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Making Win98 Look Like WinXP! SILICON CHIP AUGUST 2002 6 $ 60* INC GST ISSN 1030-2662 NZ $ 7 50 08 08 INC GST PRINT POST APPROVED - PP255003/01272 9 771030 266001 siliconchip.com.au PROJECTS TO BUILD - SERVICING - COMPUTERS - VINTAGE RADIO - AUTO ELECTRONICS Test gear special Digital Thermometer/ Temperature Controller Sound Card Interface for PC Test Instruments Digital Storage Logic Probe for Win98 Digital Instrumentation Software for your PC Contents Vol.15, No.8; August 2002 www.siliconchip.com.au FEATURES 7 Digital Instrumentation Software For Your PC Free software from the Internet lets your PC function as an audio oscilloscope, spectrum analyser, voltmeter or signal generator – by Peter Smith 14 The How, Where & Why Of Tantalum Capacitors Ever wondered where tantalum capacitors come from. Chances are they started life underground in Western Australia – by Peter Holtham Digital Instrumentation Software For Your PC – Page 7. PROJECTS TO BUILD 22 Digital Storage Logic Probe It interfaces to a Win98 PC to give you more flexibility than you ever though possible – by Trent Jackson & Ross Tester 34 A Digital Thermometer/Thermostat It covers the range from -55°C to 1200°C and has an over or under temperature alarm and switched outputs for thermostatic control – by John Clarke 58 Sound Card Interface For PC Test Instruments You can have a virtual electronics lab in your PC. Just attach this simple interface to your sound card – by Peter Smith 71 Direct Conversion Receiver For Radio Amateurs; Pt.2 Second article has the full construction and alignment details. We also include tips on using it – by Leon Williams Digital Storage Logic Probe – Page 22. COMPUTERS 33 Spruce Up Your Desktop With XP-Style Icons Can’t afford to upgrade to WinXP? This simple freeware utility gives your Win95/98/Me desktop a more modern look – by Greg Swain SPECIAL COLUMNS 30 Circuit Notebook (1) Soldering iron tip preserver; (2) TV relative signal strength meter; (3) Simple card access control system; (4) Petrol/gas switch for a Pajero 53 Serviceman’s Log Digital Thermometer/Thermostat (-55°C To 1200°C) – Page 34. When two faults are better than one – by the TV Serviceman 82 Vintage Radio The Ferris 214 Portable Car Radio – by Rodney Champness DEPARTMENTS 2 4 80 91 Publisher’s Letter Mailbag Product Showcase Silicon Chip Weblink www.siliconchip.com.au 88 90 94 96 Ask Silicon Chip Notes & Errata Market Centre Advertising Index Sound Card Interface for PC Test Instruments – Page 58. August 2002  1 PUBLISHER’S LETTER www.siliconchip.com.au Video cassette recorders: the end is nigh Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Eighteen years ago, in July 1984, writing the editorial for “Electronics Australia” magazine, I went out on a limb and stated that the VHS format had won the battle against the Beta format video machines. That editorial caused untold angst in certain sections of the electronics industry at the time. I was thorough­ly lambasted, large advertising contracts were cancelled and so on. Yet as little as six months later, it was all over, including the shouting. VHS definitely did win the war. Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Jim Rowe, B.A., B.Sc, VK2ZLO Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Leo Simpson Phone (02) 9979 5644 Fax (02) 9979 6503 Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490 All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Noble Park, Victoria. Distribution: Network Distribution Company. Subscription rates: $69.50 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. E-mail: silchip<at>siliconchip.com.au Now, almost 18 years to the day, it is possible to forecast the end of domestic VCRs and this time around there is not likely to be much controversy (I hope). The signs are all there – prices for basic VCRs have dropped to less than $200, tapes are really cheap and DVD releases of movies are now very plentiful and getting cheaper by the day. For anyone who has DVD player, buying a VHS-movie is unthinkable because DVD image quality is far better. With these trends in mind, you have to wonder how long it will be before video shops cease stocking video tapes for rental or for sale of new release movies. If you go into any video store you will soon realise that it is the DVDs that are the hot items, not video tapes. And once the video shops do cease handling video tapes for rental then it really will be all over. What about recording video programs, you might ask? Well, VCRs are still the only way to do it cheaply and people still want to “time-shift” programs but I get the impression that it is less used than once was the case. In any event, lower priced recordable DVDs are not far away and when they eventuate you can bet that they will quickly swamp the market. So we really are seeing a product, the VCR, coming to the end of its life cycle. All told, it has lasted, or will last, about 30 years or so, not long for a product that has involved such a high level of technology. Mind you, if your present VCR is on its last legs, you might want to think about buying a new one. They are not going to get much cheaper and if you have a big collection of video tapes you will still want something to play them on over the next ten years or so. Apart from that, will anyone mourn the passing of the VCR? Not really, I think. I doubt whether servicemen will care much either, particularly as they have been doing less and less serv­ice on them over the years – and they always were a mechanical nightmare anyway. And how many people ever learned to program their VCRs? Precious few! Roll on technology! Leo Simpson ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip www.siliconchip.com.au Try these NEW USB Solutions! Data Logging/Digital I/O/Timer Counters/Industrial Control 12 Bit 16 CH A/D CH D/A PCI A PCI BUS based A/D D/A card with programmable I/O control Cat 17077-7 $699 Let your computer play in the real World! 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Pictures are illustrative only. info<at>mgram.com.au SHOREAD/MGRM0802 MAILBAG RIAA preamplifier may need more gain My reason for writing concerns the magnetic cartridge preamplifier design published in the March 2002 issue of SILICON CHIP. In the article, it is suggested that the output of a magnet­ic cartridge is typically 5-10mV at centre frequencies. However, this is really only the case for lower-quality cartridges, which tend to have poor tracking and high distortion. High quality cartridges, such as those made by Shure and Ortofon, are more likely to have an output of 2-3mV. As I recall, even the Stanton 68x series of cartridges, which were considered to have higher-than-average output, gave a nominal 4mV. The issue is important because an RIAA preamplifier using a single stage of IC amplification is limited to a gain of about 40dB (ie, x100) at centre frequencies. This is because almost an extra 20dB of gain is required to provide the low-frequency boost. For good quality audio reproduction, a gain after feedback of 60dB is about the limit for good-quality ICs, whether they be single (TL071, NE5534 etc) or dual (LM833, NE5532 etc). The technical reasons for this limit are well-explained in Analog Digital’s application notes for one of their high-performance linear ICs (type OP27, I think). With a cartridge delivering 2-3mV of output and a 40dB RIAA preamplifier, the output level will be 200-300mV, considerably less than the norm for modern peripherals such as CD players, tuners, VCRs and cassette decks, most of which have a nominal output of 1V or more. This discrepancy can have some uncomfort­able, and even damaging, consequences if one forgets to adjust the volume control before switching from the record player to some other input. The simplest solution to this problem is to add a buffer stage (x4 is about right) after the RIAA preamplifier. However, I seem to recall that lower overall noise can be obtained by divid­ ing the required x400 or x500 amplification about equally between two 4  Silicon Chip IC stages. A modified version of the 2-stage RIAA preamplifi­er designed by David Tilbrook (ETI September 1981) does this job quite nicely and delivers an output level which is more consist­ ent with modern peripherals. I was pleased to see the use of a PC-mounted toroidal transformer (available from Altronics and specialist suppliers) in the RIAA preamplifier design. I have used these transformers in a number of my projects and have been impressed by their construction, quietness and low external field when used in sensitive audio equipment. Brian Knight, Evandale, SA. Comment: you are right in that some cartridges may need an addi­ tional stage of amplification to bring them up to par. However, there is no particular benefit in splitting the gain evenly between two stages. The reason for this is that the noise performance of the whole preamplifier is largely determined by the input stage of the first op amp. Solar panels not worthwhile in NZ Very gratifying to see both Leo Simpson and Ross Tester, in the editorial and article in the March 2002 issue, showing a healthy dose of common sense about the usefulness of solar power at this stage of development. Often I have cringed when I have heard some “greenies” proclaim their short-sighted vision of how much better the world would be if only we would let them have things their way. The greenies have a noble attitude but bless their well-meaning hearts, I think their reason and their logic sometimes let them down. In NZ where I live, I am always amused when I see environ­mentalists buying solar panels to get “free, non-polluting” electricity. NZ’s power is generated by the environment itself (how friendly can it get?) using hydroelectric and geothermal methods and these sources of energy will probably be provided freely by Mother Nature until Judgement Day! I might have a blinkered view but I still think it’s a bit loony for environmentalists in NZ especially to waste good money buying expensive, inefficient solar gear which has already harmed the environment by its manufacture. SILICON CHIP’s reportage of solar energy should be compul­sory reading for all “fad” environmentalists. Keep up the good work. Stan Hood, Christchurch, NZ. Are photovoltaic cells really green? Thank you for your March feature article “Solar Power for All”. Given the current environmental “Solar is Green and Green is Good” hype, it is pleasing to see that someone is willing to scrutinise the claims made by manufactures and others on the performance of photovoltaic cells. However, there is one question I have regarding photovol­ taic cells when ever their performance/efficiency is discussed. Does a photovoltaic cell produce more energy in its lifetime than it takes to manufacture it? I think this question is more funda­ mental in the debate of claims that photovoltaic cells are clean, green and non-polluting than cost/efficiency issues. I suspect not, however I don’t have any conclusive proof of this. My argument here is what’s the point in expending energy making photovoltaic cells (and in the process producing CO2 as nearly all Australian electricity production does) if they don’t return an equivalent amount plus interest. Don’t get me wrong, I do believe that www.siliconchip.com.au photovoltaic cells have their place in power production (eg, remote areas where there is no power grid). However, as an “alternative” power source in urban areas the energy equation just does not stack up. Glenn Mayall, Gosford, NSW. Tip on making PC boards Further to the excellent article by Heath Young in the February 2001 issue on making PC boards by toner transfer, your readers might like to know that using a modern family iron can be less than successful for a number of reasons, including steam holes, not hot enough and not heavy enough. I discovered that if the iron can’t make the paper go brown – it is not hot enough. I bought an ancient 700W Hecla electric iron (heavy, no steam holes, no thermostat!) for $5 from a local market and it works great. Rob Clark, via email. BassLink should be done properly Wow! You certainly nailed your colours to the mast. I hope you haven’t hoist your petard there by mistake. I am referring to your editorial on the new Lucas Heights reactor in the May 2002 issue of SILICON CHIP. I want to support you and I think your “We were here first” argument has much merit. I enjoy remembering that when Tullamarine airport was being built, the Government tried to do the right thing by erect­ ing many large signs proclaiming, “Warning! Airports are noisy neighbours!”. Controversial projects usually become controversial for good reason; they have benefits and liabilities. It isn’t good science and it isn’t good engineering to shut our eyes to the liabilities, and it isn’t smart to ridicule people who remind us of the liabilities and who seek to minimise the harm done by those liabilities. Before complaining of a “low level of scientific knowledge” it is useful to remember that science includes much more than physics and electricity. It is useful to remember that green and environmentalist groups are usually populated by people of above average www.siliconchip.com.au education and that we technologists probably should welcome their input when they remind us of design criteria that we might otherwise forget. The BassLink project is a particularly unfortunate example. The opposition to the project isn’t the irrational “in there and against it” you imply. The opposition is to doing the job badly. The environmentalists want what we technologists should want – a project of which we can be proud, not ashamed. Keith Anderson, Kingston, Tas. USB light not a new idea In your March 2002 edition, your article entitled “The Itsy-Bitsy USB Lamp” is a great idea and I’m sure a lot of readers will be making one. There is one problem with the article though, and I quote from paragraph 4: “It is such a delightfully simple idea we’re wondering why no-one ever thought of it before.” Actually, there is a similar commercial product that I believe I saw advertised or in shops 12 months ago. Just to check my sanity I did a quick check on www.google.com (key words USB and LIGHT) and came up with a number of results, the most relevant being: http://www.kensington.com/ products/pro_cas_d1334.html This device has a flexible shaft, it stays in the shape it’s bent to, plugs into a USB port and uses a white LED to provide light, so it’s not exactly the same. Mark Grover, Adelaide, SA. The Tiger comes to Australia The BASIC, Tiny and Economy Tigers are sold in Australia by JED, with W98/NT software and local single board systems. Tigers are modules running true compiled multitasking BASIC in a 16/32 bit core, with typically 512K bytes of FLASH (program and data) memory and 32/128/512 K bytes of RAM. The Tiny Tiger has four, 10 bit analog ins, lots of digital I/O, two UARTs, SPI, I2C, 1-wire, RTC and has low cost W98/NT compile, debug and download software. JED makes four Australian boards with up to 64 screw-terminal I/O, more UARTs & LCD/keyboard support. See JED's www site for data. Intelligent RS232 to RS485 Converter The JED 995X is an opto-isolated standards converter for 2/4 wire RS422/485 networks. It has a built-in microprocessor controlling TX-ON, fixing Windows timing problems of PCs using RTS line control. Several models available, inc. a new DIN rail mounting unit. JED995X: $160+gst. Www.jedmicro.com.au/RS485.htm $330 PC-PROM Programmer Fuel cells not necessarily clean and green Thank you for the article on fuel cells in the May 2002 issue. It is most interesting and informative. However, I wish to correct some common misconceptions regarding these devices as power sources. Firstly, they are not “emission free”. As the diagram on the opening page of the article shows, their exhaust is water (H2O) which is “emitted” from the cell. However, I will concede that they do not emit carbon dioxide and I suppose we should say they are continued next page This programmer plugs into a PC printer port and reads, writes and edits any 28 or 32-pin PROM. Comes with plug-pack, cable and software. Also available is a multi-PROM UV eraser with timer, and a 32/32 PLCC converter. JED Microprocessors Pty Ltd 173 Boronia Rd, Boronia, Victoria, 3155 Ph. 03 9762 3588, Fax 03 9762 5499 www.jedmicro.com.au August 2002  5 Mailbag: continued from page 5 “non-Greenhouse contributing” rather than “emission-free”. However, the source of their fuel, hydrogen, is possibly not “non-Greenhouse contributing.” Pages 12 and 13 list a number of makers of fuel cells in the USA and show that most operate on hydrogen from an unnamed source. If this source is (for example) an electrolytic process powered by electricity from natural-gas, oil or coal-fired power stations, it may be that the use of the cells on this fuel will contribute more CO2 to the Greenhouse effect than would the use of conventional fuels in our cars. The DaimlerChrysler cells derive their hydrogen from sodium borohydride, which is derived from borax. My Macquarie Dictionary tells me that borax, sodium borate, is a substance “occurring naturally or prepared artificially”. What is the energy consump­tion involved in preparing the hydrogen fuel from borax? Is the borax naturally occurring or if not, what is the energy consump­tion required to obtain it? What happens to the waste products from these processes? A number of the cells are claimed to operate on ethanol as a fuel. Ethanol, C2H5OH, contains carbon. What happens to this carbon? The carbon in ethanol represents a little over half the energy contained. If we allow that this energy is “lost”, the overall efficiency is much lower, roughly 33-40%. And how much energy is used in extracting the hydrogen from the ethanol so that the fuel-cell can use it? UTC’s petrol-powered fuel cell and Suzuki’s natural-gas cell have the same problem. I am not sure how much of the total energy in petrol is contributed by the carbon; for propane, a major constituent of natural gas, it is about 50%. Again, this is apparently not utilised by the fuel-cell, nor are we told how much energy is wasted in extracting the hydrogen. Additionally, these two petroleum-based fuels are sources of Greenhouse-contributing CO2. Ethanol is not considered as such, since it is usually derived from growing plant matter and is part of a “local” carbon cycle. 6  Silicon Chip Petroleum fuels, on the other hand, are generally held to contain the carbon which was extract­ed from our atmosphere as it changed from CO2-rich to O2-rich, aeons ago. It is not considered desirable to release this carbon back into the atmosphere. While I see fuel-cells as a desirable energy source to replace the internal combustion engine, I feel we should beware of the “hype” extolling them as the ultimate cure for our Greenhouse problems. We must realise that a lot of the information we are being given is aimed at selling the cells, rather than at fully informing the public. Greg Mayman, via email. Comment: we have not yet finished the fuel-cell story. Ultimate­ ly, the hydrogen for solar cells will have to be produced direct­ly from water by solar power if the whole process is to be really clean. And we’re not talking about using solar cells for electro­lysis of water – stay tuned! Bosch ignition schematic wanted I have a V8 VS Commodore and I need a schematic diagram for the ignition module. Bosch only gave me the pinouts of the module and this is all they can help me with. Any help would be appreci­ated. Mark Sully, PO Box 274, Niddrie, Vic 3042. marksully<at>piarc.com.au Fax (03) 9366 6872. LP Doctor is a great project After six months and hundreds of LPs, I can only say of your “LP Doctor” that it’s one of the best projects you’ve ever described. The “LP Doctor” has given a whole new life to my record collection. On some discs, the click detection LED flashes con­ tinually, yet the music sounds clean and not at all disturbed by the short interruptions as the clicks are removed. It’s a great project and one that I use every day. One thing though: what are the parameters for the treble filter? I can’t detect any difference with the filter in or out! Does that mean that I have an inbuilt organic filter? Which components should I change to increase the slope of the filter? In the May 2002 issue, you described a “32 LED Knightrider”. I particularly liked the idea of a programmable stop light for vehicles. I’ve seen something like that before but it wasn’t as versatile as your project. This was quite interesting, although I probably won’t build one at the moment. On the other hand, I can see me building a slightly differ­ent project. I envisage a multi-LED panel that spells out STOP when I hit the brakes but can also be reprogrammed to spell out BACK OFF when I am too closely approached by one of those charac­ ters who like to attach their bonnet to one’s exhaust pipe! It would probably take more than 32 LEDs but I am sure there would be plenty of readers who would appreciate the chance to warn off those inconsiderate and impatient drivers one meets every day. Jim Lawler, Hobart. Tas. Comment: the treble filter is very gentle, only -3dB at 10kHz and -12dB/ octave above that. The reason you cannot hear any dif­ference is that your own inbuilt filter probably cuts in well below 10kHz, perhaps as low as 5kHz or 6kHz. And it will be a “brick wall” filter rather than -12dB/octave. Having said that, the treble filter could be made to have a much more apparent effect by increasing the 560pF capacitor at pin 6 of IC5b (& IC7b) to .001µF and the 150pF feedback capacitor to 270pF. This will drop the -3dB point to 5.6kHz. 5.25-inch floppies revisited Here’s a novel recycling tip which has a mental challenge as well. 5.25inch floppy disks still have a use – for CD storage from multi-disk CD-R spindle packs! Cut them right along the base near the opening and remove the magnetic disk. Slide in your CD-R and it’s now in its own padded storage packet. Put the 5.25-inch floppy with the CD inside back into the paper jacket and voila, instant transport case! Brad Sheargold, via email. www.siliconchip.com.au By PETER SMITH Any PC with a sound card can function as a digital oscilloscope, spectrum analyser, voltmeter and signal generator. It’s just a matter of installing the right software, much of which can be downloaded for free or at low cost from the Inter­net. E LSEWHERE IN THIS ISSUE, we describe a simple adapter that provides a safe and easy way of connecting test probes to your sound card. Below we introduce some of the important principles of sound card-based digital instrumentation and follow up with a quick rundown on some of the more popular software packages that are available. Digital instrument basics Digital instruments have many advantages over their analog cousins. Take the oscilloscope, for example. Digital ’scopes can store waveforms in memory or on disk for www.siliconchip.com.au comparison with “live” waveforms, or play them back at a later time for detailed examination. And once a waveform is stored digitally, it is easily manipulated (level-shifted, filtered, transformed to the frequen­cy domain, etc) for display in a variety of formats. The downside is that digital instruments are often expen­sive, standalone devices with a CRT or LCD display, multiple CPUs and complex data capture electronics. However, much cheaper solutions based on the PC platform are now readily available. These utilise the existing processing power and graphics capabil­ities built into all PCs, thereby greatly reducing costs. PC-based solutions range from small external data acquisi­tion pods (we reviewed such a device in the June 2000 issue) through to add-on cards that plug into a free expansion slot. These are cheap by comparison to the standalone devices but still too costly for those of us on tight budgets. PC sound card The simplest and cheapest solution utilises hardware that already exists in all multimedia PCs – the sound card. It might seem unusual that a PC sound card could be used as the basis of any data acquisition system. However, one of the main components of all sound cards is an analog-to-digital (A-D) converter, a core function of even August 2002  7 amplitude of that signal. The digital values are then processed by software to drive on-screen voltmeter displays or to plot waveforms on an oscilloscope X-Y grid. Let’s look at some of the more important aspects of the analog-to-digital conversion process in a little more detail. Resolution Fig.1: Oscilloscope 2.51 uses large vertical sliders for program­ming the sweep, gain, trigger level and delay settings for both channels. A-D converter resolution is characterised by the number of digital bits that it takes to represent the results of a conver­sion. Older sound cards, such as the classic SoundBlaster 2.0 and SoundBlaster Pro, have only 8-bit resolution. All recent PC sound cards have 16-bit (or higher) resolution, which equates to 216 (65,536) possible discrete values. To make some sense of this, we need to know the upper and lower limits of the voltage that can be sampled by the converter. Sound cards typically have a 0-2V input span. Applying some simple maths, we find that 2V divided by 65,536 gives 30.5µV – a respectably small slice indeed. Bandwidth Fig.2: real-time signal spectra can be examined in FFT (Fast Fourier Transform) display mode. In this shot, Oscilloscope 2.51 plots a simple 4kHz square wave (the large spike) and its har­monics. Fig.3: many ’scopes support an X-Y mode, where the amplitude of the second channel is plotted against the amplitude of the first. Here we’re using Oscilloscope 2.51’s delayed sweep function and X-Y mode to get a new perspective on our measurements! the most expensive digital instruments. In simple terms, the A-D converter’s job is to periodically sample the incoming analog signal and come up with a digital value that represents the instantaneous 8  Silicon Chip Equally important as the signal amplitude is its frequency. Sound card converters operate at a known (programmable) sampling period under control of a crystal-locked clock. All this means is that each conversion cycle occupies a precise period, easily measured and manipulated by software to glean the signal frequen­cy. Naturally, the faster the input signal can be sampled, the more accurate the displayed result. Imagine, for example, a sinewave signal with a period of 100µs. If the A-D converter samples at, say, 20µs intervals, then what you would see on an oscilloscope display wouldn’t look much like a sinewave. Instead, it would look like an ascending and descending “staircase”. It follows that the faster the signal is sampled, the smaller the steps will be and the less visible the staircase effect. When the sampling rate is much higher than the signal frequency, software interpolation removes virtually all traces of this “digitisation” and the waveform looks much the same as it would on a traditional analog scope. Apart from affecting how waveforms appear on an oscillo­scope display, the sampling frequency is important for another reason. It must always be at least twice the frequency of the signal being measured, otherwise a problem called “aliasing” occurs (see Fig.12). Most sound cards have a maximum sampling rate of 44kHz, so the highest frequency you can expect to measure accurately is 22kHz. The minimum frequency that can be measured is about 20Hz, due to AC-coupling at the sound card inputs and a high-pass filter in the A-D block. This can be an annoying limitation when the signals you’re measuring contain a DC component but a good multimeter will usually fill in the gaps. Storage As each A-D conversion is completed, software reads the result and stores it sequentially in a block of memory www.siliconchip.com.au Fig.4: this view shows TrueRTA’s oscilloscope and signal generator. The signal generator and righthand toolbar can be detached from the main display if required. (or “storage buffer”). As mentioned above, each cycle occupies a precise period, so the storage locations also act as time mark­ers. Once the buffer is full, oscilloscope software can be used to read the contents and plot the traditional amplitude versus time waveforms. Of course, this is a very simplified description of the process. Depending on the particular software and the active instrument, mathematical calculations may need to be performed on all or part of the buffer contents before the results can be displayed in the appropriate format. For example, voltmeter software might need to extract average, crest factor and RMS values from the raw data. Triggering The storage buffer is in effect “circular”. Once full, old data is overwritten with new as the entire cycle repeats. Howev­er, although the A-D converter may be sampling and converting at full speed (called “free-running”), the software does not neces­ sarily immediately write the results to the buffer. Rather, it monitors the incoming data for predefined trigger conditions. On most sound card-based software, the triggers are programmable to specific voltage levels – either positive (rising) or negative (falling). Without some means of synchronising the signal with the beginning of the buffer, even simple waveforms would be impossi­ble to comprehend on an oscilloscope; they Fig.6: the “front panel” of Osci – it’s almost as easy to use as rotary dials and switches! www.siliconchip.com.au Fig.5: plot of a 2kHz square-wave on TrueRTA’s spectrum analyser. This is the “level 3” version of the product, which allows up to 60 frequency bars (1/6 octave) across the horizontal axis. Display update speed can be traded off with accuracy to suit the speed of your hardware – necessary because this analyser is a real CPU hog. would appear to jitter and jump across the horizontal axis. In fact, most digital in­struments need reliable triggering in order to make accurate measurements. For greater versatility, many digital ’scopes provide a variable pre-trigger (or “delay”) time. This simply means that a certain number of samples are written to the buffer before the trigger condition is met. Generating output So far, we’ve only talked about instruments that utilise sound card inputs. Not surprisingly, a good deal of software is available that makes use of the outputs as well. In operation, an analog output voltage is generated by the sound card’s digital-to-analog (D-A) converter. Software feeds a stream of 16-bit digital data into the D-A block, where it’s converted to analog, filtered and then amplified before appearing on the card’s output sockets. As you can see, this process is similar to the signal input side, except in reverse! Digital signal generators are the most-used output Fig.7: Osci’s waveform display can be dragged away from the main window and resized as required. The dark lines on the display are measurement cursors that we used to determine the frequency and amplitude of the sinewave. August 2002  9 What’s A Spectrum Analyser? Most of our readers will already be familiar with the oscil­loscope. These instruments display signals in the time domain. The horizontal axis is graduated in time and the vertical in amplitude. This format is ideal for determining time, phase and amplitude information. On the other hand, spectrum analysers display signals in the frequency domain. Frequency is displayed on the horizontal scale, and is divided into bands, or octaves. The lower frequency bands are on the left, with progressively higher frequency bands to the right. The scale is logarithmic, such that each octave or fractional octave is equal in width. The amplitude of the signal is displayed on the vertical axis, which is graduated in deci­bels. A spectrum analyser enables us to see certain information that is just not visible in the time domain. For example, a sinewave may look good in the time domain but show visible distortion in the frequency domain. Also, a noise signal may look totally random in the time domain but in the frequency domain one frequency may be dominantly present. In audio frequency work, the spectrum analyser is commonly used to measure signal-to-noise instru­ments. Together with the instruments we mentioned earlier, they provide a convenient means of analysing a host of analog circui­try. Just like their analog counterparts, digital signal genera­tors provide the usual sinewave and square-wave outputs with programmable frequencies and amplitudes. Some even include sweep generators and noise sources for frequency response and distor­tion analysis. The software OK, now that you’re familiar with some of the basic terms, let’s examine a few of the more popular digital instrument pack­ages that are available on the Internet. We have selected five quite different software packages that we think demonstrate the capabilities of sound cardbased instrumentation quite well. These are all listed in Table 1, along with the links to their download sites. Some are free for non-commercial use, while others are offered on a shareware basis. Many more are available – too many for us to seriously evaluate here. Our advice is to shop around and be sure to “try before you buy”! For additional software, point your browser to www.google.com and search for sound card oscilloscope software. Oscilloscope 2.51 The first package we examined is titled simply “Oscillo­ scope 2.51”. It runs on Windows 95 & 98 (a Windows 3.1 version is also available) and requires only an 80486 processor and an 8-bit sound card. In common with most packages, it includes a dual-trace storage ’scope, as well as a real-time spectrum analyser. All major functions are controlled via a series of “clickand-drag” sliders on the righthand side of the display (see Fig.1). Vertical trace position, gain, and trigger level are all independently programmable for left (Y1) and right (Y2) channels. In single trace (YT) mode, two trigger delay sliders pro­ vide coarse and fine adjustment of the amount of 10  Silicon Chip ratio, distortion, intermodula­ tion distortion and frequency response. A mathematical process called Fast Fourier Transforms (FFTs) is used to convert signal information from the time domain to the frequency domain. To complicate matters further, analyser software often includes several complementary FFT “windowing” functions. Unfortunately, a detailed explanation of windowing, or FFTs for that matter, is well beyond the scope of this article. However, plenty of information on the subject is available on the Internet and in printed form. pre-trigger data written to the buffer. In dual trace and X-Y mode, these sliders vary the time delay between the Y1 and Y2 channels. The gain settings control software gain only; hardware gain must be varied via the Windows audio mixer software. In addition, the product of the left and right sliders is used to determine gain when in spectrum analyser mode. This provides a convenient, faster-than-linear adjustment rate. The sampling rate can be set to 11.025kHz, 22.05kHz or 44.1kHz. On all but the slowest (486) hardware, it makes sense to sample at the maximum supported frequency for best accuracy. The buffer (and hence display) refresh rate can be programmed to any realistic value, with the default of 330ms being too slow for smooth updates. High-performance PCs will support a much faster rate than this. Frequency measurements are made by left and right-clicking on the oscilloscope display. Oscilloscope 2.51 measures the period between the selected points and displays the result on the status line. In Spectrum Analyser mode, it’s only a matter of running the mouse over the area of interest, as the frequency of the plot at the cursor position is displayed in real time. A snapshot of the buffer can be saved to disk as an ASCII file for use by other CAD packages. Of course, you can also cut and paste the 8 x 10 graticule display into your favourite graph­ics program for documentation purposes as needed. All up, this tidy little package uses few resources but offers a lot. However, it lacks a means of calibrating the input signal levels, so all amplitude measurements should be considered relative rather than true. TrueRTA TrueRTA (Real Time Audio Spectrum Analyser) is a complete suite of audio test instruments. The latest release (V2.0 as we write) is available in four distinct levels. The levels differ in functionality and price, with level 1 www.siliconchip.com.au Fig.9: if you need a simple no-cost generator, check out Sound­Arb. You can even roll your own waveforms! Fig.8: WaveGen can generate just about any waveform you care to name. Digital signal generators are quite frequency-accurate but distortion at the high and low ends of the scale must be considered. available free of charge. TrueRTA runs on all 32-bit versions of Windows and requires a Pentium 200 (or equivalent) processor with 64MB of RAM and a 16-bit sound card as a minimum. Included in the package is a spectrum analyser, oscilloscope, digital multimeter and signal generator. This package is aimed squarely at the audio test and devel­opment area. The built-in signal generator (with digital sweep function) and the spectrum analyser enable quick evaluation of audio circuit performance. In addition, support is provided for a calibrated microphone input, enabling loudspeaker and acoustic environment testing. As with most packages, the input sampling rate can be set to any one of the standard sound card values between 8kHz and 48kHz. User controls are intelligently arranged and clearly la­belled (see Fig.4) and the instruments are dead easy to drive. You simply select between the oscilloscope or spectrum analyser instruments and then fine-tune the settings using buttons and drop-down menus on a detachable toolbar. The digital ’scope provides both single (left or right channel) and dual-trace (left & right channel) modes, as well as channel addition and subtraction. The horizontal axis can be programmed from .05ms to 200ms per division, while the vertical axis ranges from a low 100µV per division right up to 5V per division. The ranges are variable in the traditional 1-2-5 steps via rows of buttons on the toolbar. The digital voltmeter displays the RMS value of the refer­ence channel in the top left corner of the graticule. If you decide to purchase one of the higher-level versions, you get additional voltmeter readouts of dBu, crest factor in dB (ratio of peak to RMS level) and crest factor in mV/V. The reference channel, by the way, is the one that you select as the trigger source. Triggering is automatic – no provi­sion has been made for varying the level or polarity. A single click on the toolbar switches to spectrum analyser mode (see Fig.5). The graticule is now displayed in logarithmic format – the vertical axis in dB and the horizontal axis in bands of frequencies. The free version of the software provides only a single octave across the horizontal, which equates to 10 bands (or bars) in the 10Hz-22kHz spectrum. Pay money, and you can select from 1/3, 1/6, 1/12 or 1/24 octave (30, 60, 120 or 240 bar) displays. The horizontal scale can be expanded for detailed examina­tion of a particular frequency range by modifying the upper and lower frequency limits. Similarly, vertical scale limits can be adjusted to zoom in on an area of interest. TrueRTA’s signal generator includes both sinewave and pink noise output. The output level is variable MORE FROM YOUR EFI CAR! Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication  Making Your EFI Car Go Harder  Building A Mixture Meter  D-I-Y Head Jobs  Fault Finding EFI Systems  $70 Boost Control For 23% More Grunt  All About Engine Management  Modifying Engine Management Systems  Water/Air Intercooling  How To Use A Multimeter  Wiring An Engine Transplant  And Much More Including Some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc P&P To order your copy, call (02) 9979 5644 9-5 Mon-Fri with your credit card details! www.siliconchip.com.au August 2002  11 over the entire range of the sound card’s D-A circuitry and the sinewave frequency is variable from 5Hz to 24kHz. Higher-level versions of the product include a logarithmic sine sweep function for more accurate frequency response measurements. Unlike the previous package, this one includes comprehen­ sive calibration features. The Fig.10: if you want to do serious work Fig.11: AudioTester’s spectrum analyser professional version (level in the audio spectrum, AudioTester is a dual-channel affair, allowing direct 4) even includes a feature to offers a comprehensive range of FFT comparison between reference and test functions. signals. remove the “coloration” that sound cards inevitably add to Trigger levels are independently programmable for your distortion and frequency channel 1 (left) and channel 2 (right) via vertical sliders response measurements. and can be of either positive or negative polarity. Auto As this package focuses on the real-time aspect of triggering is also provided, as is variable trigger delay and audio work, it does not have a number of features that a single sweep mode. are handy for general electronics bench work, such as Left and right channels can be added, subtracted and/ moveable measurement cursors, triggering options and or in­verted. The inversion function could be handy if you storage capabilities. have a sound card that inverts input signals (don’t laugh, Osci we’ve heard of some that do!). Waveforms are displayed on a standard 8 x 10 gratiThis is one of the best of the low-cost digital ’scopes cule that can be detached from the main window and that we’ve seen. Although the shareware version is not resized to suit your needs (see Fig.7). Optionally, the crippled in any way, it does have a maximum use period X and Y-axis settings can be displayed right on the of 15 minutes. Once this expires, the program terminates graticule – a very handy feature for documentation and you need to relaunch it. Of course, if you like the purposes. product, you can license it for a nominal fee and get rid Osci’s display can be printed on demand or copied to of this annoyance. the Windows clipboard for pasting into your favourite Osci runs on Windows 95, 98 and NT4 and requires at application. In addition, the buffer contents can be saved least a Pentium 266 with 32MB of RAM and a 16-bit sound as an ASCII file for use in other programs. card. If you want to run a signal generator in parallel with The storage buffer generally holds more than can the ’scope, your sound card and its driver software must be dis­ played on-screen at one time, so a horizontal support “full-duplex” mode. This applies to all packages, scroll bar at the bottom of the display allows quick by the way, not just Osci. panning from buffer beginning to end. A nearby “x10 All sound card sample rates up to 96kHz are accomMag” button allows you to instantly zoom into areas of modated, as is 24-bit resolution for those cards that interest. support it. In addi­tion, Osci supports up to three sound Getting accurate waveform measurements is easy with cards, so you don’t need to dismantle your existing audio this package. Click on the start point with your left mouse setup. button, drag the horizontal and vertical rulers that appear The Osci user interface is uncomplicated and easy to to the end point and release, and hey-presto – the period, drive (see Fig.6). Vertical (Y) axis settings are variable from frequency and amplitude of the bounded area appear as 100µV per division up to 2V per division, while horizontal if by magic! (X) axis (or “timebase”) settings are variable from 20µs to Finally, all your settings can be saved as “presets” for 200ms per division in the usual 1-2-5 steps. quick restoration later. Table 1: PC Instrumentation Software Package Licence Download Link Oscilloscope 2.51 Freeware polly.phys.msu.su/~zeld/ osci ll.html True RTA Level 1 is free, Levels 2-4 are acti vated on purchase www.trueaudi o.com Osci, WaveGen, AudioTester Shareware (30-day eval uation) www.sumuller.de/audiotester SoundArb Freeware Analyzer 2000 Shareware (30-day eval uation) www.brownbear.de Freeware hel iso.tripod.com/download/ download.htm Digital Sound Generator 12  Silicon Chip www.wavebuilder.com WaveGen WaveGen is a comprehensive standalone signal generator. Tone, impulse and sweep generators are all included and accessi­ble from the front panel. WaveGen can be used in conjunction with Osci (they’re from the same author), so system requirements are the same for both packages. The maximum D-A conversion rate of the sound card deter­mines the highest output frequency. For a www.siliconchip.com.au typical 48kHz card, the highest frequency will be 24kHz. The minimum frequency is listed as 0.1Hz but this seems a bit optimistic as it dips well under the lower frequency limit of around 20Hz for most sound cards. Generator frequency can be programmed in 0.1Hz, 10Hz and 1kHz increments. As you can see from Fig.8, all the usual waveform types can be generated. In addition, WaveGen will play back any user-de­fined WAV file. Output levels can be adjusted with either “analog” or “digital” control buttons. As far as we could determine from the documentation, the 0dB to -96dB digital level adjustment is soft­ware-based, whereas the 0dB to -48dB analog adjustment controls the Windows mixer. No calibration is provided for the line output socket. Instead, when using WaveGen for frequency response and distortion measurements, the documentation suggests that you feed the right line output directly back to the left line input, so creating a “reference” channel. The right output also connects to the input of the circuit under test, while the output of the circuit under test is con­ nected back to right line input. This method allows you to com­pare the differences in the two waveforms on an oscilloscope or spectrum analyser display. The spectrum analyser instrument in AudioTester (which we mention below) expects this connection and can automatically compensate for sound card amplitude and fre­ quency response characteristics. Virtually all generator parameters can be configured via setup buttons on the front panel. We won’t bore you with all the details here. Instead, why not download WaveGen and check them out for yourself! SoundArb This is a no-frills, easy-to-drive signal generator. It runs on Windows 95 and above, requires a 16-bit sound card and only minimal PC hardware – and it’s free! A shot of SoundArb’s super-simple front panel is shown in Fig.9. Sine, square, triangle, sawtooth and white noise wave­ forms can all be generated, as can user-defined arbitrary wave­forms. These are loaded from a simple ASCII file, which can be manually created or generated by software. Normally, SoundArb outputs the selected waveform on both the left and right channels. Optionally, a synchronisation signal can be output on the right channel Fig.12: the A-D converter must sample the input signal at least twice as fast as its frequency otherwise “aliasing” re­sults. Here, the input signal (shown in red) would need to be sampled at least twice each period but instead it’s sampled only once every 2/3 period. Therefore, the frequency of the signal is erroneously calculated to be much lower than it really is (as shown in green). instead by choosing the “Right channel sync” option. The output amplitude is set by a horizontal slider and is uncalibrated. SoundArb provides simple triggering options and these include “Free run”, “One-shot” and “Burst”. The burst mode length is programmable in cycles. AudioTester AudioTester boasts just about every feature imaginable. Like TrueRTA, it includes an oscilloscope, spectrum analyser and signal generator but lacks a separate voltmeter. We’ve mentioned this package only because it originates from the same author as Osci and WaveGen. These two standalone instruments are apparently intended to replace the oscilloscope and signal generator that are part of the AudioTester suite. To date, the author has not released a standalone version of the spectrum analyser, so AudioTester is still available to fill in the gaps. Like Osci and WaveGen, the spectrum analyser in AudioTester is packed with features. We’ve run out of space to describe them here but we’ve included a couple of screen shots (Figs.11 & 12) to whet your SC appetite! UM66 SERIES TO-92 SOUND GENERATOR. THESE LOW COST IC’S ARE USED IN MANY TOYS, DOORBELLS AND NOVELTY APPLICATIONS 1-9 $1.10 10-24 $0.99 25+ $0.88 www.siliconchip.com.au August 2002  13 These days more and more electronic equipment uses tiny tantalum capacitors, with capacitance values that were impossible in such small volumes only a few years ago. This is the story of how they are made. The how, when, where and why of a Tantalum Capacitor By PETER HOLTHAM 14  Silicon Chip www.siliconchip.com.au J ust as silicon chips pack more and more function into less and less space, other electronic components have also shrunk. Tiny surface mount resistors replace the wire-ended components of just a few years ago. Capacitors used to be bulky items –even the low voltage types. But like resistors, they too have shrunk to minuscule proportions. Few people realise that the key to making some of these very tiny capacitors is found deep underground in Western Australia. It is the rare mineral tantalite, a complex oxide of iron, manganese and tantalum, and the principal source of tantalum metal. Two mines in the state supply more than a quarter of the world’s annual tantalum requirements. One is outside the small town of Greenbushes, 250km south of Perth. The other is at Wodgina in the remote Pilbara region, 1500km north of Perth. Australian gold mining company Sons of Gwalia owns both and together they form the world’s largest known tantalum resource. Fifty eight million kilograms of tantalum (as tantalum pentoxide) has been found, enough to give both mines at least 25 years more life. The tantalum bearing ore is mined from huge open pits by drilling and blasting. Every tonne mined Wodgina requires the remov(Tantalum) al of nearly seven tonnes of waste rock. The ore trucked out of the pit contains just over 200 grams of tantalite mineral per tonne (or 200 parts per million), far too Greenbushes (Tantalum/ Lithium) little to be saleable. So the trucks These two mines in Western dump their loads Australia produce more than 25% at processing plants of the world’s tantalum requirements. close to the mines. And yes, we know Tassie is missing! Here, crushers followed by grinding Sons of Gwalia sells all its tantalite to mills pulverise the ore to a powder. two customers, Cabot Corporation in This allows the few specks of denser the USA and the German company, tantalite to be separated from the great H.C Starck. bulk of lower density waste minerals. These companies extract tantalum A final clean-up using electrostatic metal from tantalite by chemical separators and high intensity magnets means rather than smelting. The produces a saleable concentrate con- tant-alite is dissolved in hydrofluoric taining up to 40% tantalum pentoxide. and sulphuric acid and then extractLast year these two West Australian ed into a solvent leaving impurities mines produced just 500 tonnes of behind in the acid solution. tantalite from 2.4 million tonnes of ore. Tantalum is stripped from the sol- It starts deep underground as the rare mineral tantalite, a complex oxide of iron, manganese and tantalum. There are just 200g of tantalite in every tonne of ore mined! This is the Wodgina open-cut mine in the Pilbara, N-W Western Australia. www.siliconchip.com.au August 2002  15 The tantalum processing plant at Greenbushes, in southern West Australia. This plant also produces lithium. vent in the form of tantalum fluoride. is why you don’t find air-spaced 1µF Finally, sodium reduction of the flu- capacitors! oride produces powdered tantalum It is clear from the equation there metal. are two things you can do to decrease More than half the tantalum goes the plate area: increase the dielectric into the manufacture of capacitors, constant (K) or decrease the plate twenty-five billion of them in 2000, spacing (d). up from 13 billion in 1995. Some capacitors use mica, another So why is tantalum used? What’s so mineral, as the dielectric material special about it that allows a tantalum between the plates. Mica has a diecapacitor to pack so many microfarads lectric constant of seven (Table 1). So into such a small volume? A look at a 1µF capacitor with one millimetre what a capacitor is and how it works thickness of mica dielectric will be provides the answer. seven times smaller than the air spaced A capacitor is basically two con- version. In fact, mica occurs naturalductors separated by an insulator or ly in very thin sheets. So the plate dielectric. In an air-spaced capacitor, spacing (d) could be much less than the conductors are metal plates and Uses of Tantalum Metal Uses of Tantalum Metal the dielectric is air. The value of a Chemicals 10% Chemicals 10% Metal working 15% capacitor, C, depends on the area A Metal working 15% of the plates, the dielectric constant K of the insulation between them, and its thickness d. Here is the equation: one millimetre, making the capacitor even smaller. In tantalum capacitors the dielectric is tantalum pentoxide, Ta2O5, which has a K of 26. Despite the relatively modest K compared with the very large values of some ceramics, capacitor manufacturers use tantalum for a number of reasons. Firstly, and most importantly, it is a ‘valve’ metal (another is aluminium), meaning it forms a uniform stable oxide on its surface. It is easy to make tantalum pentoxide layers less than 15µm (one millionth of a metre) thick. It is this thinness of the dielectric layer that more than compensates for the comparatively low value of K. At the same time, the layer has a high dielectric strength, meaning it is able to withstand the large electric fields that occur in the capacitor. Secondly, tantalum can be made extremely pure. It melts at 2996°C and any impurities present evaporate off at much lower temperatures. High purity of the metal substrate guarantees high quality oxide films. Finally, tantalum is easy to work. It can be produced as a powder, rolled into sheets and drawn into wires. It is almost immune to corrosion by acids and is stable with respect to temperature. Temperature stability translates into excellent temperature performance in the finished capacitors. They are capable of working from -55 to +125°C Electronics 55% Electronics 55% C = E0K(A/d) E0 is the dielectric constant of free space; it has a value of 8.85 x 10-12 farads per metre. The key to using this equation correctly is to get the units right. K is a ratio and has no units, area A must be in square metres and dielectric thickness d is in metres. The capacitance is then in farads. The equation can be turned around to find the area of the plates for a particular value capacitor. For example, if you tried to make a 1µF capacitor with two plates separated by one mm of air (K for air is one), the plate area would be nearly 113 square metres. Which 16  Silicon Chip Fig.1 (left): uses of tantalum metal. Electronics, partic-ularly tantalum capacitors, takes the lion’s share of world-wide tanatalum production. Special alloys 20% Special alloys 20% Material Air or vacuum Table 1: the dielectric of many common (and some less common) materials. While not up there with most ceramics it is significantly higher than many other materials traditionally used for capacitor production. Dielectric Constant K 1 Paper 2-6 Plastic 2-6 Glass 5-8 Mica 7 Aluminium oxide 8 Tantalum pentoxide 26 Ceramic Variable 12-30,000 www.siliconchip.com.au High power microscope pics of two types of tantalum powder: nodular (left) and flake (right). with little variation in electrical properties. Capacitor manufacture starts with powdered tantalum metal. The typical particle size for a high voltage capacitor is 10µm. Because the dielectric layer eats into the particle, the thicker layers needed for a high voltage capacitor might consume the entire particle if it were any smaller. As the equation above shows, capacitance is proportional to surface area. In the past 10 years, tantalum powder manufacturers have been able to change the shape of the particles from simple spheres through flakes to complex coral structures. Each change in shape has increased the capacitance-voltage product (CV) of the powder. CV is a measure of the volumetric efficiency of a capacitor, or the number of microfarads (µF) in a given volume. Values have increased from 8000µFV/gram for simple particles to 27,000µFV/gram for coral structured particles. What this means is simply that tantalum capacitors have steadily become smaller. Surface-mount tantalum capacitors are now available in the 0402 format; that’s 0.04 by 0.02 inches, or 1mm by 0.5mm. The powder is mixed with a binder and compressed under high pressure around a tantalum wire to make a small ‘slug’. The wire will eventually become the anode of the capacitor. Heating the slug of powder and binder under vacuum at high temperature (1500-2000°C) fuses the individual particles together. They form a strong porous sponge, with a huge internal surface area. Connecting the slug to a positive voltage and dipping it into an acid bath allows a small current to pass through it (see Fig.2). This electrolytic process creates the dielectric layer of tantalum pentoxide on all the exposed tantalum surfaces of the sponge. The applied voltage sets the thickness of the layer. The higher the voltage, the thicker the oxide layer. As you can see from the first equation, a thicker layer gives a lower value of capacitance. But it also means a higher voltage rating for the finished capacitor. Typically, the layer is around 0.25µm thick. What does this mean for a typical 25µF 25VW tantalum bead capacitor two or three millimetres in size? Putting the values for C, K and d into the second equation shows that the surface area inside the capacitor is around 209cm2. That’s about one third the area of this page. Now look at the dielectric strength of the layer and the electric field it has to withstand in operation. The dielectric strength is simply the working voltage (25) divided by the layer thickness (0.25m), in this case an amazing 125kV per millimetre. So far we have half the capacitor –one electrode of tantalum metal sponge and the dielectric of tantalum pentoxide. Now the second electrode is added. The slug is dipped into manganese nitrate solution which fills up all the pores in the sponge. Heating the slug drives off the water and decomposes the nitrate to manganese dioxide, which now becomes the second electrode (Fig.3). The manganese dioxide cathode layer provides the capacitor with a unique ‘self-healing’ mechanism. If there is a localised imperfection in the dielectric, a heavy current will flow in this region. Resistance of the manganese dioxide causes it to heat up and change to a more resistive form, plugging the imperfection. Once the manganese dioxide layer is in place, a cathode wire is glued on using a combination of graphite and silver loaded epoxy. Welding a wire to the stub of tantalum wire in the slug creates the anode lead. Fig.3 shows the layers of the finished capacitor. All that remains to be done is to decide on the packaging method. Tantalum capacitors come as either surface mount-chips or wire-ended beads, with chips outnumbering beads by four to one in recent years. The body is coded with its capacitance value and voltage rating, and then if it tests OK, the capacitor is ready to leave the factory. So next time you casually reach for a tiny surface-mount tantalum capacitor, spare a thought about how it was made and where the raw material came from. It may well have started life deep underground in Western Australia. SC Acknowledgement: Our thanks to Suzanna Hughes and Kevin O'Keefe, Sons of Gwalia Ltd, and John Gill, AVX Ltd Tantalum Divi-sion, for their assistance with this feature. .     Cathode wire Acid bath Tantalum slug DC Volts Fig.2 (above): the making of a tantalum capacitor. An electrolytic process deposits a very fine layer of tantalum pentoxide – the dielectric, on a tantalum metal slug. The coated slug is then dipped in manganese nitrate and heated, which creates the cathode of manganese dioxide. The finished capacitor is shown in graphical form in Fig.3 (right). www.siliconchip.com.au Manganese dioxide (cathode) Tantalum pentoxide (dielectric) Tantalum metal (anode) Tantalum wire stub Anode wire August 2002  17 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 DIGITAL STORAGE LOGIC PROBE for Windows 98 Design by Trent Jackson Words by Trent Jackson and Ross Tester Here’s another reason not to throw out that old computer. This fully functional Digital Storage Logic Probe is driven by a Windows-based PC. With it you can view and record valid TTL and CMOS logic levels via 32-bit Windows software. And we even supply the software! I f you have ever needed to design, service or troubleshoot digital equipment, you’ll know just how valuable a logic probe can be. Well, this one goes one step further: connect it to your PC’s parallel port 22  Silicon Chip running Win98 and you can not only view logic states, you can record them, save them for more analysis or comparison, print them and more. You can also locate and store high or low-going pulses via software latching and even disable unwanted logic highs or lows (via software). Unlike most conventional DSOs (Digital Storage Oscilloscopes) and similar devices, this device records true bit values – 0s and 1s – not waveforms or voltages. www.siliconchip.com.au You can switch between TTL and CMOS circuitry. In TTL circuits, which always operate from a 5V supply, any voltage less than 0.8V is considered to be a logic “low” and any voltage greater than 2.0V is considered to be a logic “high”. Intermediate voltages are not valid. In CMOS circuits, which can operate anywhere between about 3V and 15V, it’s not quite so simple. Any voltage less than 26% of the supply voltage (Vcc) is considered logic low, while any voltage higher than 73% of Vcc is considered logic high. How does the logic probe know what the Vcc is? Simple – it takes its power from the circuit under test! The vast majority of CMOS circuits operate with levels between 5V and 15V (3-5V operation is rare) so for simplicity, the Logic Probe has been designed to work with 5-15V levels. Virtually any PC which can handle Windows 98 can be used, though a Pentium-class is recommended. The parallel port is used, optically isolated from the logic probe to prevent damage to the port (and possibly the PC) should a worst-case scenario occur. We all know that Murphy’s law says that any scenario which does occur will be worst-case! The probe is connected to the inverting input of one of IC1’s two comparators and to the non-inverting input of the other. IC1 is an LM393, a dual precision comparator. The two elements are connected to form a standard window comparator, one gate (IC1a) detecting TTL/CMOS switch. In TTL position (which assumes a 5V supply), the divider selected ensures that 2.0V is applied to one comparator and 0.8V to the other, thus giving us the required TTL logic state conditions. In the CMOS position (which can have a wide Vcc range), the other divider puts 73% Vcc on one comparator and 26% on the other – thus achieving the CMOS logic state conditions. Full optical isolation from parallel port The open-collector outputs Fully TTL & CMOS co mpatible of both the comparators are Probe over-voltage pr connected to optocoup-lers otection VCC reverse-polarity OPTO 1 & 2, the outputs of protection which in turn connect to Low cost and very ea sy to build printer port pins 10 and 11. 32-bit Windows 98 ba A third optocoupler sed View and record logi (OPTO3) connects to pin 12 c levels – its purpose is solely to let Save and open record ed data the software know that there Print out recorded da ta is VCC present. All three optos have 10Ω suppressor resistors between them and the printer valid high logic voltages (above its port. They are low in value due to the reference voltage) and IC1b detecting fact that the parallel port has its own valid low logic voltages (below its pull-up resistors. reference voltage). While higher values would be deThe reference voltages are provided sirable, they cannot work in this case by two voltage dividers across the because there would be too much voltsupply rail. These connect to IC1’s age drop across them – and they could other inputs. The reference voltages also slow the operation of the port. vary depending on the setting of the The six diodes connected to the Features: • • • • • • • • • How it works Starting at the probe, we can see a 4.7kΩ isolating resistor and then a pair of signal diodes and a zener diode. The signal diodes will clip any negative or positive-going spike which may be present when measuring, while the zener will clamp any high voltage to a safe level. The .01µF capacitor provides not only high frequency roll-off but also gives a small amount of hysteresis to the circuit. It will also tend to integrate square wave inputs to some degree and while this is undesirable, experience has shown that the overall performance of the probe is largely unaffected. The probe is held at a nominal 39% Vcc by the 560kΩ/360kΩ voltage divider across the supply. This keeps the unconnected probe in “no man’s land”, ie, indeterminate logic state, to avoid false conclusions when reading. www.siliconchip.com.au Looking at the rear of the case, showing the 26-way IDE cable which connects to your PC’s parallel port. You will probably have to make this cable yourself. August 2002  23 24  Silicon Chip www.siliconchip.com.au K D3 1N914 A K A K + 10F K 1N914 ZD1 15V 1W 0.1F A 360k 32.5% Vcc 0.1F DIGITAL STORAGE LOGIC PROBE A 1N4004 .01F 4.7k K D2 1N914 0.1F A D1 1N4004 Fig.1: the complete circuit of the logic probe shows just how few parts there are in it. Basically, it’s just two comparators, some opto-couplers and a few LEDs! 2002 SC GND PROBE GND VCC 3-18V MAX! S2 100k 180k 560k 4.7k 100k + 26.7% Vcc TTL 100k CMOS TTL 150k CMOS ZD1 0.8V 73.3% Vcc 2.0V 15k 360k S1b S1a 6 5 2 3 A E K LEDS 1 & 2 4 IC1b IC1: LM393 IC1a 8 B C BC548 LED2 7 LED1 1 1k A RED C K K LED3  A K  A B E Q1 BC548 A GRN 2.2F 4.7k K   2 1 2 1 2 K K K K K K 150  OPTO3 4N25 47  OPTO2 4N25 47  LED3 TRI COLOUR A GRN A RED 300 300 D4-9: 1N914 10F 4.7k 1 OPTO1 4N25 4 5 4 5 4 5 A D4 A D5 A D6 A D9 A D8 A D7 10 10 10 10 18-25 7 6 5 4 3 2 13 12 11 10 CON5 TO PRINTER PORT data lines of the parallel port (pins 2-7) form two “OR” gates (D4-D6 form one, D7-D9 form the other). These two gates have their outputs connected, via current limiting resistors, to the anodes of a bicolour LED (LED3). This method has been used to obtain reasonable brightness from the LED by effectively paralleling the currents from the data lines. The LED shows the high (red) or low (green) logic levels. However, it can also show whether the probe is floating (flashing green) or no Vcc (flashing red). We haven’t yet mentioned Q1, the 1kΩ resistor and LEDs 1 and 2. They form a 2.5V regulated supply for the three optocouplers. This is essential due to the fact that the supply voltage can be anywhere from 3–18V. The LEDs are not used for their light emission (in fact, they’re sealed inside the box!). Rather, they are used for the fact that when forward biased, each will have a constant voltage across them (about 1.5V). Therefore Q1’s base is held at a constant nominal 3V. With about half a volt or so drop across Q1’s base/ emitter junction, the emitter voltage remains at a constant 2.5V, give or take. And speaking of supply, as we mentioned before this is taken from the circuit under test (by means of cables with mini crocodile or IC clips). The CMOS VCC can be anywhere from Everything mounts on the one PC board except the banana sockets, bicolour LED and the two switches. Construction is quite straightforward. 3- 18V. D1 isolates the supply and provides reverse-polarity protection; the 10µF and 0.1µF capacitors provide some smoothing and bypassing. Connecting cables The connection between the probe 150k 100k 560k 360k 0.1F 0.1F 4.7k 914 D2 Fn01 15V ZD1 401 LM393 12080340 2.2F GND VCC GND S2 POWER S1 TTL/CMOS 100k 0.1F 914 4.7k D3 4.7k 100k 300 PROBE Fu01 LED2 .01F + 47 LED1 Fu2.2 47 150 300 1 1 1k OPTO2 OPTO3 4N25 4N25 1 15k 1 360k 10 10 OPT01 4N25 1 914 914 914 914 914 914 D7 D8 D9 D6 D5 D4 Q1 D1 1N4001 1Q 4.7k 10 + 401 1 1 10F 401 BICOLOUR LED 10F Fu01 + 10 180k (IDC PLUG AND CABLE TO PC PRINTER PORT) CON3 hardware and computer is via a standard 26-way flat ribbon cable. One end of this cable is fitted with a keyed 26-way IDE female plug (which mates with a 26-way male socket mounted on the PC board); the other end is fitted with a standard Fig.2: you should be able to match this component overlay and wiring diagram very closely to the photo above to make construction simple! www.siliconchip.com.au August 2002  25 A close-up of the inside of the box to help you with the 15-way rainbow cable wiring. Use the same colour cable as we did and make life easy on yourself! parallel port (Centronics-type) IDE plug. It is most unlikely that this cable will be an off-the-shelf item so you are going to have to make it up yourself. It is relatively easy to do – while a special tool is normally used to fit IDE plugs to cables, it can be done in a bench vise. IDE plugs are not soldered – tiny, sharp “fingers” pierce each wire in the cable and make connection. A clip holds the whole thing together when assembled. Have a look at our close-up photo of the cable and you’ll see that at both ends, the cable loops through the plug and then turns back on itself. The loop takes the strain off the connection itself. You may also see a tiny arrow moulded into the PC board-end plug. This shows pin 1 and is usually the pin which the red stripe on the cable connects to. In our case, though, the red stripe goes to the opposite end. At the parallel port plug, when you hold the plug with pins towards you so that you are looking at a letter “D”, the red stripe goes to the bottom. The other cables you will need include a set of power cables and probe cables. A collection of these is shown in the main photograph and at the end of this article – all are fitted with banana plugs at one end to go into matching sockets on the probe case. The other ends can be multimeter-type probes, small crocodile clips, IC connecting clips, and so on. The choices depend on the way you want to use the probe. Construction The project is mounted in a medium sized (130 x 67 x 40mm) jiffy/zippy box and, with the exception of the switches, bicolour LED and four input sockets, all components mount on a single-sided PC board measuring 95 x 57mm and coded 04308021. And here’s the fully-opened-out project, completed and ready to close up. Notice the thin cut-out in the case (top right) for the IDE cable to pass through. 26  Silicon Chip We printed this little label to go on the case to show what the cable went to... www.siliconchip.com.au Before you start PC board construction, use it (or a photocopy of the PC board artwork in Fig. 4) as a template to drill four mounting holes in the lid of the case. Locate the board centrally and drill four 3mm holes in line with the four holes at the corners of the PC board. After checking the board for defects, start construction by soldering in the resistors, 15 PC stakes and four wire links. You might have to scrounge a 30mm length of tinned copper wire for the longest link because it will probably be too long for the usual source of link wire, cut-off resistor pigtails. Next, solder in the capacitors, diodes, on-board LEDs and the transistor (remember almost all those components are polarised). Likewise, all the ICs are polarised so you not only have to get them in the right spots, you have to get them the right way around! The last “component” to go on the PC board is the 26-pin parallel port cable connector. You will note that one side of this connector has a notch cut in it. This notch goes to the outside of the PC board. Leaving the board for a moment, it is now time to drill the case for the terminals, LED and switches. Photocopy the drilling diagram and temporarily sticky-tape it to the bottom of the case (the bottom of the case actually becomes the top!). Use this as a template to drill the holes (take note of the various sizes). And while you’re about it, you need to file a very narrow (about 1-1.5mm deep) slot in one edge of the case to allow the parallel port cable to pass through without being guillotined when you screw the case and lid together. Parts List – Digital Storage Logic Probe 1 PC board coded 04308021, 95 x 57mm 1 plastic utility case, 130 x 67 x 44mm 1 front panel label, 124 x 63mm 1 DPDT toggle switch (S1) 1 SPDT toggle switch (S2) 4 insulated banana sockets (2 red, 2 black) 1 26-way PC-mounting IDC header socket (male) 1 26-way IDC plug (female) 1 25-way D25 male IDC plug 1 150mm length 15-way rainbow ribbon cable 15 PC stakes 4 10mm M3 tapped spacers 8 5mm M3 screws 4 rubber feet Semiconductors 1 LM393 dual comparator (IC1) 3 4N25 optocouplers (OPTO 1,2,3) 1 BC548 or similar NPN transistor 1 15V, 1W zener diode (ZD1) 2 red LEDs, 5mm (LED1, LED2) 1 tricolour LED, 5mm (LED3) 1 1N4004 silicon power diode (D1) 8 1N914 silicon small signal diodes (D2 - D9) Capacitors 2 10µF 25VW PC mounting electrolytic 1 2.2µF 16VW PC mounting electrolytic 3 0.1µF 50VW MKT polyester (code 104 or 100n) 1 .01µF 50VW MKT polyester (code 103 or 10n) Resistors (1%, 0.25W) 1 560kΩ 2 360kΩ 1 180kΩ 1 150kΩ 3 100kΩ 1 15kΩ 4 4.7kΩ 1 1kΩ 2 300Ω 1 150Ω 2 47Ω 4 10Ω 4-band   OR VGS2 Graphics Splitter NEW! HC-5 hi-res Vid eo Distribution Amplifier DVS5 Video & Audio Distribution Amplifier Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. 5-band For broadcast, audiovisual and film industries. Wide bandwidth, high output and unconditional stability with hum-cancelling circuitry, front-panel video gain and cable eq adjustments. 240V AC, 120V AC or 24V DC. High resolution 1in/2out VGA splitter. Comes with 1.5m HQ cable and 12V supply. Custom-length HQ VGA cables also available. Check our NEW website for latest prices and MONTHLY SPECIALS www.questronix.com.au Email: questav<at>questronix.com.au Video Processors, Colour Correctors, Stabilisers, TBC’s, Converters, etc. All mail: PO Box 348, Woy Woy NSW 2256 Ph (02) 4343 1970 Fax (02) 4341 2795 Visitors by appointment only www.siliconchip.com.au QUESTRONIX August 2002  27 protruding PC board-mounting screwheads don’t scratch any surface you sit the unit on. And that’s it! All we have to do now is look at the software and the operation of your probe. The software The software, DSLP.exe, operates under Windows 98 and has the standard “look and feel” of your other Windows programs. When you open DSLP, you’ll find a window with a number of panes. Top left is a measurement box which indicates standard logic conditions at a glance, with a time-delayed bar graph immediately underneath. Next down is a settings box which enables you to toggle common settings on and off – it is used to enable and disable various parameters such as logic high and low, whether the pulses latch and so on. The probe sensitivity slider sets the sampling rate and hysteresis levels. On the right top side of the window is the system box – the heart and soul of the software. This pane enables you to set the parallel port address (three most common ports shown) and also gives you the status of the port, whether hardware is connected or not and whether or not power is connected. Clicking on the reset binary digit data buffer box will clear all current data in the recorder box. For good measure, there is a realtime 24-hour system clock readout. Finally, across the bottom of the window is a binary data recorder, where incoming data is recorded in a true bit fashion. All of these settings and controls will become self-explanatory as you Fig.3: this is the window which should greet you when you run the DSLP.EXE file. The various panes are quite self-explanatory. 10uF 10uF 1 104 104 Q1 1 1 1 28  Silicon Chip Now it’s time for final assembly. First of all, mount the PC board on the lid using 10mm tapped stand-offs. If you want to save a couple of bob, you could just use some screws through the lid with a nut both sides of the PC board. Plug the parallel port connector cable into its socket on the PC board (remember that keyway) and place the lid/PC board assembly down into the box so the parallel port cable lies in the slot you filed in the edge of the case. Screw the case and lid together and fix four rubber feet to the lid so the 2.2uF 10nF 104 This slot needs to be just wide enough to accommodate the cable (about 34mm) and ours was about 25mm from the end of the case. Before you mount the LED and input sockets through the bottom of the case, the front panel needs to be fitted. It can be either glued on or stuck on with (thin!) double-sided adhesive tape. Take care not to mark the panel from here on. Use the diagrams and photos to locate the various bits. When all (including the bicolour LED) are in place, you can connect the PC board to the case with a length of 15-way rainbow cable (it’s a lot easier to follow using rainbow cable than ordinary IDE cable!). If you use the same colours as we did, you can use the photos and drawings to ensure the right wire goes to the right PC stake. When soldering to the bicolour LED, take careful note as to which leads are which: the cathode (K) is the centre lead while the green anode is closest to the tab on the side of the LED. Therefore, the red anode is closest to the flat side. All three leads should be shortened considerably to avoid the chance of shorting – ours were cut to about three or four millimetres long. 1 04308021 Fig.4: full size artwork for the PC board. Even if you don’t make your own board, a photocopy is always handy as a drilling template. www.siliconchip.com.au use the probe. Interfacing the hardware and software This is extremely straightforward. As long as you are using a Pentium-based PC (or equivalent) and running Windows 98 (and of course your hardware is assembled correctly and you have loaded the software on your computer!), you should not have any problems. Plug ’er in and away she goes... The software, dslp.zip, can be downloaded from www.siliconchip. com.au It is a 2MB file so be patient! Once downloaded and unzipped, run “setup” and it will install automatically. When you run the unzipped dslp. exe file, you should be greeted with a window as shown in Fig.3. From there, it’s just a matter of selecting your parameters and using the probe. A selection of the connector cables you could need for this project. At left is a “curly cord” multimeter probe which is ideal as a data probe; the other cords have various types of clips for connecting to the circuit under test. All have banana plugs on one end. Operation The software basically works like this: assuming a valid high level voltage is detected by the probe (and therefore present on pins 2 and 5 of IC1,) pin 1 of IC1a will go low, forward biasing OPTO1’s LED and causing its transistor to conduct. This pulls pin 10 on the parallel port low. The software reads this and processes it accordingly. It will also write a data value of 56 decimal to the parallel port, taking pins 5,6 and 7 high – in turn, lighting up the green LED in bicolour 8 8 LED3. Detecting and processing 6.5 6.5 6 63 a valid low level voltage is achieved in exactly 18 the same way, except 8 8 that IC1b, OPTO2 and pin 11 are involved. 29 Similarly, the soft18 ware writes a value of 7 decimal to the port, sending pins 2, 3 and 4 high, lighting the red 18 18 18 21 22 LED in LED3. 125 If the LED is flashing, (either colour) you have either of the two “error” Figs. 5 & 6: 1:1 artwork for the front panel and a drilling template for the case. The panel artstates as shown on the work, along with the PC board pattern, can be downloaded from www.siliconchip.com.au SC front panel. www.siliconchip.com.au August 2002  29 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. Soldering iron tip preserver Although 60/40 solder melts at about 200°C, the tip tempera­ture of a soldering iron should be at about 370°C. This is neces­sary to make a good quick joint, without the risk of overheating delicate components because the iron has to be kept on the joint for too long. Unfortunately, at this temperature, the tip oxidises rapid­ ly and needs constant cleaning. That’s where this circuit can help – it keeps the soldering tip to just below 200°C while the iron is at rest. Oxidisation is then negligible and the iron can be brought back up to soldering temperature in just a few seconds when needed. In addition, normal soldering operation, where the iron is returned to rest only momentarily, is unaffected because of the thermal inertia of the iron. Two 555 timers (IC1 & IC2) form the heart of the circuit. IC1 is wired as a monostable and provides an initial warm-up time of about 45 seconds to bring the iron up to temperature. At the end of this period, its pin 3 output switches high and IC2 (which is wired in astable configuration) switches the iron on – via relay RLY1 – for about one second in six to maintain the standby temperature. The presence of the iron in its stand is sensed by electri­cal contact between the two and some slight modification of the stand may be necessary to achieve this. When the iron is at rest, Q1’s base is pulled low and so Q1 is off. Conversely, when the iron is out of its stand, Q1 turns on and pulls pins 2 & 6 of IC2 high, to inhibit its operation. During this time, pin 3 of IC2 is low and so the iron is continuously powered via RLY1’s normally closed (NC) contacts. Note that the particular soldering iron that the circuit was designed for has its own 24V supply transformer. Other irons may need different power supply arrangements. The warm-up time and standby temperature can be varied by altering R2 and R5, as necessary. Alan March, North Turramurra, NSW. ($40) TV relative signal strength meter This circuit was designed to assist the installation of TV antennas. The signal is monitored using a small portable TV set and this circuit monitors the output of the TV’s FM detector IC via a shielded lead. To initially calibrate the meter, adjust trimpot VR2 to zero the meter. Trimpot VR1 is a sensitivity control and can be set for a preset reading (ie, 0dB) or can be calibrated in milli­volts. 30  Silicon Chip Rotating the antenna for a minimum reading on the meter (indicating FM quieting) gives the op- timum orientation for the antenna. Ted Sherman, Kawhia, NZ ($30) www.siliconchip.com.au Simple card access control system This card access control system for medium-to-low security situations can be built at a relatively low cost and is more fun than a keypad. The circuit can be driven by the smallest of microcontrollers, say a PIC12C508A, and only requires simple assembly code to run. The concept is quite simple – a cardboard or plastic card (with holes punched) is slipped between two PC boards separated by a plastic spacer. This spacer also helps to guide the access card into position. When the access card is inserted all of the way to the back of the spacer, it hits a small rubber mat attached to a flexible metal clip which makes up one half of the “card present” switch. This flexible clip is forced against a small metal con­ tact plate, resulting in the trigger line going low. This tells the microcontroller that a card is pres­ent. The microcontroller can then pulse the clock line while reading the sense line. A low signal on the sense line indicates the presence of a hole. If you are using the unit in bright sunlight, it is advis­able to read the sense line with an A/D converter input, to allow for variations in ambient light conditions. If no A/D converter input is available, a simple op amp input circuit would work just as well. www.siliconchip.com.au The circuit uses infrared LEDs and phototransistors, while the access card is covered with IR lens material on each side. This not only minimises problems with ambient light but also means that the holes in the access card are hidden (infrared lens material is readily available in sheets from Farnell Electronics). IC1, a 4017B decade counter, counts up on every clock cycle (only one pin high at any time) from the microcontroller. Its outputs in turn drive LEDs 1-7 via IC2, a ULN2003 Darlington array. If a LED shines directly onto its corresponding phototran­ sistor (Q2Q8) via a hole in the access card, the phototransistor will turn on, pulling the sense line to ground. The sense line is fed back to the microcontroller. If the correct sequence of photo­ trans­istors turns on, the micro­con­troller turns on transistor Q1 to activate the relay and the door strike mechanism. David Kadow, Norwood, SA. David Kadow is this month’s winner of the Wav etek Meterman 85XT true RMS digita l multimeter. August 2002  31 Circuit Notebook – continued Petrol/gas switch for a Pajero My current vehicle, a Pajero, was modified for dual fuel – ie, petrol and gas. However, it’s necessary to run the vehicle on petrol at regular intervals to stop the injectors from clog­ging up. This simple circuit allows the vehicle to be started using petrol and then automatically switches it to gas when the speed exceeds 45km/h and the brake pedal is pressed. Alternatively, the vehicle may be run on petrol simply by switching the existing petrol/ gas switch to petrol. You can also start the vehicle on gas by pressing the brake pedal while starting the vehicle. The circuit is based on an LM324 dual op amp, with both op amps wired as comparators. It works like this: IC1a buffers the signal from the vehicle’s speed sensor and drives an output filter network (D1, a 560kΩ resistor and a 10µF capacitor) to produce a DC voltage that’s proportional to the vehicle’s speed. This voltage is then applied to pin 5 of IC1b and compared with the voltage set by trimpot VR1. When pin 7 of IC1b goes high, transistor Q1 turns on. This also turns on transistor Q2 when the brake pedal is pressed (pressing the brake pedal applies +12V from the brake light circuit to Q2’s emitter). And when Q2 turns on, relay 1 turns on and its contacts switch to the gas position. Trimpot VR1 must be adjusted so that IC1b’s pin 7 output switches high when the desired trigger speed is reached (ie, 45km/h). In effect, the speed signal is AND’ed with the brake light signal to turn on the relay. The vehicle has been running this circuit for several years now and is still running well, with no further injector cleans required. J. Malnar, Gordon, ACT. ($40) Silicon Chip Binders  Heavy board covers with mottled dark green vinyl covering  Each binder holds up to 12 issues  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5.50 p&p each (Australia only; not available elsewhere). Buy five and get them postage free. REAL VALUE AT $12.95 PLUS P & P Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. 32  Silicon Chip www.siliconchip.com.au COMPUTER TWEAKS DO YOU LIKE the look of Microsoft’s new Windows XP operating system but cannot afford to upgrade? Here’s how to spruce up your existing Win95/98/Me desktop by substituting WinXP-style icons. You can even change your wallpaper to an XP theme. By GREG SWAIN Along with many other improvements, Windows XP comes with an impressive new look and that includes redesigned icons. Unfortunately, many of us don’t have the hardware that’s necessary to run Windows XP and are better off sticking to Windows 95/98 or Windows Me for the time being. You can, however, update your existing desktop by converting to WinXP-style icons. This can be done using one of several freeware/shareware utilities (eg, “XP Icon Raider”) that are now available on the Internet. And if you must have it, you can install WinXP-theme wallpaper as well. It’s not a bad idea to back up your PC’s registry before making these kinds of changes. If you don’t now how to do this, go to www.google.com and search for Windows 98 backup registry (for example) – there will be plenty of “hits” with all the details on what to do. To install XP icons on your Win98/ Me desktop, first shut down all running applications, then go to: www.skylarkutilities.com/program. pcs?xp-icon-raider and download xpiraider.zip (134kB). This unzips to three files (including a readme) and there’s no installation routine as such – just double-click xpiraider.exe to bring up the dialog box shown in Fig.1, select which icons you wish to change and click the “Apply” button. Selecting “Class Icons” changes the icons for My Computer, My Documents, Network Neigh­borhood and the Recycle Bin; the “Shell Icons” button changes the appearance of disk drives and the Start Fig.1: XP Icon Raider v1.01 from Skylark makes it easy for you to update the icons on your Win95/98/Me desktop to the XP look. It’s also easy to change them back again. www.siliconchip.com.au Menu; and the “Associates” button updates many of the icons assigned to files. When you click Apply, your PC will immediately perform a hard restart so make sure that you don’t have any other programs running when you do this. If you want to revert to the old icons, just relaunch XP Icon Raider, turn off the appropriate buttons and click Apply once more. Of course, the shiny new icons won’t give you the considerable benefits that Windows XP has to offer. For that, you’ll have to buy your own copy but if you have the hardware to run it, it’s a worthwhile upgrade. What about “XP-theme” wallpaper? There are lots to choose from at: http://sardaulkar.planetarrakis.net/ wallpaper.htm Want more? – search the Internet. But personally, I think wallpaper is just there to slow your SC machine down. Figs.2&3: here’s what the icons on a Win98 desktop look like after running XP Icon Raider. Fig.4 at the top of the pages shows the updated Start menu. August 2002  33 This thermometer uses a K-type thermocouple probe and is ideal for both industrial and inhome use. It can measure temper­atures over the range from -55°C to 1200°C and includes under and over-temperature alarm outputs, which can be used to provide thermostatic control. By JOHN CLARKE A CCURATE TEMPERATURE measurements are vital during many industrial processes that involve heating or cooling. That’s because too much or too little heat can give poor results, so it’s necessary to ensure that the temperature is accurately controlled. Kilns, for example, often operate at 34  Silicon Chip temperatures in excess of 1000°C and measuring temperatures of this order requires a probe that can cope with the heat. Further down the scale, a probe can also be used to measure the temperature of solder in a solder bath – eg, for tin-plating or wave-soldering PC boards. In the latter case, the sol- der must generally be maintained at a fairly constant temperature to ensure correct adhesion. Accurate temperature measurements are also vital in the refrigeration industry. After all, many foods and other products can quickly spoil unless kept below specific temperatures. This new Digital Thermometer/ Thermostat can measure temper­atures from -55°C to 1200°C, depending on the probe that’s used. Its resolution is 0.1°C for measurements from -55°C to 199°C, and 1°C for measurements 200°C to 1200°C. However, the measurement accuracy itself depends on the calibration and the linearity of the probe used. Typically, the accuracy is within 2% of reading for meas­ www.siliconchip.com.au urements up to 500°C. Table 1 shows the expected readings from the Digital Ther­mometer for a given temperature. A bi-colour LED situated on the front panel of the instru­ment is used as the temperature “alarm”. It simply changes colour when the measured temperature either rises above or drops below a preset “alarm” temperature (as set by a pushbutton switch). At the same time, a small piezoelectric buzzer inside the case provides an audible alarm when the preset temperature is reached. The buzzer can be left out of circuit if an audible alarm is not required. The unit also provides two outputs to drive external relays (if required) for thermostatic control. One of these outputs is used to control the “under-temperature” relay, while the other controls the “over-temperature” relay. In use, the relays could typically be used to automatically switch heating elements, fans or refrigeration units on or off. K-type thermocouple As mentioned above, this design uses a K-type thermocouple (a thermocouple consists of two dissimilar metals) as the temper­ature probe. A K-type thermocouple uses an alloy of chrome and nickel (called Chromel) for one wire and an alloy of aluminium, manganese, silicon and nickel (called Alumel) for the second. The two wires are insulated and only make contact at one end – ie, at the temperature probe end. The other ends of the wires are sepa­rately connected to a 2-pin plug Basically, a thermocouple’s operation relies on the princi­ple that two dissimilar metals produce a voltage which is depend­ent on temperature. Fig.1 shows how the thermocouple (Sensor1) is connected to the thermometer circuit. A K-type thermocouple produces a voltage output that chang­ es by 40.44µV/°C. This change in output per degree C is called the “Seebeck Coefficient” – it refers to the output change that occurs due to the temperature difference between the probe end and the plug end of the thermocouple. If both ends are at the same temperature, there will be no output voltage. It follows that if we know the temperature at the plug end of the www.siliconchip.com.au Fig.1: block diagram for the Digital Thermometer/ Thermostat. IC1 amplifies the thermocouple output and drives the LCD module and comparator IC2. thermocouple, we can calculate the temperature at the probe since we also know the Seeback coefficient. For example, if the plug end is held at 0°C, the output will increase by 40.44µV for every 1°C above zero. Similarly, the output will decrease by 40.44µV for every 1°C drop in temperature. This means that the output voltage from the thermocouple will be at 404.4mV at 10°C and at 1.01mV at 25°C. If we then multiply the thermocouple output by 24.73 using an amplifier (op amp IC1), we effectively convert the output from 40.44µV/°C to 1mV/°C. This can then be used to give a direct readout of the temperature on a panel meter. Compensating the output In practice, our thermometer operates somewhat differently because we don’t keep the plug end of the thermocouple at 0°C. Although this MAIN FEATURES • • • • • • • • • -55°C to 1200°C reading (dependent on probe) 0.1°C resolution to 199.9°C 1°C resolution to 1200°C Under and over temperature alarm indication Suitable for driving relays for thermostat control Adjustable alarm temperature AC plugpack or 2 x 9V battery operation LCD readout Compact case could be done using an ice bath that is constantly stirred and topped up with ice, it’s too cumbersome to be a practical proposition. Instead, we compensate the thermocouple output by firstly measuring the temperature at the plug end using a semiconductor sensor (Sensor2 in Fig.1). We then add 40.44µV for every 1°C that the thermocouple plug end is above 0°C. Normally, if the thermocouple plug is at 25°C (ie, at about room temperature), its output will be 1.01mV lower than it would be if it were at 0°C. By adding an extra 1.01mV to the reading (ie, 25 x 40.44µV), we obtain the correct result without having to keep the plug end at 0°C. Note that there are several dissimilar metal junctions within the connections between the thermocouple plug and amplifi­ er. These include the Chromel to copper junction and the Alumel to copper junction on the PC board itself. However, these do not contribute to the overall voltage reading after calibration provided they are all kept at the same temperature. As a result, the PC board has been designed to help main­ tain similar temperatures at these junctions by making the copper connections all the same size. And once the PC board is installed inside its case, the inside temperature will remain fairly con­ stant. Note, however, that if the thermocouple lead is extended, it is necessary to use the same thermocouple wire for the whole length between the probe and plug. In addition, an op amp with an extremely low input offset voltage change with temperature is used for August 2002  35 36  Silicon Chip www.siliconchip.com.au SC 2002 + + TP3 A K 1N4004 + VR3 10k +2.49V + -9V TP4 + 100k VR2 10k 1k D2 1N4004 D1 1N4004 IC1 7 +16V 0.1F -16V 470F 25VW -9V 1k 10k OUT GND GND OUT REG2 7909 IN IN TP2 VR4 500 VR5 500 6 10F 25VW 10k 0.1F REG1 7809 -9V 4 3 LM627 2 470F 25VW 0.1F 0.1F 1.1k 430 750k 100k SENSOR1: K TYPE THERMOCOUPLE 5.6k ADJ SENSOR2 LM335 S1 POWER ADJ -2.49V D6 1N914 VR6 10k D5 1N914 D4 1N914 VR1 10k LM335, LM336 3.3k ADJ ADJ D3 1N914 TP1 NC NO VR7 1k S3a 10F 25VW 10F 25VW VR8 500 22k -9V TP5 +9V C 0.1F S2: POS1 -55° - 199.9°C POS2 -55° - 1200°C 2 RANGE 1 S2a -2.49V 5.6k 27 470 5.6k +2.49V K-TYPE THERMOCOUPLE THERMOMETER/THERMOSTAT 12V AC IN REF2 LM336 -2.5 REF1 LM336 -2.5 3.3k -9V 4 IC2 OP77 7 -9V  6 A E B K A + 1 A 2 -2.49V -16V D8 1N914 K 11 DP1 ZD2 15V 1W B B S2b 2 1 150 0.5W 2.2k 10k 10k 2.2k ZD1 15V 1W 150 0.5W C 5 COM D G 8 RFL 2N7000 6 INLO S 9 RFH A K 10 ROH 12 IN TO RELAY1 COIL -1V G NO NC OUT Q3 2N7000 10k TO RELAY2 COIL GND OUT 7809 IN S D BUZZER* *ONLY ONE BUZZER USED BUZZER* 7909 GND DISP- 4 DP2 C S3b Q2 BC327 Q1 BC337 LED C E E C LCD MODULE INHI 7 +16V D7 1N914 +2.49V LED1 RED/GRN  2.2k BC327, BC337 S3: PUSH TO SET ALARM TEMP 2 3 10F 25VW 10M +9V Fig.2 (left): the complete circuit diagram for the Digital Thermometer/ Thermostat. IC1 acts as a non-inverting amplifier with a gain of 24.73 for Sensor1 (a K-type thermo­couple), as an inverting amplifier with a gain of 0.1009 for Sensor2 and as an inverting amplifier with a gain of 0.1106 for REF1. IC2 compares the output of IC1 with a reference voltage derived from VR7 and drives the under and over-temperature alarm circuits (Q1, Q2 and a buzzer). IC1 (LM627). In fact, this op amp has a maximum drift of 0.6µV/°C between -25°C and 85°C. Assuming that its temperature changes by 40°C, this would contrib­ute a maximum of 24µV to the thermocouple output – equivalent to just under 0.6°C. As shown in Fig.1, IC1’s output is fed to comparator IC2. This comparator also monitors the voltage at the wiper of the Set potentiometer (VR7). If the temperature goes above the set value, then IC2’s output goes low. Conversely, if the temperature goes below the set value, the comparator’s output goes high. This output drives the bi-colour LED and also drives two transistors stages to control the relays and the buzzer. Note that the buzzer can be wired in one of two positions. In one position, it sounds only when the temperature rises above the set value. Conversely, in the other position, it sounds only when the temperature falls below the set value. Note also that we have specified an OP77GP (or OP07CN) op amp for IC2. This device has similar specifications to the LM627 but note that, because of its internal diode clamps, we cannot use an LM627 for IC2. The OP77GP and OP07CN have clamping too but it is imple­mented differently. As a result, the op amp’s input impedance always remains high which means that it doesn’t load down any voltages at its inputs. And here’s an interesting twist: although we cannot substi­tute an LM627 for IC2, the reverse isn’t true for IC1! An OP77GP or OP07CN can be used instead of the LM627. Watch this point when building the PC board. Circuit details Refer now to Fig.2 for the complete circuit of the K-Type Thermocouple Thermometer/Thermostat. As before, www.siliconchip.com.au IC1 provides the gain for the thermocouple output while Sensor 2 and REF1 provide the compensation for the thermocouple probe. As shown, the thermocouple’s output is fed to IC1’s non-inverting input (pin 3) via a low-pass RC filter to remove RF signals. Thus, IC1 functions as a non-inverting amplifier for thermocouple signals. Its gain is set by the feed­back components connected between pins 6 and 2, together with the 430Ω resistor to ground, and is adjusted using VR4. As explained above, this stage has a gain of 24.73 (ie, giving 1mV/°C at pin 6). This involves adjust­ing VR4 (during calibration) for a resistance of 204Ω (ie, 1 + 10,204/430 = 24.73). Sensor2, an LM335 temperature sensor, is used to measure the temperature at the plug end of the thermocouple. In opera­tion, this device provides a nominal 10mV/°C output. It is sup­plied with current from the -9V rail via a 5.6kΩ resistor and its output (at the negative terminal) is fed to pin 2 of IC1 via 100kΩ and 1.1kΩ resistors. As a result, IC1 functions as an inverting op amp stage for signals from Sensor 2. In this case, its gain is 0.1009 (ie, 10204/(100,000 + 1100) so Sen­sor2’s nominal 10mV/°C output is reduced to 1.009mV/°C at IC1’s output. Trimpot VR2 allows Sensor2 to be adjusted so that IC1’s output in fact changes by 1mV/°C. This matches the 1mV/°C output from IC1 due to the thermocouple and so Sensor2 provides temper­ature compensation. Offset voltage One problem with Sensor2 is that its output at 0°C is 2.73V as opposed to 0V from the thermocouple. So while Sensor2 can provide the required 1mV/°C temperature compensation, it has a 2.73V offset voltage which must be corrected. This translates to an offset voltage of 275.5mV at IC1’s output (since IC1 has a gain of 0.1009 for signals from Sensor2). This offset voltage is corrected using voltage reference REF1. This device delivers a nominal 2.5V but this can be adjust­ed over a small range using VR1 at it ADJ (adjust) terminal. Diodes D3 and D4 provide temperature compensation for the sensor, so that its output remains constant over a wide temperature range. In practice, VR1 is used to adjust REF1 to give 2.490V, as this provides Table 1: Thermocouple Calibration Thermocouple Thermocouple Temperature Output (Degrees C) (mV/(Degree C) -60 -2.243 -40 -1.527 -20 -0.777 -10 -0.392 0 0 10 0.397 20 0.798 25 1.000 30 1.203 40 1.611 50 2.022 60 2.436 80 3.266 100 4.095 120 4.919 140 5.733 160 6.539 180 7.338 200 8.137 220 8.938 240 9.745 260 10.560 280 11.381 300 12.207 320 13.039 340 13.874 360 14.712 380 15.552 400 16.395 420 17.241 440 18.088 460 18.938 480 19.788 500 20.640 520 21.493 540 22.346 560 23.198 580 24.050 600 24.902 620 25.751 640 26.599 660 27.445 680 28.288 700 29.128 720 29.965 740 30.799 750 31.214 760 31.629 780 32.455 800 33.277 820 34.095 840 34.909 860 35.718 880 36.524 900 37.325 920 38.122 940 38.915 960 39.703 980 40.488 1000 41.269 1020 42.045 1040 42.817 1060 43.585 1080 44.349 1100 45.108 1120 45.863 1140 46.612 1160 47.356 1180 48.095 1200 48.828 Display Reading (Degrees C) -55.5 -37.8 -19.2 -9.7 0 9.8 19.7 24.7 29.8 39.8 50.0 60.2 80.8 101.3 121.6 141.8 161.7 181.5 201.2 221.0 241.0 261.1 281.5 301.9 322.5 343.1 363.8 384.6 405.4 426.4 447.3 468.3 489.4 510.4 531.5 552.6 573.7 594.8 615.8 636.8 657.8 678.7 699.6 720.3 741.0 761.7 771.9 782.2 802.6 822.9 843.2 863.3 883.3 903.2 923.0 942.8 962.4 981.9 1001.3 1020.6 1039.8 1058.9 1077.9 1096.8 1115.5 1134.2 1152.7 1171.1 1189.4 1207.5 August 2002  37 are effec­ tively in parallel with the 430Ω resistor). However, their effect is really quite small (less than .06%) and, in any case, is easily corrected during calibration. Range switch The rear panel carries two sockets – one for the thermocouple and the other for the power supply. In addition, there are two access holes for the screw terminal blocks. the lowest change in value with tempera­ture. This 2.49V output is fed to pin 2 of IC1 via a network consisting of a 100kΩ resistor, trimpot VR3 and a 750kΩ resistor. VR3 allows IC1’s gain to be precisely adjusted for this signal, so that it cancels the 275.5mV offset generated by Sensor2. Note that the 750kΩ resistor and VR3 also have some effect on the gain of IC1 for the thermocouple (since they In summary then, IC1 provides us with a 1mV/°C output, as measured by the thermocouple probe. This means that at 200°C, its pin 6 output will be at 200mV which is sufficient to overrange a 200mV LCD meter (as used here). Consequently, a voltage divider is included immediately after IC1, so that the meter can display temperature measurements above 200°C – ie, up to 1200°C. This divider consists of a 10kΩ resistor, a 1kΩ resistor and a 500Ω trimpot (VR2) connected in series to ground. In practice ,VR2 is set to 111Ω, so that IC1’s output is divided by 10 at the junction of the 10kΩ and 1kΩ resistors. Range switch S2a is used to select between the two tempera­ture ranges (ie, either -55°C to 199.9°C or -55°C to 1200°C). From there, the signal is applied to the pin 7 input (INHI) of the LCD module. In addition, the divided signal on position 2 of the range switch is fed to the inverting input of comparator IC2. Alarm indication Fig.3: the top trace is this scope shot shows the 50Hz square-wave drive to the unused decimal point DP2. This square wave is in phase with the LCD backplane signal (not accessible from the pins of the LCD module). The lower trace is the inverted (out-of-phase ) signal at the drain of Mosfet Q3. This out-of-phase signal drives decimal point (DP1) when the -55°C to 199.9°C range is selected. 38  Silicon Chip IC2 compares this divided signal with the voltage on its non-inverting (pin 3) input, as set by trimpot VR7 (Alarm Set). This trimpot is fed by a divider network connected between the +2.49V and -2.49V rails and to ground. It allows the voltage on pin 3 to be adjusted between -5.5mV and +120mV (in practice, it’s a little more than this), corresponding to setting the alarm threshold between -55°C and +1200°C. The -2.49V rail is obtained using another LM336-2.5 refer­ence (REF2). This works in a similar fashion to REF1, with VR6 setting the output to -2.49V. If the voltage at pin 2 of IC2 is higher than the voltage on pin 3, the pin 6 output goes negative and sits close to the -9V supply rail. This indicates the “over-temperature” condition and turn on the green LED in LED1. At the same time, D8 is for­ward biased and PNP transistor Q2 turns on and drives the buzzer (if connected). In addition, Q2 drives Relay 2 (if connected) via a www.siliconchip.com.au 150Ω resistor in series with the -16V supply. Zener diode ZD2 is included to limit the voltage across the buzzer if a relay is not connected. Conversely, if pin 2 is lower than pin 3, IC2’s output will swing close to the +9V rail. This indicates the “undertempera­ture” condition and turns on the red LED in LED1. It also turns on Q1 to drive the buzzer and Relay 1 (if these are connected). As before, a 150Ω 0.5W resistor is included in series with the supply rail to the relay. This resistor value is suitable for use with 12V relays with coil resistances ranging from 285Ω to 400Ω. Note that although two buzzers are shown on the circuit, only one is used in practice. If an audible alarm is re­quired when the temperature goes above the set level, connect the buzzer to Q2. Alternatively, if an audible alarm is required when the temperature drops below a certain value, connect the buzzer to Q1. The 10MΩ feedback resistor between pins 3 & 6 of IC2 provides hysteresis for the comparator. In operation, the resis­tor pulls the voltage on pin 3 an extra 350µV higher when pin 6 goes high and lower by about 350µV when pin 6 goes low. This set the hysteresis to 3.5°C but this can be increased by using a smaller value for the feedback resistor. Setting the alarm temperature Pressing switch S3a connects VR7’s wiper directly to pin 7 of the LCD module. This allows the module to indicate the set alarm temperature. This can be altered by using a small screw­driver to vary VR7 (which is a 10-turn trimpot) through a small adjustment hole in the front panel. LCD module The LCD module is operated from a nominal 5V supply using the +2.49V and -2.49V reference voltages provided by REF1 and REF2. As shown, the COM, RFL (Ref-Low) and INLO (In-Low) inputs all connect to ground, while the ROH (Reference) output at pin 10 sits 100mV above ground and provides the 200mV (ie, twice the reference voltage) full-scale range for the display. This pin is connected to the RFH (Ref-High) input. Unfortunately, the LCD module used in the prototype (Jaycar Cat.QP5570) doesn’t have an output that can www.siliconchip.com.au Parts List 1 PC board, code 04208022, 117 x 102mm 1 plastic case, 140 x 110 x 35mm 1 front panel label, 132 x 28mm 1 12VAC 100mA plugpack 1 LCD 3.5-digit panel meter (Jaycar QP-5570, Altronics Q-0571 – see text) 1 ‘K’ type thermocouple with probe (Sensor1) 1 ‘K’ type thermocouple panel socket (Farnell Cat 708-7949) 2 2-way PC mount screw terminals (5.04mm pin spacing) 1 DC power socket 1 mini PC-mount buzzer (7.6mm pin spacing) 1 12VAC 100mA plugpack 1 SPDT toggle switch (S1) 1 DPDT toggle switch (S2) 1 DPDT momentary pushbutton switch (S3) 1 10-way pin header socket (2.54mm pin spacing) 1 2-way pin header socket (2.54mm pin spacing) 1 5mm LED bezel 1 200mm length of red hookup wire 1 200mm length of black hookup wire 1 200mm length of yellow hookup wire 1 200mm length of white hookup wire 1 200mm length of green hookup wire 1 150mm length of 0.8mm tinned copper wire 4 M3 x 6mm screws 4 50mm long cable ties 19 PC stakes 1 LM335 temperature sensor (Sensor2) 1 BC337 NPN transistor (Q1) 1 BC327 PNP transistor (Q2) 1 2N7000 N channel signal Mosfet (Q3) (for decimal point switch­ing on LCD) 1 7809 regulator (REG1) 1 7909 regulator (REG2) 2 1N4004 1A diodes (D1,D2) 6 1N4148, 1N914 diodes (D3-D8) 2 15V 1W zener diodes (ZD1,ZD2) 1 5mm bicoloured LED (2-leads) LED1 Capacitors 2 470µF 25VW PC electrolytic 4 10µF 25VW PC electrolytic 5 0.1µF MKT polyester (code 100n or 104) Resistors (0.25W, 1%, 50ppm/°C or better tempera­ture coefficient) 1 10MΩ 3 2.2kΩ 1 750kΩ 1 1.1kΩ 2 100kΩ 2 1kΩ 1 22kΩ 1 470Ω 6 10kΩ 1 430Ω 3 5.6kΩ 2 150Ω 0.5W 2 3.3kΩ 1 27Ω Trimpots 4 10kΩ horizontal cermet trimpots (VR1, VR2, VR3, VR6) (code 103) 1 1kΩ horizontal multi-turn trimpot (VR7) (code 102) 3 500Ω horizontal cermet trimpot (VR4, VR5, VR8) (code 501) Semiconductors 1 LM627CN, OP27GP, OP77GP or OP07CN op amp (IC1) 1 OP77GP or OP07CN op amp (IC2) 2 LM336-2.5 2.5V reference (REF1,REF2) Extra parts required for battery operation 2 9V batteries 2 battery snap-on connectors 2 battery clip holders (Altronics S 5050) 1 DPDT toggle switch (S1) 2 M3 x 6mm screws and nuts directly drive the decimal points. As a result, Mosfet Q3 has been included to drive decimal point DP1. In order to turn DP1 on, it must be driven using an invert­ed version of the LCD’s backplane signal. This signal operates at about 50Hz. The voltage swings between the DISP- level (which is about -1V below ground) and the 2.49V positive supply. This gives a square-wave drive of 3.49V peak-to-peak. Q3 monitors the high-impedance backplane signal on one of the unused August 2002  39 12V AC INPUT SOCKET TO OVER ALARM RELAY2 decimal points (in this case, DP2 at pin 12). When the voltage goes high, Q3 switches on and the drain voltage is pulled to the -1V level. Conversely, when the backplane signal goes low, Q3 switches off and the drain is pulled to the +2.49V supply via a 10kΩ resistor. As a result, the drain voltage is an inversion of the back­plane signal and this drives decimal point DP1 via range switch S2b and Set switch S3b. Note that while the decimal point can be displayed by con­ necting its pin directly to the positive supply, it is not a recommended practice. There are a couple of reasons for this: first, it places a DC voltage on the segment which can shorten the life of the LCD; and second, the decimal point segment would appear rather washed out instead of fully black. K-TYPE THERMOCOUPLE SOCKET (FOR SENSOR1) TO UNDER ALARM RELAY1 TATSOMREHT/RETEMOMREHT K EPYT SENSOR2 LM335 TP1 + 430 10F 25VW 1 IC2 OP77 D6 1 D4 914 5.6k VR6 10k Alternative LCD panel meter 5.6k DNG q2.49V TUOTUC DCL 13 12 1110 9 8 7 6 5 4 Q3 2N7000 2 1 VR5 500 +2.49V 1k TP2 TES 2.2k D7 914 D8 914 22k HCTIWS 914 470 D5 1k 3.3k 0.1 10k q2.49V 10k By contrast, the alternative LCD module from Altronics (Cat. Q-0571) does include a decimal point drive output (pin 10). This means that Q3 and its associated 10kΩ resistor are no longer required if the Altronics module is used. Instead, the decimal point driver output at C pin 10 is connected directly to NO the NC contact of switch S3b. Fig.8 shows how the Altron­ NC ics module is used. Note the different pin numbering. 27 + VR8 500 100k REF2 LM336-2.5 TP3 VR4 500 BC337 750k VR7 1k (-) 10F 25VW BC327 TP5 11 IC1 LM627 2.2k 10F 25VW Q2 D3 VR1 10k VR3 10k 1.1k 0.1 0.1 10M 7909 0.1 REG2 10F 25VW Q1 914 VR2 10k TP4 100k 0.1 3.3k REG1 7809 REDNU MRALA 25VW (BUZZER) 10k 25VW (BUZZER) 10k 470F 5.6k 2.2k 470F +2.49V ZD1 REVO MRALA 0.5W 150 D1 D2 0.5W 150 ZD2 REF1 LM336-2.5 GND 914 CA 22060140 10k LED1 S3 S2 S1 POWER LCD MODULE Fig.4: follow this wiring diagram to build the Digital Thermometer/Thermostat but note that only one buzzer is installed in the positions indicated (see text). Note also that PC stakes are installed at all external wiring positions and at the test points (TP). Q3 and its associated 10kΩ resistor can be omitted for panel meters with a decimal point driver pin (see Fig.8). Power supply Power for the circuit is derived from a 12V AC plugpack. Its output is rectified using D1 and D2 to give Table 2: Resistor Colour Codes  No.   1   1   2   1   6   3   2   3   1   1   1   1   2   1 40  Silicon Chip Value 10MΩ 750kΩ 100kΩ 22kΩ 10kΩ 5.6kΩ 3.3kΩ 2.2kΩ 1.1kΩ 1kΩ 470Ω 430Ω 150Ω 27Ω 4-Band Code (1%) brown black blue brown violet green yellow brown brown black yellow brown red red orange brown brown black orange brown green blue red brown orange orange red brown red red red brown brown brown red brown brown black red brown yellow violet brown brown yellow orange brown brown brown green brown brown red violet black brown 5-Band Code (1%) brown black black green brown violet green black orange brown brown black black orange brown red red black red brown brown black black red brown green blue black brown brown orange orange black brown brown red red black brown brown brown brown black brown brown brown black black brown brown yellow violet black black brown yellow orange black black brown brown green black black brown red violet black gold brown www.siliconchip.com.au This view shows the completed unit with the buzzer in the under-temperature alarm position. Use plastic cable ties to secure the wiring to the LCD module and switches. nominal ±16V DC rails. These rails are then filtered using 470µF electrolytic capacitors and applied to regulators REG1 and REG2 to derive ±9V rails. Alternatively, the ±9V rails can be obtained directly from two 9V batteries. Trimpot VR8 is used only for calibration and is not usually used in-circuit. During calibration, it is used to provide a small DC voltage to the non-inverting input of IC1. IC1’s output is then measured while VR4 is adjusted to give the required gain (more on this later). Construction The unit is built on a PC board coded 04208021 and this fits into a low-profile plastic case meas­uring 140 x 110 x 35mm (W x D x H). www.siliconchip.com.au Begin by checking the PC board for breaks or shorts in the copper tracks and check that the holes sizes for the larger components are correct. The PC stakes (used at all external wiring positions and test points) should be a tight fit into their mounting holes, while 1.5mm holes are required for the screw terminal blocks. Note that there is a rectangular cutout at the front of the PC board – see Fig.4. This cutout provides clearance for the bottom of the LCD module. It allows the LCD module to be slid down far enough to clear the moulded ridges at the front of the case lid. Fig.4 shows how to build the plugpack-operated version, while Fig.5 shows the changes required for the battery-operated version. Note that the latter does not require REG1, REG2, D1, D2, the 150Ω resistors or the 470µF capacitors. Install the PC stakes, resistors and wire links first. Table 2 shows the resistor colour codes but it’s also a good idea to check the resistor values using a digital multimeter. The diodes can go in next, followed by zener diodes ZD1 and ZD2. That done, install LED1 at maximum lead length, taking care to ensure that it is correctly oriented. It is later bent over at right angles and clipped into a matching bezel on the front panel. Now for the semiconductors. These include Sensor 2, REF1, REF2, regulators REG1 & REG2, transistors Q1 & Q2 and the two ICs. Make sure that all these parts are correctly oriented and that you don’t get any of them mixed up. The capacitors and the screw-terminal blocks can now be installed, along with the buzzer. Install the buzzer in August 2002  41 K-TYPE PROBE AVAILABILITY Altronics: Q 1092 (-20°C to 1200°C) Dick Smith: Q-1438 (-50°C to 1200°C) Jaycar: QM-1282 (-55°C to 1200°C); QM-1283 (-40°C to 250°C) Fig.5: here’s how to modify the PC board assembly for battery operation. Reg­-ulat­ors REG1 & REG2 and the two 150Ω resistors are re­placed by wire links, while diodes D1 & D2 and the 470µF capacitors are left out of circuit. the under-temperature alarm position (at right) if you want it to sound when the tem­ perature falls below the set value. Conversely, install it in the over-temperature alarm position if you want it to sound when the temperature rises above the set value. Final assembly Now for the final assembly. The first step is to secure the PC board to the base of the case using 4 x M3 screws which screw into the integral pillars. That done, work can begin on the front panel. Fig.5 can be used as a drilling template – you will have to drill holes to accept the three switches and the LED bezel, plus an extra hole to provide access to VR7. In addition, you have to make a large cutout to accept the LCD module. The cutout for the display can be made by first drilling a series of holes around the inside perimeter of the cutout hole. The piece can then be broken away and the job filed for a smooth finish. Once that’s done, affix the front panel label and install the switches and the LED bezel. The front panel can then be slid into position and LED1 bent over and pushed through the bezel until it clips into place. The LCD module can now be installed and the wiring complet­ed as shown in Fig.4. We used two header sockets (one 2-way and one 10-way) for the connections to the LCD module, so that it can be easily removed. Alternatively, the leads could be directly soldered to the pins on the module as shown in Fig.4. Note that Q3 and its associated 10kΩ resistor are either mounted on the cable entry side of the pin header socket (see photo) or soldered directly to the pins of the LCD module. Use cable ties to secure the wiring, as shown. If you are building the battery version, the two 9V batteries are secured to the lid using metal battery clips. One side of each clip is removed, after which they are secured to the side of the case using M3 x 6mm countersunk screws and nuts. The rear panel will require holes for the power socket and the thermocouple socket, plus access holes through which to pass leads to the screw terminal blocks (to wire external relays). The thermocouple socket is mount­ ed directly in-line with Sensor2. It should be mounted fairly high up on the rear panel (about 4mm from the top), since it sits directly over Sensor2 when the rear panel is in place. You will need to cut a 17 x 11mm hole to accept the sensor socket. This can be done by first marking out the cutout area, then drilling a series of small holes around the inside perimet­ er, knocking out the centre piece and filing to a smooth finish. Once that’s done, the socket can be clamped into position and short lengths of tinned copper wire run between its terminals and the adjacent stakes on the PC board. Finally, complete the construction by running the wiring to the AC power socket. Testing Before doing anything else, it’s a good idea to go over the PC board and check that the assembly is correct. In particular, check that all parts are in the correct locations and that they are correct­ ly oriented. You should also carefully check the wiring to the LCD module. That done, apply power and check that the LCD shows a reading. Now, using a multimeter, check that there is a nominal +9V at pin 7 of IC1 & IC2 and -9V at pin 4 of IC1 & IC2. If these readings are correct, check that there Fig.6: this full-size artwork can be used as a drilling template for the front panel. 42  Silicon Chip www.siliconchip.com.au The way in which the thermocouple socket is mounted and its leads connected to stakes on the PC board can be clearly seen here. Note the holes in the rear panel opposite the screw terminal blocks. is approximately +2.5V at TP1 and -2.5V at TP3. Note that these voltages could be 100mV higher or lower than the nominated values at this stage. They should all be measured with the common lead from your multimeter attached to the GND terminal near Sensor2. If everything is correct so far, you can now carry out the following steps to calibrate the in­strument: (1) Adjust VR1 for +2.490V at TP1. Similarly, adjust VR6 for -2.490V at TP3. (2) Switch off and connect a clip lead between Sensor1’s plus (+) terminal (ie, pin 3 of IC1) and ground. Also, short TP1 and TP4 to ground. (3) Apply power and measure the voltage at TP2 using a multimeter set to read millivolts. Write this offset voltage down, then switch off and remove the short at Sensor1’s plus terminal. (4) Connect a clip lead from Sen­ sor1’s plus terminal to TP5. Reapply power and adjust VR8 for a reading of 100mV at TP5. www.siliconchip.com.au Fig.7: this is the full-size etching pattern for the PC board. August 2002  43 Here’s how the two metal clips are attached to the case lid for the batterypowered version. It’s also a good idea to place some foam rubber over the PC board, so that the batteries cannot short anything out if they come loose. (5) Monitor the voltage at TP2 and adjust VR4 for a reading that’s equal to the voltage at TP5 x 24.73 + the offset voltage that was written down. For example, if TP5 is set to exactly 100mV and the recorded offset voltage is 0.5mV, then VR4 should be adjusted so that the voltage at TP2 is 100mV x 24.73 + 0.5mV, or 2.4735V. Note that it may be difficult to set VR8 to provide an exact 100mV output at TP5. In that case, just set the value to somewhere around this value and multiply it by 24.73. You then add the offset voltage and adjust VR4 for this reading at TP2. (6) Switch off and again short Sensor1’s plus terminal to ground. Disconnect the short for TP4 but leave the short to ground at TP1. (7) Using a reference thermometer of known accuracy, check its reading of the ambient temperature in °C. Add 273 to this measured value (to convert from °C to the Kelvin scale) and label this value as millivolts. Add the initial offset voltage of IC1 to this value, then switch on and adjust VR2 so that TP2 equals this value in mV. (8) Switch off and remove the short across REF1 by disconnecting TP1 from ground. Also, disconnect the short on the plus terminal of Sensor1. (9) Connect Sensor1 to its socket and reapply power. Adjust VR3 so that the voltage at TP2 in mV is equal to the current tempera­ture in °C as measured on the reference thermometer (eg, if the ambient temperature is 25°C, adjust VR3 so that TP2 is at 25mV). Fig.8: here’s how to use the Altronics Q0571 LCD panel meter in the Digital Thermometer/Thermostat. Note that Q3 and its associated 10kΩ resistor are no longer required. 44  Silicon Chip DSE KIT HAS LED PANEL METER The Dick Smith Electronics kit for this project will be supplied with a 3.5-digit LED panel meter (Cat. Q2230), instead of an LCD panel meter. This ensures a bright display but also means that the DSE kit is suitable for plugpack operation only. A few minor circuit changes were required to accommodate the LED panel meter. These design changes, along with a slightly modified PC board, have all been carried out by Silicon Chip Publications. Full details are included in the DSE kit. Note: as it stands, the DSE 3.5-Digit LCD Panel Meter (Cat. Q2220) is not suitable for use in this design. Note that this reading should also now be displayed on the LCD. On the low range, it should be displayed with 0.1°C resolu­ tion, with the decimal point lit. The high range reading will be displayed with 1°C resolution. Adjust VR5 so that the readings are the same on both ranges. (10) Press S2 and check that the alarm set temperature range can be adjusted between -55°C and 1200°C using VR7. Better accuracy can be gained by repeating this entire calibration procedure again. That’s because the adjustment of VR3 can slightly alter the overall calibration. Also, better accuracy will be achieved if the circuit is allowed to stabilise for several minutes each time power is reapplied and when components are allowed to cool to normal operating temperatures after being heated by a soldering iron (eg, as can occur during the removal of shorting leads). A 12V relay can be connected to the over or under-temperature alarm terminal block, so that it can be used to switch in a heating element or a compressor for cooling. Make sure that the relay is adequately rated for the job and note that the leads connecting to the relay contacts must be kept electrically isolated from the coil leads, particularly if mains is to be switched. By the way, we don’t recommend that you attempt to wire up a relay to switch mains voltages unless you are very experienced with high voltage work and know exactly what you are doing. In fact, that’s a job that’s best SC left to a licensed electrician. www.siliconchip.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 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 SERVICEMAN'S LOG When two faults are better than one Two identical sets seldom turn up on the bench at the same time but when they do, they can be mutually beneficial when it comes to trouble­ shooting. Voltages and CRO patterns can be compared and components swapped, which makes it easier to track down faults. I don’t normally see many JVC TV sets, a fact that I at­tribute more to their excellent reliability rather than them not being the market leaders. In fact, I feel that their circuitry is somewhat more complex than in other sets but they are certainly well built. Anyway, I was suddenly privileged to have not just one JVC set in for repair but two of the same model. They were both 1989 68cm AV-S290AUT (BY-I chassis) stereo sets. I don’t really want to dwell on how I became involved in fixing these but it went something on the lines of the old mates act and redeeming out­ s tanding favours (I seem to get into far too many of these situa­tions!). The first set (Set No.1) arrived in my workshop six months ago with the complaint that it was dead. It wasn’t really but the main 115V HT rail was extremely low and replacing capacitors C951 and C952 (220µF 160V) fixed the problem and I thought the custom­er had gone away happy. Obviously I was wrong and had done something to offend because the set recently resurfaced at my mate’s opposition workshop which isn’t all that far away. And my mate, after having had a tinker, decided to call in a favour I owed him. The fault was described as retrace lines and vertical top foldover. At my suggestion, the workshop’s technician, who I might add is a very capable lad, had changed all the electrolytic capacitors in the vertical timebase but to no avail. I don’t know what other “tinkering” might have taken place by the time the set finally came to me but www.siliconchip.com.au I was now on my own. I hate problems such as these and I am grateful that I do not do many audio amplifier repairs, as they are very similar to vertical output stages. Amplifiers have this chicken and egg problem involving feedback. One can never be quite sure where the problem starts in the feedback loop. I started by checking the voltages against those marked on the circuit. They turned out to be slightly high all round, especially around Q404. However, the oscilloscope showed a per­fect waveform arriving from pin 13 of the jungle IC (IC201) on the small signal panel to Q406 (the vertical driver), although my meter measured 0.7V at the base of this transistor instead of the 0.8V on the circuit. The main question was whether this 0.1V was critical, be­ cause the waveform became distorted on the retrace part of the waveform, at the collector of Q406. Was the transistor being forward biased adequately? The distortion showed up as a small lump on the retrace pulse. The circuit is conventional enough, with Q406 driving two transistors, Q401 and Q402, in push-pull. The unusual part of the circuit was a signal take-off between the two outputs via two zener diodes – D403 (MA4200, 20V) and D402 (MA4270, 27V). This goes to “vertical drive” transistor Q403 which in turn drives Q405. Q405 then provides vertical blanking pulses to Q404, which are fed back to Q401. There are two errors in the circuit diagram. Q401 (2SD1271A) is an NPN transistor and not PNP as marked, with the collector going to the collector of Q404. There is also an addi­tional diode (D408) between Q403 and Q405. And its anode is connected to R410, not R402. Some in-circuit resistance checks here provided no further clues and I was unsure as to what to do next. And then, as luck would have it, the identical set (Set No.2) arrived – only this one was very sick. It was severely rusted and corroded but I decided to try to repair it in the hope that this would help to fix set No.1. Unfortunately, after spending an hour on or so it, I re­alised the problems were too extensive to make a complete repair worthwhile. The set was dead, with no picture, no sound, no vertical timebase, no remote control and no teletext! And at least one component was overheating. I fixed the power supply, patched up the overheated hori­zontal output transformer and made the vertical timebase work by replacing R552 (5.1Ω 3W). Fixing the picture was much harder but the fault turned out to be diode D321 in the base circuit of Q203 and Q306. August 2002  53 Serviceman’s Log – continued The remote control failure was due to IC004 TC4049BF, a surface-mounted inverter on the “S Select Module”. I didn’t fix that but I did replace four surface mounted electros – C010, C013, C016 & C017 – which affected the set’s memory. I also let the teletext fault go but suspected Q104 on the module. The sound fault involved IC651 (TA7630P). The same fault Having done the basics to achieve a picture, it was disap­pointing to find that this set also had the same fault as the first set – retrace lines and foldover! Despite this, I still felt that I could use this second set to track down the problem. I took some voltage readings and quickly found that although the second set displayed exactly the same symptoms, the cause was entirely different. First, R409 (1.5kΩ) was getting hot and the voltages around Q404 were low this time. I replaced C403 (33µF), which decouples the other side of R409 (this resistor connects to the 115V HT rail), but it made no difference. It looked as 54  Silicon Chip though Q404 was being switched on too hard by Q403, which had voltage on its base. Shorting it to chassis reduced the strain immediately. The voltages across the output transistors were correct, so the obvious suspects were the zener diodes D402 and D403. Replacing these immediately fixed the fault. This was important, because I now had a reference set that I could use to tackle set No.1. And naturally, I hoped that the fault would turn out to be the same. Unfortunately, when I re­placed these zeners, it made no difference. The resistance of the vertical deflection coils was the same (25.4Ω) on both Panasonic tubes. Nevertheless, I swapped the chassis over to confirm that the coils were OK. I was also able to swap the small signal panels to confirm that the vertical drive was Items Covered This Month • • JVC AV-S290AUT (BY-I chassis) stereo TV set Teac CT-M761ST 76cm TV set. correct for both. I had already checked that the voltage rail (supplied via D404, R522 and D552 from pin 7 of the hori­zontal output transformer) was correct at 39.8V (nominally 41V) and I had also checked that R552 (4.7Ω) was OK. Naturally, I was still confident that I could quickly solve the problem with this simple 6-transistor circuit. It wasn’t to be – over two hours later, after I had swapped every transistor and diode with set No.2 and checked almost all the resistors, I still hadn’t found the fault. And there wasn’t much left to change. At this stage, I had a TV set with a complete new set of electros, transistors and diodes in the faulty circuit section. What’s more, the supplies were correct and the waveform was fine going in. However, it was incorrect after the driver transistor and transistors Q403, Q404 and Q405 were not being switched on because of this distorted waveform. In fact, set No.2 showed that the retrace pulses should be very tall and thin whereas on set No.1, they were small and fat with a little lump on them. I spent the next half hour checking all the possible ways this pulse could be attenuated so much, particularly concentrat­ ing on small capacitors like C404, C405, C409 and C410 but got nowhere. In the end, I was about to abandon the whole sorry mess and was contemplating whether to just swap the good parts and make one set out of the two. And then it struck me – one thing I hadn’t done was to check all those electros that had been replaced by the other technician. I knew he was conscientious and capable, so I didn’t feel he was likely to have made a mistake. But now, having run out of all other ideas, I decided to go over his work. He had in fact replaced over half a dozen capacitors but only five involved this part of the circuit – C401, C402, C403, C408 & C552. I decided to change them, as you can get faulty new parts occasionally. Replacing C401 made no difference but when I came to C402. I noticed that a 47µF capacitor had been substitut­ed for the original 2.2µF (100V) unit. That’s a huge difference – about 20 times bigger. Fitting the correct capacitor value fixed the fault com­pletely! Well, the moral of this story really www.siliconchip.com.au Kits without compromise doesn’t need reiterat­ing as it hurts! I have no excuses. The sad part is that, in all the mess, the exact cause of the original fault was never found – it was fixed somewhere along the track when one of the other parts was changed. So overall, it was an unsatisfactory end even though the set was fixed. And at least I got to keep set No.2 which can now be used as a source of spare parts for other similar sets – always assuming more come in. An intermittent Teac My next job was an equally difficult one. I was asked by the wife of one of my mates to fix their TV set. The only problem at first glance was that it was a 76cm job and weighed a few tonnes. But it was worse than that – it had an intermittent fault which meant that it really should be tackled on the workshop bench. Unfortunately for me, my friend (an ex-technician who saw the light and made a successful career change some years ago) was overseas on business. So there was no way of moving this set to the workshop. www.siliconchip.com.au The set was a 1996 Chinese built Teac CT-M761ST and it had a weird intermittent video fault that varied the colour, bright­ness, contrast and definition. Being intermittent, it couldn’t be made to perform to order and though I did see the fault in ac­ tion, I really had no idea where to start. However, after careful consideration, I decided on a stra­tegy of replacing all the electros in the power supply and those on the 210V rail to the video output stages on the CRT board. Hopefully, this would cover enough likely suspects to catch the elusive fault. And so, one clear afternoon, I called around with a service manual and the five electros I intended to replace. After removing about 50 screws, I took the back off and found the chassis moved out with the release of four more screws – but where could I put it? There is no service position – if I needed to do any work underneath, I would have to hold the chas­sis up with one hand and solder with the other. But how does one unsolder “Sound quality to die for” Rolling Stone Magazine “..A new benchmark in every criteria” Best Buys Home Theatre Speaker Kits without compromise from $312 pr to $8,863 pr FreeCall 1800 818882 www.vaf.com.au vaf<at>vaf.com.au August 2002  55 joints but nothing significant. The new fault had to be due to something I had done, as it wasn’t there before – unless some really unlucky coincidence had occurred. I checked the polarity and values of the electrolytic ca­ pacitors I had replaced. They all had higher voltage ratings and lower leakage characteristics than the originals. Perhaps one was faulty? Another five new capacitors was a small price to pay to solve the problem and it was easy to replace them again. I also examined a few other electros on the main HT rail – C719, C720 & C615 – but all were fine. Back at the house, I reinstalled the chassis and switched on only to find that the fault was still there. I measured the main 125V HT rail, which I expected to be low (it should be 122V precisely). To my surprise, it was high and varying even higher! There was nothing for it but to take the chassis back to the workshop; this was too hard to tackle in the home. No messing about using solderwick or a solder sucker without a free hand? Anyway, I eventually managed to replace the five capacitors – C7114, C717, C735, C713 & C616 – and switched the set on. Every­thing came on correctly and all was looking fine, so I switched the set to standby with the remote control and replaced the back. However, when I switched it on again, there was no picture. I assumed that I must have done something silly putting the back on, like tearing a lead out of its socket or something. I removed the back and checked everything but the set just wouldn’t cooper­ate. I could hear a varying “rustling” sound coming out of the power supply, the audio was fine, there was EHT and the CRT filaments were lit – but there was no picture! Clearly, this was not a problem that I could solve on the spot. Apart from the humiliation of looking totally stupid in front of my mate’s wife, I would be behind schedule with my remaining jobs for the afternoon if I persisted. The only thing I could do was take the chassis back to the workshop. Back on the bench, I examined it carefully. There were a few doubtful This time, I wasn’t messing about (not that I was before). First, I replaced IC701 (TDA4601), the power supply controller. I then shorted the base and emitter of horizontal output transistor Q601 and hung a 100W globe between its collector and chassis. Next, I reconnected the power and monitored the 122V rail. It started OK but began to rise fairly quickly. I measured the voltage out of the bridge rectifier to be a healthy 330V and changed C726, the main reservoir capacitor, just in case. I then checked the voltages on all nine pins of IC701 and they were close to those marked on the circuit, the exception being pin 5 (“V” Protect) K&W HEATSINK EXTRUSION. SEE OUR WEBSITE FOR THE COMPLETE OFF THE SHELF RANGE. 56  Silicon Chip www.siliconchip.com.au which I measured at 7.0V (it should be 8.2V). Another thing I noticed was that the rustling sound became worse with the meter on pin 3 (error feedback). The voltage here was 2.1V which was close enough to the 2.0V specified. Ironically, I am very familiar with this circuit – it is an extremely popular design used in many brands of TV sets. The one I have dealt with the most is the Goldstar PC-04X chassis, so I decided to compare notes with that circuit. The Goldstar has pin 5 at 7.2V and the most common fault here is C819, a 1µF 50V electro which gives precisely the same symptom as this Teac displayed now. I examined this carefully (C819 equates with C714 in the Teac) but made no progress. Next, I tried heating and freezing the components around IC701 and found R706, D736, C714 and C709 to be most affected by tem­perature. Then I began to notice more and more that there were differences between the parts shown on Teac circuit and those that were actually fitted to the set; eg, C712 is shown as 0.1µF on the circuit but a 330pF 1kV unit is fitted. Also, R714 is shown as 10kΩ but a 15kΩ resistor is fitted instead. I found more differences in other parts of the chassis but they weren’t particularly relevant to this fault. So, was the circuit correct or were the parts on the chassis correct? In the end, I decided to go with what was fitted – after all, the set had worked for six years without any trouble until now. I replaced R706, D736 and C709 and even C714 for the third time but it still made no difference. By now, I had reached the stage where I was drawing out the component layout in an effort to get to grips with it. And it was while I was drawing this layout that I noticed that C714 was shown on the circuit with its positive lead to chassis whereas in the set, it had been installed the other way round. I fitted another 1µF capacitor with the polarity reversed and tried the set again. This time, the 122V rail remained stable and there was no rustling sound – the PC board had been incorrectly marked! Black cat Triumphantly, I shot back with the chassis and refitted it but there was still no picture. I couldn’t believe this – what black cat had I seen recently? I didn’t recall walking under any ladder or being involved in any other such jinx. But it did occur to me that because the fault was produc­ing a high and rising HT, there could be components that might have been destroyed by the high voltage. I momentarily, shorted the red gun of the tube to chassis while the set was on and a bright red horizontal line appeared – the vertical IC (IC507, TDA3654) had been destroyed! Once again, I took it back to the workshop, installed a re­placement IC, then returned and refitted the chassis. This time – at long last – success! The picture was now fine and a few minor adjustments completed the job. I told my friend that I still wasn’t sure this had fixed the original intermittent fault but to keep an eye on it and let me know. Three weeks have gone by since and SC all is well but my fingers are still tightly crossed. www.siliconchip.com.au August 2002  57 Add a digital ’scope to your test bench for the price of a large pizza! By PETER SMITH Do you own a computer with a sound card? If you do, then all you need is this simple project, a little spare time and some free software to build your own ultra-low cost digital oscillo­scope – and more. The sound card in your computer is useful for a lot more that just recording and playing audio tracks. With the right software, you can have a virtual electronics lab full of digital test & measurement tools that won’t crowd your bench or break the bank! Sounds too good to be true? Admittedly, the sound card is an audio device, so the “virtual” test instru58  Silicon Chip ments will be limit­ed to work within the audio spectrum. They also lack some of the goodies that are available on their physical counterparts, such differential inputs and direct (DC) coupling – but the price is right! This project will enable you to use your PC as a digital oscilloscope, spectrum analyser and signal generator. Other more specialised instruments are also available in software form, such as signal processors, loudspeaker analysers and enclosure design­ ers, radio demodulators and decoders, and so on. If you work in education, are new to electronics or would simply like to learn about digital instruments, then this project is for you. A sound background In basic terms, a PC sound card provides an interface bet­ween the analog world and the digital internals of a PC. Signals appearing on the sound card inputs are first coupled to an analog multiplexer/mixer and then piped to an A-D (analog-to-digital) converter. Depending on your application www.siliconchip.com.au Fig.1: simplified block diagram for a typical PC sound card. software, the resultant “stream” of digitised data from the A-D converter may be further manipulated (filtered, enhanced, etc), transported elsewhere (eg, to the Internet) or just saved as a file to the hard disk. During playback, the reverse process occurs. The digitally encoded audio data is converted back to analog format by the sound card’s D-A converter, then filtered, amplified and fed to the loudspeaker and/or line output sockets. For the technically curious, a simplified block diagram of a typical sound card is shown in Fig.1. As you can see, there’s a little more to it than we’ve described. Analog and digital audio from a range of sources can be mixed and level-shifted along both the input and output signal paths. Software-based instruments that provide stimuli, such as sound generators, utilise the sound card’s D-A converter and analog output circuitry. Generally, sound card outputs can di­ rectly drive external circuitry, so no additional hardware is required. By contrast, instruments that need to acquire data, such as oscilloscopes, do so via the sound card’s analog input circuitry and its A-D converter. Software is then used to interpret the digital data stream and generate a graphical waveform display similar in appearance to conventional CRT-based (analog) oscillo­scopes. All that’s left to do then, is to apply the signals to be examined to the sound card’s inputs in suitable form. And that’s where the hardware part of our project comes in. Getting attached This simple adapter circuit provides a simple oscilloscope-like interface between the signals we wish to measure CHOOSING SOFTWARE This adapter circuit is basically designed to allow you to connect test probes to your PC’s sound card. Once the signals are in, software does the rest. There are many digital instrument software packages avail­able via the Internet, either as freeware or shareware. Our feature article on page 7 has a rundown on the some of the more popular packages that you can use. www.siliconchip.com.au August 2002  59 Parts List 1 PC board, code 04108021, 125mm x 62mm 1 plastic instrument case, 129 x 67 x 42mm (L x W x H) (Altronics H-0203) 2 single-pole 12-position PCmount rotary switches (S1, S2) 2 knobs to suit above 1 M205 500mA fast-blow fuse 1 M205 in-line fuseholder (DSE P-9962) 4 M3 x 10mm pan head screws (to attach shield) 8 M3 nuts 11 M3 flat washers 1 M3 star washer 1 M3 solder lug 1 2m length medium-duty figure-8 cable 1 80mm length light-duty hook-up wire 1 75mm length (approx.) tinned copper wire for links 1 PC board pin (“matrix” pin) Semiconductors 2 TL071CP JFET-input op amp ICs (IC1, IC2) 1 TC7660HCPA (Microchip Technology) or ADM660N (Analog Devices) 120kHz voltage inverter IC (IC3) (Farnell 703-655) 2 1N751A 5.1V 0.5W zener diodes (ZD1, ZD2) 4 1N4148 small-signal diodes (D1 - D4) 1 3mm high-efficiency red LED (LED1) and the line input on the sound card. Although we could connect our test probes directly to the sound card’s input, we’d be limited to measuring signals of just 0-2V peak. Not only that, but the card’s input would “load down” high impedance circuits such as op amp inputs and the like. To overcome these problems, the adapter provides a fixed high (1MΩ) input impedance, as well as a 6-stage attenuator to allow signals of up to 10V peak to be measured. And with a x10 oscilloscope probe, the range is extended to 100V peak. In addi­tion, an op amp stage amplifies the input by a factor of 10, thereby significantly improving the 60  Silicon Chip Capacitors 1 220µF 16VW PC electrolytic 2 100µF 16VW PC electrolytic 2 10µF 16VW SMD tantalum (surface mount) 2 0.1µF 100V MKT polyester 4 0.1µF 50V monolithic 2 56pF 50V ceramic 2 18pF 100V ceramic (Farnell 236-950) Resistors (0.25W, 1%) 2 1.5MΩ (Farnell 336-701) 2 1MΩ 2 3kΩ 2 200kΩ 2 1kΩ 2 150kΩ 2 470Ω 4 100kΩ 1 330Ω 2 27kΩ 2 100Ω 4 20kΩ 2 10Ω Connectors 2 horizontal PC-mount BNC sock­ets (Altronics P-0529) 1 3.5mm sub-miniature PC-mount stereo socket (Altronics P-0096) 1 2.5mm PC-mount DC socket (Altronics P-0621A) 1 2.5mm cable-mount DC plug 1 15 pin male ‘D’ connector with backshell Miscellaneous Shielded stereo cable for connection to sound card (3.5mm plug to 3.5mm plug); 125 x 62mm sheet of stiff cardboard/elephantide or lightgauge aluminium for shield (see text); osc­illoscope probes. signal-to-noise ratio when measuring low-level signals. How it works Fig.2 shows the complete circuit diagram of the adapter. There are three main sections, labelled “Channel 1”, “Channel 2” and “Power Supply”. As the two channels are identical, we’ll only describe channel 1. Signals applied to the BNC connector (CON1) are AC-coupled to the input circuitry via an 0.1µF capacitor. A string of resis­tors to ground along with an 18pF capacitor provides the neces­sary high input impedance (1MΩ). In conjunction with rotary switch S1, these resistors also function as a voltage divider for input signal attenuation. In all, six ranges are provided, with the topmost position passing the signal through to op amp IC1 without attenuation. To protect the op amp (and therefore the sound card) input, signal levels are clamped by D1 and D2 to within 0.6V of the positive and negative supply rails. The 1kΩ resistor shown to the left of the diodes limits the current through D1 and D2, while the 470Ω resistor limits the current into the op amp’s non-in­verting input (pin 3). Zener diodes ZD1 and ZD2 also form part of this protection scheme. Because the impedance of the supply rails is quite high, they could easily be driven above their nominal values by a large input excursion. ZD1 and ZD2 prevent this from happening by breaking down above 5.1V. This scheme also protects the inputs when power is not applied to the adapter. Input protection is limited to ± 100V maximum. This allows for times when you are measuring a level above 10V using the x10 attenuation of your probe but forget to slide the atten­ uation switch from x1 to x10. Don’t be tempted to poke around in high voltage equipment (live mains circuits, for example) – you will certainly “smoke” the adapter and perhaps your PC and your­self into the bargain! Op amp IC1 (TL071) is a high input-impedance, low-distor­t ion amplifier designed for audio work. In this circuit, it is configured for a gain of 10, with a frequency response of about 100kHz. The 100Ω resistor in series with the output provides short circuit protection and isolates the op amp from the cable and sound card input capacitance. To keep costs to a minimum and eliminate the need for yet another plugpack, we decided to power our project directly from the PC’s +5V supply rail. As luck would have it, the +5V rail is accessible via the sound card’s joystick port connector, usually situated right beside the audio input/ output sockets. Power enters the adapter via a standard 2.5mm DC socket. A little “brute-force” filtering is then applied using a 220µF ca­pacitor followed by a low-pass RC filter formed by the combina­tion of a 10Ω resistor and a 100µF capacitor. www.siliconchip.com.au Fig.2: this is the complete circuit diagram for the adapter. It consists of two switched attenuator channels which drive op amp output stages IC1 & IC2. Power (+5V) comes from the PC games port, with IC3 (a charge-pump voltage inverter) generating a -5V rail. www.siliconchip.com.au August 2002  61 now slide all the way into the case. That done, you can complete the case preparation by drill­ing and filing the required holes in the lid and sides. The easiest way to get everything to line up properly is to photocopy the templates in Fig.6, cut them out and tape each one to the indicated faces of the case. You can then centre-punch directly through the templates to get accurate targets for drilling. Always start with a small drill size and work up to the required size in several stages. The larger holes can be finished off using a tapered reamer. Board assembly Fig.3: follow this diagram when installing the parts on the PC board. Note that the two 10µF SMD (surface mount) capacitors adjacent to IC3 are installed on the copper side of the board, as shown in one of the photos. The TL071 op amps (IC1 & IC2) require both positive and negative supply rails. The negative rail is obtained by inverting the +5V rail using a charge pump voltage inverter (IC3). We chose a TC7660H device for this job because its 120kHz switching fre­quency is well above the audio spectrum. In addition, we’ve used surface-mount capacitors in the pump circuit to reduce radiated noise that could otherwise easily find its way into the high im­pedance attenuation networks. The -5V (nominal) output on pin 5 of the inverter is cleaned up using a second low-pass filter, which removes most of the ripple and noise. Finally, high frequency decoupling of the 5V rails is provided using four 0.1µF ceramic capacitors. Preparing the case Before mounting any components on the PC board, you will need to perform some minor surgery on the case internals (assum­ing that you are using the recommended case). Initially, the PC board should fit neatly inside the lip of the case but will rest on top of the integral guides. If it’s a little oversized, then trim the board to fit using a fine file. Next, cut away all of the guides with sidecutters or a sharp knife so that you’re left with reasonably smooth internal surfac­es. The PC board should Table 1: Typical PC Sound Card Specifications Frequency response ..................................................................20Hz - 20kHz Signal to noise ratio ...............................................................................>90dB Total harmonic distortion .........................................01% <at>1VRMS into 10kΩ Line-in impedance ...................................................................................47kΩ Line-in sensitivity .................................................................................. 2V P-P CD audio-in impedance ...........................................................................50kΩ CD audio-in sensitivity .......................................................................... 2V P-P Microphone-in impedance .......................................................................600Ω Microphone-in sensitivity ..........................................................10-200mV P-P A-D & D-A resolution .............................................................................16 bits Sample rate ........................................................................................ 4-48kHz Output power (speaker-out) ........3W into 32Ω (6W into 4Ω on some mod­els) 62  Silicon Chip Using the overlay diagram of Fig.3 as a guide, begin by installing the three wire links and all the resistors. Follow with the capacitors, noting that the electrolytic types are polarised and must be oriented as shown. The two 10µF tantalum capacitors are miniature surface-mount devices that need to be mounted on the solder (copper) side of the board. The mounting area must be well tinned, clean and free of excess solder. Position the banded (positive) end as shown in Fig.3 and solder the device in place using a fine-tipped iron. After soldering, use your meter to check for solder bridges between pads, as they can be difficult to spot with the naked eye. Install the diodes (D1-D4, ZD1, ZD2) next, aligning the cathode ends (mark­ ed with a band) as shown. IC1, IC2 & IC3 can go in next and again, orientation is important. These are static-sensitive devices, so it’s a good idea to wear an earthed antistatic wrist strap and to use a soldering iron with an earthed tip. Once they’re in, install the four connectors (CON1-4) and the GND pin. Before soldering, ensure that they’re seated squarely against the surface of the PC board. The two rotary switches (S1 & S2) are next on the list. Before installation, they need to be reconfigured to limit their rotation from the default of 12 positions to just six positions. To do this, remove the nut, washer and locking ring. Notice how the tab on the locking ring can be inserted into one of 10 holes, numbered 2-11. Re-insert the tab in the number “6” hole and check that you have six possible shaft positions. Repeat this procedure for the secwww.siliconchip.com.au This is the completed PC board assembly, ready to be attached to the lid of the case. Note the metal shield which is mounted on the copper side of the board using machine screws and nuts. The inset at top left shows how the two 10µF SMD capacitors are installed. ond switch and then solder them into position. Once again, make sure that they are seated firmly against the PC board surface. The last component to be mounted is LED1 (the power indica­tor). Slip the LED into place with the flat (cathode) side aligned as shown in Fig.3 but don’t cut the leads short or solder it just yet. Next, remove the nuts and washers from the rotary switches, leaving the locking rings in place, and fit the case lid. That done, turn the assembly upside-down and manoeuvre the LED into its hole in the lid. Ideally, the shoulder of the LED should be slightly proud of the inside surface of the lid. Now solder and trim the leads. hold on the cable to prev­ent stress on the solder joints. Making the power cable Testing the power cable Fig.4 shows the wiring for the power cable. You can see that we’ve opted to fuse the +5V rail right at the source, using an in-line fuse. This provides an extra measure of safety should the tip of the DC plug accidentally contact something that it shouldn’t! To protect the cable and provide effective strain relief, use a couple of layers of heatshrink tubing or insulation tape on the cable at the point where it passes through the backshell clamp. The clamp needs to have a firm Don’t be tempted to skip this step! Before connecting the cable, use your multimeter to verify that the positive and nega­ tive wires are not shorted together. Next, plug the cable into the joystick port and with your multi­ meter set to “DC Volts”, carefully measure the voltage at the DC plug. The tip (or “cen­tre”) of the plug should measure +5V (±0.25V) with respect to the outer shell. If you measured +3.3V instead of +5V, then unfortunately you have one Table 2: Resistor Colour Codes             No. 2 2 2 4 2 4 2 4 1 2 2 www.siliconchip.com.au Value 1.5MΩ 1MΩ 200kΩ 100kΩ 27kΩ 20kΩ 3kΩ 470Ω 330Ω 100Ω 10Ω 4-Band Code (1%) brown green green brown brown black green brown red black yellow brown brown black yellow brown red violet orange brown red black orange brown orange black red brown yellow violet brown brown orange orange brown brown brown black brown brown brown black black brown 5-Band Code (1%) brown green black yellow brown brown black black yellow brown red black black orange brown brown black black orange brown red violet black red brown red black black red brown orange black black brown brown yellow violet black black brown orange orange black black brown brown black black black brown brown black black gold brown August 2002  63 losses in the voltage inverter circuitry and the ±5% margin on the +5V rail, the negative rail should fall within approximately -5V to -4.55V. Finally, rotate S1 and S2 to position “6” (fully clockwise) and measure both op amp outputs. They should be with­ in a few millivolts of the ground rail. Shield’s up Fig.4: these diagrams show how to make the power supply cables. Note that the cable at right is only necessary if your games port supplies +3.3V instead of +5V. of the few late-model cards that provide this lower, non-standard voltage on the game port connector (so much for backward compatibility!). In this case, you will need to delve into your PC’s internals to get access to the +5V rail. A spare disk drive power connector is a convenient connection point. Fig.4 also shows the wiring details for this alternate power supply connection scheme. Basic checks Before we’re ready to connect the stereo cable and launch the software, we need to perform a few quick DC voltage checks on the completed board. The following measurements are all with respect to ground. Simply connect the negative lead of your multi-meter to the ground point provided by the PC board GND pin (between CON2 & CON4) and use the positive lead to make each measurement. Apply power and check that you have +5V (±0.25V) at pin 8 of IC3, pin 7 of IC1 and pin 7 of IC2. Next, check for -5V at pin 5 of IC3, pin 4 of IC1 and pin 4 of IC2. Note that with the The metal shield is exactly the same shape and size as the PC board. It can be made from a thin sheet of tinplate or by gluing aluminium foil to a piece of stiff cardboard or elephantide insulation material. 64  Silicon Chip The adapter’s high input impedance makes if susceptible to radiated noise in its immediate environment. Typically, the 240V AC mains and your PC’s monitor are the worst noise generators. To minimise noise pick-up, the adapter could be installed in a metal case but to keep costs to a minimum, we’ve presented the finished project in a plastic instrument case instead. We achieved good results without a metal enclosure by fitting a shield (or “ground plane”) to the underside of the PC board. The shield is exactly the same dimensions as the PC board and can be fashioned from a variety of materials. We glued ordi­nary heavy-duty aluminium cooking foil to one side of a sheet of elephantide material and then cut out the required shape with kitchen scissors. Any thin conductive material should be suitable but ideally, it should be insulated on one side so as not to short protruding component leads to ground. An old scrap of blank single-sided PC board material would also be a good choice. To fix the shield to the underside of the board, first insert an M3 x 10mm screw in the corner hole closest to IC1. This screw will be used as the ground connection point, so place a star washer and solder lug under the head before winding up a nut from the copper side of the board. That done, fit screws and nuts to the remaining three corners, then invert the board and place flat washers on all four screws. Next, with the conductive side facing away from the PC board, slide the shield over the screws (you remembered the holes, right?), install another four flat washers and wind on the remaining nuts. Make sure that all component leads are well clear of the shield and use your meter to verify that the shield makes good electrical contact with the lug. To finish the job, connect the solder lug to the ground pin (between www.siliconchip.com.au The DC power socket and the output socket (for the sound card) are accessed through matching holes in the rear panel. CON2 & CON4) using a short length of light-duty hook-up wire. Signal generator cable Well, that completes the hardware that you’ll need to use with the oscilloscope and spectrum analyser software. If you’d also like to use the sound generator included with many software packages, then the only additional requirement is a simple cable – see Fig.5. All analog signals from your sound card are AC-coupled to their output sockets, hence the need for the termination resis­tors. Be sure to insulate all connections and use insulated crocodile clips or probes. Quantifying measurements Most digital instruments provide some degree of input level (gain/attenuation) selection. Add to this the range switches on the adapter, and it can all seem a little confusing! Just how do you determine the magnitude of your measurements? The 2V positions on the adapter’s range switches pass the measured signal without any change in level. Ranges below this point provide amplification (gain) of the input signal, whereas ranges above provide attenuation. The table included on the front panel (see Fig.6) lists a multiplier, or scale factor, that can be used to calculate the actual signal level. For example, with 8.5V input to the adapter and a switch position of 10V, the voltage applied to the sound card input will be 8.5 x 0.2 = 1.7V. Let’s try that in reverse. If your digital oscilloscope is set to 500mV/div and the waveform peak measures 1.5 divisions, then the voltage at the sound card’s input must be 750mV. So, if the Fig.5: this cable can be used if you’d also like to use the signal generator instrument included with many software packages. MINI SUPER DRILL KIT IN HANDY CARRY CASE. SUPPLIED WITH DRILLBITS AND GRINDING ACCESSORIES $61.60 GST INC. www.siliconchip.com.au August 2002  65 The completed adapter is shown here fitted with two oscilloscope test probes, plus the power supply and sound card cables. adapter range switch is set to 500mV, then the actual applied voltage is 1/4 x 750mV = 187.5mV (or 132mV RMS). Note that if you set your oscilloscope to read 2V/div, then the adapter switch positions now directly reflect what you see on the screen. With the adapter switched to 200mV, you’re reading 200mV/div; and at the 500mV setting, you’re reading 500mV/div, etc. Digitally accurate? It’s important to be aware of the limitations of your new digital instruments before relying on them for serious work. In practice, the resolution and The PC board is installed by first inserting the BNC connectors through their holes and then flexing back the rear of the case slightly as the back of the board is lowered into position. 66  Silicon Chip accuracy of any measurement system that relies on a sound card depends on the characteristics of the card itself. Table 1 lists the specifications of a typical sound card. The frequency response of the card will also be the band­ width of the digital instruments (’scope, multi­ meter, spec­trum analyser, etc). This assumes that you’ve set the sampling rate to maximum (usually either 44kHz or 48kHz). This also means that it you measure signals above 22kHz, the results will be inaccurate. That’s because the sam­pling rate must be at least double the signal frequency. A sound card’s 16-bit A-D converter can measure 65,535 dis­crete voltage levels, so with a 2V span it has low µV resolu­tion. However, this doesn’t mean that your digital instruments will be able to measure signals in the µV range! In practice, the PC power supply, sound card, cable and adapter all add a certain amount of low-level noise (called the noise “floor”), so that the smallest voltage you’ll be able to measure accurately will be in the mV range. Our prototype showed less than www.siliconchip.com.au 1mV RMS noise but this will almost certainly be different on your system. Most software includes at least rudimentary calibration for the line-in socket. You’ll need a sinewave signal generator and multimeter for some, while others utilise their inbuilt digital signal generators and a line-out to linein loop cable for the task. Be sure to check the documentation for details, as methods vary considerably. If you wish, you can include the adapter in the signal loop during calibration to improve overall accuracy. Be sure to set the rotary switches to the 2V positions for 0dB gain. The maximum voltage that can be applied to the sound card’s line-in socket is 2V P-P, or about 1.4V RMS. In practice, we found that our Sound­ Blaster Live card began clipping at just over 1V RMS. To ensure accurate measurements, it’s a good idea to use the ’scope to check for clipping before switching to other in­struments such as the spectrum analyser. Staying alive To wrap up, a word of warning about measurement techniques is in order. Be aware that the ground (0V) line of a PC’s power supply is connected to mains earth. Because the adapter is effec­tively an extension of the PC circuitry, it’s BNC connectors are also at mains earth potential. This doesn’t cause a problem if the circuit you’re probing is floating (ie, isolated from earth). If, however, the circuit has a return path to earth, then be sure to connect your probe’s ground clip to a point that’s also at earth poten­tial. If the chosen point is above earth potential, then current will flow around an earth “loop”. If the potential difference is high, the results can be disastrous! A good example is the prim­ary side of any off-line switchmode power supply. Connecting a probe ground clip to most points in one of these suckers will generate more fireworks than New Year’s Eve on the Sydney Harbour Bridge! Some readers would undoubtedly point out that this problem could be overcome by floating either the circuit under test or the test equipment itself (eg, by lifting the earth or by using an isolation transformer). Our advice is simple – don’t do it! Seek advice from an experienced technician if you’re not sure what you’re SC doing! www.siliconchip.com.au Fig.6: here are full-size artworks for the front panel (top), the front and rear panel drilling templates and the PC board pattern. August 2002  67 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/ Pt.2: By LEON WILLIAMS, VK2DOB Last month, we gave the circuit details of this new Direct Conversion Receiver. This month, we conclude with the full construction and alignment details. There’s also a few tips on using the completed unit. A single PC board coded 06107021 (172 x 134mm) accommodates virtually all the parts, so building this receiver is really easy. Fig.5 shows the layout details. Before installing any of the parts, check that the holes for the larger components such as the coil formers www.siliconchip.com.au are the cor­rect size. If not, enlarge them with a suitable drill bit. The assembly can now be started by installing the seven wire links, making sure that they are straight and that they lay flat on the PC board. Follow these with the smaller components, such as the resistors, diodes, RF choke, trimpots and PC stakes. It’s a good idea to check the resistor values with a digital multimeter before installing them on the board. Because this is an RF project, it is important that you keep all component leads as short as possible to avoid any un­wanted feedback and instability. In short, make sure that all components are mounted close to the PC board. This is also the reason why IC sockets are not used for the ICs, apart from the PIC chip. Next install the headphone socket, IC socket and the ca­pacitors. Start with the smaller capacitors and progress to the larger electrolytics, ensuring they August 2002  71 Fig.5: install the parts on the PC board as shown here, taking care to keep all leads as short as possible. The PIC microcontroller (IC1) is installed in a socket and should be left out of circuit until after the power supply checks have been completed. are installed with correct polarity. Follow this with the transistors (Q1 & Q3-Q7), FET (Q2), voltage regulators (REG1-3), varicap diode package VC1, crystal (X1) and the ICs, leaving the PIC chip until later. Note that the transistors, FET, BB212 (varicap diode pack­age) and the small voltage regulators are all similar in ap­pearance, so double check that you have installed them in the correct 72  Silicon Chip locations. The 8V regulator (REG2) runs cool and doesn’t need a heatsink. Winding the coils Fig.6 shows the winding details for the coils, including the wire size, the start and finish pins and the number of turns required. If you are new to radio building and not familiar with coil winding, a few comments will probably be helpful. All the coils need to be wound before they are installed on the PC board. Let’s start with the BPF coils – T1 and T2. They comprise a 6-pin base, a metal can and a 5mm former into which a ferrite slug is screwed up and down to alter the inductance. The first step is to place a drop of superglue on the bottom of a former (make sure that none gets into the threaded section) and then press it at right angles into the centre hole of a 6-pin base. Then, once the glue has set, you begin with the winding that has the larger number of turns. www.siliconchip.com.au Table 2: Capacitor Codes              sol­dering the wire to the finish pin. You can now complete the coil by installing the wind­ing with the least number of turns over the top of the first winding, starting from the bottom. Solder this winding to its respective start and finish pins as before, then screw in a ferrite slug. The second BPF coil (T2) is wound the same way, noting the different pins for the start and finish of the windings. This coil is also fitted with a ferrite slug. The mixer transformer (T3) is a bit different in that it is wound on a 2-hole balun former – see Fig.6. A turn here involves passing the wire up through one hole and then back down through the second hole. The secondary is wound first and consists of eight turns either side of a centre tap. To wind it, first take a Fig.6: the above table shows the winding details for the various coils. T1, T2 & L1 are wound on 5mm formers fitted with a 6-pin base, while T3 is wound on a ferrite 2-hole balun transformer. Note that T1 & T2 (but not L1) are fitted with ferrite slugs. To do this, first run the wire down the inside of the start pin and solder it to the end of the pin. That done, start at the bottom of the former and wind on the required number of turns, keeping them next to each other in a single tight layer. The trick now is to hold the turns tight while you run the free wire down the outside of the winding and inside the finish pin. Finally, solder to the end of that pin. Although the heat Value IEC Code EIA Code 0.1µF 100n  104 .022µF  22n 223 .01µF  10n  103 .0047µF  4n7  472 .0033µF  3n3  332 .0015µF  1n5  152 470pF 470p  471 330pF 330p  331 220pF 220p  221 33pF  33p   33 10pF  10p   10 5.6pF  5p6   5.6 from the soldering iron should melt the wire enamel to allow soldering, you will probably find it easier if you scrape some of the enamel off the ends of the wires first. Cut off the excess wire from both pins when you have finished the winding. It may sound difficult at first but it will become easier with practice. And here’s a tip – wrapping a piece of adhesive tape around the winding makes it easy to keep it in place while Table 1: Resistor Colour Codes  No.   1   6   4   4   4   1   5   8   3   2   2   1   3   6   1   2 www.siliconchip.com.au Value 1MΩ 100kΩ 47kΩ 22kΩ 20kΩ 11kΩ 10kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1kΩ 560Ω 150Ω 100Ω 10Ω 4.7Ω 4-Band Code (1%) brown black green brown brown black yellow brown yellow violet orange brown red red orange brown red black orange brown brown brown orange brown brown black orange brown yellow violet red brown orange orange red brown red red red brown brown black red brown green blue brown brown brown green brown brown brown black brown brown brown black black brown yellow violet gold brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown yellow violet black red brown red red black red brown red black black red brown brown brown black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown black black brown brown green blue black black brown brown green black black brown brown black black black brown brown black black gold brown yellow violet black silver brown August 2002  73 The metal shield was made out of scrap tinplate. The two holes provide access to VR4 & VR5. length of wire about 600mm long and pass one end through one of the former holes, leaving about 50mm at the other side. While holding this short end in place, wind on eight turns around the centre of the former. Now bend the remaining wire into a sharp ‘U’ shape about 20mm from the former and twist the wires together to form the centre tap. That done, continue winding another eight turns in the same direction as before. When completed, the ends of both wires and the centre tap should be at the same end of the former. Next, move the secondary wires aside to avoid getting them mixed up. You can then complete the coil by taking another length of wire and winding on four turns over the top of the secondary to form the primary. The local oscillator coil (L1) is wound in a similar fash­ ion to the BPF coils, except that it only has one winding. You will need to make sure this coil is wound tight and the wire can’t move. Any movement will alter the local oscillator frequen­ cy and move the station off tune. The easiest way to do this is to coat it with glue or silicone adhesive after it’s wound. Before soldering the coils into place, check that they sit neatly and that the formers are perpendicular to the PC board. Also, when installing the cans for T1 and T2, make sure that they are positioned centrally about the former so that the slugs can be screwed up and down through the hole in the top of the can. The slugs used for T1 and T2 have a strip of rubbery mate­rial glued to one side. This is included to stop the slugs 74  Silicon Chip from moving during normal use and altering the tuning of the coils. You will probably find that this makes them quite difficult to move and excessive force on the brittle core can cause them to break. If you find that this is the case, scrape away some of the rubbery material with a sharp knife so that they are still firm in the former but can be moved freely with an alignment tool. Final assembly Now for the final assembly. First, cut the pot shafts to the required length using a small hacksaw and break away the anti-rotation spigot. That done, install the three pots on the PC board, making sure that the correct pot goes in each location. Next, scrape away some of the passivated coating on the top of the Main and Fine tune pots (VR2 & VR3) and connect a length of tinned copper wire between their bodies and also to ground on the PC board (see Fig.5). This stops 50Hz hum from being picked up by the pots and modulating SOFTWARE The PIC software files can be downloaded from the SILICON CHIP Web site. The files DCRX.ASM and DCRX.HEX are combined in a single zip file called DCRX-ASM-HEX.ZIP. To program your own PIC chip you will need the file DCRX.HEX, while studying the DCRX.ASM source code will reveal the secrets of how a humble PIC can measure high frequencies and sound Morse code! the local oscillator. A metallic shield must be placed over the local oscillator components so that it is not affected by quick changes in temper­ature or by external magnetic fields. This shield can be made from scrap PC board or, as in the prototype, constructed from tinplate (eg, from a food can). Fig.7 shows how the metal shield is made. Begin by cutting out the cross shape, then drill the two holes and remove all burrs along the edges with a file. That done, bend the tinplate along the dotted lines and run a bead of solder on the inside of each corner where the sides meet. Finally, place the upturned metal box over the local oscillator components – the holes line up with trimpots VR4 & VR5 – and solder it to the four PC stakes. The PC board is now finished and you can start work on the case. Using the photographs as a guide, start by drilling the holes for the power supply binding posts and for the antenna socket on the back panel. The front-panel holes can then be drilled using the accompanying artwork as a template. You will need to drill three holes for the pots, two for the pushbutton switches and one for the headphone socket. Alternatively, you can drill the holes in the front panel after first affixing the adhesive label. In each case, it’s best to drill a small pilot hole first and then carefully enlarge the hole to the correct size using a tapered reamer. Now, with the front and rear panels removed, place the PC board on the bottom of the case so that its front edge will butt up against the front panel. www.siliconchip.com.au This view shows the completed PC board assembly, prior to fitting the metal shield over the local oscillator section at lower left. The metal shield is secured by soldering it to four PC stakes. Note that the PC board will not sit flat at this stage, because some of the mounting pillars on the base interfere with the soldered connections. You can fix that by removing the offending pillars, either by drilling them out with a large drill or by cutting them off with a large pair of side­cutters. Once the case is ready, install the antenna socket and the binding posts on the rear panel. Note that an earth lug must be attached to the antenna socket (it’s secured by one of the mount­ing screws), to provide an earth connection point. The two push­button switches can also be installed on the front panel at this stage, with the red FREQ switch at the top. Once that’s done, attach the front www.siliconchip.com.au panel to the PC board and secure it by installing the pot nuts and washers (the washers go behind the nuts). You can then slide the assembly into the slot at the front of the case and fasten the PC board in place using four small self-tapping screws. Finally, fit the rear panel in place and wire the antenna socket, the power supply binding posts and the pushbutton switch­es to the PC board stakes using light-duty hookup wire. Test & alignment Before applying power, have a good look over the PC board one last time. A few moments spent here looking for components with the wrong value or in the wrong position could save you hours of frustration later on. Once you are satisfied that everything is correct, follow this test procedure to check out the receiver: (1). Set all the trimpots and the frontpanel controls to mid-position and plug a pair of headphones (or a loudspeaker) into the headphone socket. (2). Connect the receiver to a regulated DC power supply of around 12V and connect a multimeter – set to read DC current – in series with the positive lead. (3). Apply power and check that the current drawn is about 50mA. If you don’t get this, switch off quickly and check for errors. (4). Assuming all is OK, turn the Gain control (VR6) clockwise and check that you can hear some hiss in the headphones. This indicates that at least the audio stages are working. (5). Disconnect the multimeter from the supply lead, reapply power and check the voltages at the outputs of August 2002  75 The rear panel carries the two binding post terminals for the power supply plus the SO239 antenna socket. You can replace the binding post terminals with a 2.5mm DC power socket if you wish but make sure you get the polarity right. regulators REG1 and REG3. In each case, you should get a reading of +5V. You can also check for +8V at the output of REG2. Note: you will either have to temporarily remove the metal shield or remove the entire assembly from the case (so that you have access to the underside of the PC board) in order to do this. All regulator outputs should be accurate to within 250mV. Once again, if any measurements are incorrect, switch off immediately and check for errors. (6). If all voltage checks are OK, turn off the power and install the PIC chip. That done, reapply power and check that you hear three beeps in the headphones (each time power is applied, the PIC chip does a reset and generates three beeps to indicate that it is operating correctly). (7). Press the FREQ switch and the frequency of the local oscil­lator should be heard. Don’t worry about what it is at this stage – just use it to adjust the level trimpot (VR1) for an acceptable level in the headphones. 76  Silicon Chip (8). If you have a signal generator, inject a low-level signal at about 7.1MHz into the antenna socket. Set the Gain control (VR6) for a relaxed volume and adjust the cores in T1 and T2 with a suitable alignment tool for maximum volume. The BPF is fairly broadband, so there is no need to stagger tune the two coils to obtain a flat pass band. If you don’t have a signal generator simply connect an antenna, tune to a station around the middle of the band and adjust the cores in T1 and T2 for maximum volume. Freq. counter programming Now that the receiver is operating, let’s check the fre­quency counter operation and programming options. As previously stated, when you press the FREQ switch, the current frequency of the local oscillator is announced in Morse code. In addition, each time either switch is pressed and acknowledged by the PIC soft­ware, a short burst of tone is heard in the headphones. Pressing the MEM switch, however, gives one of two possible outcomes. If the next switch pressed is MEM again, the current frequency of the local oscillator is stored in the PIC’s EEPROM memory and two beeps will be heard (the EEPROM retains its cont­ents even if the power is removed). Alternatively, if the next switch pressed is the FREQ switch, the frequency stored in the EEPROM (not the current frequency) will be sounded in Morse code. This is a simple single-memory store and allows you to store a particular frequency and then retrieve it at a later stage – unless you overwrite it of course! Pressing the FREQ and MEM switches at the same time places the frequency counter in program mode and a long beep will be heard. At this point, pressing the FREQ switch toggles between long and short Morse modes. Long mode is where all the frequency digits are sounded; eg, 7123450. Short mode only sounds the kHz digits – in this example, the digits 123. This option will be the normal www.siliconchip.com.au setting and is used to speed up the Morse sounding. In any case, you will normally know what the MHz digit is and we are not usually interested in the fre­quency digits below 1kHz unless we are doing some testing or alignment. Pressing the MEM switch moves you onto the Morse speed setting, where two long beeps will be heard. Pressing the FREQ switch toggles between the three Morse speed settings. Pressing the MEM switch will return you back to the start of the program­ming mode. Each time a length or speed option is selected with the FREQ switch during programming, the current frequency is sounded using the selected options. Pressing both switches at any time exits programming mode and returns the frequency counter to normal operation. The pro­gram settings are stored in EEPROM and so do not get erased when power is turned off. The very first time you power on the receiver, the values in the stored frequency area of the PIC’s EEPROM will be unknown. As a result, strange readings may occur when the MEM and then the FREQ switches are pressed to read the stored frequency if one has not been stored previously. To avoid this situation, press the MEM button twice to store a valid frequency after the first power on. Once an initial frequency is stored in EEPROM, the MEM switch can then be used normally. Calibrating the counter To check and adjust the accuracy of the frequency counter, you will need to connect an external frequency meter to pin 6 of IC2b. That done, press the FREQ switch and compare Fig.7: here’s how to make the metal shield that goes over the local oscillator circuitry. Cut out the cross shape and drill the two holes before bending the tinplate down along the dotted lines. the frequency heard in Morse code with that displayed on the frequency meter. If they are the same or within a few tens of hertz, then no adjustment is really necessary. If you do want to improve the accuracy, this can be done by adjusting VC1 with a small screwdriver and then pressing the FREQ switch to check the change. Continue until the frequency heard in Morse code is the same as that displayed on the frequency meter. If you can’t get the frequency correct, you may have a crystal that’s too far off frequency, so try another. You may also need to alter the 33pF capacitor if you have changed the crystal and are still having no luck. Don’t be too concerned about obtaining absolute accuracy, as the base PARALLAX BS2-IC BASIC STAMP $112.00 INC GST www.siliconchip.com.au August 2002  77 If you don’t have access to a frequency meter, a reasonably accurate way of adjusting the crystal oscillator is to zero-beat to a known frequency carrier. At this point, the local oscillator and the carrier frequency will be the same. Press the FREQ switch and adjust VC1 as before. Setting the LO Fig.9: this front-panel artwork can be cut out and used direct if required. It can be protected behind a thin sheet of clear Perspex. resolution of the PIC software counter is only ±10Hz. Also, in normal use, you don’t need to know the tuned frequency to better than 1kHz accuracy. What’s more, the PIC oscillator will probably drift to a small degree over time and with changes in temperature. 78  Silicon Chip The local oscillator (LO) is a free-running HF oscillator and as a result it is quite normal for some frequency drift to occur immediately after power is applied. It stabilises within five minutes or so and drift after this warm-up period is quite small. For this reason, make sure the receiver is powered on for at least five minutes before adjusting the oscillator range. At this point, you need to decide what the range of the local oscillator – and hence the tuning range of the receiver – is going to be. In the prototype, the lower frequency was set to 7.000MHz and the upper frequency set to 7.200MHz. The LO adjust­ment procedure is as follows: (1). Set the Fine tune control (VR3) to mid-position and rotate the Main tuning control (VR2) fully anticlockwise, then move it a few degrees clockwise from the stop. (2). Press the FREQ switch to check the frequency. Adjust the “Low Set” trimpot (VR5) with a small screwdriver and check the frequency again. Repeat this procedure until the frequency is at the desired lower limit. (3). Rotate the Main tuning control (VR2) fully clockwise and then move it a few degrees anticlockwise from the stop. Now set the upper frequency limit in the same fashion as before, this time by adjusting the High Set trimpot (VR4). Note that there is some interaction between the High and Low trimpot settings, so you may need to repeat the last two steps a couple of times to obtain the desired range. It’s also possible that you may not be able to set the range correctly, because of component tolerances or because the coil (L1) is way off its intended inductance. If you can’t get the range low enough, try adding a turn or two to L1. Conversely, if the range is too low, take a turn or two off. (4). Check the frequency range of the Fine tuning control by rotating it to one stop, pressing the FREQ switch and then rotating to the other stop and again pressing the FREQ switch. You should achieve a range of around 1-2kHz either way. Note: this simple fine tuning system results in more range at the high frequency end than at the low frequency end. Once setup has been completed, attach the top case half with the two screws supplied and the receiver is ready for use. Operation Finally, here are a few tips to help you get the best from your receiver. First, when selecting a power supply, don’t be tempted to use a standard 12V plugpack. These are generally unregulated, producing up to 17V or so with no load. More importantly, they produce large levels of hum and this will be injected into the sensitive audio stages of the receiver. For this reason, it’s best to use a small 12V regulated supply or a battery that’s capable of supplying a few hundred milliamps. A regulated 12V or 13.8V DC plugpack or “power pack” is ideal. Don’t use a switchmode supply though as this will almost certainly create noise problems. Tuning SSB and CW stations is often difficult for the uninitiated. That’s because the tuning is fairly critical and also because the tone of the audio changes as you tune across the signal. The trick is to first set the Fine tune control to midway and tune in the signal as best you can using the Main tuning control. After that, it’s simply a matter of slowly rotating the Fine tune control until the voice sounds natural. For Morse code signals, just adjust the Fine tune control until the audio tone is easy to listen to. Because this receiver does not have an automatic gain control (AGC), you will need to adjust the Gain control to suit the level from different stations. Always start out with the Gain control set around three quarters and then advance it if the level of the signal is too low. If the gain is set too high and you are wearing headphones, a sudden burst from a strong signal will be most unpleasant. The receiver was designed for head­ phone use and so the output power is not particularly high. However, an efficient loudspeaker mounted in a suitable enclosure can be used if pre­ferred. Finally, to get the best from the receiver, it should be connected to an antenna resonant on the 40m band and www.siliconchip.com.au Fig.8: here are the drilling details for the front panel. The larger holes are best made by first drilling small pilot holes and then enlarging them to size using a tapered reamer. with an impedance of 50Ω. A good performing and easy-to-build type is a wire dipole fed with coaxial cable. www.siliconchip.com.au If you don’t have one alrea­dy, consult an antenna book for guidance or search the Internet for designs. SC ELAN Audio The Leading Australian Manufacturer of Professional Broadcast Audio Equipment Featured Product of the Month PC-BAL PCI Format Balancing Board Interface PC Sound Cards to Professional Systems Not only do we make the best range of Specialised Broadcast "On-Air" Mixers in Australia. . . We also make a range of General Audio Products for use by Radio Broadcasters, Recording Studios, Institutions etc. And we sell AKG and Denon Professional Audio Products For Technical Details and Professional Pricing Contact Elan Audio 2 Steel Crt South Guildford WA 6055 Phone 08 9277 3500 08 9478 2266 Fax email sales<at>elan.com.au WWW elan.com.au Subscribe & Get this FREE!* *Australia only. Offer valid only while stocks last. Buy a 1- or 2-year subscription to SILICON CHIP and we’ll mail you a free copy of “Computer Omnibus”. Or you can choose “Electronics Testbench”. Subscribe now by using the handy order form in this issue or call (02) 9979 5644, 8.30-5.30 Mon-Fri with your credit card details. August 2002  79 PRODUCT SHOWCASE OK, so what do you do with ’em? Branco Justic, head honcho at Oatley Electronics, has a well-earned reputation for sniffing out some intriguing products and then selling them at bargain prices. One we spotted in last month’s Oatley advert in SILICON CHIP is no exception. It’s the innards of a 240V ceramic fan heater. Apparently these failed QC so they weren’t suitable for use as a heater but Branco couldn’t resist them – or their controller PC boards (a couple of pallets of them!). There are three separate ~800W ceramic heaters built into one unit, each individually connectable. Each is about 500Ω cold but around 65Ω hot (not linear). A 240V 80mm diecast fan blows air through the elements. At $15 each you’re getting a very cheap fan (priced diecast fans lately?) and the heater elements effectively for nothing. The question is, what can you use the ceramic heater for? Branco suggests they could be good for a variety of heating purposes (incubators, photo chemicals, etc), especially as they still produce good heat down to about 50V or so. Or perhaps they could form a high power dummy load. Or an interesting desk ornament/paper weight. Put on your thinking caps and see what you come up with! The heaters are also supplied with a heavy duty 3-pole rocker switch. The controller boards are sold separately (with connection diagram but no circuits available). They have some triacs, opto couplers, a transformer and even a couple of mercury (“tilt”) switches on them, all for just $12.00. Contact: Oatley Electronics Ph: (02) 9584 3563 Fax: (02) 9584 3561 Website: www.oatleyelectronics.com Source for FETs with pilot lights . . . AC Electronics have been appoin-ted Australasian distributors of the Svetlana range of high quality audio vacuum tubes. This includes the popular EL34 and 6L6GC tubes as well as the 300B, 6550C, KT88 and EL509. The long awaited Svetlana 12AX7 has just been released. In addition they are stocking the large range of Golden Dragon tubes including the KT66 and KT88 GEC look-alikes and the super 300BM, plus the EI Yugoslavian Elite Gold series covering 12AT7, 12AU7, 12AX7 together with 6CG7, 6DJ8, 12BH7A and EL84 – all with gold plated pins. For industrial and high-power transmitting requirements they distribute Global Tubes of the USA. To complement their vacuum tubes, AC Electronics have also been ap- pointed distributors of the Hammond range of “Classic” audio transformers for single-ended and push-pull/ultra-linear use. They will also supply Hammond universal power transformers and chokes. Contact: AC Electronics PO Box 487, Drysdale Vic 3222 Ph: (03) 5257 2297 Fax: (03) 5257 1773 email: acourtney<at>pacific.net.au Weather forecast station has wireless (LIPD band) outside sensors Everyone is interested in the weather – and what it will do next! Jaycar Electronics have a rather neat weather station which gives you the current temperature both inside and out (outside via a 433MHz wireless sensor) along with relative humidity and temperature trends. It also has an alarm clock and calendar inbuilt and it even has a storm warning alert and over/under temperature alerts. The main display unit is 117 x 127 x 27mm so is large enough to be seen from quite a distance. Contact: Extra sensors are avail- Jaycar Electronics able (approx. 30m range). PO Box 6424, Silverwater NSW 1811 With 1 sensor the unit Ph: (02) 9741 8555 Fax: (02) 9741 8500 (XC0295) is priced at Website: www.jaycar.com.au $99.00 80  Silicon Chip www.siliconchip.com.au Radio Projects for the Amateur Volume 2, the sequel to the now-out-of-print Volume 1, presents about 50 projects of interest to amateur radio operators, covering everything from receivers and transmitters through to test equipment and even antennas and masts. The projects are presented very much in “amateur” style with hand-drawn circuit diagrams and component layouts. That’s not a criticism, it’s a style which many “home brewers” have become accustomed to because that’s how they keep their own circuits etc filed away! It’s available direct from the author/publisher (see below) or through the WIA VK2 Division bookshop (http://members.ozemail.com.au/~vk2wi/bookshop/index.htm). Price including GST is $24.95. AUDIO MODULES broadcast quality Contact: Drew Diamond 45 Gatters Rd, Wonga Park Vic 3115 New clamp meters, tough leather cases from Fluke Fluke has introduced a new, smaller- size range of clamp meters that fit more easily into tight places. The 321 and 322 meters measure to 400A AC and 600V AC, up to 400W. The 3322 will measure to 600V DC and has a 40A range for accurate low-current measurement. Both feature auto shut-off, soft-sided carry gase, test leads, batteries and two year warranty. Also new to the Fluke range are three sizes of tough, premium cases, made from top grain leather with rugged snaps, reinforced rivets and heavy duty stitching. There is one case for meters/test leads, one for electrical testers and another for all other accessories. All can be worn on a belt. Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 Ultra-mini four-port USB hub Contact: Fluke Australia Ph: (02) 8850 3333 Fax (02) 8850 3300 Website: www.fluke.com How do you easily find a satellite signal? With less and less analog transmission, finding a satellite TV signal these days by manual searching is becoming quite difficult. (For example, PAS-2 now has only digital signals). Sure, if you’re a professional installer you can buy an $X000 Spectrum Analyser – but for most mere mortals they’re a tad out of reach! Satellite TV specialists Av-comm have come up with a much cheaper alternative – a Spectrum Monitor. This device connects to the satellite receiver and tells it to sweep over the band, without processing the received signals on the way. It then outputs any received signals as a video graphic which can be displayed on most video monitors via the video input. Each satellite signal found (or more correctly each transponder) is shown as a new peak on the screen. It’s a quick-n-easy way to graphiwww.siliconchip.com.au cally display received signals – say, as your dish is swept across the sky. The larger the peak in the display, the stronger the received signal. And while it is not calibrated, the peaks have some relativity to each other as far as frequency is concerned (we’ve seen this device used with frequencies written all over the glass monitor screen in marker pen!). It can also be used to set polarisation (simply by turning the LNB on the dish through 90° and checking for a peak). If you’re into satellite TV reception, always searching for new signals, the Spectralook from Av-comm could be a godsend. It is priced at $329 – dearer than a satellite signal meter but much, much more useful. Contact: Av-Comm Pty Ltd Ph: (02) 9939 4377 Fax: (02) 9939 4376 Website: www.avcomm.com.au The Ultra-Mini 4 Port bus-powered USB Hub from Targus allows any notebook or desktop computer to enjoy plug and play connection with multiple input/output USB devices. The hub is ultra lightweight and compact (95 x 42 x 20 mm) and has full overload protection on each port to prevent any danger of power shutdown, Each port glows blue when powered up. It comes with a 1m cable. The hub is suitable for both PC and Apple notebooks or USB-enabled desktops with Windows 98, 2000, Me, XP or Mac operating systems. The Ultra-Mini 4 Port USB Hub has a recommended retail price of $49.95 and is available throughout Australia wherever quality computer accessories are sold. Contact: Targus Australia Ph: (02) 9807 1222 Website: www.targus.com.au SC August 2002  81 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG The Ferris 214 Portable Car Radio Ferris Radio concentrated predominantly on producing car radios, some of which were “portable” (and heavy) and could be used in a car on 6V or 12V or in the home on 240V AC. Here we look at their model 214 portable car radio which used germanium transistors. As well as portables, Ferris produced some DC-to-AC con­ v erters and multiband car radios (BC band and a couple of short­wave bands). In addition, during the first few years of black and white TV, they produced a 32V vibrator-powered TV receiver; quite a boon in country areas. During the era in which Australian manufacturers made tran­sistor radios, Ferris produced some quite high-performance port­able sets which could be used as car radios. AWA and Astor made similar units. They could be changed from car to portable use by just unclipping the set and withdrawing it from the vehicle mount cradle. This month I am describing one of these later sets, the 214. Initial inspection I received a phone call from a man who wanted his Ferris car radio/portable overhauled. It was mounted in Despite its age, the old Ferris car radio was in remarkably good condition. For in-car use, the unit slid into a cradle mounted under the dashboard and was switched to use the vehicle’s antenna. 82  Silicon Chip an old Chrysler Valiant utility which he takes to vintage/veteran vehicle gather­ings but, unfortunately, the set was not well. And so he brought it (and the Valiant) around so I could have a look at it before committing myself. When he turned the set on, some rather strangled sounds came out of the speaker. Tuning across the band, I could hear a number of stations and so I thought that the set would be an economic proposition to repair (the owner didn’t want to spend a mint). I then asked him to start the engine so I could check whether the vehicle interference was suppressed. Oh boy, the interference generated by the ignition system into the radio had to be heard to be believed! Well, that could wait. The more immediate problem was the horrible performance of the receiver. The set was removed from the vehicle and it really looked little the worse for wear – rather surprising considering its 30 years of portable and in-vehicle use. A couple of bars in the speaker grille had been broken but in other respects, the case’s condition was quite fair. These sets were built into a moulded metal case so that the works are shielded against ignition interference when they were used as a car radio. I told him that I might not be able to replace the missing bars in the speaker grille, which he accept­ed. He said the grille can’t be seen when the set is in the vehicle cradle anyway. He was mainly interested that the set should work – not that it look a million dollars. Once marked, the metalwork on these sets is not easy to restore to pristine condition. Stripping down First, it was time to strip the set down and see what was causing the www.siliconchip.com.au This inside view shows the PC board from the component side. Note the 3-section tuning gang. The loudspeaker frame was shorting against one of the metal cans when the covers were fitted. horrible audio quality. Fortunately, the receiver came complete with a miniature circuit diagram pasted onto the inside of the cabinet. It was rather hard to read but I was able to get a larger copy from a fellow member of the local vintage radio club. I looked rather carefully at the circuit to determine exactly what each section did and how it did it – particularly the facilities that allowed the change from portable to car radio use and vice-versa. At the aerial/antenna end of the set, the signal input is switched between the loop-stick antenna (when used as a portable) which is outside the metal case and the car radio coil which is inside the shielded case (quite nifty). I then looked at how the switching was done to go from the 9V portable battery to the 12V car battery. The receiver itself is isolated from the metal case so it can be used with either positive or negative-earth vehicles. A particular point of interest was how the operating condi­ tions are changed in the set to allow it to work from 12V or 9V. It was quite simple really: the 9V battery was left in circuit www.siliconchip.com.au at all times and the 12V vehicle supply “charged” it via resistor R33. This is a rather rough way of doing things as the 9V battery may be “charged” at up to 150mA when the vehicle battery is fully charged and the receiver volume is low. However, at high volume, the battery supplies some current to the receiver, thus acting as a crude “voltage” regulator in this mode. It must have been rough on the 9V battery and I wonder how long it would have lasted with this sort of treatment. The receiver circuit is quite straightforward for a set of this era (1960s). Australian manufacturers produced some excel­lent transistorised designs in the years before the Japanese forced them out of the market. Australian sets of this era commonly had RF amplifiers and this Ferris design is no exception. The receiver has an RF stage, followed by a autodyne converter, two IF amplifying stages, a diode detector, two class-A audio amplifiers and finally a trans­formercoupled class-B push-pull output stage. No fancy, tricky circuits here. Many will remember that autodyne converter circuits were not too highly thought of in valve receivers and were replaced by triode hexode converters in the mid 1930s. However, the auto­ dyne works well in transistorised equipment and is almost universally used to do the superhet conversion work in domestic broadcast receivers. Fixing the audio distortion Unfortunately, the set had been used as a car radio without the 9V dry battery fitted (this battery is no longer available). This concerned me as it meant that the set had been running on voltages as high as 14V instead of the intended 9V. In particu­lar, germanium transistors such as the AC128s in the audio output section are not particularly tolerant of excessive voltages. Often, they will run for a short time on the higher voltages and then go into distortion, after which there is virtually no out­put. This occurs because the transistors draw increased current as a result of the higher voltage and then they go into “thermal runaway” where the current keeps on increasing, in many cases until the transistors are August 2002  83 Fig.1: the circuit used eight germanium transistors and featured diode detection and a push-pull audio output stage. 84  Silicon Chip destroyed. Some do return to normal once they’ve cooled down but failures are common. I initially thought that one or both AC128 transistors had been damaged. However, before consigning them to the rubbish bin, I decided to do a number of checks. I connected the set to 9V from my small regulated power supply and found that the distor­tion noted earlier was still quite evident. I then checked the voltages around the AC128s and found them to be as per the cir­cuit diagram. Signal tracer checks Remember, with PNP transistors everything is referenced to “+”, which is “earth” or common. I suspected that the speaker may have been faulty and substituted my 9 x 6-inch test speaker but the quality was still terrible. I then thought that it was time to bring out the heavy artillery, so I fired up my signal tracer and checked each stage for audio quality and volume. Initially, all went well – the volume increased as I moved from the base of Q5 to its collector, then onto Q6 and from there to the push-pull bases of the AC128s. However, when I transferred the probe to the AC128 collectors, the volume was down and the distortion was horrific. But despite the low output, the collec­tor current through this stage was high (as shown by the voltage across R31). So I now knew where the problem lay. I then found that slight pressure on the circuit board could cause the volume to increase dramatically, the quality to return and the collector current to reduce or vice versa. Ah ha, a cracked circuit board track – or so I thought. And so, with the set operating, I checked the various vol­tages around the output stage but there was no indication of hairline cracks in any of the copper tracks. I also checked for short circuits all around the output stage of the receiver and could find nothing at fault. In the process, I replaced a couple of yellow ceramic capacitors with the red mark on them (Ducon “red caps”), as they have a reputation of not being all that reliable but that didn’t help. To add to my problems, parts accessibility in this stage is rather poor and it’s difficult to inspect components, even with a headset magnifier and a mirror. In fact, once some components had been removed for inspection, their replacements had to be installed on the other side of the board due to the difficult access. I was getting nowhere fast – just the slightest touch on the board could cause to behave or misbehave. In the end, I decided to replace C25. It is awkward to get at but that fixed the problem. I checked the removed capacitor and it appeared OK. So what had caused a couple of hours of frustration? Perhaps the capaci­tor was faulty, despite the test, or perhaps there was sliver of metal causing an intermittent short in this area. Anyway it works well now. Another serviceman/restorer had apparently given up on the set so the owner informed me. Fortunately, the set didn’t have major problems. However, if critical parts – such as the audio output transformer – had failed and were unavailable, I would have replaced the audio output stage altogether. SILICON CHIP’s CHAMP amplifier which uses an LM386 audio amplifier is a good candidate for this job. By the way, germanium transistors are now harder to obtain than valves. Silicon transistors can be used in place of germani­ um transistors in many cases but the base biasing has to be altered to suit. Reducing the voltage The next task was to reduce the rail voltage to the tran­sistors to around 9V, regardless as to whether the set was con­nected to its own battery or to the vehicle battery. There are a few ways that this can be done but I settled for a simple method that closely mimics the set’s operation when a battery is fitted. This simply involved fitting three 3V (0.5W) zener diodes in series across the battery plug, to regu­late the voltage to a nominal 9V. In addition, I added a 33Ω 0.5W resistor in series with R33 to reduce the current from the car battery. As a result, the voltage applied to the receiver does drop below 9V at high volume but this doesn’t cause any problems with the performance. Close inspection of the circuit diagram reveals that the 214 was made in two versions: one for use with a 12V car battery (9V internal battery) and the other for use with a 6V car battery (6V www.siliconchip.com.au Photo Gallery: Columbus Discovery Model 66 Manufactured by Radio Corporation of New Zealand during the 1940s, the Columbus Discovery Model 66 was a 6-valve 2-band receiver that came in both console and mantel models. They were fairly conventional superhet receivers with 455kHz IF stages and covered the broadcast band from 550-1600kHz and a shortwave band from 9.4-15.6MHz. The valve line-up was as follows: 6K7 (RF amplifier); 6J8 (converter); 6B8 (IF amplifier, detector & AGC); 6J7 (audio amplifier); 6V6 (audio output); and 6X5 (rectifier). (Photographs & diagram courtesy Ted Sherman, Kawhia, NZ). www.siliconchip.com.au August 2002  85 The loopstick antenna was mounted at the top of the receiver, outside the metal case (so that it wasn’t shielded). Note that the “common” tracks on the PC board operated at +12V with respect to the chassis. internal battery). This simply involved changing four resis­tor values. A general check-over I reconnected the set’s speaker and found that it was caus­ing distortion so I ratted my supply of speakers and found a 5 x 4-inch Plessey speaker that exactly matched the faulty one. I also decided that I should check the audio output to see whether the AC128s had been damaged but after listening to the receiver, it was apparent that they had survived their ordeal. Next, I connected the RF signal generator, modulated by a 1kHz tone, to the receiver and connected an oscilloscope to the audio output. The 1kHz sinewave looked very good and even when the volume was increased to the point of distortion, I found that both transistors clipped symmetrically. The alignment was also checked and it was found to be spot on in the IF amplifier and only required trimmer TR3 to be peaked at the high-frequency end of the dial. The set had retained its alignment well, despite the rough time it would have had over its life. As mentioned earlier, the case was marked but it wasn’t practical to repaint the painted sections. However, 86  Silicon Chip the chrome work came up quite well using automotive polish and a little elbow grease. The scratches are not obvious now. Unfortunately, the old battery had been left in the set and the chemicals had leaked and eaten into the case. The battery type used in this set (2761) is no longer made but this is not really a problem. If the owner wants to use the set on batteries, a 6-cell AA battery holder (plus 6 x AA cells) and a battery snap connector would do the trick. Like anything painted red that is exposed to sunlight, the dial pointers had changed from red to an off-white colour. For this reason, I keep a small tin of red enamel paint and, using a small artist’s brush, I painted the pointers so that they now look like new. In-car reception The final test of the receiver was when it was mounted back in the Valiant utility. The reception was initially quite fair but when the engine was started up, the interference was horren­dous. It looked as though I’d have to do some work on the vehi­cle’s antenna system. Suddenly, I remembered that we had been using the set on its own internal loopstick antenna. I switched the set to the external car radio antenna and the reception was now delightful, with virtually no interference – the antenna system was in good order. When restoring and installing a car radio, it is necessary to check two things: interference from the car ignition system and the tuning of the antenna coil. Interference is usually cured (assuming that all the ignition suppressors are in place) by making sure that the base of the antenna is actually earthed (via the coaxial cable braid) to the vehicle. Cleaning rust from around this area usually cures the problem unless there is a break in the braid. The antenna is very short so it is coupled very closely to the antenna coil. The antenna and the coaxial cable all act as part of the tuned circuit. With this all connected and the anten­ na fully extended, the receiver is tuned to around 1400kHz and the antenna coil trimmer is adjusted with a small screwdriver for best performance. The trimmer is accessed through a small hole alongside the tuning control. In this case, the old Ferris receiver performed well right across the broadcast band so the trimmer (TR1) didn’t have to be adjusted. I returned the set to the owner but he rang me a day later and said that it was blowing fuses. He brought it www.siliconchip.com.au back and testing revealed that a short existed between the +12V rail and the set’s frame. Dismantling the set revealed that the short disappeared when the back was removed. Some plastic electrical tape was put over the vulnerable sections of the PC board but the short reappeared when the back was replaced. I pulled the front and back covers off and the short disappeared again. At this stage, I suspected a short from the circuit board common (+) to the loud­speaker frame (-). In this set, the speaker fits between the transistors, various other components and the coil cans. Using a dentist’s mirror, I observed that one coil can did seem to be very close to the speaker frame. I put some tape over the can and that fixed the problem – success at last. Summary Ferris made some excellent radios and this is one of them. It is capable of being used as a portable or as a car radio with equally good performance. Its all-metal case ensures that it is well-shielded against car ignition interference. This view shows the Ferris receiver sitting in its cradle, beneath the dashboard of the old Chrysler Valiant utility. They don’t make ’em like this any more! It’s also is rather weighty for a transistor radio but is extremely robust. This is a set well worth having in any collection and it is still a very practical receiver nearly 40 years after it was manufactured. Vintage radios certainly don’t have to sit on a shelf SC gathering dust. WHEN QUALITY COUNTS. . . valve equipment manufacturers and repairers choose only the best... Valves - SVETLANA GOLDEN DRAGON EI ELITE GOLD GLOBAL TUBES 6L6GC, 12AX7, 300B, 6550, EL34, EL509, KT88, KT66, 4-300BM, 300BM 6CG7, 12AX7,EL84 - gold pins Hi Power Transmitting & Industrial Transformers - HAM M O N D C L A S S I C Single-ended 25 watts Push-pull / Ultra-Linear 10 to 120 watts Power - universal primary, secondary to 250mA Filter chokes - to 300mA HAMMOND MANUFACTURING TM Svetlana Stockists - NSW Victoria New Zealand MEGtronics - 02 9831 6454 Electronic Valve & Tube Company - 03 5257 2297 Resurrection Radio - 03 9510 4486 Logic Research Electronics - 07 849 5293 DEALER ENQUIRIES WELCOME Distributed by www.siliconchip.com.au 76 Bluff Road St Leonards VIC 3223 PO Box 487 Drysdale VIC 3222 AUSTRALIA Tel: +61 3 5257 2297 Fax: +61 3 5257 1773 August 2002  87 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; or send an email to silchip<at>siliconchip.com.au Knock sensing for programmable ignition I wanted to know if the Programmable Ignition kit from the June & July 1999 issues has provision to be used with a knock sensor to retard timing if detonation occurs? Does the kit in its current form allow the use of vacuum advance or is it purely just what you put in the program? What mods do you have to make to the engine or distributor to make this work? (P. S., via email). • You might want to have a look at our Knock Indicator project from the April 1996 issue. However it does not act to retard ignition. Nor does the programmable ignition setup act on the vacuum advance. Speed alarm cooks resistor I recently decided to build the Speed Alarm (November & December 1999) as I had a close call with a speeding fine. I talked my friend into also buying a Jaycar kit and set about building the two of them. Turn on resulted in the 10Ω 1W resistor smoking away. I later found out that I had reversed How to eliminate the distributor I wish to convert my car ignition system to distributor-less operation, ideally using one or two Hall Effect sensors to trigger the electronics to fire the coils or ignition systems. I’m not sure how to achieve the electronics part to count the pulses from the Hall triggers to fire the correct coil/cylinder. Naturally, there are quite a few aftermarket manufacturers who produce such complete packages but they are quite expensive. Can you help? (P. W., via email). • Have a look at the High Energy Ignition circuit in the July 1998 is88  Silicon Chip the polarity of one of the two 47µF electrolytic capacitors. Thinking this was the culprit, I replaced the electros, the 7805 regulator and the 10Ω resistor but the resistor still smokes. What have I missed, so I can finish my speed alarm and build the second one? I hope that the microprocessor is still OK as they sure are expensive to replace. (P. C., via email). • Assuming that you did not reverse the polarity of the DC supply when you first connected your project, the most likely reason for the smoking 10Ω resistor is that ZD1, the 16V input protection zener diode, is reversed. Speed control for LGB trains With regards to the motor speed control project in the June 1997 issue, would it be feasible to use this as a variable speed control unit for LGB type model trains? Could the REF from pin 14 be used for the reference on a suitable DAC and the output of the DAC, with a suitable buffer, be used in place of VR1 which is 5kΩ pot? (R. M., via email). • We would not recommend this circuit for model trains. We have pub- sue. It can be triggered by Hall Effect pickups and con­tains the necessary interface circuitry. If you are going to use one coil per cylinder you will need one Hall Effect pickup per cylinder. If you only want one Hall Effect device, operating from a toothed vane on the harmonic balancer (say), then you will need counter circuitry and some method of identifying the firing point for cylinder one, for correct timing. You also need to allow for ignition advance. Without going to a full engine management system, you are really facing compli­cations. Our preferred method would be to convert the distributor to Hall Effect or reluctor pickup. lished quite a few train controllers over the years. Have a look at the design featured in the October, November & December 1999 issues. Its output can be made compatible with the higher voltage needed by LGB models by substituting a transformer with a higher secondary voltage. Speed control for a golf buggy I have taken over an electric golf buggy business and need help in designing a new speed controller. The one used at the moment is unreliable. The buggy is run by a 12V 180W DC motor and the electronics has two MJ802 transistors which are prone to blowing under load. The motor can pull up to 45A. What sort of circuit would your suggest? (J. E., via email). • Mosfets are the answer. Have a look at the 50A speed control published in the May 2000 issue. Voltage checks when building the Theremin I am constructing the Theremin which appeared in the August 2000 issue of SILICON CHIP. I have only a basic knowledge of electronics, so I have a few questions. Firstly, both the DC socket and the S1 power switch have three connectors and in the component overlay in Fig.5 of your article only two connectors are featured on both of these for wiring. I am not sure which connectors on these components I should be using or does it even matter? Secondly, when setting up or tuning the Theremin you de­ scribe checking voltages at various points. For instance, “there is a nominal +6V between the case of one of the transformer coils and pin 8 of IC2 & pin 6 of IC3. The voltage should be between +5.6V and +5.8V.” Plus, there are other references to checking voltages at the cathode of diode D1 when aligning the volume plate, etc. As I am a newbie, can you tell me www.siliconchip.com.au exactly how I go about doing this? I have a multimeter but am never exactly sure where to put the probes to check all of these things. In fact, a beginner’s article on exactly how to use a multimeter to check your work and find faults in a circuit would be greatly appreciated in your magazine. (Z. C., via email). • The switch should be wired so that its two terminals are closed when set to the ON position. You can check this by select­ing “ohms” on your multi-meter then using the two terminals that show a short circuit (zero ohms) when the switch is on. Make sure that the terminals become an open circuit (high resistance) when the switch is set to off. The best way to check the DC socket is to plug in the plug­pack and measure the voltage on the socket terminals. Do this before soldering the DC socket to anything. The positive terminal is the one which shows positive voltages on the multimeter when the red multimeter lead is connected to it. The black multimeter lead connects to the negative terminal on the socket. Measuring voltages on the Theremin circuit is done similar­ly. Connect the black multimeter probe to the case of a transformer, then measure voltages with the red probe. They should be similar to those quoted in the article. If you are having trouble with measuring voltages on the circuit, you could just try the Theremin without voltage checks and adjust the cores of the transformers as described while skipping the voltage measurements. Turbo timer countdown problem I purchased a Turbo Timer kit as described in the November 1998 issue of SILICON CHIP and upon testing it I discovered that when the ignition switch is left on the timer is activated and starts counting down, so when the ignition is ultimately switched off there is no countdown. What should I do? (G. B., via email). • Try increasing the capacitor value at pin 4 of IC1. This 100µF capacitor holds the timer reset until after a set time determined by the 10kΩ resistor connecting to the 12V. A value of 470µF should be enough to extend the reset time so the circuit will not trigger with power on. www.siliconchip.com.au Temperature compensation for pH meter I am writing to inquire if it would be possible to modify the pH meter for swimming pools (published in April 1988) so that temperature could be compensated for automatically. I was thinking of putting an LM355Z in series with the 6.8kΩ resistor (insulated and on a length of wire so it can be placed in the solution) but I’m not sure of the correct way to do this. I want to feed the output voltage to an ADC so I can automate the pH con­trol system and log the data on a PC. The temperature will vary from day to night and this is why I want to compensate the tem­ perature automatically. Do you have any suggestions? (J. E., via email). • The temperature compensation in the pH meter changes the slope characteristic from the sensor. In other words, just adding or subtract- Minimitter tuning is odd I’ve had a strange problem with the FM Stereo Minimitter described in the April 2001 issue. Adjusting L1 works fine but L2 seems to have no effect. The radio receiver I’m using indicates FM stereo regardless of the tuning of L2. Could you please advise me on this? (B. M., via email). • We suspect that coil L2 is not connected electrically to the PC board. Check that there is continuity through the coil by measuring its resistance between the relevant tracks on the PC board (using a multimeter). The most likely cause is that the enamel insulation has not been cleaned off the wire ends. Alternatively, the capacitor across L2 may not be soldered correctly or it is the wrong value. It should be 47pF. Or maybe the 3-10pF trimmer is shorted or L2 is wound or termi­nated incorrectly. Tachometer with shift indicator Jaycar has suggested that I contact you with my need for an automotive tachometer with a bargraph display. I am not interest­ed in knowing the actual value of the engine rpm, just ing an external voltage will not alter the slope. This would require some sort of variable resistance which changed with temperature instead. You may be able to use a thermistor which is altered with parallel resistance to set the resistance change with temperature. Alternatively, the measurement can be altered in your computer to follow the graph in Fig.1 of the pH meter article. A separate temperature input for the computer would be required. Apart from this, the pH probe does not change much in output over the normal range of temperatures expected to be found, especially in Australia where temperatures are reasonably stable over a season. Maybe your automation can tolerate ignoring any tempera­ture changes? an indica­tion when approaching the upper and lower limits of engine speed and guidance in selecting the best speed for gear changing. The bargraph display, if mounted remote from the rest of the elec­tronics, could be quite small and unobtrusive, yet very effective if mounted, say, with double-sided tape centrally just outside the glass of the instrument panel. (J. B., via email). • Have a look at the Rev Limit Controller that we published in the April 1999 issue. While specifically intended as a rev limit­er project, it can also be used as a Shift Light. We can supply the April 1999 issue for $7.70 including postage. Optical pickup for Rev Limiter My car is a 1993 Nissan Silvia which uses a LED system inside the distributor. I was just wondering if there is a dif­ferent pickup circuit for the Rev Limiter described in the April 1999 issue. If not, which of the two systems would work, reluctor or the Hall Effect system? (G. H., via email). • We published details of how to use an optical pickup in the Ask Silicon Chip pages of the August 1998 issue and the Circuit Notebook section in the October 2000 issue, page 58. The August 1998 version should suit. August 2002  89 Optocoupler breaks down in welder If possible, could you please help me with the following problem? We have an inverter welder that has been imported from Europe. The machine has an input rating of 230VAC and the manufac­turer has stated that running the welder at 240VAC would pose no problem. The problem is that a MOC3023 optocoupler is breaking down and letting AC flow back through the circuit and cause the solenoid to chatter. The optocoupler drives a gas solenoid rated at 230VAC 13.5VA and incorporates an RC circuit which consists of a .022µF capacitor and a 22Ω watt resistor connected in parallel. My question is, would the 10V Question on modifying PC power supply With respect to the article entitled “Use your old PC power supply for high current outputs” in December 1998, how high is the “high current”. Also, have you ever described the theory behind high power Mosfet auto amplifiers? Can the output current of the Power Supply for Amateur Transceivers described in May/June 1991 be increased to around 30A relatively easily? (T. C., via email). • The December 1998 article dealt with modifying a standard PC power supply to deliver slightly higher voltage; eg, 13.8V in­stead of 12V. Typically, you can get 8A from the 12V rail and 20A from the 5V rail. We have not published any theory behind Mosfet car amplifi­ ers. They increase in the primary generate a sufficient increase in the breakdown voltage to cross the protection threshold and blow the optocoupler? And is there any formula to work out what the break-down voltage would be? (P. D., via email). • The MOC3023 only has a 400V blocking rating so depending on what it is driving, it could easily be fragile, especially in a welder. Given that its load is only a low current, the designers probably thought that it would easily handle the job. Our ap­proach would be to use the MOC3023 to drive a 600V Triac but one with a low holding current or alternatively, shunt the solenoid with an incandescent lamp to ensure reliable operation. You may also need Varistor protection in the circuit. are just standard Mosfet amplifiers powered by a DC-DC inverter. The output of the 13.5V 25A supply cannot be increased without substantially upgrading the major components. How to connect a subwoofer amplifier I’d be the first to admit that I am a novice in the field of electronics. With perseverance and a lot of reading I had thought that I had developed a basic understanding of audio amplifiers, until now. I have built a couple of amplifier modules supplied by Dick Smith Electronics, namely the 100W module (Cat. K3442) and the more powerful 300W beast, primarily to power subwoofers for my home-theatre system. Each amplifier module has the Sub Bass Processor preamp module (DSE Cat. K5403). My dilemma is this: if I use the subwoofer out jack on my surround receiver I get virtually no signal through either amp module. If I connect the same subwoofer output to my small 30W bookshelf stereo and get this to power my subs, I get thumping bass but only 30 watts worth. Obviously there is signal coming out of the sub out jack, so why is it lost between here and my speakers? (S. F., via email). • The sub-bass processor should not be connected to the sub­woofer output of your surround sound receiver. The sub-bass processor is intended for those people who do not have a subwoof­er output from their receiver. Try connecting the subwoofer signal directly to your 100W amplifier. You should get heaps of bass. Bridging audio amplifier modules I’ve bought two power amplifiers from Dick Smith Electron­ ics (Cat K3442) and I would like to bridge them. What do I need and can it be done? (E. P., Vermont, Vic). • There is a problem in bridging these amplifier modules. As they stand, they will deliver 100W into 4Ω or 50W into 8Ω. If they are bridged, they will only deliver 100W into an 8-ohm load. They cannot drive a 4-ohm load in bridge mode, since each module cannot drive a 2-ohm impedance. Notes & Errata Touch/Infrared Light Dimmer, January & February 2002: the circuit diagram (Fig.3) should show the .01µF capacitor and 1MΩ resistor connected to pin 6 (RB0 input) of IC1 and not to the A2 terminal of TRIAC1. The PC board pattern and overlay diagram SC are correct. 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. 90  Silicon Chip www.siliconchip.com.au SILICON CHIP WebLINK How many times have you wanted to access a company’s website but cannot remember their site name? Here's an exciting new concept from SILICON CHIP: you can access any of these organisations instantly by going to the SILICON CHIP website (www.siliconchip.com.au), clicking on WebLINK and then on the website graphic of the company you’re looking for. It’s that simple. No longer do you have to wade through search engines or look through pages of indexes – just point’n’click and the site you want will open! Your company or business can be a part of SILICON CHIP’s WebLINK . For one low rate you receive a printed entry each month on the SILICON CHIP WebLINK page with your home page graphic, company name, phone, fax and site details plus up to 50 words of description– and this is repeated on the WebLINK page on the SILICON CHIP website with the link of your choice active. Get those extra hits on your site from the right people in the electronics industry – the people who make decisions to buy your products. Call SILICON CHIP today on (02) 9979 5644 A 100% Australian owned company supplying frequency control products to the highest international standards: filters, DIL’s, voltage, temperature compensated and oven controlled oscillators, monolithic and discrete filters and ceramic filters and resonators. Hy-Q International Pty Ltd Tel:(03) 9562-8222 Fax: (03) 9562 9009 WebLINK: www.hy-q.com.au RCS Radio has available EVERY PC Board ever published in SILICON CHIP, EA, ETI and AEM (copyrighted boards excepted). Many late boards are available ex stock, others can be made to order within a few days. Custom & production boards too! RCS Radio JED designs and manufactures a range of single board computers (based on Wilke Tiger and Atmel AVR), as well as LCD displays and analog and digital I/O for PCs and controllers. JED also makes a PC PROM programmer and RS232/RS485 converters. Jed Microprocessors Pty Ltd VAF Research offers Speakers for the Audiophile Purist or Home Theatre Extremist. Home Entertainment Equipment and Accessories. They have ready-to-assemble loudspeaker kits along with quality drivers from the world's leading suppliers. VAF Research Pty Ltd When it comes to purchasing quality products over the Web, you can count on the Wiltronics team to provide you with the best value for money. For over 25 years, Wiltronics has supplied the needs of the Electronics Industry, and look forward to continuing this service. Wiltronics Pty Ltd Tel: (03) 9762 3588 Fax: (03) 9762 5499 Tel: 1800 818 882 Fax: (08) 8363 9997 WebLINK: jedmicro.com.au WebLINK: vaf.com.au Looking for GENUINE Stamp products from Parallax . . . or Scott Edwards Electronics, microEngineering Labs & others? Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. See our website for new range of ATOM products! International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. For everything in radio control for aircraft, model boats and planes, etc. We also carry an extensive range of model flight control modules including GPS, altitude and speed, interfaces, autopilot and groundstation controllers. More info on our website! Av-COMM Pty Ltd Silvertone Electronics MicroZed Computers Tel: (03) 9762 3588 Fax: (03) 9762 5499 WebLINK: wiltronics.com.au Tel/Fax: (02) 9533 3517 Tel: (02) 9738 0330 Fax: (02) 9738 0334 Tel: (02) 6772 2777 Fax: (02) 6772 8987 Tel:(02) 9939 4377 Fax: (02) 9939 4376 WebLINK: microzed.com.au WebLINK: avcomm.com.au WebLINK: silvertone.com.au We specialise in providing a range of Low Power Radio solutions for OEM’s to incorporate in their wireless technology based products. The innovative range includes products from Radiometrix, the World’s leading manufacturer. SPECIALISTS in AUDIO, VIDEO, CD, DATA Media and Multimedia manufacturing & wholesale. We also specialise in DVD Production & editing. We can produce Short Run or Bulk CD Audio, CD Rom & DVD projects. Distributor of Emtec (by Basf) TDK, HHB and Quantegy Professional Products. Want to start Programming the PIC Micro? Take a look at our PIC Development board. Dedicated to the PIC Micro, We design and manufacture PIC Micro project kits, from the simple to the complex. Our range is constantly growing, so keep checking our web site for updates. · Hifi upgrades & modification products - jit- Tel/Fax: (03) 9378 4288 Syd: (02) 9660-1228 Melb: (03) 9859-0388 WebLINK: cia.com.au/rcsradio TeleLink Communications Tel:(07) 4934 0413 Fax: (07) 4934 0311 WebLINK: telelink.com.au www.siliconchip.com.au www.siliconchip.com.au PRO-COPY Tel: (08) 9375 3902 Fax: (08) 9375 3903 WebLINK: procopy.com.au MicroByte Electronics WebLINK: microbyte.com.au ter reduction and output stage improvement. · Danish high-end hifi kits - including preamps, phono, power amps & accessories. · Speaker drivers including Danish Flex Units plus a range of accessories. · GPS, GSM, AM/FM indiv. & comb. aerials. Soundlabs Group WebLINK: soundlabsgroup.com.au ugust 2002  91 AAugust REFERENCE GREAT BOOKS FOR ALL PRICES INCLUDE GST AND ARE AUDIO POWER AMP DESIGN HANDBOOK PIC Your Personal Introductory Course From one of the world’s most respected audio authorities. The new 2nd edition is even more comprehensive, includes sections on load-invariant power amps, distortion residuals and diagnosis of amplifier problems. 368 pages in paperback. Concise and practical guide to getting up and running with the PIC Microcontroller. Assumes no prior knowledge of microcontrollers, introduces the PIC’s capabilities through simple projects. Ideal introduction for students, teachers, technicians and electronics enthusiasts – perfect for use in schools and colleges. 270 pages in soft cover. By Douglas Self. 2nd Edition Published 2000 by John Morton – 2nd edition 2001 89 $ $ VIDEO SCRAMBLING AND DESCRAMBLING FOR SATELLITE AND CABLE TV by Graf & Sheets 2nd Edition 1998 AUDIO ELECTRONICS By John Linsley Hood. First published 1995. Second edition 1999. If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. $ 79 $ UNDERSTANDING TELEPHONE ELECTRONICS By Stephen J. Bigelow. Fourth edition published 2001 4th EDITION Based mainly on the American telephone system, this book covers conventional telephone fundamentals, including analog and digital communication techniques. Provides basic information on the functions of each telephone component, how dial tones are generated and how digital transmission techniques work. 402 pages, soft cover. 65 GUIDE TO TV & VIDEO TECHNOLOGY 3rd EDITION By Eugene Trundle. 3rd Edition 2001 Eugene Trundle has written for many years in Television magazine and his latest book is right up to date on TV and video technology. The book includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover. 3rd EDITION $ By Tim Williams. First pub­­lished 1992. 3rd edition 2001. By Ian Hickman. 2nd edition1999. 63 $ Based mainly on British practice and first published in 1997, this book has much that is relevant to Australian systems as a guide to home and small business installations. A practical guide to installation of telephone wiring, ranging from single extension sockets to PABX, with the necessary tools, test equipment and materials needed by installers... 178 pages in soft cover. 92  Silicon Chip EMC FOR PRODUCT DESIGNERS ANALOG ELECTRONICS Essential reading for electronics designers and students alike. It will answer nagging questions about core analog theory and design principles as well as offering practical design ideas. With concise design implementations, with many of the circuits taken from Ian Hickman’s magazine articles. 294 pages in soft cover. VIDEO & CAMCORDER SERVICING AND TECHNOLOGY by Steve Roberts. 2nd edition 2001. 67 85 $ Widely regarded as the standard text on EMC, provides all the key information needed to meet the requirements of the EMC Directive. Most importantly, it shows how to incorporate EMC principles into the product design process, avoiding cost and performance penalties, meeting the needs of specific standards and resulting in a better overall product. 360 pages in paperback. 99 TELEPHONE INSTALLATION HANDBOOK $ 43 85 $ by Steve Beeching (Published 2001) Provides fully up-to-date coverage of the whole range of current home video equipment, analog and digital. Information for repair and troubleshooting, with explanations of the technology of video equipment. 318 pages in soft cover. 67 $$ www.siliconchip.com.au BOOKSHOP WANT TO SAVE 10%? 10% OFF! SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! ENQUIRING MINDS! LOWER THAN RECOMMENDED RETAIL PRICE Power Supply Cookbook Analog Circuit Techniques With Digital Interfacing by Marty Brown. 2nd edition 2001. An easy-to-follow, step-by-step design framework for a wide variety of power supplies. Anyone with a basic knowledge of electronics can create a very complicated power supply design . Magnetics, feedback loop, EMI/RFI control and compensation design are all described in simple language. 265 pages in paperback. by T H Wilmshurst. Published 2001. 93 $ Microcontroller Projects in C for the 8051 by Dogan Ibrahim. Published 2000. 69 $$ Through graded projects the author introduces the fundamentals of microelectronics, the 8051 family, programming in C and the use of a C compiler. The AT89C2051 is an economical chip with re-writable memory. Provides an interesting, enjoyable and easily mastered alternative to more theoretical textbooks. 178 pages in paperback. 69 $ Antenna Toolkit by Joe Carr. 2nd edition 2001. Together with the CD software included with this book, the reader will have a complete solution for constructing or using an antenna - bar the actual hardware. The software is based on the author’s own Antler program, which provides a simple Windowsbased aid to carrying out the design calculations at the heart of successful antenna design. Free software CD included. 253 pages in paperback. Electric Motors And Drives O R D E R H E R E ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ by Howard Hutchings. Revised by Mike James. 2nd edition 2001. 59 $ ANALOG ELECTRONICS..................................................$85.00 AUDIO POWER AMPLIFIER DESIGN...............................$89.00 AUDIO ELECTRONICS.....................................................$85.00 EMC FOR PRODUCT DESIGNERS...................................$99.00 GUIDE TO TV & VIDEO TECHNOLOGY............................$63.00 PIC - YOUR PERSONAL INTRODUCTORY COURSE........$43.00 TELEPHONE INSTALLATION HANDBOOK.......................$67.00 UNDERSTANDING TELEPHONE ELECTRONICS.................$65.00 VIDEO & CAMCORDER SERVICING/TECHNOLOGY........$67.00 VIDEO SCRAMBLING/DESCRAMBLING..........................$79.00 POWER SUPPLY COOKBOOK..........................................$93.00 M'CONTROLLER PROJECTS IN C FOR 8051..................$69.00 ANALOG CIRCUIT TECHNIQUES WITH DIGITAL INT......$69.00 ANTENNA TOOLKIT.........................................................$83.00 INTERFACING WITH C.....................................................$63.00 ELECTRIC MOTORS AND DRIVES..................................$59.00               ORDER TOTAL: $...................... P&P Orders over $100 P&P free in Australia. AUST: Add $A5.50 per book NZ: Add $A10 per book, $A15 elsewhere 83 $ Interfacing With C by Austin Hughes. 2nd edition 1993. Reprinted 2001. VERY POPULAR BOOK NOW BACK IN STOCK WITH A NEW LOWER PRICE! For non-specialist users – explores most of the widely-used modern types of motor and drive, including conventional and brushless DC, induction, stepping, synchronous and reluctance motors. 339 pages, in paperback. Covers all the analog electronics needed in a wide range of higher education programs: first degrees in electronic engineering, experimental science course, MSc electronics and electronics units for HNDs. Text is supported by numerous worked examples and experimental exercises. 312 pages in paperback. $ 63 Anyone interested in ports, transducer interfacing, analog to digital conversion, convolution, filters or digital/analog conversion will benefit from reading this book. The principals precede the applications to provide genuine understanding and encourage further development. 302 pages in paperback. TAX INVOICE Your Name_________________________________________________ PLEASE PRINT Address ___________________________________________________ ___________________________________ Postcode_______________ Daytime Phone No. (______) __________________________________ STD Email___________________<at>_________________________________ ❏ Cheque/Money Order enclosed OR ❏ Charge my credit card – ❏ Bankcard ❏ Visa Card ❏ MasterCard No: Signature______________________Card expiry date PLUS P&P (if applic): $........................... TOTAL$ AU.............................. POST TO: SILICON CHIP Publications, PO Box 139, Collaroy NSW, Australia 2097. OR CALL (02) 9979 5644 & quote your credit card details; or FAX TO (02) 9979 6503 ALL TITLES SUBJECT TO AVAILABILITY. PRICES VALID FOR MONTH OF MAGAZINE ISSUE ONLY. ALL PRICES INCLUDE GST MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $20.00 (incl. GST) for up to 20 words plus 66 cents for each additional word. Display ads: $33.00 (incl. GST) per column centimetre (max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. Taxation Invoice ABN 49 003 205 490 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ 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______________ 94  Silicon Chip FOR SALE CABLE SPECIALS: POWER, 3 Phase, Underground, 0.6Kv, Ex British Aerospace 500 metres $3 / metre O.N.O 1 drum. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. BATTERIES SPECIALS: 9 Volt DURACELL, Made In U.S.A, Ex Olympic Boxed Lots of 48 $50 plus $15 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. UNIVERSAL DEVICE PROGRAMMER: Low cost, high performance, 48-pin, works in DOS or Windows inc NT/2000. $1320. Universal EPROM programmer $429. Also adaptors, (E) EPROM, PIC, 8051 programmers, EPROM simulator and eraser. Dunfield C Compilers: Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $198 each. Demo disk available. ImageCraft C Compilers: 32-bit Windows IDE and compiler. For AVR, 68HC11, 68HC12. $396. Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x, 89Sxx in both DIP and PLCC44 and some AVR’s, most 8-pin EEPROMS. Includes socket for serial ISP cable. $220, $11 p&p. SOIC adaptors: 20 pin $99, 14 pin $93.50, 8 pin $88. Full details on web site. Credit cards accepted. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. (02) 9896 7150 or http://www.grantronics.com.au EXTENSION CORD SPECIALS: 10 METRE, CLICK Heavy Duty, Ex Olympic Brand New Unopened boxed Lots of 5 $30 plus $15 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. FIRE EXTINGUISHER SPECIALS: CHUBB Dry Powder 1.5kg, EX OLYMPIC Boxed $25 plus $15 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. www.siliconchip.com.au ATMEL STK500 DEVELOPMENT KIT. Starter and development kit for most AVR microcontrollers, not used, $140.00. 0418 805545, 08 8364 6818 or lachlanp<at>adam.com.au IBM Master Clock: Pendulum type, Electromechanical, 24 Volt DC, Original, Hand Painted Face Lettering IBM, Serviced, new French Polish, Ex British Aerospace, Keeps Good Time, $7500. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. HELMET SPECIALS: Motor Cycle, ex Olympics $20 Terminator 2 Movie Policeman Type, various sizes. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. ELECTRONICS HOBBYIST (Sydney northern suburbs) having Workshop cleanup, several items to sell / give away. Details at: www.sonymusic.com.au/business/ mastering/downloads/Cleanup.zip DOUBLE ADAPTORS: Ex Olympic, Boxed Lots of 10, $20 plus $15 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Silverwater in Sydney. A genuine interest in electronics is a necessity. Phone 02 9741 8555 for current vacancies. TELEPHONE EXCHANGE SIMULATOR: test equipment without the cost of telephone lines. Melb 9806 0110. http://www.alphalink.com.au/ ~zenere KITS KITS AND MORE KITS! Check ‘em out at www.ozitronics.com BARCODE READERS: Ex British Aerospace, Portable Hand Held 6 only $50 each $300 P&P $30. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. A NEW RANGE of European kits made by SMART KIT now available in Australia at www.q-mex.com.au RCS HAS MOVED to 41 Arlewis St, Chester Hill 2162 and is now open, www.siliconchip.com.au Mark22-SM Slimline Mini FM R/C Receiver • • • • • 6 Channels 10kHz frequency separation Size: 55 x 23 x 20mm Weight: 25gm Modular Construction Price: $A129.50 with crystal Electronics PO Box 580, Riverwood, NSW 2210. Ph/Fax (02) 9533 3517 For price list, write Acetronics 5/32 Seton Rd, Moorebank 2170 or email acetronics<at>acetronics.com.au Phone (02) 9600 6832 www.acetronics.com.au FOUR WAY Power Board with Spike Protection: Ex Olympic, $10 plus $15 P&P (Buy 5 and no P&P). Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. ALLEN KEY SPECIALS: Metric Sets $9, Imperial Sets $9, Ex Olympic P&P $10. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. New New New email: youngbob<at>silvertone.com.au Website: www.silvertone.com.au Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. with full production. Tel (02) 9738 0330; Fax 9738 0334. rcsradio<at>cia.com.au; www.cia.com.au/rcsradio CCTV things Better-Prices Better-Range Cameras from $34 * PC Video & Audio Recording Dial In/Out S/W $99 * FREE things <at> www.allthings.com.au/free TELEPHONES: Ex British Aerospace, used but work. $15 each plus $15 P&P Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. INFRARED Acrylic: black to the human eye, transparent to CCTV camera that has IR capability, 3mm thick, 104mm x 52mm. $20 each plus $5 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. CABLE SPECIALS: Screened Multi Core, Under Ground, Ex British Aerospace, New On Reels, 50 Pair, 26 Pair, 15 Pair all with tight woven screen and drain wire, cores are multi stranded. $2 / metre drum lots. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Elec­tronics (02) 9586 4771. sesame777<at>optusnet.com.au; http:// members.tripod.com/~sesame_elec SCREW DRIVER SETS: Ex Olympic, Crescent Type $25 P&P $15. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. CCTV CAMERA HOUSINGS: IP 67 NATA Laboratory Certified, Designed In Australia, Made In Australia, by Australian Video Systems, TYPE CH 750, Brackets, Sun Shield, IP67 Conduit, Current the professionals choice! $240 plus GST + $15 P&P. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. continued on page 96 August 2002  95 NOW AVAILABLE FROM Advertising Index AC Electronics.............................87 www.siliconchip.com.au Project Reprints Limited Back Issues Acetronics....................................95 Allthings Sales & Services...........95 Altronics................................. 68-70 Av-Comm Pty Ltd....................91,95 If you’re looking for a project from ELECTRONICS AUSTRALIA, you’ll find it at SILICON CHIP! We can now offer reprints of all projects which have appeared in Electronics Australia, EAT, Electronics Today, ETI or Radio, TV & Hobbies. First search the EA website indexes for the project you want and then call, fax or email us with the details and your credit card details. Reprint cost is $8.80 per article (ie, 2-part projects cost $17.60). SILICON CHIP subscribers receive a 10% discount. We also have limited numbers of EA back issues and special publications. Call for details! Dick Smith Electronics........... 18-21 visit www.siliconchip.com.au or www.electronicsaustralia.com.au Hy-Q International........................91 Elan Audio....................................79 Emona..........................................57 Grantronics..................................94 Harbuch Electronics.....................81 Instant PCBs................................95 24 Volt To 12 Volt DC Converters: Designed and manufactured in Australia by Australian Video Systems Pty Ltd, 5 amp, switchmode, $85 plus GST. Current Product. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. PADLOCK SPECIALS: Ex Olympic, Boxed Lots of 10, $40 P&P $15. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. COMPONENTS CLEARANCE SALE & specials. Go to www.lazer.com.au ALARM SPECIALS: Ex Olympic, DSC PC 550 with manual, siren , 1 x PIR Key Pad, Transformer $150 P&P $20. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. WEATHER STATIONS: Windspeed & direction, inside temperature, outside temperature & windchill. Records highs & lows with time and date as they occur. Optional rainfall and PC interface. Used by Government Departments, farmers, pilots, and weather enthusiasts. Other models with barometric pressure, humidity, dew point, solar radiation, UV, leaf wetness, etc. Just phone, fax or write for our FREE catalogue and price list. Eco Watch phone: (03) 9761 7040; fax: (03) 9761 7050; Unit 5, 17 Southfork Drive, Kilsyth, Vic. 3137. ABN 63 006 399 480. ELECTRONICS GARAGE clearance: see http://members.ozemail.com. au/~smparkinson/forsale/ for details or phone 0412 715548 for details. All items are located in Kew, Melbourne. 96  Silicon Chip CCTV Acrylic Domes: Designed and manufactured in Australia by Australian Video Systems Pty Ltd, 150mm, 250mm, 275mm, 383mm. Masked, tinted, Infra Red, Clear or Dummy! Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. Jaycar ................................... 45-52 MEGAPHONES; TOA; BE HEARD! Ex Olympic $65 + GST P&P $15 Batteries Included, Shoulder Harness, used at Sydney Olympics 2000. Australian Video Systems Pty Ltd. Ph: (02) 9879 6782. Oatley Electronics......................IBC Audio, Video, S-Video and VGA cables distribution amps, switchers, adaptors, price lists at: www.questronix.com.au Quest Electronics.........................26 USB KITS: DDS-HF Generator, USB Compass, 4-channel Voltmeter, I/O Relay Card. Also Digital Oscilloscope and Temperature Loggers. www.ar.com. au/~softmark Silicon Chip Binders.....................32 KIT ASSEMBLY SC Electronics Testbench..........IFC NEVILLE WALKER KIT ASSEMBLY & REPAIR: • Australia wide service • Small production runs • Specialist “one-off” applications Phone Neville Walker (07) 3857 2752 Email: flashdog<at>optusnet.com.au Silvertone Electronics.............91,95 WANTED WANTED: OATLEY GERMAN PRINTERS OR PARTS. Good price paid. Can pick up in Melbourne or pay post from elsewhere. Please email: platypus<at>ains.net.au JED Microprocessors................5,91 MicroByte Electronics..................91 Microgram Computers...................3 MicroZed Computers...................91 Ozitronics.....................................95 Printed Electronics...................... 95 Procopy........................................91 RCS Radio..............................91,95 RF Probes....................................26 Silicon Chip Bookshop........... 92-93 SC EFI Tech Special................OBC SC Computer Omnibus................79 Eco Watch....................................96 Soundlabs Group.........................91 VAF Research.........................55,91 Wiltronics.................13,56,65,77,91 _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: RCS Radio Pty Ltd. Phone (02) 9738 0330. Fax (02) 9738 0334. www.siliconchip.com.au (NEW) COMMUNICATIONS SPEAKERS: High quality NOKIA brand speakers with 1.5M cable and 3.5mm plug swivel bracket and mounting screws etc. Ideal for mobile use. $6 ea or 3 for $15 **NEW KITS**NEW KITS** 2.4Ghz 4 CHANNEL VIDEO AND STEREO AUDIO TRANSMITTER AND RECEIVER KITS & ANTENNA PLANS. SOUND CARD INTERFACE: These simple and easy to build kits are ideal or AS featured in this magazine. experimentation for radio LAN or amateur TV. Requires Turn your PC into an oscilloscope with this kit. We will 12VDC. MINI 2.4GHz VIDEO supply the complete kit including project case, knobs, TRANSMITTER MODULE: label, PCB-all onboard 15 x 15 x 5mm. This is the smallest 2.4 GHz components Plug Pack transmitter we have seen. Requires 5Vdc and connectors. and will transmit up to 100M with a 30mm Software is free to do wire antenna. Mini module + Pre-built receiver Around $25 download from the net. (K171C +K171A) $169 Available late August. STEREO AUDIO Send E-mail Please, VIDEO don't ring TRANSMITTER / BRAND NEW 250VA TOROIDAL TRANSFORMERS : 2 X 120V primary, 2 X 9V secondary Weighs 4Kg. No mounting hardware available. $25 ea. (NEW) MULTI FUNCTION DIGITAL STORAGE LOGIC PROBE RECEIVER KIT: BATTERY CHARGER / This kit contains DISCHARGER: AS featured in this magazine. K171C & K171D New in original box with Turn your PC into a digital modules & inc. instructions. This unit was storage probe with this kit. PCBs & all ondesigned to charge NI-CD & We will supply the complete board parts. These NI-MH mobile phone batteries kit including project case, PCB's house voltage of 4.8V, 6.0V and 7.2V. knobs, label, PCB, all onboard Operates from 12-24V DC input. Features regulators & RCA connectors on the receiver only: components Plug Pack & include processor control & multi stage charge (K171B) $119 connectors. Software is free indicator. By changing the value of one resistor it can 2.4GHz STEREO AUDIO VIDEO TRANSMITTER to do download from the net. Around $40 charge higher voltages, although a higher voltage MODULE: Will transmit up to 100 metres with a 30mm Available late August. Send E-mail Please don't ring plugpack is required for 9.4V or higher. Includes cigarette wire antenna. Std. TX module + (K171C) RX module: STEPPER MOTOR DRIVER KIT: lighter lead, 12V / 1A DC plugpack & instructions for (K171D) $99 This kit is designed to drive 5 or 6 wire stepper motors and modifications for higher voltages. The unit has battery 2.4 GHz VIDEO TRANSMITTER ANTENNA PLANS : charging terminals but the user will have to make their Check our website for downloadable plans to build a is based on three common ICs & four Mosfets (IRFZ44). own adaptor to interface to a battery. The plugpack antenna made from a "PRINGLES" chip container to suit This controller operates in either free-standing mode or supplied alone is worth around $30 retail. Weight is 0.9kg. this kit. We tested one of these antennas fitted to the PC controlled. Operates from 8 to 35V DC. PCB This charger requires a small voltage across the battery receiver only, over a distance 500M we received great measures 72 x 42mm. Kit includes PCB and all on-board components. The software is not supplied but can be before it will start charging - therefore it won't be able to audio and video signal. downloaded from http://www.metalworking.com or start charging a completely flat battery. (ZA0100) $29 (NEW) DECOR COOLER BAGS: http://www.kellyware.com No case Brand new high quality large is supplied. Published in Decor brand 28 litre cooler (NEW) SONIC BRAND HEAD Silicon Chip Magazine bags in their original sealed CLEANING FLUID & TAPE: (May 2002) (K179) $24 plastic bags, leak proof, triple This cleaning kit contains Non-abrasive Mini stepper motor: layer insulation, durable head cleaning tape but most importantly (MS55) $7 each. Package ( Kit outer fabric, wipe clean waterit contains an acid free cleaning fluid plus stepper motor): (K179M) $29 proof inner liner, available in (15ml) (most likely ISOPROPYL blue or red, easily fold into a ALCOHOL) 4 for $2 ** BARGAIN ** flat compact shape these retail (NEW) for around $40: (ZC0120) $16 each (NEW) INDUSTRIAL COUNTER: HENGSTLER COLOUR PANASONIC \model# 0711100. Industrial counter with CHRISTMAS a 6 digit LED display, 2A SPDT relay LIGHTS contact output, needs a 12V DC power supply and a closed mechanical contact (80LIGHTS) or a saturated transistor to clock (Active Plug-pack not "low"). Battery included but may need supplied, changing: (ZC0116) $33 each EX-OLYMPIC $ 2 95 With camera In original (NEW) ZERO-CROSSING SOLID packaging STATE RELAY (SC842910): (may be shop Maximum switching current is 25A, soiled) $8 Maximum Switching voltage is REMOTE CONTROL 12-280V AC and Control Voltage TRANSMITTERS 90-240V AC. (RL7A) $25 (NEW) Zero-Crossing Solid State Relay (SC844910): Brand new Radio Shack two PANASONIC MONITOR / TV Maximum switching current is 40A, Maximum Switching channel crystal controlled Slightly Used TC-14S15A 34cm Colour / Audio /Video voltage is 12-280V AC and Control Voltage 90-240V AC. MULTI STD. Monitor system with an added bonus of built (RL7B) $33 27MHz transmitters with 2 3 in Television & with full function remote control in original (NEW) Zero-Crossing Solid State Relay (SC868110): position joystick, need 9V battery, boxes. As used buy the worlds athletes during the Maximum switching current is 95A, Maximum Switching style can differ from the pictured Olympics. The Easicon Menu features colourful icons for voltage is 24-520V AC and Control Voltage 5-30V DC. unit: $7 Ea. Or 2 for $10 greater ease when making settings & adjustments. (RL7C) $89 Choose among English, Chinese, Russian or Arabic for (NEW) Zero-Crossing Solid State Relay (SC869110): the on-screen prompts. RRP: $419. Features inc. A/V in & Maximum switching current is 125A, Maximum Switching We have more used test equipment coming all the out to cascade to other monitors etc. 34cm High Contrast voltage is 24-520V AC and Control Voltage 5-30V DC. time and we need to clear stock to make way for the Tinted Picture Tube Picture Improvement Circuitry, Check the following website for more information: next lot. The only way to make sure you don’t miss Channel Colour Set : High, Std. & Low, Picture Menu : http://www.celduc-relais.com/uk/biphase.asp> (RL7D) out is to subscribe to our bargain corner & receive Dynamic, Std, Soft, Two Colour Temp. : High, Low $100 advanced notice by E-Mail Easicon Menu, Child Lock, 2 AV Input (F+R) / 1 AV Just send us a blank E-Mail to... Output, Weight : 9.6kg, 358 H, 389 W, 380 D. WEIGHT (NEW) ALCATEL ESWA HEATING CABLE: 9.6 Kg. BUT WAIT... THERE IS MORE... You also get a Type TXXP 500V - 0.70 OHM/M - (2893). part b a r g a i n c o r n e r - s u b s c r i b e colour CMOS camera with audio & a suitable plug pack. No.(099956) or (0.20 ohm/m) part N0. (099957)This <at> o a t l e y e l e c t r o n i c s . c o m ALL FOR JUST $295. All you have to do is fit common extremely strong high quality cable is designed to be RCA connectors to the camera cables. embedded into concrete. Can be used for many applications, but is especially attractive to those who wish USED) LOW COST PRINTER: to lay into their concrete (when building) so that they can These serial interface printers are in have localised heating. Constructed of three 1 mm wires good condition & were made in at the centre and then wrapped with 4mm (diameter) of England. With ribbon installed. A black silicon, with a plastic sheath. Total width is ~5 mm. rugged printer & is useful for Point of Minimum purchase of 10 metres. $7 for 10M Sale applications. It is able to be used on a wide variety of hardware not POWER TRANSISTORS 2N3055... confined to a PC. Most equipment (ZB0340) $50 each New TO3 package metal cased power transistors, large with a std RS232 port is capable (limited quantity) but limited stock: $1.20Ea. or 10 for $8 of using this printer. MORE NEW STOCK CK O ST !!! W W NE NO IN www.oatleyelectronics.com Orders: Ph ( 02 ) 9584 3563, Fax 9584 3561, sales<at>oatleyelectronics.com, PO Box 89 Oatley NSW 2223 www.siliconchip.com.au August 2002  97 major cards with ph. & fax orders, Post & Pack typically $7 Prices subject to change without notice ACN 068 740 081 ABN18068 740 081 SC_AUG_02