HI-FI STEREO VALVE AMPLIFIER INFRA -RED VIDEO LINK ... · hi-fi stereo valve amplifier video box...

HI-FI STEREO VALVE AMPLIFIER

VIDEO BOX

INFRA -RED VIDEO LINK

PEEP ALARM

FUNTRONICS: UGHT/DARK INDICATOR

DATA FILE: AGC MICROPHONE PREAMP

e 0 MAPLIN PROJECTS BOOK FIFTYONE

EDITORIAL

(This Project Book replaces Issue 51 of'Electronics' which is now out of print.Other issues of 'Electronics' will also bereplaced by Project Books once they are

out of print.For current prices of kits please consultthe latest Maplin Catalogue or the freeprice change leaflet, order as CA99H.

Editor Robert Rail WMCompiled by Mike HolmesContributing Authors Alan Williamson. Gavin

heeseman Robert f Iliol. Robert Penlold. Chris Barlow

Production Co-ordinator Alan WraighlPrint Co-ordinator John CraddockArt Director Peter RlackmorePublications Manager Roy SmithDevelopment Manager Dave GoodmanDrawing Office Manager John DudleyTypesetting Bowl LauenanPublished by Maplin Electronics PlcPrinted by Mayhew McCrimmon Printers L IdMail Order P 0 Box 3. Rayleigh. Essex SS68LRTelephone Retail Sales: (0702) 554161Retail Enquiries: (0702)552911.Trade Sales: (0702)554171Cashtel: (0702)552941General: (0702) 554155Fax: (0702)553935 1 Telex: 995695

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Copyright All material is sabred to worldwide copyrightproleci ion and reproduction or imitation in whole or earns

expressly !orb Oden The Publishers, Maplin Electronics Plclake all reasonable care to prevent intim loss or damage of

any kind being caused by any matter published in this ProtectBook Save insofar as prohibited by English law liability 01every kind including negligence is disclaimed as regards any

person in respect Ihereol Where errors occur corrections winbe published as soon as possible atlenvards Permission toreproduce printed circuit board layouts commercially or

marketing 01 kds must be sought from the publisherCopyright 1993 Maplin n Electronics plc

PROJECTS

-1 HI-FI STEREO

/ VALVEAMPLIFER

g INFRA -RED

0 VIDEO LINKI Enables wirelesstransmission of videosignals using infra -red

light.

11FUNTRONICS:

LIGHT/DARK

INDICATORPart of a beginner's

series presenting asimple light levelindicator.

14

I A review of a superb

Hi-Fi amplifier thatsounds as good as

it looks!

`PEEP' ALARMI A compact, low -poweralarm unit that is lightlevel triggered.

-f DATA FILE: AGC

/ U MICROPHONE

PREAMPI Application circuit forthe versatile SL6270VOGAD IC.

VIDEO BOXIA low-cost, highquality video fader and

signal processing unitwith numerous facilities.

FOR MAIL-ORDER ENQUIRIES,

PLEASE DO NOTCALL OUR

SHOPS AS THEY WILL BE

UNABLE TO HELP YOU.

Send all mail to:

P.O. Box 3, Rayleigh, Essex. SS6 SLR.

S

elleman

tereo

Part One - The Reviewby Alan Williamson

For those of you who have lusted after avalve amplifier for years, but are unableto afford one due to their high cost(compared to transistor designs), yourfetish can now be satisfied. With theintroduction of the Velleman K4000 valveamplifier (tube amplifier to our Americanfriends) into the Mapl in range of kits youcan now turn your fantasy into reality. TheK4000 is a fixed -bias ultra -linear design,delivering 95 watts in class A/B1 (seebelow), the first 15 watts are in class A.

Classy OperatorClass A is the situation when the anodesof both valves on each half of the outputtransformer primary are conducting at alltimes. Class A/B1 operation occurs whena signal is large enough to cut the valve oftduring the negative half of the cycle (onlyone valve is cut off at any time because ofthe inverted phase) and the cathodes arealways negative with respect to the grid.

4000

alve Amplifier

SpecificationOutput power:

Power bandwidth (max. output, -3dB):Frequency bandwith iref. 1W, -3dB):Harmonic distortion:

Signal to noise ratio:Channel separation:Input impedance:Input sensitivity:Loop feedback:Damping factor:

2 x 200W music power2 x 95W rms in class A/B12 x 15W in class A10Hz to 60kHz4Hz to 100kHz0.08% (1 kHz, 1W)0.63% (1 kHz, 95W)>102dB (A weighted at 95W)>67dB (at 95W)100kfl0dB (775mV for 95W)18dB25

Incidentally, Class A/B2 operation is suchthat, when one valve is conducting andthe cathode of the other valve is drivenpositive with respect to the grid; thisrequires power to drive the grid ratherthan a voltage.

Weight TrainingSo what do you get for your money?Well for a start you don't get a flyweight

amplifier (it weighs 20kg!), the physicaldimensions are 423 x 383 x 150mm(whd), including the mains switch andspeaker terminals. In the kit you geteverything you need to build the amplifier,rig -it down to the last nut and bolt. Youmay, however, prefer to use an alternativeaudiophile cable and components (seelater) to those supplied with the kit -please let us know the results.

The impressive looking, and sounding, K4000 amplifier.

When built, the amplifier is rathereye-catching - with the valves on display,as can be seen from the photograph.Styling is in a similar fashion to that of theBeard P35 or Audio By Design (formerlyAudio Innovation) First and Secondamplifiers.

CircuitryThe amplifier is a little unusual as itemploys toroidal transformers in theoutput stages and power supply, but therest of the circuit is fairly standard.

Referring to Figure 1, the input of theamplifier is AC coupled to one half of anECC82 in the preamplifier stage (the otherhalf being used for the other channel). TheECC82 is used as a buffer and pre -gainstage, without the use of cathodedecoupling, and is not included in thefeedback loop.

An ECC83 is used in the mainamplifier proper. Half of the ECC83 isused as a gain stage, with the overallfeedback loop terminating at the cathode,while the other half of the ECC83 is usedas a phase-splitter.

The outputs of the phase-splitter thenfeed two parallel pairs of EL34s inthe fixed -bias ultra -linear push-pullconfiguration. Power from the outputvalves is converted from high voltage lowcurrent, to low voltage high current viathe ultra linear transformer, connectionsto the outside world being made by eitherthe 811 or 411 tap, the overall feedbackloop is taken from the 811 tap.

Although the EL34s are running atnear maximum voltage, each valve is onlydelivering around 24 watts. A single EL34can handle a maximum 48 watts, so youcould say that the EL34s are conservativelyrun, which helps to extend valve life.

The Meaning of LifeA nominal figure for the lifetime of a valveis given at around 5000 hours, but valvesshould be replaced on a fairly regularbasis, around every 1000 hours or so.

Ageing valves are generally noticedby a softening of the sound which canmanifest itself in different ways, a lossof detail in the treble; speed, slam andarticulation in the bass; a general blurringof information and a fuzzy stereo image.

Terminal ConditionWARNING: The amplifier must always beterminated with a speaker load BEFOREpowering up, otherwise serious damage tothe output valves and/or transformer mayresult.

Large Scale IntegrationThe amplifier was slotted into my usualstereo, which took the place of my trustyEdison Twelve (also valve, a triodecoupled class A, 12 watter), althoughthe Edison is no longer in production,the nearest living relative is the Audioby Design series 200, which sells forapproximately £450 (at the time of goingto press).

Thu K4(100 %ith its covers removed.

The rest of the system consists of aVoyd Valdi turntable fitted with a RegaRB300 arm and Audio Technica 007cartridge, this feeds a home made headamp (based around the LT1028 Op -amp,better than my Audio South transformer,but that's another project). The preamp(valve) is a heavily modified AudionPremier. The speakers are a temporarypair of LNB 7s (a 70 litre transmission linedesign). Audio Note silver interconnectsand Audio Note green/white speakercable were used to stitch the systemtogether.

A little consideration must be usedwhen siting the amplifier. If you havechildren or pets you won't be able to leavethe amplifier on the floor, and I doubt ashelf would be strong enough to take theweight. Placing the amplifier betweenthe speakers or on large cabinets is also ano -no, otherwise you may end up with afeedback problem. You won't get a howl -round, but it will affect the sound quality(valves are mechanical devices, if you tapor flick any of the valves with your fingernail, you will be able to hear a ping fromthe speaker(s) which will last for severalseconds -a characteristic commonlyknown as 'microphony').

Another thing that must be taken intoaccount is that the amplifier needs plentyof ventilation, so you can't put it into acabinet. The amplifier should also be keptout of draughts and away from plants -plants don't always like the hot air! Theother reason you should keep plants awayfrom the amplifier, is that some of themsweat and, sometimes, 'those people withgreen fingers' are not always careful whenwatering. Water dripping onto a hotvalve, even a single drop, would provedisastrous ending up in a pyrotechnicdisplay - pretty but expensive! At the

end of the day it would be best to use theamplifier on a proper equipment table,such as the ones manufactured byTarget, Mana Acoustics, Oasis, SoundOrganisation, etc.

AcclimatisationSerious listening didn't take place for acouple of days - until the amplifier hadsettled in. I used the time to re -adjust tothe sound my stereo made using this amp,which is quite different from what I amused to.

The first thing I noticed about theamplifier was what 'appeared' to be a lackof top -end, I say 'appeared' because thetop -end is all there, it just doesn't grab youby the throat. I also discovered during thefirst couple of days that the Audion is notan ideal match for the Velleman, whichdidn't help matters.

Substituting the Audion for an'experimental' bodged -together transistorpreamp brought the top -end out alright,only now it was slicing my ears off!, sothe Audion was recommissioned for thelistening tests and the 'experiment' wentinto the bin.

Eventually I was able to jiggle thetonal qualities of the system to somethingthat was acceptable by changing theinterconnect and speaker cable.

Serious ListeningThe sound stage is more tangible andthree dimensional than the Edison, thestereo image has good depth and height,the width extended well beyond thespeakers, but I did notice a couple ofthings. The musicians seemed to havetaken a step backwards into the mix, thiswas not a bad thing really as the soundstage became more stable and realistic.

2

IN

LFInput

GND

Pre -Amp PCB

+V3

R59

C21.: R60

OVC20 1/2 V6

OV

* See note in text

OUT

f 1 f2

Main Amp PCB -V

+V30

R52

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R30

R31

R19

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8

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The other thing I noticed was that thestereo image seemed to be grainy, similarto looking through a net curtain or lookingat a photograph printed in a newspaper.I wondered if this graininess could be dueto the ceramic capacitors in the circuit?There are two per channel, one at theinput of the amplifier and the other is inthe feedback loop. I replaced both of themwith polystyrene types (4 in total, BX24Band BR375). The sound quality improvedquite a bit and the stereo image wasn'tgrainy any more. It seemed as thoughsomeone had filled in the area betweenthe spots! The mid range and treble wasalso of a more liquid quality, a simple andworthwhile modification.

The one thing that really impressedme about the amplifier is the amount ofgrunt it has in the bass; it is deep, solidand powerful, basically it's got balls,even at low volume.

After listening to the Velleman for acouple of days, I felt that I was not reallygoing to be able to find the limitationsof this amplifier in my system. A quickphone call to my friend arranged theuse of his stereo over the weekend.

My friend's system is what somemight call 'over the top' depending onyour point of view. The turntable is anOmega Point Mentor, fitted with a Breuertype 8 arm and a Kiseki Blackheartcartridge, Audio Research SP11 preamp,two pairs of Ray Lumley M150 poweramps and Snell AIII speakers. Thesystem is wired together using Cardasinterconnect and speaker cable.

Both pairs of Lumleys weredisconnected and the Velleman wasslotted in place. Unfortunately becausethe Cardas cable is so large, the Vellemanwould not accept two pairs of cables sothe Snells could not be bi-wired. Halfan hour was allowed for the amplifier towarm up before listening commenced.

A record was put on the turntable, thearm cue lowered and we both sat back tolisten. After the first track my friend lookedat me and said, "Hmmm,... ain't bad is it!"

My initial comments about the lackof top end is unfounded in this system.Although the top end didn't sparkle quiteas much as with the Lumleys, it certainlywasn't dull, but it was improving all thetime, even after 4 hours of continuousmusic it was still getting better.

I have a feeling that with theamplifier's excellent dynamics and tonalcharacteristics, it has primarily beendesigned with CD in mind, unfortunatelyI didn't have one to hand to confirm mysuspicion.

I have to admit the performance ofthe amplifier did surprise me a couple oftimes. Playing 'The Game' from NusratFateh Ali Khan's Mustt Mustt album (RealWorld LP15) made the floor shake in avery meaningful way. The Velleman wasmaking the Snells move a lot of air, somuch so that my friend is now consideringreplacing a pair of the Lumleys with theVelleman to drive the bottom half of theSnells. (A pair of Lumleys are more than

The K4000 kit of parts.

71/2 times the price of the Velleman.)The other thing that surprised me was

that the Velleman didn't sound too outof place in a system of this calibre, it hasits limitations; even the Lumleys havelimitations, but there again doesn't everything!

This amplifier loves music, anymusic, especially solo acoustic. Thedouble -bass and tablas on the track'Prancing' from Colin Walcot's CloudDance album (ECM 1 1062) was veryholographic; I could almost walk aroundthe instruments. The sitar and double -basson 'Eastern Song' from the same albumhad wonderful presence, the whole roomseemed to energise. Small nuances couldbe heard on the Egberto Gismonti Sol DoMeio Dia album (ECM 1 1116). I couldhear the rasp of his fingers moving overthe strings, I also could hear his sleevebrushing on the guitar body quite clearly,the saxophone also had a lovely bite to it,spine tingling even.

Modern pop/rock/indy recordings(although not the best) are reasonablywell reproduced, I thoroughly enjoyedlistening to 'Fishing and Bags' on PILs'Album' (Virgin OVED 245). Morrissey'sAlsatian Cousin (Viva Hate, HMV label,Virgin CDS 3787) just totally bowled meover. Another surprise the amplifier had instore for me was that I originally wrote -offBig Audio Dynamite's Megatop Phoenixalbum (CBS 465790 1) as a poorrecording. Not so, the bass and drum kitvia the Edison was over blown which wasmost evident on 'Start, Rewind and TheGreen Lady', it was previously about astight as... II'm sorry but I can't print that- Ed!]. But when played through theVelleman it is tight and very deep, it's justthat the Edison bottles out - sic.

On the down side, the only faults thatstick out are that the amplifier does tend tolose the fine detail of the music and it doestend to compress the three dimensionalimage into a wall of sound when the goinggets fast and furious (the amplifier didn'tlike the Sex Pistols [who does? - Ed.]). Butthere again the Velleman doesn't carry astate-of-the-art price tag and you also havethe fun of building it yourself.

During the listening tests I waslimited to the amount of equipmentavailable, I would have liked to have hada chance of using the amplifier with awider variety of speakers. But given theamplifiers tonal characteristics it shouldbe able to fit in to any good quality systemthat is on the neutral to bright side, or anyone using a pair of small speakers thatcould do with a bit of beefing up.

Unfortunately, I am not able to vouchfor the amplifier's performance withdifficult (highly reactive) loads, a pair offull range ribbon speakers would havebeen handy to find out how the amplifiercoped.

To fully exploit the Velleman K4000,a system entry level would require aminimum of a specialist turntable ora two box CD player.

Does the amplifier represent value formoney? Only you can decide this, but ifyou can justify spending this sort of moneyon an amplifier, then you owe it toyourself to investigate this one further.

I'm personally going to have to buyone to play with.

NOTE: Part Two, which gives fullconstruction details, can be foundin Issue 52 (XA52G).

4

InFRA-REDVIDEO Link

B Y GAVIN CH

Part One:The

Transmitter

FEATURES* Range up to 100m* 12V operation* Replaces long video cables

The Infra -Red Video Link allows thetransmission of monochrome compositevideo over a distance of up to 100 metres.The system makes use of large Fresnellenses tofocus the infra -red energy atmuch greater distances than are possibleusing standard techniques.

Circuit DescriptionFigure 1 shows the circuit diagram of thetransmitter The power supply is connectedvia SKI. Diode DI provides reverse -polarity protection. The circuit requires twoseparate supply rails: a 12V, high current

EESEM AN

The Video LinkTransmitter PCB.

APPLICATIONS* Point-to-point video link* Security* General Communications

Power Supply Voltage 12V to' 4VPower Supply Current

(Quiescent)RangePCB Dimensions

Focal Length of LensPeak Ir'ra-red

Wavelength 940nmComposite Video

InpvVideo Bandwidth

150mA at 12VUp to 100m83 x 83mmapprox.

270mm approx.

1V peak -to -peak4MHz

Table 1. Prototype Specification.

supply; and a 5V, low current supply.Regula-.or RG1. with its associated com-ponents, provides the regulated 5V supplyfor IC1. A composite video signal, at astandard 1V peak -to -peak level, is appliedto the circuit between P1 and P2.

A video signal essentially consists ofthree parts; synchronisation (sync) pulses,a luminance (brightness) signal, andchrominance (colour) information. Thecircuit makes use of only the sync andluminance components; for practical pur-poses, the chrominance signal can beignored. Separating the sync and lumi-nance signals allows each of these to be

5

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Figure 1. Circuit diagram.

C6

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handled separately, as each requiresdifferent processing.

The high frequency luminance signalis separated and processed by ICld and e.It is necessary for the overall gain of thecircuit to peak at high frequencies tocompensate for the poor response of theinfra -red emitter at higher frequencies.Capacitors C6, C9 and C10 provide highfrequency peaking.

The sync signal is processed by ICla,b and c to remove the high frequencyluminance signal, and to produce cleanframe and line sync pulses.

ICH forms part of an AGC (automaticgain control) amplifier. The output from

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Figure 2. PCB legend and track.

6

Close-up of PCB, showing mounting (and wiring) of infra -red emitter.

this stage is rectified by D4 and fed to TR1,which maintains a relatively constant signalin the system, helping to prevent overload-ing. Preset resistor RV1 adjusts the AGClevel, and indirectly controls the outputlevel of the transmitter.

The sync and luminance signals arerecombined after processing, and are fedto output transistor TR4, which drives thehigh power infra -red emitter, IR1. IR1 ispositioned at approximately the focallength of a large Fresnel lens such that theinfra -red energy is focused to infinity.

ConstructionAfter identifying the components andensuring that all are present, insert andsolder them onto the PCB, following theinstructions given below and referring to

the legend shown in Figure 2. If you havehad little, or no, experience of electronicproject construction, then please refer tothe Constructors' Guide (included with thekit), for useful practical information.

Start assembly by fitting the resistors,as these are fairly low profile componentswhich may be difficult to fit at a later stagein construction. When fitting the IC socket,make sure that the notch at one end of thesocket corresponds with that on the PCBlegend; do not fit the IC until all othercomponents have been soldered in place.

The PCB pins should be fitted next,these being inserted into the PCB and thenpressed home using a hot soldering iron.When the pins are heated to the correcttemperature, very little pressure is requiredto push them into place. There are two

Screen

P5

PCB

Bracket

Cathode(Case)

Anode(Tag)

M2.5 x1 2mrn Bolt

Transmitterdiode

Anode(Tag)

q.

I M2.5 Nut

Insulatingbush

TR4

Insulating q. 3 x M3 Nutswasher

IMM

3 x

1 2mrnM3Bolts

wire links on the PCB, and both of theseare fitted in normal operation. Link LK1connects the output of the driver stage tothe power output stage and may be omittedif it is required to drive the power outputstage directly via P3 and P4, as may benecessary in some non-standard applica-tions. For standard operation using compo-site video, however, LK1 must be fitted.

Next, fit the capacitors, rememberingto fit the electrolytic capacitors the correctway around. Please note that C3 and C4share the same '+' symbol on the boardlegend. All semiconductors must also befitted with correct polarity, as shown on thePCB. The infra -red transmitter diode ismounted on a metal bracket, which in turnis mounted on the component side of thePCB, as shown in Figure 3. The diode ismounted through the hole in the bracket;this arrangement should provide a rela-tively tight fit, and the small sachet ofepoxy glue supplied with the kit can beused to hold the diode even more securelyin position. Four nuts and bolts are used tofasten the bracket to the PCB. The diode iswired onto P5 (anode) and P6 (cathode)on the PCB, using the screened cablesupplied. The leads of the diode should becut to 10mm and bent in such a way as toreduce the possibility of shorting. Sleevingmay also be used if necessary, but theleads of the diode are comparatively rigidand should stay apart once correctlypositioned.

The transistors (and regulator RG1)are fitted so that their cases correspondwith the relevant outlines on the PCB. Ahole is provided on the PCB, allowing theregulator to be bolted to the PCB using anM3 nut and bolt; however, this is optionaland it is not essential to do this. TR4 usesthe diode bracket as a heatsink to aid heatdissipation, and is mounted as shown inFigure 4, using the M2.5 nut and bolt

Figure 3. Mounting the emitter diode and diode bracket. Figure 4. Mounting TR4 onto the bracket.

7

Infra -Red Video Link transmitter with top lid removed, showing internal assembly detail.

supplied in the kit. Please note: thetransistor needs to be insulated from thebracket with an insulating bush and agreaseless washer.

TestingBefore applying power to the circuit, it isrecommended that you double-check yourwork to ensure that all of the componentsare fitted correctly, and that there are nodry joints or solder bridges. Power supplyconnections are made via a PCB -mounted2.5mm power socket; the outer part of thepower plug should be connected to OV,

and the inner part to +V. The circuitrequires a 12V to 14V DC power supplycapable of supplying at least 500mA.Although the module has its own on -boardregulation and decoupling components, itis recommended that a power supply witha suitably smooth output is used to preventany unwanted modulation of the supplyrails. A suitable power supply for the unit isYZ21X. The composite video input signalsare applied to P1 (input), and the return(ground) to P2 (OV), via the BNC inputsocket. The input signal level should beapproximately 1V peak -to -peak.

It is not possible to test the unit fullywithout the appropriate infra -red receiver,or a full set of test equipment. The receiverwill be detailed in the next issue of'Electronics'. If you have an oscilloscopeset up to display a video signal, it ispossible to make basic tests on the unit.Apply a video signal to the input, andmonitor the signal between P3 and ground(P4). Set RV1 to the centre of its travel, asmarked by the arrow on the PCB legend.The oscilloscope should display a similarwaveform to that of the original sourcevideo signal, although the levels willprobably be different. The waveformdisplayed is that of the drive signal to thepower output stage. If the signal on P6 ismonitored, a somewhat compressed ver-sion of the signal should be displayed onthe scope screen; this corresponds to thevoltage across IR1. Although these testsare relatively simple, they allow the basicoperation of the circuit to be assessed. Thesetting of preset RV1 depends on thelocation of the transmitter and receiver,and should be left until both units are inplace and the system is up and running.

HousingAn undrilled case is supplied in the kit, tohouse the transmitter. The drilling detailsare shown in Figure 5. The box has slots tohold the Fresnel lens in place. In each case,the PCB is mounted using 4 x M3 nutsand bolts. 1/4in. spacers are used toposition the PCB at the correct height inthe case. The PCB is mounted such thatthe vertical part of the 'diode bracket' ispositioned 270mm from the lens (as

85

10

All dimensions in mm

NOTE:-Take all dimensionsfrom the bottom ofthe box from thetriangle slotted end.

Triangle slotted end

6 51

50

END PANELr

:13 -12mm dia. hole

I

. ,

4 x 3mm dia. holes

I I 1

8mm dia. hole

- - - -! 1_444i i

1443

20 re 6.5

65.5

10.5 74

Square slottedend for lens.

4 x 3.5mm dia. Countersunkholes to suit M3 C/5 bolts.

BASE OF BOX

Figure 5. Drilling details.

8

Front of unit, showing mounting of Fresnel lens.

accurately as possible); this is approxi-mately the focal length of the lens and hasbeen found to provide the optimum range.Figures 6 and 7 show how to mount thelens and PCB in the case (see note below).The input (BNC) socket, SK2, is mountedon the rear panel, and is wired to the PCB.The power socket (SK1) does not requireany additional wiring, being PCBmounted. It is, however, necessary to drill asuitable hole in the rear panel of the box toallow a 2.5mm power plug to be inserted.

The Fresnel lens, as supplied, is toolarge to fit into the end of the box suppliedin the kit, and a box to hold a lens of thissize would not be practical in many cases.It is therefore necessary to cut the lens tothe correct size to fit into the box, and thisis 103mm x 103mm. It is important thatthe lens is cut as carefully and accurately as

_.. 0,p,p,

ov0) Screen Flt Fresnel lens,---"' Into square slot

OVScreen

In box.Diode bracket ---------,..46

0 0270mm

Cl C

Fit rear panel intoslot in box.

O 0

1----PCB

//Figure 6. Positioning the PCB and wiring SK2.

Rear

Bracket Lens

M3 Nut

,PCB

1.13 I/4 inchspacer

X_//A // /7/1//////// j 1.//// // / /7///// /I1 M3 x

6mm Bolt

Figure 7. Mounting the PCB, lens and rear panel.

9

E

Cut square fromcentre of lens

Fresnel lens

103mm

Figure 8. Cutting the Fresnel lens.

possible to ensure a correct fit. In addition,when trimming the lens down to size,material should be cut equally from thefour sides so that the central point of theconcentric rings is in the centre of thesquare, as shown in Figure 8. The box isnot resistant to water and if the system isused outdoors, a degree of waterproofingwill be necessary. This may be achieved bysmearing a thin layer of silicone rubber

sealant around all of the box joints,including the grooves for the lens and therear panel. A suitable sealant is YJ91Y. It isrecommended that where possible, theunit is mounted in a sheltered location.

Mounting ConsiderationsIt is necessary to provide a securemounting point for the transmitter andreceiver units. This may be achieved in a

variety of ways; one method, used for theprototype, makes use of small speakerstands (stock code GL18U), which aresupplied in a pack of 2 with a selection ofdifferent types of bracket. The stands areparticularly useful as they allow the bracketto be moved freely for alignment purposes,and also clamp securely in place whenalignment is complete. There are obviouslymany different methods of mounting thetransmitter and receiver units, and themost suitable method must be chosen foreach individual situation.

It is important that the finishedtransmitter is NOT pointed directly at thesun, as the lens could focus the sun's raysonto the PCB, emitter diode or associatedcomponents, generating heat and causingirreparable damage. This considerationmay dictate where the unit is mounted,and in problem cases it may provebeneficial to devise a protective hood forthe front of the unit, to shield the lens fromdirect sunlight.

NOTE: Part Two, which givesdetails of the matching receivercan be found in Issue 52 (XA52G).

INFRA, RED VIDEO LINK TRANSMITTER PARTS LISTRESISTORS: All 0-6W 1% Metal Film (Unless specified) D2-5 1N4148 4 (QL80B)R1 7511 1 (M75R) IR1 I/R Photo Emitter 1 (KW66W)R2,6 1M 2 (M1M)R3,9 82k 2 (M82K) MISCELLANEOUSR4,8,10,13,18 100k 5 (M100K) PI -6 Pin 2145 1 Pkt (FL24B)R5,7,12 1k 3 (M1K) 14 -Pin DIL Socket 1 (BL18U)R11,15 4k7 2 (M4K7) PCB 1 (GHO1B)R14 3k9 1 (M3K9) SK2 BNC Square Socket 1 (YWOOA)R16,21 8200 2 (M820R) SKl PCB 2.5mm DC Power Socketl (FKO6G)R17 10k 1 (M10K) I/R Video Case 1 (GL48C)R19,29 6k8 2 (M6K8) Fresnel Lens 1 (KW60Q)R20 3911 1 (M39R) Diode Bracket 1 (KW65V)R22 15011 1 (M150R) Insulator TO220 1 (QY45Y)R23 560k 1 (M560K) Plastic Bush 1066 1 Pkt (JR78K)R24 22011 1 (M220R) Low Capacitance Cable lm (XR19V)R25 33052 1 (M330R) TC Wire 1.6mm 16swg 1 Pkt (BLI IM)R26 1k5 1 (M1K5) Pozi Screw M3 x 16mm 1 Pkt (JC70M)R27 12k 1 (M12K) Nut M3 1 Pkt (JD61R)R28 2211 Wirewound 3W 1 (W22R) Bolt M2.5 x 12mm 1 Pkt (JY31J)RV1 2k2 Hor Enclosed Preset 1 (UH0113) Nut M2.5 1 Pkt (JD62S)

Bolt M3 x 12mm 1 Pkt (JY23A)CAPACITORS Double Bubble Sachet 1 (FL45Y)

2200µF 16V PC Electrolytic 1 (FF60Q) Spacer M3 x 1/4in. 1 Pkt (FG33L)C2 100µF 16V Minelect 1 (RA55K) Instruction Leaflet 1 (XK44X)C3,5,14,17 141 16V Minelect 4 (YY34M) Constructors' Guide 1 (XH79L)C4,7,8 li.LF 63V Minelect 3 (YY31J)C6 100pF Ceramic 1 (WX56L)C9,16 470pF Ceramic 2 (WX64U)C10 150pF Ceramic 1 (WX58N)C11,19,20 100nF 16V Minidisc 3 (YR75S)C12,15 220pF Ceramic 2 (WX6OQ)C13 1nF Ceramic 1 (WX68Y) The Maplin 'Get -You -Working' Sp -vice is available forC18 lOnF Ceramic 1 (WX77J) this project, see Constructors' Guide or current

Maplin Catalogue for details.SEMICONDUCTORS The above items are available as a kit, which offers

74HCU04 1 (UB04E) a saving over buying the parts separately.RGI µA7805UC 1 (QL31J) Order As LP59P (UR Video Link Tx Kit).TR1 VNIOKM 1 (QQ27E) Please Note: Where 'package' quantities are stated in theTR2,3 2N7000 2 (UF89W) Parts List (e.g., packet, strip, reel, etc.), the exact quantityTR4 VN66AF 1 (WQ97F) required to build the project will be supplied in the kit.D1 1N4001 1 (QL73Q)

10

AllYou Need

to Build Your Own

Ty run ,sk

ooruclPROJECT

No4

LIGHT -DARKINDICATOR

Text by Robert Penfold

This is the fourth in a seriesof easy -to -build electronicprojects for complete

beginners, who require a simpleand fun starter to electronic projectbuilding. These projects are idealfor the young person as iosoldering is needed. All the projectsare built on the same type and sizeof plastic 'peg -board'. The onlytools needed to build this project,anc the others in the series, are apair of wire cutters/strippers and asmall screwdriver; a par of plierswould also be useful.

This Month'sProjectLight -operated switches are muchused in day-to-day life, such as instreet light switches, lift-aoorprotectors, and other similar uses.This project is a very simple light -operated switch. In fact, it simplyswi,ches on a light -emitting diode(LED for short) indicator if it detectsthe absence of light. Wit -t a simplechcnge to the circuit, this project willdo the opposite - in other words, itwill operate the LED indicator if thelight level is above a certain amount.

The finished Light -Dark Indicator.

Please note that the tools and thebcttery are not included in the kit.

11

How it WorksThe circuit diagram for the light -operated switch is shown in Figure1. This is the darkness detectorversion of the unit (The 'lightness'detector is dealt with later). At theheart of the circuit is LDR1, the'photocell'. This component isknown as a 'light dependentresistor' (LDR for short), whichmeans simply that its electricalresistance changes in sympathywith the light level that it receives.In darkness, LDR1 has a very highresistance, but in strong light itconducts electricity quite well.

Let us look, first of all, at howthe circuit behaves in darkness.In this case, LDR1 has such a highresistance that it has very little effecton the circuit. The current throughresistors R1 and R2 is enough toswitch on the transistor (TR1), whichin turn switches on the LED (LD1).R3 reduces the current flow to alevel that is safe for both TR1 andLD1. D1 is a protection diode whichis included in all 'Funtronics'projects. All this does is to 'block'the supply, should you accidentallyconnect the battery around thewrong way. This is because D1(and all other types of diode, forthat matter) allows electricity toflow in one direction only.

If the room is lit, or the unit isplaced in daylight, the light levelreceived by LDR1 is quite high.Because its resistance decreases,this component 'taps off' most of thecurrent that would flow into the'base' of TR1 if no light were to fallon LDR1. As a result, not enoughcurrent is present at this point toswitch TR1 on, and so LD1 remainsturned off. The circuit does notprovide a true 'switching' (in otherwords, on/off) action; in otherwords, LD1 will light up dimly, overa small range of 'in-between' lightlevels.

Getting itTogetherFirstly, read through this section andthen carefully follow the instructions,one step at a time. Refer to thephotographs of the finished projectif this helps.

1. Cut out the component guide -sheet provided with the kit (whichis a full-size copy of Figure 2), andglue it to the top of the plasticboard. Paper glue or gum shouldbe okay. Do not soak the paper withglue, a few small 'dabs' will do.

2. Fit the link -wires to the boardusing the self -tapping screws andwashers provided. The link -wiresare made from bare wire. Loopthe wire, in a clockwise directionaround each screw to which it mustconnect, taking the wire under thewashers. Do not fully tighten ascrew until all the leads that are

>13 R1

33k

LD1 A

Red SZ\.\LED

K

R21k2

ORPLDR112

R3

390R

TR1

K

D11N4001

BC548

81

9V

Figure 1. The Light -Dark IndicatorCircuit Diagram. LDR1 is the photocell.

under it are in place, and do notover -tighten the screws, otherwisethe plastic board may be damaged.

3. Recognise and fit thecomponents, in the order givenbelow, using the same methodas for the link wires. Cut thecomponents' wires so that they arejust long enough to loop around thescrews; otherwise long leads leftflapping around may touch eachother (this is known as a 'short-circuit') and may stop your circuitfrom working.

a) The first components to befitted are Resistors R1, R2 and R3.These are small sausage -likecomponents having a lead -out wireat each end, and four colouredbands around their bodies. Thefourth band tells us how near to thegiven value the resistor is likely tobe. This fourth band is known as the

0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0R30 0 o Dl o 0

0 00 0

0 0

0

0

0

0

0

0 00

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0

0 0 0 0 0 00 0 0 0 0 0

'tolerance' band, and is gold incolour. However, we are interestedin the first three bands, which tellus the value of the resistor. For R1,these bands are all orange. Thecolours for R2 are brown, red, andred again. The colour of R3's firstthree bands are orange, white andbrown. These three coloured bandson each resistor tell us that: R1 hasa value of 33,000 ohms, which isoften written as 33 kilohms (or33kn for short); R2 has a valueof 1,200 ohms (written as 1 k2 forshort); and R3 has a value of 390ohms (written as 390R for short).Unlike diodes or transistors, itdoes not matter which way roundresistors are connected.

b) Next fit the LED, LD1, which isa 'blob' of clear red plastic, with twowires coming out of one end, asshown in Figure 3. It is fitted in theposition shown on the guide -sheet,and must be connected the rightway round - or it will not light up.One side of the LED is flattened (thelead on this side of the LED is knownas the cathode (K), while the lead onthe other, rounded, side is called theanode (A)). Make sure that the LEDsare fitted so that the 'flattened' sidesline up with the drawing of the LEDprinted on the guide -sheet.

c) The next component to befitted is D1, which is a small tube -likecomponent having a lead at eachend of its black body, as shownin Figure 4. Like LD1, it must beconnected the right way round(In other words, D1 is a 'polarised'

O 0O 00 0O 0O 0 0O 0 0O 0 0O 0 0O 0 0O 0 0O 0 0O 0 0O 0 0 0 o Boo o 0 0 0

O 0 LDR1 oo o o o o o 0

0 0

O 0O 0O 0O 0O 0

A000KoA e o oLD10 0 0 0 0 0 00 0 0 0 0 0 1 0

O 0 0 0 0 0 00

0

K

0

0E oo 0O 0

Co c

O o RedO 00000

TR1 0 0 Black 0O 0 0 0 0 adoo o o 0 0 0O 0 0 0 0

O 0 0 0 0 0 00 0

O 0 0 0 0 0 0 0 0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

O 0 0 0 0 0O 0 0 0O 0 0 0O 0 0 0O 0 0 00

0

0

0

0

0

LIGHT-DARK INDICATORPROJECT NO.4

0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0

O 0 00 0 0

O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0 0 0 0O 0.0 0 0

O 0 0 0 0

O B1

Figure 2. The component guide -sheet for the Light -Dark Indicator.12

Figure 3. LED (LD I ) connections.

component). Its 'polarity', whichtells us the way in which it must bepositioned, is indicated by a white(or silver) band close to one end ofthe body. The diode should be fittedso that the band lines up with thaton the drawing of the diode on theguide -sheet.

d) TR1, the transistor, shouldnow be fitted to the board. This hasa small black plastic body with threelead -out wires. It will be markedwith the type number, which in thiscase is 'BC548'. Other markingsmay also be present; you will haveto get used to picking out theimportant markings on chips andtransistors (and ignoring theothers!). You must ensure that TR1is fitted to the board correctly.Figure 5 shows which lead is which,making this task easy.

e) Next, fit LDR1, which is athick disc -shaped componenthaving two lead -out wires. Theshiny surface with the visible zig-zag'pattern' is the light sensitive one,and should face upwards. Thedistinctive pattern is in fact the trackof light sensitive material (cadmiumsulphide in this case). LDR1, beinga resistor, can be connected eitherway round.

f) Lastly, fit the batteryconnector and battery, Bl. Theconnector must be attached to theboard with its coloured leads thecorrect way round. The batteryconnector has two press -stud clipson a piece of plastic and two wirescoming from it, coloured red andblack. The red and black leadsshould be connected as shown onthe guide sheet. The 9V PP3 typebattery should be connected to thebattery connector; it will only fitproperly one way round.

Diode

Ancde(A) Cathode(K)

Figure 4. Diode (D1) connections.

Testing and UseAfter checking that everything isin the right place and properlyconnected to the terminals, connectthe battery to the battery dip.LD1 should not light up when theassembied unit is placed in daylight.Even the lower light levels producedby most electric lighting should keepLD1 turned off. Therefore, if LD1switches on, disconnect the batteryAT ONCE and recheck the wiring.In particular, make sure that LD1,D1, TR1, and the battery ore fittedthe right way round.

Emitter (E)

Base (B)

Collector (C)

Figure 5. Transistor (TR1) connections.

If LD1 does not switch on, tryplacing your hand over LDR1, sothat it receives very little light. Thisshould force LD1 to come on.Although the circuit does notprovide strict on/off switching, youshould find it difficult to positionyour hand so that LD1 slows withanything less than full brightness.The high signal gain of the transistorensures that only a very narrowrange of light levels give 'in-berween' brightness from LD1.

Using the Circuitas a LightDetectorIn order to get the unit to work as alight detector, simply swap over R1and LDR1. When LDR1 is subjectedto eight conditions, TR1 is nowprovided with an input current. TR1then switches on, and 'urns on LD1.When LDR1 is in darkness, very littleor no input current is supplied toTR1. Neither TR1 or LD1 areswitched on as a result.

Uses of the Light-Dark IndicatorWith LDR1 and LD1 within onlycentimetres of each other, the unithas little practical use. However, ifyou connect either LDR1 or LD1 tothe main unit via a piece of two-waycable (which can be a few metreslong if necessary), LDR1 or LD1can be remotely located from therest of the unit. A useful purposefor a project of this type is aphotographic darkroom indicator.In this case, the unit would be set upas a darkness indicator, with LDR1mounted inside the darkroom, andLD1 mounted outside

If LD1 is switched on, this wouldindicate that the room was dark.In other words, developing of filmcould be taking place, and so it maynot be safe to enter the room. Onthe other hand, LD1 being switchedoff indicates a high light level in theroom, telling us that it would safe toenter (assuming, of course, that theunit's battery had not run down!)

AvailabilityThe Funtronics Light -Dark Indicatoris available from Maoiin Electronics,through our chain of regionalstores, or by mail order, order codeLP93B.

13

by Gavin Cheeseman

The Peep Alarm is a light -operatedsounder, simple but effective in itsoperation. In a dark environment, theunit remains quiet, and is for all practicalpurposes switched off. However, whenlight falls on the alarm's photosensor, theunit emits a loud, shrill tone. In addition.a light emitting diode (LED) illuminates.providing secondary indication that thecircuit has been triggered. An on -boardlight sensitivity control is included in thedesign to allow operation in a variety ofsituations, over a range of light levels.

Circuit DescriptionFigure 1 shows the circuit diagram of themodule. The circuit is based around a4093BE CMOS quad Schmitt NAND IC(IC1). Diode D1 prevents damage to thecircuit if the battery is unintentionallyconnected the wrong way round. Thephotosensitive device used is an ORP12light dependent resistor (LDR), chosen forits wide change in resistance relative to acomparatively small change in light level.Together with R1, R2 and RV1, LR1 formsa potential divider. As light falls on LR1, itsresistance decreases, reducing the voltageat the centre of the divider chain. Whenthe voltage level drops to the switchingthreshold of ICla, the output of the gateswitches from low to high. The output ofICla is fed to IC1b, which forms a gatedoscillator. When the logic level on pin 5 ishigh, the oscillator operates, but when thelevel is low, the oscillator is disabled. Theoperating frequency of the oscillator isdetermined by R3 and Cl, the suppliedvalues of R3 and Cl generating a frequencyof approximately 4-6kHz. IC1c forms aninverting buffer between the oscillator andsounder PZ1. Diode D2 is used to protectIC1 from any high voltage spikes which thesounder may produce. The output of IClais also fed to IC1d, which drives lightemitting diode LD1. Resistor R4 limits thecurrent through the LED.

FEATURES* Low Quiescent Current Consumption * Operates

From 9V PP3 Battery * Simple Effective Design* Fibreglass PCB * LED Alarm Indicator * LightSensitivity Control * Reverse -Polarity Protection

APPLICATIONS* Door Open Reminder * Case Alarm

Photo 1. Assembled Peep Alarm wth lid removed, showing positioning of PCB and battery.

14

Photo 2. The complete Peep Alarm prior to final assembly.

+V DI1N4001

2

By

IC I o4093BE

IC 1b4093BE

R41 k

OP3

LED \--"7LD1 \

o P4ICId

4093BEJ11 '""-\

121

9

8

ICI c 02 A40938E 1N4001 /

10

0 PS

PZI


ConstructionThe design uses a high quality, single -sided, glass fibre PCB, with a screen -printed legend, see Figure 2. Insert andsolder the components onto the PCB,referring to the component legend, startingwith resistors R1 to R4 and capacitor Cl.Fit the IC socket, ensuring that the positionof the notch at one end of the socketcorresponds with that on the componentlegend. Do not fit the IC at this stage.PI to P6, the PCB pins, are inserted intothe PCB from the track side using a hotsoldering iron. The head of the pin shouldbe heated to the extent that very littlepressure is required to press it home intothe PCB. After the pin has been inserted itmay then be soldered. Preset resistor RV1is inserted so that its case correspondswith the outline on the component legend.When fitting Dl and D2, it is importantthat the correct polarity is observed; thenegative end of the diode, indicated by aband at one end of the component, shouldbe inserted so that it matches the bandprinted on the legend. Light dependentresistor LR1 should be mounted at a heightof 10mm above the PCB, as shown inFigure 3. ICI may then be inserted into thesocket. The IC should be positioned so thatthe notch at one end of the component

MNPL INCHS6C ISS. I


PCB

10mm

Figure 3. Mounting LR1.

corresponds with that in the socket. Thebattery clip is wired to PI (red) and P2(black). The light emitting diode, LD1,is soldered between P3 (anode) andP4 (cathode). The cathode of the LED isindicated by a flat edge on the side of thecomponent body, and by the shorter of thetwo leads. PZ1, the piezo sounder, is wiredbetween P5 and P6. All connections areillustrated in Figure 4, together withassembly information.

HousingThe Peep Alarm is housed in a small plasticbox, which is included in the kit. The PCBis held in the box using M3 nuts and bolts,as shown in Figure 5. Additional M3 nutsare used as spacers under the PCB. Theeasiest method of assembly is to first insertthe bolts into the underside of the box.Thread an M3 nut onto each of the boltsand screw down until locked into position.Now fit the PCB over the bolts, and lock itinto place using a second set of M3 nuts.It is necessary to remove some of themoulded plastic guides from the end of thebox to allow the battery to fit comfortably.It is also necessary to drill several holes inthe box. Apart from those used to mountthe PCB, holes must be drilled in the caselid, so that light can fall on LR1, and toallow the buzzer to be heard as loudly aspossible. The drilling details are shown inFigure 6. Piezo sounder PZ1 should beheld in place on the inside of the box lid(as shown in Photo 2), using the epoxyadhesive supplied in the kit. This deviceshould be pressed, as tightly as possible,against the lid until the adhesive sets. Note:the hole in the centre of the sounder mustcorrespond with the hole in the box lid.

TestingBefore testing the module, it is a good ideato double-check your work to make surethat all of the components are insertedcorrectly, and to ensure that there areno dry joints, or solder bridges betweentracks. If all is well, connect a 9V alkalinetype PP3 battery to the battery clip,observing the correct polarity. Place themodule in a well -lit area, and adjust presetresistor RV1 until the sounder emits a loudhigh-pitched tone. If the unit is then placedin the dark (i.e. there is very little lightfalling on the sensitive surface of LR1),PZ1 should stop sounding. During theperiod when the unit is sounding, LD1should glow, providing a secondaryndication that the unit has been triggered.If you do not require LD1, this component'nay be omitted without any detrimentaleffect on the operation of the circuit. RVIadjusts the sensitivity of the unit to light,

15

Box

LD I

Cathode(Flat edgeand short

lead)

Box lid

P30P40

P6

1RV1 1

LR1

5r. P2 P1

PP3 Battery

P2 Black P1 Redwire(-) wire(+)

PZ1

GluePZ1 to lid

Removeguides

Figure 4. Assembly and wiring diagram.

The assembled PCB

Power Supply:

Quiescent current drain:Operating current:Alarm Frequency:

9V alkaline typePP3 batteryless than 1µA14mA4.6kHzapproximately

PCB Dimensions: 41 x 34mmapproximately

Table 1. Specification of prototype.

and in practice it is necessary to adjust thiscontrol for optimum performance in anyone particular situation. The circuit is setfor maximum sensitivity when RV1 is fullyanticlockwise.

Using the ModuleThe Peep Alarm may be used in a varietyof applications requiring a light -operatedalarm. In a typical application, it couldbe used to provide an indication thata cupboard or case is open; a situationthat could arise from an attempt to gainunauthorised access, or simply by leavingit open unintentionally. The alarm is purelyintended to give a local indication, andis not designed to be audible over a longdistance. Obviously the alarm will onlyoperate in an environment where there isa significant increase in light level whenthe cupboard or case is opened. The PeepAlarm is, however, designed to operateover a wide range of ambient light levels.

Another application for the PeepAlarm is in a dark -room, where it couldbe used to give warning when the dooris opened, or a light is switched on.

In a dark environment, the circuit isin its quiescent state, and therefore drawsvery little current; in this condition, the unitshould operate for many hours from analkaline PP3 battery. When the unit issounding, the current drain is severalmilliamps; for this reason it is recommendedthat the unit is not left in the triggered statefor more than a few minutes at a time,otherwise the battery will become quicklydrained.

Table 1 shows the specification of theprototype Peep Alarm; the figures statedmay vary slightly in practice due tocomponent tolerances.

Box M3 Nuts

Inn11111

M3Countersunk

screw

p n r, PCB

1 1 1 1 1 I I I

r'S 0.

J

Figure 5. Mounting the PCB.

End view 5.2mm Dia.Hole

17

30

10

5mm Dia. Hole

30 10114 11 Remove guides

this end

2 x 3.2mm Dia. HolesCountersunk frombase to suit M3C/Sk heodscrew

25

All dimensions in mmNot to scale

12mm Dia. hole5mm Dia. hole

Box lid

4 x ExistingQ.u) C/Sk holes

CD

1

41 014 29

Figure 6. Drilling details.

16

PEEP ALARM PARTS LISTRESISTORS: All 0.6W 1% Metal Film (Unless specified) PCB 1 (GHO6G)R1,2 10011 2 (M100R) ABS Box 2002 1 (WYO3D)R3 1M 1 (M1M) Pozi Screw M3 x 10mm 1 Pkt (LR57M)R4 1k 1 (M1K) Nut M3 1 Pkt (JD61R)RV1 100k Vert Enclosed Preset 1 (UH19V) Double Bubble Sachet 1 (FL45Y)

CAPACITORSCl 270pF 1% Polystyrene 1 (BX50E)

Instruction. Leaflet 1 (XT41U)Constructors' Guide 1 (XH79L)

SEMICONDUCTORSIC1 40936E 1 (QW53H) The Maplin 'Get -You -Working' Service is available forD1,2 1N4001 2 (QL73Q) this project, see Constructors' Guide or current

Maplin Catalogue for details.MISCELLANEOUS The above items are available as a kit, which offersLD1 LED Red 5mm 2mA 1 (UK48C) a saving over buying the parts separately.PZ1 Low Profile Sounder 1 (KU57M) Order As LP5OE (Peep Alarm Kit).LR1 LDR ORPI2 1 (HBIOL) Please Note: Where 'package' quantities are stated in the

PP3 Clip 1 (HF28F) Parts List (e.g., packet, strip, reel, etc.), the exact quantityPin 2145 1 Pkt (FL24B) required to build the project will be supplied in the kit.14 -Pin DIL Socket 1 (BL18U)

17

6116270AGO MICROPHONE

PREAMPLIFIER

`Data Files' are intended as'building blocks' for constructorsto experiment with and thecomponents supplied providea good starting point forfurther development.

1WW 1LT IE s* CONSTANT OUTPUT SIGNAL * FAST ATTACK

* LOW POWER CONSUMPTION * SIMPLE CIRCUITRY* SINGLE -ENDED OR DIFFERENTIAL INPUT

APPLICATIONS* Audio AGC system * Transmitter overmodulation protection

* Tape recorders * Audio surveillance

The SL6270 is a small 8 -pinIntegrated Circuit (IC)combining the functions of anaudio amplifier and VoiceOperated Gain AdjustingDevice (VOGAD). It isdesigned to accept smallsignals from a microphoneand to provide an essentiallyconstant output signal from an

input covering a range of50dB. The dynamic range,attack and decay timesare controlled by externalcomponents. The device willoperate over a wide rangeof power supply voltagesbetween 4.5V to 10V andconsumes only 9mA from a 9Vbattery. Figure 1 shows the IC

pinout, and Table 1 gives theelectrical characteristics ofthe device.

IC DescriptionFigure 2 shows the blockdiagram of the SL6270. Itspositive power supply inputis on pin 3, which should bedecoupled to OV ground by a

small 100nF ceramic capacitor.Pin 6 is used as a common OVground return for all stageswithin the device.

The AGC controlledpreamplifier stage has a truedifferential input on pins 4and 5, allowing it to be drivensingle endedly without theproblems caused by other

18

forms of push-pull circuits.The applied audio signal mustbe AC coupled to the input viaa capacitor, and in the singleended mode it can be appliedto either input. Each input hasa very low impedance, only15011 if single -ended, doublingup to 30012 if differential modeis used. Signals of less than afew hundred microvolts areamplified normally, but as theinput level increases the AGCbegins to take effect and theoutput signal on pin 8 is heldconstant at approximately90mV rms over the full inputrange of 50dB, see Figure 3.The test conditions used toobtain this graph were asfollows: power supply voltage+6V, input frequency 1kHz,ambient temperature +25°C,single -ended input. In orderto ensure that internal offsetswithin the amplifier are of suchpolarity as to inhibit oscillationat the onset of AGC, a 22k

PROTOTYPEPower Supply Voltage:Power Supply Current:Microphone Input:input Impedance:

Voltage Gain:Maximum OutputMinimum Load Impedance:Frequency

Bandwidth (-3dB):

SPECIFICATION+4.5V to + 10V (P6) and OV (PS)11mA ( +9V Supply)Electret or Dynamic insertsElectret 4k712 (P1) and OV (P2)Dynamic 15012 (P3) and OV (P2)Dynamic 30012 (P3 and P4)52dB90mV rms (P9) and OV (P10)11c12

300Hz to 3kHz

AGC time F-const. '

Preamp Eoutput

vcc EPreamp E

input "'

Main amp.output

Main amp.i npu.

OV

.Preamp!now

Figure 1. IC Pin connections.

extends beyond 1MHz, seeFigure 4. However, thisbandwidth car be restrictedby placing an externalcapacitor between pins 7 and8. These are the input andoutput connections of themain ampliftr, which has aninternal 10kiz resistor to setthe flat response open loopgain. As the value of theexternal capacitor increases,the upper frequency responsedecreases and for radiocommunications this isnormally chosen to give a-3dB point at 3kHz, whichcorresponds to 4.7nF. Inaddition, the dynamic rangeand sensitivity of the systemcan be reduced by placinga resistor between thesetwo pins, and as its valuedecreases, the voltage gainof the main amplifier willcontinue to drop. Anapproximate reduction of 20dBin gain can be achieved with a

Test conditions - Supply voltage Vcc: 6V Input signal frequency: 1kHz Ambient temperature: - 30°C to +85`C

CharacteristicValue

Units ConditionsMin. Typ. Max.

Supply currentInput impedanceDifferential input impedanceVoltage gainOutput levelTHDEquivalent noise input voltage

40

55

5

150

300

52

90

2

1

10

140

5

rnA

1/

11

dB

mV rms%

p.V

Pin 4 or 5

72µV rms input pin 44mV rms input pin 490mV rms input pin 430012 source, 400Hz to 25kHz bandwidth

Table 1. Typical electrical characteristics.

resistor should be connectedfrom pin 5 to the OV supplyline.

The output from the AGCpreamp stage (pin 2) iscoupled via a capacitor to theinput of the main amplifier (pin7). The low frequency (LF)response of the system isdetermined by the value ofthis capacitor and the internal68012 resistor on pin 2.For normal speech radiocommunications, this couplingcapacitor is chosen to give a-3dB output amplitude pointat 300Hz, which correspondsto 2.2/1F. The LF response canbe extended down to 100Hz orless by simply increasingthe value of this capacitor,although values greater than100/AF are not recommended.

The combined amplificationsystem has an upperfrequency response which

CC

100nFm.

OV

f-

I150R

Preampinputs

15 OR

Preampoutput

880R

I AGC

ov

Main amp.2 7 input

10k

2k

1

AGCdetector

AGC timeconstant

OV

8

Main amp.I output

Figure 2. Block diagram.

19

value of 11(12, but values lessthan 6801/ are not advised. Thefinal audio output on pin 8 hasa small DC offset voltage, so itis good practice to use an ACcoupling capacitor beforeconnecting it to any othercircuits. To ensure a good LFresponse into loads as low as11(11, this capacitor should benot less than 22,uF.

The main amplifier alsodrives the AGC detector, andthe DC voltage generated bythis circuit is directly related tothe signal level applied to thepreamp input pins 4 and 5.This control voltage is used toprogressively reduce the gainof the preamp as the inputlevel increases. Because ofits careful design, the devicehas an extremely high inputdynamic range and using thesame test conditions as before;Figure 5 shows the distortioncharacteristics at various inputlevels.

The AGC attack and decaycharacteristics are set bythe external RC timingcomponents on pin 1.Normally the SL6270 isrequired to respond quicklyby holding the output levelalmost constant as the inputlevel is increased. This attacktime is set by the value of thecapacitor C4, and is definedas the time taken for the outputto return to within 10% of theoriginal level following a20dB increase in input level.A fast attack response canbe obtained by using anelectrolytic capacitor in therange 22µ.F to 47µ.F. The decaytime is set by the value of theresistor R6, which dischargesthe current held by thecapacitor, the recommendeddecay rate beingapproximately 20dB/second,and this slower response timeis obtained by using a value of

Maplin KitA kit of parts, including a smallfibreglass PCB with printedlegend, is available as stockcode LP98G. The basic kit assupplied is for use with radiocommunication equipment,and Table 2 shows thespecification of the prototype.Because the SL6270 maybe used in many variedapplications, some of thecomponent values suppliedin the basic kit will notbe suitable, so alternativevalues must be calculated to

100

90

80

70

60

50

40

30

2010uV 1 00uV 1mV

INPUT (RMS)1 OmV 100mV

Figure 3. Input/output characteristics.

Figure 4. Frequency response.

determine the new workingparameters.

Figure 6 shows the circuitdiagram of the module, and ascan be seen, some additionalcomponents have beenincluded to provide thefollowing extended features.A low noise transistor, TR1, is

used to provide a suitableinput for an electretmicrophone insert which isincluded in the kit. A presetresistor, RV1, provides themeans of adjusting the audiooutput level. Finally, terminalpins are provided for the off -board connections:

P1. Electret microphone insertsignal input.

P2. Electret microphone insertOV ground.

P3. Dynamic microphoneinsert signal input 1.

P4. Dynamic microphoneinsert signal input 2.

0

0

-10

- 20

- 30

- 40

- 50

-60

SECOND HARMONIC

THIRD HARMONIC

10 100SINGLE ENDED INPUT (mV RMS)

Figure 5. Distortion products versus input signal.

20

P5. OV ground power supply(-V battery).

P6. +V power supply input(+4.5V to +10V).

P7, P8. Dynamic range andsensitivity reduction(4k7 or lk resistor).

P9. Audio output (90mV rmsinto lk).

P10. Audio output OV ground.

All the components and theirrelative positions are shown inFigure 7.

Using the ModuleThe electret microphoneinsert connections to themodule are illustrated inFigure 8a. This wiring diagramalso shows the power supply,audio output and optionaldynamic range/sensitivityreduction resistor. If youintend to use a low impedancedynamic insert (not suppliedin kit) then the option outlinedin Figure 8b (single -ended),or 8c (differential) shouldbe followed, taking note ofthe necessary componentchanges to the PCB:

Remove R 1, R2, R3, Cl andTR1.

Reverse the polarity of C2.

To minimise any strayelectrical noise pick-up, theconnecting leads between themicrophone insert and themodule should be kept asshort as possible, e.g. lessthan 50mm. For longerruns screened cable isrecommended (as supplied inkit) but this too should be keptas short as possible, e.g. lessthan 500mm. When usingelectret or dynamic single -ended inserts, miniaturesingle core screened cable issuitable. However, when usinga dynamic microphone in thedifferential input mode, as inFigure 8c, open wires or twinoverall screened cable canbe used. To ensure effectivescreening, the outer braidingof the cable should always beconnected to the OV groundon P2.

The module is designed tooperate over a wide supplyvoltage range and hasa relatively low powerconsumption, making itsuitable for battery operation.A good quality alkaline 9V PP3battery is capable of runningthe circuit for a considerableperiod of time. For this reasona PP3 battery clip is alsoincluded in the kit. However,



Close-up of assembled PCB.

MC1Elecret microphone

insert

4.5V to 10V +VPowersupplyinput OV

Outputlevel

No connection

No connection

Optionaldynamic

range andsensitivityreduc'ion

Output

OV

4k7or1k

Figure 8a. Wiring diagram A.

no on/off switch is suppliedbecause of the numerousswitch styles, types andswitching methods available,here are just a few to choosefrom:

Toggle, Rocker, Rotary, Slide,Push and microphone PTT.

On most radiocommunication microphonesan integral Push -To -Talk (PTT)switch is used to activate thetransmitter. If this switch has aspare set of contacts then thepower to the module can onlybe applied during the transmitperiod, so this techniqueextends the operational lifeof the battery. If you do notintend to use a battery thenit is important that thepower supply is adequatelydecoupled to prevent audio,digital, or mains derived humand noise from entering thecircuit via the supply rail.

Screened cable should alsobe used on the audio outputof the module and be kept asshort as possible, e.g. less than3 metres. To ensure effectivescreening the outer braidingof the cable must beconnected to the OV groundat P10. The output level of the

module is adjusted by RV1,with its minimum setting at

the fully counterclockwiseposition, see Figure 8.

With no additional resistorplaced across pins P7 and P8the sensitivity of the modulewill be at maximum. Under thiscondition any low level soundpicked up by the microphonewill be highly amplified. Ifthere is an unduly high levelof distracting backgroundnoise the overall speechintelligibility will suffer.To minimise this effect thesensitivity of the modulemust be reduced by addinga resistor across P7 and P8,see Figure 8. As its valuedecreases, so also will thesensitivity, until the permitted6801/ minimum is reached.After some experimentationthe following resistor valueswhere chosen:

No resistor = full sensitivity.

4k7 resistor = mediumsensitivity.

lk resistor = low sensitivity.

As the sensitivity decreasesit will become necessary tospeak louder, and/or closerto the microphone in order tomaintain the same averageoutput level.

21

Dynamic microphone insert

No connection

4.5V to 10V +VPower -supplyinput OV

OV

No connection

OP2

OP1

OP6

OP6

C2P3

ReverseP4 polarity

RV1°-

P 0 P9 IN P7 00 0 \\IWMAXP8 0

Optionaldynamic

range andsensitivityreduction4k7Or1k

Outputlevel

Note:-Remove the followingR1 ,R2,R3,C1 and TR1.Note:-Reverse the polarity of C2

Output

OV

Figure 8b. Wiring diagram B.

No connection

No connection

4.5V to 10V +VPowersupplyinput OV

OP1

OP6

OP6P (59

Dynamic microphone insert

0

P2P3

C2

ReverseP4 polarity

RV1\-1-

MAX

Optionaldynamic

range andsensitivityreduction

4k7Or1k

CJ

OutputOutput

level

Note:-Remove the followingR1 ,R2,R3,C1 and TR1.Note:-Reverse the polarity of C2

Output

OV

Figure 8c. Wiring diagram C.

SL6270 AGC MIC PREAMPLIFIERPARTS LISTRESISTORS: All 0.6W Metal Film (Unless specified)R1,2R3R4R5RV1

CAPACITORS

4k74701222k1Mlk Cermet Preset4k7lk

Cl 1nF CeramicC2,4C3,7C5C6

2 (M4K7)1 (M470R)1 (M22K)1 (M1M)1 (WR40T)1 (M4K7)1 (M1K)

1 (WX68Y)2/.;,2F 63V Minelect 2 (YY32K)22p,F 16V Minelect 2 (YY36P)100nF 16V Minidisc 1 (YR75S)4n7F Ceramic 1 (WX76H)

SEMICONDUCTORSIC1 SL6270IC2 2SC2547E

MISCELLANEOUSP1-10 Pin 2145

8 -Pin DIL SocketPCBQuickstick PadsPP3 ClipMin Screened CableSubmin Omni InsertInstruction LeafletConstructors' Guide

1 (UM73Q)1 (QY11M)

1 Pkt (FL24B)1 (BL17T)1 (GHOOA)1 Strip (HB22Y)1 (HF28F)lm (XR15R)1 (FS43W)1 (XT26D)1 (XH79L)

OPTIONAL (Not in Kit)Alkaline PP3 Battery 1 (FK67K)

The Maplin 'Get -You -Working' Service is not availablefor this project.

The above items (excluding Optional) are availableas a kit, which offers a saving over buying

the parts separately.Order As LP98G (SL6270 AGC Mic Amplifier).

Please Note: Where 'package' quantities are stated in theParts List (e.g., packet, strip, reel, etc.), the exact quantity

required to build the project will be supplied in the kit.

22

by Chris Barlow

Specification of PrototypeDC Power requirement:DC Current:Video system:Video gain:Frequency bandwidth:Input impedance:Output impedance:Video control:

Synchronized switches:

Composite sync:

Timing outputs:(All + I2V CMOS)

+ 12V120mAComposite PAL colour video; IV peak -to -peak0dB10MHz75i2 (nominal)75i 2 (nominal)Fade to blackExternal controlVideo normal or invertedVideo defeatColour burst defeatOutput defeatOn/offExternal inputComposite syncInverted composite syncVertical syncOdd/even field indexVideo blankingInverted video blank:rigColour burst gateInverted colour burst gate

To fade out an audio signal is arelatively simple task, beingachieved by reducing the ampli-

tude of all its frequency components atthe same time. In its most basic form thiscan be accomplished by using nothingmore than a potentiometer, tapping offthe required amount of audio signal.However, composite video signals aremade up from several different elements(colour, brightness and timing), and if all

are reduced by the same amount at thesame time, the picture will begin to breakup lorg before maximum fade to blackis reached.

To maintain a stable picture, a morecomplex signal processing arrangementis required. The Video Box, shown inblock form in Figure 1, permits thereduction in amplitude of picture infor-mation, while maintaining the level of thetiming signals used to synchronize it. To

FEATURES* Composite Colour

Video In/Out* Sync In/Out* Fade to Black* Normal or Negative

Picture* DC Video Control* Picture Synchronized

Switch Functions

pplications* Picture Fader

* Vid.eo Dubbing

* Video/SyncSplitter/Combiner

* Video BuildingBlock

* Video Enhancement

achieve this, the incoming compositevideo signal must be split up into itscomponent parts, each of which undergoselective processing. Following this, thesecomponents are re -assembled, to producetl e final composite output. An additionalvideo inverter has been included, allow-ir.g the option for a negative picture to bedisplayed (useful for home video andlong distance/satellite TV enthusiasts!).Apart from its own function as a videofader, the system timing signals havebeen made available, and as a result thefinished unit can be used as a versatilebuilding block for use within other videoprojects.

Circuit DescriptionIn addition to the block diagram shown inFigure 1, a detailed circuit diagram isprovided in Figure 2. These two diagramsshould assist you when following thecircuit description, or fault-finding in thecompleted unit. For the circuit to functioncorrectly, it must be powered from awell -regulated + 12V DC supply. Thissupply enters the unit on PL6, and musthave the correct polarity (negative on pin1 and positive on pin 2), otherwisedamage may occur to the semicon-ductors. The main supply decoupling isprovided by C2, 15, 19 and C22; with Cl,14, 18, 21 and C27 giving additional high -frequency suppression.

The incoming video is connected toPL1 (pin 1 ground, pin 2 signal), and isterminated by R 1. The video signals areAC -coupled via C3 into the video buffer,

23

El CD CD El ri 11 CIan emitter -follower stage based aroundTR I. This signal is fed to the followingvideo processing circuits:

Sync amplifier IC 1.Normal video switch IC3.Video inverter amplifier TR4.Colour burst signal gate IC3.

The function of IC1, the syncamplifier, is to obtain the maximumamount of sync information from thecomposite video signal. This is broughtabout by the circuit's combination of gain,DC input bias and frequency response.The cleaned -up and filtered signal is thenfed via C7 to the input (pin 2) of the syncseparator, IC2. This LM1881 device is adedicated chip that extracts the timinginformation (sync) from the processedcomposite video signal. Four major syncsignals are produced by the IC:

1. Composite sync (on pin 1).2. Vertical sync (on pin 3).3. Colour burst gate (on pin 5).4. Odd/even field index (on pin 7).

These timing signals are at + 12VCMOS logic levels, and are used by someof the other stages within the Video Boxsystem to synchronize events. They arealso available (some with inverted logic)on PL2. Here, the inverted compositesync is provided by IC5b, while theinverted colour burst gate is supplied byIC5c. The inverted composite sync from

pin 4 of IC5b passes through an invertinggate, IC5a, before being mixed back withthe picture information at TR11. This gateis used to turn off, or remove, thecomposite sync from the final compositevideo output, which appears at pin 2 ofPL7. This function is activated when SIand/or S2 are closed.

The composite sync signal is alsoused by the input detector (TR2) andvideo blanking (IC6) circuits. With nosignal present at the video input (PL1 pin2), no sync pulses will be produced byIC2. Under this condition, TR2 will notconduct, so indicator LD I will not light up- until a signal is available. From thecomposite sync, the video blankingcircuit generates a timing signal, which isused by the main video amplifier toensure that only picture information isprocessed. This blanking signal is alsoavailable on PL2 pin 9, with its invertedlogic condition present on pin 8. The finetuning of this event is controlled by RV4,which is used to set the start (or leftedge), while the end (or right edge) ofthe picture line is set by RV5.

The vertical sync signal from pin 3 ofIC2 is used to control the sync -lockedswitch functions; video normal/inverse,video defeat, colour defeat and outputdefeat. This signal is also available on pin1 of PL2. By locking these switches to thevertical sync, a cleaner and moreprofessional picture change is obtained.

This is achieved by using a quad D -typelatch IC4 (4042BE), which has its clockinput (pin 5) connected to the verticalsync signal. Only when this signal ispresent will the output of this IC changestate upon operating one of the abovefunction switches, the sync -locked logicoutputs from this IC being used to controlthe system's sync, colour -burst and videoprocessing circuits.

The colour -burst gating signal frompin 5 of IC2 is connected to pin 6 of PL2,and the input of IC5c (which is used as aninverter). The output of this inverter isconnected to pin 7 of PL2, and alsopasses via R34 to the colour -burst signalgate IC3. However, before it reaches itsfinal destination it can be interrupted bybeing pulled down to ground by thecolour -burst and/or output defeatswitches.

The odd/even field index signal frompin 7 of IC2 is not used by the Video Box.However, it is available on pin 2 of PL2 forpossible use in additional circuitry. Forexample, this output could be useful inframe memory storage applications, or inextracting test signals that may occuronly in alternate fields.

There are two paths that the videosignal can take on its way to the mainvideo processing amplifier, both of whichpass through IC3. This analogue switch-ing device is used to select the normal orinverted (picture negative) video infor-

Videoinputo --

VideobufferAmpTR1

VideoInverter

AmpTR4

SyncAmpIC1

Sync separatorIC2

Burstgate

output0

Invertedburst

Normal goievideo switch output0---IC3

Invertedvideo switch

IC3

IC5

Odd/Even-0 field index

output

Videoblanking

IC6, 5

Invertedblanking

output

Blankingoutput

0

Compositesyncoutput

0

Invertedcomposite

syncoutput

Vertical0 sync

output

Syncdefeat

Colour burstsignal gate

IC3

VideoInputAmpTR3,5,6

Video levelcontrol FET

TR7

Main video amp

VideooutputAmpTR8,9

DC Videofade control

RV3, TR1 0

VideoNor/Inv

Colour burstdefeat

Videodefeat

Outputdefeat

IC4 IC4 IC4 IC4

S3 6 S4 (!) S5 O S1

Video Burst Video AllNor/Inv On/Of f On/Of f On/Off

IC5

Video/syncmixer &

output bufferTR1 I

S2

OSync

On/Off

Videooutput

ExternalsyncInput

0

Sync locked switch OV

Figure 1. Block diagram.

24

1_

a

Pi Er

al 1

C=

is

al

$2

_44;

9

O

tta

O

ir.0

Or3 all alO .0

2 2 ? 2 2a t 191 ,91

ra t;sa ;

iJi

51

ens

1r: s

thi it

2 2

IF F

as asd


25

C CI

0

RV 1

-1-Ft 1,33

LIMN

PIP

LIMN

U

ICS

LIMN

R9 F

-r- C7 TR2

LIMN

V1

1C21C2cs

4 R IS FC9 -1=i-

TR3

TR4

n[12

R14 I- -I R16 I- 0

PL3

LIMN LINK

C181.

19

LIMN

R37 I-

IC6 c26

r-i

LIMN

U

DI.

LIMN

Rvs C I I

TR$

UC13

11RPL IN V 10E0 1305

PL4

-.L-LN33 XI

RI1.4

-r -r -r

PLS PL6 PL 7

-4 R31 F

TR8RV2


mation, and is controlled by two of thelogic outputs from IC4 (S3). When thenormal (or non -inverted) signal isselected, the signal path is from theoutput of the video buffer amp, TR1, to theinput of the main amp, TR5. When theinverted signal is selected, the video pathis from the output of the video inverteramp, TR4, to the input of the main amp,TR5. The DC bias for both TR4 and TR5 isprovided by TR3, and is set by RV1.

The colour -burst signal must remainat a constant level as the video pictureinformation is reduced. Otherwise, themonitorNCR will try to over -compensateby increasing the colour intensity as thevideo level is reduced. Eventually, itscolour -killer circuit will operate. At the

point just before this threshold isreached, the colour video information willappear very noisy (when viewed on amonitor) before suddenly cutting out,leaving a black -and -white (monochrome)picture on the screen. The colour -killercircuit is included by the majority ofvideo/TV equipment designers to accom-modate the possibility of a monochromesignal, or if the overall signal is too weak/noisy to reproduce a good enough qualitycolour picture.

The colour -burst is maintained bygating the composite video signal fromTR1 at a precise moment in time, and thenre -combining it after the video levelcontrol circuit, TR7. This signal gating isachieved by IC3, which receives its

switching control signal from the logicoutput of IC5c. However, it can beremoved if the colour -burst defeatswitch, S4, and/or output defeat switch,Si, is activated.

The main video level processingamplifier consists of four stages:

1. The DC bias for the input buffer issupplied by TR3. The output of thisstage is determined by the level ofvoltage applied to the base of TR3 byRV 1.

2. The input buffer, formed by TR5 andTR6, then conditions the video signalinto a form suitable for feeding TR7,the video level control FET.

3. TR7 is controlled by the DC voltage

26

F-7

ACTUALSIZE

Photo 1. Completed PCB.

applied to its gate; the higher this is,the higher the amplifier gain will be.This voltage is supplied by the DCvideo fade control transistor, TRIO. Apotential divider on the base of TRIO iscreated by using three resistors: afixed resistor, R38; a preset, RV6; and arotary (or slide) control, RV3. Thecombined value of R38 and RV6 setsthe maximum voltage limit, whichcorresponds to the maximum videolevel. However, as the value of RV3decreases, this voltage will drop untilthe zero point is reached, correspond-ing to minimum video level. Thevoltage output from TRIO is groundedby the video blanking circuit, which isbased around IC5d and IC6. This hasthe effect of turning off the main videoamplifier during the sync and colour -burst time slots. The voltage can alsobe manually grounded if the videodefeat (S5) and/or output defeat (Si)switches are activated. Additionally, itcan be grounded by an externalinfluence applied to pin 2 of PL5 .

4. The output amplifier, comprised ofTR8 and TR9, receives the videosignals from TR7, and the colour -burstsignal from IC3. Two capacitors, C16and VC1, are used to set the injectionlevel of the colour burst. A second DCbias control, RV2, sets the black levelof the video signal.

The output from the main videoprocessing amplifier is supplied to TR11,where the previously extracted com-posite sync is mixed with it to producethe final composite colour video outputsignal. As well as mixing the two signals,TR11 acts as a buffer, providing a lowimpedance 75R output drive whichpasses through C23 and C24, onto pin 2 ofPL7. This video/sync mixer stage can alsobe supplied with external sync informa-tion applied to pin 9 of PL3.

Sectionthroughhousing,

Solder toconductor

Clampinsulation

Insert terminalinto housing

.1111 -7!10,17

Lockingtab

Figure 4. 'Irmiriating the wires.

PCB AssemblyAll the ir.formation required to help youwith soldering and assembly techniques,should you need it, can be found in theConstrnc:ors' Guide included in the ki:(also separately available as stock codeXH79L). The printed circuit board (PCB)is a single -sided glass fibre type, chosenfor maximum reliability and mechanicalstability. Removal of an incorrectly -fittedcomponent can be fairly difficult withoutdamaging it, or the PCB, in some way, soplease double-check each componenttype, value, and polarity (where appro-priate) before soldering! The PCB has alegend to assist you in correctly position-ing each item (see Figure 3). It is usuallyeasier tc start with the smaller compo-nents, such as the resistors. Next, mountthe ceramic, polylayer, polystyrene andelectrolytic capacitors. All the diodeshave a band at one end; be sure toposition them according to the legend.When installing the transistors, makecertain that each case matches its outline.This aiso applies to the IC sockets and`Minicon' connectors, where you shouldmatch the notch with the block on thelegend. The next components to beinstalled are the five preset resistors

(RV I, 2, 4, 5, 6) and the trimmer capacitor,VC1. Only after all the other componentshave been fitted should you then carefullyinsert the relevant ICs ir.to their sockets,making sure that you correctly orientatethem. Finally, do not forget to fit all tenwire links. These can be made fromcomponent lead off -cuts, or the 22SWGtinned copper wire included in the kit.Fhoto 1 shows in detail the completedPCB assembly.

This completes the assembly of thePCB, and you should now check yourwork very carefully, making sure that allthe solder joints are sound. It is also veryi:nportant to ascertain that the solder sideof the circuit board does not have anytrimmed component leads protruding bymore than 2mm, as a short-circuit mayotherwise result.

Final AssemblyNo specific box has been designated forthe project, as your finished unit couldcontain other PCBs (e.g. video digitiserand computer cards). However, the basicunit fitted nicely in to an ABS consoleM6006 (stock code LH66W). This, and theadditional connectors and hardware, arelisted under 'Optional' (Not in kit), in theparts list. Once you have completed themechanical assembly Df the unit, youshould check your work very carefullybefore proceeding to the wiring stage.

WiringIf you purchase the Maplin kit (stockcode LP48C), it should contain a onemetre length of ten -way ribbon cable.This is used for all the DC connections.However, no specific colour has beendesignated for each wire connection; thischoice is left entirely to you. Colouredwire is used to simplify matters, making iteasier to trace separate connections tooff -board components, just in case there

27

Blanking

LD1Signal

input LEDInvertedblankingInvertedburst OV

gate

Burst S2 External PowerSync sync inputgate

On/Off input +12VInverted

S4Burst

OV OVcompositesync

Composite On/Off O Externalsync 55 video

Odd/even Video control

field On/OffOV

index S3 Video VideoVertical

syncVideo

Nor/Inv fade output

Mox

Videoinput

SiAll

On/Off RV3'10kMin

OV OV OV

1

PL1

1 ..PL2 PL3

Timing outputs

RV1B Videobias

Leftedge

RV4 RV5

Rightedge

RV6

1T' r--1.. 1..1

PL4 PL5 PL6 PL7Maximumvideolevel

Blacklevel

0

0RV2

Figure 5. Wiring.

HMOis a fault in any given part of the circuit.Miniature 7511 coaxial cable is used forthe video in/out signals on PL1 and PL7,and it is most important that the braidedscreen should not be able to come intocontact with the centre conductor, oranything connected to it. All the wireconnections to the PCB are made using'Minicon' connectors; the method ofinstalling these is shown in Figure 4. Awiring diagram, which shows all of theinterconnections on the PCB, is given inFigure 5. The actual physical connectionsto the rotary video fade potentiometer,and the optional slide control, are shownin Figure 6.

This completes the wiring of theVideo Box and you should now checkyour work very carefully, making surethat all the solder joints are sound.

Testing andAlignmentThe initial DC testing procedure can beundertaken using the minimum amount ofequipment. You will need a multimeterand a well -regulated + 12V DC powersupply, capable of providing at least150mA. All of the following readings aretaken from the prototype using a digitalmultimeter, and some of the readings youobtain may vary slightly, depending uponthe type of meter used!

Before you commence testing theunit, set the PCB presets (RV1,2,4,5,6 andVC1) to their half -way positions, and thethe off -board function switches (S1,2,3and 4) to their 'open' or 'off positions,Ensure that the rotary (or slide) videofade control, RV3, is set to its maximumlevel, as shown in Figure 6. DO NOTconnect any power or video signals to theunit at this stage of testing.

The first test is to ensure that thereare no short-circuits before connectingthe unit to a DC power supply. Set your

TERMINAL BLOCKSPL1 PL2 PL3 PL4 PL5 PL6 PL7pin 1 = OV pin 1 = OV pin 1 = 10.8V pin 1 = OV pin 1 = OV pin 1 = OV pin 1 = OVpin 2 = OV pin 2 = 12V pin 2 = 12V pin 2 = 4.7V pin 2 = 0.5V pin 2 = 12V pin 2 = OV

pin 3 = OV pin 3 = 12Vpin 4 = OV pin 4 = 12Vpin 5 = 12V pin 5 = 12Vpin 6 = 12V pin 6 = 12Vpin 7 = OV pin 7 = OVpin 8 = 12V pin 8 = 12Vpin 9 = OV pin 9 = OVpin 10 = OV pin 10 = OV

SEMICONDUCTORS

TR1 TR2 TR3 TR4 TR5 TR6 TR7 TR8 TR9 TRIO TR11E = 6.3V E = OV E = 3.2V E = 0.6V E = 3.9V E = 3V S = 3V E = 3V E = 11.5V E = 4V E = 3.2VB =7V B =0.1V B =3.8V B = 1.3V B =3-2V B =3.6V G = 0.5V B =3.6V B = 10.9V B =4.7V B =2.5VC = 12V C = 10.8V C = 12V C = 8.6V C = 3-6V C = 12V D = 3V C = 10.9V C = 2.5V C = 12V C = OV

ICI IC2 1C3 IC4 ICS 106pin 7 = 12V pin 8 = 12V pin 14 = 12V pin 16 = 12V pin 14 = 12V pin 14 = 12V

Table 1. DC test measurements (read with a digital voltmeter).

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Photo 2 (above right): Correctly aligner picture (monitor screen).Photo 3 (above left): Correct composite video waveform (CRT display).

Photo 4 (above riglu): Incorrectly aligned picture (monitor screen).Photo 5 (above left) Incorrectly aligned picture (C FIT display).

Photo 6 (abcce right): Incorrectly aligned Mack -level - too low (monitor screen).Photo 7 (abc .eft): Incorrectly aligned black -level - :oo low (CRT display).

Photo 8 (above right): Incorrectly aligned black -level - too high (monitor screen).Photo 9 (ai-ove left): Incorrectly aligned black -level - too high (CRT display).Figure 6 Video fade potentiometers.

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multimeter to read 'OHMS' on its resist-ance range, and connect the two testprobes to pin 1 and pin 2 of PL6. With theprobes either way round, a readinggreater than 6011 should be obtained. If amuch lower reading is registered, thencheck that solder joints and componentleads are not shorting between tracks.Next, monitor the supply current; set yourmeter to the DC mA range and place it inseries with the positive line, pin 2 of PL6.Connect up and switch on your regulated+ 12V power supply, ensuring correctpolarity. A current reading of approxi-mately 110mA should be obtained, andthe signal input indicator LD1 should notbe illuminated. Switch off, disconnect thepower supply and remove the meter.

Reconnect the power supply, and setyour multimeter to read DC volts. All ofthe voltages are positive with respect toground, so connect your negative testlead to any of the OV ground pins on theterminal blocks:PL1 pin 1 PL5 pin 1PL2 pin 3 or pin 10 PL6 pin 1PL3 pin 7 or pin 10 PL7 pin 1PL4 pin 1

The voltages present on the PCBassembly should approximately matchthe readings shown in Table 1. Whenthese tests have been completedsuccessfully, remove power from the unit.

To commence the video testing andalignment, you will require some addi-tional video equipment and test gear. Youwill need a source of composite colourvideo which could be a VCR, TV tuner,video camera or pattern generator. Toobserve the resultant output, you willrequire a composite colour video monitor(or a TV/VCR with a video input) and a20MHz oscilloscope with TV coupling. Ifyou haven't got access to the more exoticvideo test gear, DON'T PANIC! - it is stillpossible to obtain acceptable resultsusing only the video equipment and yourown visual judgment. The picture imageused in our tests was taken from a colourvideo camera, and is of the 1992 Maplincatalogue.

Connect the video source to theinput (PL1), and the monitor to the output(PL7). If you have an oscilloscope, set itup as follows: TV coupling; horizontaltime -base 10/1s; auto -trigger with nega-tive polarity; vertical input 0.2V/div DCcoupled. Next, connect its vertical inputto the video output on PL7.

Ensure that all of the functionswitches on the Video Box are set to their'off' or 'open' positions, and that the videofade control, RV3, is set to maximum.Apply power to the unit and, if all iscorrect, then LD1 should light and youshould observe a clear high -qualitypicture on the monitor screen (see Photo2) and a composite video waveform onthe oscilloscope display (see Photo 3).However, this is unlikely since none of thepresets have been critically adjusted, andso the picture is more likely to resemblethe one shown in Photos 4 and 5. Eachpreset will affect a particular parameterof the video signal. Interaction may occur

Photo 10 (above right): Left-hand edge RV4 (monitor screen).Photo 11 (above left): Left-hand edge RV4 (CRT display).

Photo 12 :above right): Fight -hand ecge RV5 (monitor screen).Photo 13 :above left): Right-hand edge RV5 (CRT display).

Photo 14 (abcve right): Composite sync removed (monitor screen).Photo 15 (abcve left): Composite sync removed (CRT display).

Photo 16 (above right): Cclour-burst removed (monitor screen).Photo 17 (above left): Colour -burst removed (CRT display).

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r

Photo 18. Picture distortion (monitor screen).

between several of these adjustments,and so progressive re -calibration may berequired.

The first adjustment is to set thecorrect input and black -level bias points.As RV1 is turned anticlockwise, thepicture quality will progressively deterio-rate as the level of high -frequencydistortion increases. This will continueuntil the picture inverts on highlights, asshown in Photo 18. Turn RV1 clockwiseuntil this effect is corrected; over -adjustment of this preset will have anadverse result on the inverse -videomode. The black -level is set by RV2, andas this is turned anticlockwise the videoinformation will progressively drop downinto the sync region, eventually causingpicture break-up (see Photos 6 and 7). Ifthis preset is turned too far clockwise, thepicture will look washed out (see Photos8 and 9). RV1 and RV2 do have a smalleffect on each other, and so progressivere -adjustment may be necessary.

The next parameter to correct is theamount of picture information shown onthe screen. The left-hand edge isadjusted using RV4, while the right-handedge is set by RV5 (see Photos 10 to 13inclusive)

If an oscilloscope is not available,RV6 and VC I will not be as easy to set upas the other presets. This is because RV6sets the maximum video level, and mostmodern equipment can accept a sig-nificantly over -driven input, particularlyVCRs, which feature a video AGC circuit.The colour -burst signal level, set by VC1,is used to control the colour intensity ofthe picture. To calibrate the unit to give astandard 1V peak -to -peak video output,an oscilloscope will be required (seePhoto 3). However, a rough setting can bemade by comparing the relative bright-

ness and colour intensity of the directvideo signal to the processed one.

Finally, test the following functions:

1. Range -test the video fade control, RV3.The control should give completecontrol from maximum picture level,down to a black screen (as shown inPhoto 19).

2. Output defeat switch, Si. All videosignal components should be blockedwhen SI is closed.

3. Sync defeat switch, S2. The compositesync pulses should be removed whenS2 is closed, resulting in a slippingpicture, as shown in Photos 14 and 15.

4. Video invert switch, S3. Picture shouldbecome a 'negative' image when S3 isclosed - see Photo 20.

Photo 19. Video fade to black (CRT display).

5. Colour -burst defeat switch, S4. Thepicture should change to a black -and -white one when S4 is closed; refer toPhotos 16 and 17.

6. Video defeat switch, S5. Only the syncand colour burst information should bepassed when S5 is closed, producing ablank screen, as can be seen fromPhoto 15.

Using the Video BoxThere are two major factors which cancause a reduction in performance fromthe Video Box. Firstly, if a + 12V DCpower supply with poor smoothing orregulation is used, some of the functionswill not work properly and the overallpicture quality will suffer. For this reason,it is strongly recommended that if aready -built DC supply is used, it should

Photo 20. Inverted picture (monitor screen).

be the regulated 300rrA 12V typefeatured in the 1992 Maplin Catalogue(stock code YB23A). If you are construct-ing your own, it should incorporate a +12V regulator, such as the p.A78M12UC(stock code QL29G). Please note that theVideo Box is NOT reverse -polarityprotected, and so damage will occur tothe circuit if the power supply connec-tions are reversed. Secondly, if an inferiorvideo signal is fed into the unit then apoor quality signal will be produced. Thiscan result in a dim, fuzzy and possiblyunstable picture on the monitor screen.

The main function of the Video Box isto provide the ability for fading thepicture information down to a blankscreen. This effect can be used as a 'fade-in' or 'fade-out' on dubbed recordings(e.g. camcorder to VCR), !ending a moreprofessional appearance to your videoproductions. The whole picture, but notthe sync, can be suddenly switched onand off by operating the video defeatswitch, S5. The output defeat switch, SI,can appear to have a similar effect, but asit switches off all the signal components,your video equipment can take sometime to re -synchronize to the signal.

Two additional video effects havebeen provided for. When operated, thepicture inverse switch, S3, produces a'negative' image. This unusual effect hasoften been exploited by pop video andsci-fi film makers. The colour burst defeatswitch, S4, should have the effect ofturning off the colour circuits within yourvideo equipment. This function is com-monly referred to as the 'colour -killer'circuit (as discussed earlier), and whenactivated has the effect of producing ablack -and -white picture It is unlikely thatyou will ever need to use the sync defeatswitch, S2, as this removes the compositesync from the video signal. However, ifthe Video Box is used as part of a largervideo system, it may be necessary toswitch off its own recovered sync, orpossibly feed in external sync.

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Modification toVideo BoxIt has recently been reported that whenusing the Video Box with certain VHSvideo recorders, a colour shift ordistortion to the picture may be notice-able. To correct this, the followingmodification should be implementedwhen first building, or to update, your kit.

Add a 47µH Choke (Order CodeWH39N) in series with resistor R21; seeFigure 1. As there is no physical positionon the PCB for this additional component,it must be fitted as shown in Figure 2.De -solder, and lift out of the board thelead of R21 nearest to the edge of thePCB. Next, insert the choke and solder itin place. Finally, solder the free end ofR21 to the free end of the choke.

S

.1 I

Figure 1. Modified circuit. Figure 2. Positioning the choke.

VIDEO BOX PARTS LISTRESISTORS: All 0.6WRI 8211R2 6k8R3,29,32,33,35,36,39,41 10kR4,24,42 47011R5,6,7,13,14,16,21,22,28,43R8,11,27,40R9R10R12,34,38,44R15,23R17R18R19R20,25R26R30R31R37,46R45RV1,2RV3RV4-6

CAPACITORSC1,9,14,17,18,20,21,27C2,3,4,10,11,15,19,22C5,13C6C7,8,24C12C16C23C25C26VC1

1% Metal Film (Unless specified)1 (M82R)1 (M6K8)

lk2k756011560k4k7220111k5390112k2100112701115011

8201115k27klk Hor Enclosed Preset10k Min Pot Lin22k Hor Enclosed Preset

100nF 16V Minidisc

47p.F 25V PC Electrolytic22pF Polystyrene560pF Polystyrene100nF Poly Layer100pF Polystyrene68pF Polystyrene470µF 16V PC Electrolytic680pF Polystyrene2n2F Polystyrene65pF Trimmer

SEMICONDUCTORSIC1 LF351IC2 LM1881NIC3 74HC4066 (12V)IC4 4042BEIC5,6 4011BETR1,2,3,4,6,8,10 BC184LTR5,9,11 BC214L

8 (M1OK)3 (M470R)

10 (M1K)4 (M2K7)1 (M560R)1 (M560K)4 (M4K7)2 (M220R)1 (M1K5)1 (M390R)1 (M2K2)2 (M100R)1 (M270R)1 (M150R)1 (M820R)2 (M15K)1 (M27K)2 (UHOOA)1 (JM71N)3 (UH04E)

8 (YR75S)

8 (FF08J)2 (BX24B)1 (BX33L)3 (WW41U)1 (BX28F)1 (BX27E)1 (FF15R)1 (BX34M)1 (BX37S)1 (WL72P)

1 (WQ30H)1 (UL75S)1 (UF 10L)1 (QX19V)2 (QX05F)7 (QB57M)3 (QB62S)

TR7 BF244AD1,2,4,5,9,10,11 1N4148D3,6,7,8 BAR28

MISCELLANEOUSLD IPL1,4,5,6,7PL2,3

LED Red2 -Way Latch Plug10 -Way Latch Plug2 -Way Latch Housing10 -Way Latch HousingLatch TerminalMiniature Coax10 -Way Ribbon CableTC Wire 0.71mm 22swg8 -Pin DIL Socket14 -Pin DIL Socket16 -Pin DIL Socket47µ.H ChokePCBInstruction LeafletConstructors' Guide

OPTIONAL (Not in Kit)RV3 10k Min Slide Pot Lin

Slide Knob BKr.ob K14BLED Clip 5mmSPST Ultra Min ToggleAC Adaptor RegulatedABS Console M6006BNC Round Socket 7511Panel Mount Power Socket 2.5Self Tap Screws No.4 x

1 (QF16S)7 (QL80B)4 (QQ13P)

1 (WL27E)5 (RK65V)2 (RK66W)5 (HB59P)2 (FY94C)3 (YW25C)lm (XR88V)lm (XR06G)1 Reel (BL14Q)2 (BL17T)3 (BL18U)1 (BL19V)1 (WH39N)1 (GE85G)1 (XTO4E)1 (XH79L)

1 (JM85G)1 (YGO9K)1 (FK39N)1 (YY40T)5 (FH97F)1 (YB23A)1 (LH66W)2 (FE31J)1 (JK1OL)1 Pkt (FE68Y)

The Maplin 'Get -You -Working' Service is availablefor this project, see Constructors' Guide or current

Maplin Catalogue for details.The above items (excluding Optional) are available

as a kit, which offers a saving over buyingthe parts separately.

Order As LP48C (Video Box Kit).Please Note: Where 'package' quantities are stated in thePans List (e.g., packet, strip, reel, etc.), the exact quantity

required to build the project will be supplied in the kit.

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