGENERATOR

Eico has introduced a new IC digitalcolour -bar generator, model 388. Thenew unit, housed in a hand -sized case,weighs only 12 ounces yet deliversaccurate signals for test and alignmentof any coloL r or black -and -white tele-vision receiver.

The unit provides the followingdisplays on -.;hannels 2,3, or 4: gatedrainbow pattern for chromirenceadjustment with ten standard 2o I ou rbars, single cot for static convergenceadjustment, dot raster for finalconvergence, nonlinearity correction,pincushion, single vertical line forhorizontal cantering, eight ve-ticallines for width and nonlinearity adjust-ment, single horizontal line for verticalcentering, eight horizontal lines forheight and nonlinearity adjustment,single crossbar for centering andpositioning and crosshatch pattern forfinal convergence.

Model 38f operates from two stan-dard 9 -volt batteries or nickel-cadiumcells. The unit also features an LEDfor power -on indication, crwtal-controlled oscillator and timingcircuits for Er -eater stability. EicoCanada Ltd., 20 Millwick Dr., Weston,Ontario.

VOTES CASHED INA preset cash register, normally foundin cafeterias and fast food outlets,turned out to be 'as speedy as a largecomputer' in processing election nightreti, rns for the City of Brampton.

It's believed to be the first time inNorth America that a cash registerhas been used to tally election results.Two machines were used by the city-both NCR 225 preset electronic cashregisters - with one handling Councilresults, the other School Board results.

Tl-e principle of a preset machine issimple. The price of a hamburger forexanple, is established at 69c and thisprice is preset into system memoryand a 'Hamburger' key is assigned.Every time this key is depressed, theregister recalls the preset price andadds it to the total sale. To order 5hamburgers, depress item quantity (5)and Hamburger; the rest is automatic.

Tha preset machine also allows forthe L se of 'open' keys, that is a keywith no preset price to record miscell-aneous items. For the election all keyswere made open keys, thus allowingthe c ty to index the number of votesinstead of a price.

Sutstitute Joe Smith, Mayoral can-didate, for Hamburger and each timethe Joe Smith key was depressed itactivated the inventory counter tocount the number of polls reportingand record the votes.

As :he polls closed in Brampton,Deputy Returning Officers tallied uptheir totes and telephoned the resultsto Brampton's Centennial Centre,where the poll number and the totalnumber of votes for each candidatewere then entered on color -codedslips (different color for each cashregister). The slip was handed to theappropriate operator and a duplicatecopy was given to a clerk whose jobwas to keep track of those polls thathadn't been reported.

The 225 operator indexed the num-ber of votes and then depressed thebuttor for the candidate. Each timethe candidate's button was depressed,the system's memory recorded thatanother poll had been accounted for.System readouts were taken periodic-ally during the evening, recording a

candidate's total votes by the numberof polls reporting to date; this infor-mation was then transmitted to themunicipality's main offices for entryon a lzrge election board. It tookonly 10 minutes from the time a DROphonec in his totals to the resultsappearing on the election board.


NEWS DIGESTCB EXPANSIONEffective from April 1, 1977, the GRSwill be expanded to 40 channels from22. This is in line with the US exp-ansion. At the same time, morestringent standards have been intro-duced with regard to unwantedradiation from CB rigs. The newstandards are given in Radio StandardsSpecification 136, Issue 5, whichshould be obtained by anyone wishingto submit equipment to the DOC fortype -approval.

Equipment for 40 channel oper-ation may be sold before April 1,

unlike the situation in the US, whereseveral distributors were warned bythe FCC for selling 40 -channel rigsbefore January 1. However, all suchequipment must carry a label whichincorporates the statement 'Licens-able under Issue 5 for 40 channelsafter April 1, 1977 and consequentlyfully compatible for licensing underIssue 4 for 22 channel operation untilApril 1, 1977'.

Other quotes from Telecommuni-cations Regulation Circular 40:

'GRS licensees making use of thenew 17 channels after April 1 shouldbe aware that this spectrum is present-ly occupied by licensees in the private

Commercial Land Mobile Service.Although encouraged to apply for newfrequency assignments they have beengiven the option of remaining on theirpresent assignments until they findit convenient or necessary to re-locate. Inter-sevice interference pro-tection will not be provided be theDepartment. In the interim periodGRS licensees are requested to co-operate where possible with existinglicensees on these frequencies.

The Department will continue tomonitor the growth of the GeneralRadio sevice and its impact as a sourceof interference to broadcasting andother radio services with a view to theapplication of more stringent tech-nical standards should they becomenecessary. In addition it may bedesirable in the future to graduallyphase out the double sideband modein favour of single sideband trans-missions thus eventually doubling thenumber of channels available in thisService. Should such measures becomenecessary, purchasers of equipment areassured that there would be a reason-able amortization period to allowconventional AM double sidebandequipment to obsolesce.'

ELECTRONICS CONFERENCEThe International Electrical Electron-ics Conference and Exposition will beheld on September 26, 27 and 28,1977 at Exhibition Place, Toronto,it was announced by ConferenceChairman Douglas M. Hinton of BellCanada. The three-day, biennial event,sponsored by the IEEE, combinesinternational government and industryexhibits with the presentation oftechnical papers on the latestdevelopments in the field. It attractsdecision -makers and researchers inbusiness, education, government andindustry from Canada, the US andabroad.

The technical papers, which will bepublished in digest form for world-wide distribution, will cover suchdiverse areas as telecommunications,media electronics, standards, safety,components, EMC, power and bio-medical electronics. Chairman of theTechnical Program is Geoffrey Beding-ham of Canadian Motorola.

A highlight of the Conference andExposition is expected to be thetraditional banquet at which theTanner Lecture will be delivered.

For information regarding exhibits,technical papers and registration,contact: International Electrical Elec-tronics Conference and Exposition,1450 Don Mills Road, Don Mills,M3B 2X7.

CANADIAN COMPUTER CRAZEThe hobby computer mania whichhas swept America now seems to behitting Canada. In Toronto alone,3 stores have opened selling computersin kit or assembled form. Most pop-ular seemto be the IMSAI 8080 andthe Processor Technology systems.In Toronto at least, it seems that youcan -now shop locally when you go tothe computer store!First Canadian Computer Store, Ltd.,44 Eglinton Ave. W.,Toronto, M4R 1A1.

The Computer Place,186 Queen St. W,Toronto, M5V 1Z1.

Compu termaster Systems,67 Gloucester St,Toronto.

SAY, WHAT'S THE TIME?An electronic wristwatch that talkshas been patented by Robert Lester,president of Intersonics Corp. in NewYork. The Sonatime watch will havea conventional LCD display, and willalso pronounce the time through aminiature speaker fed from a ReadOnly Memory containing digitisedspeech. How long before we have a'Slimmers' Watch' that speaks yourweight?

CGE USE VIRCanadian General Electric has intro-duced a domestic colour TV set whichincorporates - for the first time in aCanadian -made set - a circuit todetect and decode a special tint andcolour intensity reference signal as itwas actually produced at the studio.

The introduction of this special cir-cuit into a home TV receiver marksthe first time that a fully automaticcolour TV has been made available tothe consumer.

Today most colour TV programsoriginating from the mjor US networksare broadcast with this reference,called a Vertical Interval Reference(VIR) signal. Many of these programsare reproduced on Canadian TV withthe VIR signal.

The Canadian Radio and TelevisionCommission has approved in principlethe use of the VIR system in Canada.Within the next year or so most TVstations in Canada are expected toinclude the VIR signal on domest-ically produced programs.

An on/off switch on the TV set'sfunction panel controls the VIRcircuit. If the signal is not being broad-cast with a particular program, the setcan be adjusted for colour level justlike a conventional TV.

The VIR system is being intro-duced in a 20 -inch model and plansare to add the feature to other modelsin the line within the next year, accor-ding to Bill Sinclair, Manager -Market-ing, CGE Home EntertainmentProducts.

CB SPEAKER

Philips Electron Devices has justreleased the AD555, an extensionspeaker for all mobile or fixed CBstations. The AD555 uses a 4 inchweather -proofed cone speaker in amoulded high -temperature plastic case.The unit is rated at 6W, and theresponse curve is tailored to voicefrequency response. The unit comeswith an adjustable tilt metal bracketand mounting hardware.

The AD555 has a suggested listprice of $19.95 and is availablethrough authorized Philips Deforestdistributors and dealers.


FREQUENCY COUNTER

A new frequency counter, model FM -7is available from Metermaster.Manufactured by Non Linear Systems,the FM -7 uses CMOS construction.Sensitivity is 30mV with the 7 -digitLED display having a resolution of1Hz. The battery -powered unit is idealfor audio, broadcast, amateur, CB andindustrial frequencies.

Also from Metermaster is a newclamp -on ammeter capable of meas-uring DC, AC and AC superimposedon DC. The YEW model 3228 is aportable clip -on ammeter designed to

measure DC and AC current from50mA up to 20 Amps without break-ing the circuit under test.

The instrument will measurecurrent with excellent linearity andhas a flat frequency response up to2kHz. It is unaffected by position ofthe current -carrying conductor in theclamp and has an accuracy of ±2.5%.Battery operation is standard, withoptions including use on AC line and a100mV recorder output. Metermaster,214 Dolomite Dr., Downsview,Ontario M3J 2P8.

FM BOOSTERNow from Magnum Electronics Inc.,of 72-74 Stafford St., Toronto,Ontario M6J 2R8, is the Magnum85FM Power Antenna. This is basically(or at least seems so to us) a VHFpreselector with a gain of 35dB and7dB noise figure. The tuning on theunit we tried was extremely sharp -spurious rejection and image rejectionare quoted as 90dB and 85dBminimum respectively. This unit willgive a worthwhile improvement inareas of fringe reception.

AM BROADCAST RF AMPLIFIERNational Electrolab Ltd. has intro-duced their new model R FA-5AM RFamplifier for off -air monitoring.Features include a built-in carrier -levelmeter which provides an accurateindication of transmitter radiatedpower. An Automatic Gain Controlcircuit keeps RF output constant forup to 30dB variations in day/nightsignals.

The amplifier also has an optionalalarm package providing audible andvisual alarms in the event of a carrieror audio failure. In addition, anoptional audio output package willprovide a balanced 600 ohm outputfor an off -air audio feed to studiomonitors as well as a high-fidelitysignal for distortion and frequency -response measurements. NationalElectrolab Ltd., 1536 Columbia St.,North Vancouver, BC. V7J 1A4.

BATTERIES BOOSTED

Canadian General Electric are promot-ing sales of their "Recharge BatterySystem" with this counter display.Rechargeable batteries are an attrac-tive proposition because they can berecharged up to 1,000 times and cangenerally be expected to last as longas the product in which they are used,whether that be a movie camera,photo flashgun, tape recorder, CB orham radio, calculator or any otherbattery operated product.

C.G.E. N.-Cad batteries are avail-able in AA, D.C., and 9 Volt sizes. Inaddition, the BC -3 can be used inconjunction with battery holdermodules to recharge the cells. At localdealers now.

SCIENCE BOOK'Scientific Models for Experimenters'by Dr. Harry E. Stockman is writtenfor first year college students, butmore than 60 models are describedwhich can be built by high-school stu-dents participating in a Science Fair.Included are novel Electric Motors,Newton -Law demonstrators, NetworkModels and Theorems, extending tothe new General Twoport Theorem,Amplifiers, etc. A considerable part ofthe book deals with Medical Elec-tronics, Biophysics, Helmholz' ZETAPotential, Heart and Brain -Wave Moni-tors, extending into Parapsychology.The 400 -page book sells for $10.95plus postage. SERCOLAB, P.O. Box78, Arlington, Mass. 02174.

COLOURFUL VTRSInternational Video Corp. of CanadaLtd., has developed a new add-on forits IVC 700 and 800 video taperecorders which will improve thecolour quality. Chromacon, as thesystem is called, operates by down -converting the chrominence signalsand recording them directly.

NEW SOUND CATALOGUEArgos Sound of Genoa, III., has justreleased a new 12 -page, three colorcatalogue with photos and descriptionsof their complete line of soundsystems and components. Included is alarge selection of sound columns, aswell as portable sound systems, baffle/speakers, wall baffles and CB base andmobile speakers. Specifications includeweights and measures in the standardand metric systems. Each product isdescribed according to its acousticalapplication to specific market areas.For further information, write:ArgosSound, 600 South Sycamore, Genoa,Illinois 60135, or their Canadianvents, Leigh-Marsland EngineeringLtd.

CB BONANZA23 channel CB transceiver prices are;Plummeting as suppliers find them-selves stuck with more sets than theycan sell. The introduction of 40channel sets in the States means thatwould-be customers are holding offbuying, and so manufacturers arecutting prices, planning free extras,and some are considering pushing theirsets in Canada where we still have only23 channels. Watch for a price drop!


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Speakers are to be mounted from the front and flush with the face of the baffle. The

grille cloth should be an open weave material that you can breathe through easily ...make sure the grille clears the speaker by at least 3/8". We suggest you line the cabinetwith two inches of damping material making sure the front and vent are clear. Follow

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DOMINION RADIO & ELECTRONICS COMPANY535 YONGE STREET - TORONTO, ONTARIO - M4Y 1Y5 - TELEPHONE: (416) 922-1818

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PUBLICATIEIS

FROM ETIFROM THE PUBLISHERS OF

ELECTRONICS TODAY INTERNATIONAL

IRCUIT

1

RIM the Otitiffebert e electronics telly Mternatioial

Take the mysteryout of elettroolor withthis straightforwardlogical course

/ varigarair

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

TOP PROJECTS No. 4:A collection of 28 constructional projectsreprinted frcm ETI. This is the fourth in aseries publish ed by the British ed tion (Nos.1,2, and 3 are not avaiiable). P-ojects arecomplete arid include: Sweet Sixteen StereoAmp, Waa-W.sa, Audio Level Meter, Expand-er/Compressor, Car Anti -Theft Alarm, Head-light Reminder, Dual -Tracking P3wer Sup-ply, Audio Millivoltmeter, ThermocoupleMeter, Intrucer Alarm, Touch Sw t:h, Push -Button Dimmer, Exposure Meter, PhotoTimer, Electronic Dice, High Power Beacon,Temperature Controller, Electrcric One -Armed Bandit plus many more.

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

ELECTRONICS - IT'S EASY:

Volumes 1 ar.d two of the best introductoryseries to electronics ever published in a mag-azine. Volume three, completing the series,will be available in a few months.

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

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

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

These boo6ss have sold extremely well inAustralia and in Britain. In Holland theyform the basis for a correspondence course.

$[6.00 FOR BOTH, $3.50 INDIVIDUALLY

i'MPLE15:710S TESTERHI Fl AMP SW i.SW. CAR ALARMDICE. Aurao MILLIVOLIMPUSH BUTTO '

TI TOP PRO$115,0$3.,e

TRACKING P. S.ER ALARM. PHOTO is

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Power SuppliesWaveformsFiltersDigital SystemsLogic

THESE PUBLICATIONS ARE AT PRESENT ONLY AVAILABLE FROM ETI

Send your orders, with payment, toETI PUBLICATIONS

Electronics Today InternationalUnit Six

25 Overlea BoulevardOntario M4H 1B1

Please specify which publications you require, and print your name and ac dress clearly.


ETI

i144WATT STEREOThis simply -constructed amplifier gives high quality reproduction forsurprisingly low cost. The five watts per channel output is sufficient for theaverage listening room even when inefficient loudspeakers are used.

THIS PROJECT UTILISES A NEWadvance by IC manufacturers. A fewyears ago no one would havebelieved a complete stereo hi-fiamplifier could be made from justtwo ICs plus a few passive com-ponents. Today more and morecomponents are contained withinthe IC so a power amplifier is aseasy to use as an op -amp.Easy to build - Readers who werepreviously apprehensive aboutbuilding audio power amplifiersshould have no trouble with thisdesign - there is little to go wrong.Adequate Power - The output isunlikely to be found lacking unlessthe loudspeakers are very ineffi-cient. Speakers of this type usuallybelong to the hifi enthusiast whospends lots of money on his system;the inefficiency of the speakers iscompensated for in the amplifier. Inan average set-up it is unlikely thatyou would, under normal listeningconditions, be able to tell thedifference between the ETI444 anda twenty watt amplifier.

specificationMEASURED PERFORMANCE OF PROTOTYPEETI 444

POWER OUTPUTInto 8 ohms

DISTORTIONAt 3 watts outAt 4 watts outAt 5 watts out

FREQUENCY RESPONSEHigh-level input

SENSITIVITYMagnetic inputHigh level input

LOAD IMPEDANCE!NPUT IMPEDANCE

Magnetic inputHigh level input

SIGNAL TO NOISE RATIOHigh level inputPhono input (ref 10 mV in)

5 watts per channel

0.15%0.5%3.0%

+10 dB,-3 dB 4 Hz to 200 kHz

1.5 my190 mV8 ohms or higher

approx. 100 kapprox. 10 k

67 dB64 dB unweighted

16 ETI CANADA - FEBRUARY 1977

FIVE WATT HI-FI AMPLIFIERLM379 - National Semiconductorrecently supplied ETI with samplesof their new dual five -watt audioamplifier IC - the LM379. Thecircuitry around the IC is verysimple in comparison to most ofthose previously available. The gainis set in a similar way to that for anoperational amplifier: by the ratio oftwo resistors in the feedbacknetwork. In addition the IC featuresinternal stabilization, current limit-ing and thermal protection.

-110W it works

Preamp - We decided to try the ICin conjunction with the dual low-

noise preamplifier IC also fromNational Semiconductor - theLM382. The combination results ina simple stereo amplifier whichworks very well indeed.

Whilst tone control could beachieved very simply it was decidedthat the performance of the ampli-fier deserved good treatment. So weuse more effective tone controls.

The result is a five -watt stereoamplifier, ET1444, simple andinexpensive to build, and with asurprisingly high performance.

CONSTRUCTION

As with most straightforward pro-jects the use of a printed circuitboard is not only desirable from anease of construction point of view,but it also helps to ensure identicalresults to those of our prototype.

The components may be assem-bled to the board in any order butwe find it preferable to assemble thelow -height components first, ie,resistors, diodes. Before installingIC2 make sure that a hole of about 6mm diameter is drilled in the boardat the end where the heatsink is to

THE OUTPUT OF a magnetic cartridge isnormally of the order of 5mV at 1kHz.However, in the recording process the highfrequencies are recorded at a higher ampli-tude than the low frequencies (in order toreduce noise). The curve of amplitude -versus -frequency that is used is known asthe RIAA curve. When the record is re-played the reverse characteristic of gain -versus -frequency must be applied to restorea flat frequency response. This process inthe amplifier is known as equalization.

The first stage of the ETI 444 amplifieruses an LM382 dual low -noise preamplifierIC. This stage is designed to amplify and toequalise the output of a magnetic cartridge.Note that many of the resistors needed to

bias the IC (and to provide equaization)are provided within the chip and very fewexternal resistors are reqired to make itfunction as an RIAA compensated amp-lifier.

The second IC is an LM379 - a dualstereo power amplifier which providessix watts RMS per channel with supply railsof ±13 volts. The IC is unusual amongstpower amplifiers in that it can be used in asimilar fashion to conventional op -amps(except that it is capable of driving a lowimpedance load of 8 ohms).

The gain -versus -frequency response of thepower amplifier is set by the bass and treblecontrols. The overall gain is set by the ratioof 1 + R15 / (R17 + RV4). The part of RV4

corresponding to a particular amplifier isthat between the wiper and the outside tagconnected to the amplifier. Thus the gain ofthe two amplifiers may be varied different-ially by varying RV4 (which acts as abalance control). The level of the input tothe power amplifier is set by RV1 (whichacts as a volume control). Switch SW1selects the input to the power amplifierfrom either the RIAA power amplifier orfrom tuner tape or auxiliary inputs asrequired.

The power supply is simply a bridgerectifier and centre -tapped transformerarrangement which provides ±-12Vdc. Withboth channels driven this is adequate toprovide an output of 5W per channel beforeclipping.


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be mounted (after the IC isinstalled). Take care that all polar-ized components, such as diodes,ICs, electrolytic capacitors andintegrated circuits, are mountedwith the correct orientation.

Solder 25 to 50 mm lengths oftinned wire to each of the lugsthe potentiometers and then mountthe potentiometers in the appro-priate position by threading thetinned copper wires through theholes provided in the printed -circuitboard. Pull the wires down so thatthe lugs are almost flush with theboard and the potentiometers are allin line. Then solder the wires.

The heatsink may now bemounted onto IC2 using a singlenut and bolt. Care must be taken toensure that the heatsink does nottouch any of the potentiometers asit is at a potential of -12 volts.

The unit may now be mechani-cally assembled by securing it to thefront panel by means of thepotentiometer shafts and nuts, andby fitting two 6.4 mm spacersbetween the rear of the board andthe chassis.

Finally wire the unit as shown inthe component overlay diagram.

continued overleaf

80

---Ir-i-r:FOLO HERE

3.2mm DIA

".1

40

I

MATERIAL 1mm ALUMINIUMANODISED OR SPRAYED BLACK

NB: Do not paint area of heatsinkthat is in contact with the IC.

Fig -3. The heatsink for the LM379. Theheatsink described will get quite hotwhen the amplifier is run at full output.If it has been blackened by painting itmay smell a little at first but this willsoon pass away. For normal domesticlistening this size heatsink will be foundto be entirely adequate but if the amplifieris to he run continously at full sinewaveoutput it would be advisable to increasethe size of the heatsink. No damage canbe caused by using the smaller heatsinkhowever as the IC is thermally protectedand will simply shut down if it gets toohot.

Fig.2. PCB overlay and interconnection diagram.


FIVE WATT STEREO

-Parts LIS

ResistorsR1,2 1 k

R3,4 100 kR5,6R7,8R9,10R11,12R13,14R15,16

5k627 k47 k5k627 k10k

R17,18 100

Fig.4. PCB Pattern (full size).

CapacitorsC1,2 0.1 p.F polyC3,4 0.33 RF poly -

1/4W 5% C5,6 0.0015 p.F poly/ceramicC7 -C12 10µF 16 VC13,14 0.002 p.F poly/ceramicC15,16 560 pF ceramicC17,18 100 j.LF 16 VC19,20 2200 p.F 16 V'C21 10µF 16 VC22 0.033 p,F 125V AC

PotentiometersRV1 10 k log rotary dualRV2 25 k lin rotary dualRV3 100 k lin rotary dualRV4 500 ohm lin rotary wirewound

1000µF 16 V will do if 2200 j.LFis not available.SemiconductorsD1 -D4 1N4001 or similarIC1 LM382IC2 LM379

SwitchesSW1 2 pole 4 position rotarySW2 2 pole rockerMiscellaneous2 Two pin speaker sockets2 Four way phono sockets4 Rubber feet2 6.4 mm spacers5 Knobs2 Core flex, plug, clamp, grommet

Chassis and wooden sleeve to suit.Panel mounting fuseholder &250 mA fuse to suit.Screened cableHeatsink to Fig. 3.120V Neon indicator

Transformer 117V to 9-0-9V at 1.5APCB ETI 444 - $6.00 post paidfrom CANMOS, PO Box 1690,Peterborough, K9J 7S4.

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For valuable soldering information send self-addressed stamped envelope toKester for a FREE Copy of "Soldering Simplified".

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Philips DeForest: Speakers for people who listenWoofers from 5" to 15", midranges in both dome and core styles and newversions of the famous Philips domed tweeter are ideal for communications,experimental or hi-fi application. Philips system -matched crossovernetworks in six configurations make virtually any combination possible.

DeForestComplete kits range from bookshelf models to state-of-the-art packages q,oudspeakersthat look and perform like speakers costing substantially more. Details fromPhilips or a Philips dealer.

ElectronDevicesDivision

For performance data and locationof your nearest dealer write to:Philips Electronics Limited,601 Milner Avenue, Scarborough,Ontario M1B 1M8.Attention P Thorne.

PHILIPSETI CANADA - FEBRUARY 1977 21

MORE THAN JUST A LANDMARK

THE

CNTIOWER

PARIS HAS THE EIFFEL TOWER,Rome, the Colosseum and now,Toronto has its own landmark. All onethousand eight hundred and fifteenfeet of it. The CN tower - the world'stallest free-standing structure. Massive,breathtaking - a Canadian engineeringshowcase. But the tower is more thana public attraction; it is a workingtower, designed as a transmissionfacility for the city's broadcast media.

The tower, which is located inToronto's south-west section, aboutone-third of a mile from Lake Ontario,was built primarily to improve signalstrength for the local television andFM radio stations. Severe ghosting andweak FM signal problems had existedthroughout the city. High-rise apart-ment and office buildings combinedwith the city's topography, impededbroadcast signals, distorted their trans-mission and consequently limitedcoverage. With its 1,815 -foot height,the tower eliminates ghosting for thelocal stations and extends televisioncoverage up to 50 percent with noincrease in power. By increasing theradio horizon or line -of -sight, thetower has also extended and improvedFM reception.

CENTER OF A CENTER

The tower was originally conceivedto be the centre -piece for Metro -Centre, a billion -dollar redevelopmentproject for downtown Toronto, cover-ing 190 acres of land owned byCanadian National and CanadianPacific. Programed for completionover a 15 -year span, the centre was tohave included an integrated transport-ation facility, a commercial office areaand a residential section. Early in 1973with civic support for the centre ebb-ing, CN began construction of thetower in an effort to keep the totalproject alive, but a year later Metro -Centre was shelved.

Work on the mammoth structurebegan in February, 1973. To accom-odate the foundation, 62,000 tons ofgrey Dundas shale were removed. Inthe final stages of excavation, about50 feet below ground, the shale wassmoothed and a one -foot thick blanketof concrete was poured over the rockbase. On top of this blanket, a 22 -footthick concrete foundation was formed.For added strength, the foundationincluded a maze of 500 tons of steeland 40 tons of tensioning cables. With

the foundation completed, workersbegan pouring concrete into a slipformwhich was used to form the tapered Y-shaped tower. A special concrete mix-ture was poured 24 hours a day, fivedays a week for eight months, to form1,464 feet of the tower. In total53,000 cubic yards of concrete wereused with over 80 miles of steel cable.The cable increased the strength of theconcrete to 6,000 pounds per squareinch. An additional 5,000 tons of re-inforcing steel and 600 tons of struct-ural steel were used before the struct-ure was complete.

BOBBING BOMBSIGHTSTo make sure the tower was being

built straight, engineers used threeGerman -made optical plumbs or'bombsights' as well as the traditionalplumb bob. The plumb bob consistedof a 250 -pound steel cylinder attachedto a steel cable. Every measurementwas checked and cross-checked: Theresult: the concrete portion of thetower varies from absolute verticalplumb by a maximum of 1.1 inches.

In August 1974, 45 -foot steel anglebrackets were bolted to the tower atthe 1,100 foot level. The brackets


were used to support the Sky Pod, aseven -storey circular structure whichhouses the public observation areas,the revolving 416 -seat dining room andthe broadcast transmission equipment.The brackets were in place for over ayear while workmen used more steeland concrete to mate the Sky Pod tothe tower.

Above the Sky Pod, at the 1,464 -foot level, another 16 feet of specialconcrete was poured to serve as basefor the transmission mast.

TOWERING OVER THE USSRIn early March 1975, a giant Sik-

orsky Skycrane helicopter topped thetower off by putting into place the335 -foot steel transmission mast. Withthe last section in place, the CN towersurpassed, by more than 67 feet,Moscow's Ostankino Tower, whichpreviously held the record.

To control the sway and vibrationcaused by heavy winds, two dampers,or absorbers, were installed two-thirdsof the way up the mast. Designed by ateam of Canadian engineers, the damp-ers are finely tuned to two differentfrequencies to counter the motion ofthe mast and tower.

SNOWED UNDERRadome, a 11/2 -inch thick glass re-

inforced plastic cover was installed toenclose the mast. Used to combat

heavy winter icing caused by freezingrain, the shape and surface of theradome will cause any major ice build-up to break up and fall like snow.

MAST-ERY OF THE AIROn the mast itself there are four

arrays. The CBC, on channel 5, has an8 gain, single channel directional VHFantenna. The 55 -foot tall array is at amean height of 1,572 feet.

CFTO-TV Ltd., channel 9, also usesa directional VHF antenna with a gainof 11. The 49 -foot high array is at the1,635 -foot level.

Channel 19, CICA and CBLFTchannel 25, form an omnidirectionalUHF array. Set up as a dual 31 gainantenna, the array is 60 feet tall and islocated at the 1,695 -foot mark.

CITY TV, channel 79, has a 25 -footlong by 5 -foot diameter omnidirec-tional UHF array, while provision hasbeen made to accomodate UHFchannels 45, 51, and 57 on a 50 -footthree channel array.

Along with the arrays for TV, thereis a master FM antenna. Measuring 60feet high by 26 feet in diameter, theantenna enables CHFI, CKFM, CHIN -FM, CHUM -FM, and CBC-FM to trans-mit simultaneously. The array is a highpower circulary polarized antennausing cross -dipoles. The array is at thelowest end of the mast. Each station

using the tower has its own set oftransmitters which are located on theuppermost floors of the Sky Pod.

PUBLIC MICROWAVESOn the lower section of the Sky

Pod are CN's microwave facilities. Partof a national network, microwave isused by CN for point-to-point trans-missions of business information, highspeed computer data, and network TVbroadcasting. In addition to the broad-cast and microwave facilities, thetower also has a land mobile systemwhich greatly improves two -communi-cations around the city. The public hasnot been completely ignored when itcomes to the electronic features of thetower. At the reception area located inthe entrance to the tower, is a wall oftelevision monitors, digital weatherdisplay devices and the first computerportrait printer in Canada. It can tele-type a visitor's picture in less than twominutes.

Built at a cost of 57 million dollars,the tower, which has an expected life -span of 200 years, is expected toattract three million visitors a year.For most of them, the tower means abreathtaking ride on the high-speedelevators to the observation decks, orthe revolving restaurant. But forToronto's broadcasters and theiraudiences, the tower is much, muchmore.

L J rTh

OK, all you budding authors, we know you're out there.ETI, as you may have noticed is the only Canadianmagazine for the electronics hobbyist and enthusiast. Now,we like to think of you all frantically rushing about buyingcomponents for, and building, our projects. But we knowyou won't all do that - it would be very boring if you did,because some of you are doing your own things, designingyour own projects, and sometimes, getting them to work.

So, if you've built something interesting, and it works,perhaps you would like to see it as an ETI project. We evenpay you for the privilege of seeing your pride and joy inprint. Or, perhaps you haven't built anything you feelworthy of the accolade, but you could write an interestingfeature article.

Either way we'd like to hear from you. This is yourmagazine in many ways - and by the way, if you'vejust designed a computer -controlled hi-fi based on threechips, please telephone!

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TELEPHONE: (416) 922-1818


Is this a high, low or a critical day in your life? Findout on this

BIORHYTHMCALCULATORThe Casio Biolator is an eight -digit calculator withbuilt-in 99 year calendar and digital biorhythmcomputer.

We all know of the monthly cycle of hormones in women, butdid you know there are similar cycles in all people, irrespectiveof age or sex? At the beginning of this century a Germandoctor discovered that the body is regulated according tothree cycles of differing periods. The 23 -day cycle is the onethat describes variations in physical health, strength, endurance,etc. In the first half of the cycle (days 2 to 11) the staminais high and the body is in good shape. In the second half ofthe cycle (days 13 to 23) the body is more tired and prone toillness.

The theory puts special importanceon the crossover days, the days betweenthe positive and the negative ha!ves ofthe cycle. On these days the conditionof the body is undergoing its fastestrate of change and the likelihood ofan accident or sudden worsening ofan illness is higher than at any othertime of the month. Days 1 and 12 ofthe physical cycle are critical days.

The two other cycles concern thecondition of one's mental performanceand this is looked at from two view-points - activity in the subconsciousregions of the brain and activity in thefully -conscious regions.

The theory holds that there is a

28 -day cycle in the activity of themind's emotional, or instinctive, pro-cesses. For the first fourteen days ofthe cycle one's intuition is keenest,the artistic side of your personalityis at its most creative and your naturalcharm is at a maximum. However forthe next fourteen days life is morehumdrum and you are advised to

be careful with your relationshipswith other people. On the criticaldays (1 and 15) your non -rational sideis likely to dominate your normalrestraints, resulting in 'irresponsible'behaviour, slips of the tongue, quarrels,etc. On the Casio machine this cycleis called the sensitivity cycle.

The third rhythm is the intellectualcycle of 33 -day period. When thecycle is high, thinking power is atits greatest; judgement, wit and con-centration are at their best. When thecycle goes low it is the time for mundanework, for activities low in their de-mands on concentration. Days 1 and 17are the critical days when errors arelikely, when the memory might fail,when accidents might result from sillymistakes.

These then are the three biorhythms,the physical (23 -day) the sensitivity(28 -day), and the intellectual (33 -day).According to the theory all threerhythms start their upward half -cycleon the day you are born. And in the

O Sul1 Mon2 1e3 Wed4 Thu5 Fri6 Sat

The biorhythm graph as printed on the front of the calcu ator. The P, S, and I wave-forms represent the body's physical, sensitivity (emotional) and intellectual cycles.

first 58 years of your life each day willbe under the influence of a uniquecombination of these three variables.How the Biolator worksThe Biolator is based on a 4 -function,3 -register, 8 -digit, calculator with auto-matic constant. Readout is on a greendigitron tube display. This sectionworks just like an ordinary calculatorof this type: algebraic logic is used,there is an overflow indicator, thedecimal point is fully -floating andleading zeroes are suppressed.

Now to the interesting bit. Thiscan be examined from two aspects:calendar calculation and biorhythm cal-culation. The calender covers all datesfrom 1901 to 1999 inclusive. It is ac-cessed by inputs in the format: 76.10.21. (for 21st October 1976) where thethree decimal points are lit by pressingthe DATE button after entering eachpair of figures. The calendar then replies(instantaneously) by displaying 76.10.21-4, the 4 after the - signifyingthat the 21st of October 1976 lands ona Thursday. By this method the day ofthe week for any given date can becalculated.

If after one date has been enteredthe operator presses the - (minus)button and enters another date, then hecan find the number of days betweenthese two dates by pressing the =button. So 76.10.21.-4 minus 73.02.09.-3 equals 1716 days. This facilityhas obvious uses in calculating daily,weekly, or monthly rates when you


THE DESIRABLE AFFINITY CONDITIONSplayers as soon as they know fixturedates, and so on.

SPOUSELOVERFRIENDCO-WORKERTEACHERSPORTS MATECO -ADMINISTRATORCO -RESEARCHERSECRETARY

PhysicalHigh

High

HighHigh

SensitivityMedium

HighHigh

MediumHighHighHigh

Low

IntellectualHigh

HighHighHigh

MediumHighHigh

know a specific quantity of a resourcewas expended between two given days.

Biorhythm calculationTo find a person's biorhythms on a givenday you first enter that date and sub-tract the date of birth of the personin question (as if you were calculatingtheir age in days). However, instead ofpressing the equals button after enteringthe second date, you press the 610button. The biorhythm computer nowreplies by displaying -PP.SS.I I-, wherePP gives the status of the physicalrhythm, SS the status of the sensitivityrhythm, and II the status of the intel-lect rhythm. These numbers correspondto the day of the cycle for each rhythm,they do not show amplitude. To inter-pret the numbers there is a graph abovethe display and a chart on the back ofthe calculator.

The product of 23, 28, and 33 is21252 which means that there are this

many possible permutations of the threerhythms, and these permutations followthe same sequence for all people.

No matter when you were bornyour biorhythms on day 14610 of yourlife will be -06.23.25-. The Biolatorworks by calculating your positionon its 21252 -day biorhythm sequence.

Using the BiolatorIn calculating your own biorhythmsyou can arrange your diary to avoiddisappointment. Picking a day fora wedding, for an interview or a driv-ing test, planning an expedition ortraining for .sportsmen, warning yourfriends or family in advance of your'off' days, etc., can be done with a

simple calculation.The Biclator can be used to calculate

the daily condition of other people, too.Businessmen can forecast the good daysfor their key personnel (or the bad daysof their rivals!), team managers can pick

Interesting conclusions can be drawnwhen you consider the biorhythmsof two people, with respect to eachother. The time difference between theindividual rhythms of two people willalways remain constant - if two people'semotional rhythms are in phase they'llalways stay in phase. The differencebetween the rhythms can be calculatedeasily by finding the condition of theolder person on the day the youngerone was born. This then can be usedto map the affinity of the two people:High affinity for one cycle is whenthe two waveforms are in phase (thedifference numbers are high or low),low affinity is when the waveformsare out of phase (difference numbersaround half a period), and mediumaffinity corresponds to a phase dif-ference of about ninety degrees. Onthe physical biorhythm, for example,high affinity is shown by differencenumbers like 1 to 5 and 20 to 23, lowaffinity is shown by numbers 9 to 16,and other numbers show medium af-finity.

To interpret the significance of af-finity the table above has been drawnup.

The Biolator comes with an instruct-ion booklet and a simulated leathercase. It is attractively styled in a plasticcase with a brushed aluminum frontpanel. Typical discount price is $29.95.

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Depth: 8"

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No matter how much you paidfor your receiver... we guarantee

to improve FM performance.

RF Gain 35 db max. deviation AL 5 db.RF Stages: 3 (L and C tuned)

Noise Figure 7 db max.Transistors: 1 Fet J type and 3 bi-polar types

Spurious Rejection 90 db min.Indicator Dial: "Led"

Image Rejection 85 db min.Power Supply: Continuous 'ON" Type

Input 75/300 Ohm Output 75/300 Ohm

HERE'S HOW IT WORKS

RECEIVER OR TUNER

BEFORE

SIGNAL METER

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AFTER

TYPICAL RECEPTION

SIGNAL R

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SV4

POWER SLEUTH

A SIMPLE EXPLANATIONTO INCREASE YOUR RECEPTION

is uses range from improving reception of FMsignals in problem -ridden city cores (apartments) allthe way to fringe areas (up to 150 miles) where FMreception may now be impossible. Canadian andforeign patents pending.

The 85 FM is the world's first tunable FM powerantenna.It also serves to sharply separate signals, and toprevent overloads on receivers or tuners.The FM 85 is easy to install and operate. All that isrequired is a screwdriver.The 85 FM is guaranteed forever against defects inworkmanship, and parts are guaranteed for 5 years.

Suggested Retail Price $98.50

FTE MOBILE SLEUTH

Also available in AM/FM shortwave automobileantenna. The FTE Mobile Sleuth does for yourcar what the FM Power Sleuth does for your home.

MAGNUM ELECTRONICS INC.2-74 STAFFORD STREET, TORONTO, ONTARIO M4J 2R8

(416) 364-6754


IINITYOR

SPEA

SYSTIby Peter J Thorne

LOUDSPEAKER ENCLOSURES -thewooden boxes that make or break thesound quality - are not easy for thehobbyist to make unless he's a realcarpentry nut. However, the enclosuredecribed here can be easily built byanyone (famous last words?!). Wesimply used prefinished shelving, avail-able at Simpsonsstores across Canada, held togetherwith glue from a hot -glue gun. Theresult - an attractive looking unit, forwhich we selected a pair of top qualityloudspeakers.

Using four pieces of 12" x 24" andone piece of 12" x 36" costs $18 to$36 (depending on the source ofshelving). For this you get all cornerssquare and all edges veneered, so thebox is easy to make and also looksgood, thus solving the two majorproblems of home construction.

Now let's add to this mixture witha really good measured design, andsome top quality speakers. The PhilipsDeForest 9710MC is an 8" wide -range20 watt speaker that is available inter-nationally and is used in monitors for

102

92

82

72

62

5210

Fig.l.1.12givesnoisesixteen

96 dBi 1 m Level #." di\-01

r"..., i -At t//#

#

"P\P%1\\

.'-\ /9

I1

V

100 1kHz 10kHz 20kHz

Frequency responses. The upper curve shows the anechoic response withwatts input, microphone 1 metre from speaker, on axis. The lower curvethe energy response in a reverberant room, with 1.12 watts input of pinkand the microphone 3.5 metres from the speaker. The integration time was

seconds.

some CBC stations. Optionally we canadd one of the latest Philips dometweeters, an AD0162T15. With a verysimple crossover capacitor this addssparkle at the high frequency end. Theoverall response characteristics areshown in Fig.1: these curves weremade on the prototype enclosure bythe Philips Loudspeaker laboratories inDendermonde, Belgium. The tweeterresponse is omitted from these curves,but you can see that the live roomresponse is very smooth. This test,using pink noise, corresponds wellwith actual home listening conditions.

CONSTRUCTIONFig.2 shows how the cabinet isassembled: sides A and B are 12"x 24"shelves as bought. The back and baffleare the same, but with 2" cut off oneend. The top, C, and bottom, D, arecut from each end of a 36" long shelfso they are just over 12" wide inorder to avoid the back and baffleoeing a too -tight fit.

We put the box together with hotglue, using a USM Thermogrip Model204 glue gun. This came from Simp-sons at less than ten dollars includingglue stacks and caulk. The advantage ofusing hot glue is that it only takes aminute or so to bond after pressing theglue -coated edges together. We used nobattens, nails or screws to hold thecabinet together, except the two 2"offcuts from panels E and F. Thesewere glued to the inside of the cabinetshell as baffle supports.

Note that a manufacturer wouldnot assemble an enclosure in thismanner, because there probably isn'tenough strength to withstand shippingshocks. However in most homes this isnot a problem!


DIY SPEAKER

-Parts List

Prefinished shelving:4 pieces 12 x 24ins., 1 piece 12 x 36ins.

Loudspeaker" 8in. wide -range:Philips DeForest 9710MC.

Tweeter' 4in. dome:Philips DeForest AD0162T15, or also suit-able: AD0161T15.

Crossover Capacitor*:

2.2uF or 2uF paper, or bipolar electrolytictype.

Glass fibre batt, approx 2ins. thick: 15 x 48ins.

Terminal strip: 2 connection type, for cabinet rear.

Wire, insulated, stranded: 6 feet.

Tools required: jig -saw, drill (for pilot hole for saw blade),hot -glue gun with glue stick and caulk, sold-ering iron (for speaker wires.

'Available from Dominion Electronics orGladstone Radio in Toronto; Addisons TVParts Ltd., or Payette Radio in Montreal.

THE BAFFLE BOARDThe enclosure is ported (hole B, Fig.3).This enhances the bass output, andmakes sealing of the internal cabinetedges less important, though the caulk-ing supplied with the glue gun shouldbe used for this purpose. The portused was a quart plastic ice-cream con-tainer, with the bottom cut off. Thisgives an almost perfectly proportionedtube for this cabinet size (1.25 cubicfeet). When you cut hole B, measureyour carton first to make sure itdoesn't fall through the hole!

The holes for the 9720M speakerand the AD0162T15 are cut using ajig -saw or a router. If you have neitherthe lumber yard can be conned intocutting them when they're not busy.The exact location on the board of allthree holes is not too critical. Wescrewed the big speaker and hot -gluedthe other speaker and the port inposition, but be careful with the port,since the glue is nearly hot enough tomelt the plastic. Wire up the speakersto a pair of terminals mounted on theback panel. Don't forget the crossovercapacitor (see Fig.4).

Opposing surfaces of the cabinet

interior should be lined with acoustic-ally absorbent material. We used a

single R7 glass fibre insulation batt,(sneaked from the attic - or often alumber yard has a burst bag around,from which one batt can be 'lib-erated'). This can be glued or stapledin position. Wear gloves when doingthis, as glass fibre can temporarily irrit-ate the skin. Snip off a piece of theglass fibre and wrap and tape it roundthe outside of the plastic port. Thiswill dampen any resonance of theplastic.

Test the enclosure - at fairly lowvolume - before glueing, screwing, orcaulking the baffle in position. Thisensures the speakers are okay andwired up. When reassured, fit thebaffle and relax to good sound.

NOTES ON MATERIALSThe best shelving to use is veneeredwood. This is also one of the cheapest(the source is Taiwan). Be careful ifusing vinyl, as we're not sure about thelong term adhesion of some materials,and some vinyls easily split from thechipwood core. If you're hung up onrosewood vinyl, or some similar exotic

finish, we'd suggest scraping off thevinyl at the edges to be glued.

You can of course use plain chip-board, but watch dimensions; somenominal 12" chipboard we checkedwas only 11Y2" wide. Chipwood edgescan be filled with polyfilla, sandedsmooth and then primed and painted.

You can use other speakers thanthe Philips DeForest units specified: ifso, the response curves will be verydifferant.

RATINGThis enclosure is quite efficient, i.e. itputs out considerable sound at quitelow powers. The speaker ratings are aconservative 20 watts RMS continuousand the enclosure is suitable for usewith amplifiers from 5 to 30 wattsRMS (per channel).

Peter J. Thorne is the author ofPractical Electronics Projects forModel Railroaders' published in theU.S.A. and distributed in Canada byKalmbach Publishing Co., Milwaukee.


7

F ig.3.

_7 457.51 '1.-

A

7.825 in DIA

A

.

---\1194)

f4 in356)

'2.825 in(73) DIA

Ap 4.675 in *

75 in

r.l 0(118) DIA

197)

I

?4.5(111

2.5 in

(64).0 12 in

A 1.,__ 3.7 5i n_i....1951

-05

5)

21 in(534)

/ ////////// // ///

N

N

MATERIAL. 0.75 in PREFINISHEDSHELVING

DIMENSIONS IN BRACKETS AREIN MILLIMETRES

* See text 24 in(610)

12 in(305)

SECTION AA


electronics todayWhat's in the March issue

INDUCTION BALANCEMETAL LOCATOR Microfile

Microprocessoratwork

PRODUCE A CIRCUIT whichfeeds a modulated 100kHz signalinto a coil of about six inchesdiameter. Lay another coil ofsimilar diameter next to, andslightly overlapping that coil sothere is virtually no inductivepick-up. Amplify greatly the smallsignal that is picked up but gate itso that an audio amplifier will justnot produce an output.

When the coils are brought near

metal the electro-magnetic fieldsare disturbed and an output isproduced. That's the theorybehind our induction balancemetal locator which will bedescribed in next month's issue.We don't pretend it's easy to build(though the electronics presentfew problems) but our prototypewill sniff out a quarter at nine inchesand that's very much better thanany design published up until now!

ATA SHEETiTl REFERENCE GUIDE

Computers for smallBusinessesMINICOMPUTERS continueto fall in price and increase inperformance. Once theexclusive companion of thelarge corporation, computersare now finding their wayinto smaller and smallercompanies, reducing drud-gery and improving effi-ciency (when properly used).The day will soon be with uswhen any company bigenough to have a telephoneswitchboard will boast itsown computer.

SHORT CIRCUITSWE CONTINUE our series whichbegan in this issue with anotherthree Short Circuits:1. Test -bench Amplifier. Usefulby itself but ours has been modi-fied simply to act as an audiomillivoltmeter as well.2. LED Dice Unit. An electronicdice using only two ICs and sixinexpensive LED's.3. Two Tone Doorbell. Anotherstraightforward project for thehome - this time using a 555.

DISCO MIXER4116

110,11

This articlearticle describes a generalpurpose mixer which can betailored by the reader to meet aspecific application. Prefade'listen' is included as a facility andallowance is even made forbalanced inputs.The articles described here are in anadvanced state of preparation but circum-stances may necessitate changes in theissue that appears.


Ron Harris reports on

MANY READERS will have heardwhisperings of something big brewingin the semiconductor industry - talk ofa new device. It is big; and here for thefirst time in North America ETI takesthe wraps off VCT. The Voltage toCurrent Transactor will get its comm-ercial launch from Texas Instrumentsearly in 1977, no doubt accompaniedby the usual choir of angels and 200 -piece brass band.

So before all the shouting beginswe went to talk to the co -inventor,Professor W.Gosling of Bath Universitywhere the device was initially develop-ed. If you're sitting comfortably we'llbegin!

The basic op -amp has been with ussince the days of the tube, and whensemiconductors crept up on us, it wassimply re -designed to use transistors.This, in the opinion of many designers,means that the advantages of transist-ors are not being fully exploited.

BASIC IDEASOne of the better improvements to

the basic op -amp was the comparatorinput designed by Carl S. Brinkler - aname to which we shall return - and

Fig. 1. Internal circuit of the prototype VCT. The

AN INVENTION

THAT WILL

CHANGE THE FACE

OF ELECTRONICSpatented in April 1965. However Mr.Brinkler was still dissatisfied with theop -amp and some years ago begandiscussions with Professor Gosling,with a v,ew to producing a totally newcircuit block. The basic guidelineswere finally set as being that1. No feedback should be needed tostabilise the device by limiting thehigh frequency response, or to definethe stage gain.2. Both the input and output ports'must be totally floating - a true fourterminal device. This leads to muchgreater freedom with respect to theoutput - it can quite simply be fed intoanywhere!3. The output should be a constantcurrent source i.e. very high imped-ance. Then, should a voltage output berequired at any time, a resistor needonly be inserted across the port.

TEXAS AND THE PROTOTYPESIn 1974 Texas Instruments author-

ised Carl Brinkler to undertakeresearch into producing such a device.Because of the scope and magnitude ofthe task, it was to be a joint under-taking with Bath University i.e.

'F?" in the middle is external.

Professor Gosling. In the autumn of1974 the microcircuit design wasbreadboarded up for the first timewith discrete components, and early in1975 the first I.C.s rolled out of theovens. The first vast improvement overthe op -amp to become apparent wasthe stewing rate, up to 20V permicrosecond, as compared to0.5V /microsecond for the 741

The offset on these prototypes was--110mV due to the layout not beingtotally symmetrical. Productionmodels, when they appear, will have amuch much lower offset. Up to thispoint in the proceedings, the projecthad been running on a shoe -string. Butwith the prototypes showingincredible potential, Texas whippedthe whole show off to Dallas for devel-opment. They feet the VCT is thegreatest advance in circuit design for along time, and we have to agree withthem.

ABILITIES IN CIRCUITLet's take a look at what the VCT

will do. Figure 1 shows the internalcircuit of the Mark 1 VCT. The thicklines represent multiple emitters,and these provide the current gain.You may recognise the current mirrorsaround the top centre of the circuit.

The agreed symbol for the VCT isshown below, the circuit is that used

bias current

BR


The agreed symbol for VCT.

31

VCTfor all linear applications. For a volt-age input, we get a pure constant curr-ent output. Both input and outputimpedances are very high, around 10sof Megohms in the production devices.

There is a fixed ratio between Vinand 10, which is set by one fixed resist-or R. i.e. lo = k 1/R Vin. The constantk can be designed to be any value - itwill be four in the Texas VCTs. A biascurrent is applied down BR, and thedevice can only output twice as muchcurrent as it draws through BR. Earlydevices will be 20mA output VCTs,but later marks will be up in the ampsrange. A ±15V rail is used with theVCTs, and a 13V signal is quite perm-issable!

Some circuits now, for instance anamplifier:

Non -inverting:

VCT as an amplifier.

Voltage gain = k. R L/R

The simplicity of gain inverting arisesbecause the output port naturally hasa fixed phase relationship to the input.Since we get a current out for a volt-age in, a VCT connected thus:

VCT as a simple resistor.

will look like a resistance, value R/kohms.

Consider however a device crossconnected:

O

VCT

VCT working as a negative resistance.

What we have now, looking in at theinput terminals, is no less than a negat-ive resistance! i.e.

Vin= -const.10.

What's more, the transfer character-istic is perfectly linear!

Applications are literally infinite.Anything an op -amp can do, so can aVCT - only usually it does it better!For instance an integrator:

V input

At point A we have f Vin dt since theoutput is a constant current whichfollows the input voltage. If we feedback this integral to the input so:

gut

VCT differentiator

the output will be the differential ofVin.

Gyrators are by now quite commonplace, but what about one which canreach inductor values of 10s of Henrysand with a Q of well over 100? Easy!Values of Q up to 200 have beenachieved experimentally. This circuitintroduces the concept of using :woVCTs together. Texas are packagingthe VCT in a 16 -pin DI L dual package.There are more pins to a VCT than a

VC T VCT

0

0

A VCT gyrator.

741, since we have those already ment-ioned, plus a centre tap on the outputwhich is not always used, but extendsthe versatility.

AMAZING GRACE

The application we found initiallymost amazing is the VCT's ability toreplace a transformer, better than atransformer! All transformers exhibitsome power loss, but this circuit has aselectable loss factor, which naturallycan become a gala if so desired.

VCT as a transformer.

Transformer Ratio = (R 1/R2)'/,.

Choose R such that R2=R1R2 to giveno loss/gain it circuit i.e. a perfecttransformer.

NON-LINEAR

We will consider just one non-linearapplication to show it can be done -

that of a limiter. Since the VCT canoutput only 2x bias current with

bias current


we will get a characteristic

V OUT IB.....RL k/R L

- 1B RL

very simply indeed with only tworesistors.

It is apparent from the preceedingcircuits that one of the biggest gainswhen using VCTs, is in reducingexternal component count over a

similar op -amp or discrete circuit. Inindustrial applications this will lead toless P.C.B. design and assembly com-plications, with resultant reduction incosts.

Another gain is the fact that whenused as an inverting amp, no inputresistor is used to drop the signal, as itis in op -amp circuits. In these circuits,since the input is usually a virtualearth, most of the signal is dissipatedin the resistor, with a resultant poorsignal-to-noise ratio upon amplific-ation at the output. With VCTs noresistor is required, and this gives adistinct improvement in S/N ratio,with the attendant gain in dynamicrange.

THE PRICE OF A FUTURE

One question remains - how much?Well, this depends entirely on TexasInstruments, and the marketing policythey persue. No doubt the price willbe high at first, falling as the volumeof sales climbs, as it surely must.Interestingly, the VCT occupies onlyhalf the chip area of a 741 op -amp,but whether this affects pricingremains to be seen. We'll keep you in-formed of developments, as we're con-vinced you'll be hearing much more ofVCT in the years to come.

OUR THANKS and congratulations toProfessor W Gosling of Bath University,England, who provided the information forthis article.

QUALITY COMPONENTS"YOUR ORDER -HERE TODAY ,GONE "OMORROW"

Our semiconductors are first line quality from mar,,manufacturers only. We usually stock Motorola, RCAFairchild, National, or GE devices. All items are brandnew, no "allouts, re -brands, seconds, no tricky adw-rising such as "100% functional" etc. All fully quara,teed. Items listed below are in stock for immedvqshipment. We can supply almost any device Or

special order and at competitive prices. Write forquotation on any device not listed

TTL

7400 25

7402 .25

7404 .28

7406 .32

7403 75

7410 .33

7413 .69

7414 1.90

7420 29

7427 .45

7440 .29

7441 1.25

7448 1.08

7460 .29

7451 .29

7473 .50

7474 .50

7475 .70

7476 .58

7046 52

7490 .78

7491 1.20

7492 79

7493 .73

74121 .63

74123 1.29

74191 20574192 1.70

74193 1.70

74194 1.60

74196 1.55

CMOS

4000 32

40016 .35

40028 .35

4007 35

001113 .35

401213 .35

4013 .68

4017 1.80

4018 1.80

00238 36

4024 1.90

4025B .35

4027 90

4046 2.40

4049 .03

awls 1.62

40528 1.62

40668 99

4071B 35

40728 .35

4061B .35

40828 .36

4511 2.894528 1.86

LINEAR301A .48

308A 1.36

311 1.20

360914 1.80

381N 2.30

3829 2.30

LINEAR555 .66

556 1.55

567 1.80

709 52

710 1.20

723 1.05

733 1.50

741CH .49

741CN 49

1458 .85

2240 4.50

3900 1.25

3909 1.30

Bon 6.50

7035 1.65

7806 1.65

7812 1.65

7815 1.65

C43140 1.75

TransistorsP52222 4/1.00PN3663 4/1.002N3904 4/1.00293906 4/1 00

254401 4/1.20255172 5/1 00NIPSA13 .49

MPSA18 75

MPSUO4 1.12

MPF102 49

253055 1.25

SPECIALS: 74C00 .25 74CO2 .29 293702 6/100

293704 6/130 259071ARA Sensitive Gets Then 1.43

2N6239.4A,200V SCR 105 194001 .16 194032 .14

19404.20 1y406.1.5 154146 10/100

RESISTORS - DEPOSITED CARBONFILM, 1/4 AND 1/2 WATT, 5%

Any EIA standard value. 1 ohm through 4.7 rnegohms.

5 of any one value and wattage .25 100 of one value. 3.50100 mixed, 5 per value 4.00

ELECTROLYTIC CAPACITORS

Axial Leads

4.70/50V .20

10u1/25V 20

100/50V 22

220/25V 22

220/50V 25

47uf/25V 24

47uf/50V 29

1000/25V 26

1000/50V .36

220W/25V 35

2200/50V 52

470u1/25V .50

SPECIAL -AXIAL LEAD

Axial Leads

470u1/50V .59

1000uf/16V 52

1000W/25V .59

1000W/40V .95

1000uf/63V 1.25

2213310/16V .87

2200W/40V 1.20

Radial Leads

4.7uf/50V 14

10uf/25V 13

100/50V .16

22u1/25V .15

ELECTROLYTICS

Radial Leads

22uf/50V .20

47ufi25V .20

1000/25V 23

2213u1/16V 25

470u1/16V 39

Dipped Tantalum.47of/36V .30

1.O551/35V .33

2.2uf/35V .36

I 7uf:16V 35

10uf/16V .42

10W/35V .55

100/50V 8/1 00

DATA AND APPLICATION BOOKSTTL IC's 592 pages 4.03

Linear Data 957 pages 5.00

CMOS Data 256 pages 3.00

Transistors 288 pages 3.00

Memory IC's 592 pages 4.00

Understanding CMOS. Progr

Audio Handbook 1.00

Interface IC's 464 pages 4.00

Linear Appl. 1 4.00

Linear Appl. 2 3.00

Special Function IC's 3.00

rnmed Learning Course. 200

SOCKETS DIP Soldertail,8 pin Nickel -silver .25

14 pin Nickel -silver .31

16 pin Nickel -silver .37

18 pin NickersOver 40

low profile

24 pin Nickel.SrIver 50

8 pin Gold Clad 34

14 pin Gold Clad 11

16 pin Gold Clad 47

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ETI SUPPLEMENT

555 TIMERDESCRIBED BY

R. M. MARSTON

APPLICATIONSTHE 555 TIMER is a highly versatile low-cost IC that isspecifically designed for precision timing applications,but which can also be used in a variety of monostablemulti -vibrator, astable multivibrator, and Schmitttrigger applications. The device was originallyintroduced by Signetics, but is now available under the'555' designation from many other manufacturers.

The 555 has many attractive features. It can operatefrom supply voltage in the range 4.5V to 16V. Itsoutput can source (supply) or sink (absorb) any loadcurrent up to a maximum of 200mA, and so candirectly drive loads such as relays, LED's, low -powerlamps, and high impedance speakers. When used inthe 'timing' mode, the IC can readily produce accuratetiming periods that can be varied from a fewmicroseconds to several hundred seconds via a singleR -C network. Timing periods are virtually independentof actual supply rail voltage, have a temperaturecoefficient of only .005% per °C, can be started via aTRIGGER command signal, and can be aborted by aRESET command signal.

When used in the monostable mode, the ICproduces output pulses with typical rise and fall timesof a mere 100nS. It can be made to producepulse -width modulated (PWM) pulses in this mode byfeeding fixed frequency clock pulses to the TRIGGERterminal and, by feeding the modulation signal to theCONTROL VOLTAGE terminal.

When used in the astable mode both the frequencyand the duty cycle of the waveform can be accuratelycontrolled with two external resistors and one capacitor.The output signals can be subjected to frequency sweepcontrol, frequency modulation (FM), or pulse -positionmodulation (PPM) by applying suitable modulationsignals to the CONTROL VOLTAGE terminal of the IC.

THE 555: HOW IT WORKSThe 555 is available under a variety of specific typenumbers but is generally referred to simply as a '555timer.' The device is available in a number of packagingstyles, including 8 and 14 -pin dual -in -line (DIL) and8 -pin TO -99 types. Throughout this article all circuitsare designed around the standard 8 -pin DIL versions ofthe device.

Fig 1 shows the outline and pin notations of thestandard 8 -pin DIL version of the 555, and Fig 2 shows

GROUND

TRIGGER

OUTPUT

RESET

Vcc

DISCHARGE

THRESHOLD

CONTROL VOLTAGE

Fig. 1: Outline and pin notations of the standard 8 -pin dr1version of the 555 timer 1. C.

the functional block diagram of the same device (withinthe double lines), together with the connections forusing it as a basic monostable generator. The followingexplanation of device operation assumes that the 555 isused in the monostable configuration shown in Fig 2.

The 555 houses 2 diodes, 15 resistors, and 23transistors. These components are arranged in the formof one voltage -reference potential divider, twovoltage -comparator op -amps, one R -S flip-flop, a

low -power complementary output stage, and a slavetransistor. The voltage -reference potential dividercomprises three 5k0 resistors in series, and is

connected across the supply lines. Consequently, 2/3V appears at the junction of the upper two resistors of

RT

0

CONTROLVOLTAGE

,Vcc 0 0

0 ,VccRESET

OR4 RL

RI5k

THRESHOLD

0

R25k

R35k

DISCHARGE

CT

OP AMP

OP AMP

R

FLIPFLOP

a

OUTPUTSTAGE

C11

555TIMER

GROUND

0TRIGGER

0OUTPUT

ov

Fig. 2: Functional block diagram (within the square) of the 555timer i. c., together with the connections for using the i.c. as abasic monostable generator or timer.

the potential divider, and is fed to one input terminal ofthe upper voltage -comparator op -amp and 1/3 V,appears at the junction of the two lower resistors of thepotential divider, and is fed to one input terminal of thelower voltage -comparator op -amp. The outputs of thetwo comparators control the R -S flip-flop, which in turncontrols the states of the complementary output stageand the slave transistor. The state of the flip-flop canalso be influenced by signals applied to the pin 4RESET terminal.

When the monostable or timing circuit of Fig 2 is inits quiescent state the pin 2 TRIGGER terminal of thechip is held high via Rl. Under this condition Q1 is

driven to saturation and forms a short circuit acrossexternal timing capacito- CT, and the pin 3 outputterminal of the IC is driven to the low state. Themonostable action can be initiated by applying a

negative -going trigger pulse to pin 2. As this pulse falls


555 TIMER APPLICATIONSbelow the 1/3 V00 reference value of the built-inpotential divider the output of the lower voltagecomparator op -amp changes state and causes the R -Sflip-flop to switch over. As the flip-flop switches over itcuts off Q1 and drives the pin 3 output of the chip tothe high state.

As Q1 cuts off it removes the short from timingcapacitor CT, so CT starts to charge exponentiallytowards the supply rail voltage until eventually thevoltage across CT reaches 2/3 Vcc. At this point theupper voltage comparator op -amp changes state andswitches the R -S flip-flop back to its original condition,so Q1 turns on, rapidly discharging CT, andsimultaneously the pin 3 output of the IC reverts to itslow state. The monostable operating sequence is thencomplete. Note that, once triggered, the circuit cannotrespond to additional triggering until the timingsequence is complete, but that the sequence can beaborted at any time by feeding a negative -going pulseto pin 4.

The delay time of the circuit, in which the pin 3output is high, is given as

t = 1. 1 RT CT

where t = mS, RT = ka and CT = uF. Fig 3 showshow delays from 10 uS to 100 seconds can be obtained

100

10

01

0011 100

rnS mS

TIME DELAY, t

Fig. 3: 555 time delays for different values of resistance andcapacitance.

= 1 1 CT RT

WHEN t= mS

RT - k

CT

RT

100,s

10SEC SEC

100SEC

by selecting suitable values of CT and RT in the range.001 uF to 100uF and 1 k0 to 10MQ. In practice, RTshould not be given a value less than 1 kO or greaterthan 20MQ, and capacitor CT must always be alow -leakage component. Note that the timing period ofthe circuit is virtually independent of the supply voltagebut that the period can be varied by applying a variableresistance or voltage between the ground and pin 5CONTROL VOLTAGE terminals of the chip. This facilityenables the periods to be externally modulated orcompensated.

The pin 3 output terminal of the IC is normally low,but switches high during the active monostablesequence. The output can either source or sink currentsup to a maximum of 200mA, so external loads can beconnected between pin 3 and either the positive supplyrail or the ground rail, depending on the type of loadoperation that is required. The output switching riseand fall times are typically about 100 nanoseconds.Having cleared up these points, let's now go on andlook at some practical applications of the 555 timer I.C.

50 SECOND TIMERThis 50 second timer or pulse generator gives a directvoltage output at pin 3 which is normally low, but goes

high for the duration of the timing period. Optionalcomponents R4 and LED (shown dotted) give a visualindication of the timer action. The circuit works in thesame basic way as already described, except that thetiming action is initiated by momentarily shorting pin 2to ground via START switch S,. Note from the circuitwaveforms that a fixed -period output pulse is availableat pin 3 and an exponential sawtooth with an identicalperiod is available at pin 7: The sawtooth waveform hasa high output impedance.

The basic timer circuit of Fig 4 can be varied in anumber of ways. The timing period can be madevariable between approximately 1.1 seconds and 110seconds by replacing R, with a 10k() fixed resistor anda IMO variable resistor in series.

OUT

5 to 15V .Ve

R34.7k

oR4;470

!LED

o

S1

LI STARTRESET°.

tit

Fig. 4: Circuit andwaveforms of simplemanually -triggered 50second timer or pulse PIN 3J

generator (OUT)

PIN 2IS1)

PIN 7

IC1)

Vcc

00

R1 _f 10k

470k

ClT100ti F

01/

OV

OV

1Mis

0 11,

The period can be further varied, if required, byswitch -selecting decade values of timing capacitance.The dotted section shows how the circuit can beprovided with a RESET facility, so that a timing periodcan be aborted at any time, by taking pin 4 to thepositive supply rail via resistor R5 and wiring RESETswitch S2 between pin 4 and ground.

The timing circuit of Fig 4 can be used to drivenon -inductive loads at currents up to 200mA directly.They can be used to drive inductive relay loads by usingthe basic connections shown in Fig 5

The Fig 5 circuit is designed to apply a connection toa normally -off external load for a pre-set period of 50seconds when START switch S, is momentarily closed.The relay is normally off, but turns on for the 50 secondperiod when tie timing cycle is initiated. D2 is wired inseries with the relay coil to counteract the slight residual

TO BREAKLOAD

TO MAKELOAD

12V

D1 RLASIN 12V ;:4001 60

We

Dv

Fig. 5: Relay -output timer makes or breaks connection to loadfor pre-set period of 50 seconds when S, is momentarilyoperated.


voltage that appears at pin 3 of the IC under the OFFcondition and thus ensure that the relay turns fully off.The dotted section shows how this circuit can be usedto switch off a normally -on load.

Note in Fig 5 and all other relay -output circuitsdescribed here, that the relays used can be any 12 volttypes that draw ON currents of less than 200mA, e.g.,that have coil resistances greater than 600.

The basic relay -driving timer circuit of Fig 5 can beadapted for use in a variety of useful applications Sometypical examples are shown in Figs 6 to 9.

V4

92 PON DONS

I 0 Isec lOset

2 9 Claw 100%H,

Fig. 6: Relay -output general-purpose timer covers 0.9 sec to100 sec in two decade ranges.

Fig 6 shows the practical circuit of a relay -outputgeneral-purpose timer that covers 0.9 seconds to 100seconds in two decade ranges: The circuit has a RESETfacility provided via S2, so that timing periods can beaborted part way through a cycle if necessary. Anoteworthy feature of this circuit is that the maximumtiming periods of each decade range of the timer can beprecisely pre-set via R5 or R6, which effectively shuntthe built-in potential divider of the 555 and thusinfluence the timing periods: This facility enables thecircuit to give precise timing periods even whenwide -tolerance timing capacitors are used.

To set up the Fig 6 circuit, first set R, to maximumvalue, set RANGE switch S3 to position 1, activateSTART switch SI, and adjust R5 to give a timing periodof precisely 10 seconds. Next, set S3 to position 2,activate START switch SI, and adjust R6 to give atiming period of precisely 100 seconds. All adjustmentsare then complete, and the timer is ready for use.

DELAYED HEADLIGHT TURN-OFF

Fig 7 shows the practical circuit of an automaticdelayed -turn-off headlight control system for auto-mobiles. This facility enables the owner to use the carlights to illuminate his path for a pre-set time afterparking as he leaves the garage or walks along adriveway, etc. The circuit does not interfere with normalheadlight operation under actual driving conditions. Itworks as follows.

When the ignition switch is turned to the ON

VEHICLES-r-BATTERY 12V

-L-

OV ICHASSIS)

Fig. 7: Automatic delayed -turn -out headlight control systemfor automobiles.

OFFHEADLIGHT:WITCH

ON

HEADLIGHT

position current is fed to the coil of the relay via D3 andthe 12 volt supply rail, so the relay turns on andcontacts RLA/ 1 close. As the contacts close theyconnect the 12 volt supply to the timer circuit and tothe headlight switch. Thus, under this 'ignition on'condition the headlights operate in the normal way.Note that, since one side of C2 is connected directly tothe positive supply rail and the other side is taken to thepositive rail via R2, the capacitor is fully dischargedunder this condition.

The moment that the ignition switch is turned to theOFF position the D3 -derived current supply to the relaycoil is broken, and simultaneously a negative -goingtrigger pulse is fed to pin 2 of the 555 as the C2 -R3junction drops to ground volts and C2 charges up. Now,relays are inherently slow -acting devices, so contactsRLA/1 do not open instantaneously as the ignitionswitch is turned off. Conversely, the 555 is a very fasttriggering device, and the instant that the trigger pulseis generated via the turn-off action of the ignition switcha timing cycle is initiated and current is fed to the relaycoil via output pin 3 of the IC as it goes high. Thus therelay remains on for a pre-set period after the ignitionswitch is closed, and the positive supply rail remainsconnected to the headlight switch for the duration ofthis period. With the component values shown thisperiod is roughly 50 seconds.

At the end of the 50 second timing period, pin,3 ofthe 555 switches to the low state and the relay turnsoff. As it does so, contacts RLA/ 1 open and remove thesupply from the timer and the headlight switch, and theheadlights turn off. The operating sequence is thencomplete.

Readers may care to note that the above system ofoperation is consistent with the practice adopted inmany modern vehicles of feeding the headlight switchvia the ignition switch, so that the headlights operateonly when the ignition is turned on. On older types ofvehicle, where headlight operation is independent ofthe ignition switch, a manually -triggereddelayed -turn-off headlight or spotlight control facilitycan be obtained by using the circuit shown in Fig 8. Theaction of this circuit is such that, if the vehicle is parkedwith its lights off, they turn on for a pre-set 50 secondperiod as soon as a push-button START switch is

momentarily closed, and at the end of this period turnoff again automatically.

The Fig 8 circuit uses a relay with two sets ofnormally -open relay contacts. The timing sequence isinitiated by momentarily closing push-button switchS,. Normally, both SI and the relay contacts are open,so zero power is fed to the timer circuit and the lightsare off. C is discharged under this condition.

When S, is momentarily closed power is fed directlyto the relay coil, and the relay turns on. As the relay

VEHICLESBATTERY-L-

OFFo HEAD ORLIGHT

RLASWITCH

OV ICHASSIS)

Fig. 8. Manually -triggered delayed -turn-off head- or spot -lightcontrol system for automobiles.

HEAD ORSPOT LIGHT


555 TIMER APPLICATIONSturns on contacts RLA/ 2 close and apply power to thevehicle lights and contacts RLA / 1 close and applypower to the timer circuit, but pin 2 of the IC is brieflytied to ground via C2 and R3 at this moment, so anegative trigger pulse is immediately fed to pin 2 and atiming cycle is initiated. Consequently, pin 3 of the 555switches high at the moment that the relay contactsclose, and thus locks the relay into the ON conditionirrespective of the subsequent state of START switchS,, so the lights remain on for the duration of the 50second timing cycle. At the end of the timing cycle pin3 of the I.C. switches to the low state, so the relay turnsoff and contacts RLA /1 and RLA / 2 open, disconnect-ing power from the timing circuit and the lights. Theoperating sequence is then complete.

PORCH LIGHTFinally, to conclude this 'Timer Circuits' section of the555 story, Fig 9 shows the circuit of a relay -outputautomatic porch light control unit that turns the porchlights on for a pre-set 50 second period only whensuitably triggered at night time or under 'dark'conditions: The circuit is triggered via switch S,, whichmay take the form of a microswitch activated by a porchgate or a pressure -pad switch activated by body weightand concealed under a porch mat or rug.

The operation of the Fig 9 circuit relies on the factthat for correct timer operation the negative -goingtrigger pulse that is fed to pin 2 of the IC must fallbelow the internally -controlled '1 /3 Vcc' voltage valueof the 555. If the trigger pulse does not fall below thisvalue, timing cycles can not be initiated by the triggersignal.

OUT TOPORCHLIGHTS

0415E7 TRIG

LEVEL)47k

Fig. 9. Automatic porch light turns on for a pre-set period onlywhen triggered at night.

In this design, light -dependent resistor LDR and pre-set resistor R4 are wired in series as a light -dependentpotential divider. One side of switch S, is taken to theoutput of this potential divider, and the other side of theswitch is taken to pin 2 of the IC via the C2-133combination. Under bright or daylight conditions theLDR acts as a low resistance, so a high voltage appearsat the output of the potential divider. Consequently, theact of closing S, causes a voltage pulse much higherthan '1/3 V' to be fed to pin 2 of the chip, so the timeris not triggered via S, under the 'daylight' condition.

Conversely, the LDR acts as a high resistance underdark or 'night' conditions, so a low voltage appears atthe output of the potential divider. Consequently, theact of closing S, causes a voltage pulse much lowerthan '1/3 V' to be fed to pin 2 of the IC, so the timecircuit is triggered via SI under the 'night' condition.

In practice, the LDR can be any cadmium -sulphidephotocell that presents a resistance in the range 1 k0 to100k() under the required minimum 'dark' turn -oncondition, and R4 can be adjusted to preset the

minimum 'dark' level at which the circuit will trigger.Note that the trigger signal is fed to pin 2 of the IC viathe C2 -R3 combination, which act as a trigger signalconditioning network that effectively isolates the d.c.component of the LDR-R4 potential divider from thetrigger pin of the IC.

MONOSTABLE PULSE GENERATOR CIRCUITSAll the 555 timer circuits that we have looked at so faract essentially as monostable multivibrators or pulsegenerators. The 555 can be used as a conventionalelectronically -triggered monostable multivibrator orpulse generator by feeding suitable trigger signals to pin2 and taking the pulse output signals from pin 3. The ICcan be used to generate good output pulses with periodsfrom 51,13 to several hundred seconds. The maximumusable pulse repitition frequency is approximately100kHz.

The trigger signal reaching pin 2 must be a carefullyshaped negative -going pulse. Its amplitude must switchfrom an OFF value greater than 2/3 V to an ON valueless than 1/3 V (triggering actually occurs as pin 2drops through the 1/3 V value). The pulse must havea width greater than 100nS but less than that of thedesired output pulse, so that the trigger pulse isremoved by the time the monostable period terminates.

One way of determining a suitable trigger signal forthe 555 monostable circuit is to convert the input signalto a good square wave that switches between groundvolts and the full positive supply rail voltage, and thencouple this square wave to pin 2 of the IC via a simpleshort time -constant C -R differentiating network, whichconverts the leading or trailing edges of the square

R32 2k

C4 R4

luF 10k

R510k

R2

2.2k

C2

.001uF

012N3704

U13 -PIN DIL

555TIMER]

4

R6 ,)LEVEL)

OUTOUT

5 p --

C3

.01uF

5V to 15V +Ve0

-I- C1

(SEE TABLE)

0V

Cl1 VALUE I PULSE WIDTH RANGE]

10uF 1 90mS 1.2sec.luF 9mS - 12OrrS01uF 0.9roS - 12mS.01uF 90uS 1 2mS

1201uF 1 9uS 120uS 1

Fig. 10a: Simple add-on pulse generator is triggered byrectangular input signals: circuit can be used at triggerfrequencies up to 100kHz.

wave into suitable trigger pulses. Fig. 10a shows apractical circuit that uses this basic principle, but isintended for use only with input signals that are alreadyof square or pulse form.

Here, transistor Q, converts the rectangular inputsignal into a signal that switches between the groundand positive voltage rails, and the resulting signal is fedto pin 2 via the C2 -R2 differentiating network. Thecircuit can be used as an add-on pulse generator inconjunction with an existing square or pulse generator.Variable -amplitude output pulses are available from pin


3 via variable potential divider R6. The output pulsewidths can be varied over more than a decade range viaRI, and can be switched in overlapping decade rangesby using the values of Cl listed in the table. With thecomponent values shown the pulse width is fullyvariable from 9 uS to 1.2 seconds. Note that C3 is usedto decouple the pin 5 CONTROL VOLTAGE terminaland improve the circuit stability.

Fig 10b shows how the above circuit can bemodified so that it can be driven from any type of inputwaveform, including sine waves. Here, ICI isconnected as a simple Schmitt trigger, which convertsall input signals into rectangular output signals, andthese rectangular signals are used to drive the 1C2monostable circuit in the same way as described above.The Fig 10b circuit can thus be used as an add-on pulsegenerator in conjunction with an existing waveformgenerator of any type that produces output signals withpeak -to -peak amplitudes greater than 1 /2 V.

t 1 Ate

'

1----4,

"OM 0 L.*-4tlut 21,

MetaMORE IMAM

Va

/I OIL665m

1C1

C20010

eRAVEOW

Ca

. ttlIC1R1

E EARLE,Et AR 10 044 RI

tECRL

Tat,

14

"" T i

Fig. 10b: Improved add-on pulse generator is triggered by anyinput waveform.

Fig 11 shows how two basic monostable pulsegenerators can be connected in series to make adelayed pulse generator, IC1 is used as aSchmitt trigger and IC2 controls the delay width andIC3 determines the output pulse width: The final outputpulse appears some delayed time after the initialapplication of the trigger signal. This circuit can bemade into a self-contained instrument by building it intothe same cabinet as a simple square wave generator,which can be used to provide the necessary drivesignals.

Fig. 11: Add-on delayed pulse generator is triggered by anyinput waveform. For C1 (and C7) values, see table in Fig 10a

Any number of basic monostable pulse generatorscan be wired in series to give a sequential form ofoperation. Fig 12 for example, shows the circuit andwave -forms of a 3 -stage sequential generator, whichcan be used to operate lamps or relays, etc., in a

pre-programmed time sequence once an initial STARTcommand is given via push-button switch S,. Note thatthe pin 4 RESET terminal of all ICs are shorted togetherand positively biased via R7, and that these terminalscan be shorted to ground via SET switch S2: This SETswitch should be closed at the moment that power is

Fg. 12: 3 -stage sequential timeror pulse generator.

01.1111101

first applied to the circuit, to ensure that none of the ICsare falsely triggered at. this moment.

Finally, three or more monostable circuits can beconnected, via C9, in a continuous loop, with theoutput of the last monostable feeding back to the inputof the first monostale, to form a 'chaser' circuit inwhich the sequential action repeats to infinity. This typeof circuit can be used to drive lamp or LED displays, etc.Note tnat the circuit is again provided with the S2 SETfacility, so that the circuit can be emptied at themoment that power is first applied.

ASTABLE MULTIVIBRATOR CIRCUITSFig 13 shows the practical circuit of a basic 1 kHz astablemultivibrator, together with the formulas that define thetiming of the circuit. Note that TRIGGER pin 2 of thechip is shorted to the pin 6 THRESHOLD terminal, andthat timing resistor R2 is wired between pin 6 andDISCHARGE pin 7.

When power is first applied to the circuit C1 starts to

+t1

k-- T

12.

OUT

t1 = 0.693(R1 r R2IC1

t2 = 0 69314321C1

T = 0.6931R1 r 2R2IC1f 1 44

(131 r 7R210

0

IF R2 IS GREATER THAN R1:

tl 0.7 R2 C1t2 0.7 R2 C1T 14 R2 Cl

R2 C1

Fig. 13: Basic circuit of 1KHz astable multivibrator, withtiming formulas.

charge exponentially (in the normal monostable fashion)via the series R1 -R2 combination, until eventually theCl voltage rises to 2/3 V. At this point the basicmonostable action terminates and DISCHARGE pin 7switches to the low state. C1 then starts to dischargeexponentially into pin 7 via R2, until eventually the Clvoltage falls to 1/3 Vcc, and TRIGGER pin 2 isactivated. At this point a new monostable timingsequence is initiated, and Cl starts to recharge towards2/3 V, via R1 and R2. The whole sequence thenrepeats add infinitum, with C1 alternately chargingtowards 2/3 V, via R 1 -R2 and discharging towards1/3 V via R2 only.

Note in the above circuit that, if R2 is very largerelative to R1, the operating frequency of the circuit isdetermined essentially by the R2 and C1 values, andthat a virtually symmetrical output waveform is


555 TIMER APPLICATIONSgenerated. The graph of Fig 14 shows the approximaterelationship between frequency and the C1 -R2 valuesunder the above condition. In practice, the R1 and R2values of the circuit can be varied from 1 kO up to tensof megohms. Note, however, that R1 has a significant

100

10

.0010.1Hz

9,-,

9,,.>,

9,' ,,4

92

'_,4

Hz

10Hz

100Hz kHz

10kHz

100kHz

ASTABLE FREQUENCYFig. 14: Approximate relationship between Cl, R2, andfrequency when R2 is large relative to R1

effect on the total current consumption of the circuit,since pin 7 of the IC is virtually grounded during half ofthe timing sequence. Also note that the duty cycle ormark/space ratio of the circuit can be pre-set at anon -symmetrical value, if required, by suitable choiceof the R1 and R2 values.

The basic circuit of Fig 13 can be usefully modifiedin a number of ways. Fig 15, for example, shows how itcan be made into a variable -frequency square wave

5V to 15V Ve

R44.7k R1 1k

OUT

R310k

C2 .01uF

R2100k

CI OluF

T oovFig. 15: Variable frequency square wave generator covers therange 650Hz- 7. 2kHz approximately.

generator by replacing R2 with a fixed and variableresistor in series. With the component values shown thefrequency can be varied over the approximate range650Hz-7.2kHz via R2.

Fig 16 shows how the circuit can be further modified5V to 15V We

R54.7k

OUT

91 1k

R2 100k021N 914 R3 1k

Cl .OluF

TC2o.01uF T0,

R4100k

Fig. 16: Astable multi with mark and space _periodsindependently variable over the approximate range 7.5µs to7501.is

so that its MARK and SPACE periods are independentlyvariable over the approximate range 7.54S to 750 /IS.Here, timing capacitor C1 alternately charges viaR1 -R2 -D1 and discharges via R3 -R4 -D2.

Fig 17 shows how the circuit can be additionallymodified so that it acts as fixed -frequency square wavegenerator with a mark/space ratio or duty cycle that isfully variable from 1% to 99%. Here, C1 alternately

OUT

0

5V to 15VVe

111 1k

R2 100k

R3 1k

02IN 914

C2Cl.OluFOFT 0 ov

Fig. 17: Astable multi with duty cycle variable from 1 to 99%with frequency approximately constant at 1.2kHz.

charges via R1 and the top half of R2 and via D1, anddischarges via D2 -R3 and the lower half of R2. Notethat the sum of the two timing periods is virtuallyconstant, so the operating frequency is almostindependent of the setting of R2.

GATING A 555 ASTABLEThe 555 astable circuit can be gated ON or OFF, viaeither a switch or an electronic signal, in a variety ofways. Figs 18 and 19 show two basic ways of gatingthe IC via a switch.

In Fig 18 the circuit is gated via the pin 4 RESET

PRESSS.1

OV -

5V to 15VVe

Cl01uF

OV

Fig. 18: Gated 1kHMZ astable with 'press to turn-off' or 'pressto turn -on" operation.

terminal. The characteristic of this terminal is such that,if the terminal is biased significantly above a nominalvalue of 0.7 volts, the astable is enabled, but if the.terminal is biased below 0.7 volts by a current greaterthan 0.1 mA (by taking the terminal to ground via aresistance less than 7k(), for example) the astable isdisabled and its output is grounded. Thus, the Fig 19circuit is normally on but can be turned off by closingS1 and shorting pin 4 to ground, while the circuitshown in dotted lines is normally gated off via R4 butcan be turned on by closing S2 and shorting pin 4 to thepositive supply rail. These circuits can alternatively begated by applying suitable electronic signals directly topin 4.

The Fig 19a and 19b circuits are gated via the pin 2TRIGGER and pin 6 THRESHOLD terminals. Thecharacteristic here is such that the circuit functions as anormal astable only as long as pin 6 is free to swing upto 2/3 V and pin 2 is not biased below 1/3 V. Ifthese pins are simultaneously driven below 1/3 V the


51

OV-

5V to ISV

RI 10k

R2 75k

R --114-m DI SEE TEXT/

Si

Fig. 19A: Alternative gated 1kHz astable with press toturn-off' operation.

astable action is immediately terminated and the outputis driven to the high state. Thus, the Fig 1 9a circuit isnormally on but turns off when S1 is closed. Note thatan electronic signal can be used to gate the circuit byconnecting a diode as indicated and eliminating SI. Inthis case the circuit will gate off when the input signalvoltage is reduced below 1/3 Vcc.

The Fig 19b circuit is connected so that it is normallygated off by saturated transistor Ql, but can be gated

5V to I 5V

.(PRESS St1"

ov1

Fig. 19B: Alternative gated 1kHz astable with press toturn-off" operation.

on by closing S1 and thus turning the transistor off.This circuit can be gated electronically by eliminatingR5 and S1 and applying a gating signal to the base ofQ1 via a 10k() limiting resistor. In this case the astableturns off when the input signal is high, and turns onwhen the input signal is reduced below 0.7 volts or so.

All the 555 astable circuits that we have looked atcan be subjected to frequency modulation (FM) orpulse -position modulation (PPM) by simply feeding asuitable modulation signal to pin 5. This modulationsignal can take the form of an A.C. signal that is fed topin 5 via a blocking capacitor, as in the case of Fig 20aor a D.C. signal that is fed directly to pin 5, as in the caseof Fig 20b. The action of the chip is such that thevoltage on pin 5 influences the width of the 'mark'pulses in each timing cycle, but has no influence on the'space' pulses. Thus, since the signal on pin 5

influences the position of each 'mark' pulse in eachtiming cycle, this terminal provides pulse -position

5V to 15V .Ve

;OV

OV

51

\ 1

5V to 15V One

MODULATIONINPUT

SPACE PULSE WIDTHS CONSTANTMARI( PULSES VARIABLE

Fig. 20. Alternative ways of obtaining frequency or

pulse -position modulation (FM or PPM) from the 555 astablecircuit.

modulation (PPM), and, since the signal influences thetotal period of each cycle (and thus the frequency of theoutput signal), the terminal also provides frequencymodulation (FM). These facilities are useful in specialwaveform generator applications, as is shown in thenext section.

MISCELLANEOUS ASTABLE APPLICATIONSThe 555 astable multivibrator has three outstandingadvantages over other types of astable circuit. First, itsfrequency can be varied over a wide range via a singleresistive control. Second, its output has a lowimpedance and can source or sink current up to200mA. Finally, its operating frequency can readily bemodulated by applying a suitable signal to pin 5 of theIC. These features make the device exceptionallyversatile, and it can be used in a vast range of practicalapplications of interest to both the amateur andprofessional usef.

MORSE PRACTICE OSCILLATORFig 21 shows how the 555 timer I.C. can be used as amorse-code practice oscillator. The circuit acts as a

MORSE 5V to 15V +Ve

KEY

RJS6R

OV

Fig. 21: Code -practice oscillator with variable tone(300Hz..3kHz) and variable volume.

R210k

CI022uF

100k(TONE/

normal astable, with frequency variable over theapproximate range 300Hz - 3kHz via TONE controlR3. The 'phone volume is variable via R5, and the'phones can have any impedance from a few ohms upto megohms. The circuit draws zero quiescent current,since the normally -open morse key is used to connectthe circuit tc the positive supply rail, which can haveany value in the range 5 volts to 15 volts.

Fig 22 shows now the 555 astable circuit can beused in LED flasher applications. This circuit operates atapproximately 1 Hz, and has a single LED. The Fig 22circuit has a single LED output; the dotted sectionshows how a second may be added, such that one LEDis on while the other is off, and vice versa. Any types ofLED's can be used in this circuit. Series resistors R, or

LEO

Re4/OR(NOMINJ,L)

LED

5V to 15V 'VI

V

C2014F

H110

75

-0

OV

Fig. 22: Single and dual output led flashers give symetrical 1Hz

outputs.


555 TIMER APPLICATIONSR4 determines the ON current of each LED.

Fig 23 shows how the Fig 22 circuit can be modifiedto give automatic dark -activated operation. Here, R4and R5 are wired as a fixed potential divider that sets1/2 V, on the emitter of Ql, LDR and R7 are wired asa light-sensitive potential divider that applies a variablevoltage to the base of 01, and the collector of Q1 istaken to RESET pin 4 of the IC, which is normallybiased to ground via R6.

SV to 15V ve

RlOk0 1.014 R4 .1.

1.2k liatJi V

! . 1 U e .01

25370 ifl PI OIL Vill=I ii

L--555

TIMER.1111.4 5

113

410R

NOMINAL) CI- 10uF

.010LEO

OV

Fig. 23: Automatic (dark -activated) flasher.

In use R7 is adjusted so that the voltage to the baseof Q1 is greater than 1 /2 V, under 'daylight'conditions, so Q1 is cut off, but under 'dark' conditionsQ1 base is biased below 1 /2 Vcc, so it is driven on.thus, under daylight conditions Q1 is cut off, so the555 astable is disabled, with its output driven low, by4.7k0 resistor R6 which is wired between pin 4 andground. Under 'dark' conditions, on the other hand, Q1is biased on, so pin 4 is positively biased, and theastable operates normally and activates the LED.

The LDR used in the above circuit can be anycadmium -sulphide photocell that presents a resistancein the approximate range 4700 to 10k0 under theminimum 'dark' turn -on condition.

The dotted section shows how the 555 astablecircuit can be used as a 12 volt relay pulser, whichturns the relay on and off at a rate of one cycle persecond. The relay can be any type with a coil resistancegreater than 600.

ALARM GENERATORFig 24 shows the connections for making an 800Hzmonotone alarm -call generator. The circuit can be usedwith any supply in the range 5 to 15 volts, and with anyspeaker impedance. Note, however, that Rx must bewired in series with speakers having impedance lessthan 750, and must be chosen to give a total seriesimpedance of at least 750, to keep the peak speakercurrents within the 200mA driving constraints of the555. The available alarm output power of the circuitdepends on the speaker impedance and supply voltage

5V to 15V rVe

SPKR0

C3 100uF

1 8

Ea 8 PIN DIL Wei 555MI 11114TIMER,

75R TOTAL

C2 OluF

Fig. 24: 800Hz Monotone alarm call generator.

01 10k

R2100k

C1

.01uF

OV

let

Ihl

Ve

/

Fig. 24 a, b, c, d: Monotone alarm activated by dark (2), light(b), under -temperature (c), or over -temperature (d).

used, but may be as great as 750mW when a 750speaker is used with a 15 volt supply.

The above circuit can be modified so that it isactivated by darkness (a), by brightness (b), by anunder -temperature (c), or by an over-temperature (d).Pin 4 is disconnected from the + Ve supply, andconnected to the triggering circuit, which is designedaround 01. This works in the same way as alreadydescribed for the automatic (dark -activated) LEDflasher. The LDR used in the light -activated versions ofthis circuit can be any cadmium -sulphide photocellsthat present resistances in the approximate range 4700to 10k0 at the desired turn -on levels. The thermistorsused in the temperature -activated versions of the circuitcan be any negative-termperature-coefficient types thatpresent resistances in the same range at the requiredturn -on temperatures.

ALARMS AND SIRENSThe next 4 diagrams show a variety of useful alarm-callgenerator circuits. The Fig 25 circuit generates an800Hz pulsed tone alarm call. Here, IC1 is wired as an800Hz alarm generator, and IC2 is wired as a 1 Hzastable which gates IC1 on and off via D1 once everysecond, thus causing a pulsed -tone output signal to begenerated.

Fig. 25: Pulsed -tone (800Hz) alarm call generator.


The Fig 26 circuit generates a warble -tone alarmsignal that simulates the sound of a British police siren.Here, IC1 is again wired as an alarm generator and IC2is wired as a 1 Hz astable multivibrator, but in this casethe output of IC2 is used to frequency modulate IC1 viaR5. The action is such that the output frequency of IC1alternates symmetrically between 500Hz and 440Hz,taking one second to complete each alternating cycle.

CO 100u

75RTOTAL

SPAR

5V To I

.1, .,..IliBIIBORla= sis-Td'iimmmit TIMERmil _ei4TIMER NI

IMORS IOY IC2

440 - 500113 ASTABLE

OluFC2

0,FT

52

BIER. ASTABLE

0 OV

Fig. 26: Warble -tone alarm -call generator simulates Britishpolice siren.

CO

The circuit of Fig 27 generates a 'wailing' alarm thatsimulates the sound of an American police siren. Here,IC2 is wired as a low frequency astable that has acycling period of about 6 seconds. The slowly varying'ramp waveform on C, of this chip is fed to pnp emitterfollower Q1., and is then used to frequency modulatealarm generator IC1 via R6. IC1 has a natural centrefrequency of about 800Hz. The circuit action is suchthat the alarm output signal starts at a low frequency,rises for 3 seconds to a high frequency, then falls over 3seconds to a low frequency again, and so on addinfinitum.

Fig 27: 'Wailing' alarm simulates American police siren.

Finally, to complete this quartet of alarm generatorcircuits, the Fig 28 circuit generates a siren alarm signalthat is a simulation of the 'Red Alert' alarm used in theSTAR TREK T.V. programme: This signal starts at a lowfrequency, rises for about 1.15 seconds to a highfrequency, ceases for about 0.35 seconds, then starts

Fig. 28: 'Red alert' siren alarm simulates Star Trek alarm

signal.

rising again from a low frequency, and so on addinfinitum. The circuit action is as follows:

IC2 is wired as a non -symmetrical astablemultivibrator, in which C1 alternately charges via R1and D1, and discharges via R2, thus giving a rapidlyrising and slowly falling 'sawtooth' waveform acrossCl. This waveform is fed to pnp emitter follower Ql,and is thence used to frequency modulate pin 5 of IC1

via R6. Now, the frequency modulation action of pin 5of the IC1 astable circuit is such that a rising voltage onpin 5 causes the astable frequency to fall, and viceversa; consequently the sawtooth modulation signal onpin 5 causes the astable frequency to rise slowly duringthe falling part of the sawtooth and collapse rapidlyduring the rising part of the sawtooth. The rectangularpin 3 output of IC2 is used to gate IC1 off via npncommon emitter amplifier Q2 during the collapsing partof the signal, so only the rising parts of the alarm signalare an fact heard, as in the case of the genuine STARTREK 'Red Alert'.

MISCELLANEOUS APPLICATIONSTo complete the 555 story, this final section shows amiscellany of 555 applications, of varying degrees ofusefulness. Fig 29 shows how a single 555 can be usedas the basis of an event -failure alarm or a missing -pulsedetector, which closes a relay or illuminates an LED if anormally recurrent event fails to take place.

+VA

01

IN4001 NOTE.Rd SELECT RI AND Cl

470R VALUES TO SUITAPPLICATION

CLOCK INPUT

(PULSE ORSWITCH)

o OV

Fig. 29: Event -failure a/arm or missing -pulse detector has relay

or LED output.

The operating theory of the circuit is fairly simple.The 555 is wired as a normal monostable pulsegenerator, except that transistor Q1 is wired acrosstiming capacitor C1 and has its base taken to TRIGGERpin 2 of the IC via R3: The TRIGGER pin is fed with atrain of pulse- or switch -derived clock input signals fromthe monitored event, and the values of R1 and C1 areselected so that the monostable period of the IC is

slightly longer than the repetition period of the clockinput signal.

Thus, each time a clock pulse arrives, a monostabletiming period is initiated via pin 2 of the IC, and C1 isdischarged and the pin 3 output is driven high via

transistor Q1. Before each monostable period canterminate, a new clock pulse arrives, and a newmonostable period is initiated, so the pin 3 outputterminal remains high so long as clock input pulsescontinue to arrive within the prescribed period limits.Should a clock pulse be missed, or the clock periodexceed the pre -determined limits, however, themonostable period will be able to terminate normally,and pin 3 of the IC will go low and drive the relay orLED on. The circuit thus functions effectively as an


555 TIMER APPLICATIONSevent -failure alarm or missing -pulse detector. With thecomponent values shown, the monostable has a naturalperiod of about 30 seconds. This period can be variedvia R1 and C4 to satisfy specific requirements.

Fig 30 shows how a couple of 555s can be used tomake a pulse -width modulation (PWM) circuit. Thiscircuit can be used for transmitting coded messages, orfor applying variable power to a load at maximumefficiency.

Here, IC1 is wired as a 1 kHz astable multivibrator,which is used to feed a continuous train of clock pulses

5V 10 I5V Vo

CP .019F OUT

0-- 730101I

Fig. 30: Pulse -width modulation (PWM) circuit.

CO

479F

MODULATIONINPUT

to the pin 2 TRIGGER terminal of IC2, which is wired asa normal monostable multivibrator or pulse generatorand has a natural monostable period of approximately0.36mS. The external modulation signal is fed to thepin 5 CONTROL VOLTAGE terminal of the monostablevia C4, and determines the instantaneous widths of thegenerated pulses. Thus, the circuit generates a train ofpulse -width modulated (PWM) pulses at a fixedrepitition frequency of 1 kHz.

SCOPE TIMEBASEFig 31 shows how a basic 555 monostablemultivibrator can be modified so that it generates a

OV

L..1rITN DIE VALUES SNOWNP WM - POWS AT 9V

Fig. 31.- Triggered linear -ramp generator can be used as thebasis of an oscilloscope timebase.

linear ramp waveform of fixed duration each time it istriggered: This circuit can form the basis of an excellentoscilloscope time -base generator. The circuit works justlike a normal monostable circuit, except that timingcapacitor C1 is charged via constant -current generatorQ1 during each timing cycle, thus causing a linear rampvoltage to be generated across Cl.

When a capacitor is charged via a constant -currentgenerator, the voltage across the capacitor rises linearlyat a predictable rate that is determined by themagnitudes of the charging current and the capaci-tance. The relationship can be expressed as:

Volts -per -second= I /C, when I is expressed in Ampsand C is expressed in Farads.

In this circuit the charging current can be varied over

the approximate range 904A to 1 mA via R4, thusgiving rates of rise on the .01 µF capacitor of 9V-per-mSto 100V-per-mS. Now, remembering that eachmonostable period of the 555 circuit terminates at thepoint when C1 voltage reaches 2/3 Vcc, and assumingthat a 9V supply is used (giving a 2/3 Vcc value of 6V),it can be seen that the monostable cycles of the Fig 32circuit have periods variable from 6664S to 604S.Periods can be increased beyond these values byincreasing the C1 value, or vice versa. Note when usingthis circuit that its supply rail must be stabilised if stabletiming periods are to be obtained.

If the circuit of Fig 31 is to be used as the basis of anoscilloscope timebase, note that the input driving signalmust first be converted to a good square wave, fromwhich suitable trigger pulses can be derived via C3 andR5. The minimum useful ramp period that can beobtained from the circuit is about 54S, which, whenexpanded to give full deflection on a ten -division 'scopescreen, gives a maximum timebase speed of0.54S -per -division. Flyback beam -suppression signalscan be derived from the pin 3 OUTPUT terminal of theIC.

The 'timebase' circuit gives superb signal synchro-nisation at trigger frequencies up to about 1 50kHz. Ifthe timebase is to be used with input signal frequenciesgreater than this, the input signals should be divideddown via a single- or multi -decade digital divider. Usingthis technique, the timebase can be used to view inputsignals up to many MHz.

Fig 32 shows how a 555 can be connected for useas a simple but effective Schmitt trigger orSine/Square converter. The circuit acts as a goodconverter at input frequencies up to 1 50kHz or more. Itworks by changing its output state each time the pin 2input signal swings from above the 2 /3 Vcc level to

5V to 15V Ve

RI 100k

=

OV

WEI

OV

81PIN DIL555

TIMER4 5

SINEWAVE Cl luFINPUT

R2 100k

R3 10k

SQUAREWAVE

OUTPUT

C2 .01uF

Fig. 32:32: 555 Schmitt trigger circuit acts as excellentsine/ square converter up to about 150kHz.

below the 1/3 Vcc level, or vice versa. Resistor R3 iswired in series with pin 2 of the chip to ensure that theinput signal is not adversely influenced by the transitionaction of the IC.

Fig 33 shows how the basic Schmitt circuit can beadapted to a dark -activated relay driving application bywiring light -dependent potential divider R1-LDR to thepin 2 input terminal of the IC. This circuit has aninherently high degree of input backlash, and is likely tobe of value in only very specialised applications.

A far more useful relay -driving switching circuit isshown in Fig 35. This circuit has negligible inputbacklash, and can be used as either a light- or


12V +Ve

Fig. 33: Dark -activated relay switch has built-in backlash.

temperature -activated switch. In light -activated appli-cations R1 is wired in series with a cadmium -sulphidephotocell that presents a resistance in the approximaterange 4700 to 10k0 at the required turn -on level.Dark -activated operation can be obtained by using theconnections shown in Fig 34a or light -activatedoperation can be obtained by using the connectionsshown in Fig 34b.

Fig. 34: Minimum -backlash relay swi ch can be activated bydark (a), light (b), under -temperature (c), or over -temperature(d).

For temperature -activated operation, R1 must bewired in series with a negative -temperature -coefficientthermistor. This thermistor must present a resistance inthe range 4700 to 10k() at the required turn -on level.Under -temperature operation can be obtained by usingthe connections shown in Fig 34c, or over -temperatureoperation can be obtained by using the connectionsshown in Fig 34d.

I kHz ANALOGUE FREQUENCY METERThis circuit needs a square -wave input drivirg signalwith a peak -to -peak amplitude of 2 volts or greater. Inthis circuit the 555 is wired as a standard monostablemultivibrator or pulse generator, and is powered from aregulated 6V supply. Transistor Q1 is used to amplifythe square wave input signals to a level suitable fortriggering the monostable stage, and the output of themonostable is fed to 1 mA fsd meter M1 via multiplierresistor R5 and offset -cancelling diode Dl. This metergives a reading that is directly proportional to thefrequency of the square wave input signals, and itsoperating theory is as follows:

Each time the monostable multivibrator is triggeredit generates a pulse of fixed duration and fixedamplitude. If we assume that each generated pulse hasa peak amplitude of 10V and a period of 1 mS, and thatthe pulse generator is triggered at an input frequency of500Hz, it can be seen that the pulse is high (at 10V) for500mS in each 1000mS (one second) total period, andthat the MEAN value of output voltage measured overthis total period is 250mS/1000mS x 10V = 5V, or


50% of 10V. Similarly, if the input frequency is 250Hzthe pulse is high for 250mS in each 1000mS totalperiod, so the mean output voltage equals250mS/1000mS x 10V= 2.5V, or 25% of 10V.Thus, the mean value of output voltage of the pulsegenerator, measured over a reasonable total humber ofpulses, is directly proportional to the repititionfrequency of the generator.

Normal moving coil meters are 'mean' readinginstruments, and in the Fig 35 circuit a 1 mA f.s.d.moving coil meter is wired in series with voltagemultiplier resistor R5, which sets the meter sensitivityat about 3.4V fsd, and is connected so that it reads the

Fig. 35: Simple 1 kHz linear -scale analogue frequency meter.

mean output voltage of the pulse generator. This meterthus gives a reading that is directly proportional tofrequency, and the circuit thus acts as a linear -scaleanalogue frequency meter. With the component valuesshown the circuit is intended to read fsd at 1 kHz. To setup the circuit initially, simply feed a 1 kHz square wavesignal to its input, and then adjust R2 (which controlsthe pulse lengths) to give full-scale reading on themeter; all adjustments are then complete.

The full-scale frequency of the above circuit can bevaried from about 100Hz to about 100kHz by suitablechoice of C1 value. The circuit can be used to readfrequencies up to tens of MHz by feeding the inputsignals to the monostable circuit via a single- ormulti -decade digital divider, thereby reducing the inputfrequencies to values that can be read by themonostable circuit. The circuit can form the basis of anexcellent and inexpensive multi -range linear -scaleanalogue frequency meter.

"Do you think we should bring in thegenerating boys before we hit the marketwith these." 45

ETI uau SHEETMC 1312/15/14P CBS SQ LOGIC SYSTEM MOTOROLA

A complete SQ decoder system in threechips. The MC1312P is the decoder andconsists of two high input impedance pre-amplifiers which are fed with left total, LT,and right total, RT, signals. The preamp-lifiers each feed two all -phase networkswhich generate two LT signals in quadratureand two RT signals in quadrature. The foursignals are matrixed to yeild left front, leftback, right front and right back signals (LF',LB', RF', RB').

The MC 1314P is a voltage controlledattenuator, a gain control and balanceadjustment unit for e:.,e with any quadra-phonic system. It has four channels whosegain can be varied by an external dc voltage.In addition, the relative gain betweenchannels can be set by three external dcvoltages. Thus with four variable resistorsthe master volume LF/RF, LB/RB and F/Bbalance may be controlled.

Power Supply Requirements:Nominal Signal Level.Maximum Input Voltage:Input Impedance,Output trnpedance.Total Harmonic Distortion.

at 1 HzVoltage Gain (at quiescent):4 Channel Volume Control:4 Channel Balance Control:

60 mA at 20 V0.5 V1.9 V2 MO2 kO0.2% at nominal input1.0% at maximum input1.0Range 70 dBTracking - within 3 dB-35 dB at -20 dB gain

ELECTRICAL CHARACTERISTICS

Characteristic TypSupply Current Drain 16 mAInput Impedance 3.0 MDOutput Impedance 5.0 kitChannel Balance ILFIRFI 0 dB

Voltage Gain LF/LT or RF/RT 0 dB

Relative Voltage Gain Lg'/LF'.LE' measurements made with LT input, RE' measurements made withRT input.

-3.0 dB

Maximum Input Voltage for 1%THD at Output RT or LT 2.0 VIRMS)Total Harmonic Distortion AT or LT 0.1 %

Signal to Noise Ratio 'Short:Circuit Input Vo - 0.5 VIRMSIwith Output Noise Referenced to OutputVoltage, V01 IBW - 20 He to 20 kHz)

A/

80 dB

Characteristic TypMaximum Gain I V8 6 V) 1.0 dBMinimum Gain I VE, - 0 V) 0.5 dB dBGain Spread@ Gain , Mac 1.0 dBTotal Harmonic Distortion (Vie = 0.4 Vrms, max gain) 0.2 %Signal 'Noise Ratio 120 Hz 15 kHz Bandwidth) Note 1.

VIN - 0.4 Vrms (ref)80 dB

Channel Separation 60 d6Balance Control Range V8 - 6.0 V I= Mac Gainl 20 dBGain Reduction (V4' - V 12' = 3.12 Vdc compared to

Va' = V12' :- 0.60 Vdc. VCC ' 25 Vdc)14 dB

Supply Current )max gain) I VIN = 0 V)1mm gain) WIN - 0 V)

19 mA9.0 mA

Input Impedance 13 kStOutput Impedance 2.0 kitControl Current 14 or 112 -20.e AInterrnodulation Distortion 111 = 7 kHz, 12 e 60 Hz) 0.6 %

CharaCtOf KIM TyeStipp's, Current (Pin 1210 VIN 0

P VIN s 1 4 Vrms7 0 mA15 mA

Input Resistance P Pin 1. 15. 16 20 !azOutput Resistance @ Pin 3. 5 1.5 IsSt

Paraphase Fiber Resistance @ Pin 9, 10 4.0 k II8 ront-Elack Logic Discharge Resistance ife Pm 7.8 5.0 kitBias Voltage 110 k to ground) @ Pin 13 1.4 VdcLogic Contrni Input Current @ Pin 2

I V2- VI 3 0, V2- 0)sO 5 mA

Relative Output ChangeFront Output With LB or RB input, Of back output with LB or RF inputs 2.8 viv

L PhaseShift

NetworkLF' Output

Lg' Output

L PhaseShift

Network

LT Input

Gnd

LF/RFBalance

RF Output

RF' Input

ControlFront GF

LF' Input

LF Output

F/B Balance

Volume

RF' Input

LogicControl

ControlFront GF

TF2

ControlBack GB

TB1

TB1

TF1

The logic circuitry for the system is inthe MC1315P which provides the basic logicfunction to enhance the front to backseparation in the CBS SQ four channeldecoding system. This device is designed tointerface with the MC1312 decoder and MC1314. The MC1315 provides dc logicenhancement control signals which extendthe performance of the basic SQ system tothe levels desired for top -of -the -line systems.

MC1312P

MC1314P

MC1315P

Rg' OutputR Phase

ShiftNetwork

VCC

RF' Output

R PhaseShift

Network

RT Input

VCC

Lg/RgBalance

Rg Output

R g' Output

ControlBack GB

Lg' Input

Lg Output

Gnd

Rg' Input

LF' Input

Gnd

Bias

VCC

AGC

Filter Back

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MC 14543CL/P LCD DISPLAY DRIVER MOTOROLA

The MC1453 BCD -to -seven segmentlatch/decoder/driver is designed for use withliquid crystal readouts, and is constructedwith complementary MOS (CMOS) enhance-ment mode devices. The circuit provides thefunctions of a 4 -bit storage latch and an8421 BCD -to -seven decoder and driver.

In order to drive LCD displays, whichrequire a non -polarised drive, the MC 14543has a 'phase' input. With a square waveapplied to this pin, the output phasereverses in step, thus satisfying the require-ment. To drive common anode LEDdisplays, Ph input should be held high, andlow for common cathode LEDs. Other

display types can be driven, but witntransistor interface.

This device contains circuitry to protectthe inputs against damage due to high staticvoltages or electric fields; however, it isadvised that normal precautions be taken toavoid application of any voltage higher thanmaximum rated voltages to this high imped-ance circuit.For proper operation itrecommended that Vin and Vout be con-strained to the range VSS --<..(Vin or Vout<VDD..

Unused inputs must always be tied to anappropriate logic voltage level (e.g., eitherVSS or VDD).

LOGIC DIAGRAM

> > 13 0-->0

2 0--[>0

_ 4

AI 7 OH>0---

LD 1 0->D-4,---->0-/

-Do

Phase 6 0---[>0-*

9a

10

11 r

12

13 e

-0 15

14 t,

ELECTRICAL CHARACTERISTICS

Characteristic

VDD

Vdc

MC14543CL/CP

Unit.25°C

Min Typ Ma.

lutput Voltage '0- Level 50 0 001 Vdc10 0 00115 0

"1- Level 5 0 4 99 5 010 999 10

15 15

Noise Immunity (V.,,, .,... 3 5 Vac/ 50 15 225 VileIV°, ...- 70 Vdcl 10 30 450tVou, -?- 10.5 Vdcl 15 6 75IVou, 5., 1 5 Vdcl 50 15 225 VdcIVo,.j1 -<... 3 0 Vdcl 10 30 450(Vout 4.5 Vdcl 15 6 75

Output Drive CurrentIVOH 2.5 Vdcr Source 50 -020 -1 9 mAdcIVOH = 9.5 Vdcl 10 -020 -1 01V0s4 = 0.5 Vdcl 10 97IVOH = 135 kirk/ 15 39(VOL 04 Vdcl Sink 50 020 0 78 mAdc

(VOL -0.5 Vdc) 10 050 20

1V0L 95 Vdcl 10 114

'VOL -1 5 Vdcl 15 78

Input Current 10 pAric

Input Capacitance 50 17,

Quiescent Dissiprition '1I0L 15 pF. I 0 MHz)PD - (4 8 mW MHz( f 0 000025 mW 5 0 0 000025 0 25PD - 119 rnW;MHz1 f 4. 0 00010 mW 10 0 00010 1 0

PD 143 mW MHz) f 0 00023 mW 15 0.00023

Minimum Latch Disable its

Pulse Width IStiohinq Date)50 125 3751(1 50 1501,-, 40

MC 14543Output

Ph

FLUORESCENT READOUT

vss

F ilamentSupply

VSS or appropriatevoltage below VSS'

INPUTS OUTPUTS

LD BI Ph DC13 Ari b c id e I g Dispiay

x I 1 0 X X X X 0 0 0 0 0 0 0 Blank1 1 0 0 0 0 0 0 1 1 1 1 1 1 0 0

1 0 0 0 0 0 1 0 1 1 0 0 0 0 1

1 I 0 0 0 0 1 0 1 1 0 1 1 0 1 2

1 0 0 0 0 1 1 1 1 1 1 0 0 1 3

1 0 0 0 1 0 0 0 1 1 0 0 1 1 4

1 0 0 0 1 0 1 1 0 1 1 0 1 1 51 0 0 0 1 1 0 1 0 1 1 1 1 1 6

1 0 0 0 1 1 1 1 1 1 0 0 0 0 7

1

1

0 0 1 0 0 0 1 1 1 1 1 1 1 81 0 0 1 0 0 1 1 1 1 1 0 1 1 91 0 0 10100000000 Blank1 0 0 10110000000 Blank1 0 0 11000000000 Blank1 0 0 11010000000 Biank1 0 0 11100000000 Blank1 0 0 11110000000 (bank0 0 0 XXXX '''

1 1 1 t Inverse of OutputCombinations

Displayas above

Above


Yamaha B-1 amplifier withUC-1 control unit.

VERTICAL RT POWER AMPLIFIERPRODUCES OVER 200W

PER CHANNEL - AND IT'SCLEANER SOUNDING THAN

VALVES

CONVENTIONAL POWER OUTPUTtransistors produce a fairly high level ofdistortion as a result of the non -linearityof their transfer characteristics. In facttransistor manufacturers have beensearching for many years for a solidstate device which would havecharacteristics more nearly equivalent tothe hitherto ubiquitous tube.

Professor J. Nishizawa's developmentof the field effect transistor providedthe break -through that had long beensought. The characteristics of theseF ET s, when compared with the con-ventional bipolar transistor, are firstlythe elimination of carrier storageeffects, reducing switching or notchdistortion when used in Class AB or Bpower stages, and extremely rapid riseand decay times. High order harmonicdistortion is dramatically reducedbecause of the squareness of the transfercharacteristics and the power driverequirements are extremely low.

Unlike bipolar transistors, when the'temperature rises the quiescent currentdecreases and so the big drawback ofbipolar transistors, thermal runaway, isvery conveniently avoided. When placedin a power output stage of a power amp-

lifier this provides the opportunity todevelop extremely low open loopdistortion and, in theory, almost theultimate in power amplificationcharacteristics.

The B-1 Power Amplifier is a

braggart's delight! It's bigger, heavier,more powerful (within limits) and hasbetter performance than any otherpower amplifier in its class that we haveever tested. It also has many mostvaluable features that are not commonlyencountered.

The B-1 unit is a big ventilated blackbox on which are mounted a powerON/OFF switch, two speaker levelcontrols and three LED s indicating theoperation of the overload protection,the state of the thermal overload pro-tection and power ON/OFF.

These controls are set in an anodisedaluminium panel which is readilyremoveable to enable it to be inter-changed with a Basic Amp ControllerUC-1 which includes two large peaklevel meters with the unusually widedynamic range of -50 dB to +5 dB.These are also calibrated in terms ofwatts into an 8 ohm load; i.e., a range ofup to 0.01 W to 300 W. This unit allowsthe connection of any one or more ofup to five pairs of stereo speakers eachwith its own pair of individual pre-setlevel controls, the load terminals forwhich already exist on the rear panel ofthe main amplifier.

PROTECTION RACKET

Main amplifier features include com-pletely separate power supplies for leftand right channels and a third powersupply for the relay control functions.These are activated via a relay from thefront panel power switch such thatwhen the power is switched on thespeaker protection muting circuitoperates to disconnect the speaker loadsuntil the amplifier voltage conditionshave stabilised.

There are two separate protectioncircuits whose operation is indicated onthe front panel. These are, firstly,thermal protection - designed to cutoff the power supply if there is anydanger in any circuit elements rising to atemperature exceeding 100°C: simul-taneously, the speaker protection circuitwill be activated cutting off the sound.This circuit is self re -setting when theinternal temperature returns to a safelevel. A second protection circuitoperates on overloads resulting fromthree distinct conditions. Firstly, thespeakers are disconnected if a DC levelexceeding ±2 volts is detected at the outoutput terminals. Secondly, the mutingcircuit already mentioned is activatedimmediately following power turn -on toeliminate loudspeaker thumps andthirdly, the power supply is discon-nected whenever an abnormal voltage orcurrent is detected in the output


YAMAHA 111

VERTICAL FET POWER AMPLIFIERcircuitry. This provides amongst otherthings protection against short circuitson the output or loads of less than 4ohm impedance. This feature maypreclude the amplifier being used withsome 4 ohm speakers - the impedanceof which falls to well below 4 ohms atsome frequencies.

A rumble filter with a 12 dB peroctave filter (below 10 Hz) protects theloudspeakers from low frequencytransients. The control switch for thisfilter is at the back of the unit.

MEASURED PERFORMANCEOur past experience with Yamaha

products has been that the manu-facturer's specification is generallybettered. The Yamaha B-1 was noexception. It has a frequency responsewhich was +0 -0.4 dB from 10 Hz to122 kHz, a straight line on a levelrecorder. The manufacturer's powerratings were easily exceeded, both with8 ohm and 4 ohm loads, being 210watts into an 8 ohm and 220 watts into4 ohm with both channels driven. Thepower bandwidth was 5 Hz to 50 kHz -precisely as stated by the manufacturer.

Distortion is very low indeed - overmost of the frequency and poweroutput range the unit introduced no

MEASURED PERFORMANCE OF YAMAHA 8-1 POWERAMPLIFIER - SERIAL NO. 2869

Frequency Response:

Power at Clipping Point:(Both channels driven)

Power Bandwidth:

-0.4 dB at 10 Hz and 122 kHz-3.0 dB at 2.3 Hz and 122 kHz'

210 watts (8 fl 1 kHz)222 watts (4 E2 1 kHz)

E Hz: 144W 8S2 0.13% THD50 kHz: 105 W 8 S2 0.3% THD

Total Harmonic Distortion:(Both channels driven) 100 W 8 St

Noise:

Hum

Sensitivity:

Input Impedance:Output Impedance:

I W 8 .S-2

100 Hz 0.03%1 kHz <<0.01%6.3 kHz 0.07%

100 Hz1 kHz6.3 kHz

<0.03%<0.03%

0.04%

- 99 dB re max. power i.e. 0.46 mV-106 dB (A) " "-126 dB "

60 mV input gives 1 watt (852)

92 k52 at 1 kHz0.08 S2 at 1 kHz

*Max measurable frequency with test gear used.

YAMAHA VERTICAL FET CONSTRUCTION

As the vertical FET illustration below shows, thesource, gate and drain are aligned vertically, permit-ting much higher power capacity. Each element ofthe mesh is, in effect, equivalent to an independentFET; a single Yamaha vertical FET contains tens ofthousands of such elements.The mesh itself measures 5-10p across. To assurehighest possible drain -source and drain -gate break-down voltage, impurity concentration is reduced to alevel far below any previous semiconductors, througha special epitaxial layer formation method.

Conventional FET Construction

Source Gate DrainN Stratum

NStratum--) N Stratum

P Base

Arrow shows current flow direction

Yamaha Vertical FET Mesh Configuration


increase in distortion beyond theinherent distortion of our measuringsystem.

Yamaha conservatively state that atone watt output, the distortion at 1 kHzis 0.03%-and 0.04% at 20 kHz. Ourfindings indicated that under thoseconditions the distortion was respective-ly less than 0.02% and less than 0.03%respectively. At 100 W output thedistortion was very much less than0.01% (being typically less than0.005%) and at 6.3 kHz it was a precise0.07%.

Until recently it was generallybelieved that ultra -low distortion levelswere irrelevant.

Nevertheless there is increasingevidence that basic design improvementssuch as those incorporated in theYamaha B-1 amplifier result in audibleimprovements - even though theseimprovements are not necessarilymeasurable by standard steady-state testmethods.

Noise was found to be -99 dB withrespect to maximum output or, if youprefer it, less than half a millivolt at theoutput terminals. Hum was an extra-ordinarily low -126 dB with respect tomaximum power output.

SUMMARYAs hard as we tried we could in no

way fault the performance of this unit,except lamely to say that when wepicked it up we found it too heavy!

Currently research shows that amp-lifiers offering higher linearity withlower levels of inverse feedback offervery good transient performance.

We think, but cannot prove, that thesubjective performance of this unit isbetter than other amplifiers using con-ventional bipolar transistors but musthonestly say that we have not positivelyproven it so, on the basis of instru-mental measurements.

Let's just say that we believe the B1is the cleanest performing amp we haveever heard.

Qr./4 & Pa", 50 08 0,10,www

LOWFREQUENCYRESPONSEOF THETHE

YAMAHA 0-1POWER

AMPLIFIER14

"NORMAL"MODE

SHOWINGEFFECT OFRUMBLEFILTER.

30/7/76DFC

J81

Hz W. Sneed rnm/sec P.P.' Speed mm/ rW 11 1 11 IF V

:0 Hz 50

OP 1124 5+",1,014 Prepuec, Scala b, I/ 10th.

2'0 501' 1000 20010 5000 10000 20000 40000 0 A 8 C L.

200 Lowe! 11612/21121 A 8 C Lon

IAI

L

We are looking for someone to work on the editorial ofETI-Canada in Toronto.

As it's far easier to teach someone the journalistic sidethan the electronics side, it's an electronics person we'relooking for.

Prime qualifications are a genuine interest in electronicswith a bias towards the hobby side. A fair knowledge ofmodern circuitry, components and developments is alsonecessary but we're not looking for a designer and manyenthusiasts have the necessary knowledge.

The work will consist of some writing, some research,some working on other people's originals. The name of thegame is accuracy: presenting information in the mostreadable form and making sure it's correct.

We've no strong views on age but guess the successfulapplicant will be in his/her twenties. Salary is negotiable.Incidentally, this is not just a 'prestige' ad - it's genuineand it certainly isn't just put in to fill an odd space!

Apply in writing, with resume, as soon as possible to:The Publisher,Electronics Today International,Unit 6,25 Overlea Boulevard,Toronto,Ontario,M4H 1B1.

Then well like to have

a word with you.


ETI project

rfi0ON TESTERMeasuring the speed of your reactions can be fascinating. Ourproject not only allows you to do this to a considerable degree ofaccuracy, but allows for competition between two players.

THE MOST NOTICEABLE EFFECTof a night on the town, apart from therevolving universe, is the immediateslowing up of a person's reaction time.The project to be described here willgive an indication of that time,measured to 1/100ths of a second.

There are two possible versions ofthe project; which one you builddepending on the usage or abusage youintend to subject the unit to.The 'standard' version if you like, is

the TTL circuit of Fig.1, which can berun from a battery pack as a

portable unit.

PLAYING THE GAMEThe tester provides an intriguing

party game which will cause many anargument. It is set up as a contest bet-ween two people, with indication ofwho has won - and the winning time.It might be an idea to take some read-ings on the known drinkers at the startof that party - and when their reac-tions have slowed to half, pack 'em offin a taxi!

Playing the game is simple. Thecontestants man the switches on thefront panel, and a 'referee' takes theremote start switch. By pressing thishe lights the 'GO' lamp on the panel,and starts the timer. Whichever of theplayers pushes his button first, lightshis own 'WIN' lamp, and stops thecount at his/her reaction time.

CONSTRUCTIONBuilding up the 'standard' version is

best done by constructing the displayand counter sections first. Check theformer by applying a high level to pins7, 1, 2, 6, in turn of ICs 3 and 4.The numbers 1, 2, 4 and 8 willappear on the display if all is well.

Remove the 'decimal point' pin onthe displays, this will vary from type totype, ours were DL707s. This aidslocation on the P.C.B. The lead fromthe hand-held unit to the main unitmust be screened - four -core individualscreen recording lead is ideal - other-wise stray capacitance can 'clock' the7490 without the switch being operat-

ETI

REACTIONTESTER

2

WIN

1

OWIN GO

STOP RESET STOP

ed. Ground one end to pin 2 of thesocket on the unit, and the switch endto the output (ground) side.

We used a plastic box for theremote button. If you are going to usea line supply, check the output of thisbefore applying Vcc to the circuitry.Too high (>7V) will send the logic tojoin its ancestors on that great bread-board in the sky.

Possible modifications and add-itions to the basic unit are legion. Weoriginally used a 7400 as the oscilla-tor, but settled on the discretecircuit for simplicity. No doubt thelogic hounds will return it, but watchout for resistance values, no higherthan 20k with TTL. The frequency is alittle low for TTL to be entirely athome in any case.

A 'self -test' facility could be added,using an 'almost random' start circuitemploying say, a 7413 device. Wirethree of the inputs to the gate high,bya potential divider, and the fourthgoes to the mid -point of a series R -Ccombination across the supply. Makethe R variable, then if the C is largeenough, an appreciable time will elapseuntil the voltage at the fourth inputrises enough to turn on the gate. Whenit does the Schmitt will turn hard on,and provide a suitable pulse to gate theoutput of the oscillator into the count-er. Leave the pot uncalibrated, andthere really is no way of knowing


DISPLAY1

3 9III

fgabcde

15 1413 12 1110 916

IC3 7447-8 6 2 1 7

DISPLAY

III3 9 14

1fgabcde

15 141312 11 10 916 7447 IC48 6 2 7

PresstoReset

R153k3

R16 R1768k 68k

C2 0.1uF

R18 j LED33k3

C2 I 0.1uF

Fig. 1: Circuit Diagram of the Tester.

Q1 to Q4 can be any general purposesilicon NPN types such as 2N2222

S1a

S2a\LED1

7,4

Fig. 2: PCB foil pattern - full size.

R13 270

R21 39k R22 39k

D1

S5On off

R2C270

-r6V

T

MM. Novi it works-

If we begin with the display driver/counter section, we see that the counting isdone by two cascaded 7490 devices. Theseare working as +10 BCD counters, and theoutputs feed two 7447 BCD decoders/display drivers. The input pulses, 4.2V p -psquare waves, are generated by Q1 and Q2in a multivibrator mode at a frequency ofapproximately 100Hz. Greater accuracycan be obtained by making one of the charg-ing resistors (R16 or R17) variable, andtuning the oscillator to exactly 100Hz. Inthis way the tester will read exact reactiontimes, ± .01 secs.

When the 'Go' button is pressed, greenLED3 in the front panel lights, and pulses arefed into the counter chain. When either con-testant's switch (Sla, S2a) is pushed, thelink between oscillator and counter isbroken and the counter will 'hold' thenumber of pulses that have entered i.e. timein 100ths of a second.

At the same time Slb and/or S2b oper-ate the Vindicator' circuit comprising Q3and Q4. Either one of the LEDs can lock onturing off the other transistor, and so ensur-ing only one light can be on at any giventime - that corresponding to the first buttonpushed. Diode D1 serves both as a voltagedropper to bring Vcc down to a logic supplylevel (5.4V) and also to prevent damage dueto supply reversal.

a

re


REACTION TESTER

Parts ListResistorsR1-14, 23 33ORR15, 18 3K3R16, 17 68KR19, 20 27ORR21, 22 39KAll V4W 5%CapacitorsC1, 2 0.1mF minifoil etc.

Transistors01,2,3,4 2N2222 or similar

DiodesD1 IN 4001 or equivalentLED 1, 2 RED 0.2"LED 3 GREEN 0.2"Integrated CircuitsIC1, 2 7490IC 3, 4 7447

SwitchesSW1, 2 Double Pole Changeover-

Push On, Push Off.SW3 Single Pole, Single Throw-

Push to Break, non locking.SW4 Double Pole Changeover-

non locking.SW5 Single Pole, Single Throw-

rocker type.PCB ETI 570 - $5.85 post paid fromCANMOS, PO Box 1690, Petert °rough

MiscI.C. socketsBattery holder to suit(Use 4 x Type C Alkaline version)Boxes to suit5 pin chassis skt5 pin in -line plug1m 4 core individual screened leadBoard spacers etc.

LED1 and 2 anodeLED1 cathodeL E D2 cathodeVcc from switch

SW1b contactSW2b contact

SW1b POLEOV I SW2b POLE

PINS 5 and 2 of SKT Fig. 3. Component overlay.

SW1a

PIN 3of SKT

exactly when the circuit will fire theLED Anyway we offer the idea forexperiment - no guarantees!

By speeding up the clock oscillatorto 1kHz, and adding a third 7490/7447 stage, timings can be taken in1/1000ths of a second, or up to 9.99seconds, depending on which end youadd it! If anyone takes 9 seconds tofind the button - call the undertaker.

Many more ideas will undoubtedlyoccur to the constructor - it is a caseof knowing where to stop.


SHORTCIRCUITS

This new series will describe straightfor-ward projects but they are not necessarilysimple in their operation or aimed at thebeginner. We plan to carry between twoand four such projects each month.

PATCH DETECTORTHERE IT STANDS: gleaming. Onthe surface, a secondhand car in reallygood nick but think! Modern mater-ials, especially resin body filler and aquick paint job with the spray guncan make a rusty heap look like a newcar.

Our Patch Detector will quicklyfind areas of the body -work whichhave been filled - or even patchedwith aluminum.

Only a handful of components areused. The key to the operation is thetransistor output transformer; we usedseveral types and they all workedwithout any difficulty.

It is necessary to modify the trans-former. First remove the shroud overthe laminations. Then, using a pair offine -nosed pliers carefully remove thelaminations, These are held togetherby wax: the first lamination may be

-Parts ListQI Transistor 2N2222 etcRI Resistor 47k 1/4WCl Capacitor 0.1/AF disc ceramic etcC2 0.01812FC3 10011F 12V electrolyticTi Armaco AT 49 (Electrosonic)Earphone: 81L type, 3.5mm jack plugEarphone socket, 3.5mmPCB to design shownSmall plastic boxEveready 216 and connector

-How it worksThe circuit is a Hartley oscillator usingan AT49 as the inductor. The primaryof Ti is tuned by CI and feedback isprovided by C2. The secondary of Ticonnects via the socket/switch to theearphone.

Due to the modification of the trans-former, when metal is brought near tothe open end of the E laminations thisalters the inductance of the primary andconsequently the frequency of the noteproduced.

Cl. C2 and RI all affect the noteproduced and as long as R1 is notreduced below 33k, these may bemodified to give the desired frequency.Current drain from the battery will bebetween 5 and 10mA. Fig. 3. PCB foil pattern - full size.

FVF:FROM RATTER

TO EARPHONE SOCKET

T1MODIFIED AT49

SOLDEREDTO PINS ON BOARD(FOR SUPPORT)

Fig. 1. Circuit diagram of the detector.


Fig. 2. Component overlay.

55

Short Circuits

Fig. 4.- The wiring and modifications to theearphone sockettricky to remove but thereafter youwon't have any difficulty. The lamin-ations in the AT49 (and the otherswe tried) are E shaped with a barenclosing the exposed end, they arelayed alternately.

When all the laminations have beenremoved reassemble them all the sameway round to form an E. Fit this backinto the transformer and replace theshroud.

We used a small plastichand - held box and built a smallPCB to hold the components. Thetransformer can't fit directly onto thePCB so two thick wires are solderedto the shroud, these in turn aresoldered to the PCB, this effectivelystands the transformer away from theboard.

A hole is necessary in oneend of the plastic box to take the

Internal view of our Patch Detector. Notehow the transformer fits through a hole cu' inthe short end of the case.

transformer's face; the open ends ofthe E should face out.

The circuit is simple and will onlybe used with an earphone so an on -offswitch will just complicate mattersInstead the switch section of the ear-phone socket is bent so that itswitches on when the earphone isinserted.

An Eveready 216 will fit nicelyacross the end of the box if oneof the plastic buttresses on the pillarand two pips inside the same area arecut away.The circuit is really a simple metal

locator. In free air an audio tone isheard but when run along the body ofa car the note is lower. When filler isencountered the note rises: evenalumin urn causes note change. Thereis no danger of the unit scratching thepaintwork as the only thing to touchthe bodywork is the soft plastic of thetransformer's former.

A change in note can be detectedwhen sheet steel is about 10mm(3/8in) from the laminations. Greatersensitivity is not an advantageincidentally.

HEADS 011 TAILSTHE MULTIVIBRATOR IS ONE OFthe most commonly -used circuitblocks in electronics - especially indigital circuitry. And the multivibratorforms the basis of this 'head or tails'project.

The multivibrator is a basic form ofsquare -wave oscillator which in ourdesign runs at about 700Hz wheneverthe push-button is pressed. When thebutton is released the oscillator willstop and the circuit will assume one ofthe two possible stable states. EitherQ1 will be conducting and Q2 will becut off, or Q2 will be conducting andQ1 will be cut off. Whichever tran-sistor is conducting draws enoughcurrent down through the resistor andthe light -emitting diode (in series withits collector) to cause the LED tolight.

Notice that the circuit is symmet-rical and that the two transistors arecross -coupled between their collectorsand bases (via R3, C1 and R4, C2). Ifcorresponding components on eachside are matched there is equal prob-ability of either transistor being on

LED1

Zi

R1

390 RR247k

b

01

2N2222

R347k

RV147k

R447k

R547k

b

a

k

4

SW1

LED2

Zs.

9VBATTERY

R6390 R

e

Q22N2222

Fig 1 The circuit of our Heads -or -Tails unit

when the button is pressed. However,electronic components do not haveexactly the values they are supposedto have so it is necessary to includepotentiometer RV1 to adjust for

equal probability. Alternatively itmay be useful to maladjust RV1 sothat the effect of bias on the resultscan be assessed.

When either Q1 or Q2 is on, as saidbefore, the associated LED will be on


Parts ListRi

C1,2

S.W.1 On/off switch

Q1,2

P.B.1LED 1,2 Light emitting

Battery PP3Battery clipAluminum box 4 x 2 x 1PCB to design shown.

PotentiometerCapacitorsTransistors

Press to make

ResistorR2-5 ResistorR6 ResistorRV1

390R 1/4w 5%47k 1/4w 5%390R 114w 5%47k trim22nF polyester2N2222

diodes (large type)

ins.

-110W it works

Internal view of the completed unit

LED 1

a0 f-R

R2 1

billrPO46j°16Fg. 2: The PCB layout. Full size 50 x 40mm

This circuit may be considered as a multi -vibrator, when the button is pressed, and asa flip flop when the button is released. Ifinitially we consider the circuit with R2,R5, Cl and C2 deleted we have a standardflip flop. If Q1 is on, it robs current fromthe base of Q2, thus turning it off.Transistor QI will be held on by the currentthrough R6 and R4. However, if Q2 is on,the reverse is the case. Thus only one of thetransistors can be on at any time - neverboth.

The addition of R2, R5 and Cl, C2, will

not alter the above, providing the pushbutton is not pressed. However if the buttonis pressed the current through R2 and R5will try to turn on both transistors.

Take the case where initially Q1 is onand Q2 is off. The voltage on the collectorof QI will be about 0.5 volts and the voltageon Q2 collector, about seven volts. Wetherefore have about 6.4 volts across C2 (asthe base of QI is at about 0.6 volts). Whenthe button is pressed Q2 will turn on and itscollector will drop to 0.5 volts.

However a capacitor cannot instantlychange its voltage and the base of QI will

therefore be forced to -5.9 volts whichturns off the transistor. Capacitor C2 thendischarges via R2 and R4 until the base volt-age is again at +0.6 volts when Q1 will turnon again. This however forces the base ofQ2 to -5.9 volts (due to Cl,thus turningQ2 off. This process continues back andforth until the push button is released. Thecircuit then stops in the state it was at theinstant of releasing the button.

To add bias to the circuit RV1 can beadjusted to change the discharge time of Clor C2 by up to 50%. In this case the twotransistors will not be on for equal timesand the results will be biased towards oneside.

LEDs are included in the collectorcircuits of each transistor to indicate whichtransistor is on. If, for display purposes,a slower -running unit is required the valuesof Cl and C2 may be increased. If both are10 microfarad electrolytic capacitors therate will be about 1.5 seconds. Make sure ifelectroytics are used that the positiveterminal is connected to the collectorof the transistor.

ToPB1 ---. {-1114-10

11\0 C2 C1

-CDFr75a

aOc6e- R6LED 2 CA2

1 1

To BatterySW1 -ve

Fig. 3: The component overlay

and this gives us our 'heads' or 'tails'indication. When the button is pressed,however, the LEDs are switched onand off alternately at a rate of 700Hz.The switching cannot, of course, beseen due to the limited flicker -frequency response of the eye. BothLEDs will therefore appear to beilluminated.

CONSTRUCTION

The unit can be assembled onto asmall printed -circuit board such as thatillustrated .

The main points to watch are thatthe transistors are correctly orientatedand that the LEDs are wired correctly.

The unit should be thoroughlychecked - a transistor or LED can bedestroyed if it is wrongly connected.Double-check the battery connection- a reversed battery can also destroysemiconductors.


Short Circuits

SCR TESTERSCRs ARE INCREASINGLY beingused for power control in mainscircuitry (e.g. sound -to -light convertersand drill speed controllers) and also inbattery circuits (e.g. flash triggers).Testing any semiconductor can be abit of a problem if you have to setup a test board to do the job, so thatthere are now many circuits availablefor transistor testers. Now, here's asimple SCR tester which will give aninstant indication of a faulty device.CONSTRUCTION

As can be seen from the circuitthere are only a handful of compon-ents but we opted to mount most ofthese onto a small tag -board; there arealmost as many components on thefront panel, however.

SCRs come in a variety of encapsul-ations; the small ones are usually inTO5 cans and a socket is fitted to thefront panel to accept these directly.Other types are not suitable for plugg-ing in so the connections to the socketare taken to three sockets into whichextension leads with alligator clips canbe plugged.

-11oW it worksOn switch on, assuming a good SCR, there isapproximately 20V AC across the SCR, butit does not conduct so that with no currentflowing through R2, no volts are droppedacross it, hence neither LED will light. WhenP/B1 is pressed, thyristor gate current willflow, and the thyristor will turn on whenthe anode is positive with respect to thecathode. Thus, for half of each cycle,current will flow through R2, so that LED1will light up.

If both LEDs light up, this means thatthe SCR is conducting both ways, i.e.internally short circuiting. If neither LEDlights up, when PB1 is pressed, the SCR hasfailed open circuit.

-Parts ListT1NEONCl131R1R2R3, 4LED 1LED 2

117V - 25V .3A min. trans240V TYPE0.1.PF 160V1N4001100R ihvNi100R 5W W/W1k2 V4WGREEN TIL 209 TYPERED TIL 209 TYPE

PB 1 Push to test typeSWI OFF/ON mains toggleTO5 Transistor test socket, banana sockets,mains cable, miniature tag board. feet.Aluminum case (6 3/8" x 2 7/8" x 1 7/8")(162 x 73 x 48mm)2 'standoffs' '/zin.Nuts and bolts.

T1117V / 20-25V

300mA

NEON

DEVICE UNDER TEST

D11 N4001

C10.11/F

G

P/Ei 1.1 0

R1

1000 '5W

R210005Ww/W

LED1 LED2(GREEN) (RED)

Fig. 1: Circuit of the SCR Tester.

The completed unit is built into a strong aluminum box.


The majority of the components can be wiredto a small tag board.

12 VDC (ft 3 AMPS REGULATED, CONTINUOUS DUTY CONVERTS CB, HAM RIGS TO HOME

115V to 12VDC converter!Built-in automatic RESETcircuit breaker. Powerful 3amps (8 amps peak) makestt ideal for SSB rigs, toolAttractive walnut like metalmodern -de .ign cbinet (5e4 l.s x21/4 '7. Big U.S.maker design. Built-in cir-cuit breaker. Front panelhas OFF -ON switch andLED light. For 116 VAC80 cycle. Wt. 5 lba.

Oat. Ne. 203452

2495 120ELOTO PRLAMIP I" VAC MOTOR IMADV TO 00 WITNI ALL CORDS

ofLOSILT MOTOROLA

ITS READY TO GO! Platoo,: 115 VAC opera-tion. An exceptional feature: 116 VAC olotcw, to ',VOWFREE" heavy duty wheel; built In power OUggigi balk -in prearnP. panel, black -and -silver trim:nod x 81/2 x4 Ws. beery duty plastic.Depth 11%.. Wt. 3 lba.Cat. No. 203444

TOUCH TONEWANNAANA1

ENCODERKIT*

REPETER NOM..

as OrrICE

30/0:T°'"1.26M, 2 -meter and 6 -meter amateur radio operators.if your rig is mobile convert it easily to mobiletelephone station and enact your home, shop. school.factory TTE-100 tour, tone encoder kit. Kit includes:Chomerica touch tone pad, Motorola MC14410 chip,trimpot, resistors, men r, diagram, and G-10 pc board.Electrical specs: 12-16 volt, 5 mile rmas I, 4 voltsPP output. Lean 1 -MC crystal. Cat. No. 20 3315

Cat. No. Description Sale BUY 'EM253149 Touch Tone Pad 54.502013x2 MC1.1410 Chip 10.30 SEPARATELY25 3393 P.C. Boar,' 2.95

"POCKET."

vat3 for 548.

$16.88 MIRRORED 3- SCALE

20,000 OHMS PER VOLTDesigned to train engineers of the top electronics school:BELL & HOWELL, famous maker of precision photo-graphic equipment! Compact and versatile, with fea-tures found only in costly test equipment. Constructedwith 1% precision resistors and D'A.rsonval metermovement for precision readout accuracy. Low volt -tags range. for solid state testing. Insulated hi -Impactplastic case. Input impedance 20,000 ohms pervolt DC, 10,000 ohms per volt AC. MeasuresDC Volts: 0-25-50-250-500-2500; AC Volts 0-10-E0-100-500-1000; DC current 0-50uA-2.5ma-250ma:Ohms: X1000, X10,000. Measures db from -20 to+22. Pocket site, measures 3" x VA" x 21/2". In-cludes pal, of unbreakable 34" test probes with pinJacks. Thumbwheel ohms adjust. Require. standard AAPenlite battery (not included), Wt. 8 ass. No.203580

MICROPROCESSORSD 8008 $14.95 0 8080 $24.95O 2102-1 $1.95O 1702-A $9.95 MM5262 $1.95

8 FOR $11.953 FOR $25.003 FOR $3.00

Rotron Fans 118 VACI Cempactl Lightweight! Only 4-11/1.1E' en.

x 1 Va' MoldPans by Rotron. Used extensively for hi -e eqpt becauseof low -met, dependable cooling, as well as flushing

omputers, power supplies, office equipment, lightprojectors, transmitters, receivers & more? Weighs only1-1b. LOW NOISE LEVEL! Humidity & moisture resis-tant motor. REVERSIBLE AIR FLOW! Impedance pro-tected. Suitable for -40° to +160° F. Both 116 VAC,9200 rpm, 15 watts, .18 ampa. Hi -impact, flame retard-ant polycarbonate propellers in a reinforced phenolicventuri block. Removed from new eritaptnent. Mont,hack gurrantee. 11/3 lbs. 203108 MuffIrd. 3 -blade

la10111011

88

20-ZVF ROM T1

ANODETEST SOCKET

QEDLED 2

11()

GREENLED 1

IKI

IAI

GATE TESTSOCKETVIA PB 1

CATHODETEST SOCKET

Test gear tends to be mishandledand a nice strong aluminum case isadvisable in view of the propensity ofsmall test gear to disappear under pilesof components at the back of theworkbench.

In a no-go condition, both LEDswill light under a short-circuit cond-ition so don't be misled by the greenlight being on.

OPERATION1. Insert SCR.2. Switch on. If either or both LEDs

come on, reject the SCR.3. Press button 1. LED1 only should

come on; if anything else happens,reject the SCR.

.13aoho .5" redoutal7 -minute snoossi

Beeper 1021 With

V 010010conar ol I

Blinking aeicat.e0,.,sec a

BKRONOS

ON°. 2L3505 - 4 Digits.5" READOUTS; Kit.ON.a. 21-3507 - 6 Digits.3" READOUTS; Kit.

epin'Time

MACHINES

1995New from Kronos at an alarrotri low price. Compact.it fits in palm of your hand (only 41/2 x 4 xBeautifully designed far any room or oflIce-EASYFUN TO BUILD! Attractive gray plastic case withchrome trimmed transparent red panel. Pushbuttonswitches control: alarm time/real time display, minutesnet, hours set, snooze. Uses famous National h1M5376clock chip and minimum of parte. Complete kit withatep-by-step instructions. Wt. 10 ova. Na. 203505

DIGITAL CLOCK 054 -digit, 0'5" Dig"' MODULEISI

WITH at BUILT-IN Cat. Ne.

20.3411

Clock.. LED, built-in redfilter, with a MM5385 mul-ti -function larm chip,p,

on a 3 x 13/4 xmodule. Has all neces-

sary discrete components:mounted on module by fac-tory, to require only fifunction switches, bright-ness and voltage dividercontrol, 12-16 volt fila-ment transformer, AC linecord and case. Makes eaai-buiot-in alarm and radioAlarm ON/OFF. Instructionand hookup diagrams.Shpg. wt. 7 ors. iii

FAIRCHILD, NATIONALVOLTAGE REGULATOR PANIC

YOUR , S TO -440 or TO, CASESCHOICE ' POSITIVE OR NEGATIVE

1-APAP RATING - -

Cat. 203449 Positive Voltage State voltage and coosCat. 203450 Negative Vnitage .style when ordering.

Tiarms: Add postage Rated) net 30 MIN. ORDER S6Phone: Wakefield, Mass. (617) 245-3829Retail: 16-18 Del Carmine St., Wakefield, Postage)

POLY PAKS CriEappll'sorEid,BOX 942G LYNNFIELD, MASS. USA 01940


12 X $1.25 +$5$12?

wromiEFORYOFFER

PEOPII THE PIPIM11.1111 OFEtECTEORIC1 TODAY INTEEMHOPIAL

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Not

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AUTOMOBILE ENGINE TUNING IS Agrossly misused and misunderstoodoperation. To many it implies someesoteric knowledge or ability - oflistening to an engine and somehowdeducing that the ignition must beadvanced - or the mixture strengthrichened a bit on the front carburettor.

In reality it consists almost entirelyof ensuring that ignition andcarburetion is adjusted to the vehiclemanufacturer's specifications.

No more - no less.But to do this it is virtually essential

to use at least some basic instrumenta-tion; a dwell meter, a tachometer, agood exhaust gas analyser - and pre-ferably an ignition analyser.

Many car enthusiasts have at least atacho/dwell meter - but few haveaccess to an ignition analyser for suchdevices are costly indeed. Neverthelessif a few limitations are acceptedvirtually any standard oscilloscope canbe used as an ignition analyser simplyby making a couple of very simplecapacitive probes - which can be assimple as clothes pegs and a few squareinches of aluminium foil.

An ignition analyser displays wave-forms from the primary or secondaryside of the vehicle's ignition system.Surprisingly perhaps, this waveformprovides information not only aboutthe ignition system in general but alsoabout carburetion, and a number ofmechanical conditions.

The analyser can do this becausethe voltage required to fire a petrol/airmixture in an engine is affected bymany different variables including air/fuel ratio, cylinder compression,ignition timing, ignition polarity, sparkplug gap and condition etc, etc.

THE SECONDARY WAVEFORMThe simple waveform shown at the be-ginning of this article is a typicalsecondary waveform that is derivedfrom the secondary (or high voltage)side of the ignition system. This wave-form is the one most commonly usedsince phenomena occuring in .he

primary side of the system will bereflected through the coil windings andappear in the secondary pattern.Point A: is the instant at which the con-tact points open thus causing themagnetic field to collapse through thecoil's primary winding. A very highvoltage is thus generated in the second-ary winding and this continues to rise -until a spark jumps across the dis-tributor rotor gap and the spark pluggap (point B). The voltage at which thisoccurs is known as the 'ionization" orthe 'firing' voltage and may be any-where between 5 kV and 15 kV depend-ing on the factors outlined above.Points C-D: after a very short, time the

voltage drops substantially but the arcis maintained (point C). The subsequentsection from point C to point D isknown as the spark line and whenviewed on a 'scope the amount bywhich this line slopes away from thehorizontal is directly related to resist-ance in the plug and coil ht leads(ignition suppression). A slope of 30°or so is OK - if it's more than that thenit's worth checking lead resistance withan ohmeter. The total resistancebetween the centre terminal of the coiland the centre electrode of the plugshould not exceed about 20 k assumingthe rotor gap is shorted out of course!Actual resistance is not critical butanything more than 30 k may causeproblems. Resistance over 50 k almostcertainly will.

Point D: the section immediately fol-lowing the end of the spark line(point DI should be a series of diminish-ing oscillations. These should appear asour illustration. If there are no oscil-

FIRINGLINE ----a.

ZERO ALINE

FIRINGSECTION

1E POINTSOPEN

I POINTS1/ CLOSE

INTERMEDIATESECTION

DWELLSECTION

F


'Scope testyour car

lations - or just or or two - then it'sa safe bet that there's a shorted turn inthe coil. It may not have broken downcompletely yet but it's a safe bet itshortly will. (See also below).Point E: is where the contact breakerpoints close. It is essential that there isa gap between the last oscillation ofthe preceding section and point E forotherwise the diminishing coil energywill be fed into the now closed pointsthus preventing the coil re -building itsmagnetic field for the next cycle ofignition.

A great deal may be learnt by study-ing point E carefully, point misalign-ment, point bounce, burnt points etcmay be spotted at this part of thewaveform. The correct waveform atpoint E should be a short downwardline followed by six or so diminishingoscillations.

0KV

CONTACT POINT INDICATIONS

Unusual point opening signal (note hashextreme right of picture) burnt or arcingpoints.

Spike on spark line. Point arcing caused byfaulty capacitor.

OKV

Points bouncing probably caused by weakclosing spring.

0KV

Points misaligned - or dirty.

Point F: magnetic energy will now buildup in the coil until Point F. This is ineffect the same point as our previouspoint A but in the next firing sequence.The section from points E to F isknown as the dwell section and shouldoccupy roughly the proportion of thetotal, waveform as shown in our maindrawing. Dwell is adjusted by varyingthe contact breaker gap and should beset using a dwell meter.

SPECIFIC INDICATIONSFiring waveforms should be observedwith the engine warm and running atabout 1000 rpm - that is about 400rpm higher than normal tickover speed.

Check each section of each firingsequence slowly and carefully. Thevarious figures shown in this articleindicate how specific faults will showup.

FIRING LINEAll firing lines should be of roughlyequal height. If any plug is 10-15% ormore higher than the rest, connect ajumper lead to earth and short out at,the plug terminal. If the firing line nowdecreases the fault lies within thatcylinder - either a faulty plug orunusually weak mixture (probablycaused by a leaking inlet manifoldgasket). If the firing line does notdecrease there is a partial open circuitin the associated plug lead or thatlead is not making firm contact withthe connector within the distributorcap.

If the firing lines are unequal on amulti-carburettored engine check to seeif the lines which are higher correspondto those cylinders fed by one commoncarburettor. If so it is probable that themixture from the carburettors is un-balanced. A further but less commonfault that may be spotted this way isan eccentric distributor cap - the gapbetween rotor and distributor contactsbeing wider on one side than the other.

At some time during the check'snap' the throttle wide open momentar-ily, meanwhile watching the firing lines.They should all rise by about the sameamount. If one or more lines risesubstantially higher than the others thenthere is an open circuit plug lead orresistor, a wide plug gap or badlydeteriorated plug electrode.

One or more lines staying lower thannormal indicates spark plug breakdownor insulation breakdown in the circuitconcerned.

5KV

SNAP THROTTLE INDICATIONS

OKVPIMIIIMMIM111=1111MIIIIIMIUMMINMIWO1uis1vp1ummonwill1111111

All lines should rise but remain even.

15KV

10KV

5KV

0KV 'WI Wort %IR WI

One line breaks up. Insulation break down -probably spark plug fouling. Extreme caseswill show similar signal under normalsteady running.

10KV

5KV

0KV

One line rises above rest. Wide plug gap,partial break in suppression resistor, pluglead etc.

COIL OUTPUT ANDINSULATION TESTWhile the engine is running disconnecta plug lead and observe the firingpattern for that cylinder. The firing lineshould rise to about two to three timesits previous level (to about 20 kV) and

should extend below the base line byabout half the upward distance.

If the firing line is short or inter-mittent - or if the lower section doesnot appear - then there is an insulationbreakdown in the distributor cap, plugleads, rotor or coil.

COIL AND CAPACITORA series of diminishing oscillationsshould be observed at point D in thewaveform. If these do not appear, orare truncated, there is either a shortedor crossed turn in the coil - or thecapacitor is breaking down.

BREAKER POINTSPoint E on the main waveform. Thedrawings accompanying this articleshow various fault indications. Notehowever that faulty point action mayalso show up at the point openingposition (A). Check breaker pointaction with the engine running at allspeeds. Weak or incorrect breaker


SPARKCOIL

Connect the 'scope to the vehicle'signition system like this.

TAIGGFIN/PUT

ok

TO CHASSISOF C A c

A motor vehicle's ignition system produces output voltages varyingfrom 3kV to 20kV or more. These high voltages must be reduced toa workable level before coupling into an oscilloscope.

The simplest way of doing this is via a resistive voltage divider -however a capacitive divider will work equally well (we are dealingwith ac signals) and is simpler to connect.

We can make one of the capacitors by wrapping a piece of Alfoil- about 50mm long - around the required lead and connecting thisfoil to the scope. A more professional approach is to glue a shortlength of split tube to a clothes -peg - as shown in the accompanyingphotograph. This will have a capacitance of about 1pF - not muchbut ample for the massive signals we are sampling.

A second capacitor of about 1000pF should be connected asshown. The capacitive divider thus formed divides the input signalby about 1000:1 thus reducing the input signal to a workable 3 - 20volts. A 1M resistor should be connected across the 1000pFcapacitor to provide a dc load.The technique in use: Place the 1pF capacitor over the main leadfrom the coil to the distributor and connect it to the 'Y' input ofthe scope.

If the scope has a trigger input, this may be used to lock in theignition signal. Just make up a second capacitive pick-up and placethis around number 1 plug lead. Once again use a 1000pF capacitoras a divider but bridge this capacitor with a 10k resistor - not 1M as

previously.

A simple pick -off can be made by glueing short lengths ofsplit metal tube to a clothes peg.

Start the motor and adjust the 'Y' gain and timebase frequencyto give four (or six or eight) complete firing sequences across thescreen. The first complete pattern will be number 1 cylinder and therest will follow in the eng ne firing order.

All waveforms may be superimposed by expanding the trace andtriggering via the X input.

If the scope does not have a trigger input, synchronization isslightly harder to achieve. Number 1 cylinder may be identifiedsimply by shorting out that cylinder momentarily.

When the scope is connected as described above, the ignitionwaveform will appear inverted relative to that seen on a commerc-ially produced ignition analyser - and the waveforms shown in thisarticle. It is surprisingly easy to adapt to an inverted picture, how-ever, if this is found to be a problem, it can be remedied simply bycoupling the signals into the scope via a simple 1:1 transformer.Details will vary from one scope to another but all that is basicallyneeded is two coils of wire taped together. It may be necessary toreduce the 1000pF capacitor/s to 470pF. Just connect the second-ary to give the correct picture.

If possible, arrange to calibrate the scope's vertical axis so thatthe magnitude of the signals may be measured. This is best donesimply by taking average indications from several vehicles and'calibrating' by transferring data from the graphs in this article. Theresult may not be accurate, but only a rough guide is required.

springs will cause the points to bounce- and this is readily seen on the scopepattern.

COILWith very few exceptions - notablyon some Citroens - the high voltageside of a vehicle's ignition system is

designed to have positive earth -regardless of overall vehicle batterypolarity.

The reason for this is that electronsare emitted more readily from a hotsurface than a cold one so as a sparkplug centre electrode always runshundreds of degrees hotter than theside electrode the ignition system is

devised so that a negative potential isapplied to the centre electrode.

If this polarity is reversed, theplug will require an extra 5 kV or moreto fire it - and that voltage may not beavailable from the coil under heavyload - or when running at light throttleat high speed (remember a weakmixture needs a higher voltage to igniteit than a rich one.

If you are checking polarity on aspecialist ignition analyser then thepolarity is correct if the pattern is asshown in the illustrations in this article.If you are checking it with a standardscope (with no inverting device) thenthe pattern should be upside down ifpolarity is correct. (See inset for fullexplanation).

Polarity is corrected simply byreversing the coil terminals. (Incorrectpolarity is usually caused by a mechanicreplacing a coil intended for a negativeearth vehicle with a coil meant for apositive earth vehicle - or vice -versa. Itmay also, but less probably, be causedby an incorrectly manufactured coil, orless likely, by the vehicle's polaritybeing accidentally reversed by thebattery being connected the wrong wayround).

MIXTURE STRENGTHThis section is intended for the luckyman who has access to an exhaust gasanalyser and tachometer as well as ascope.

If cylinder compression pressures areidentical, plugs in good order and evenlygapped, and plug leads and distributorin good order - then any significantdifference in firing line heights willalmost certainly be caused by differingmixture strength from one cylinder toanother.

The voltage required to fire a richmixture is substantially less than for aweak mixture: for instance a 12:1 ratiomay need 3 to 4 kV - whilst a 15:1ratio may need 7 to 9 kV (typically).Thus even quite small differences inmixture strengths will be reflectedquite dramatically in firing line height.

The only accurate way to adjustmixture strength is as follows:

Connect a tachometer to the engineand adjust slow running to 1000 rpm.Without looking at the gas analyseradjust mixture strengths so as toproduce the highest tickover speedwhilst maintaining the firing lines atan even height. If necessary reduce thetickover speed to keep it around 1000

Continued on p.77


4 raisons

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de reparation

de suntonisateurs

SUMSIM111Selle18

Service le meme lourNoire service de huit heures signifie queles syntonisateurs sont repares etretournes le jour meme.

Seules des Dieces originates sontutilisees dans la reparation de synton-isateu rs.

G-arantie d'unMain d'oeuvre et pieces sont garantiespour un an a partir de la date dereparation.

nUP/PSS:1'Nous les re-parcns tous: couleur, noir et

lampe, transistor ou syntonisa-teurs. a capacite variable . . . Toutes lesmarques, tous les modeles.

VHF ou UHF $13.95 Combinaison UV $21.95(Pieces rrajeures et Iivraison en plus...net au detaillant).

PTS ELECTRONIQUE CANADA LTSERVICE DE PRECISION DE SYNTONISATEUR

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Demandez notre Guide ce remplacement et notreCatalogue de pieces. PTS Canada offre egalement unassortiment complet cHnstruments de verificationassemble d'avance ou en pieces detachees.


microtheMICROCOMPUTERSOperating and programming your own digital computer.

THANKS TO TECHNOLOGICALadvance in LSI manufacturing and thelow costs of mass production, the micro-computer is now within the reach ofthe average person. At a cost of onlytwo or three weeks wages, these mac-hines are giving private individuals inAmerica the means to exploit and en-joy a pastime that only two years agowas restricted to the very rich orprivileged (i.e., those working in theindustry).

It all started when minimum systemmicrocomputers appeared on the mar-ket. They were more specifically aimedat companies that needed systems,

By Kevin Barnes

but didn't want the expense and worryof design and development. But manywere sold to individuals who wantedfirst-hand experience of a new techno-logy, or who were dedicated builderswho had worked their way throughradios, oscilliscopes, digital clocks andtelevision sets and now relished the chal-lenge of a digital computer. Realisingthe potential of a new market, severalcompanies developed systems theythought would be suitable, and offeredthem for sale. The response was forthousands of Americans to buy andinstall them in their homes, boatsand cars. Because of thei- high speeds

No, you can't use it for your homework . . . I'm loading in tomorrow'srunners.

(in excess of 100,000 operations persecond) and versatility, owners founduses almost too numerous to mention,and were rewarded with fun and profit.Some used their computers to run trainsets. By having a number of trainmanoeuvers pre-programmed in thecomputer, they were able to directtheir trains to more complex and realis-tic operations. Routines in the programwere used to create hills, slopes, etc:conditions closely approaching those inreal life.

The computer also allowed operat-ion by one pair of hands where severalpairs were needed before. For example,

This is what an evaluation card looks like. This is built up from theMotorola evaluation kit (the MEKI. You can see space on theboard for adding extra memory or developing a system.


MICROCOMPUTERSone man used his computer to controlthe stage lighting for his local dramaclub. With all the lighting set-ups pre-programmed, the transition from oneset-up to another required pressing justone switch where before several switch-es were needed. This allowed morelighting changes with less chance oferror.

There is also a growing group ofamateur radio operators who com-municate to one another via their com-puters. Their machines allow them totranslate directly from morse to writtentext and from the keyboard to a modu-lating signal. They are also using pro-gram routines to look for errors andimprove readability. With their highspeed, these same devices monitor theoperation of the radio shack and keepthe log. Amateurs have also gainedpermission from the FCC to exchangeinformation using the ASCII code(the most common general purposecode used in the computing industry).And there has been at least one reportof a pair of amateurs communicatingvia their computers and ASCII throughthe OSCAR orbiting satellite.

Complex gamesMany people are using their micro-

computers to play games. The computercan be used to play against or as ameans of playing (as one would use amonopoly board or a pair of dice).The variety of games range from simpleones like Two Up or Roulette to morecomplex games like Poker or Checkers.But the most interesting games are thesimulation games, where the programmakes the computer behave as if it wasa completely different machine, suchas a car or an aeroplane. Here theswitches on the front panel of thecomputer become the controls of thecar or spaceship and the operator be-comes the driver or astronaut whoseskill must now be put to the test.

Simulation is not limited to mimi-cry of machines. It has also been usedto reconstruct events. Popular games ofthis type include running horse racesor playing a game of basketball. Thenthere are the popular war games like'Tanks and Artillery'.

The hobbyists are also finding practi-cal uses for their systems. The systemused for playing poker during leisuretime can become an elaborate burglaror fire alarm at night. Or it can be usedto teach children maths. The computercan put a question to the studentand later correct his answer beforegoing to the next question. It can alsokeep a record of what questions couldnot be answered. Valuable feedbackto act upon!

13usinessBusiness and engineering programssuitable for home machines are nowstarting to appear. They vary fromsimple programs to calculate interest toelaborate ones that are almost a

complete accounts system. This allowsthe computer owner a chance to recoversome of the cost of his machine. Theengineering programs are equally variedand range from a simple random numbergenerator to programs capable ofperforming circuit analysis of groupings

of over 100 components.As the numbers of hobbyists have

increased, computer clubs have sprungup to help them. Here individualsget together to share ideas and to swapsoftware (programs) and to comparetheir efforts with those of others.Clubs have also been formed where allthe members own the same brand ofcomputer; this is a characteristic of thecomputer industry where they arecalled 'users groups'.

Three applications for microcomputers . . . these examples are taken from a Motorola ad whichappeared in a US magazine. All these systems use the Motorola 6800 microprocessor.

HONEYWELL

Vehicular traffic management isrecognised as one of the great practicaltransportation problems. Honeywellattacked this problem with theprogrammable, multi -purpose, Type140 controller for both intersectionand freeway ramp applications. Ithas the speed, capacity, and versatilityfor uses from simple, fixed, timecontrol to sophisticated, trafficresponsive, centrally directed operation,yet it's low cost. The centralprocessing unit is Motorola's MC6800 microprocessor.

HYCEL

It's a desk -size, 30 -channel, automated bloodanalyzer for medical laboratories. It performsover 3,000 tests per hour, selectively andsequentially, while continuously trackingpatient identity and sample status. Maximumtest time is ten minutes, from sample pickupto completion. The HYCEL M is big newsin the medical test instrument field, andHYCEL calls it the "ultimate analyzer". Allmachine functions are automatically controlledby the instrument's Motorola's MC6800microprocessor.

CHRYSLER

Chrysler developed the lean burn system to permitengines operating in their cars to meet emissionstandards without catalysts, while giving improvedfuel economy on either leaded or unleaded gas.Servicing this innovative system also called for aninnovative new concept in diagnostic testing Chryslerhas called the MC6800 microprocessor based portablediagnostic tester they designed to meet this challenge"an ideal service tool " for its veratility and economy.

C


These clubs are having an importanteffect on the hobby. Many people whowant to own a computer come fromoutside the computer industry, anddon't know what to ask for whenshopping. They also find the jargonused very perplexing at first. By goingto club meetings they meet peoplewho are able and willing to answertheir questions and advise them onthings they should know. This is im-portant because the initial purchase isalmost always the Central ProcessingUnit (CPU) and its design and limitat-ions dictate the development of thesystem.

A close up of the CPU board with the actual microprocessor (in this case an Intel 8080)indicated by a pen. This board also has the clock on it and the clock crystal may be seen inthe upper right hand corner.

LITERATUREon the chip, the system and programs.

Why are manufacturers putting their marketing effort into distribution of thisliterature?Because before you buy an evaluation board you're going to need lots ofinformation ...

EACH KIT COMES WITH A PILE OFinformation, designed to offer assistancein three main areas:1. Details on how to put the kit to-

gether and how to operate it..2. Technical details on the micro-

processor and the support chipssupplied to make the microcomputer.Such information usually includesdetails on the microprocessor in-struction set, timing diagrams, andloading rules as well as applicationinformation.

3. Programming manuals with detailedexplanations of the software sup-port available. These programmingmanuals go beyond evaluation boardsand deal with commercial timesharing services and developmentalsystems. The cost of such systems isan order of magnitude greater than

the price you pay for your evaluationkit.

To the hobbyist the first two listedabove are the most important, especiallythe technical details and applicationnotes. It is this information you willhave to use to interface to yourcomputer. It is strongly recommendedthat you at least have a look throughthis material before buying an evaluationboard for two reasons:

First, to give a measure of thedifficulty involved in making the systemwork so you can decide whether yourknowledge and experience is up to sucha project.

And second, to learn what theevaluation board involves; this inform-ation can help you decide which systemto choose.

The documentation that came with theevaluation boards we are looking at thismonth. You can see the different amounts ofinformation offered by each manufactJrer.However, much of this information wi'l be oflittle practical use to the amateur.


HI eta Fricrofile

WHAT IS AMICROPROCESSOR?There is no shortage of technical information on microprocessors but most of it is ratherdaunting when you first see it. We asked Dr Tim Hendtlass of the Royal MelbourneInstitute of Technology briefly to explain these devices to our readers, assumingonly a basic knowledge of logic circuitry.

MY AIM IS TO SHOW WHAT Amicroprocessor is and how it relatesto a microcomputer. I make no apologyfor treating the subject in a simple wayand in particular for using analogies tonon -electronic situations. When thegeneral idea of what a microprocessorcan do has been grasped then you canread the manufacturers' literature andsome of it at least make sense.As you get more familiar with a

particular device (and nothing canbeat hands-on experience for this)more and more will fit into place.Those strange letter groupings whichseem so daunting at first are in realitya concise and powerful way ofconveying information amongst theinitiated .The problem,as usual, is howto be initiated.

One more thing before I get down toit: microprocessor is a long word and itjust calls out to be abbreviated. Themost common short form is MPU andI will use this often in the rest of thearticle. An MPU is a super logic chip thatcan be any one of a number of ordinarylogic chips at any given time; this is

not the same thing as having separatechips. It's rather like some children's

tool sets which consist of one handleand several attachments, each of whichfits into the handle to give a particulartool: a hammer, a saw, etc. You can,in principle at least, do any job with thiscombination tool set that you could dowith separate tools - but it will takelonger because every time you want touse a different tool you have to takethe oldone on. The MPU is an electroniccombination set.

Impersonating digital circuitsThe number of digital electronic

tools you can make out of an MPUis fixed at the time of manufacture,but it will almost certainly include theability to be an AND gate, an OR gate,a NOT or inverting gate, an ADDER,or a SHIFT REGISTER. (In order tobe useful an MPU must be able toperform other types of operation,but we will meet these later when theneed for them has become apparent.)The type of digital circuit an MPU will

impersonate at any time is determinedby a set of voltages applied to certain ofthe pins on the IC. This set of voltages(each of which can have either of two

WALK LIGHT ON?

AND

CROSSING CLEAR?

N

CLEAR FOR 200 YARDS TOLEFT?

CLEAR FOR 200 YARDS TORIGHT?

4'OR --00- WALK

levels and is one bit of information)is referred to as the instruction. Atypical MPU might have eight voltages(eight bits) to its instruction word,or byte, which gives 256 possibleinstructions (not all of which areused). Fifty to eighty instructionswould make up a normal instructionset. Before I leave the tool kit analogueI must caution you not to takefar. In particular, combination tool setsare often of inferior quality to the toolsthey replace; but an MPU is every bitas good as the individual logic ICsit replaces (except for speed).

One difference between usingindividual logic ICs and using an MPU isthat the former are supplied in hardwareform,often in parallel, and severaloperations can be happening at the sametime. Consequently the solution isobtained very quickly - the only limitis gate propagation delay. The MPU cando only one thing at a time so the logicmust be performed sequentially andthis requires some extra steps comparedto hardwired logic. Both Figure 1 andFigure 2 show ways of arriving at adecision about whether it is safe to crossthe road at traffic lights.

WALK LIGHT ON?

AND

CROSSING CLEAR?

CLEAR FOR 200 YARDS TOLEFT?

CLEAR FOR 200 YARDS TORIGHT?

SAVE

VOR WALK

Fig. 1

68

Fig. 2


microfileMPU or hardwired logicFigure one uses parallel logic and weconsider 'is the walk light on?' AND'is the crossing physically free ofobstructions?' The resulting bit of infor-mation is ORed with the result of theless legal 'is the road clear for 200yards to the left?' AND 'is the roadclear for 200 yards to the right?' Noteboth AND functions are performedat once.

In Figure 2 we see that the MPUcan't dO two functions at once; we haveto save or store the result of the firstoperation while we perform the second.This bit of information is recalled afterthe second AND operation has beencompleted and then the OR operationcan be carried out as in Figure 1.

This storing and recalling , or generallymoving around bits of informationinternally is a very important type ofoperation to a microprocessor.

The storage room inside the chip isvery limited and often it is necessary foran MPU to store information outsideand bring it back later.

The IF instructionWhen we looked at Figure 2 you mighthave noticed a redundancy in the logic.If the answer to the first ANDing is yesthen there is no need to perform thesecond AND function at all, as the

decided. However we must still have theability to perform the second AND , incase the answer to the first one is no.After the first AND we need to makea decision (based on the result) as towhat to do next.

This is a jump on condition instruct-ion - IF the answer is yes, go to theoutput; but IF the answer is no go tothe second AND. This is shown diagram-matically in Figure 3; note there are twoexits from the decision box, oneshowing the path taken if the answer isyes, the other showing the path if theanswer is no. Also note we have told themicroprocessor what to do if the answerto both ANDs is no (go back to the

A complete microcomputer system comprising microcomputer, teletype, a twin floppy disk storeand a EPROM programmer. The single diskette holds as much information as would be containedon 1.5 km of paper tape of the type shown on the top of the microcomputer (about 2.5 millionbits).

beginning and go through it all again andkeep doing this until the answer to oneof the ANDs is yes). What we have justdrawn is called a flow chart.

MPU or Hard -wired logic?Up to now it may seem thatI have been stressing the over-heads involved in using an MPU andyou may be feeling that it wouldn't beworth it just to replace a few ICs. Youwould be quite correct; an MPU wouldbe more bother than help. Remember,though, that this same MPU can, withthe help of a set of instructions, do thesame job as hundreds or thousands ofICs. Also, if you wanted to change thefunction performed by that array ofhardwired ICs you would probably havea long job with the soldering iron andside cutters ahead of you. With the MPUthe hardware changes will be minimal, ifindeed any. Instead you change theseries of instructions (in honesty let itbe said that it can take a surprising

lit CROSSING CLEAR

.11 START

WALK LIGHT ON?

AND

NO

CLEAR FOR 200 YARDS TOLEFT

AND

--Ow CLEAR FOR 200 YARDS TO ArRIGHT?

YES

V

WALK -T

YESt

E: IT Fig.3

amount of time to get the instructionsequence correct so that the MPU doeswhat you want it to!).

Once these series of instructions(called programs) are written they canbe stored and one program can bechanged for another in almost no time.Finding when it becomes profitable touse a microprocessor then is quite acomplicated decision based on howmany ICs it replaces and how many dif-ferent jobs you would like the samehardware to do. As a rough rule ofthumb, if you need thirty to fifty SSIand MSI packages to do the job - andyou don't need the whole job done inmicroseconds but can afford milli-seconds - then you should seriouslylook at using a microprocessor.

The idea of a program consisting of aseries of instructions presented to thepins of the chip leads us to realise that amicroprocessor chip is an incompleteunit on its own. Where do we storeprogram for example? A microprocessorthen is only a part of a greater wholeand this greater whole is called a micro-computer.

THE MICROCOMPUTERFigure 4 is my personification of anydigital computer in general and a micro-processor -based microcomputer inparticular. I have changed my model ofan MPU - now I think of it as a keenand eager clerk at a desk, able to ADD,SUBTRACT, AND, OR, X -OR, NOT,STORE, RECALL and TEST, and withbaskets labelled "PENDING" totemporarily store the pieces of paper(data) on which to work. Someone hasto give this MPU the input data onwhich to work - and take the finished


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data away again. This is the role of theinput/output, the circuits which enablethe MPU to communicate with the out-side world.

The Program. Also, our MPU, althoughkeen, cannot begin until someone tells itwhat jobs to do and in what order. Theprogram we referred to before is theMPU's equivalent of the office super-visor and is stored in the microcom-puter's memory where the MPU can getat it by a special kind of recall instruct-ion (program fetch). The baskets refer-red to before can only hold one byte ofinformation each and soon the MPU willhave run out of space to store infor-mation unless provided with auxiliarystorage (filing cabinet in an office, morememory in a microcomputer).

The Master clock. Although it mightseem that our computer is complete,one potential problem remains. What ifthe MPU is getting information from thefiling cabinet while the input/output ispouring data on one end of the desk andremoving some from the other end andthe supervisor (who has been callinginstructions out far faster than they canbe done) is already into tomorrow's

job? Clearly something is needed tokeep everybody in step (personification- an army drill sergeant (in an office?);reality - a pulse generator called a

master clock).

Memory. The program or list of instruc-tions may be stored in read-only mem-ory (ROM) where it is safe from beingaltered - in fact, if it is in ROM, youcan't normally alter it even if you wantto. The working memory or auxiliarystorage must be in read/write memory(RWM). RWM is often (though ratherconfusingly) called random access mem-ory (RAM) - we will bow to popularusage and also use this latter term.

Program may also be stored in RAM

RWM or RAMRead/write memory is organised as a ran-dom access memory so you can addressthe various cells in it in any order (unlike ashift register, for example, where the cellsmust be addressed in a particular order).However, read only memory is also organ-ised as a random access memory - hencethe possibility of confusion with the com-mon usage.

along with the temporary storage - it isup to the programmer to see that theMPU does not accidentally write over itsprogram or read some temporarilystored data thinking it to be program. Ifthis latter should happen no physicaldamage will result, but it is hard to pre-dict what the microprocessor will do -especially if the data happens to be oneof the combinations of bits which doesnot correspond to a valid instruction.(Remember not all possible combin-ations of bits in the instruction word areused).

Also most, though not all, RAM isvolatile - that is to say the contents arelost whenever the power supply isturned off. If you have program youwill want again in a volatile RAM youmust save it in some non-volatile form.(On paper tape or magnetic tape forexample) before turning the power off.

NEXT MONTH Dr Hendtlass willfinish this article with 'The micro-processor at work'. He will take youthrough a program step by step andexplain what a subroutine is and howit can save time for the programmer.


00111111111111111111111010NOWMPINWOOMMIIMMMOMOMONIONNOMORIMMEM,MI

MICRO -68bElectronic Product Associates, Inc.,1157 Vega Street, San Diego, CA92110, announces the availability ofthe new MICRO -68b microcomputer.The MICRO -68b comes completelyassembled with hex keyboard, 6 digitLED display, 8K RAM, 1K PROM

monitor, CRT/TTY/Audio Cassetteinterface. It is housed in a ruggedizedaluminum cabinet with a 13 slotEXORcisor-compatible mother boardand 20A power supply. The 6800 -based MICRO -68b lists for $1878.00south of the border and is availablefrom stock.

MICROCHESSNow available is a chess -playingprogram for the MOS Technology6502 -based KIM -1 microcomputer.The Microchess program does notrequire the KIM -1 to be modified inany way, as it occupies only 1100of the 1152 available bytes of RAM,and all moves are entered and dis-played via the KIM keyboard anddisplay. The program has several levelsof play, and may be set up for 3, 10or 100 seconds per move.

Documentation supplied covers a

source listing, Player's Manual, anddescription of the strategic algorithms,so that it is possible to modify andexpand the software. Microchess is

available for $10.00 from :Microchess,1612-43 Thorncliffe Park Dr., TorontoOntario, M4H 1J4.

MICROPROCESSOR TRAININGSDS Technical Devices Ltd. offers anevening course designed around theM6800 microprocessor. The coursefeatures a hands-on, applicationsoriented approach and is aimed atthose who desire to gain actual hard-ware and programming experience.An extensive set of notes withnumerous examples is provided.Demonstration models developedespecially for this course provide ameans for the students to relate theirprogramming to real world situations.

The SwTPC 6800 microcomputersystem is used throughout this coursebecause its I/O structure and assoc-iated peripheral gear make it wellsuited to a course of this nature.

The course utilizes an evening courseformat rather than the usual intensive3 or 4 day format to allow thinkingtime for the participants to develop,debug and test programs over an ext-ended period of time.

The first course in this series is

scheduled to start on February 8,1977 in Winnipeg, Manitoba.

SDS are inviting enquiries frominterested parties who wish to estabfish this training series in other cities.They can help you get started --contact them for details at:SDSTechnical Devices Ltd., 1138 MainStreet, Winnipeg, Manitoba, R2W 3F3.

GET YOUR MITS ONMITS, the manufacturer of the Altairrange of hobby computers, haveannounced four new products. The88 - Mux is a 24 channel multiplexer,companion card to the 88 - Analog/Digital Converter. It features differen-tial inputs, with independent gainsetting and scale factoring on eachchannel Input filtering can also beadded to provide the desired roll -off characteristics. The 88 - Muxwill be available within 60 days oforder placement at a cost of $319

(assembled only).The 88 - PROM Programmer will

program the standard 1702A EPROMin less than three minutes. The unitconsists of a separate chassis (with24 pin zero insertion force socket)and an interface card that plugs intothe 8800 bus. The software driverfor the programmer is supplied onPROM. The assembled unit costs

$455.Also from MITS is the 88 - S4K,

a synchronous 4K memory boardwhich runs with no wait states at themaximum CPU speed. The memoryrelies solely on the CPU for timingsignals - there are no single shotsand no critical on -board timing.Price? $155 (kit), $255 (assembled).

Finally, the Altair 7000 Graphics/Printer is an electrostatic printerplotter and graphics hard -copy outputdevice that is plug -compatible withthe 680 and 8800 via one PIO port.It can print up to 160 characters persecond (80 characters per line) in a

5 x 7 dot matrix. By means of anextra, eighth printing electrode, it canalso plot and produce pictures, eitherin outline or shaded form.

Horizontal resolution is up to128 dots/inch and vertical reso-

lution is 65 dots/inch. The Altair7000 will be available from MITSat a cost of $785. MITS, 2450 AlamoS.E., Albuquerque, NM 87106.

MICROCOMPUTER HARDWARETc support M6800 -based equipmentdevelopment, Motorola has introducedchassis, card cages and a power supplyfo- the MICROMODULE products.

Two card cages are available; onewith 5 card slots, the other with 10.Both card cages have mother boardsthat are compatible with the Micro -modules and all of the EXORcisormodules. In addition, the cages can bemounted on five different axes.The unit price for a 10 -card cageis $147; a 5 -card cage is $98. (US).

Power supply outputs are 15A at+5V DC, 2.5A at +12V DC, 1.5A at-12V DC, and 0.1A at 8V AC. Shortcircuit, overload and overvoltage pro-tection are provided.

Two chassis models are available:again, 5 & 10 card cage versions. Bothfit into a standard 19" RETMA rack,and include a power supply, cover andhinged front panel. Unit prices are$660 for the 10 -card version and $610for the 5 -card chassis. The powersupply is available separately for$295, again US price.

Technical Information Center,Motorola Semiconductor Products Inc.PO Box 20294, Phoenix, AZ 85036.


4 reasons pts canadaoffers the best intuner repair serviceSAME DAY SERVICEEight hour service means that tuners are repaired andready to go the same day we receive them.ORIGINAL PARTSOnly original parts are used on all tuner repairs.ONE YEAR WARRANTYWorkmanship and parts are warranted one year fromthe date of repair.VERSATILITYWe repair them all - color, Black & White Tube, Elec-tronic/Varactor or Transistor . . . Any Make, AnyModel, including foreign makes.

VHF or UHF...$13.95 UV -COMB. $21.95(Major Parts and Shipping Extra...Dealer Net)

Ask about our Tuner Replacement Guide and PartsCatalog. PTS Canada also has a complete line of tunertesting instruments, fully assembled or in kit form.

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FUNCTIONS AND FEATURES. Display: 5 digit mantissa 2 digit exponent.Number entry is floating point and/orscientific notation; results in scientific nota-tion. Logic: Reverse Polish notation.

Functions: Sins, cosine, arctangent (radians),log, alog (base 10) square root, reciprocal,change sign. clear/clear entry. Memory: store, recall, exchange.'Size: 6" x 2-7/8" x 1'4" Use on desk orhandheld. Non -slip rubber feet, big greendisplay, 9V battery or Gladstone's ACAdapter.

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tech tipsSINGLE POINT STEREO INPUTSELECTOR

OV0

SW1

0+Ve

CLOCK3

h 4013

13

IC1a)L

IC1b

CLOCK1 12

154013

QIC 1c

3

IC1d

13'4012

Four different inputs can be switchedthrough by the continual pressing ofSW1.

IC1 is a dual 'D' type flip flop. TheQ outputs are connected to the Dinputs so that the clock inputs aredivided by two. The two flip flops are

5

8

11

13

A BC DLEFT INPUTS

I1 14 Cie 112

4016

S

4016

11

3

9

10

2

3

EFT0

10

11 121

AI

B

RIGHT0

T INPUTS

connected in series, giving a two -stagebinary counter.

IC2 is a quad AND gate. This isused to decode the four states of thecounter. The outputs are used tocontrol the quad switches at IC3 andIC4 (4016AE).

20r-:

_, -N

cTo 302

10µ400V

+12V OR -12V

IGNITION SWITCH

H.T. COIL

AUTOMOBILE IMMOBILIZATIONIn order to discourage theft of anautomobile, many people incorporatea 'secret' switch to break the ignitioncircuit (usually in series with the keyswitch). This system is very easily by-passed using 'jumper' leads.

POINTS

DISTRIBUTOR

CAM

A more effective method ofimmobilisation is shown in Fig.1, alsousing a 'secret' switch. A 10uF/400Vcapacitor is switched across the pointspreventing the ignition being started;at the same time this prevents the useof 'jumper' leads.

Fig. 1

OV

V+ (10-30V)

Fig. 2

DRIFT FREE CURRENT SOURCEThe conventional type of constant -current source, as shown in Fig.1, willdrift in output current immediatelyafter switch -on. This is because of thevoltage drop across 01, causing a sig-nificant amount of power to be dissip-ated n the transistor, heating it and itsVbe. Hence the output current slowlyincreases after switch -on, typicallyreaching a stable value about twominutes later. In tests the currentincreased by about 4% for a small sig-nal transistor dissipating 100mW.

This effect is greatly reduced by theconfiguration shown in Fig.2, whichfixes the voltage across Q1 at a verylow ilevel by virtue of the common -base transistor Q2. The main voltagedrop occurs across Q2, leaving about600mV across Ql, this being set up bythe two extra diodes in the bias chain(D1, D2) which fix the emitter potential of 02.

tech-tips100,000 MEGOHM DC PROBE!The input current of a junction FET,usually less than lnA, flows out of thegate, and is constant at a particulartemperature, provided the voltageacross the device is constant. Bymaking the gate positive to the sourcethis leakage current can be made toflow back into the device, reducing theinput current almost to zero.

FET A should be a low loss, lowVp device (ideally Vp should be about0.5V). FET B must be somewhathigher but is less critical, the bargainpack is usually a good source of suchdevices. Forward bias should be about150mV and current through the FETsabout 400mA.

The mercury cell holds the voltageacross the input FET constant at 1.5V(1.35V plus 150mV) and the silicondiode in the op amp's negative leadprevents the cell from dischargingwhen the power is off.

By adjusting values in the potential

1M

32NPUT

MERCURY CELL

divider it is possible to achieve inputcurrents within a few picoamps either

V SILICON DIODE

TO -ye RAIL

0 -9Vway and to measure the voltage on asmall capacitor without changing it.

LED COUNTERThe astable multivibrator is used togenerate pulses which operates thefour integrated bistables. The 7490gives a binary counting sequenceand the 7490 gives a BCD count.This circuit is very useful for testingthe IC's.

'WARMTH' INDICATORThe sensing element used was a therm-istor, attached to the outlet which iswarm when the pilot light is on. Arod -type thermistor was used forcheapness, with a resistance of about3k @ 200C, but a bead type wouldwork as well and with a faster responsetime.

Two gates of the 7400 provide aSchmitt trigger with a low hysteresis(determined by the 18k feedbackresistor) and the third gate inverts thatoutput. When the pilot light is on, the

0

2N3904 or similar

input of IC1 is high, IC3 output islogic 0 and LED2 (green) is on. Ifthe pilot lights fails, the temperaturefalls, all ICs change state, LED2 goes

.5V

ALL IC, ' 7400

off and LED1 (red) comes on.The temperature at which the

changeover takes place is set by the 1kpreset.


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4°° Parts VS1,98Include. resistors, cap,transformers, mongers, di-odes, etc. for .p.c. work.Preformed, dumped intobarrels by fsctorld. 100 %-Cat. Ne, 263401

K 184 9,KEYBOARD

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BARREL KIT #182JUMBO RED LEDS15 for $1.98100% material, user ran -collation from factorydumps. eV 10 mil.. Fo100's of projects, red lens.Cot. No. 20 3369

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BARREL KIT #161.POP' PLASTICTRANSISTORSas for $.9820304 s with some21.1890tra of 100% mate-sal. TO -92 Preformed.

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IT #134CALCULATOR C141

BARREL KIT #133C-MOS IC'S

IT #131TANTALUM

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$1.98 -riLOC, omoraotoeolia.1...dTfllitt:

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15 for ... -------$1.98 ,

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10 for $1.98Mst. GE type, CDS Lyda-Mixed by factory. Big jobfor us to separate. 100 %good. Cat -lie. 20 3052

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100 for $1.98Cosmetic reject, electri-cally fine business! Youcheck 'ern. It's not for us.Adt. voltages. 20 3204

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BARREL KIT #88 'LITRONICS LEDREADOUTS ,A

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KIT #67NATIONAL IC BONANZAHOBBY100 for =It

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BARREL KIT #116LEDS

40 for 4-$1.98 Untested747... 727i.. shark., ,

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KIT #701 -WATT ZENERS100 for $1.98Factory same as 400-mw's.Never -to -de -again offer. 6.0. 10, 12, 15V. underglass. Double plug.Cat -No -X3.02741 Untested.

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10 for jraiwinBARREL KIT 445741 MINI DIP"BO AAAAA "

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BARREL KIT #371 AMP "BULLETT"RECTIFIERS Untested

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Hobby tyj_,_ factory fah-outs, 262024 Ulatosted

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Fallouts of the famous203055. 20 2617 109.%

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Hi-Fi mfr's Mel! inventor,.but he dumped 'do in bar-rel.. Preformed. for PC use./Used values tool 20 2405

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KIT #12POWER TAB TRANS40 for 4111,.,.$1.98 .

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BARREL NIT 711POWERnoms-REGISTERSTRANSISTORS40 for

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KIT #7VOLUME CONTROLBONANZA, Z-7,..-..

U "7404N 70 LJ SPI741600 .88.6300TYPE SALE N7 NNNNN .880 S0749514 76 0 5

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0 5117402N .16 D 514744614 .799 C 51474106N .63 0 52174173N 1.39

$1.98.NPN, plastic T0220 type.Assorted 2N numbers.No. 20 2425 Unteateo.

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0 511740911 .16 .0 SO1747014 .45 H 12474

0 S117410N .16 CI 5147472N .34 901741250 99 0 M47418511 1.755N74126N .59 0 51474190N 1.15

0 5 NNNNN PI .25 0 "747" .74 ° 51474132N 1.00 0 51174191N 1.0545 C 5147474N .31 -

BARREL KIT #41

100 for -an-$1.98 Untested.

ff,,,,no rues Mayelude 25. 50. 100, 200,400, 600. 800 and 1000volters, 202417

KIT d 3ca"-154148/914SWITCHING DIODES100 for $1.98

Imagine ,aai, ,,,,trhisigdiodes at these prices!Cat.No. 262418 Untested.

BARREL KIT .72LINEAR OR AMPS,DIPS 75 for" $i, 98teetedMay include 709'.. 7.11...,703's, 560 series. 556 in-eludes 2512410

BARREL KIT #1DIP IC'S.

75 for $1.98Marked 14 and/or with 16pin dips, may include gates,registers, flip RUM coon,ere 202415 Voted

0 0 SN70141N .68 1p 38174192N .67

0 SN7417N .32 0 5074750 .4

o 5074200 .16 0 511747614 .31 0 51474145N .89 0 51174193N .63

0 5117421N .29 0 5147471114 .79 511 NNNNN N 1.29 0 514 lllll N .73

0 5/17423IN .35 0 911745311 .6 D SN74150N .99 0 5147419614 .85

CISN7421101 .27 U 514746514 AS 8 5N7413t 0 .70 0 5117419IM 1.49

D 5/17430N .10 0 511746911 1.95 0 9074133N .65 0 51174199N 1.4941340 1.03 0 91174200N 3.95

0 5147437N .26 0 V1749014 .44 0 5147 0 51174251N 1.09"7415714 .70 0 51174264N 5.955147431IN .26 C 5147491N .73 0

L3 914744011 .16 C 5/474920 .47 0 5117N .85 0 50742650 5.99

0 9147441N .64 0 514749311 .47 0 5074138 .

Cat. No.201981HONEDBARREL KIT #5SCRS, TRIACS,QUADRAdS30 for-$1.98 R. factory

Lstockl All the 10;in tpcat.No. 20 3019 untestyed .

Terms: Add postage Rated: net 30 SALEPhoto: Wakefield, Mass. (617) 245-3829Retail: 16-18 Del Carmine St., Wakefield, 0 Send for FREE

MINIMUM ORDER - $6.00 SPRING CATALOG

POLY PA I( S C.O.D.Yi MAY 1P.O. BOX 942G LYNNFIELD, MA. USA 01940 BE p


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

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

DIFFERENTIAL TEMPERATURE SENSOR AND ALARM SYSTEMThe circuit is comprised of three parts(i) the differential temperature sensor(ii) a differential amplifier to providegain (iii) a swit circuit tomonitor the output from the different-ial amplifier.

Two diodes D1 and D2 are used asprobes for the sensor. A small preset,RV1 provides fine adjustment of thecurrent through each branch so as togive zero differential output betweenD1 and D2 when they are at the sametemperature.

A gain of 500 must be provided atthe differential output to provide auseful voltage to switch the LED's(....ie IV corresponding to 10C.) RV2provides fine adjustment of the gainand RV3 adjusts the CMRR.

A potential divider network is setup by RV4, R9, R10, RV5 to providethe necessary switching voltages forthe voltage comparators, thus enablingLED1 or LED2 or LED3 for voltagesset up by RV4 and RV5 -3V and+5V.

SETTING UP

1. Adjust offset -null on all Op. Ampsfor zero output by connectinginput terminals together and takingto ground and adjusting eitherRV6, RV7 and RV8.

2. Adjust CMRR for differential amp-lifier by shorting input terminalsand connecting to +15V line, thenadjusting RV3.

3. Apply probes D1 and D2 to aliquid, say at room temperature,and adjust RV1 until there is zerooutput across collectors of T1 andT2.

0

0

1 R

ZD1

R3

REMOTE PROBES

02

57 RV2

SET5 GAIN

0IBALANCE

RV1

R8

741

4RV6

RV3 SF CMRR

1V/4C DIFFERENTIALOUTPUT

HIGH FAIL I 50C/

R11

R12

LED1

R1

'71LED2

LOW FAIL I- - 3PC1

LED3

'PASS'

COMPONENT LISTRESISTORSR1R2,R3R4,R10,R13R5,R6

2.2k51k

1k2k

RV4,RV5RV6,RV7,RV8TRANSISTORST1,72DIODES

2.2k10k

2N2222

R7,R8 910k D1,D2 1N4004R9 39052 D3,D4 1N914R11,R12 1.2k LED1,LED2 miniature REDPRESETS LED3 miniature GREENRV1 100E2 ZD1 400mW, 3V3RV2,RV3 100k 3 Operational Amplifiers 741

4. Apply probe D1 to a liquid at a

temperature 100C different fromabove, then adjust gain controlRV2 until there is 10V at the diff.amplifier output. The CM RR

should again be set.5. Adjust RV4 and RV5 so that the

comparators switch at -3V and+5V corresponding to -30C and-F5oc.

7400 SIRENThe siren consists of two oscillatorswhich generate the tones. A third osc-illator is used to switch the others onand off alternately, giving the twotone effect

By changing the capacitor valuesdifferent tones can be produced.

IN

IN

OUT

IN

IN

OUT

GND

7400

4k7

0.11AF 0.15F 0 1pF

113

0.1pF4k7 4k7

2A

0.2sF

1C

4k7

220pF

025F4k7 4k7

A

220/ F

47OR

811 15052

PIN 7's OVPIN 14's 55V

OV

76TOP VIEW


CANADIANREPRESENTATIONWANTED

For a well established manufact-urer and importer in the USA,with well rounded lines of:

MicrophonesP.A. & Paging Hornsand Accessories

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CANMOS ElectronicsBOX 1690, PETERBOROUGH, ONT. K9J 7S4

FIRING LINE INDICATIONS

10KV

5KV

0KV

Normal pattern:Note that the firing line for cyl. 1 appearsat the extreme end of the trace. The remain-ing cylinders then appear in engine firingsequence.

5KV

0KV

Firing lines even but high:Excess plug gaps, rotor gap, break in coilht lead, mixture too lean ignition retarded.

15KV

10KV

5KV

0KV

Firing line high on ONE cylinder:Break in plug lead, broken electrode inspark plug. To test short plug - if linedrops, problem is within cylinder.

5KV

0KV

Firing lines uneven:Break in plug leads, worn plugs, burntdistributor cap contacts, uneven air/fuelmixture.

ADVERTISER'S INDEX

ABBEY 4CANMOS 33,77DELHI 72DOMINION 14,23ELECTRA 10GAMASONIC 6,25GLADSTONE 8,72HEATHKIT IFC,10I LP 3KESTER SOLDER 20MAGNUM 8,23MUELLER 14PACO OBCPHILIPS 21POLY PAK 59,75PRECISION TUNER 64TEKTRONIX IBC

continued from p. 63

rpm. Finally richen the mixture a shadsuntil tickover speed drops by about50 rpm.

Then and only then - look at the gasanalyser. You should now have a read-ing somewhere between 14:1 and 15:1.If you haven't then there's somethingwrong with the carburetion system -an air leak in the induction manifold:incorrect float chamber level: blockedslow running jet or something.

WHEN REPLYING

T i ADVERTISMENTS

PLEASE MENTION

ETI


OPEN CIRCUITTechnician's column

by Tom Graham

Here it is!

As this new format is designed to please everybody interest-ed in electronics from the veriest beginner to the electronictechnician level, we would appreciate your comments,pro and con, as this is your magazine and we want to doeverything in our power to please everybody as best we can.Be assured that we will carefully scrutinize each and everyletter; especially the ones with adverse comments so thatwe can try to serve you better.

OTEA revisited

We got quite a lot of feedback from my editorial in the Fallissue of the electronic workshop wherein we discussed thefact that all electronic servicemen and Companies shouldjoin the Ontario Television Electronics Association. Most ofwhat we got were phone calls from small, independent ser-vicemen across the province saying that they never evenreceived an application in the mail from the OTEA askingthem to join.

Of course the prime reason for this just naturally has tobe that they don't have your name on the mailing list.Furthermore, even we probably don't have all of the namesof every service shop on our mialing list. Undoubtedly,now that we are on general newsstands, a lot of previouslyunknown companies and independents will be seeing thisfor the first time. So in case you fall in either of the lattercategories, here is where you write for information.

Norman W. Matthews, Managing Director,Ontario Television Electronics Assn.,13 Queen St. S., Elmira, Ont. N3B 2S5.Telephone: (519) 669-8410.

While on this subject, a new member of the OTEA wroteme from Cornwall, asking how he could go about gettingthe information on where to go to write the exams inorder to obtain his Ontario Certificate of Qualification.Seems he got a rather brusk brush-off from the localCommunity College. Previous to this I thought that all of

the Ontario Colleges could give this exam. Not so, it ap-pears. However, members of the OTEA are having negotia-tions with the Ontario Ministry of Educational Programsto try to clear up this matter and, hopefully, to get somesort of standardization throughout the province.

In the meantime, it appears that once again Ontario,with 40% of Canada's population within its borders is

lagging way behind Quebec and Alberta to name just twoprovinces that I know of for sure that are working veryclosely with their provincial electronic associations to notonly provide excellent educational programs, but also put-ting some teeth into laws designed to practically eliminatethe 'moonlighters'.

But of course this is the reason in both cases; both ofthese provinces have very strong provincial associations.And it is the prime reason why Ontario needs a strongprovincial association itself.

I'm very pleased to hear from Norm that they arealready starting to do something about this situation. Butthey need every member they can get. It's an old adage ofcourse that there is strength in numbers, but it is so verytrue in the case of the television and radio serviceman.Because there are so many people reading this that neversaw that artic e I wrote; (this issue has 30,000 circulationas compared to our former 10.561 . . . ) I'll repeat part ofthat editorial titled "You can win a million". I made thepoint that a lot of servicemen stopped reading the noticefrom OTEA when they saw the price. Then I likened thisto the fact that just about everybody who balked at samevery probably has gambled from $50.00 to $100.00 andmore on the almost impossible odds of winning a milliondollars on the various lotteries that are going on all thetime. After making the point that joining the provincialassociation was betting on a sure thing and then ended thearticle with the following paragraph.

"For my money, if you don't join your local, provincialand national associations very soon, you may be out ofbusiness with the next 5 years.

Wanna bet?


A NEW LOW-COST,DUAL -TRACE SERVICE OSCILLOSCOPE

FULLY BACKED BY TEKTRONIX

Now for only $495 you can get aportable, 10 MHz dual -trace ser-vice oscilloscope. The 18 lb.TELEQUIPMENT D61a nas front -panel controls that are easy tounderstand, easy to use. Full -sen-sitivity X -Y gives you vector dis-plays that are in true phaserelationship-displays that youcan rely on. And automatic selec-tion of alternate or chopped modeand automatic selection of tv lineor frame triggering make this os-

cilloscope ideal for classroomuse as well as the service shop.

D61a features a bright 8 x 10 cmdisplay, and 10 mV sensitivity indual -trace and X -Y operation. Itis fully backed by a standardTektronix one-year warranty andmay be serviced at any ofTektronix Service Centres nation-wide. Call your nearest fieldrepresentative for specificationsand ordering information on tne

new D61a and other low costTELEQUIPMENT Oscilloscopesor contact Tektronix Canada Ltd.CDN Sales Price FOB Destination. FST extra.

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Availrtde in Canada through SPECIAL OFFER: Save $10.00! Send any 3 labels from these products,plus $10.00 and this address panel and we will give you a two year subscrip-6or to ELECTRONICS TODAY. A regular $20.00 value. Offer expires:.pail 30, 1977. Valid only in Canada.

.MCO ELECTRON1,3'; Ti.).! 45 s..inson street montreal, quebec h4r 2e1 tel.: (514) 748-6787

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