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Learn How Your Car’s Airflow Sensor Works $4.50 NOVEMBER 1993 NZ $5.95 INCL GST SERVICING – VINTAGE RADIO – COMPUTERS – AMATEUR RADIO – PROJECTS TO BUILD : s i h t d l i Bu JUMBO CLOCK High-Efficiency Inverter For Fluorescent Tubes ➥ Operates 18W or 36W tubes from a 12V battery & is ideal for emergency lighting or as part of a solar installation • Siren Sound Generator: Fire, Police & Ambulance • Building The Stereo Preamp With IR Remote Control • Review: Tektronix TDS 544A Colour Oscilloscope November 1993  1 REGISTERED BY AUSTRALIA POST – PUBLICATION NO. NBP9047 Vol.6, No.11; November 1993 FEATURES FEATURES   4 Electronic Engine Management, Pt.2 by Julian Edgar Airflow measurement THIS JUMBO CLOCK uses giantsized (70mm-high) LED displays & has battery backup, AM/PM indication & automatic display dimming at night. Find out how it works & how to build it by turning to page 16.   8 Review: Tektronix TDS 544A Colour Oscilloscope by L. Simpson Four channels & a sampling rate of 1 gigasample/sec 53 The World Solar Challenge by Brian Woodward Technology & the latest solar-powered racers 72 Review: Epson’s Stylus 800 InkJet Printer by Darren Yates Seven resident fonts plus 360dpi graphics capability 80 Review: The Autoplex Unimeter by Darren Yates Multi-function instrument interfaces to a PC PROJECTS PROJECTS TO TO BUILD BUILD BOASTING AN EFFICIENCY of better than 80%, this inverter circuit is designed to operate either 18/20W or 36/40W fluorescent tubes from a 12V battery. Construction starts on page 26. 16 Build A Jumbo Digital Clock by Darren Yates New clock has giant-sized LED displays 26 High Efficiency Inverter For Fluorescent Tubes by John Clarke Use it for camping, emergency lighting or in a solar installation 56 Stereo Preamplifier With Remote Control, Pt.3 by John Clarke All the construction details 64 Build a Siren Sound Generator by Bernie Gilchrist Simple circuit generates police, fire engine & ambulance sounds SPECIAL SPECIAL COLUMNS COLUMNS 34 Serviceman’s Log by the TV Serviceman Keeping within the customer’s budget THIS SIMPLE PROJECT uses just one IC & a couple of transistors to generate three siren sounds: police, fire engine & ambulance. It is powered from a single 1.5V cell & is ideal for games & models – see page 64. 42 Remote Control by Bob Young Preventing damage to RC transmitters & receivers 70 Computer Bits by Darren Yates More experiments for your games card 82 Vintage Radio by John Hill The vexed question of originality DEPARTMENTS DEPARTMENTS   2   3 40 69 86 Publisher’s Letter Mailbag Circuit Notebook Order Form Product Showcase 90 92 95 96 Back Issues Ask Silicon Chip Market Centre Advertising Index AIRFLOW MEASUREMENT is an important function in electronic engine measurement. In Pt.2 of our series this month, we discuss the various types of airflow sensors – details page 4. November 1993  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Marketing Manager Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 1a/77-79 Bassett Street, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER The Australian Very Fast Train We have been pleased to read that the Australian fast train proposal is about to get another run and has been given support by the Federal Minister for Industry, Mr Griffiths. Let us hope that the new consortium, called Spreedrail, does not get bogged down as did the original VFT proposal. It soured because the consortium members were apparently more concerned with being able to profit from land development along the VFT corridor than with the economics of the proposal itself. If similar attempts are made to gain special tax treatment for this new proposal then it deserves to fail again. Apart from that, it seems as though the public do support the concept of an Australian fast train. It would greatly speed traffic between our capital cities and would be an overall plus for the environment, especially when compared with an equiv­alent expansion of aviation and road transport. The initial $2.4 billion proposal is for a link between Sydney and Canberra with a travelling time of just over an hour. Then the system would be extended to Brisbane, Melbourne and Adelaide, in that order. There is no doubt that the fast train proposal is technically feasible. It is to be based on the proven and very successful French TGV and the Speedrail consortium is headed by GEC Alsthom which manufactures the TGV. So the technical exper­tise is there, both Australian and overseas-based. The big problem will be in getting the system off the ground and with a minimum of government involvement, although that is probably a vain hope. And once the project is under way, all parties involved will need to devise methods of running it which will circumvent the many inefficiencies which bedevil our existing rail transport systems – a 100+ year old legacy of state government insularity and selfishness, hidebound bureaucracies and unions who are concerned only about survival. If the old ways of working are allowed into the fast train system, it will be a finan­cial disaster. This need not be so. Australians have an excellent record for bringing large projects to completion on time and under budget and then running them as efficiently as anywhere in the world. Our large mineral projects are enough evidence of that. Let us hope that this excellence is brought to bear in the Australian fast train project. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG Making PC boards with a photocopier After reading a letter on making PC boards with a photocopier in the May 1993 issue, I resolved to give it a go and have finally managed to get around to it. Here are a few comments on my efforts. I followed closely the procedure in the letter. Unfortunately for me, only about 40% of the toner transferred from the plastic to the copper. So I varied the idea a little by using an iron (clothes) and using a technique similar to that used for iron-on clothes patches or tee-shirt transfers. Make a photocopy of the circuit design onto a piece of special thermal photocopier plastic (component side, so invert most magazine diagrams). Put something flat and rigid onto the ironing board (to stop movement), then on top of that put the blank PC board (copper side up), and put the plastic transparency on top of the copper. Put a piece of material over the plastic to act as a pressure pad and so the plastic doesn't melt onto the iron. With the iron at its hottest temperature, iron away! Stop ironing when the material starts to tinge. Carefully take the PC board with the transparency still attached and dip it into cold water to cool it down. Peel the transparency off the board. Hopefully there will be nothing much on the transparency and some nice black tracks on the copper. You will definitely need your etch resistant pen to touch up though. I have had about 80% transference. Now just put the board into the ferric chloride (or whatever you use) and let it etch. During the ironing process, make sure the transparency doesn't slide about or you will smear the tracks all over the place. Use a firm pressure on the iron. If a few more people experiment with this idea, perhaps someone will find a compound that can go in between the plastic and the copper and facilitate the toner transfer. On another subject, what do you do with old ferric chloride? I would like to dispose of it in a fashion that has least impact. A look through the Newcastle Yellow Pages in the waste disposal section and a few phone calls to some of the listed waste disposalists didn't help much. D. Burke, North Lambton, NSW. Comment: We agree that the disposal of spent ferric chloride is a problem and perhaps the best approach is to contact your local municipal council. They generally can accept it, either on particular clean-up days at designated depots, or you may be able to hand in a sealed container at your local tip. Error in battery status monitor The circuit in Circuit Notebook, page 16 of the July 1993 issue of Silicon Chip looks very useful. However, in this item Mr. Ritson refers, in the first line of the second column, to "The 560W resistor" but fails to show one in his circuit. Nor is there a 560W resistor in the original circuit in the March 1990 issue. I would be grateful if you would insert a correction in the magazine. A. J. Lowe, Bardon, Qld. Comment: the live common with pin 16 of IC1 should go to +Vcc, then all the LEDs are connected to +Vcc via a common 560W resistor. Live & dead chassis It has come to our notice that the Serviceman article in the October 1993 issue of Silicon Chip has made a mistake in the identification of the following TV sets: National Panasonic models TC-48P10 and TC-1480A. The Serviceman states that both these models are the M15D chassis, when in actual fact they are both M15L chassis. As he explains, "D" for dead and "L" for live – could be disastrous. We are in the business of producing a fault finder library, as our advertisement in your magazines states. Our sources are the National office in Brisbane and Hi Country Service Data, Cooma, NSW. Keith Jakins, Technical Applications, Kenmore, Qld. Comment: the Serviceman has admitted his mistake on page 34 of this issue. It came about partly because he tests and repairs all sets using an isolation transformer. D & K WILSON ELECTRONICS Have you found those components yet? We know that it can be difficult, frustrating and a waste of your valuable time. So why haven’t you contacted us? We specialise in hunting down and locating components – old, obsolete, leading edge, normally available but now scarce due to allocation by overseas manufacturers. Integrated circuits, resistors, capacitors, transistors, diodes, valves, varistors, etc. Any brands Let us save your valuable time Contact us now on 833 1342 We are also distributors for Electrolube lubricants and chemi­cals Hakko - desoldering & soldering irons; SMD tools; replacement parts NTE - replacements semiconductors 2/87a Queen St, St Marys, NSW 2760. Phone (02) 833 1342 Fax (02) 673 4212 AUDIOPHILES! Now high audiophile quality components & kits are available in Australia. Buy direct & save. *Kimber, Wonder, Solen & MIT Capacitors *Alps Pots *Holco resistors *High Volt. Cap. *Gold Terminals & RCA *WBT Connectors *Kimber Cables * Interconnect Cables *Output Transformers (standard or customised) *Power Transformers *Semiconductors *Audio Valves & Sockets *Wonder Solder *Welborne Labs Accessories Valve & Solid State Pre-Power Amplifier Kits *Contan Stereo 80 Valve Power Amp. (As per Elect. Aust. Sept. & Oct. ’92) *Welborne Labs Hybrid Preamp. & Solid State Power Amplifier Send $1.00 for Product Catalog PHONE & FAX: (03) 807 1263 CONTAN AUDIO 37 WADHAM PARADE MT. WAVERLEY, VICTORIA 3149. November 1993  3 Electronic Engine Management Pt.2: Airflow Measurement – by Julian Edgar One of the fundamental parameters which an electronic engine management system must sense is the mass of air passing into the engine. If the Electronic Control Module (ECM) cannot measure airflow, then the amount of fuel that must be added cannot be determined. Use of engine revs (rpm) is insufficient, because the engine may be on the over-run – for example, when driving down a hill with a closed throttle. Even using the throttle position switch (which senses throttle plate opening) in conjunction with rpm is not sufficient to provide accurate airflow data, because actual engine load will not be indicated. Instead, airflow monitoring is carried out by a specific device designed to measure either air mass flow or air volume flow in conjunction with air The vane-type airflow meter is common in early engine management systems & is still currently fitted to some engines. The damping chamber is the curved extension in the foreground. 4  Silicon Chip temperature. Other systems look at the manifold vacuum (or boost) and calculate the airflow indirectly from this variable. Vane airflow meters The vane airflow meter is one of the oldest airflow sensors employed in engine management systems. Developed by Bosch (as almost all engine management technology has been), the vane airflow meter is common on engines made from about the mid 1970s to the present. The vane airflow sensor (Fig.1) consists of a pivoting flap, which obstructs the engine’s combustion airflow when the engine is not running. Once the engine starts, a low air pressure is experienced on the upstream side of the vane, causing the flap to open a small distance. As the throttle is opened further, the flap is deflected to greater and greater openings. To prevent the flap from overshooting its ‘true’ position, another flap is connected at right-angles to it. This secondary vane works against a closed chamber of air, thus damping the motion of the primary sensing flap. Mechanically connected to the pivoting assembly is a poten­tiometer, usually comprising a series of carbon resistor seg­ments. As the vane opens in response to airflow, the wiper arm of the potentiometer moves across the AIR STACK STEADIES SENSOR PLATE DAMPER CHAMBER COMPENSATION PLATE AIR FLOW Fig.1: a vane type airflow meter. A potentiometer connected to the pivoting vane assembly is used to vary the output voltage from the meter in response to air flow. segments, changing the resist­ance. A regulated voltage is fed to the airflow meter and so, as the vane moves in response to airflow variations, the output voltage from the meter also changes. A spiral spring with an adjustable preload is used to relate the angle of the flap to the airflow and to ensure that the flap closes when no airflow is present. A by­pass is also constructed around the measuring flap. Air movement through this bypass passage is controlled by an adjustable screw, giving control over idle mixture. A vane-type airflow meter measures just the volume of air passing through it, rather than the air’s mass. It’s the mass of the air which is important in determining the appropriate amount of fuel to be added, however. Because the temperature of the combustion air affects its density, temperature sensing is there­fore also built into the airflow meter. Temperature sensing of the airflow is carried out using a thermistor which is located within the main body of the airflow meter. Typical resistance values for this sensor are 2-3kΩ at 20°C, falling to 0.1-0.4kΩ at 60°C. In practice, vane-type airflow meters will operate well for long periods of time. The exception to this is if they experi­ence an engine backfire. This shouldn’t happen in a properly tuned engine-managed car but is a possible scenario when carrying out EFI modifications or running on LPG. A backfire will often slam the vane shut with such force that it distorts the aluminium casting, subsequent- This view shows what’s inside the base of a vane-type airflow meter. The carbon resistor segments are clearly visible (the black rectangles), while below it the spiral spring can be seen inside the tension pre-load wheel. ly causing binding when the flap is deflected by the airflow. When operating properly, the flap should move through its full travel with only light finger pressure. Hot-wire airflow meters The major disadvantages of the vane-type airflow meter are that it senses air volume instead of mass and it restricts the airflow, both because of the need to displace the moving flap and because the cross-sectional area of the flow-path is generally small to increase flow velocity. The next Bosch invention – the hotwire airflow meter – overcomes these disadvantages. Used in engines built BYPASS AIR METERED AIR SAMPLE SEAL AIR FILTER ELEMENT SEAL AIR FILTER CASE AIR INLET AIR-FLOW SENSOR (ULTRASONIC) Fig.2: basic construction of an ultrasonic airflow sensor (Mitsubishi). November 1993  5 The temperature sensor is at the front of the vane airflow meter. The rectangular flap behind it is the vane, shown here in the rest position. from about 1985 to present, it’s the most common type of airflow sensor currently used. The hot-wire (or mass sensing) airflow meter uses a Wheat­stone bridge circuit – see Fig.4. A very thin (0.07 mm) platinum wire is formed into a triangular shape and is suspended within the combustion airflow. The platinum wire forms one arm of the bridge and is maintained at a constant temperature. As the mass of air passing the wire increases, the wire is cooled and its resistance drops. The heating current now imme­ diately increases in response to the bridge becoming unbalanced and returns the wire to its original temperature, thus restoring the balance. The greater the heating current required, the great­er the voltage drop across a resistor which is in series with the platinum wire. The voltage drop across this resistor is therefore related to the rate of airflow into the engine. Very quick response – in the region of milliseconds – is gained using this system. Because resonant pulsing is a potential problem in the airflow meas- urement of reciprocating engines, this very fast reaction time is important. A platinum-film resistor is used for temperature compensation, with quick reaction from this device also needed for accuracy. To make sure that the platinum wire remains clean, it is heated to red-hot for one second each time the engine is switched off. This action burns off any dirt or other contamination which may have settled on the wire. A potentiometer is placed within the bridge circuit to allow idle mixture variations to be set. In some applications, the platinum wire is replaced with a hot-film resistor. Hot wire airflow meters should last for ever under normal operating conditions. Physical interaction with the platinum wire will cause damage and so screens are placed at each end of the meter by the manufacturer. A massive backfire will also destroy the meter. I’ve seen one totally wrecked with a huge nitrous-oxide and turbo induced explosion! Karman Vortex meters Used solely in Mitsubishi vehicles, the Karman Vortex air­ flow meter (Fig.2) is also one of the few engine management devices not invented by Bosch! In this type of airflow meter, vortices are generated in the air as it flows past vortex generators. The frequency of these vortices is related to the volume of air passing through the meter. Ultrasonic waves are used to measure the frequency of the generated vortices. These are propagated at right angles to the airflow and are detected by an ultrasonic receiver located on the other side of the tube. Various receivers, amplifiers and pulse shapers are then used to give an output signal which is interpreted by the ECM. For performance applications (on turbo Mitsubishis, for example) the meter can be replaced by a rewritten software pro­ gram within the ECM. This can be done because the airflow meter is utilised by the ECM only at low throttle angles. MAP sensor Manifold Absolute Pressure (MAP) sensing is used in place of an airflow meter is some systems & has the advantage of not causing any restriction to intake airflow. This photo shows a Holden MAP sensor. 6  Silicon Chip A manifold absolute pressure (MAP) sensor can also be used to derive airflow. When the throttle valve is near shut with the engine running, a high negative pressure is present in the manifold (or plenum chamber as it The MAP sensor & its associated assembly is usually mounted on the firewall. The tube connected to the sensor goes to the plenum chamber to sense manifold pressure, while the small cham­ber is for damping pressure pulses. more usually is in an EFI car). As the throttle opening increases, the pressure approaches atmospheric and, in a turbo car, the manifold pressure can then go on to become positive. Thus, the manifold pressure will have a direct relationship with the combustion airflow. MAP sensors work in one of two different ways: (1) either as a variable capacitor with the plates being moved closer to­gether under greater air pressures, or (2) as a strain gauge which forms part of a Wheatstone bridge. While MAP-sensing tends to be used more on simple engine management systems (like single point injection systems), all of the programmable aftermarket injection systems (Autronic, Motec, etc) also use this approach to airflow sensing. Top racing cars – like the current Group A Touring Cars – are therefore using MAP sensing in conjunction with throttle opening and rpm to sense load. One convincing argument for MAP sensing is that, when the throttle is quickly opened, the ECM can start supplying more fuel and/or different ignition advance before the engine rpm (and therefore airflow) starts to rise. In other words, ECM reaction to quick changes can be faster. Because the MAP sensor derives its pressure sensing from a small-bore tube connecting it to the plenum VORTEX STABILISER PLATE FILTER TRANSMITTER VORTICES VORTEX POLE AIR RECEIVER MODULATOR TO ECU Fig.3: an ultrasonic airflow meter works by measuring the frequency of the vortices generated as the air flows past a vortex pole. Fig.4: external view of a hot wire airflow meter. chamber, sensing airflow in this indirect manner causes no restriction on intake airflow. A mixture of hardware and software is now available which allows the replacement of restrictive vane airflow meters with a MAP sensor. This is especially useful in high performance, naturally aspirated engines. That’s all for this month. In Pt.3 of this series, we will take a look at how an engine management system can be modified by changing the software in SC the main memory chip. November 1993  7 Equipment Review Tektronix TDS 544A colour oscilloscope Tektronix has long been regarded as one of the leaders in oscilloscope technology & it has confirmed its position with the release of the model 544A & 644A digitising oscilloscopes. We recently reviewed the 544A, a 4-channel model with 1 Gigasam­ple/second sampling rate, 500MHz bandwidth & a colour screen. By LEO SIMPSON New developments in digital scopes continue to come thick and fast but with the release of these colour scopes, Tektronix has changed the whole ball game. Just as colour has made a huge difference to the way in which we use computers then so it will be with oscilloscopes, particularly multi-channel models which display so much information on the screen. That really sums up the reason for having colour. If you are using a scope mainly just to display one or two chan­nels and you don’t use a lot of the on-screen measurement cap­ability of a modern digital scope, then you probably don’t need colour. But if you are displaying two or more channels plus a lot of on-screen information and perhaps even with FFT (spectrum analysis), then colour can make a world of difference. Consider for a moment the situation if you are displaying two channels on a typical CRT readout scope. As well as the traces themselves, the scope will usually display the vertical attenuator settings for both channels, timebase settings (main & delayed) and possibly also the trigger conditions. Possibly you will also have horizontal and vertical cursors and that usually implies voltage or time measurements too. And if you select other measurements as well, the screen can end up being a mass of confusion, particularly if some of the digital information is over-writing the traces. In a normal scope, the only way to reduce the confusion is to get rid of the digital on-screen information but with the Tektronix colour scopes you don’t have to. Not only is each channel trace displayed in a different colour but the digital information relevant to each channel is displayed in the same colour as the relevant trace. This makes an enormous difference in interpreting what is going on. Colour also lets you overlap traces and still be easily able to distinguish between them. This can be really helpful when you have pulse waveforms that are almost impossible to distinguish when the traces overlap. How the colour is added The Tektronix TDA 544A is a 4-channel 500MHz oscilloscope with a 1 Gigasample/second sampling rate. The addition of the colour display makes a dramatic difference to the way in which informa­tion can be shown on the screen. 8  Silicon Chip While the addition of colour to an oscilloscope may seem a radical enough feature in itself, the way in which it has been incorporated to these new scopes is even more radical. If you have read any of our reviews of the new digital scopes in Fig.1: this is a screen showing the Snapshot – demonstrating all the automatic measurements possible except for phase & delay (with respect to another channel). These measurements apply to the 48kHz sine waveform shown in Fig.2. the last two years or so, you will already know that most of these do not use a conventional cathode ray tube with electrostatic de­flection and PDA (post deflection acceleration) for fast writing speeds. Nor do digital storage scopes use expensive storage CRTs. Instead, all the analog signals fed to the channel inputs are sampled and converted to digital values. After that they are converted to be displayed on a raster-scanned CRT (cathode ray tube) in exactly the same way as on a computer monitor. In fact, some digital scopes can be connected to a VGA computer monitor to take advantage of a larger screen size. So you could be forgiven for thinking that Tektronix has incorporated colour into these new scopes by employing the equiv­alent of a VGA colour screen and whatever electronics are required to drive it. But you would be wrong. The Tektronix 544A (and 644A) does in fact employ a monochrome raster scanned CRT but the colour is added by a liquid crystal shutter in front of the screen. The CRT provides the video or luminance information while the LC shutter provides the colour. This is quite a differ­ent approach to that used by, say, LCD video projectors such as the Sanyo PLC-200P reviewed in the March 1993 issue of SILICON CHIP. Those units use a metal halide projector lamp, dichroic mirrors and three LCD panels to provide the red, green and blue pixel information. Fig.2: this is the waveform referred to in Fig.1 but shown with variable persistence. This is depicted as a spectral colour display with red showing the most frequently occurring parts of the waveform. Other colour persistence palettes are available, including greyscale. In these new scopes, they use the Tektronix patented Nucolor liquid crystal shutter. The shutter is an electrically switchable colour filter made up of two fast liquid crystal optical switches known as “pi cells” plus a combination of colour and neutral polarising filters. A colour screen is produced by having the CRT sequentially produce the red, blue and green video information on the screen while the LC shutter is switched to transmit red, blue and green respectively. Alternate video fields, viewed through the switched coloured filters, thereby create full colour images with a maximum of 256 colours. In more detail, a video frame for the Tektronix LC shutter has three fields – red, green and blue. The frame rate is 60Hz while the field rate is 180Hz. The horizontal scan rate is 91kHz. LC shutter advantages The advantages over a conventional triad or vertical slot shadow mask CRT include higher screen resolution, much greater contrast (up to 100:1), no convergence or purity problems and high colour saturation. In addition, the system is more rugged than a shadow mask tube. Of course, this is not the first time that liquid crystal shutters have been used to produced different coloured traces on a scope (Tektronix did it several years ago) but the Nucolour system is greatly refined and produces a much higher contrast than was achieved previously. If colour was the only new feature of the TDS 544A it would be most worthy of review but this scope is loaded with features that will make other scope manufacturers sit up and take notice and these are in addition to the awesome sampling rate of 1 gigasample/ second or the resulting bandwidth of 500MHz. It is a full 4-channel scope with sensitivity adjustment avail­able on each channel, from 1mV/div to 10V/div (or 10mV to 100V/div with 10:1 probes). Vertical sensitivity can be adjusted in the usual 1,2,5,10 sequence or continuously, using the Fine­scale softkey. The timebase is impressive, variable from 10 seconds/div to 500 picoseconds/div. That is a range of 2 to 1010! Vertical accuracy is quoted as ±1% while timebase accuracy is an in­ credible ±.0025%. While some recent digital scopes have tended to be smaller and lighter than their analog cousins, this new model from Tektro­nix is fairly bulky and heavy. Its overall dimensions are 420mm wide, 195mm high and 415mm deep. It weighs about 12.3kg, depend­ing on options. The screen size is 140 x 115mm, although the active screen is somewhat smaller than this. The scope has a very large fan on the side of the case and yes, it is fairly noisy although it is hard to see how that can be reduced. After all, the case is absolutely chocka-block with electronics. User interface One very attractive feature is the November 1993  9 This photo shows the Tektronix TDA 544A scope connected to a VGA monitor. While the reproduction may not fully show the dif­ference, the scope display is much sharper & has much better contrast. user interface, the system of menus and softkeys which make a complex instrument such as this easy to use. Without the system of softkeys (12 keys, below and to the left of the screen) it would have been impossi­ble to provide all the functions which are available. Tektronix has improved on the system which is used in the TDS 320 model (reviewed in the July 1993 issue of SILICON CHIP) by adding help screens for just about every function. These are displayed (white text on a blue screen) in much the same way as the help screens for the better software packages. So if you’re lost in the labyrinth of automatic test func­tions, just hit the HELP button followed by the function button you’re about to use and the screen pops up with an explanation. What a revelation! Triggering from everything Also very fancy is the selection of triggering functions you can have, particularly as far as video waveforms are con­cerned. The basic trigger choice is between edge triggering, logic triggering, pulse triggering or video triggering and as you might expect with an instrument of this calibre you can trigger on video line in a frame. Video formats supported are PAL, NTSC, SECAM and HDTV (including Japanese, US and European formats) but if you want 10  Silicon Chip something else such as CGA, VGA or something more exotic you just select FLEXFORMAT with one of the softkeys at the bottom of the screen. You can then program in the parameters of the video format you want: sync pulses, frame rate, number of fields, number of lines and so on. Thus, the TDS 544A can cover any video format, even those that have yet to be thought of. You can also trigger off any line in a video frame, using the numeric keypad or the select knob. Nor is the comprehensive video triggering necessarily the highlight of the seemingly dozens of triggering options. If you select pulse triggering, for example, you then decide to nominate the width of pulses to trigger on or ignore and you can also select glitch or “runt” triggering. Many readers will be familiar with glitch triggering and the TDA 544A can be programmed to specify the width and polarity (negative, positive or both) to accept or reject. The TDA 544A can trigger on glitches as short as two nanoseconds. Runt triggering So what is “runt” triggering? A runt is a pulse which is not up to scratch. Say you have pulse train in a circuit with an amplitude of 6V but every now and again the circuit fails to operate properly. You suspect it may be due to a pulse of insuf­ficient amplitude but with an ordinary scope that is all you can do – have your suspicions. With the TDA 544A, you can program it to look for the runt! You do this by programming in the thresholds which can be positive or negative. How can runts occur? One possibility is from an AND gate where two or more inputs change simultaneously. Finally, the TDA 544A has logic triggering whereby it can trigger on logic state (high or low, or for logic conditions which you define). For example, you could select an AND condition for the four input channels and the scope would then trigger on a true or false condition, again selected by you. You can also select for OR, NOR and NAND conditions. Measurement options As with many other digital scopes these days, the TDA 544A provides for a wealth of automatic measurement functions which can be brought into play by pressing the softkeys. Parameters such as frequency, period, risetime, fall time, duty cycle and so on are routine. All you need is a stable waveform and the relev­ant part of the waveform displayed. For example, the scope will not reliably measure frequency unless you have at least one cycle of the waveform displayed. And if it cannot measure the parameter reliably, it will tell you. But with so many measurement possibilities it can be a real pain trying to select the measurement you want, remembering that you can do these measurements for any or all of the four chan­nels. Tektronix has thought of that and by pressing the Snapshot softkey you can bring up all measurements which are possible for a channel, except for delay and phase. The screen shot of Fig.1 demonstrates this together with the relevant waveform in Fig.2. Variable persistence Among the many options for display is one called “variable persistence”. This is used to accumulate waveform dots which appear and disappear over time according to a decay constant which you can select. This can be useful for displaying the way in which a waveform varies over time. However, in this case the colour of the waveform varies depending on its frequency of occurrence. To explain this further, a typical sine waveform with superimposed noise will have a statistical mean waveform exactly corresponding to a sinewave but with deviations due to the noise. In effect, with variable persistence the waveform will “thicken up” due to the noise. However, on the TDA 544A the variable persistence is portrayed as a variation in colour from the most frequently occurring parts of the waveform to those that seldom appear. Thus, depending on the persistence time, you can readily see the effects of random noise, glitches and so on. Nor do you have to settle for one type of colour for variable persistence; you can have three colour palettes. The first of these is “Temperature” whereby the most often occurring waveform is in red ranging down to blue for the least. Or you can have a “Spectral” palette, whereby violet portrays the most common parts of the waveform ranging to red for the least. Or the third pos­ sibility is “Gray Scale” with white for the most down to light grey for the least. Waveforms displayed in variable persistence mode cannot be saved, as one of the Help screens points out, but you can save a printout – see Fig.2. Output options Today’s high end digital scopes cannot be regarded as com­plete unless they have comprehensive facilities for hard copy of waveforms and the ability to be part of a data acquisition sys­tem. To this end, the TDA 544A has a Centronics parallel inter­face (via DB25 socket), serial port, GPIB port and a socket for connection of a VGA colour monitor, to let you take advantage of a large colour screen. The latter is really good in teaching situations although the waveform resolution is not as good as from the scope itself, as you would expect. The TDA 544A also has its own floppy disc drive which you can use for waveform capture or printouts. It is a standard 3.5-inch 1.44MB drive with IBM DOS formatting. It means you can store waveforms for subsequent display on the scope or you can take the data and incorporate it into reports. That is what has been done for the screen shots in this article. The screens have been captured as EPS (encapsulated PostScript®) files and then taken straight into PageMaker® for the page composition. However, there are a wealth of other print formats that can be used including HPGL, TIFF, BMP, PCX and so on. You can also use a range of inkjet, laser, thermal and dot matrix printers. Tektronix Fig.3: a 48kHz sinewave displayed in Hi Res mode whereby the sampling rate is greatly increased to improve display resolution. Note the measurement menu at the right of the screen. Fig.4: this is the TDA 554A’s 1kHz calibration waveform depicted in Hi Res mode & showing one of the triggering menus. Note that triggering can be edge, logic, pulse or video. can even provide for colour printouts with one of their colour print­ers. Reviewing a complex product such as this really does place us in a quandary. No matter how long the review is, there are many features which will either be glossed over or omitted alto­gether. So what we are presenting is really just a brief review. We have not said anything about the FFT feature, programming and the very extensive programming manual. A typical demonstration by one of Tektronix’ sales engineers will take several hours and again, the demo will not show every feature. However, no matter how you look at it, the TDA 544A is a very impressive product which is at the leading edge of technolo­gy. None of this comes cheap of course and nor would you expect it to. Prices range up from around $15,000, depending on the op­tions fitted and supplied. The warranty is three years. For further information on the TDA 544A, contact SC Tektronix Australia Pty Ltd on (008) 023 342. November 1993  11 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Build this Jumbo Digital Clock Do you need a clock with a very large digital display? This Jumbo Clock uses 7-segment LED displays that are 70mm high. It has battery backup, automatic display dimming at night, AM/PM indication & a 12hour display. By DARREN YATES 16  Silicon Chip OK, I admit it. Digital clocks are now so common that you can go down to your local supermarket and pick one up for around $15. So what? Have you ever tried to repair one of those clocks? Do you how they work? Taking the back off won’t give you any clues on either front. You’re just confronted with a single chip (or more often these days, a single blob) and little else. Embedded inside this blob is a single large scale integration (LSI) chip which con­tains virtually the entire clock circuit. You’ll learn more by staring at a blank wall than looking at that blob! However, when you build your own clock, you get a circuit diagram that shows you how it works and, should anything go wrong, you can fix it yourself without too many problems. And by sticking to discrete ICs, you can buy the replacement parts just about everywhere. More importantly, you learn how the clock works. In partic­ular, you learn about counters and crystal oscillators, and about LED displays and how to drive them. It may cost you more to start off with but it’s always money well spent. The odds are that if you have a well-stocked junkbox, then you’ll have many of the parts already. The Jumbo Clock featured here has the added attraction of having very large display digits. It is designed to hang on a wall and can be easily read at distances of 40 metres or more. It’s just the shot for a factory or small business, or any appli­cation that requires a large viewing distance. CRYSTAL OSCILLATOR ÷16384 IC1 ÷2 IC2a ÷60 IC3 TIME SET MINUTES 12-1 CLOCK PULSE IC9b TIME SET HOURS CLK IN AM/PM LATCH IC8b TEN-HOUR COUNT AND LATCH IC8a,IC9a BCD COUNTER 3 IC7 BCD COUNTER 2 IC6 CIN CO BCD COUNTER 1 IC5 Block diagram The main sections of the clock are shown in the block diagram of Fig.1. It uses an accurate frequency reference which is divided down and used to clock a number of BCD counters and a latch. There are three BCD counters in all – two to count the min­utes and one to count the hours from 0-9. All three counters drive 7-segment LED displays via NPN transistor buffers. The latch provides the 10-hour count and drives two seg­ments of a fourth LED display. Let’s go through the block diagram step-by-step and explain how it all works. Basically, you can think of a clock as a specialised coun­ter that increments once every minute. Unlike a conventional counter, it is presettable and has a somewhat unusual count sequence; eg, it counts from 59 to 00 and from 12 to 1. Let’s begin with the section that generates the pulses. These have to be accurate and that means that we can’t use a simple RC-type oscillator to do the job. This type of oscillator drifts with temperature and any frequency variations can trans­ late into quite large errors. DISPLAY DIMMER IC4d Fig.1: the Jumbo Clock uses a crystal-controlled oscillator (IC1) to generate an accurate reference frequency. This frequency is then divided down & used to clock BCD counters IC5-IC7 & a latching circuit (IC8a & IC9a). These in turn drive four 7-segment LED displays, while IC8b drives the AM/PM indicator. What’s needed is a very accurate frequency reference and this has been obtained by using a digital watch crystal. This type of crystal oscillates at 32.768kHz and this is divided down Main Features • Jumbo-sized 4-digit LED read­ out. • • 12-hour operation. • Automatic display dimming at night. • • • AM/PM indication. Separate hours & minutes settings. Crystal-controlled timing. 12VDC plugpack power supply with back-up battery. by 16,384 to obtain an accurate 2Hz square-wave signal. To obtain one pulse every minute, we need a frequency of 0.0166Hz and so our 2Hz signal must be further divided by 120. This is achieved by first passing it through a divide-by-2 stage and then through a divide-by-60 stage. The resulting 0.016Hz signal is fed into counter 1, which is the 0-9 minutes counter. Its carry out (CO) output goes high on the 10th count and clocks counter 2 which counts the tens of minutes. Because the maximum count that the minutes counter can display is 59, we have to detect the 60th count and this is done by checking counter 2’s display driver outputs. When the 60th count is reached, the first two counters are reset and counter 3 is incremented by one. Finally, the CO output from counter November 1993  17 18  Silicon Chip 39pF 22k 12 13 8 CK R 10 D +V1 E C 10 10 330  330  E C +V1 11 9 47k 680  B Q28 BC548 IC8b Q2 BC558 B Q S Q 14 +V1 VC1 5-30pF X1 32.768kHz 10M 11 11 +V1 9 11 5 DP 11 12 f 7 IC4c 8 e 4 3 12 13 +V1 DISP4 SC23-12EWA IC1 4060 16 2 1 R 4 D 5 3 C E +V2 22k Q6 BC558 B +V1 Q3 BC548 B 100k 6 IC8a 4013 3 CK Q S 6 7 Q E C 47k 4 1 D IC2a Q 2 4013 Q 3 CK 7 5 14 5 8 b S 8 c d B 1k 7 E e R f 15 6 g a 2 c b 1 d DISP3 SC23-12EWA e f 4 7x 330  B 7 g CLEN CLK 16 .001 100k .001 9 8 2 1 99 C +V1 10 E CK D 8 S 8 R 10 Q 13 MINUTES S3 .001 D1 1N914 IC9b .001 +V1 11 11 10k 4081 14 6 4 IC4a 5 11 6 1 15 13 12 Q21-Q27 7xBC548 5 DP C 10 12 13 9 CO a IC7 4026 DISEN 7 IC9a 4013 Q 2OUT CK D 3 3 5 9 R Q2B Q3B 14 4 R TIME SET S1 7 CLKA IC3 ENB 4518 Q4A 14 11 10 10 6 16 1k +V1 100pF a 3 c d IC6 4026 B 1k 1 9 7 CLK 15 g 5 6 B 7 4 8 2 1 .001 10 IC4d CLEN R 7x 330  Q14-Q20 7xBC548 11 6 f 1k 1 2 0.1 DISP2 DP SC23-12EWA 2 E C e D2 1N914  33k LDR1 10 12 13 9 b DISEN 16 47k D3 .001 1N914 HOURS S2 12VDC 500mA PLUG-PACK 3 47k 9 8 47k +V1 47k 47k E OUT 5 +V2 a CO +V2 D7 1N4004 2.2k E C C E GND 7812 Q5 C BC337 B Q1 BC548 B Q4 BC558 IN JUMBO CLOCK 10 E C IC4b 3 100 25VW D4 1N4004 1 c d IC5 4026 100k B 8 7 E C e 16 4 2 7x 330  g 1 B 7 R CLEN DISP1 SC23-12EWA 6 f 11 6 DISEN 3 +V1 100pF Q7-Q13 7xBC548 10 12 13 9 b CLK B 100 16VW C E VIEWED FROM BELOW 9V BATTERY BACKUP D6 1N4004 D5 1N4004 9 8 15 2 10 E C V1 I GO +V1 ▲ Fig.2 (left): all the IC numbers on the circuit diagram are directly related to the circuit diagram. IC5 is the 0-9 minutes counter, IC6, the minutes tens counter, IC7 the 0-9 hours counter, & IC8a & IC9a the 10-hour count & latch circuit. These drive the LED displays via transistors Q2 & Q7-Q27. 3 clocks a latch when a count of 10 hours is reached. This latch not only drives the two segments of the fourth LED display but also drives a display latch to give AM/PM indication. It also provides a reset pulse to counter 3 for the transition from “12” to “1” – more on this later. Time setting is achieved by feeding the 2Hz clock signal directly into counters 1 and 3 so that the minutes and hours can be incremented separately. This makes time-setting a breeze. Circuit diagram Fig.2 shows the full circuit details of the Digital Clock. Note that all the IC numbers on the block diagram can be related directly to the circuit diagram. IC5 is the 0-9 minutes counter, IC6 the minutes tens counter, IC7 the 0-9 hours counter, and IC8a & IC9a the 10-hour count and latch circuit. In greater detail, IC1 is a CMOS 4060 14-bit counter and oscillator which has its frequency set by a 32.768kHz watch crystal. A 39pF capacitor provides the correct loading for the crystal to ensure that it operates correctly, while a 5-30pF trimmer capacitor (VC1) allows the crystal frequency to be trimmed slightly so that the clock keeps accurate time. The output from pin 3 of IC1 is the required 2Hz square-wave signal (ie, the crystal frequency is divided by 214). This signal is divided by flipflop IC9a to produce a 1Hz signal on pin 1 which, among other things, is used to flash the two centre decimal points on the display to divide the hours and minutes digits. The 1Hz signal from IC2a is also fed to a divide-by-60 circuit based on IC3, a 4518 dual BCD counter. Both count­ers inside this IC are connected in cascade, with AND gate IC4a used to detect a ‘6’ output from the second counter. Pin 4 of IC4a drives an RC time constant consisting of a 10kΩ resistor and a .001µF capacitor. Each time IC3 reaches a count of 60, pin 4 of IC4a goes high, the capacitor charges and pin 15 of IC3 is pulled high. Thus, IC3 is reset to 00 a short time after the count of 60 is reached. As a result, each time IC3 counts to 60, pin 4 of IC4a briefly switches high. IC4a thus delivers a 0.016Hz pulse train (ie, one pulse per minute) and this signal clocks minutes BCD counter IC5 via D1. Depending on the count, IC5’s a-g segment outputs then drive LED display DISP1 via buffer transistors Q7-Q13 and their associated 330Ω current limiting resistors. Similarly, counters IC6 and IC7 drive DISP2 and DISP3 via transistors Q14-Q27. IC5’s CO output clocks IC6 (the minutes tens counter) on every 10th count, as described previously. It’s here that we strike the first wrinkle. When IC6 reaches a count of six, two things must happen: (1) IC5 & IC6 must both be reset to zero; and (2) a clock signal must be applied to hours counter IC7. As it turns out, we can easily detect the 6th count by monitoring the “b” and “e” outputs from IC6. When a `6' is to be displayed, the “b” output segment is low and the “e” segment output is high. These two conditions only occur together at the 6th count. Thus, on the 6th count, transistor Q1 will be off and pin 8 of IC4b will be high. Pin 9 of IC4b also goes high on the 6th count and thus pin 10 switches high and clocks hours counter IC7 via D2. IC4b then resets IC6 a short time later via the RC delay circuit connected to its output. Because the time constant of this RC circuit is very small, the observer doesn’t see the ‘6’ appear. The output pulse from IC4b is still long enough to clock hours counter IC7, howev­er. Hours counter This is where things start to get a little tricky. That’s because IC7 must cycle from 1 to 9 to 0 (as in 1am-10am or 1pm-10pm), then from 1 to 2 (as in 11am-12pm or 11pm-12am), then from 1-0 again and so on. This sequence is impossible for a 4026 UP counter to do on its own but it can be done by adding a small amount of extra circuitry based mainly on IC9a. We’ll look at this in some detail shortly. IC8 is a 4013 dual D-type flipflop, with IC8a connected as a latch to drive the leading display. Because this display either shows a ‘1’ or is off, segments “e” and “f” are tied together via 1kΩ resistors and driven by the Q-bar output of IC8a via transis­tor Q2. When Q-bar is low, Q2 turns on and the two segments light to show a “1”. Conversely, when Q-bar is high, Q2 and the seg­ments are off. IC8a is clocked by the CO output of IC7. When IC7 reaches a count of 10, its CO output goes high and Q-bar of IC8a goes low, thus turning on Q2 and RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   3 ❏   7 ❏   1 ❏   2 ❏   1 ❏   1 ❏   4 ❏   1 ❏ 23 Value 10MΩ 100kΩ 47kΩ 33kΩ 22kΩ 10kΩ 2.2kΩ 1kΩ 680Ω 330Ω 4-Band Code (1%) brown black blue brown brown black yellow brown yellow violet orange brown orange orange orange brown red red orange brown brown black orange brown red red red brown brown black red brown blue grey brown brown orange orange brown brown 5-Band Code (1%) brown black black green brown brown black black orange brown yellow violet black red brown orange orange black red brown red red black red brown brown black black red brown red red black brown brown brown black black brown brown blue grey black black brown orange orange black black brown November 1993  19 PARTS LIST 1 PC board, code 04108931, 245 x 215mm 1 red Perspex panel, 250 x 220mm 1 3.5mm DC socket 1 12VDC 500mA plug pack 1 PC mount 9V battery holder 1 light dependant resistor (LDR1, Jaycar Cat. RD-3480) 3 pushbutton momentary switches (S1,S2,S3) 4 25mm tapped spacers 4 10mm x 3mm machine screws 1 32.768kHz watch crystal (X1) 1 9V battery 12 PC stakes Semiconductors 1 4060 oscillator/14-bit counter (IC1) 3 4013 dual D flipflops (IC2,IC8,IC9) 1 4518 dual 4-bit BCD counter (IC3) 1 4081 quad 2-input AND gate (IC4) 3 4026 decade counter/display drivers (IC5-IC7) 24 BC548 NPN transistors (Q1,Q3,Q7-Q28) 3 BC558 PNP transistors (Q2,Q4,Q6) 1 BC337 NPN transistor (Q5) 1 7812 3-terminal regulator 4 SC23-12EWA commoncathode 7-segment 70mm LED displays (DISP 1-4) 3 1N914 signal diodes (D1-D3) 4 1N4004 silicon diodes (D4-D7) the “e” and “f” segments of the leading hours digit. Now let’s see how IC7 cycles through its count sequence. As already discussed, clock pulses are applied to IC7 at regular 1-hour intervals via diode D2. Assume for the moment that the time is currently 1:59; ie, IC7 is at a count of “1”. When the next clock pulse arrives, IC7 goes to a count of 2 (ie, we have 2:00 on the displays) and this causes the “2OUT” pin (pin 14) to go low. This low transition is ignored by the clock input of IC9a, since this flipflop can only change state when its clock input goes from low to high (provided its Reset input is low). When the next clock pulse occurs, IC7 goes to a count of “3” and pin 14 of IC7 goes high again. This high is applied to the clock input of IC9a but IC9a ignores the clock pulse on this occasion. That’s because its reset input (pin 4) is held high by the Q-bar output from IC8a. However, when the count in IC8a and IC7 reaches 13, Q-bar of IC8a is low. IC9a thus switches its Q output (pin 1) high on receipt of the clock pulse and this resets both IC7 and IC8a. Q-bar of IC8a now goes high again and turns off transistor Q2 and the leading digit (ie, the leading digit is blanked). At the same time, IC7 is reset to “0”. But we don’t want the hours units display to show “0”; we want it to show a “1” instead. That’s achieved by using the Q-bar output of IC8a to clock IC9b when it switches high to turn off the leading hours digit. When that happens, IC9b’s Q output switches high and feeds a clock pulse to IC7 via D3 to that IC7 immediately advances to a count of 1. IC9b then resets itself almost immediately via the RC time constant on its pin 13 output. In summary then, the hours count­ers (IC7 & IC8a) count to 12 and are reset to 0 on the 13th count. IC7 is then immediately clocked to produce a “1” on the display. This all happens very quickly so that, as far as the observer is concerned, the display goes straight from “12:59” to “1:00”. Q3, IC4c and IC8b are used to drive the AM/PM indicator. Q3 inverts the 2OUT output from IC7 and drives one input of AND gate IC4c, while the Q output of IC8a drives the other input Capacitors 2 100µF 25VW electrolytic 1 0.1µF 63VW MKT polyester 6 .001µF 63VW MKT polyester 2 100pF ceramic 1 39pF ceramic 1 5-30pF trimmer capacitor (VC1) Resistors (0.25W, 1%) 1 10MΩ 1 10kΩ 3 100kΩ 1 2.2kΩ 7 47kΩ 4 1kΩ 1 33kΩ 1 680Ω 2 22kΩ 23 330Ω Where to buy the parts Kits for this project will be available exclusively from Jaycar Electronics Pty Ltd, who sponsored the design. 20  Silicon Chip This view shows the completed Jumbo Clock with the Perspex cover in place. The time-setting switches & the LDR (which controls the display dimming) are at top right. LED BRAKE LIGHT INDICATOR This “brilliant” brake light indicator employs 60 high intensity LEDs (550-1000mCd) to produce a display that is highly visible, even in bright sunlight. The intensity produced is equal to or better than the LED brake indicators which are now included in some late model “upmarket” vehicles. The LED displays used in most of these cars simply make all the LEDs turn on every time the brakes are applied. The circuit used in this unit can perform in this manner and, for non-automotive applications, it can be customised to produce a number of sweeps (110) starting at the centre of the display and with a variable sweep rate. It not only looks spectacular but also attracts more attention. All the necessary “electronics” is assempled on two identical PCBs and the resulting overall length of the twin bargraph dis­play is 460mm. It’s simple to install into a car since only two connections are required: Earth and the brake­ LASER SCANNER ASSEMBLIES These are complete laser scanners as used in laser printers. Include IR laser diode optics and a very useful polygon scanner ( motor-mirror). Produces a “fan” of light (approx. 30 deg) in one plane from any laser beam. We provide information on polygon scanner only. Clearance: $60 400 x 128 LCD DISPLAY MODULE – HITACHI These are silver grey Hitachi LM215XB dot matrix displays. They are installed in an attractive housing and a connector is provided. Data for the display is provided. BRAND NEW units at a low: $40 LASER OPTICS The collimating lens set is used to improve the beam (focus) divergence. The 1/4-wave plate and the beam splitter are used in holography and experimentation. All are priced at a fraction of their real value: 1/4 wave plate (633nM) ..............................$20 Collimating lens sets ..................................$45 Polarizing cube beam splitters ....................$65 GREEN LASER TUBES We have a limited supply of some 0.5mW GREEN ( 560nm) HeNe laser tubes. Because of the relative response of the human eye, these appear as bright as about a 2mW red tube: Very bright. We will supply this tube and a suitable 12V laser power supply kit for a low: $299 CCD ELEMENT BRAND NEW high sensitivity monolythic single line 2048 element image sensors as used in fax machines, optical charachter recognition and other high resolution imaging applications: Fairchild CCD122. Have usable response in the visible and IR spectrum. Supplied with 21 pages of data and a typical application circuit. $30 INFRARED TUBE AND SUPPLY These are the key components needed for making an INFRARED NIGHT VIEWER. The tubes will convert infrared light into visible light on the phosphor screen. These are prefocussed tubes similar to type 6929. They do not require a focus voltage. Very small: 34mm diameter, 68mm long. All that is needed to make the tube light connecting wire. The case for the prototype unit which would be suitable for mounting on the rear parcel shelf, was mainly made from two aluminium “L” brackets that were screwed together to make a “U” section. A metal rod and its matching holders (commonly available from hardware shops) are used for the supporting leg. $60 for both the PCBs, all the onboard components & instruc­tions: the 60 LEDs are included! We also have available a similar kit that does not have the sweeping feature. It produces similar results to the commercial units installed in cars: all the LEDs light up when power is applied. $40 for both the PCBs and all the onboard components. This kit is also supplied with the 60 LEDs and it uses different PCBs, that have identical dimensions to the ones supplied in the above­ mentioned kit. operational is a low current EHT power supply, which we provide ready made or in kit form: powered by a 9V battery and typically draws 20mA. INCREDIBLE PRICING: $90 For the image converter tube and an EHT power supply kit! All that is needed to make a complete IR night viewer is a lens an eyeiece and a case: See EA May and Sept. 1990. ALUMINIUM TORCHES – INFRARED LIGHTS These are high quality heavy-duty black anodised aluminium torches that are powered by four “D” cells. Their focussing is adjustable from a spot to a flood. They are water resistant and shock proof. Powered by a krypton bulb – spare bulb included in cap. $42 Note that we have available a very high quality INFRARED FILTER and a RUBBER lens cover that would convert this torch to a good source of IR: $15 extra for the pair. PASSIVE NIGHT VIEWER BARGAIN This kit is based on an BRAND NEW passive night vision scope, which is completely assembled and has an EHT coaxial cable connected. This assembly employs a high gain passive tube which is made in Russia. It has a very high luminous gain and the resultant viewer will produce useful pictures in sub-moonlight illumination. The viewer can also be assisted with infrared illumination in more difficult situations. It needs an EHT power supply to make it functional and we supply a suitable supply and its casing in kit form. This would probably represent the best value passive night viewer that we ever offered! BECAUSE OF A SPECIAL PURCHASE OF THE RUSSIAN-MADE SCOPES, WE HAVE REDUCED THE PRICE OF THIS PREVIOUSLY ADVERTISED ITEM FROM $550 TO A RIDICULOUS: $399 This combination will be soon published as a project in EA. NOTE THE REDUCED PRICE: LIMITED SUPPLY. Previous purchasers of the above kit please contact us. 24VDC TO MAINS VOLTAGE INVERTERS In the form of UNINTERRUPTABLE POWER SUPPLIES (UPS’s).These units contain a 300W, 24V DC to 240V 50Hz mains inverter. Can be used in solar power systems etc. or for their original intended purpose as UPS’s. THESE ARE VERY COMPACT, HIGH QUALITY UPS’s. They feature a 300W - 450W (50Hz) SINEWAVE INVERTER. The inverter is powered by two series 12V 6.5Ahr (24V). batteries that are built into the unit. There is only one catch: because these NEW units have been in storage for a while, we can not guarantee the two batteries for any period of time but we will guarantee that the batteries will perform in the UPS’s when these are supplied. We will provide a 3-month warranty on the UPS’s but not the batteries. A circuit will also be provided. PRICED AT A FRACTION OF THEIR REAL VALUE: BE QUICK! LIMITED STOCK! $239 ATTENTION ALL MOTOROLA MICROPROCESSOR PROGRAMMERS We have advanced information about two new STATE OF THE ART microprocessors to be released by Motorola: 68C705K1 and 68HC705J1. The chips are fully functional micros containing EPROM/OTPROM and RAM. Some of the features of these new LOW COST chips include: *16 pin DIL for the 68HC705K1 chip * 20 pin DIL for the 68HC705J1 chip * 10 fully programmable bi-directional I/O lines * EPROM and RAM on chip * Fully static operation with over 4MHz operating speed. These two chips should become very popular. We have put together a SPECIAL PACKAGE that includes a number of components that enable “playing” with the abovementioned new chips, and also some of the older chips. IN THIS PACKAGE YOU WILL GET: * One very large (330 x 220mm) PCB for the Computer/Trainer published in EA Sept. 93; one 16x2 LCD character display to suit; and one adaptor PCB to suit the 68HC705C8. * One small adaptor PCB that mates the programmer in EA Mar. 93 to the “J” chip, plus circuit. * One standalone programmer PCB for programming the “K” chip plus the circuit and a special transformer to suit. THE ABOVE PACKAGE IS ON SPECIAL AT A RIDICULOUS PRICE OF: $99 Note that the four PCBs supplied are all silk screened and solder masked, and have plated through holes. Their value alone would be in excess of $200! A demonstration disc for the COMPUTER/TRAINER is available for $10. No additional software is currently available. Previous purchasers of the COMPUTER/ TRAINER PCB can get a special credit towards the purchase of the rest of the above package. PLASMA BALL KIT This kit will produce a fascinating colourful changing high voltage discharge in a standard domestic light bulb. The EHT circuit is powered from a 12V supply and draws a low 0.7A. We provide a solder masked and screened PCB, all the onboard components (flyback transformer included), and the instructions at a SPECIAL introductory price of: $ 25 We do not supply the standard light bulb or any casing. The prototype supply was housed in a large coffee jar, with the lamp mounted on the lid – a very attractive low-cost housing! Diagrams included. LASER DIODE KIT – 5mW/670nm Our best visible laser diode kit ever! This one is supplied with a 5mW 670nm diode and the lens, already mounted in a small brass assembly, which has the three connecting wires attached. The lens used is the most efficient we have seen and its focus can be adjusted. We also provide a PCB and all on-board components for a driver kit that features Automatic Power Control (APC). Head has a diameter of 11mm and is 22mm long, APC driver PCB is 20 X 23mm, 4.5-12V operation at approx 80mA. $85 PRECISION STEPPER MOTORS This precision 4-wire Japanese stepper motor has 1.8 degree steps – that is 200 steps per revolution! 56mm diameter, 40mm high, drive shaft has a diameter of 6mm and is 20mm long, 7.2V 0.6A DC. We have a good but LIMITED supply of these brand new motors: $20 HIGH INTENSITY LEDs Narrow angle 5mm red LED’s in a clear housing. Have a luminous power output of 550-1000mCd <at> 20mA. That’s about 1000 times brighter than normal red LED’s. Similar in brightness SPECIAL REDUCED PRICE: 50c Ea or 10 for $4, or 100 for $30. IR VIEWER “TANK SET” ON SPECIAL is a set of components that can be used to make a complete first generation infrared night viewer. These matching lenses, tubes and eyepieces were removed from working tank viewers, and we also supply a suitable EHT power supply for the particular tube supplied. The power supply may be ready made or in kit form: basic instructions provided. The resultant viewer requires IR illumination. $180 We can also supply the complete monocular “Tank Viewer” for the same price, or a binocular viewer for $280: Ring. MINI EL-CHEAPO LASER A very small kit inverter that employs a switchmode power supply: Very efficient! Will power a 1mW tube from a 12V battery whilst consuming about 600 mA! Excellent for high-brightness laser sights, laser pointers, etc. Comes with a compact 1mW laser tube with a maximum dimension of 25mm diameter and an overall length of 150mm. The power supply will have overall dimensions of 40 x 40 x 140mm, making for a very compact combination. $59 For a used 1mW tube plus the kit inverter. OATLEY ELECTRONICS PO Box 89, Oatley, NSW 2223 Phone (02) 579 4985. Fax (02) 570 7910 MAJOR CARDS ACCEPTED WITH PHONE & FAX ORDERS P & P FOR MOST MIXED ORDERS AUSTRALIA: $6; NZ (Air Mail): $10 November 1993  21 VC1 Q3 100k 1 D3 100k .001 .001 1k 1 1 S2 47k Q6 47k Q1 47k 1 IC6 4026 IC7 4026 IC8 4013 LDR 47k 33k Q4 100pF 9V BATTERY IC4 4081 IC9 4013 S1 100pF 1 D2 100k 10M 39pF D5 D1 10k XTAL .001 1 IC3 4518 .001 .001 1 10k 7812 1 IC2 4013 4.7k D7 IC1 4060 47k I G O D6 1 100uF 22k 100uF D4 S3 IC5 4026 .001 47k DISP4 DISP3 DISP2 Q8 Q7 330  Q9 330  Q10 330  Q11 330  Q12 330  Q13 330  Q14 330  Q15 330  Q16 330  330  Q17 Q5 330  1k Q18 330  Q19 330  Q20 330  Q21 330  Q22 330  Q23 330  Q24 330  Q25 330  Q26 330  Q27 330  680  330  330  Q28 1k Q2 2.2k 22k DISP1 0.1 DC SUPPLY SOCKET Fig.3: all the parts for the Jumbo Clock are mounted on one large PC board. Take care when installing the LED displays, as DISP2 & DISP4 must be installed upside down (see text). Power for the circuit comes from a 12V DC plugpack supply, while a 9V battery powers the timekeeping circuitry during blackouts. (pin 12) of the AND gate. Pin 11 of IC4c thus clocks IC8b every 12 hours to toggle the AM/PM indicator. The AM/PM indicator itself is actually the decimal point on the leading digit. A very simple trick is used so that it appears in the top lefthand corner of the display – the display is in­stalled on the PC board upside down! minutes. The circuit works like this: when S1 is pressed, 2Hz clock pulses from IC1 are coupled through to S2 and S3. If S2 is now pressed, these 2Hz pulses are differentiated by a .0015µF capaci­tor and fed to pin 1 of IC7 to increment the hours display. Similarly, if S3 is pressed, the minutes 0-9 counter is clocked. Time setting IC4d, Q4, Q5 and an ORP12 light dependent resistor (LDR1) provide the automatic dimming function for the LED displays. The LDR and its series 33kΩ resistor form a variable voltage divider, the output of which Pushbutton switches S1, S2 and S3 perform the time setting function. To set the time, S1 (TIME SET) is held down and then either S2 pressed to set the hours or S3 pressed to set the 22  Silicon Chip Display dimming depends on the ambient light level. This output is fed to one input of AND gate IC4d. The other input of IC4d is driven by a 512Hz square-wave signal derived from pin 4 of IC1. If the ambient light level is high, the resistance of the LDR is low and the output from IC4d is also low. Conversely, if the light level is low, the LDR’s resistance is high and IC4d gates through the 512Hz squarewave signal from IC1. IC4d drives PNP transistor Q4 via a 47kΩ base current-limiting resistor. When IC4d’s output remains low (ie, the light level is high), Q4 turns on and thus Q5 also turns on and the displays are driven at a 100% duty cycle to provide maximum brightness. Conversely, when the light level is low, IC4d switches Q4 and thus Q5 on The three time-setting switches are mounted by soldering their pins to PC stakes, as shown here. Make sure that the switches are correctly oriented (flat side to top of board) – see Fig.3. The LDR is mounted with its leads left at full length & can be installed either way around. and off at a frequency of 512Hz. Q5 in turn switches the displays on and off at this frequency to reduce the display brightness. Note that the jumbo-sized 70mm LED displays used in this project have the same pinouts as the smaller types but each segment contains five LEDs in series. This makes it necessary to use transistors Q7-Q27 in order to obtain sufficient display brightness. Power supply Power for the circuit is derived from a 12V DC plugpack supply. The incoming DC is fed via reverse polarity protection diode D4 to a 3-terminal 12V regulator. Two separate supply rails are then derived from the output of the regulator via isolating diodes D5 and D7. The +V1 rail powers all the timekeeping circui­try and the driver transistors for the LED displays, while the +V2 rail powers the dimming circuit which in turn controls common digit-driver transistor Q5. A 9V backup battery is used to supply the timekeeping cir­cuitry if the mains fails. This battery is isolated from the +V1 rail via D6 which is normally reverse biased. When the mains fails however, D6 becomes forward biased and the battery takes over and supplies power to the +V1 rail. During this time, diode D5 is reverse biased and so Q5 is off and the LED 24  Silicon Chip displays are blanked. This was done to conserve the batteries in the event of a long blackout. The LED displays come back on again and show the correct time as soon as the mains power is restored. Construction All the components for the digital clock are installed on a single PC board coded 04108931. Fig.3 shows the parts layout on the board. Before installing any of the parts, check the board carefully for etching defects (eg, shorted or open-circuit tracks). There shouldn’t be any problems here but it’s always best to make sure. When you’re satisfied that everything is correct, you can start construction by installing PC stakes at all external wiring points and at the switch mounting positions. This done, install the wire links, resistors and capacitors. Make sure that the wire links are straight so that they don’t short against other parts. You can straighten the link wire if necessary by clamping one end in a vice and then stretching the wire slightly by pull­ing on the other end with a pair of pliers. The semiconductors can now be installed on the PC board, followed by trimmer capacitor VC1 and the 32.768kHz watch crys­tal. Be sure to use the correct part at each location and check that all parts are correctly oriented. In particular, check the transistor type numbers carefully and note that all the ICs face in the same direction. The 3-terminal regulator is installed with its metal tab towards the adjacent power diodes (see Fig.2 for the pin connection details). LED Displays Now for the four LED displays. These are installed directly on the board but there is a catch – displays 2 and 4 must be installed on the board upside down (ie, their decimal points must be at top left – see Fig.3). The other two LED displays (1 & 3) are installed in the usual manner (ie, decimal points at bottom right). Push all the displays down onto the board as far as they will go before sol­dering their pins. Once the displays are in, the board can be completed by installing the pushbutton switches, the battery holder and the LDR. The LDR can be installed either way around and should be soldered in with its leads at maximum length, so that it sits about 25mm above the board. The three pushbutton switches are mounted directly on top of the previously installed PC stakes. Be sure to orient the flat side of each switch body as shown in Fig.3 and make sure that the are vertical and don’t lean to one side. A red Perspex cover was fitted to the prototype to enhance the appearance of the LED displays and to hide the circuitry. This cover measures 250 x 220mm and is mounted on the board using four tapped 25mm spacers and 3mm screws. You will need to mark out and drill a mounting hole in each corner of the cover, plus clearance holes for the time-setting switches and the LDR. The clearance holes are best made by first drilling small holes and then enlarging them to size using a tapered reamer. SILICON CHIP BINDERS BUY A SUBSCRIPTION & GET A DISCOUNT ON THE BINDER (Aust. Only) Testing These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers and are made from a dis­ tinctive 2-tone green vinyl that will look great on your bookshelf. ★ High quality. ★ Hold up to 14 issues (12 issues plus catalogs) ★ 80mm internal width. ★ SILICON CHIP logo printed in gold-coloured lettering on the    spine & cover. Yes! Please send me ________ SILICON CHIP binder(s) at $A14.95 each (incl. postage in Australia). NZ & PNG orders please add $5 each for postage. Not available elsewhere. Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­_________________________ Card expiry date______/______ Name _____________________________________________________ Street _____________________________________________________ Suburb/town __________________________ Postcode______________ SILICON CHIP PUBLICATIONS PO Box 139, Collaroy, NSW 2097, Australia. Phone (02) 979 5644 Fax: (02) 979 6503. ✂ Now for the smoke test. Connect the DC plugpack supply and switch on – you should immediately get a readout on the displays, although it might not make much sense at this stage. That’s because the 4026 counters can switch on in a random mode and produce incorrect symbols. To correct the displays, all you have to do is press the time setting buttons (ie, Time Set + Hours and Time set + Minutes) until the counters are clock­ ed and revert to a valid condition. If the clock doesn’t work, switch off and check for wiring errors. In particular, check for incorrect parts placement on the PC board and for shorts between soldered joints on the back of the board. If the displays don’t make much sense, check for shorts between the display segments and that the displays have been correctly oriented (displays 2 & 4 must be installed upside down). If all is well so far, connect the 9V battery back-up battery, set the time and switch off the mains power. The display should now go out but the timekeeping circuitry should continue to function. Leave the mains power off for a few minutes, then switch it back on again. The display should now come back on and show the cor­ rect time. Check that diodes D5 and D6 are correctly oriented if you strike problems here. Finally, check that the display dimming feature works by covering the viewing hole for the LDR. The accuracy of the clock can be adjusted by monitoring it over a 24-hour period and tweak­ing VC1 on a trial and error SC basis. November 1993  25 A high efficiency inverter for f luorescent tubes This high efficiency inverter will power either an 18W or 36W slimline fluorescent tube from a 12V battery. It can be used for camping, emergency lighting or as part of a solar powered lighting installation for remote areas. By JOHN CLARKE Fluorescent lighting has many benefits over incandescent lamps. Fluorescent tubes use far less power than the equivalent light output incandescent lamps. They also provide a relatively diffuse light since the light is emitted from a large surface rather than from the virtual point source of a light bulb. Battery powered fluorescent inverters are very common these days. You can find them in small portable lamps, in caravan, bus and boat lighting and in automotive inspection lamps. In most of these, a self-oscillating single transistor inverter steps up the voltage 26  Silicon Chip from the battery to a high AC voltage sufficient to start the tube. Once the tube is lit, the inverter transformer then provides current limiting for safe operation. This is a simple system that works but it does have a few problems. Firstly, these simple inverters are not very efficient. This is because the inverter must provide a very high voltage (usually in excess of 1000V AC) in order to start the tube but only deliver 100V or less once the tube has fired. This means there are considerable losses in the inverter transformer and to a lesser extent in the transistor drive circuitry. Because of this, simple inverters are rarely practical for tubes of more than 20 watts output. Another problem with simple inverters for fluorescent tubes is their lack of voltage regulation. This makes no allowance for the fact that the voltage across a battery falls as it becomes discharged. Consequently, the tube may be over-bright on a fully charged battery and become noticeably dimmer as the battery discharges. A consequence of brute force starting and overdriving when running is shortened tube life. For maximum life, they must be started correctly and some form of regulation must be included to avoid overdriving the tube when the battery voltage is high. Our new inverter design overcomes the above shortcomings and has high efficiency. It can be made to suit 18W and 20W tubes or 36W and 40W tubes. The tube filaments are preheated for cor­rect starting and the circuit incorporates voltage regulation so that the tubes will have long life. Furthermore, MOSFET DRIVERS AND CONTROLLER FEEDBACK START-UP CIRCUIT +340V 12V BATTERY STEP-UP TRANSFORMER AC RECTIFIER AND FILTER The 340VDC is applied to the fluorescent tube driver cir­cuit. This is essentially a free-running oscillator once the tube is running but a start-up circuit is required to allow the tube to fire. The start-up circuit applies a pulse train to the oscil­lator and if a tube is connected, the oscillator runs at a fre­quency set by the series inductor (L) and resonant capacitor (C) across one end of each tube filament. The resulting current through the resonant capacitor heats up the tube filaments and allows the tube to fire. The circuit then changes to a different operating mode. Inductor L limits the current to the tube and the operating frequency becomes lower as set by a saturable transformer. The AC capacitor is used to prevent DC being applied to the tube. DC can cause mercury migration to one end of the tube which will ul­timately reduce the operating life. 0V OSCILLATOR WITH SATURABLE TRANSFORMER FLUORESCENT TUBE DRIVER DC-DC CONVERTER Circuit details AC CAPACITOR INDUCTOR (L) FLUORESCENT TUBE RESONANT CAPACITOR (C) Fig.1: this block diagram shows the main circuit features of the fluo­rescent inverter. Note the feedback to maintain a constant DC voltage from the rectifier output. This ensures constant brightness with varying battery input voltage. since the tubes are run at a very high frequency, there is no flicker, either at start-up or during running. Nor is there is any hum or audible whistle and radio interference is low. The inverter is designed to be housed in a standard 18W or 36W batten fitting so that the fluorescent inverter and lamp are an integral unit. Block diagram Fig.1 shows the block diagram of the fluorescent inverter circuit. It comprises a DC-DC converter (which steps the 12V up to 340V DC) and a fluorescent tube driver circuit. The DC-DC converter employs a step-up transformer which is driven by two Mosfet transistors at a frequency of around 120kHz, as set by a switchmode controller IC. The resulting high voltage AC output from the transformer is rectified and filtered to provide DC. Feedback is applied from the output to the switchmode controller IC to maintain the DC voltage at 340V. • • • • • • • • • Main Features Suitable for 18W and 20W or 36W and 40W tubes High efficiency Fast starting without flicker Filaments preheated Constant lamp brightness from 11-14.4V supply Light output equal to conventional mains-powered lamp Reverse polarity fuse protection Fuse protection for faulty tube Low electromagnetic radiation The full circuit for the fluorescent inverter is shown in Fig.2. At the heart of the DC-DC converter is IC1, a TL494 pulse width modulation (PWM) controller. It contains a sawtooth oscil­lator, two error amplifiers and a pulse width modulation compara­tor. It also includes a “dead time” control comparator, a 5V reference and output control options for push-pull or single ended operation. Oscillator components at pins 5 and 6 set the operating frequency of the pulse width control at about 120kHz. This fre­quency was selected to obtain the maximum power output from the transformer. The PWM controller generates variable width output pulses at pins 9 and 10, to ultimately drive the gates of Mosfets Q1 and Q2 via paralleled buffers in IC2. Mosfets Q1 and Q2 drive the centre tapped primary winding of transformer T1. The centre-tap of the transformer’s primary winding connects to the +12V supply while each side of the prim­ ary winding is connected to a separate Mosfet. Each Mosfet is driven with a square wave signal so that when Q1 is on, Q2 is off and when Q2 is on, Q1 is off. With Q1 on, 12V is applied to the top half of the transformer primary winding. Because of transformer action, the lower half of the transformer primary winding also has 12V across it. Similarly, when Q2 turns November 1993  27 Q4 BUK457-600B S G N3 330  1W 330  ZD3 12V 1W on, 12V is also impressed across the top primary winding. The resulting 24V peak-to-peak waveform on the primary is then stepped up by the secondary winding. High speed diodes D1-D4 rectify the AC output from trans­former T1, while a 0.1µF 250VAC capacitor filters the rectifier output to provide a stable voltage. We can get away with such a small value filter capacitor here because the operating fre­quency is so high. 36W AND 18W FLUORESCENT INVERTER 8.2k 3T 6T 0.4mm DIA ENCU N3 N2 24T N1 F2 400mA 200mA F1 5A 2A FL1 18W 4 E1 9 36W 11 1k 7 9 14 1k 10 E2 16 7 IN(+) .001 5 15 13 4.7k 2 1M 0.1 47k 14 5V IN(-) FB GDS 4.7k 6 IC1 TL494 1 8 11 12 3 GND 16T 12 8 15 2 3 1 IC2 4050 5 0.1 6T 470 25VW G 6 S D Q2 MTP3055E 10 S D G Q1 MTP3055E 4 0.1 ZD1 16V 1W 470 25VW 82  F1 +12V 28  Silicon Chip 3T 0.25mm DIA ENCU 470 25VW S2 4T F2 L1 10uH S1 4T F1 T1 0.1 FEEDBACK D3 270k 270k 0.1 63V DIAC1 ST2 22  680pF N1 3kV N2 D4 150k D5 1N4936 150k 330  1W 330  330  1W D1 D2 150k 150k 136T 0.1 250VAC 4x1N4936 +340V T2 330  1W ZD2 12V 1W L2 900uH Q3 BUK457-600B D G S D .001 3kV F2 0.1 250VAC FL1 Fig.2: the complete circuit of the fluorescent inverter. The DC-DC inverter section runs at about 120kHz while the fluorescent driver section runs at 65kHz for 36W tubes and 110kHz for 18W tubes. Feedback Feedback from the high voltage DC output is derived from a resistive divider (two 270kΩ and an 8.2kΩ resistor) and applied to the internal error amplifier in IC1 at pin 1. If the DC vol­tage becomes greater than 340V, the pulse width drive to the Mosfets is reduced until the correct voltage is obtained. Simi­larly, if the voltage drops below 340V, the pulse width is increased until the correct voltage is achieved. The DC gain of the error amplifier is 213 times, as set by the 1MΩ and 4.7kΩ resistors at pin 2. The 47kΩ resistor and 0.1µF capacitor across the 1MΩ feedback resistor provide fast AC re­sponse from the circuit. Power to IC1 and IC2 is supplied via an 82Ω resistor from the +12V battery supply and filtered with a 470µF capacitor. A 16V zener diode protects the circuit from high voltage tran­sients. To eliminate RF noise generated by the switchmode DC-DC converter from being radiated by the supply leads we have includ­ed a filter comprising inductor L1 and a 0.1µF capacitor (at the input). Fluorescent driver The fluorescent tube driver comprises Mosfets Q3 and Q4, transformer T2 and associated components. The fluorescent tube is driven via inductor L2 and the N1 winding of transformer This photo shows the gate drive pulses to Q1 & Q2 in the DC-DC converter when driving an 18W tube. The gate pulse width will be greater when the circuit is driving a 36W fluorescent lamp. T2. The N1 winding drives the gates of the Q3 and Q4 Mosfets via the N2 and N3 windings which are antiphase connected. When power is first applied, there is 340V DC between the drain of Q3 and the source of Q4. The 0.1µF capacitor adjacent to Diac1 begins to charge via the two series 150kΩ resistors. When the voltage reaches about 30V, the Diac fires and discharges into the gate of Q4. Zener diode ZD3 protects the gate from overvol­tage. Mosfet Q4 is now switched on and current can flow from the +340V supply via the fluorescent tube top filament, the .001µF 3kV capacitor, the second tube filament, the 0.1µF 250VAC capaci­tor, inductor L2 and transformer T2’s N1 winding. Current flow in N1 will then apply gate drive to Q3 via N2 and switch off gate drive to Q4 via N3 (due to the polarity of the windings). If this oscillation does not occur, the 0.1µF capacitor again charges up and the Diac fires to switch on Q4 again. Ul­ t imately, oscillation will occur with Q3 and Q4 switching on and off in alternate fashion. The frequency of operation is set by the combined inductance of L2 and the N1 winding and the .001µF capacitor across fluorescent tube FL1. The oscillator current now passes through the fluorescent tube’s filaments and allows the normal mercury discharge to take place inside the tube. When this happens, the .001µF capaci­tor across the tube is effectively shunt­ed out by the mercury discharge. These are the starting pulses present at the drain of Q4 with no tube in circuit. Pulses from Diac1 drive the base of Q4 and switch it on. Note that a 10:1 probe was used for this meas­urement. This takes place at a peak voltage of about 100 volts. The frequency of oscillation is now determined by the prop­erties of the core of transformer T2. As the current builds up in winding N1, the core begins to saturate. When this happens, the flux in the core stops changing and the gate drive to Q3 or Q4 ceases. The flux now collapses to drive the opposite Mosfet and this process continues to maintain oscillation. Current through the tube is limited by the current at which the T2 core saturates and the L2 inductance. These two components provide the same current limiting function for the tube as does the ballast in a conventional fluorescent lamp fitting, except that the frequency is many times higher than 50Hz. The start-up circuit, comprising the 0.1µF capacitor and Diac1, is prevented from interfering with the normal operation of the circuit by diode D5. The diode discharges the 0.1µF capacitor every time Q4 is switched on, thus preventing the Diac from fir­ing. The gate drive to Q3 and Q4 is limited using two parallel 330Ω gate resistors and 12V zener diodes which clamp the gate voltage to a safe value for the Mosfets. The 330Ω resistor from gate to source provides a load for transformer T2 so that the saturation characteristic for the core can be accurately set. Note that while Mosfets Q1 and Q2 in the DC to DC converter are fitted with heatsinks, Q3 and Q4 switch only small currents and therefore they do not require heatsinks. However, during the switch-over process, when one Mosfet is switched off and the other turns on, the Mosfet which is turned This is the waveform at the drain of Q4 when driving an 18W tube. The overall amplitude is 330V peak to peak & the fre­quency is 110kHz. November 1993  29 12V off commutates whereby its internal reverse diode briefly conducts. This commutation can lead to high dissipation in the Mosfets. To reduce this dissipa­ tion to almost zero we have connected a snubber network to the output (ie, the junction of Q3 and Q4). The snubber network consists of a 680pF capacitor in series with a 22Ω resistor. The two 150kΩ resistors connecting from the 680pF capacitor to the +340V supply act as a load for the circuit if the fluores­cent tube is not present. F1 0.1 82  470uF L1 .001 47k 1M 1k 1k IC1 TL494 4.7k 0.1 ZD1 1 4.7k 0.1 1 IC2 4050 270k 470uF T1 GND TERMINAL 1 470uF Q1 270k D1-D4 0.1 250VAC 0.1 150k 680pF 150k 150k 22  ZD3 Q4 330  330  150k ZD2 Q3 N2 330  T2 N3 330  330  330  N1 0.1 250VAC L2 F2 1 .001 3kV TO TUBE END TO TUBE END 30  Silicon Chip Fig.3: the PC board layout. Note that transistors Q1 & Q2 are fitted with heatsinks & note also that high voltages are present on the board when power is applied. Q2 ST2 6 F1 S2 F2 S F 1 10 PRIMARIES: 4T, O.5mm DIA. ENCU SECONDARY: 136T, 0.4mm DIA ENCU Fig.4: the winding details for transformer T1. Note that the primary windings are bifilar. Circuit changes 8.2k 0.1 T1 S1 5 There are a few changes to be made to the circuit, depend­ing on whether it is to be used with an 18W or 36W fluorescent tube. These are shown in the table on the circuit. The input fuse (F1) is 2A or 5A and the winding details of transformer T2 are varied. The reason why transformer T2’s windings are varied is to vary the frequency of the fluorescent driver circuit and thereby set the current through the tube. For 18W tubes the frequency is 110kHz and for 36W tubes the frequency is about 65kHz. While the frequency for the 36W tube is not quite halved, the changes to transformer T2, combined with the fixed inductance of L2, means that the current is doubled. High frequency operation Before concluding the circuit description, we should make a comment WARNING! This project develops potentially lethal voltag­es. At no time should any part of the circuit be touched while power is applied. This project should not be attempted by inex­perienced constructors. about operating fluorescent tubes at high frequencies. In some technical literature, fluorescent tubes are stated to be much more efficient at high frequencies. This is not true. There may be a small difference between operation at 50Hz and, say, 1kHz but above that, the light output from a fluorescent tube is directly proportional to the current through it, although there are limiting factors above which the tube becomes overheated and its life is shortened. Therefore, the efficiency of the circuit is much the same for the 18W and 36W tube versions of the cir­cuit, regardless of the fact that the operating frequencies are different. Note also that the 18W version of the circuit will work with a 20W tube and the 36W version will work with a 40W tube. The slightly higher rated (and thicker) tubes have the benefit that they are easier to start but they are more expensive. We should also make some comments about the circuit effi­ ciency. We have set the current through the respective 18W and 36W fluorescent tubes to be close to the value it would be if running in a conventional 50Hz ballast circuit. This results in the A piece of blank PC board material is used to prevent direct contact with the underside of the components board through the large cutouts in the batten base. The hole for the starter (in the batten cover) should also be sealed. The assembled PC board fits neatly in one end of the batten, as shown in the photograph at top. Make sure that the board is properly secured before fitting the cover & the fluorescent lamp. 18W version of the circuit drawing 1.5 amps from a 12V supply and the 36W version drawing 3 amps from a 12V supply. Does this make the circuit 100% efficient? The answer is clearly no since an 18W fluorescent tube does not dissipate 18 watts – a significant amount of power in an 18W fitting is dissi­pated by the ballast. Hence, while we cannot quantify the overall circuit efficiency, we can state that it is quite high and cer­tainly higher than other inverter designs intended for driving fluorescent tubes. Our estimate of the efficiency is “better than 80%”. Construction The PC board for the circuit is coded 11312931 and measures 286 x 46mm. It will fit inside a standard 18W or 36W fluorescent tube batten. Construction can begin by winding the toroids and the transformers. Let’s start with L1, the larger of the two toroids and brown in colour. Wind on 18 turns of 0.8mm enamelled copper wire with even spacing around the toroid. L2 is not a toroid but is the smaller ferrite assembly comprising a bobbin, two core halves and two clips. Before wind­ing this you will need to set the gap in the centre leg of the core halves. You will need a small file (a points or hobby sized file would be ideal) and a set of feeler gauges. Initially, place the two core halves together and observe that there is no gap between the mating surfaces of the core halves. Now file only the centre leg of one core half, making sure that you are filing squarely and evenly across the face. The required gap is 0.15mm and can be accurately measured with feeler gauges when the two halves are held together with your fingers. The whole process should not take longer than 5 minutes since the ferrite material is quite soft. Now wind 60 turns of 0.4mm enamelled copper wire onto the bobbin, with the start end soldered to pin 6. Wind each layer neatly side by side across the bobbin and insulate between each layer with a length of insulating tape. Solder the end of the winding to pin 7 on the bobbin. The inductor can then be complet­ed by fitting the core halves into the bobbin and securing them with the clips. Transformer T1 is the larger of the two ferrite assemblies. The ferrite RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 2 4 1 1 2 2 2 1 1 Value 1MΩ 270kΩ 150kΩ 47kΩ 8.2kΩ 4.7kΩ 1kΩ 330Ω 82Ω 22Ω 4-Band Code (1%) brown black green brown red violet yellow brown brown green yellow brown yellow violet orange brown grey red red brown yellow violet red brown brown black red brown orange orange brown brown grey red black brown red red black brown 5-Band Code (1%) brown black black yellow brown red violet black orange brown brown green black orange brown yellow violet black red brown grey red black brown brown yellow violet black brown brown brown black black brown brown orange orange black black brown grey red black gold brown red red black gold brown November 1993  31 Fig.5: this is the PC artwork reduced to 70.7%. To reproduce it full size, use a photocopier with an expansion ratio of 1.41. cores should not be gapped in this case since we want the gap to remain at zero. Fig.4 shows the winding details. Wind on the secondary first using 0.4mm enamelled copper wire. Termi­nate the start of the winding at pin 2 and neatly wind on one layer of wire across the bobbin. Insulate this with a layer of insulating tape. 32  Silicon Chip Note here that the start and finish of the insulating tape should begin on the underside of the bobbin (ie, the pin side of the bobbin). This will ensure that the ferrite core halves will fit over the completed windings. Continue wind­ ing until 136 turns have been wound on in several layers with insulation tape over each layer. Terminate the finish of the winding at pin 1. The two primary windings are wound bifilar (ie, two wires at the same time), with one end of each winding starting at pins 4 and 5 and finishing at pins 6 and 7, respectively. Wind on four turns, making sure that the two windings do not cross over each other. Note that there will not be sufficient room to cover the windings with insulation tape. These windings can be clearly seen in one of the photos accompanying this article. When the bobbin is completed, fit the core halves and the retaining clips. Toroid T2 is wound as detailed in the table on the circuit diagram (Fig.2). If you are making the 36W version, use 0.4mm enamelled copper wire. If you are making the 18W version, use 0.25mm enamelled copper wire. Wind on the N1 winding, keeping the windings tightly packed toward one side of the toroid. The N2 and N3 windings must be wound in the same direction as the N1 wind­ing. With the transformers and inductors complete, assembly of the PC board can proceed. Before installing components, check the board for shorts or breaks in the tracks. Also check the holes for correct sizing for each component. You will need 3mm holes for the PC board mounting, transformer T2 and for the heatsink mounting feet. Two 3mm holes are also required for a cable tie to hold down L1. Start the board assembly by inserting all the PC stakes plus the four 2AG fuse clips. This done, insert the resistors, links and diodes, followed by the two ICs. Make sure that the diodes and ICs are cor­rectly oriented before soldering. The same comment applies to the electrolytic capacitors. The ST2 (Diac1) can be installed either way around. Now install transformer T1 and inductor L1 onto the PC board, taking care that pin 1 marked on the bobbin is oriented correctly. Transformer T2 is mounted using a transistor mounting bush together with a Nylon screw and nut. L1 is held in position using a small plastic cable tie. Mosfets Q1 and Q2 are fitted with small vertical heatsinks using machine screws and nuts. Apply a smear of heatsink compound to the mating Below: this close-up view shows how transformer T2 is secured to the PC board using a Nylon screw, a transistor insulating bush & a nut. Coil L1 at the other end of the board is secured using a plastic cable tie. Be sure to install Q3 & Q4 with their metal tabs adjacent to the edge of the board. surfaces before screwing the Mosfet body to the heatsink. Each heatsink is secured using the integral mounting feet which pass through the holes in the PC board. When they are inserted into the board, use a pair of pliers to twist the feet and hence lock them into the board. This done, solder the Mosfet leads to the copper pattern. Mosfets Q3 and Q4 can also be mounted at this stage – they do not require heat­sinks. Finally, fit the fuses into the fuse clips and the board is complete. Installation We recommend that the PC board be installed into the fluo­rescent batten before testing, because the voltages developed by the circuit are potentially lethal. Before installation, the existing ballast, starter and terminal strip will need to be removed from the fluorescent batten. Now drill holes to accommodate the PC board and drill out a hole for the cord grip grommet suitable for the 12V lead entry. We mounted the board on top of a piece of blank PC board material to cover the copper tracks (any other insulating material would do), while the hole for the starter was covered using a piece of plastic and a metal clip. This will prevent direct contact with the underside of the PC board through the large cutouts in the batten base and cover. The board mounts onto transistor mounting bushes, used here as low profile spacers, and is secured at six points with screws and nuts. Connect up a length of polarised twin-lead to the 12V input and connect the wires from the tube ends to the PC board as shown on the wiring diagram. The negative terminal of the PC board is connected to chassis using a short piece of hook-up wire soldered to a solder lug. Testing Once the PC board has been installed in the batten, you are ready for testing. Insert a fluorescent tube into the fitting and apply power. The tube should initially glow with a bluish tinge for a half second or so and then come on with full brilliance. There should be no flicking during the startup phase (as is the case with normal fluorescent lights) and there should be no discernible flicker at all once the tube is at full brilliance. PARTS LIST 1 PC board, code 11312931, 286 x 46mm 1 blank PC board, 336 x 46mm 1 18W or 36W fluorescent tube batten 1 EFD25/13/9 3F3 core (no air gap), former and clips (2 x Philips 4312 020 4116 1, 1 x 4322 021 3524 1, 2 x 4322 021 3516 1) – T1 1 RCC12.5/7.5/5 3F3 ring core (1 x Philips 4330 030 3792 1) (T2) 1 RCC17.1/9.8/4.4 2P90 ring core (1 x Philips 4330 030 6031 2) –L1 1 EFD20/10/7 3F3 core, former and clips (2 x Philips 4312 020 4108 1, 1 x 4322 021 3522 1, 2 x 4322 021 3515 1) – L2 2 battery clips (1 red, 1 black) 2 vertical mount TO-220 heatsinks (Jaycar Cat. HH-8504) 4 2AG PC mount fuse clips 1 5A 2AG fuse (36W version) 1 2A 2AG fuse (18W version) 1 400mA 2AG fuse (36W version) 1 200mA 2AG fuse (18W version) 1 cord grip grommet 7 transistor mounting bushes (6 for 4mm PC board standoffs) 1 3mm Nylon screw and nut 1 small cable tie 2 3mm dia x 6mm long screws & nuts 8 3mm dia x 12mm long screws, nuts & washers 1 solder lug 1 80mm length of 0.8mm tinned copper wire 1 600mm length of 0.8mm enamelled copper wire If the inverter does not power up the fluorescent tube, switch off power immediately and check for faults. Check that all the components are located correctly and that the transformers and inductors are wound and oriented correctly. Transformer T2 must be wound with correct phasing or the oscillator will not function. You can check that the DC-DC converter is functioning by measuring the voltage between the GND terminal and F2 fusehold­er. It should be 340V DC. Use your multimeter set to read 1000VDC and check that the multime- 1 10.5m length of 0.4mm enamelled copper wire 1 500mm length of 0.5mm enamelled copper wire 1 800mm length of 0.25mm enamelled copper wire 1 2m length of twin automotive wire (polarised) 7 PC stakes Semiconductors 1 TL494 switchmode IC (IC1) 1 4050 CMOS hex buffer (IC2) 2 MTP3055E avalanche protected N-channel Mosfets (Q1,Q2) 2 BUK455-600A, BUK457-600B high voltage N-channel Mosfets (Q3,Q4) 5 1N4936 fast recovery diodes (D1-D5) 1 ST2 Diac (DIAC1) 1 16V 1W zener diode (ZD1) 2 12V 1W zener diodes (ZD2, ZD3) Capacitors 3 470µF 25VW PC electrolytic 2 0.1µF 250VAC metallised polypropylene 5 0.1µF MKT polyester 1 .001µF MKT polyester 1 .001µF 3kV 1 680pF 3kV Resistors (0.25W, 1%) 1 1MΩ 2 1kΩ 2 270kΩ 4 330Ω 1W 4 150kΩ 2 330Ω 1 47kΩ 1 82Ω 1 8.2kΩ 1 22Ω 2 4.7kΩ ter probes are in good condition before making this measurement. The voltage is potentially lethal. Further tests can be made using an oscilloscope. You must connect the oscilloscope probe earth connection to the GND termi­nal on the PC board. Keep your probe set on 10:1. You should be able to see the starting pulses applied to Q4, by measuring the waveform at the drain (metal tab) of Q4 when the tube is out of circuit. The oscillation should be observed at Q4’s drain when the tube is installed SC (see oscilloscope photographs). November 1993  33 SERVICEMAN'S LOG Working within the customer’s budget With smaller sets, the cost of any repairs must be kept under control. My main story this month is a good demonstation of that & is also an excellent example of how a minor component can cause inconvenience. The story concerns a Hanimex colour TV set, model CTV-10. It is a semi-portable type, with a 25cm screen, and is designed to operate from either 240V AC or 12V DC (eg, from a car battery). And it is around this dual operation feature that the story revolves. The owner had bought it when he retired, primarily for use in his caravan on a round-Australia trip which lasted some 12 months. And, as can be imagined, the 12V system came in for a fair amount of use during that time. But shortly after returning home, he realised that the 12V system could no longer be used, although the set continued to perform perfectly well on 240V. Well, that wasn’t much of a bind; they were not planning any long 34  Silicon Chip caravan trips in the future and, as long it functioned on the mains, it would suit their needs quite well. So that was how things went for the next 12 months or so. In fact, it would probably have continued along these lines indefinitely, if the set had not also failed on the mains. And that’s where I came in. The owner was a new customer and he set out the above his­tory before asking the vital question, “Can you fix it?” I could­n’t be sure, of course. As I explained to him, it was a set I hadn’t seen before and I had no circuit or service manual. Hope­fully, I could get data from Hanimex if necessary but, initially, I would simply look for what was obvious. Filthy lucre That was OK but then came the vital question of filthy lucre; how much was he prepared to spend on it? It was an import­ant question because I didn’t know what I would find or what data or spare parts were available. After some discussion, we settled on a figure of $100. If it looked like exceeding that figure, I would consult him first. And so he left it with me. On closer examination, I learned that the set was made in China. Later, when I delved into the innards, I wasn’t all that impressed with the construction in general. I’d seen worse but I’d seen better too. At a more basic level, I had to try to work out the power supply system and decide where to start looking. The only thing I felt reasonably sure about TC-48P10 Has Live Chassis In the Serviceman story in the October 1993 issue, I men­tioned that the Panasonic TC-48P10, and by implication the TC-1480A, had an M15D “dead” chassis. This is wrong – both sets have the M15L “live” chassis. The mistake has come about partly be­cause I test and repair all sets using an isolation transformer. was that there were two separate faults, since the two failures had occurred at different times. As it turned out, the set was basically a 12V device, with the addition of a 12V mains-driven power supply. The mains cord was fitted permanently, while the 12V cord connected to the set via a plug and socket arrangement. There was no switching involved. The 12V positive battery lead went straight to the 12V rail derived from the mains power supply. The voltage regulator IC isolated the 12V from the rest of the supply circuitry – quite an elegant system. It was the plug and socket arrangement connecting the 12V lead to the set that provided the first clue. It is a commonly used fitting, typically referred to as a DC power plug or DC jack – with matching socket. The plug, which fits on the cable, is a female fitting, and the socket, normally chassis mounted, is the male version. When I tried to push the plug into the socket it wouldn’t fit properly. Closer examination revealed that the end of the plug had been damaged. The insulation between the inner and outer conductors was deformed, as was the end of the inner conductor. Thus alerted, I pulled the back off the set for a closer examination of the socket. And this was the real culprit; it had obviously been seriously over- heated and was grossly deformed. I subsequently measured the current involved and it varied from 2.25A to 2.5A over the range 12-13.8V. That’s pretty solid for a miniature connector like this, particularly as the set would typically run for quite long periods. As a quick test, I patched a couple of leads into the cir­cuit and connected them to the 12V bench power supply. And the set sprang to life immediately, with good sound and a first-class picture. I gave it a quick check across all the channels and satisfied myself that there was nothing wrong with its operation. This clearly suggested that its failure to operate on 240V must involve the power supply. In the meantime, what was to be done about the damaged connectors? The easy way out would be to simply replace them with new units of the same design. However, knowing that they appeared to be inadequate, at least on a long-term basis, should I try to fit something better? I mulled over this latter idea at some length and was even­tually forced to the conclusion that, desirable though it might be in theory, it was not physically practical. It would have meant hacking into the chassis in an awkward spot, could not have been done neatly, and would have only added to the cost. I even discussed the problem with the owner and he agreed that it was unlikely that the 12V system would get much use from now on. So I took the easy way out. But why wasn’t the set designed to take an adequate plug and socket – even if it cost a fraction more? The supply fault Putting such questions aside, I now had to find the fault in the mains supply. It was a simple circuit, consisting of a power transformer delivering around 16V, a bridge rectifier, a 3-terminal voltage regulator and a filter capacitor. It didn’t take long to pinpoint the culprit – the trans­former primary was open circuit. It was a simple job to remove the transformer and, when I did, it revealed a small sticker saying, “Internal Thermal Fuse”. So my guess is that it was this that had failed but for what reason we will never know. In any case, the transformer was a write-off. So where to from here? There were two points to be clari­ fied: (1) the availability of a replacement and (2) the cost. This latter point was most important. Transformers are not cheap and I could see that, with labour costs, the $100 limit might be exceeded. So it was back to the customer. I had to be honest and point out that, depending on the best transformer deal I could swing, the job might cost up to $150. Was he prepared to go that far? He wasn’t too keen at first but I pointed out that we knew the set itself was OK, performed well, and that to replace it, would probably set him back $300 to $350. So, after some hesitation, he agreed. So began the search for the best transformer deal. My first choice was a Sam­ sung unit I had on hand. It was electrically suitable, was fitted with a magnetic shield similar to the origi­ nal, and looked as though it would fit physically. And, most importantly, it only cost me $36, including tax. At that price, I could do the job well under the limit. But alas for my clever thought; it was just marginally too large and there was no way I could fit it. So the next step was a call to the Hanimex spare parts department. It was a good news/bad news situation. Yes, they could supply a transformer ex-stock but the price was $73 plus tax, or about $95. Pack and post would add another $6, giving a total of about $100. I said “Ouch” under my breath and thanked them for their help. That simply was not a proposition. Even without any mark-up on the transformer, labour costs – including the work done on the 12V system – would put the total above the agreed figure. And I couldn’t justify pushing the limit any higher. I had to find a better way. Substitute transformer A colleague dropped in for a chat around this time and I filled him in on the problem, displaying the faulty transformer. His reaction was immediate: “Have a look at an old Akai video recorder, a VS-3 or VS-4. They had a transformer with a number of windings on it and it might just fit.” Being thus reminded, I realised that he could be right and that I might just have one. So it was out to the junk room where we scrabbled through the discards and, sure enough, there was a junked VS-3. So it was back to the bench and out came the trans­former. And it looked quite promising, being of a shape and size which would clearly fit. All that remained was to November 1993  35 SERVICEMAN'S LOG – CTD sort out the secondary windings and, hopefully, find one that would suit. The primary winding was easily identified, so the quickest way was to fit a power cord and plug it into the mains. Unfortunately this proved to be another setback. At switch-on there was a protesting splat and a puff of smoke; storage had apparently not been kind to this device and it was write off. But the exercise had not been completely wasted. My col­ league had started a useful train of thought and I remembered another Akai video recorder in the junk room, this time a VS-112 which is a much later model. And again, the trans­former looked very promising. It was smaller that the VS-3 unit and should fit easily. In fact, when I pulled it out and tried it in position, I realised that I 36  Silicon Chip could bolt it directly into place; a real win. So another mains test was set up. And it didn’t go splat this time. More importantly, it had three secondary windings, one at 30V and two at 16V, the latter being the more useful value. Initially, I sat the transformer on the bench and patched one of the 16V windings into the circuit for a trial run. And it worked but with one reservation; the DC voltage out was barely holding its value. I plugged it into the Variac and reduced the input voltage slightly. Sure enough the picture started to bend and pull. In short, there was not quite enough voltage at the regulator input to cope with line voltage variations. The 16V AC should have been enough but I sensed that the winding was a rather light one and that the load of the set was pulling it down. The logical reaction was to connect both 16V windings in parallel – suitably phased of course –and that solved that problem. And an hour’s bench test confirmed that the transformer was running quite cool. But we weren’t out of the woods yet. The transformer had no magnetic shield and, while it worked fine when sitting on the bench, I was worried that it could cause trouble when mounted in the set. So the next step was to mount it in the set, wire it neatly in the final form, and hope. Well, we won. There wasn’t the slightest hint of interference from the transformer, even when check­ e d on blank red, green and blue rasters. I gave the set a soak test on a daily basis for about a week before finally deliv­ering it to the customer. So what did it all cost? I charged him $125. Yes, I know, the transformer didn’t cost me anything – well not in hard cash – but it did cost me a lot in time, taking into account the problem with the first unit. So I reckoned it was a fair price. The customer thought so too; he was delighted. A day in the life ... And now, for a change of scene – and a change of pace – here are some short stories from my colleague J. L., across Bass Strait. He has sent me a number of such items and I am including as many as space will permit this time around. More next time. Over to you, J. L. The stories selected for this column are usually about unusual faults, or about common faults that require some kind of mental gymnastics to resolve. The simple faults, like replacing a shorted chopper tran­sistor and the resulting blown fuse, never seem to make these pages. Yet they constitute 99% of all jobs passing through the average serviceman’s workshop. There are times when I have a long run of routine tasks that provide no inspiration for Serviceman stories and I’m left bereft of any material to write about. So, at the suggestion of the Editor, I have decided to put together a list of common but interesting faults. One that I have just finished was an AWA video recorder, an AV47. It came in with the complaint that it “would not play through the TV set”. This was a rather ambiguous statement, since it could mean that it would not feed playback signals to the TV set, or it could mean that it would not pass off-air signals as well. The only thing to do in a case like this is to set the machine up and operate it in the way an average owner might drive it. This is not as easy as it seems, since a technician usually knows what the “TV/VCR” switch and other controls mean and would be expected to put them in the correct position. To operate a VCR in “average citizen” mode means that the serviceman has to try to forget everything he has ever learned about these devices. Then, with any luck, he will hit on AUSTRALIAN MADE TV TEST EQUIPMENT 12 Months Warranty on Parts & Labour HIGH VOLTAGE PROBE Built-in meter reads positive or negative 0-50kV. For checking EHT & focus as well as many other high tension voltages. $120.00 + $5.00 p&p This close-up view shows the heat-damaged DC plug & socket from the Hanimex CTV-10 12V supply system. the same problem as the customer did and be able to diagnose the fault straight away. In this case, I was lucky. I connected the machine to the bench monitor and tuned one to the other. The off-air picture was decidedly snowy and the off-tape picture was also extremely poor. It was snowy, had no colour and often rolled. I recorded a few minutes of program material and then played it back on another machine. The results seemed to be reasonable but I did detect some snowy scenes. It was not what I would have called a prime quality picture. Booster/modulator unit A glance at the circuit diagram in the service manual showed that both the antenna booster and the output modulator were contained in a single unit. I had a horrible suspicion that this was the source of the trouble. By attaching a test tuner I was able to determine that the output of the booster was far from up to scratch. In fact, there was far less signal coming out of the booster than there was going into it. Similarly, I was able to feed a good video signal into the modulator part of the unit and found the output to be far less than one would have expected. There is no circuit diagram pub­lished for the booster/modulator unit but I would hazard a guess that some part of the supply rail to the chips inside the unit had failed. Unfortunately, there is no way to repair these devices so I had to place an order for a new one from Mitsubishi AWA. It wasn’t cheap but the new unit cured all the problems and so the customer is satisfied with the result, if not really happy about the cost. The next job was a Sharp VC-8300X VCR, one of the first of Sharp’s front loading models. The problem here was that the machine would load and begin to play but then shut down before it showed any sign of a picture. I took the cover off the machine and tried again to play a tape. The cause of the trouble was immediately apparent. The drum was not rotating. The drum motor in this machine is not one of those modern direct drive types. It consists of a very conventional brush type motor, driving the drum by means of a wide flat belt. It didn’t take long to discover that the motor was being provided with a healthy drive voltage yet showed no signs of life. I disconnected the leads from the motor and tested it for con­ tinuity. There was none. The VC-8300X is a very old machine and probably not worth all that much. I checked with the owner to see if he was prepared to pay something like $80 for a new motor. He wasn’t, so we decided that the machine would probably have to be junked. But before taking that step, I enquired among some of my colleagues who have a stock of junk sets in their store rooms. One of them did have an 8300 and it had a seemingly good motor on the deck. We struck a quick deal and I took the motor off the wreck. I had the motor fitted and the machine up and running just 15 minutes after my return to the workshop. The owner was quite happy to have a secondhand motor fitted to his machine. The alternative would have been very much more expensive. (I later found that one of the brush springs in the origi­nal motor had been bent slightly, thus holding the brush away from the commutator. I might have been able to repair it but as I had already fitted the replacement there was no point). DEGAUSSING WAND Great for comput er mon­­­i t­o rs. Strong magnetic field. Double insulated, momentary switch operation. Demagnetises colour picture tubes, colour computer monitors, poker machines video and audio tapes. 240V AC 2.2 amps, 7700AT. $85.00 + $10.00 p&p TV, VCR TUNER REPAIRS From $22. Repair or exchange plus p&p. Cheque, Money Order, Visa, Bankcard or Mastercard TUNERS Phone for free product list 216 Canterbury Rd, Revesby, NSW 2212, Australia. Phone (02) 774 1154 Fax (02) 774 1154 The next job involved another mechanical problem, this time in a Sharp cassette deck. I plugged in a set of head­­phones, dropped my test cassette into the deck and pressed play. The sound in the phones was hardly recognisable. It was suffering from the most hideous warble I have ever heard. When I looked inside the cassette well, my eye was imme­diately caught by a large dollop of black gloop on the capstan shaft. In fact, it turned out to be a part of the pinch roller. What had happened was that the roller rubber had perished and become very soft and sticky. Part of it had torn off and stuck to the capstan. The job was relatively easy to fix. I first had to work out how to remove the pinch roller arm before I could remove the roller spindle. After that, I had to find out if I could get a proper replacement. In the event, I found an alternative in a junked deck so once again the customer scored a quick fix at a reasonable price. Thank you J. L. I like the idea of dealing with the more mundane, dayto-day, bread-and-butter jobs; it helps strike a balance. More next time. SC November 1993  37 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Low-cost controller for model trains Here is yet another train controller circuit. What’s so special about this one? Well, it provides smooth control to give a realistic effect and the parts are cheap and readily available. The speed of the train is governed by the amount of current fed to it through SCR2. This in turn depends on SCR2’s gate current, as determined by 5kΩ slider pot VR1. Built into the circuit is an automatic trip which shuts down the current supply to the locomotive in the event of more current being demand­ed than is reasonable (eg, if there is a short circuit across the rails). This feature is based on the 1.8Ω “trip” resistor at the bottom of the circuit. It works as follows. When the voltage developed across the trip resistor reach­es a predetermined value, SCR1 turns on and deprives SCR2 of its gate current during successive positive mains half cycles. As a result, SCR2 turns off and cuts the supply to the locomotive. This removes the current via the 1.8Ω sensing resistor and thus SCR1 turns 6/12V gel cell charger This circuit will charge a 6V or 12V gel battery at con­stant voltage from a DC plugpack supply. It’s based on an LM317 variable voltage regulator which has an inbuilt current limit of over 1A. Because few plugpacks can supply this current without cooking, a current limiting circuit based on Q1, Q2, R1 and R2 has been added. R1 sets the maximum current according to the formula R1 = VBE/ Imax; eg, for a 500mA plugpack, R1 = 0.6/0.5 = 1.2Ω. If the load attempts to draw more than Imax, Q1 turns on and thus Q2 also turns on and 40  Silicon Chip 2x1N4004 D1 12V 240VAC 0V 2.2k D2 VR1 5k 12V 470  D3 1N4004 100  SCR2 C106.Y1 FOR/REV S1a 100  SCR1 C103.Y1 4.7k 100 6.3VW 100  off and allows SCR2 to turn on again. Hence, if the short circuit or overload is maintained, the circuit will oscillate between the on and off conditions. If you want to operate two trains at the same time, simply switch a second 1.8Ω resistor in parallel with the existing resistor. Switch S1 reverses the polarity of the supply to the track, to provide reversing. To prevent derailments, this switch should be operated only after the locomotive has been brought to a complete standstill. Incidentally, R = 0.6/Imax INPUT 47  1.8  2W TO TRACKS 220 25VW S1b watch out for the base configuration of the C103Y1 (SCR1), as some of them apparently left the factory with their cathode and anode leads transposed – you have been warned! Finally, don’t forget to put a dab of CRC con­tact cleaner on the electrical connections of your train (wheels, motor armature, etc), as no amount of electronic wizardry will make a “jerky” train run smoothly if the contacts are dirty. B. McTighe, Minto, NSW. ($25) D1 IN4007 IN LM317 Q1 BC557 OUTPUT 6.9V OR 13.8V OUT ADJ 240  Q2 BC547 VR1 2k .01 4.7k pulls the ADJ pin of the LM317 towards ground potential. This reduces the output voltage from the LM317 until the load draws no more than Imax. D1 prevents the battery from discharging through the charger when turned off. 1k To adjust the unit, connect a 100Ω 5W resistor between the output and ground, switch on and set VR1 to give the desired output voltage (either 13.8V or 6.9V). E. Kochnieff, Lutwyche, Qld. ($15) Flash meter This photoIRD1  graphic flash­ BPW21 meter measZD1 ures the light 2200 6.5V incident upon a subject, does not require a 39k sync cable and can accumulate the result of multiple flashes. It has an extremely long reten­tion period and will cost just a fraction of the price of a commercial unit. The light is picked up by a BPW21 silicon photocell. Resistor R1 is chosen so that, in ambient light condi­tions, it does not develop across it the 1.2V necessary to charge the 0.47µF polyester capacitor via the base-collector junction of transistors Q1 and Q2. Q1 and Q2 are used as diodes with extremely low leakage – their emitters are not connected. When the flash is triggered, the voltage across R1 exceeds 1.2V and most of the current through the BPW21 charges the 0.47µF capacitor via Q1 330  Q3 2N5458 2xBC549 Q2 S1a Q1 1k 9.1k HIGH 0.47 POLYESTER S1b D1 OA91 RANGE S2 ZERO METER VR1 M1 100uA VR2 2k 0.47µF capacitor is dis­charged). The meter covers the range from f/2 to f/16 at 100 ASA film speed over two ranges. To calibrate the unit, first adjust VR2 so that the meter reads f/11 at centre scale on the high range, using a flash on manual set to give f/11 at the distance to the photo­cell. By changing the distance between the flash and the photocell, the rest of the meter can be calibrated. Finally, the BPW21 photocell was obtained from RS Compon­ents (stock no. 303-719), phone (02) 669 3666. The same part is also listed in the Farnell catalog (order code BPW21R), phone (02) 645 8888. V. Erdstein, Highett, Vic. ($20) and Q2. This capacitor is charged in propor­tion to the flash duration and intensity, and the resulting voltage across it applied to the gate of FET Q3. Q3 in turn drives a 100µA meter movement via a 9.1kΩ resis­tor. Because the gate of the FET represents a high impedance, the meter reading will be unchanged over several hours. The meter is reset by discharging the 0.47µF capacitor via a 1kΩ resistor and S1b (ie, by switching the unit off). This means that the unit must be switched off and then on again before each new reading, unless a cumulative reading is required. VR1 and the 1.5V battery are used to zero the meter before a reading is taken (ie, when the Power supply pre-regulator circuit This power supply pre-regulator circuit is designed to reduce the power dissipation in the main regulator. It does this by automatically switching between a 2-diode centre-tap full wave rectifier for low output voltages and a 4-diode bridge arrange­ment for higher output voltages. If VOUT is kept below 48V, pin 3 of IC3 is below pin 2 and thus pin 6 is low and optocouplers IC1 and IC2 are off. This effectively produces a centre-tapped full-wave rectifier circuit, with current passing only through D1, D2 and D3. If, on the other hand, VOUT is increased to greater than 48V, pin 6 of IC3 goes high and IC1 and IC2 fire SCR1 and SCR2 via diodes D4 and D5. This now effectively produces a 4-diode bridge rectifier, thereby doubling the input to the main regula­tor circuit. IC1 and IC2 minimise the surge current into the 1000µF capacitor by firing SCR1 and SCR2 at the zero crossing point, while D4 and D5 prevent re- 9V LOW +5V 1M +12V D4 1N4002 1k 4 1k 90V 240VAC D3 1N5404 45V 0V F2 2A D1 1N5404 120  SCR1 BT151800R SCR2 BT151800R 1 6 4 8.2k 2 15k 10k 2 ADJUSTABLE REGULATOR 1000 150VW D2 1N5404 1k IC3 CA3140 IC1 MOC3041  F1 2A 3 7 6 SET TRIP POINT 48V VR1 10k 86.7k VOUT 4.3k D5 1N4002 4 1 IC2 MOC3041  6 2 120  verse polarity voltages from appearing across their gate-cathode junctions. Note that the pre-regulator reverts to a 2-diode full-wave configuration if a short circuit occurs across the output when running VOUT above 48V, thus reducing the dissi­pation. G. Freeman, Nairne, SA. ($20) November 1993  41 REMOTE CONTROL BY BOB YOUNG How to prevent damage to R/C transmitters & receivers This month, we will look at some of the problems asso­ciated with maintaining the modern R/C receiver &, in particu­lar, how to minimise damage when a crash occurs. Also, there is some very practical advice on how to avoid serious damage to the transmitter. Before moving on to receivers with their problems of high “G” forces together with dust and water ingress, I feel I should round off the transmitter articles with a bit of friendly advice. I said transmitters usually have a long and placid life but I should qualify that. I am reminded of a few incidents concerning transmitters, from my servicing experience. I once had a very irate customer in Melbourne return a valve transmitter it was just 25mm thick. What’s more, the valve was on the inside of the case when it left us and now the tip of the valve was sticking out of the front of the case. Add to this the fact that all of the control levers and switches were laying flat on the front of the case instead of sticking up in the air as is normal and I just knew that something was not normal. My first thought was in keeping with the serviceman’s men­tality that Lost transmitters are not uncommon & they are also stolen occasionally. Another common threat to transmitters is being left on the roof of a car & falling off during the trip home. (tuned reed) that I had just serviced and it was not working well at all. I can assure you, that on this occasion the set was working perfectly when it left our service department (I can hear mutterings about that’s what they all say) and when I opened the package, even I could tell that the transmitter was not at all well. For one thing, when it left us the transmitter was 100mm thick and now 42  Silicon Chip the customer had been fiddling again and trying me on. As it turned out, the package had fallen off the trolley at the airport and had been run over by a truck. I apologised men­tally to my customer. Another threat to the well-being of the transmitter, in this instance the plastic case of a transmitter, is leaving it in direct sunlight in a car; particularly if they are left on the back shelf. The temperatures in a locked car in summer are quite high and I have seen a few melted transmitter cases. Lost transmitters are not uncommon, being put down some­where and forgotten. Stolen transmitters raise their ugly heads on the odd occasion, although rarely on a flying field. I must say that I have never heard of stealing on a model field and there is valuable stuff lying about all over the place. Garage thefts seem to be the most common. One very common threat to transmitters is being left on the roof of a car and falling off during the trip home. Irate wives By far the greatest threat to the well-being of transmit­ ters however is irate wives and girl friends. Do not laugh, for there is nothing more vengeful than a woman scorned. Male modell­ers can get very carried away with their second love and wives, waiting hopefully in bed until two or three in the morning before falling asleep, tend to be a bit dirty in the morning. Now the most obvious object for revenge is the transmitter. The scorned woman sees her lover fondling this object of passion and often exacts a terrible reprisal. Beatings with a hammer are not uncommon. Trips out of a second floor (bedroom?) window are not unknown. Immersion in a hot, soapy bath has been encountered. So rounding up on the care and protection of the transmitter, if you are male and must indulge in foolish, insensitive and very dangerous behaviour, lock your transmitter away in a safe place. In case you think I am joking about TRANSFORMERS Fig.1: during a crash, sharp objects at the front of the aircraft can piece vulnerable components such as receiver PC boards & fuel tanks, while heavy objects towards the rear fly forwards to cause further damage. the foregoing, my own wife, on one occasion, exhibited such a reaction after a particu­larly insensitive period of frantic model building. This was quite early in our marriage and I came in one morning after a long building session to find my wife asleep in the spare room and one of my model fuselages tucked into bed in her place. I got the message. However, let’s get back to receivers. The modern receiver is a very reliable and robust unit. It has to be if it is to survive what modern modellers subject it to. With some model aircraft now capable of 200+ km/h, a crash can be devastating, with “G” forces measured in the 100s. Statistically, the most usual cause of failure in a receiv­er is crash damage. Even here, it is usually something sharp piercing the receiver case which causes the actual damage. Thus there is much that can be done to help the receiver survive even a high speed impact. Avoid crashes Rule one is to avoid crashes like the plague. This sounds like a ridiculous statement but you would be surprised how many flyers deliberately ignore this rule, largely out of impatience, but often out of a complete lack of understanding of the concept of preventative care. Therefore let us examine each aspect in turn. Firstly, why is it important to avoid crashes? Quite apart from the obvious cost involved in a crashed model, and this can run into many hundreds or even thousands of dollars, there are other factors involved, some technical, some psychological. To begin, learning to fly a model aircraft is a difficult and time consuming process. The ultimate success depends upon a large range of factors, which include aptitude, attitude, eye­sight and hearing. However, for most people the key factor is six consecutive weekends (or flying sessions). This is the prime reason for beginners to avoid crashing, as a crash will break the consecutive training sessions whilst repairs are in progress. During this time, what has been learned will be forgotten and the process of learning in this way can stretch out to several years (assuming that the modeller hasn’t given up in disgust). So keep that impatience in check and if you are learning, always have a spare model so that continuity can be maintained. For those who have already learned to fly, the break whilst repairing the model is not so serious, except psychologically. The important point is that during a crash, components can be stressed to close to the point of failure. This is particularly true of components such as crystals and IF coils which are not restrained inside their cans. Here we move to point two, the reason for the rule. Even a thorough check by a competent serviceman may miss these stressed components. Engine vibration and high “G” manoeuvres can then cause these stressed components to let go in flight, resulting in another crash and even more stressed components. This spiral of crash, stressed components, and crash again is devastating to model builders and is the prime cause of many leaving the hobby. So when I see a flyer adopt a “she’ll be right” attitude and launch an obviously sick model, I am horrified, for in my mind’s eye I see a chain of events which may ultimately cause TOROIDAL CONVENTIONAL POWER OUTPUT CURRENT INVERTER PLUG PACKS CHOKES DESIGN APPROVAL TO AS3108 MANUFACTURE 15VA to 7.5kVA – 100kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 APOLOGY We apologise that in the October issue of SILICON CHIP the Yaesu FRG 100 receive was incorrectly priced at $999. The correct price is $1199, an increase forced upon us by exchange rate fluctuations. We apologise for any inconvenience to customers. November 1993  43 Fig.2: crash damage to the receiver can be minimised by mounting it against a bulkhead with the PC board at right angles to the direction of flight. The components should be on the side facing away from the direction of travel that modeller to leave the hobby. Now we move on to the all-important aspects: prevention of the crash and prevention of damage in those crashes that cannot be prevented. In this section, most of the emphasis will be on aircraft, for these are the most difficult models in which to apply preven­tative measures. Preventative maintenance The success of all aspects of aviation has grown largely out of the concept of preventative maintenance and crash investi­ gation. You cannot stop and pull an aeroplane over to the side of the sky. Thus, you must work to see that all possible avenues for error are eliminated. You must work to ensure that the pilot is able to get the thing By far the most important and effective aspect of preven­tion is in the installation of the radio gear. The main point to keep in mind is what sort of forces are involved in a crash. Fig.1 shows some aspects of these forces. Note that the there are three major components of destruction to keep in mind. These are as follows: (1) Sharp objects in the front of the model. Due to inertia, all components will continue to move forward and thus will meet with considerable force any sharp object situated in the front. Things such as engine mounting beams and long bolts on nosewheel brack­ets are particularly destructive. They can pierce fuel tanks, battery packs and receivers and cause irreparable damage. “Engine mounting beams & long bolts on nosewheel brack­ets are particularly destructive. They can pierce fuel tanks, battery packs & receivers & cause irreparable damage”. safely on the ground if something does go wrong and finally investigate the crashes that do occur to find out what went wrong and close the loop in further preventative measures. The successful model flyer adopts exactly the same routine. It is no accident that some modellers are forever crashing, while some fly the same old model year after year. Without labouring the point then, prevention begins in the building process. Great care should be taken to ensure that the airframe is sound in construction and true in alignment. The choice of aircraft should be appropriate, so avoid the 4-engine super scale bomber or the 200km/h pylon racer as your first model. 44  Silicon Chip (2) Heavy components behind fragile components. At times, it is useful to mount the battery pack at the rear as a means of balancing the model. But remember that this will fly through the fuselage like a bullet in a crash. Any receiver or servos in its path are going to be subject to a hammering when they meet this panjandrum. (3) Bending stresses. Components standing at right angles to the line of flight will be subject to bending stresses and thus fracture or snap off completely in a crash. Receivers are very prone to this sort of problem. Minimising the damage Now let us examine ways to minimise this damage. Engine bearers these days are a little passe, as the radial mount has largely superseded them. They are still used by some modellers to spread the engine weight and vibration back into the fuselage. A good, solid beam mount is still one of the most effective ways of dissipating engine vibration. If you do use beams, make sure there is a 2.5mm plywood bulkhead butted against the beam ends. Cut off all the nosewheel mounting bolts flush with the nuts. Finally, check for any other protruding and sharp objects in front of the receiver and servos. Lightweight covers are often sufficient to deflect flying receiv­ers. There is little that can be done about heavy objects behind fragile ones. The best fix is to try to avoid this situation, ensure they are mounted firmly and perhaps provide a deflection plate between them. Again a plywood bulkhead suffices here. Nor can much be done to protect the servos but you can protect the receiver. Firstly, ensure that the receiver is mount­ed with the PC board at right angles to the direction of flight and the components are on the side facing away from the direction of travel – see Fig.2. Receiver protection A fair amount of protection can be provided for the receiver using a modern packaging foam. To do this, construct a self-contained housing which completely surrounds the receiver. Small, individual sheets of foam push­ ed down around the receiver are not going to help when the fuselage explodes on impact, sending the receiver flying through the air. On the other hand, a thick housing will stay with the receiver and allow it to bounce along the ground without damage (hopefully). This housing can be glued or wrapped in tape; the important point is that it stays intact on impact. Make sure that the receiver is mounted against a flat bulkhead with no protrusions and that the foam is not jammed in too tight; tightly packed foam will transmit engine vibration to the receiv­er components. Some compromise may be required here on the thick­ness of the foam. You may never have a crash (think positive), but you will certainly have engine vibration for the entire life of the model. Next month, we’ll cover the technical aspects of receiver servicing. SC SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au GM’s SunRaycer still holds the record for the Darwin to Adelaide World Solar Challenge. It had a “full cockroach” shape but most of the cars in the 1993 race will have flat solar pan­els. Darwin to Adelaide: technology makes it faster The leading cars streaking south from Darwin on 7th November in the World Solar Challenge are expected to be able to cruise at more than 80km/h using just Sun power. With battery assist, they will be much faster, perhaps running at up to 140km/h. By BRIAN WOODWARD The progress in solar car technology since the last WSC in 1990 has been dramatic. Aerodynamic drag has been drastically reduced, rolling resistance lowered, electric motor efficiency improved significantly and power management exceeding 98% effi­ciency has been achieved. Solar cells have experienced the most dramatic change in the threeyear period. The last race was won by the car entered by the Swiss Engineering School of Biel. This car used sili- con solar cells developed by Professor Martin Green of Sydney’s University of New South Wales. The revolutionary ‘Green’ cells offered a huge increase in power, but at a premium. Since the last race, Professor Green’s team has been working with BP Solar to bring these new cells to a stage where they can be mass pro­duced. The result is dramatic. For a time it was thought that Australian innovation would once more miss the boat. Green cells may be efficient, acknowl- edged many industry commentators, but they were prohibitively expensive. Much less efficient, but very much cheaper amorphous silicon cells being developed in Japan were set to upstage the Green cells before they could reach mass production. Now, Martin Green’s breakthrough photovoltaic cells cost 15% less to make and offer 30% more power than conventional mass-produced solar cells. Five years ago, mono or poly­ cryst­alline cells would have cost in excess of $20/watt to make. Costs have dropped to about $3/watt which relates to a retail price of about $10/ watt – less than one third the price only a few years back. BP Solar has supplied more than 40 kilowatts of cells to cars racing in the 1993 WSC. Unisearch, the research arm of the University of New South Wales, has supplied sufficient (more than 21% efficient) cells to power four November 1993  53 During the race, telemetry will be all important in monitoring the car’s systems in order to extract the maximum performance from the solar cells. cars. These are likely to be the front running favourites in the race because to clothe a race car in the very best cells costs more than $1 million! A single seater three-wheeled race car will have an array of about 7.9 square metres of cells which, at close to 20% effi­ciency, will develop around 1500 watts in full sunlight. A few car syndicates are claiming more than this. Cells need to be managed and “power trackers” do this. One of the best is the Australian made AERL tracker with a claimed efficiency of better than 95%. Some teams with lavish research laboratories able to construct one-off equipment are expected to have a tracker offering 99% efficiency at full power (when the semi­conductor’s temperature remains below 30°C). Batteries are the big disappointment in solar racing. No significant improvement has been made in the past three years. One team has managed to improve the number of recharging cycles for red-hot racing batteries, but little else has happened in battery development. There are two categories in the race – one for cars with lead acid batteries and one for cars with more elaborate batter­ies. Cars are permitted to carry 54  Silicon Chip five kilowatt-hours of stored power. 5kWh of silver zinc batteries are worth about $40,000 and under race conditions, these can take 10 recharges. Carefully managed, they may manage 30 cycles. After that, they’re scrapped. To be competitive, a team will need, say, three sets of these batteries – or about $120,000 worth – to cope with develop­ ment, training and testing before the race itself. Motor developments Real progress has been made in electric motor design. At least three cars will have the motor inside the drive wheel’s hub. A truly leading edge design will be a DC brushless motor weighing about 12kg and offering 2.5kW of continuous power or a staggering 11kW peak power (think of those poor MOSFETs under full load!). Three teams are claiming effic­ iencies along the lines of 98% for the motor controller, 99% for the tracker and better than 96% for the motor. This will mean that these advanced vehicles will be able to claim better than 92% efficiency from the solar array to the road wheels. One such car, the Northern Territory University’s Desert Rose, has a motor of such efficiency that the team’s lead- er, Dean Patterson, can state that the car is the most efficient motor vehicle ever built. Drag & rolling resistance The last two factors which influence the success of a car are its aerodynamic drag and rolling resistance. The Swiss Engineering School of Biel’s team claims a reduc­ tion in rolling resistance for its tyres of 30% compared with conventional heavy duty bicycle race tyres. A section of the Northern Territory’s Stuart Highway race course was moulded and shipped to Switzerland where an elaborate rolling road was con­structed. At temperatures soaring above 40°C the new tyres were tested to destruction. At one stage the “Stuart Highway” broke, but the tyre survived! Aerodynamics is the last area of technology to contribute to a win. With a frontal area of about 1.1 square metres and a drag coefficient (CdA) of 0.11, these cars have less drag than a fighter airplane. One Australian car, the Aurora Q1 from Victoria, has just shifted the goal posts. Its frontal area is just 0.75 square metres and its CdA an amazing 0.095. This is almost certainly the first road registered vehicle to have an aerodyna­ mic drag of less than CdA 0.1. The performance which comes from this technology should result One of the contenders in the 1990 WSC, this entrant from Hoxan really looked the part but it did not win. This is a preview shot of the Aurora, from Victoria. This car is claimed to have a CdA of 0.095, an unheard figure up till now. in a cruising speed of 80-90km/h in clear sunlight and perhaps 140km/h with the batteries approaching meltdown. A good set of batteries will take a solar race car 200-300km in cloudy weather, or even in rain. So power management tactics will play an important in the 3004km race from Darwin to Adelaide. Part of the tactics is telemetry between the race car and its support vehicles. This technology has been accepted since the first event when the GM Holden SunRaycer’s driver was told when to take on water and when to stop to visit the ‘loo’. The support vehicle monitoring crew knew because telemetry was used to moni­tor the ambient temperature and humidity inside the race car. How much do solar race cars cost? They start at $15,000 for some of the Holden-sponsored school teams and range up to an estimate of $20 million for some of the Japanese teams. At the end of the last race, observers said that an improve­ment of 10% would give a car the winning advantage. At least half a dozen cars would appear to have made more than 30% progress over the 1990 race cars. SC It will be interesting race. November 1993  55 Stereo preamplifier with IR remote control Despite its circuit complexity, the Studio Remote Con­trol Preamplifier is easy to build. This month, we conclude with the full construction details. PART 3: By JOHN CLARKE The Studio Remote Control Preamplifier is housed in a 1-unit high black rack-mounting case. This is fitted with a screen-printed front panel which incorporates a smoke-coloured (neutral) Perspex window for the LED displays. A plastic film mask is fitted over the LED displays so that only the segments that have been lit are visible through the Perspex window. Inside the case, most of the parts are accommodated on two PC boards: a main board coded 01308931 (350 x 230mm) and a dis­play board coded 01308932 (243 x 25mm). The handheld transmitter is housed 56  Silicon Chip in a small plastic case which has a front panel label measuring 73 x 63mm. It uses two PC boards, one for the electronic circuitry and the other to provide the necessary contacts for the switch membrane. This switch membrane is acted upon by 15 plastic-chrome buttons which pro­ trude through the front panel. Before starting construction, check all three PC boards for breaks in the copper tracks or shorts between tracks. Any defects should be repaired immediately. Check that all holes have been correctly drilled also. Begin assembly of the main PC board (01308931) by install­ing all the PC stakes (at external wiring points), wire links and resistors – see Fig.7. Keep all the wire links straight to avoid shorts to neighbouring components. The 27Ω 5W resistor should be mounted about 1mm above the board to allow the air to circulate beneath it for cooling. The ICs can be installed next, taking care to ensure that they are all correctly oriented. In particular, note that IC17-21, IC23 and IC15 are oriented differently to the remaining ICs, so check these carefully. We do not recommend using sockets for any of the ICs except for IC14 (the microprocessor IC), as this could prejudice the audio performance. Once the ICs are in (do not plug IC14 in yet), install the diodes, regulators and capacitors, again taking care to ensure that all polarised components are correctly oriented. Note that the two 4700µF capacitors must be mounted on their sides as shown on Fig.7, so crystal. Do not mount LEDs 10-18 at this stage – that step comes later. Finally, tack solder the six 6mm standoffs to their mount­ing points on the underside of the PC board. This is best done by first bolting the standoffs to the board, so that they are held in the correct positions. Display board that they don’t foul the lid. Exercise caution when mounting the three 3-terminal regula­ tors, to make sure you don’t get them mixed up. Each regulator is fitted with a heatsink and fastened to the PC board with a screw and nut. Use the largest heatsink for REG1 and smear all mating surfaces with heatsink compound before bolting each assembly to the board. The relay, bass and treble pots, tone switch and headphone socket can now be mounted, followed by the 500kHz ceramic resona­tor and the 3.58MHz Below: a plastic film mask is fitted over the LED displays so that only the display segments are visible through the Perspex window. The photodiode sits behind a window in the mask to prevent reflections from the LED displays. Fig.8 shows the assembly details for the display board (01308932). Begin by installing the wire link, then install the PC stakes from the copper side of the PC board at the 1, 2 and 3 locations. This done, install the three 7-segment LED displays and the pushbutton switches. Be sure to orient each switch with the flat side of its body facing to the left and take care with the orien­ tation of the LED displays (ie, bevel towards top left). The infrared photodiode (IRD1) is mount­ed with its leads at full length and bent at right angles so that its front face sits vertically – see photo. LEDs 1-9 should only be inserted and not soldered at this stage, so that their height can be adjusted later. Be careful with their orientation, as LEDs 4-6 are dif­ferent to the others. You can easily identify their leads because the anode lead is always the longer of the two. Mating the boards The main board is butted to the back of the display board at right angles and the two soldered together via matching con­nector tracks. Before doing this however, push LEDs 10-18 through their holes in the display board, then bend their leads downwards about 3mm away from the LED bodies, ready for insertion into the main board. Now offer the front panel to the main board and insert the LED leads into their respective holes. This done, arrange the main board so that its underside is 1mm above the bottom edge of the display board, then lightly tack solder the boards together at a couple of mounting points. Check that the two boards are at right angles before soldering the remaining tracks together. Finally, LEDs 10-18 can be soldered to the main board. Position them so that they sit flush against the display board before soldering their leads, and align them in a straight line to make a good bar display. Transmitter assembly Fig.9 shows the wiring details for the two transmitter boards. Before installing any of the parts, check that the two boards fit inside the case. In particular, the 01308933 board should be fitted to the base to check that the clips hold the board correctly and that the plastic alignment pin passes through the hole in the centre of the board. If the board is too wide for the clips, carefully file it down to size. Once the board fits correctly inside the case, snip the top off the alignment CAPACITOR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.22µF   220n   204 0.15µF   150n   154 0.1µF   100n   104 .068µF   68n  683 .015µF   15n  153 .01µF   10n  103 .0047µF   4n7  472 330pF   n330   331 100pF   n100   101 39pF   39p   39 22pF   22p   22 10pF   10p   10 November 1993  57 10k 1 BASS 22k 22k 1 1k 100W 10pF 100W 1 10uF 1 IC14 MC68HC705C8P IC2 4051 47k 47k REG3 7915 330  330  330  330  330  330  330  330  1 IC20 4511 4.7M IC102 4051 47k 330  330  330  330  330  330  330  REG2 7815 1 10uF 10uF 0.1 X1 D3 10uF 47k 47k 330  100W 10uF 10uF 39pF 47k 47k 0.1 330  1 ZD2 47k 47k 330  330  330k 1k 1 1 330  39pF 10uF D13 D14 10k 1uF D12 10k D11 330  330  330  330  330  330  330  1 IC19 4511 100  0.1 330  1 0.1 100  IC108 5534 10pF 10pF IC15 AD7112CN ZD1 IC104 5534 IC8 5534 1 0.1 330  0.1 100pF 1 1k 47k 100pF 330  IC17 ULN2003 0.1 K A K A K A K A K A K A K A K A K A 330  IC21 4511 4.7k 330k 330k 1 LED10-18 1 10pF 10pF 1 IC18 ULN2003 1 IC6 5534 0.1 IC116 OP27 1 0.1 1k 1 0.1 IC16 OP27 0.1 IC4 5534 S5 IC106 5534 100  10pF 100k IC3 4053 4.7k 1k 470uF .01 1 D15 10k 330W 4700uF 0.1 4700uF 1 D9 27  5W 0.15 10uF 330  58  Silicon Chip D5-D8 15V 15V CT 0.22 1 0.1 IC23 MV601 IC9 ULN2003 4.7k 0.1 1 100k REG1 7805 10k 10k 10k 10k 10k 10k 10uF 330  0.1 IC11 4051 IC12 4013 10uF 10uF .0047 1 1 D16 22uF 120  10k D4 .01 10uF 120  10uF IC10 4042 IC13 4011 330  10k 10k 100k 100pF X2 100pF 47  47uF 6.8uF 1 1 3 IC22 SL486 2 .015 Fig.7: parts layout for the main PC board. Make sure that all polarised parts are correctly oriented & note that a socket is used for IC14. We recommend replacing IC6 & IC106 with an OP27GP or LM627 and removing the 10pF capacitors between pins 5 & 8. 22k .01 330pF 0.1 10pF .01 R OUT GND GND IC107 5534 10k W 100W 22k 22k 22k 1.5k 330pF 10pF 1k 10uF 10pF GND VCR R GND CD R GND TUNER R GND AUX1 R GND AUX2 R 4.7k 1k 1.5k Q1 10k 10pF GND VCR L GND CD L GND TUNER L GND AUX1 L GND AUX2 L Q101 1k TREBLE 4.7k 10k 33  4.7k 4.7k 330k 47k 100  47k 100  GND OUT R 22pF D101 47k 100uF BP 100  100 TAPE 4x.0047 33  IC105 5534 100k IC101 5534 16k .068 .0047 100  0.1 33  33  22pF D1 PHONES Q102 1 Q2 1 1 390 1M 1M GND IN L TAPE GND IN R GND OUT L D2 100pF .015 200k 100uF BP D102 IC5 5534 L101 10pF 10pF 47uF BP 150  0.1 10k IC7 5534 GND PHONO L 100k 390  10k 10pF 47k 10k 16k 200k 100uF BP 100  6.8uF BP 0.1 100uF BP 6.8uF BP RELAY 10k 1 0.1 .015 D10 10k 100  100pF 100k 10pF 100k PHONO R IC1 5534 L1 .068 .0047 GND 10k L OUT 47uF BP 150  LED1 LED4 LED7 K A A K K A LED2 K A LED5 A K LED8 K A K A LED3 A K LED6 K 2 S4 A S2 1 3 A S3 A K IRD1 DISP1 DISP2 LEDS10-18 K DISP3 LED9 Fig.8: parts layout for the display PC board. The infrared photodiode (IRD1) is mounted with its leads at full length & bent at right angles so that its front face sits vertically – see photo. pin with a pair of sidecutters so that it is flush with the top of the board. This will allow the IC to sit over the alignment pin. The switch matrix board (code 01308934) can now be tested in the lid of the case. It mounts with the copper side towards the keys and is oriented so that the wire entry points are to­ wards the front (see photo). Check that the PC board fits between the integral guides and is located correctly by the four align­ment pins. File down the sides of the board if it does not fit comfortably. When everything is correct, begin the assembly of the components board by installing the IC, the links and resistors. This done, install the two 100pF ceramic capacitors, the 0.1µF capacitor, the 500kHz resonator and the battery clip leads. The 220µF capacitor must be mounted on its side, so that it will fit into the case. Transistor Q1 is mounted with its leads bent at right angles and is bolted to the PC board using a screw and nut. The two LEDs are mounted without shortening their leads so that they can be bent to sit on the plastic cup rests at the front of the case. Assembly of the switch matrix board (code 01308934) simply involves installing the seven wire links. Once these are in, connect the 8-way 100mm-long rainbow cable to positions 1-8 and the 3-way 100mm-long rainbow cable to positions 9-11. The other ends of the rainbow cables are connected to matching positions on the components board. The next step is to attach the front panel label to the case lid. This done, cut out the rectangular switch holes with a sharp knife and clean up the edges with a small file. The 15 chrome buttons are now installed from inside the lid and the membrane placed in position over these buttons. The contact pads on the switch matrix board should be cleaned before it is installed in the case. Use some steel wool (not the soap pads) for this This close-up view shows how the infrared photodiode is mounted. Make sure that the bevelled edge of the photodiode is at upper right. The metal cases of the two tone control pots are earthed by connecting them together as shown here & running a lead back to the EXT EARTH socket on the rear panel. job. Polish each copper switch pad area, then apply a smear of heat­sink compound over the polished areas. This step will prevent the copper from tarnishing, which in turn would lead to intermittent operation of the remote con­trol. Note that this treatment should also be applied to tin-plated boards. Now for the final assembly. Attach the switch matrix board to the case lid with six small self-tapping screws, then clip the components board into the bottom half of the case and bend the LED leads so that the LEDs sit on the plastic cup rests. Finally, feed the battery clip leads through to the battery compartment, then clip the case together and secure it with the self-tapping screw supplied. Chassis assembly Work can now begin on the preamplifier chassis. Assuming that all the chassis holes have been pre-drilled, you can secure the side and rear panels to the baseplate but leave the front panel off at this stage. The four rubber November 1993  59 LED2 LED1 TO BATTERY A K A 11 10 9 K 220uF Q1 2. 2  8 7 6 5 4 3 2 1 100pF 10  100pF 9 10 11 10k IC1 MV500 X1 1 2 3 4 5 6 7 8 0.1 Fig.9: this is the parts layout for the transmitter PC board & its companion switch matrix board. The two are linked together via 8-way & 3-way lengths of rainbow cable. Note that the two infrared LEDs (LED1 & LED2) are installed with their leads at full length. feet should be attached to the underside of the baseplate at this stage, to prevent scratches both to the chassis and to the bench top. The 18 RCA sockets on the rear panel must be insulated from the chassis, either by using insulated sockets or by using non-insulated sockets which mount on an insulated sub­panel. The earth terminal associated with these sockets (EXT EARTH) must also be iso- lated from the chassis. Once these parts have been mount­ ed, install the fuseholder, mains cord and cord grip grommet on the rear panel, then mount the power transformer, earth solder lugs, mains terminal block and power switch. Note that it will be necessary to scrape away the paint (or anodising) from the area surrounding the mounting hole for the earth lugs, in order to ensure a good chassis con­tact. Use a screw, nut and star washer to secure the earth solder lugs, then use a multimeter to confirm that they are indeed connected to chassis (the meter should read zero ohms). Check also that the rear and side panels are electrically connected to earth by measuring the resistance between the chas­sis earth terminal and each panel. If the panels are insulated from the baseplate, you may have to remove some of the anodising from around their mounting holes. The next step is to fit the film mask to the LED displays using double-sided tape. Arrange the mask so that only the LED displays are visible through the windows and position IRD1 so that it is centred behind its allocated window – see photo. When this has been done, fit the front panel to the chassis and push the PC board assembly towards it, so that the various switches and the two tone control pots protrude through their respective holes. Assuming everything fits, the PC board can now be secured in position using machine screws and nuts. In some cases, however, it may be necessary to either file or shim the board standoffs so that all the components pass through their front panel holes without fouling. RESISTOR COLOUR CODES ❏ No. ❏   1 ❏   2 ❏   4 ❏   2 ❏   7 ❏ 14 ❏   6 ❏   2 ❏ 23 ❏   7 ❏   2 ❏   8 ❏ 35 ❏   2 ❏   2 ❏ 10 ❏   1 ❏   4 ❏  1 ❏   1 60  Silicon Chip Value 4.7MΩ 1MΩ 330kΩ 200kΩ 100kΩ 47kΩ 22kΩ 16kΩ 10kΩ 4.7kΩ 1.5kΩ 1kΩ 330Ω 150Ω 120Ω 100Ω 47Ω 33Ω 10Ω 2.2Ω 4-Band Code (1%) yellow violet green brown brown black green brown orange orange yellow brown red black yellow brown brown black yellow brown yellow violet orange brown red red orange brown brown blue orange brown brown black orange brown yellow violet red brown brown green red brown brown black red brown orange orange brown brown brown green brown brown brown red brown brown brown black brown brown yellow violet black brown orange orange black brown brown black black brown red red gold brown 5-Band Code (1%) yellow violet black yellow brown brown black black yellow brown orange orange black orange brown red black black orange brown brown black black orange brown yellow violet black red brown red red black red brown brown blue black red brown brown black black red brown yellow violet black brown brown brown green black brown brown brown black black brown brown orange orange black black brown brown green black black brown brown red black black brown brown black black black brown yellow violet black gold brown orange orange black gold brown brown black black gold brown red red black silver brown These photos show how the rubber membrane fits in position over the switch buttons in the transmitter case. The copper contact areas on the switch matrix board are smeared with heatsink compound to prevent corrosion & ensure reliable operation. Once the board is finally secured, LEDs 1-9 can be pushed into the front panel holes and their leads soldered and trimmed. The bass and treble control knobs can also be fitted. Chassis wiring All that remains now is to complete the chassis wiring – see Fig.10. By far the most tedious part of the job involves the wiring between the RCA input sockets and the main PC board. This wiring must all be run using shielded cable, to prevent hum pickup and minimise crosstalk between channels. Note that the metal cases of the bass and treble control pots are earthed by running a lead back to the EXT EARTH terminal on the rear panel. This measure prevents the preamplifier from picking up hum whenever the tone controls are touched. It will be necessary to scrape away the anodising from the bodies of the pots in order to make good solder joints. Be sure to use 250VAC-rated cable for the wiring to the mains switch, fuseholder and the transformer primary. The Active (brown) and Neutral (blue) leads from the mains cord are connect­ed to the terminal block, while the green/yellow earth wire is soldered directly to one of the earth solder lugs. Insulated sleeving such as heat­ shrink tubing should be used to cover the bare terminals of the fuseholder and the mains switch, to prevent accidental contact. Note that a 0.0047µF capacitor is soldered directly across the mains switch and this should also be covered in heatshrink tubing. The wiring can now be completed by connecting the secondary terminals of the transformer to the PC board. This done, use cable ties to secure the internal wiring at various points. This is particularly important for the mains wiring, since it prevents any leads from coming adrift and shorting to the chassis. Testing Before applying power to the circuit, check your wiring carefully and re- check the PC board against the overlay diagram. Now apply power and check the supply rails at the output of each regulator. You should get +5V from REG1, +15V from REG2 and -15V from REG3. In addition, check that there is about 7.5V across each of the zener diodes (ZD1 & ZD2). If you don’t get the correct readings, switch off and correct the problem before switching on again. Assuming that everything is OK, check that +5V is present at pins 1, 3, 37 & 40 of IC14’s socket. If this checks out, switch off and install IC14, then The switch matrix board is secured to the lid of the case using six small selftapping screws, while the components board clips into position. Arrange the LEDs so that they sit in the small cups at the front of the case. November 1993  61 17 1 16 PHONES LEFT RIGHT PHONO 1 EXT EARTH TAPE IN TAPE OUT VCR VR1 2 3 S5 5 4 3 AUX 1 AUX 2 6 9 8 11 10 13 12 5 6 8 15 14 17 DISP3 TUNER 7 10 12 16 14 DISP2 CD LED10-18 4 7 DISP1 9 11 OUTPUT 13 1 15 2 3 IRD1 S3 S2 S4 LED7-9 1 2 3 2 LED4-6 FUSE LED1-3 CORD CLAMP GROMMET A BRN POWER TRANSFORMER N BLU MAINS TERM. EARTH GRN/YEL SOLDER LUGS 62  Silicon Chip .0047 240VAC 15V 15V 240V S1 Fig.10: be sure to use mains-rated cable for all connections to the mains terminal block, fuseholder & power switch. VR2 Use cable ties to secure the wiring at various locations, as shown in this photograph. Either insulated RCA sockets can be used or you can use noninsulated types mounted on an insulated sub-panel, as shown here. apply power again. The Attenua­tion display should now show a reading of 48.0dB and the 0-9dB balance LEDs should all be lit. The CD LED should also be lit. Now press the Mute switch on the preamplifier and check that all the balance LEDs except the 0dB LED extinguish. If this works, pressing the Up and Down switches should now alter the Attenuation display in 1.5dB steps. Note that pressing the Up switch will decrease the attenuation reading, while the pressing the Down switch will increase the attenuation reading. The remote control handpiece can now be tested for correct operation. Check that the ACK (acknowledge) LED on the receiver lights when one of the remote control switches is pressed and that the appropriate LED lights when each of the Source switches (Phono, CD, Tuner, VCR, Aux1 & Aux2) is pressed. Finally, Below: the rear panel carries nine pairs of RCA sockets for the input & output connections, an earth terminal & the fuseholder. check that the Up, Down and Mute switches operate the displays correct­ ly. Note that the balance adjustment is only available when the preamplifier is unmuted. Note also that the balance display can show two LEDs lit at the same time. For balance settings of 0dB, 3dB, 6dB, 9dB and infinity, only one LED is lit but for in-between settings, two LEDs will be lit. For example, both the 0dB and 3dB LEDs will be lit for the 1.5dB setting. The Tape Monitor, Source, Mono and Stereo selection re­ quires some explanation. Initially, when power is applied, the selection is Source Stereo. You can then select Source Mono by pressing the lefthand Source switch and Source Stereo again by pressing the righthand Source Switch. The Tape Monitor selection can be either “Tape Mon Mono” (by pressing the lefthand Tape Mon switch) or “Tape Mon Stereo” (by pressing the righthand Tape Mon switch). Connecting it up plifier connects between the signal sources (Phono, CD, Tuner, VCR, Aux1, Aux2 & Tape) and the power amplifier. In fact, it’s no different from any other stereo pream­plifier in this respect. When all the connections have been made, switch on and check that you can listen to each source. Check that the volume, balance and tone controls function correctly and that plugging in a set of headphones switches out the loudspeakers. The sound from the headphones should be clean and there should be virtually no background noise. Finally, check that there are no loud clicks and plops from the loudspeakers when the power to the preamplifier is switched on and off. A faint clicking sound as the volume level is changed SC is normal. Where To Buy Kits Readers are advised that kits for this project are not expected to be available until late November 1993 at the earliest. Kits will be available from Altronics, Dick Smith Electronics and Jaycar. The Studio Remote Control Pream- November 1993  63 Design by BERNIE GILCHRIST Build A Siren Sound Generator This little circuit provides three siren sounds – Po­lice, Fire Engine & Ambulance. By making a simple modification, it can also be made to produce a sound similar to a machine gun. It is powered from a single AA size 1.5V cell & is ideal for games & models. At the heart of this project is the UM3561A, an LSI (large scale integration) device which includes a 256 x 8-bit ROM (read only memory) programmed to simulate the siren sounds via an internal tone generator and control circuitry. The only external component that affects the pitch and timing of the siren sounds is the resistor connected between the OSC1 and OSC2 terminals (pins 7 and 8) of the IC and we’ve shown its value as 330kΩ. Reducing the value of this resistor will increase the pitch of the siren sound while increasing the resis­tor will have the opposite effect (ie, lower the pitch). 64  Silicon Chip Varia­tion in the supply voltage to the IC also affects the pitch and timing but to a much smaller degree. Pin 6 on the IC (SEL1) is used to select the siren sound and this is achieved by switching it high (Fire), low (Ambulance) or open circuit (Police) with 3-position slide switch S2. TABLE 1 Ext. Supply R1 R2 3V 560W link 6V 3.3kW 10W 1W 9V 6.8kW 22W 1W 12V 8.2kW 27W 5W The output signal from the IC is a modulated pulse waveform which is roughly equal to the supply voltage in amplitude; ie, slightly less than 1.5V peak-to-peak. The output of the IC drives transistors Q1 and Q2 which operate as a Darlington tran­sistor to drive the 8Ω loudspeaker. The current drain through the speaker is limited by resistor R2. The value of R2 is a compromise between loudness and bat­ tery life. A lower value of resistor will make it louder but the battery life will be shorter. If you are using just the 1.5V cell as shown on the circuit and in the photos, you can replace R2 with a wire link. This makes the speaker quite loud but battery life will be relatively short. For an AA cell, we would expect the battery life to be no more than an hour or so. The 100µF electrolytic capacitor connected between Vdd (pin 5) and Vss (pin 2) is used to decouple the IC from the supply to the output stage. This prevents the relatively high Fig.1: the circuit is based on a UM3561A LSI chip. This includes a 256 x 8-bit ROM which is programmed to simulate siren sounds via an internal tone generator & control circuit. S2 selects between fire, police & ambulance sounds, while the 330kΩ resistor between pins 6 & 7 controls the pitch. S1 OFF D1 1N4007 ON R2 SEE TEXT 330k EXTERNAL BATTERY R1 SEE TEXT 1k 5 1.5V FIRE A LED1 GREEN 100 50VW  S2 POLICE AMBULANCE 6 7 8 VDD OSC1 OSC2 SEL1 IC1 UM3561A SEL2 VSS 1 2 OUT Q1 BC549 3 B 8 SPEAKER C E Q2 BC337 B C E K B A E C VIEWED FROM BELOW K SIREN GENERATOR S1 1.5V AA CELL PARTS LIST D1 R2 R1 330k EXT BATT IC1 UM3561A LED1 100uF K 1 1k Q1 Q2 SPEAKER S2 Fig.2: here’s how to install the parts on the PC board. If you are going to power the circuit from a 1.5V battery, leave out D1 & LED1 & install links in place of R1 & R2. Alternatively, if you intend powering the circuit from an external supply, leave the battery holder out instead & choose R1 & R2 from Table 1. current being switched through the speaker from causing interference with the operation of the IC. Three components, diode D1, resistor R1 and the green LED, are provided for use only with supply voltages of 3V or more. They can be omitted if the circuit is to be powered from a 1.5V battery. Diode D1 protects the circuit in the event that the supply voltage is accidentally reversed. Resistor R1 and the green LED form a 2.3V regulator to supply the IC. Table 1 shows the suggested values for R1 and R2 for exter­ nal supply voltages of 3V, 6V, 9V and 12V. Note that for the higher supply voltages you need to use a bigger speaker otherwise the power rating of the 50mm speaker will be exceeded. A bigger speaker sounds better too. Finally, we should mention the modification necessary if you want to obtain the machine gun sound. This requires pin 1 to be connected to the Vdd rail (ie, pin 5). In this condition, the setting of the slide switch does not matter and the machine gun sound will be emitted in bursts. Our feeling is that most people will not be interested in the machine gun sound and will build the project only for the siren sounds. Assembling the board Putting the board together won’t take long at all since there are so few parts. If you are going to power the circuit from a 1.5V battery, you will need to install the battery holder on the board and you can leave out D1 and LED1 and install links in place of R1 & R2. If you are going to power the board from 3V or higher, you will need R1, D1 and LED1 and you should leave the battery holder off the board. Fig.2 shows all these components on the board just to show their positions. Make sure you install the transistors, the IC, the diode and the LED the 1 PC board, 77 x 33mm (DSE Cat. ZA 1325) 1 AA single cell holder 1 AA 1.5V alkaline battery 1 UM3561A IC (IC1) 1 BC549 NPN transistor (Q1) 1 BC337 NPN transistor (Q2) 1 green LED (LED1) 1 1N4007 diode (D1) 1 50mm 8Ω loudspeaker 1 SPDT miniature slide switch (S1) 1 3PDT miniature slide switch (S2) 1 100µF 25VW electrolytic capacitor 1 1kΩ 0.25W resistor 1 330kΩ 0.25W resistor Note: see Table 1 for values of R1 & R2 if an external DC supply is to be used. Where to buy the kit This project was designed by Bernie Gilchrist of Dick Smith Electronics who own the copyright on the PC board. Complete kits will be available from all Dick Smith Electronics stores at $9.95. The catalog number is K-5514. correct way around and the same comment applies to the 100µF capacitor. After the components are soldered in, carefully inspect the track side of the PC board for bad joints and solder splashes. You can then connect the battery or your external DC power supply and make siren sounds to your SC heart’s content. November 1993  65 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.altronics.com.au ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS ❏ New subscription – month to start­­___________________________ ❏ Renewal – Sub. 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Please have your credit card details ready ______________________________ Card expiry date________/________ Card No. Phone (02) 9979 5644 Signature OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail coupon to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia November 1993  69 COMPUTER BITS BY DARREN YATES More experiments for your games card Games cards are more than just entertainment adaptors – they can provide a simple interface between the outside world & your PC. In this article, we turn your games card into an 8-bit A/D converter using an op amp & a transistor. When we came out with the first “Experiments for Your Games Card” article in January 1992, we looked mainly at using the existing circuitry on the card to accept analog resistive devices such as light-dependent resistors (LDRs) and thermistors. Going back briefly to what we discussed, the games card essentially contains four 555 timers (in the one chip) which are connected up as monostables. The circuit in Fig.1 gives the general idea. The setting of the joystick provides the current which charges the .01µF capacitor. The computer then keeps a record of how long the monostable output is high, once it has been triggered, by incrementing an 8-bit register. Fig.2 shows the pin-outs of the DB15 joystick adaptor sock­et. As you can see, it allows up to four analog inputs (via the joytick controls) and four digital inputs (via the fire buttons). Also included are two +5V supply rail pins and a number of GND pins. Last time, we showed you how to connect an LDR or a ther­mistor into the card to measure light and temperature. This allowed us to measure analog signals “of sorts”. The reason we say this is that using this method, you can’t just apply an analog voltage directly onto the input and that all comes down to the fact that we have to charge up a capacitor in the 555 circuit on the card. Since a capacitor charges up linearly with current and not voltage, this 70  Silicon Chip makes it a bit difficult. Also, if the capacitor doesn’t rise above +3.3V (ie. 2/3Vcc), the 555 will never reach its threshold and switch off after it has been triggered. It is this turning off which tells the computer to stop counting. If we did feed a direct analog Fig.1: the input control circuitry for a typical games card. There are four such circuits to cover all the controls on a joystick. voltage into the joystick inputs, the circuit would not respond until the capacitor’s voltage rose above +3.3V. However, we can solve that with the simple circuit shown in Fig.3. Using one op amp and a transistor, we can turn the joy­stick input into a modest fractional 8-bit analog-to-digital converter or ADC. And since the joystick port comes with four analog inputs, this gives up to four channels. Putting it simply, the op amp and transistor form a vol­ tage-to-current converter which turns our analog input voltage into a current which then charges up the 555’s .01µF capacitor. VR1 adjusts the output current to obtain the best display. Notice that we are obtaining the 5V supply for the circuit from the games card (pin 1). The op amp used is an LM358 dual package so by using just another transistor, you can get a second chan­nel. By using BASIC’s STICK command, it’s a simple case of read­ing off the 8-bit number from that command to retrieve the digi­tal code produced by the games card. Low-frequency scope Fig.2: the pin connection details for the DB15 sockets on a games card. Putting this into practice, we wrote a small program to use the card as a low-frequency oscilloscope. Because QBasic is quite slow and the STICK command even slower, the upper frequency limit is only 10Hz. This is because QBasic can only take 40 readings from the joystick every second –even with a 40MHz 386DX. This necessitates the use of a 100µF capacitor on the input so that low-frequency signals are not reduced in amplitude. Be that as it may, the display in Fig.4 shows the results of the program. Even though 10Hz is a low frequency, the circuit is still useful because it can be used to measure long term changes in circuit voltages, PIN 1 to take a look at QBa­sic. Even though QBasic is 47k only an interpreter, it is a big improvement on GWBasic and it has an easy-toQ1 22k 8 2 BC558 use screen editor and no line numbering! 1 100 IC1a 16VW LM358 The STICK command 3 makes programming the 4 PIN 3 games card quite easy 68k PIN 4 and takes the work out of having to count up registers and examine inputs Fig.3: this simple circuit functions as a voltage to current converter & connects to one of the and all the nitty gritty. It joystick pot inputs. works as follows. When you want to take a reading for an all-up cost of about $2 in parts! of the joystick port, you have to use The maximum input signal is 400mV the STICK(0) statement. When the p-p for a sinewave and 200mV for a program implements STICK(0), it not square­wave. Any more than this and only records the x-input from the the joystick counter register gives first joystick, it also takes a record of erroneous results. all joystick inputs. The good thing With the components specified, about this is that if you decide to use there is a range of about 80 to 170 on all four inputs as ADCs, this system the 8-bit range. It still has 8-bit reso- won’t travel any slower. lution – but not over the full range of STICK(0) holds the x-input from 0 to 255. No, this isn’t eight bits but Joystick A, STICK(1) the y-input from it’s not bad for $2. joystick A, STICK(2) the x-input from joystick B and STICK(3) the y-value Programming from B, but you must use STICK(0) Since January 1992, DOS 4.01 and first. For example, let’s say we wanted DOS 5 have gone by the wayside and to take 640 samples from the last two we’ve moved into the era of DOS 6. joystick analog inputs; ie, the x and y This means that many machines will inputs from joystick 2 and store them have QBasic instead of GWBasic, al- in an array for future use. These correthough the following tips are equally spond to the commands STICK(2) and valid in both. However, if you’re still STICK(3). A simple BASIC routine is working with GWBasic, you may want as follows: VR1 10k Fig.4: this sample display of the output screen is for a 5Hz 100mV RMS sinewave input signal. The on-screen instructions tell you how to expand or compress the x & y axes (note: instructions not shown here for the y axis). DIM SAMPLE1(640),SAMPLE2(640) FOR NUMBER = 1 TO 640 TEST=STICK(0) SAMPLE1(NUMBER)=STICK(2) SAMPLE2(NUMBER)=STICK(3) NEXT NUMBER Note that we must first perform a STICK(0) command before we can get information from STICK(2) or STICK(3). By using DEFINT SAMPLE1, SAMPLE2, you can speed up the program by 5-10% since operation on a single-byte integer variable is faster than floating-point variables. To save these arrays as a file, you could use the following routine: OPEN [FILENAME.EXT] FOR OUTPUT AS #1 FOR NUMBER = 1 TO 640 PRINT#1,SAMPLE1(NUMBER) PRINT#1,SAMPLE2(NUMBER) NEXT NUMBER CLOSE #1 The data is then saved in the following format: SAMPLE1(1) SAMPLE2(1) SAMPLE1(2) SAMPLE2(2) SAMPLE1(3) and so on. By replacing the OUTPUT and PRINT statements with INPUT, you can retrieve this information out of the file, for use in another program. In fact, this is a very basic model of how audio signals can be retrieved from extremely noisy sign­ als using noise averaging techniques. The stored data is fed through an algorithm which manages to remove the noise component and retrieve the original signal. You may even want to try having a crack at it if you have the relevant information. The program CRO.BAS produced the diagram in Fig.4 and can be run from QBasic or, if you have access, on a BASIC compiler. This will speed things up to a degree, particularly if you use Turbo Basic from Borland. If push comes to shove, you could probably get it to work on GWBASIC provided you add in the line numbers. The listing is too long to include here but we can provide a copy of the file on disc, as well as a complied version called CRO.EXE. If you would like a copy, write to SILICON CHIP, PO Box 139, Collaroy, NSW 2097. The cost is $10 (incl. p&p) and payment can be made either via cheque on by quoting a credit card number. Please indicate whether you require a 5.25-inch or SC 3.5-inch disc. November 1993  71 Equipment Review Epson’s new Stylus 800 InkJet printer If you’re tired of your old noisy dot-matrix printer but can’t afford to upgrade to a laser printer, you should take a good look at Epson’s new Stylus 800. With 360dpi graphics cap­ability & quiet operation, it has most of the features of a laser printer but at a lower cost. Review by DARREN YATES Inkjet printers combine the simplicity and economy of dot-matrix printers with the resolution and whisper quiet operation of the laser, without the high initial cost. As well, one of the major benefits of the inkjet printer is access to the same high quality graphics as a laser printer. Epson has recently released the Stylus 800 inkjet printer which is designed as a first-buy printer for homes and small businesses. But don’t think that means that it’s small on features. The Stylus 800 is claimed by Epson to be a revolutionary printer thanks mainly to its Multi-Layer Actuator printing head. If you’ve had a look at inkjet printers in the past, you may have seen evidence of smearing around the edges of the characters. This occurs because of the way in which the jet of ink is sprayed onto the paper at a precise position. However, Epson has developed a new head to “spit” and “cut” the ink droplet so that it doesn’t spray. It helps to improve the output and make it nearly indistinguishable from a laser printer. This makes it suitable for high-definition graph­ics as well as standard text. The Stylus 800 uses a small ink cartridge which is claimed to last around 700 pages at 1000 characters per page and, unlike laser printer cartridges which are quite expensive, replacements are available for only $28, including tax. This makes running an inkjet printer about as cheap as a dot-matrix printer. Epson has redesigned the printhead section from their SQ-870/1170 series so that the Stylus 800 has a permanent print head which requires replacement of the ink supply cartridge only. If you run in economy mode, which effectively uses less ink, the cartridge life can be further extended. This mode is ideal for draft printing work and is quite adequate for most letters, essays, school assignments and so on. Features Epson’s Stylus 800 inkjet printer is quite a compact unit which is capable of producing good quality graphics. It has seven resident fonts & can produce superscripts, subscripts, outlines with & without shadow, & underlining. 72  Silicon Chip For people with a shortage of desk space, one of the at­tractive features of the Stylus 800 is its size – it’s only 435 x 264 x 154mm which is not much larger than Epson’s old LX-400 9-pin printer. All controls except the power switch are on the front panel for easy access as well as all the status indicators. There’s even an “ink low” indicator to tell you when it’s time for a new cartridge. Inside, it has seven resident fonts including Courier, Script, Prestige and Roman but Epson’s new ESC/P2 printer control language also gives GW QUALITY SCOPES 100MHz PLUS FREE DMM A self-test function is built into the Stylus 800 & is activated by holding down the FONT button while the power is turned on. Above is just part of the resulting print out, shown about 75% of actual size. access to scalable fonts from 8 to 32 point, as well as enhanced graphics. Other printing enhancements include superscripts and subscripts, outlines with and without shadow, and underlining. Although the printer is so new that few pro­grams as yet will have a direct Stylus 800 printer driver, it operates extremely well using the LQ-870 ESC/P2 driver available in Windows 3.1. This means it can be used with a large number of drawing, CAD and desktop publishing programs with laser-like performance whilst retaining dot-matrix compatibility. It also has a 100-sheet paper tray and automatic sheet feeding, as well as single sheet manual feeding from the rear. The one thing Epson has left out which we would have liked is a tractor feed option. Because it is designed as a high-quality graphics printer, it doesn’t have a high-speed draft mode. However its speed is still a respectable 180 cps at 12cpi and 300cps at 20cpi. And of course, its whisper quiet operation makes it a delight to have sitting next to the computer. Connection to your PC is via the standard Centronics port, but if you use Epson Connect!, you can also run it from an Apple Macintosh. Impressions Our overall impressions of the printer are quite favour­ able. In just the short time we have had the Stylus 800 here in our editorial offices for review, it was quickly pressed into service once we realised its potential. On the noise-level front, it is just so much quieter than a dot-matrix printer that the cost of slightly reduced printing speed is worth the peace and quiet! It’s also quite a good deal smaller than a laser printer yet more than capable of producing high-definition graphics, including circuit diagrams and front panel artworks! The Stylus 800 retails for $649 plus sales tax where appli­cable and, as we mentioned above, ink cartridges are available for $28. For more information about the Stylus 800 and other InkJet printers, contact Epson Australia, PO Box 410, Frenchs Forest, NSW 2086. Phone SC (02) 452 0666. 40MHz ESCORT EDM-1133 20MHz • • • • • • 3¾ Digits Autoranging 8 Functions DC V, AC V DC A, AC A Ohms Valued at $127! GOS-6100 GOS643 GOS622 4 Channels 2 Channels 2 Channels 100MHz BW 40MHz BW 20MHz BW 500uV - 5V/DIV 1mV - 5V/DIV 1mV - 5V/DIV Dual Timebase to 2ns/DIV Dual Timebase to 2ns/DIV Timebase to 2ns/DIV Dual Timebase Trig Audio Trigger Level Lock Audio Trigger Level Lock Variable Hold-Off Variable Hold-Off Variable Hold-Off 20kV Accel. Voltage 12kV Accel. Voltage 2.2kV Accel. Voltage EMONA INSTRUMENTS NSW (02) 519 3933 VIC (03) 889 0427 QLD (07) 397 7427 Also available from: WA (09) 244 2777 SA (08) 362 7548 TAS (003) 31 6533 November 1993  73 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd Test Equipment Review Australian-designed Unimeter does it all If you have a workbench or workshop loaded down with test instruments, then you should seriously consider the Austra­lian-designed and built Autoplex Unimeter. It could eliminate a lot of clutter. Review by DARREN YATES The Unimeter is just as its name suggests – one instrument that can replace many of the single function pieces that clutter many benches. Not only can it auto-range measure AC and DC volts and current but it has over 100 other functions included which are selected by using the softkeys on the front panel. Some of these functions include metering for a variety of thermocouples, temperature meters for a number of IC sensors (including the LM35, AD592 and LM135), mains frequency meter, tachometer, period monitor, frequency monitor, up/down coun­ters, low-frequency sine and sawtooth generators, efficiency monitor and so on. Also available is optional software and a serial adaptor which allow you to feed data from the Unimeter to a standard PC. Thus, you can continuously monitor systems and save the data for later retrieval. You can also display the data graphically on screen for dynamic presentation and professional results. The software is menu driven and allows the user to The Unimeter is a multi-function instrument which interfaces with a PC to give on-screen displays of various measurements. Over 100 functions are accessible via the softkeys on the front panel. 80  Silicon Chip print out data and screen shots for hard copy storage. The Unimeter itself is very small, measuring just 150 x 91 x 44mm, and is designed to sit in a small instrument rack, the water and dustproof front membrane keeping the instrument free of foreign matter. Unlike many PC-interface instruments, the Unimet­er has a 4.5-digit liquid crystal display as well as the afore­mentioned softkeys. Programming Two comprehensive manuals explain how the device is programmed and also give programming examples on the RS232-RS485 data transfer protocol. Each function is explained with its own set of specifications so you know exactly what the Unimeter is capable of producing while working on that function. Easy to follow diagrams show how the front panel of the Unimeter is programmed, as well as how external devices such as the serial interface, flow meters, thermocouples and the LM35 temperature sensor are connected. Incidentally, an RS232-to-RS485 adaptor is also available, while mounting brackets and the hardware required are provided. Instructions on how to run the software are also included in the manual. This software is quite easy to use and very versatile, with on-screen graphical display of up to four variables available simul­ taneously. All inputs and outputs are connected to the back of the meter, leaving an uncluttered front panel which is easy to see and operate. Part of the design also includes the first QUADAC Quad-Slope Dual Referenced Bi-directional Conversion technique, which gives 14.5-bit conversion This screen capture shows the just four of the capabilities of the Unimeter (Function Generator, Rate Monitor, Process Meter & Linear Movement). Note that the display is normally in colour, thus giving a much more impressive readout than that shown here. but a resolution of 20 bits. This gives an overall accuracy of ±0.1% which is very good for an instrument of this type. Auto calibration is performed every 10 seconds to maintain this accuracy and ensure that measure­ments are spot-on. This is quite an amazing piece of gear when you consider that all of these functions come inside such a tiny package. It is ideal in most industrial control processes and represents a big step forward in wide-range data acquisition. One of the great things about the Unimeter is that it is designed and built in Australia and is distributed worldwide by Nilsen Instruments Pty Ltd. The cost of the Unimeter is $490 plus $400 for the optional software. Optional extras including a serial adaptor, a PLC interface and a power supply are also available (prices include sales tax). For further information, contact Allan Winford at Nilsen Instruments SC Pty Ltd, phone (03) 419 9999. November 1993  81 VINTAGE RADIO By JOHN HILL The vexed question of originality How far should one go to ensure originality when restor­ing a vintage radio receiver? Often, for all sorts of reasons, non-original parts & materials must be substituted if the set is to be restored to working order. Way back in the January 1993 issue of SILICON CHIP, the “Mailbag” page carried a letter which severely criticised me for converting a battery-powered receiver to 240V AC operation. Apparently, battery radios must remain battery radios for ever. I did not bother answering my critic at the time, mainly because of the time lag involved. SILICON CHIP operates on a two-month lead time and any reply would have taken months before it finally reached the news­ stands. By that stage, the issue would have long been forgotten. Since then, however, I have had second thoughts on the matter. Unlike my critic, many other enthusiasts share my view­point and they do not insist that originality be maintained at all cost. This month’s Vintage Radio will present some of my thoughts on maintaining originality when restoring old radio receivers. The Historical Radio Society of Australia (HRSA), of which I am a This 1930 3-valve Seyon was the first reasonably original old receiver the author found. Even then, it had the wrong output valve & its accompanying loudspeaker had long been lost. 82  Silicon Chip member, puts out a quarterly newsletter. From time to time, there have been comments in the newsletter regarding the alteration of receivers (AC conversions and the like) and the Society generally does not condone such modifications. That said, the fact remains that collectors are individuals with minds and opinions of their own. If someone wants to convert a battery receiver to 240V, then it really has nothing to do with anyone else. I know from my own experience that an AC conversion is an interesting challenge and mine eventually proved quite successful once the bugs had been ironed out. I also believe that the receiver would be much easier to sell in its present 240V form than if it had been left as a straight battery set, requiring a mountain of batteries or a special power supply to run it. Surely using a specially made modern power supply is departing from the origi­ nality aspect just as much as an AC conversion? With the set I converted, the chassis was already punched for the rectifier valve and power transformer, so why get uptight about adding these components? Even though the receiver ended up being quite unoriginal, only someone fairly familiar with that make and model of receiver would notice the difference. The modifications are not very apparent until one looks underneath the chassis, where the wiring and some components are far from authentic. But how many people are going to insist that the chassis be removed from the cabinet for an originality inspec­tion? The most critical of the “it must be original” brigade seems to be the older collectors who have been collecting most of their lives. These people have as original items in their vintage radio collections. Amplion horn speaker Early AWA Radiolettes with bakelite or timber cabinets are very collectable items. This particular series is often referred to as the “Empire State” model, due to the shape of its cabinet. The set shown is very original & includes the correct knobs, badge & speaker cloth. Although the power cord has been re­placed, it looks as though it could still be the original. A good example of some of these wrecks was described in Vintage Radio for February 1993. In this instance, an Amplion horn speaker was rebuilt from parts that were salvaged from three damaged and incomplete speakers. To make matters worse (from an originality perspective), some of the metal work was re-nickelled and some was repainted, while the timber work was fully refur­bished using satin Estapol®. I’ll pause now while everyone throws their hands up in horror. Unoriginal and all as the little Amplion may be, it looks absolutely beautiful. What’s more, I have received many a request to sell it, with offers of up to $400 being made to tempt me. Would an unrestored original with crazed lacquer and peeling nickel be more valuable? I take pride in my restorations and do them to the best of my ability. The restoration of the old Amplion horn speaker required considerable care and a reasonable degree of skill. When such a project is completed, there is a great feeling of achievement. Surely this must be more rewarding than rubbing Marveer® over the original? Timber cabinets Very few timber cabinets retain a good surface finish after 50 or more years. In the case of the previously mentioned AC conversion (which involved combining two wrecks), the better of the two cabinets was 90% bare timber with loose veneer. What is one supposed to do – keep it original or refurbish it? As far as I am concerned there is no choice in the matter. Most timber cabinets require the full restoration treatment if they are to look presentable again. Nothing looks worse than crazed or flaking lacquer – even if the remaining fragments are the remnants of the authentic original finish. On several occasions in this column, mention has been made of installing modern capacitors inside the cardboard tubes of older paper capacitors. This suggestion was included for the benefit of those who may wish to retain an authentic appearance for the under-chassis components. Personally, I have never done this and it is most unlikely that I ever will, simply because it seems such a ridiculous waste of time and effort, the result of which will be hidden from view anyway. If ever such a doctored receiver finds itself on my workbench, the first thing I will most likely do is cut out all the old “paper” capacitors. Power cords What should be done regarding the use of original power cords? Original power cords may look authentic but, in most cases, the natural rubber used in their manufacture becomes perished and no longer provides a safe level of insulation. One only has to twist some of this old power flex to hear A 1934 timber cabinet Radiolette in very original condition. The major differences between this model and the bakelite “Empire State” version were the round dial &, on later models, the valve shielding. had the advantage of picking up early radios and spare parts when they were still plentiful and in good condition. That makes keeping them original a much easier task. Today’s collector is faced with an entirely different situa­ tion because most of the receivers he finds are – more often than not – total wrecks. If the “keep it original” brigade could see some of the things I have found in various stages of disrepair, they most certainly would not want them Rear view of “Empire State” Radiolette. This 1936 model uses individual valve shields which makes valve replacement easier than the earlier model. This receiver still has its original loudspeaker. November 1993  83 Rear view of the timber cabinet Radiolette. Note the different valve shielding used in this model, compared to the unit in the bakelite cabinet. Apart from that, the two are virtually identical. the brittle rubber insulation cracking. Plastic covered wire may not look the part but it is usually a lot safer than the cord it replaces. Speaker grille cloth is another originality problem worth discussing. I have seen many restored receivers with tattered, moth-eaten speaker cloths which have been left in place because of originality. Some have even had the holes sewn together which is a fairly obvious repair. Surely some reasonably appropriate replacement material is preferable to a faded, dirty, moth-eaten original? While on the subject of originality, it is interesting to look through the 1993 Vintage Radio Calendar, keeping in mind that the featured receivers are owned by some of Australia’s foremost radio collectors. The Peter Pan on the front page of the calendar is missing all of the capital city stations that are normally marked in red on the front of the dial. That’s not very original, is it? But who is going to throw the set away because of a few missing stations and who would expect to find the red station markings on the front of the dial when polishing it? Can you pick out the sets in the calendar that may have the wrong knobs, power cords or non-original speaker cloths? Maybe, maybe not! Regardless of this, the sets in this beautifully presented calendar look the part and that’s what really counts. Old Bill, a collector Another popular Radiolette model from the author’s friend of mine, has collection. It’s not quite as original as the models quite a few interesting featured on the previous page. The speaker cloth has radios from the 1920s. I been replaced & its chassis is in only fair condition might add that not one due to surface rust. 84  Silicon Chip of them is in working order. What’s more, on closer examination, some of these sets have had quite major alterations made to them in the past and so are not very authentic at all. One such receiver is a 6-valve Mc­ Michael superhet. It is an impressive looking receiver of about 1924-5 vintage. It must be that old because it was originally made to receive the long-wave hand which was in use for a short period of time before general broadcasting switched to what is now commonly called the AM or broadcast band. The authenticity of the old Mc­ Michael has been sadly ruined due to some serviceman’s modification (a hand-wound aerial coil on a cardboard former), so that the receiver could tune into the “new” broadcast band which came into existence sometime in the mid 1920s. What should be done with such a receiver? Leave it with an “authentic modification” or convert it back to the long-wave band with further non-original circuit alterations? How extreme do you wish to be regarding originality? Originality vs practicality Now readers should not think that I am one-eyed or anti-original. I am not but I do like to think that I am reasonably practical. In fact, there are a number of receivers in my collec­tion that are very original, although they are few and far bet­ween. These receivers were in exceptional condition for their age when I acquired them and I have tried to maintain their original appearance. Some still retain their original speaker cloths and cabinet finish, while the chassis have only been cleaned and polished, not repainted. They also have the right shaped valves and, generally speaking, look the part. I can appreciate the value of such sets but if I only col­lected these “good ones”, then I would have a very small collec­tion indeed. As for the remainder of my radios, most were found in quite poor condition and I have either restored them, combined them with other similar models, or converted them to 240V opera­tion as I saw fit at the time. The veteran and vintage car people probably have similar discussions about originality. I imagine that if they strove for complete originality there would be very few old cars in working order and those that were would be rusty, smoke-belching rattle traps. I found out many years ago when driving a Skoda 1200 sta­tion wagon (one of six in Australia) that, with modifications – Austin pistons, an A40 timing chain and a Holden carburettor – it worked quite well. When the bonnet was down, no-one would have ever known the difference. Incidentally, the Skoda was given to me – that was the only way its previous owner could get rid of it. After six years, I eventually gave it away too. While improvisation can keep many an old car or radio re­ceiver in working order, keeping them completely original is another matter. Originality is a nice ideal but a fairly unre­alistic one in most instances. If an old valve radio is 100% original, then there is every chance that it does not work. If it is working, it has most likely had some of its parts replaced at some time or other and is, therefore, no longer original. As stated before, it depends on what extremes one wishes to go to regarding this matter. Some would argue that there are varying degrees of origi­nality: completely original, very original, fairly original, not very original and fairly unoriginal. No doubt you can add a few more categories to this list. It all depends on what parts are available and how much money one is prepared to spend restoring a receiver. From my point of view, I enjoy my involvement with vintage radio. I like to get old receivers working again without spending more on the project than it is worth. I think that this is where some collectors lose sight of reality because when the time comes to sell some of their wares, they cannot get back what they have spent. When all is said and done, they are only old radio receiv­ers that, until a few years ago, were being discarded in great numbers because no-one wanted them. Now, for some reason or other (so I am told), they should be maintained in their original condition. Well, I don’t think that that is being very realistic and I for one will continue to do my own thing as I see fit! No doubt, some readers will wholeheartedly support what I have written in this story, while others will This view shows the old McMichael Super-Seven superhet receiv­er that was mentioned in the text. While the receiver looks fairly genuine on the outside, a major modification to the aerial cir­cuit has spoilt the set’s originality. This close-up view shows the hand-wound aerial coil that was used to convert the McMichael receiver to broadcast band reception (the set was originally made to receive the long-wave band). Note the two IF transformers sitting next to the home-made coil. completely dis­agree. Normally, I am not so outspoken about such matters, pre­ferring to let others do as they wish without my interference. Hopefully, others will view my activities in a similar manner. However, I was challenged about the wilful destruction of two “authentic” battery powered radios. After considerable delib­eration, this has been my reply. I hope that I have not offended too many of my readers. On to more important matters next SC month. November 1993  85 PRODUCT SHOWCASE sy-chain other devices. This drive, which has a 64K buffer, is mainly intended for Apple Macintosh users because it can be plugged straight into their standard SCSI port and it's ready to go. For further information, contact Multimedia Technology on (03) 859 7105 or Panasonic Australia on (02) 986 7400. Low cost frequency synthesizer Panasonic CD-ROMs now available Panasonic expects that its CD-ROM disk drives will capture a significant percentage of the rapidly growing CDROM market in Australia. The range comprises several models, all featuring fast access times of 290ms. They are available in AT-BUS or SCSI formats and can be built-in or stand alone. Panasonic currently employs a caddy system but it expects to release traytype CD-ROMs later this year. The biggest seller of the current range is the CR-522-B internal AT-BUS drive. It can be easily installed into a spare 5-1/4" floppy disk bay. It is connected from the power supply and a 40 wire cable runs to either the controller card or directly to the sound card. The CR-522-S is designed as a stand alone unit, for those situations where a computer's power supply is inadequate to support another peripheral. It has a 64K buffer. For applications where more than one CD-ROM drive is required, Panasonic markets the model CR-501 which allows up to seven drives to be linked together in a daisy chain. External SCSI model, the Panasonic CR-501-S, has a separate power supply as well as the abililty to dai- Giant digital bargraph display Amalgamated Instrument Co. has announced the release of a new extra large digital bar graph display. Designated the model LD4-574BG, it features high visibility and high brightness 57mm LED digits which are readable from at least 25 metres away. The LD4-574BG is suitable for monitoring any industrial variable where a graphical representation as well as a digital display is required. Strain gauge, pressure transducers and load cells, 4-20mA, 0-1 volt, 0-10 volts, BCD, binary and frequency make up part of the large 86  Silicon Chip range of input types available. Analog input models are available with an inbuilt alarm relay output. For further information contact Amalgamated Instrument Company on (02) 476 2244. Capable of ultra-wide frequency synthesis, the FSC-30 and 50 are half length cards for any PC-XT/AT/386 and provide one or to two independent TTL level programmable square wave generators, at low cost. Both models come with one or two synthesisers per card, with each channel being independent of the other, and crystal controlled for excellent stability. An optional external reference input is also available, with reference source then being jumper selectable between external or on board frequency source. Software supplied with the cards provides either command line or popup menu selection of output frequency. Driver software is also supplied, with source code, for writing custom programs and an example program is included. The FSC-30 has a range of 0.024Hz to 30MHz while the FSC-50 has a range of 2.98Hz to 50MHz, with resolution for both being 27,000 steps per decade. The cards have three switchale addresses, for multiple card use, and are connected via 50W coax with BNC connectors. For further information, contact Boston Technology Pty Ltd, PO Box 1750, North Sydney, NSW 2060. Phone (02) 955 4765. Scratch remover for compact discs Harald Schmid, an inventor in Ludwigsburg, Germany has produced a kit that allows the removal of scratches from compact discs by grinding down a portion of the outside plastic shell with a specially designed sandpaper. It sounds fiendish but it is claimed to work. Despite claims that compact discs never wear like vinyl plastic records, scratches on the disc's transparent coating can interefere with the process of reading the recorded data. The result is that damaged or scratched CDs can cause players to mistrack, mute or skip. Several companies have begun marketing disc repair kits that usually include polishing and cleaning materails. Mr. Schmid's kit goes a step further by including several grades of sandpaper and guidlines for removing even fairly deep scratches. Trackmate Australia Pty Ltd, manufacturer of audio, video and computer care products, is distributing the CD repair kit in Australia. Suggested retail price of the Trackmate CD repair kit is $29.95 and it is available at all Tandy stores and selected hifi retailers. For further information, contact Trackmate Australia Pty Ltd on (02) 973 1807. Re-inking service for printer ribbons Inverell Technology Centre has introduced its new ultra high speed fabric ribbon re-inking machine. Up to now it has not been possible to accurately re-ink ribbon cartridges and these would usually be thrown away. Utilising microcomputer technology, the system can accurately re-ink the majority of fabric ribbons of any physical shape or size at speeds of up to 1 metre per second with ink densities accurately controlled. A single joystick controls all major functions of the machine to allow single handed operation. Direction of ribbon travel is automatically sensed and set, completely eliminating the need to set up motor directions. With this type of system, the most delicate ribbon cartridge may be inked as easily as the largest type available. Once the speed and pressure settings of a particular type of cartridge are decided, they can be saved in a memory and recalled later instantly. Single colour ribbons can be inked as successfully as black ribbons, and bulk rolls may be inked with an optional roll carrier. The machine can re-ink almost all dot matrix fabric printer ribbons typically at a cost of $4.50 to $9.50. Some very large ribbons are up to $30.00 each. As a general guide, ribbons are 40% of the new retail price. Quantity discounts for bulk orders are applicable, and freight is free both ways for orders over $45.00. Ribbons in lots of ten may be sent post free to Inverell Technology Centre, Reply Paid 22, 86-88 Ring St, Inverell, NSW 2360. Phone or fax 067 21 0200. CEBus AUSTRALIA KITS CEBus Australia has opened the Circuit Cellar door to bring you a range of high quality, educational electronics kits. There are three types of kit available: an Experimenter’s Kit which includes the PCBs, manuals, any key components that are hard to find and the basic software required by the finished product. Then there is the Complete Kit which includes everything above plus the additional components required to complete the kit. Finally, there is the complete kit with Case & Power Supply. Regardless of which kit you purchase you get the same high quality solder masked and silk screened PCB and the same prime grade components. Our range of kits includes: HAL-4 4 Ch, EEG Monitor, Complete kit only ................... $356.00 Experimenter’s Kits: SmartSpooler, 256K print spooler ..................................... $214.00 IC Tester, Tests 74xx00 family ICs .................................... $233.00 Serial EPROM Programmer, For 27xxx devices ............... $214.00 Ultrasonic Ranger Board with Transducer.......................... $194.00 NB: The above prices DO NOT include sales tax. Don’t forget we also have the HCS II, Home Control System, available, Its features include: Expandible Network, Digital & Analog 1/O, X-10 Interface, Trainable IR Interface and Remote Displays. Call fax or write to us today for more information. Bankcard, Mastercard & Visa accepted. CEBus AUSTRALIA. Ph (03) 467 7194. Fax (03) 467 8422. PO Box 178, Greensborough, Vic 3087. November 1993  87 VCR as the second tuner, and feeding the VCR video into one of the PIP video inputs. Imagine being able to transmit this around your house using one of your TV transmitters! The Dynalink PIP decoder, will be available, initially in limited quantities At $595. Cat # T1800 For further information contact AVComm Pty. Ltd., PO Box 225, Balgowlah, NSW 2093 Phone (02) 949 7417 or fax (02) 949 7095. TOPFET devices from Philips Picture in picture adaptor Have you ever wanted to monitor your favourite satellite channel whilst watching commercial TV? Now there is a way of doing it. The DYNALINK picture in a picture decoder, allows you to view commercial TV, whilst monitoring your favourite satellite channel, by superimposing the satellite picture in any corner of your TV screen. When something interesting comes on your satellite channel, you just press the SWAP button, and the 2 pictures are transposed, allowing you to view your satellite channel, whilst monitoring the commercical channel. The Dynallink picture in a picture decoder comes with its own remote control unit, has an inbuilt TV tuner and output modulator, has 3 video and audio inputs. The PIP channel has its own audio output, which can be fed directly into your Hi Fi system. Of course, the unit can be also used for 2 commercial channels, by using the inbuilt PIP tuner, and your present With the introduction of the BUK105-50L/S, Philips Semiconductors has extended their 3-pin TOPFET (Temperature and Overload Protected Field Effect Transistor) range with 5-pin versions. This second generation can be used as a general purpose switch for lamps, motors, heaters and solenoids in automotive and other 12-volt systems where protection of the switch and fault condition notification are required. In addition to switched operation, the BUK105- 50L/S can be used in linear mode, without loss of protection. The BUK105 can protect itself from over temperature, caused by overload Coming next month* in Silicon Chip 25 watt hifi amplifier module This neat little module uses just one monolithic power chip in a five-lead package to deliver 20 watts RMS into 4W or 25 watts into an 8W load. The module can be built to suit single or dual supplies and it is protected against short circuits and overloads. It has surprisingly good performance figures and the overall component count is low. You could use it to replace the amplifier modules in an old amplifier or as the basis for new equipment. Build an AC impedance meter Also to be featured in the coming December issue is an AC impedance meter especially designed for PA system installers. It can be used to test transformers, 70V and 100V PA lines and resistors. It has three ranges and a digital display. Stroboscope for speed measurement Most readers are familiar with strobe lamps in discos and stroboscope used to measure the speed of rotating machinery but this design eliminates the dangerous high voltage supply required for the Xenon dischaarge tube. Instead, it uses a brace of high brightness LEDs and a simple power supply. * Although these articles are planned for publication, unforeseen circumstances may change the final content. On sale, 24th November. 88  Silicon Chip or shorted load, and from overvoltage transients. An over temperature will trip a latch in the device which sets the flag and can turn off the MOSFET by discharging the gate. The latch will remain tripped until it is reset by means of the protection supply pin. An overvoltage transient will cause an off-state device to be turned on, clamping the voltage to a safe level. The new device has a vertical power DMOS output stage which features a low on-state drain-source resistance of .05W, a continuous drain current of 29 amps (120 amps peak) and a total power dissipation of 75 watts. For further information contact Philips Components, 34 Waterloo Road, North Ryde, NSW 2113. Phone (02) 805-4455. Visual Basic software Azonic, republisher for Merlin Development Pty Ltd, has announced POWRRR Chart/VB, an Australian developed software for Microsoft Visual Basic developers. POWRRR Chart/VB gives the Visual Basic developer access to charting and presentation graphics capabilities. Included in the software is stylesheet based charting, a file manager/ viewer, a complete illustration package for annotation of charts and hundreds of ClipArt samples to assist the Visual Basic developer to produce a professional paackage. POWRRR Chart/VB requires Windows 3.1, Visual Basic 2.0 or higher, a 386 computer or higher, VGA graphics or higher, 4MB RAM, 4MB available disc space and a mouse. Orders can be placed now at an introductory price of $295 from Azonic Pty Ltd. Phone (02) 878 4444. Education directory on CD-ROM Acorn Computers has released the fourth edition of its education directory. Over 2000 educational titles are listed. This allows the user to browse through the data files, searching for key words or companies or particular types of software. By keying buttons on the display the user gains access to linked pages of information which may contain screen shots, demonstation versions of the software, or further information on particular packages. The CD-ROM version of the directory is available free of charge to schools, directly from Acorn. For further information, contact Peter Revell, Acorn Computers Australia Pty Ltd, 12 Gipps Street, Collingwood, Vic 3066. Phone (03) 419 3033. TDK announces DCC tapes Send Postage Stamp For List Of Other Items Including Valves L.E. CHAPMAN TAPE DECK OR RADIO POWER LEADS Plugs and Sockets $1.50 Test prods and leads $1.50 TOUCH MICRO SWITCHES as used on TV sets. 4 for $1 TRANSISTOR EAR PIECES plug & lead 4 for $2 PUSH BUTTON SWITCHES 4 pos 50c SPEAKER TRANSFORMERS 7000 to 15/Ohm 5W $10 7000 to 3.5Ohm 15W $10 5000 to 3.5Ohm $10 SPEAKERS 5 x 7 $5    6 x 4 $4 5" 8 Watt $5 VIDEO & TV SERVICE PERSONNEL TV & VIDEO FAULT LIBRARIES AVAILABLE AS PRINTED MANUALS $90 EACH + $10 DELIVERY BOTH MANUALS VIDEO & TV $155 + $15 DELIVERY OR AS A PROGRAM FOR IBM COMPATIBLES $155 + $10 DELIVERY INLINE FUSE HOLDERS 4 FOR $1 SHIELDED LEADS 7ft 3.5 to 3.5 $1 3.5 to 6.5 $1 6.5 to 7ft 75c Inline Baynet Plugs & Sockets 4 for $1 SHIELDED CABLE 10m $2 TAG STRIPS 10 for $2 mixed FOR MORE INFORMATION CONTACT TECHNICAL APPLICATIONS FAX / PHONE (07) 378 1064 PO BOX 137 KENMORE 4069 50c 50c $1 ea 50c 10 for $1 $1 ea 3 for $1 3 for $1 $1 ea 5 for $1 3 for $1 4 for $1 10 for $1 5 for $1 4 for $1 IC SOCKETS 16 pin * 24 pin * 28 pin Four for $1 PLUGS & SOCKETS R.C.A. plugs and sockets 50c pair 2.5mm sockets 4 for $1 3.5mm sockets 4 for $1 6.5mm sockets 4 for $1 Thermistors 4 for $1 Speaker plugs and sockets 4 pin 50c pair 2 pin 50c pair POTS 1/2Meg $1.50 Dual 2 Meg Ganged Lin $2.00 1/2 Meg Switch $2.00 Dual 1 Meg Ganged Lin $2.00 1 Meg $1.50 1 Meg Dual Ganged Log $2.00 1 Meg Switch $2.00 10k Ganged Log $1.00 25k Dual Ganged $2.50 50 Ohm Single 50c ELECTROS 20UF 450V 2000UF 25V SLIDE POTS 1/2 Meg dual 1 Meg Dual 1 Meg Dual 1k Dual 25k Dual 5k Single 250k Single 10k Single $1 $2 $2 $1 $2 50c 50c 50c SPECIAL 12 Mixed Switches TWO WAY SPEAKER CROSSOVER NETWORK $2 TDK have announced the release of their DCC tape to the Australian market. Available in two record/ playback times, DCC-XG60 (60 minute) and DCC-XG90 (90 minute), the tapes are priced at $13.95 and $15.95 respectively. For further information and the address of your nearest TDK SC dealer, ring (02) 437 5100. SPECIAL PICK UP ARM Includes cartridge and stylus. Plays mono or stereo $15 5 MIXED ROTARY SWITCHES 5 for $2.50 Special TUNING CAPACITOR 2 gang covers all Aust. AM bands. $10. P&P $1.80 for one or two. CAPACITORS 6N8 150V 1000uF 16V 1000uF 50V 0.0039uF 1500V 0.0068 250V 47uF 63V 47uF 160V 470uF 16V 47uF 200V 0.1uF 250V 680uF 40V 0.027 250V 10uF 25V 22uF 160V 0.039uF 400V SPECIAL Dual VU Meters $4. P&P $1.80 for one or two $1.50 $1 $4.50 200 MIXED SCREWS self-tappers, bolts, nuts etc. 200 for $2 CAR RADIO SUPPRESSORS 4 for $2 OXTAL VALVE SOCKETS $1 each Stick Rectifiers TV20SC $2 Transistors AD61-62 pair $3 AD 149 $2 each Chrome 1/4" push on knobs RRP 1.20 EA 10 for $1 Mixed capacitors fresh stock 100 for $2 Mixed resistors all handy values 100 for $2 Slide pot knobs 10 for $1 1F 455kHz for valve radios $2 ea Telsco Microphone Ceramic $2 pp $1 SPECIAL: CELLULAR HORN TWEETER Mounting specification 12.5cm x 7.1cm. Frequency range 2000-20,000Hz. Sensitivity 105dB. Maximum power 30 Watts. Impedance 8 ohms. $12. TV CRYSTALS 4.43619kHz 03061 NDK; 8.867238kHz 03122.937 $2 each. VALVES 6K7 $10 6U7 $10 6V4 $7 6BL8 $7 6SA7 $10 12AX7 $10 6BQ5 $10 6AV6 $10 6SN7 $10 EF50 $7 6K8 $12 1S5 $7 6BM8 $10 5AS4 $10 IT4 $7 6AM8 $10 6SL7 $10 205A $10 12AT7 $10 6J5 $10 6AS6 $10 6AN8 $10 6005 $10 12DL8 $10 6136 $10 12BL6 $10 6X4 $10 6SL7 $10 12X4 $10 6BE6 $12 6V4 $8 6M5 $12 EM84 $12 IR5 $10 6LEA8 $10 6N8 $12 6BV7 $10 6EM7 $10 6AU6 $10 12AU7 $10 6LM6 $10 EF86 $10 6X9 $10 6BAL6 $10 152 $5 6AQ5 $10 122 Pitt Road, North Curl Curl, NSW 2099 Phone (02) 905 1848 Send Postage Stamp For List Of Other Items Including Valves November 1993  89 Silicon Chip (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. BACK ISSUES September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man’s Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSB Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. February 1989: Transistor Beta Tester, Cutec Z-2000 Stereo Power Amplifier, Using Comparators To Detect & Measure, Minstrel 2-30 Loudspeaker System, VHF FM Monitor Receiver, LED Flasher For Model Railways, Jump Start Your New Car March 1989: LED Message Board, Pt.1; 32-Band Graphic Equaliser, Pt.1; Stereo Compressor For CD Players; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Map Reader For Trip Calculations; Electronics For Everyone – Resistors. April 1989: Auxiliary Brake Light Flasher; Electronics For Everyone: What You Need to Know About Capacitors; Telephone Bell Monitor/ Trans- December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier IC; Installing A Clock Card In Your Computer; Index to Volume 2. mitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Electronic Pools/Lotto Selector; Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; LED Message Board, Pt.3; All About Electrolytic Cap­acitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Rad­ios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.4. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; Alarm-Triggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speed­ing Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2; PC Program Calculates Great Circle Bearings. March 1990: 6/12V Charger For Sealed Lead-Acid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer. October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station; Weather Fax Frequencies. November 1989: Radfax Decoder For Your PC August 1990: High Stability UHF Remote Trans- Please send me a back issue for: ❏ February 1989 ❏ March 1989 ❏ July 1989 ❏ September 1989 ❏ January 1990 ❏ February 1990 ❏ July 1990 ❏ August 1990 ❏ December 1990 ❏ January 1991 ❏ May 1991 ❏ June 1991 ❏ October 1991 ❏ November 1991 ❏ March 1992 ❏ April 1992 ❏ August 1992 ❏ September 1992 ❏ January 1993 ❏ February 1993 ❏ June 1993 ❏ July 1993 ❏ November 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ September 1988 April 1989 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 May 1992 October 1992 March 1993 August 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ November 1988 May 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 June 1992 November 1992 April 1993 September 1993 ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ➦ Use this handy form to order your back issues December 1988 June 1989 December 1989 June 1990 November 1990 April 1991 September 1991 February 1992 July 1992 December 1992 May 1993 October 1993 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 979 5644 & quote your credit card details or fax the details to (02) 979 6503. ✂ Card No. mitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2. Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. September 1990: Music On Hold For Your Tele­ phone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. November 1991: Colour TV Pattern Generator, Pt.1; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Modifying The Windows INI Files. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; Using The NE602 In Home-Brew Converter Circuits. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Solid-State Laser Pointer; Colour TV Pattern Generator, Pt.2; Windows 3 & The Dreaded Un­ recov­erable Application Error; Index To Volume 4. November 1990: How To Connect Two TV Sets To One VCR; A Really Snazzy Egg Timer; Low-Cost Model Train Controller; Battery Powered Laser Pointer; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Simple 6-Metre Amateur Transmitter. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; Restoring An AWA Radiolette Receiver. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape – A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. July 1991: Battery Discharge Pacer For Electric Vehicles; Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; PEP Monitor For Amateur Transceivers. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Installing Windows On Your PC; Step-By-Step Vintage Radio Repairs. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1; Build A Fax/Modem For Your Computer; The Basics Of A/D & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; Designing A Speed Controller For Electric Models. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Direct­ ories; Valve Substitution In Vintage Radios. April 1992: Infrared Remote Control For Model Railroads; Differential Input Buffer For CROs; Studio Twin Fifty Stereo Amplifier, Pt.2; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; LowCost Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; Infrared Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; What’s New In Oscilloscopes?; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Off-Hook Timer For Tele­phones; Multi-Station Headset Intercom, Pt.2. August 1992: Build An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; Dummy Load Box For Large Audio Amplifiers; Internal Combustion Engines For Model Aircraft; Troubleshooting Vintage Radio Receivers. September 1992: Multi-Sector Home Burglar Alarm; Heavy-Duty 5A Drill speed Controller (see errata Nov. 1992); General-Purpose 3½-Digit LCD Panel Meter; Track Tester For Model Railroads; Build A Relative Field Strength Meter. October 1992: 2kW 24VDC To 240VAC Sine­wave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; Electronically Regulated Lead-Acid Battery Charger. November 1992: MAL-4 Microcontroller Board, Pt.1; Simple FM Radio Receiver; Infrared Night Viewer; Speed Controller For Electric Models, Pt.1; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.2; Automatic Nicad Battery Discharger. December 1992: Diesel Sound Simulator For Model Railroads; Easy-To-Build UHF Remote Switch; MAL-4 Microcontroller Board, Pt.2; Speed Controller For Electric Models, Pt.2; 2kW 24VDC to 240VAC Sinewave Inverter, Pt.3; Index to Volume 5. January 1993: Peerless PSK60/2 2-Way Hifi Loudspeakers; Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Simple Projects For Model Railroads; A Low Fuel Indicator For Cars; Audio Level/VU Meter With LED Readout; Build An Electronic Cockroach; MAL-4 Microcontroller Board, Pt.3; 2kW 24VDC To 240VAC Sine­wave Inverter, Pt.5; Making File Backups With LHA & PKZIP. March 1993: Build A Solar Charger For 12V Batteries; An Alarm-Triggered Security Camera; Low-Cost Audio Mixer for Camcorders; Test Yourself On The Reaction Trainer; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Build An Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Step-Up Voltage Converter; Digital Clock With Battery Back-Up; A Look At The Digital Compact Cassette. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Remote Volume Control For Hifi Systems, Pt.1; Alphanumeric LCD Demonstration Board; Low-Cost Mini Gas Laser; The Micro­soft Windows Sound System. June 1993: Windows-Based Digital Logic Analyser, Pt.1; Build An AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; A Digital Voltmeter For Your Car; Remote Volume Control For Hifi Systems, Pt.2; Double Your Disc Space With DOS 6. July 1993: Build a Single Chip Message Recorder; Light Beam Relay Extender; Build An AM Radio Trainer, Pt.2; Windows Based Digital Logic Analyser; Pt.2; Low-Cost Quiz Game Adjudicator; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 1; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60LED Brake Light Array; A Microprocessor-Based Sidereal Clock; The Southern Cross Z80-based Computer; A Look At Satellites & Their Orbits; Unmanned Aircraft – Israel Leads The Way; Ghost Busting For TV Sets. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Electronic Cockroach; Restoring An Old Valve Tester; Servicing An R/C Transmitter, Pt.1. October 1993: Courtesy Light Switch-Off Timer For Cars; FM Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1; Mini Disc Is Here; Programming The Motorola 68HC705C8 Micro­ controller – Lesson 2; Servicing An R/C Transmitter, Pt.2. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier, Pt.3; Build A Siren Sound Generator; Electronic Engine Management, Pt.2; More Experiments For Your Games Card; Preventing Damage To R/C Transmitters & Receivers. PLEASE NOTE: all issues from November 1987 to August 1988, plus October 1988, January, February, March & August 1989, May 1990, and November and December 1992 are now sold out. All other issues are presently in stock, although stocks are low for some older issues. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $7.00 per article (incl. p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. November 1993  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Give the transformer a fair go I recently constructed the Universal Power Supply Board described in the August 1988 issue of SILICON CHIP. I used the Dick Smith M2856 transformer which has a multi-tapped secondary (giving 30V centre-tapped or 36V centre-tapped – Editor). I connected the 0V from the transformer to 0V on the board, 15V from the transformer to 30V on the board and the other 15V wind­ing to 15V CT on the board. I tested the output voltages from the circuit board and obtained +15V on that output but no negative voltage, then after several minutes, I had no voltage and the transformer became very hot. I took it out of circuit and found the primary winding open circuit. I returned it and obtained a replacement. It was assumed the transformer was faulty. I tested the replacement before placing it into circuit and obtained all the correct voltages. I then connected it to the circuit and the same thing happened. Surely not another faulty transformer? I checked the circuit and components and could not find any faults. Suddenly it dawned on me! I should have connected the transformer outputs to the circuit board as follows: 0V to the Problem with the Walkaround Throttle I have built the Walkaround Throttle Controller; ie, the pulse width modulated circuit described in April and May 1988 issues of SILICON CHIP. My problem is that it has lost the minimum setting for the throttle. I can adjust the maximum voltage setting via trimpot VR1, however the minimum trim­pot VR2 makes no difference and the throttle fades to zero volts by half-way; ie, from 0-50% on 92  Silicon Chip position marked CT 15V on the board; one 15V to the 30V position on the board and the other 15V tap to the 0V on the board. Even considering this to be the correct way, I do not see how connecting it the way I did would cause the primary coil to overheat. The only thing I had connected to the output of the circuit board was my multimeter to test for correct voltages. Therefore there was not any excessive current being drawn from the secondary coil. Can you offer any explanation. (W. C., Adam­stown Heights, NSW). • From your description, it appears as though you have placed a direct short circuit across one of the 15V windings of the transformer. That is why it became very hot and eventually burnt out the primary winding. Your alternative method of connection appears to be correct and should not cause any problems. The way to test these things is as you proceeded in the first place. Apply power, measure the voltages and, if conditions are not correct, switch off and check for faults. Big power supply for model motors I am interested in the circuit on page 93 of the July 1993 issue, showing how the throttle there is 0V, and from 50-100% throttle it goes from 0V to 12V. Can you help me with this problem as it affects slow start­ing by taking an eternity to reach halfway before it starts to move. It also seems to have too much inertia. (G. H., Lambton, NSW). • The fault with the minimum speed setting is likely to involve op amp IC1b which buffers trimpot VR2. This op amp is shorted or dead. Check for shorted tracks or replace the op amp package. to increase the output of a 3-terminal regulator. I have a need to supply power to small motors as used in model aeroplanes, with short time test currents of up to about 35 amps. Your circuit with two transistors is said to be capable of delivering up to 8 or 9 amps. Therefore, since the TIP2995 has a current rating of 15A, I should be able to add two more TIP- 2995s in parallel to easily supply a current of 35 amps for a short time. The power source will be a 12V car battery, which will limit the output a bit by the drop across the TIP2995s; voltage control may be lost after about 9.5 or 10 volts, just so long as the output is not limited to that voltage. 2N3055s may work better, due to their better heatsinking although the circuit would have to be changed to suit NPN transistors. I would be using an LM317 to achieve a “soft start” with a pot in place of resistor “R”, (refer to the circuit on page 210 of the DSE catalog), a meter across the output for volts & a series meter for amps. I have suitable digital meters. Your comments on this or a better way to achieve a soft start and control for test periods of a few seconds only will be appreciated. The test is to change the prop, switch on, run the volts up to the “cell equivalent” (6, 7, 8 or 10) read the cur­rent and the tacho, then shut down. The amp/hour capacity of my car battery is more than 50 times that of the nicad flight pack I will subsequently be using. Hence, volts and current will be much more stable and the battery will not require recharging after only a few minutes of testing various propellers. (R. F., Laura, SA). • Essentially, your idea is workable except that we would be inclined to use five or six TIP2995s in parallel in order to be able to handle the current. The LM317 is not suitable since it would not be able to supply the required base current for the power transistors. You will need to upgrade to an LM350 adjust­able regulator which can supply 3A. You will need massive heatsinking for the power transistors, particularly if you want to have a soft start, because this will cause very high power dissi­pation. 6V to 12V inverter wanted for a VW I own a 1965 Volkswagen which is running on a 6V system. The battery is charged by a 6V generator. My question is do you know of any circuitry that will convert 6V to 12V DC with a current capability of around 10 amps which I could use to power an amplifier. (R. C., Glen Iris, Vic). • Unfortunately, we do not have a 6V-12V DC converter. Howev­er, it may be possible to adapt the circuitry of the 12V SLA battery charger described in the July 1992 issue. You would need to modify the output transistors and the switching inductors to boost the output to 10A. How to measure power output Congratulations on a fine magazine. I am very enthusiastic about electronics as a hobby and maybe a career. Now for a few questions: how do you measure the RMS output power of an amplifi­er? Is it necessary to buy or make watt meters? I am using the ETI-1430 power amplifier with the preamplifier from the Studio Twin Fifty amplifier (described in March & April 1992). Is it possible to increase the power by paralleling the output transistors? Also, I have heard mention of “bridging” two amp­li­fiers together for increased power. How is this done? Has SILICON CHIP ever described a digital AM/FM tuner? I know you did an AM tuner but I am in need of AM and FM. When a tuner has “synthesised” stereo sound (FM), does that mean it uses the true stereo broadcast (signified by the 19kHz carrier?) or does it generate its own pseudo stereo? In short, if I transmit­ted a song on the left channel only, would the synthesised FM tuner play a song on the left channel only as well? (J. P., Teralba, NSW). • The method of measuring RMS power output of an amplifier is as follows. You need a resistive load with a power rating greater than the amplifier to be measured and with a value of 8Ω (or whatever the rated impedance is. Problem with digital voltmeter kit I have recently completed the digital voltmeter kit for cars/boats/ solar and, as happens from time to time, the thing refused to work., Actually, as far as I am concerned, this isn’t a bad thing as it makes me find out just how the particular circuit works instead of just wielding a soldering iron whilst listening to the radio. This one was particularly stubborn and, after checking everything about six times without finding a fault I decided one of the ICs must be on the blink. I am always loathe to reach this conclusion but, for once, I was correct and on replacing the BCD counter (MC14553) I got readings instead of a row of noughts. However, I still had a problem. The unit took about a minute to give a stable reading and, until then, hunted a couple of volts on either side. When it settled it was We refer to this as a “dummy” load. Second, you need to apply a sinewave signal to the amplifier. This signal normally comes from an audio oscillator. You then measure the RMS voltage at the output at just before the onset of clipping (you need an oscilloscope to judge this point). It is then simply a matter of calculating the power using the formula: P = V2/R. Increasing the power output of an amplifier cannot simply be done by paralleling the output transistors. If you did this without increasing the supply voltage you will get no power increase at all – in fact you may get slightly less. Secondly, the BC546 used as a driver transistor would not be able to supply the extra base current to the paralleled output transistors. Hence to really increase the power output of an amplifier you need to increase the supply voltage, the power supply capability and the number of output transistors. You will need bigger driver tran­sistors as well. It really amounts to a complete re-design of the power amplifier. Bridging entails the use of two mono amplifiers which are driven with outof-phase input signals. Each power quite accurate but, as I wanted to use it to check three banks of batteries (on a boat) it was not entirely satisfactory. Incidentally, the MC­14553 was the last one I replaced – I’ve changed the other three ICs as well. Finally, for want of something else to do, I finished the digital voltmeter kit by fastening the two PC boards together, back to back. I then fired it up again and, to my considerable surprise (and pleasure), the thing worked without hunting. Apart from a vague thought about a capacitive effect, I am rather baffled. Can you throw any light on the matter? (M. F., Frenchs Forest, NSW). • We are am pleased to know that you have got the project to work and suggest that there was probably some radiation of hash from the 4049 inverter chip into the op amp circuitry and this may have caused the hunting that you observed. amplifier drives one side of the speaker load and, therefore, their voltag­es add, hence the power output is quadrupled, in theory. In practice, the increase is somewhat less. SILICON CHIP has not described a digital AM/FM tuner and since these units are relatively cheap, we are not likely to describe such a constructional project. The term “synthesised” refers to the use of a frequency synthesiser to control the local oscillator frequency. In fact `synthesised’ really means the same thing as the term “digital” when referring to AM/FM tuners. Any synthesised FM stereo tuner produces true stereo reception. Even bigger inverters wanted I would like to propose the following solar based projects, to capitalise on those done by SILICON CHIP so far: (1) A step up/step down battery charger circuit that can regulate up to one kilowatt of solar panels, in three versions: 12V, 24V and 48V. For example, a basic circuit with a dif­ferent component list for each version. Have the circuit adjust­able for the different November 1993  93 Electronic cockroach not light sensitive I am a Year 10 student at Kotara High School in Newcastle, currently studying electronics. For my Year 10 major work I have elected to construct the electronic cockroach which you featured in your February 1993 edition. However, on completion of the project, I find that it does not work correctly; ie, the level of light falling on the LDRs has no effect on the speed of the motors. The motors do work and their speed can be adjusted using the trimpots. I was unable to purchase Johnson 170 motors and have used Mabuchi FA-130 instead. I was unable to purchase BD646 PNP Darlington transistors and was advised by Novacastrian Electronics that the BD650 was equivalent –these have been used. All other components are as specified. Using a multimeter, I only get an increase of about 2kΩ across the LDRs when they are covered. full charge voltages of deep cycle and normal lead acid batteries. A typical household solar set up could have 10 or more 75 watt panels, (ie, 750 watts or more). (2) An article explaining the basic operation of solar panels and regulators. For example, at a solar panel dealer I was told that they only sell normal regulators that shut off once the batteries are charged because shunt circuits waste too much energy. I think they are selling high-priced inefficient low technology to unin­formed consumers. However, until an impartial, comparison is published, the consumer will remain uninformed. Also can solar panels be damaged if they are exposed to bright sunlight with no load applied to their terminals? (3) A five kilowatt sinewave inverter in 24V and 48V versions. (4) An article explaining how to calculate the practical starting wattage of an induction motor from its running wattage. For example, I have a 240V AC water pump rated at 1.9A, (ie, 456 watts maximum). Its practical starting wattage could be as high as 94  Silicon Chip Is the DSCDO1 from Dick Smith Electronics the same as an ORP12 LDR? Examination by my teacher using a CRO revealed highs and lows where he expected them to be. Could you please offer some assistance to locate the fault? (S. H., Newcas­tle, NSW) • First, we hope you have not misunderstood what the motors are supposed to do with changes in light level. The motors either will run at the speed set by trimpots VR1 and VR2 or they will be stopped, depending on the light falling on the LDRs. The motor speed is not set by the LDRs. This is how it works. When LDR1 is exposed to bright light, pin 10 of IC1c will go lower than the pin 11 input and motor M1 will run. Conversely, when LDR1 is in shadow, pin 10 of IC1c will be higher than pin 11 and the output, pin 13, of IC1c will go low to prevent pin 6 of IC1a from going high. The motor will there­fore stop. A similar process occurs with motor M2 and LDR3. 2.2kW (for a few nanoseconds). If this value was correct I would require a 600 watt inverter which has a 2.3kW maximum intermittent rating instead of a 480 watt inverter which only has a 1kW maximum intermittent rating. How do you calculate this practical starting wattage? I would also like to see some data and articles on wind generators. (B. B., St Andrews, NSW). • We are afraid that your proposed solar panel setup with up to 1kW of panels is not practical at all. For example, if you are using a 12V version you would have to control up to 83 amps. As you can see, controlling such a huge current is not a trivial matter. It is much better to connect solar panels in series to a battery bank of 32V, 48V or higher so that the currents are manageable. Solar panels are not damaged if exposed to bright sunlight with no load applied. In fact, it is very difficult to damage them electrically in any way, even with short circuited loads. They are really only susceptible to mechanical damage, such as from hail. You should be able to get the circuit going with the DSCD01 LDRs and this is how you can set up the circuit. You will need to measure the voltage across each LDR when the same amount of light is applied to each device. Check that the voltage across each one is about the same. For the motors to run, the voltage across LDR2 must be higher than the voltages across LDR1 and LDR2. This happens when LDR2 has less light on it than LDR1 and LDR3. You may need to alter the value of the 1.2kΩ pull-up resistor for LDR2, to obtain satisfactory results. Under normal lighting conditions, the voltage across the LDRs should be about 1.5V. You may need to alter the values of the pullup resistors (the 1kΩ and 1.2kΩ resistors) for each LDR to obtain this voltage. If the voltage across each LDR is too low (below 1.5V) use a smaller value of pull-up resistance. Alterna­tively, if the voltages are too high (above 1.5V) use larger value pull-up resistors. The same comment about practicality applies to your sugges­tion for a 5kW sinewave inverter. For example, a version operat­ing from 24V would require an input current somewhere in the vicinity of 250 amps. Our 2kW sinewave inverter described in the latter half of 1992 had an input current of 100 amps or more and this really does present major engineering problems. It is not possible to calculate the starting current of an induction motor. You need to know the type of motor and its rating, the type of load and the point at which the voltage is applied. Typically though, an induction motor will draw some 10 to 15 times its normal load current at switch on. This surge current can last half a second or more, depending on how long it takes for the motor to reach full speed. There is also the ques­tion of its starting winding and how much current it draws. As you can see, designing an inverter to drive an induction motor means that a very large surge capability SC must be incorporated. MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. ANTIQUE RADIO ANTIQUE RADIO RESTORATIONS: specialist restoration service provided for vintage radios, test equipment & sales. Service includes chassis rewiring, recondensering, valve testing & mechanical refurbishment. Rejuvenation of wooden, bakelite & metal cabinets. Plenty of parts – require details for mail order. About 1200 radios within 16,000 square feet. Two-year warranty on full restoration. Open on Saturday 10am-4.30pm; Sunday 12.30-4.30pm. 109 Cann St, Bass Hill, NSW 2197 Phone (02) 645 3173 BH or (02) 726 1613 AH. FOR SALE WEATHER FAX programs for IBM XT/ ATs *** “RADFAX2” $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Suitable for CGA, EGA, VGA and Hercules cards (state which). Needs SSB HF radio & Radfax decoder. *** “SATFAX” $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Needs EGA or VGA plus “WEATHER FAX” PC card. *** “MAXISAT” $75 is similar to SATFAX but needs 2Mb expanded memory (EMS 3.6 or 4.0) and 1024 x 768 SVGA card. All programs are on 5.25-inch or 3.5-inch disks (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, Qld 4005. Phone (07) 358 2785. THE HOMEBUILT DYNAMO: (plans) brushless, 1000 DC watt at 740 revs. $A85 postpaid airmail from Al Forbes, PO Box 3919 - SC, Auckland, NZ. Phone Auckland (09) 818 8967 any time. Rotor magnets (3700 gauss) kit now available. PEER TO PEER NETWORK SOFTWARE: for IBM PCs. The “$25 Network” links 2 or 3 PCs via serial ports at up to 115K bps. Uses only 15K RAM. Only $40. “Little Big LAN” offers multi-user CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send both with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. Or fax the details to (02) 979 6503. record locking, linking via serial, parallel and/or Arcnet cards, up to 250 nodes and print spooling. Only $95. Both support printer re-direction. Prices are for a whole network. Add $3 for postage in Australia. For more information, send SASE to GRANTRONICS, PO Box 275, Wentworthville 2145. Phone A/H (02) 631 1236. BUY ME. 100% Australian Z80 Development System. Short form kit driven from MS-DOS PC printer port. Includes heaps of source code, cross assembler, circuits, Z8TBasic, etc. $38. With EPROM $52. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. 68705 MICRO EMULATOR!!!: Yes! A fair dinkum 68705 hardware ICE for $285 (B&T $330). Run programs in RAM, built-in disassembler, single step, break points, the works! It even emulates 2716, 2732 and 2764 EPROMs. Can be used with a PC, MAC etc. Optional 687053/U/R ($115) and C4/C8 ($95) programmers for direct connec­tion to 68705 emulator. Kits and further info from Graham Blowes, Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone (03) 337 1917(ah), (03) 575 3349(bh), fax (03) 575 3369. SUBSTITUTE FOR A HANDFUL OF ICs: Parallax “BASIC STAMP”. A gen­er­al purpose small circuit module, it is really a 25 x 50mm board with a computer chip (4MHz PIC 16C56), EEPROM, 8 ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my RCS RADIO PTY LTD Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ RCS Radio Pty Ltd is the only company that manufactures and sells every PC board and front panel published in SILICON CHIP, ETI and EA. RCS Radio Pty Ltd, 651 Forest Rd, Bexley 2207. Phone (02) 587 3491 November 1993  95 TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 76 1291. Fax: (065) 76 1003. ICL 286 Board Kits All in one board with two serial, printer, IBM keyboard, high density floppy & IDE mono video interface. Up to 4Mb RAM, 80286-16cpu, MS-DOS compatible, 130 page manual, small size 170mm x 255mm. Max I/O kit for PCs, 7 relays, ADC, DAC, stepper driver, TTL inputs, with software $169 PC I/O card with 8255 chip 24 I/O lines programmable as inputs or outputs $69 1.5 watt AM broadcast transmitter XTAL locked $49 2.5 watt FM broadcast transmitter 88-108MHz. $49 Digi-125 audio power amp (over 19,000 sold since 1987) 50 watt/8 $14 125 watt/4 $19 New 200 watt/2 version $29 Infrared relay kit $9 Remote control tester $4 $299 Ampo little PC All in one NEC V40 CPU board, MS-DOS compatible, high density floppy. SCSI hard disk, 2 serial, printer, solid state hard disk, IBM keyboard interface, (4W), CMOS single +5V rail, up to 768Kb RAM, 384Kb ROM, 145mm x 250mm, 98page manual. $299 P.C. Computers 36 Regent St, Kensington, SA. Phone (08) 332 6513. MEMORY & DRIVES PRICES AT OCTOBER 2ND, 1993 SIMM 1Mb x 3 70ns 1Mb x 9 70ns 4Mb (72-pin) 4Mb x 9 70ns 4Mb x 8 80ns $80 $95 $320 $270 $250 DRAM DIP 1 x 1Mb 70ns 256 x 4 70ns 1Mb x 4 Z DRIVES SEAG 42Mb SEAG 107Mb SEAG 130Mb SEAG 214Mb SEAG 261Mb 28ms 15ms 16ms 16ms 16ms $10 $8 $35 $190 $283 $290 $343 $390 IBM PS.2 50/55/70 70/35 90/95 2Mb 4Mb 4Mb $130 $320 $320 TOSHIBA T3200SX T44/6400 T5200 4Mb 4Mb 8Mb $340 $340 $680 MAC 2Mb SI & LC 4Mb P’Book $150 $330 CO-PROCESSORS 387SX to 25 $110 387DX to 33 $110 Laser PTR HP with 2Mb $203 Sales tax 21%. Overnight delivery. Credit cards welcome. UNUSUAL BOOKS: Electronic Devices, Fireworks, Locksmithing, Radar Invisibility, Surveillance, Self-Protection, Unusual Chem­ istry and more. For a complete catalog, send 95 cents in stamps to Vector Press, Dept S, PO Box 434, Brighton, SA 5048. 96  Silicon Chip Antique Radio Restorations.........95 A-One Electronics............ 23, 38-39 Av-Comm.....................................55 Cebus Australia...........................87 Contan Audio.................................3 David Reid Electronics ..............81 Dick Smith Electronics...... 12-15,43 D & K Wilson Electronics...............3 Emona.........................................73 Harbuch Electronics....................87 Instant PCBs................................96 1st Floor, 100 Yarrara Rd, PO Box 382, Pennant Hills, 2120. Jaycar ................................... 45-52 Tel: (02) 980 6988 Fax: (02) 980 6991 PELHAM LCD Alphanumeric Display Board Software Remote Preamplifier Microprocessor NICAD BATTERY Charger Conditioner Analyser. As featured in SILICON CHIP. September 1993. Complete kit $135.00. Built and tested $185. P&P $10. C.I.E., 524 Abernethy St, Kitchener, NSW 2165. Phone (049) 91 1389. Altronics ................................ 66-68 Ring for Latest Prices Software allows a PC to drive the Alphanumeric display board (SC May 93). Available in 5.25" or 3.5" MS-DOS format for only $9.95 + $2.05p+p. I/O pins, board space includes prototyping area. Program it on a PC (only 33 instructions) with development kit which includes one “BASIC STAMP” ($245 incl. post), extra modules ($66 incl. post). Send 45c stamp for more information. Parallax distributor and techni­cal support in Australia: MicroZed Computers, PO Box 634, Armi­ dale, NSW 2350. Facsimile (067) 72 8987. MICASOFT Electronics and Computing tutor program, written in UK, ideal for TAFE, schools, or individual use. Now available in Australia. Send $1.80 in stamps for demo disk (tell us what size). MicroZed Computers, PO Box 634, Armidale 2350. Advertising Index Heart of Remote preamplifier project (SC Sept 93) and Remote Volume Control (SC June 93). 68HC705C8P preprogrammed microprocessor. Only $45 + $6p+p. SILICON CHIP magazine, (02) 979 5644. Payment by cheque/money order or credit card (BankCard, MasterCard, Visa) EEM Electronics Printed circuit board assembly, switchmode power supplies repaired. Design work from start to finish. Ring anytime 9am-9pm Mon-Sun. (03) 4011393 SPRINKLER CONTROLLER KITS: standard and enhanced versions avail­ able. Very reliable and versatile designs control 8 stations and have 32 programmable START and RUN times. These kits use latest technology I2C chips (refer SILICON CHIP July 1992). All settings stored in EEPROM. Kits come complete with LCD and case. Standard version $135 incl. p&p. Enhanced version uses 68705U3 and has built-in calendar, allowing day of fortnight watering, (ie SA, SU, MO, etc), externally triggerable cycles and rain switch software. $175 incl. p&p. Requires 24V AC. Relays JV Tuners.....................................37 Oatley Electronics...................21,87 L.E. Chapman..............................89 PC Computers.............................96 Pelham........................................96 Peter C. Lacey Services..............34 Philips Test & Measurement......IFC RCS Radio ..................................95 Rod Irving Electronics .......... 74-79 Silicon Chip Back Issues....... 90-91 Silicon Chip Binders....................25 Technical Applications.................89 Tektronix..................................OBC Tortech.........................................43 Transformer Rewinds...................96 _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. • H. T. Electronics, 35 Valley View Crescent, Hackham West, SA 5163. Phone (08) 326 5590. extra at $3.75 each (require 9 for full kit). Kits and further info from Graham Blowes, Mantis Micro Products, 38 Garnet St, Niddrie 3042. Phone (03) 337 1917 (AH), (03) 575 3349 (BH). Fax (03) 575 3369. PRINTED CIRCUIT BOARDS for the hobbyist. For service & enquiries contact: T. A. Mowles (08) 326 5590.