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How To Fix Damaged Hifi Speakers SILICON CHIP NOVEMBER 1997 $5.50* NZ $6.50 INCL GST C I M A N Y D 'S A I L AUSTRA E N I Z A G A M S C ELECTRONI SERVICING - VINTAGE RADIO - COMPUTERS - SATELLITE TV - PROJECTS TO BUILD PRINT POST APPROVED - PP255003/01272 Full-range motor speed controller ISSN 1030-2662 Easy-to-build cable & wiring tester Programmable musical doorbell 11 November 1997  1 9 771030 266001 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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 Contents Vol.10, No.11; November 1997 FEATURES   4  Understanding Electric Lighting; Pt.1 This new series looks at the different types of lights available & describes how they work. In Pt.1, we look at the basic units & terms – by Julian Edgar   9  Microsoft’s Power Toys: Tweak Your PC’s Interface This handy collection of utilities from Microsoft lets you enhance your Windows 95 interface – by Greg Swain 14  Replacing Foam Speaker Surrounds You don’t have to throw away those expensive drivers when their foam roll surrounds perish. Here’s a simple fix to get them going again – by Bill Hendry Replacing Foam Loudspeaker Surrounds – Page 14 72  Making Old Ships Go Faster Novel marine propulsion system for refurbished container ships PROJECTS TO BUILD 18  Heavy Duty 10A 240VAC Motor Speed Controller This new speed controller can be used with power tools rated up to 10A & gives smooth control from zero to full speed – by John Clarke 40  Easy-To-Use Cable & Wiring Tester Compact device employs four LEDs to speedily indicate the health of a pair of wires. You can use it to test cables & wiring systems – by Leon Williams 54  A Regulated Supply For Darkroom Lamps Don’t let variations in the mains supply ruin your prints. This circuit will keep the enlarger lamp at a constant colour temperature – by Rick Walters 62  Build A Musical Doorbell It plays a sequence of nine notes each time someone presses your doorbell button. You program it to play the tune you want – by Bob Flynn Heavy Duty 10A Motor Speed Controller – Page 18 Easy-To-Use Cable & Wiring Tester – Page 40 SPECIAL COLUMNS 30  Serviceman’s Log From soap to Teletext – by the TV Serviceman 66  Radio Control How does a servo work? – by Bob Young 76  Vintage Radio The 4-valve Airzone superhet – by John Hill 80  Computer Bits Relocating your CD-ROM drive – by Jason Cole DEPARTMENTS   2  Publisher’s Letter  3 Mailbag 38  Circuit Notebook 53  Order Form 89  Ask Silicon Chip 91 Notes & Errata 95  Market Centre 96  Advertising Index Musical Doorbell – Page 62 November 1997  1 PUBLISHER'S LETTER Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 and maximum * Recommended price only. 2  Silicon Chip EMC regulations a disadvantage for Australia Over the last year or so there has been considerable angu­ish in the Australian electronics industry over the complexity and costs of complying with the new EMC standards. In essence, these EMC (Electromagnetic Compatibility) regulations appear to have been introduced with little consultation with industry. If there had been widespread consultation, the overwhelming reaction would have been that we don’t want or need these regulations. The real problem with these regulations is that they close­ly follow the European standards which appear to have been framed to make it as difficult as possible for countries outside Europe to get their products in. If Australia was a major exporter of electronic and elec­trical products to Europe there might be some point in adopting these standards but we’re not. And those Australian manufacturers who do export to Europe will automatically comply with European standards anyway. This is the same story as with the proposed reduction of mains voltage in Australia from 240VAC to 230VAC. We wrote about this in the April and May 1994. That will still happen by the way but there will be no benefit to Australia, only costs. What’s in the new EMC regulations for Australian consumers? As far as we can see, very little. All electrical and electronic products being sold in Australia now must comply with the new standards and that means that they will either be dearer than they otherwise would have been or they will be withdrawn from sale, to avoid the costs of compliance. In the meantime, big and small Australian companies, whether they are exporting or not, still must bear the costs of compliance. There is also some anecdotal evidence that imported pro­ducts which supposedly do comply with the standards actually produce quite high levels of interference. However, it seems that the bureaucrats are more interested in checking the paperwork to see that products have been approved than whether approved pro­ducts actually produce interference. That stands to reason, doesn’t it? Their thinking would be, “If it’s approved, it must be OK”. By the way, I am all for EMC regulations but we don’t need the draconian regulations we have now. And nor, interestingly enough, does the USA. They have not moved to meet European stan­dards and why should they? They have their own set of regulations set by the FCC and other bodies and they are quite adequate. And so were our previous standards but they were not enforced. I believe that ultimately the whole process of EMC enforce­ment is in danger of falling into a heap. Unless the Spectrum Management Authority, now merged into Australian Communications Authority, has the staff to actually check that approved products radiate low levels of interference or are not subject to interference, then there is not much point in having the regulations in the first place. In fact, it is highly likely that the ACA does not have enough staff to even check that all the electronic and electrical products being sold in Australia actually are backed with the paperwork to show they comply. To do so, they will need to audit each and every business in Australia involved in importing, distribution or retailing. That’s an enormous task. The big problem for Australia in all this is that there are not enough organisations or individuals in Australia who are willing to speak out against these initiatives when they are first mooted. We spoke out against the initiative to reduce the 240VAC mains voltage but the response was a big yawn. Well, Australia will pay dearly, just as we will for these EMC regulations. If you want to find out more about EMC you can check it out on the Internet at http//www.aca.gov.au Leo Simpson MAILBAG Upgrading a 486 I recently had the experience of installing AMD 5x86-133 CPUs in two 486 motherboards, one a Chic­ ony brand, the other a Biostar with a UMC chipset, neither of which was designed with a 586 CPU in mind. The AMD 5x86-133 CPU can be made to work in a motherboard not specifically designed for it by jumpering it as per an AMD DX4-100 “plus” or “enhanced” CPU; ie one with power management functions. Jumpering it as a plain AMD or Intel DX4-100 will not work. Choose a 3.45V supply voltage and a 33MHz CPU clock. At this point the BIOS will identify the CPU as an AMD DX4 running at 100MHz. For the CPU to run at its rated 133MHz, a “clock multiplier” jumper must be set. Look for a jumper whose function is “jumper open = 3x clock, jumper closed = 2x clock”. A Biostar manual describes this jumper as “DX/DX4 open, DX2 closed”. A DX4-100 CPU can run (internally) at either 3x or 2x the motherboard clock. Normally the bus clock is set to 33MHz, and the CPU clock = 3x 33 = 99MHz. I suppose one could use a bus clock of 50MHz and CPU clock = 2x 50 = 100MHz. I suspect that the latter combination would result in faster I/O (eg, faster graphics and disc I/O) at the same internal CPU speed. I haven’t tried this, though. A 5x86-133 CPU uses a clock multiplier of either 3x or 4x. In this case, the jumper described above has a slightly different meaning. An open jumper selects a 3x clock as before (99MHz), but a closed jumper selects a 4x clock (133MHz). This jumper may take some finding. For those with a multimeter, one side of this jumper is connected to earth, the other to pin R-17 (CLKMUL) of the CPU. When correctly set, the BIOS sees the CPU as an AMD DX4 “plus” running at 4x 33 = 132 MHz. Be sure to enable write-back mode for the internal CPU cache (16K). I wonder if a system using a clock-doubled 486DX4-100 CPU on a 50MHz bus (assuming this were possible) would be faster than the same system using a 5x86-133 CPU on a 33MHz bus? What about a 586-133 running at 120MHz in clock tripled mode on a 40MHz bus? F. Zabkar, Barrack Heights, NSW. Video security sign has a drawback I have just read the Video Security article on page 62 of the September edition of SILICON CHIP. I feel that anyone contem­ plating using the sign on page 67 should consider the following scenario. Having just burgled your neighbour’s home, burglars about to burgle yours are confronted by this sign. Now they must burgle your home in order to retrieve the tape linking them with the neighbour’s burglary. If after ransacking your home they are unable to locate the tape, their options are limited, one being to torch your home in order to destroy the evidence. A safer solution for a low security site such as a home is a sign that reads: “This property is under VIDEO SURVEILLANCE with Off-Site Recording”. Any VCR used for recording should be well-hidden. If the power meter box is not secure, then a UPS (low cost computer type may be adequate) should be used to power the VCR, cameras, etc. Although probably unnecessary for a home but certainly of value for shop and business surveillance is a dummy VCR complete with tape placed in a prominent position. This tape may be easily taken by or handed over (under threat) to a burglar. K. Forknall, Northlands, WA. Backing up is important Referring to your editorial in the July 1997 issue of SILI­CON CHIP, I think you hit the nail right on the head. Many people don’t even think of or are even told about backups. This could be due to the view of sales people assuming that the purchaser will only use the machine for trivial or unimport­ ant tasks; eg, playing games. In many cases the machine will work OK for a long period of time but one day it may play up. What’s the next step? – try to find what’s caused the corruption and get a backup disc out and restore the corrupted files. If you don’t have a backup the data is unrecoverable and you’ll never see it again. Even with disc repair utilities such as Norton’s this will not guarantee to get any or all of your data back! I recently purchased a backup tape drive for my machine to complement an already numerous set of backup floppy discs. Desp­ite this, a couple of months ago I lost a file due to corruption and ended up recreating it from a printout because the corruption had unknowingly been saved and both machine and floppy had the corrupted file. You can never be too cautious! S. Sidoti, Lilyfield, NSW. Burst charging does the job I have been evaluating Nicad Battery Charger designs lately with the intention of building two permanent installations for domestic use. Two articles from SILICON CHIP have been brought to my attention, these being in the May 1994 and October 1995 is­sues. Both these featured projects using the Philips TEA 1100 IC which, if I have read and understood both articles correctly, rely on “Delta V” voltage detection to terminate normal charge mode and progress to trickle charge. The reason I mention these two articles is that I have also read the excellent article by Horst Reuter from Smart FastCharg­ers in the January 1996 issue of SILICON CHIP. In his article he mentions that he is of the opinion that once the charge voltage peak is reached and the voltage levels out, any nicad battery still charging in the normal charge mode and which reaches the point where the voltage starts to drop (the “Delta V” continued on page 7 November 1997  3 Pt.1: Units and Terms Electric Lighting In this new series on electric lighting, we will look at the different types of lights available and describe how they work. But let’s first examine the basic units and terms. By JULIAN EDGAR Looking around as you travel at night through city streets, you can’t help but wonder at all the different lights. Bright yellow street lights, white fluorescent tubes positioned behind glowing signs, small intensely bright lights used in shop dis­plays – they all use different technology to turn night into day. Like most tech4  Silicon Chip nology, we tend to take the presence of electric light for granted – until the power goes off or a blown lamp makes our car a one-eyed monster. But did you know that the output of a fluorescent tube decreases at lower temperatures, or that more infrared energy than visible light is emitted by the humble light bulb? That the pressure of the gas inside a light bulb changes as it gets hot­ter? That it’s not just your imagination that objects change colour under different lights? That excess lighting in offices places a large load on the airconditioning equipment? That not cleaning lights can effectively decrease their output by 25% after a few years? In this series we will answer questions like these and also examine all of the common types of electric lighting used. There’s certainly a lot more to it than initially meets the eye and that includes answering an apparently simple question – how do we describe the amount of light produced by a lamp? Luminous intensity Luminous intensity is measured in Candela (cd) in both the imperial and metric systems. The origins of the unit can be directly traced back to candles made of whale fat. In 1860, a unit of luminous intensity known as the “candle” was established. This used, as the base standard, a candle made from a specific quantity of sperm whale fat burning at a speci­fied rate. Later gas flames also used this unit, with a then-typical gas flame having a luminous intensity of 16 candles. Early incandescent lights had a luminous intensity of a similar magnitude! In 1909, the candle was redefined in terms of a group of carbon filament incandescent lamps having precise filament dimen­ sions and operating with a defined voltage. By 1937, the defini­tion included a blackbody radiator which at the temperature of solidification of platinum had a luminous intensity of 60 candles per square centimetre. In 1948, the unit was renamed the candela and in 1979 its definition was changed to involve the radiation of light of a single wavelength at a precise power. As an example of a real world use, luminous intensity is used to describe the amount of light emitted in selected direc­ tions from lamps and fittings. Fig.1 shows an example of the intensity distribution of a 150 watt PAR (“Portaflood”) bulb. Fig.1: the luminous intensity distribution of a PAR-type 150W bulb. Luminous intensity is measured in candelas. Here it can be seen that directly in line with the beam axis, the bulb has an intensity of 12,000 candelas, falling off to only 1,000 candelas at 20° to the tightly-focused beam. (Murdoch, B. Illumi­nation Engineering). Fig.2: the eye is most sensitive to light with a wavelength of 550 nanometres (yellow-green light). At wavelengths either side of this, the sensitivity falls rapidly. At 450nm (violet), the sensitivity of the eye has typically dropped by over 96%! This change in sensitivity must be taken into account when measuring luminous flux. (Murdoch, B. Illumination Engineering). Luminous flux Luminous flux is measured in lumens, which is abbreviated to lm. Just as there is an electrical power input measured in watts, there is a “light power” output measured in lumens. The reason that “light power” is not measured in watts is because the response of the eye to different colours needs to be taken into account. The part of the radiation spectrum that we can see lies between wavelengths of 380 nanometres (blue) and 780 nanometres (red). While an instrument designed to measure radiation power will read the same at all wavelengths (assuming equal power across the spectrum), the eye has varying sensitivity to differ­ ent wavelengths. A close light source producing one watt of radiation at 555nm (yellow-green light) gives a very strong sensation of light because the eye is very sensitive to this wavelength. However, at wavelengths either side of 555nm, the sensitivity of the eye rapidly decreases, as shown in Fig.2. This means that expressing the light power output in watts is not helpful – if the light power is at a wavelength that we can barely see, then even kilowatts of light power may be useless for practical illumination. Instead, to obtain a measure of the luminous flux of a light, the radiant flux (measured in watts) is weighted by the frequency response curve of the eye. This means that if the light emits a great deal of radiation at 555nm, its lumen rating will be high. Conversely, if the light radiates at a wavelength to which the eye has a low sensitivity, it will have a low lu- minous flux value even if the radiated power is quite high. The lumen is therefore a unit based on human response and cannot be defined as a purely physical quantity, as can the watt. Interestingly, individual response curves often differ from the typical curve shown in Fig.2. That means that my 5 lumens may not be quite the same as your 5 lumens! Luminous flux measurements are widely used in lighting. A typical application is in expressing luminous efficacy, a meas­urement of how much light output there is for a given electrical power input. It is expressed in lumens/watt, abbreviated to lm/W. A typical incandescent light bulb November 1997  5 Above: the reduction in illuminance that occurs at increasing distances from directly beneath a lamp can be seen in this photo. This pattern of illum­inance can be plotted on an isolux diagram such as the one shown in Fig.4. compared with the traditional white painted backing plates. Illuminance has a luminous efficacy of 8-17 lm/W, while a low pressure sodium discharge lamp (the yellow ones used for highway lighting) has a vastly better effic­acy of 100-200 lm/W. If you were paying the electrical bill (and ultimately you are), which one would you use to light a highway? Another use of luminous flux is to Location express the actual light output of a luminaire (light fittings are known as luminaires in lighting parlance.) The total light output of the luminaire divided by the light output of the lamp gives the Light Output Ratio (LOR). The LOR of a fluorescent luminaire can be increased by up to 40% by the use of high quality reflectors, Maintained Illuminance (Lux) Instrument assembly 1500 Garment manufacture - sewing 750 School classroom 500 Cinema auditorium 50 Kitchen work areas 500 Hospital ward at night Operating theatre (local lighting) 1 100,000 Toilets 100 Supermarket 750 Fig.3: the CIE recommended illuminance levels for various activi­ties. (Philips Lighting Manual). 6  Silicon Chip Illuminance is expressed in lux, abbreviated to lx and is a measurement of how many lumens there are per square metre. There are recommended values of maintained illuminance for various activities, with Fig.3 showing some International Commission on Illumination (CIE) suggestions. Because of the drop in illu­minance as lamps age and luminaires get dirty, “maintained” in this context refers to the actual illuminance obtained with regular maintenance. On a flat outside surface where there are few reflections, it is quite easy to plot lines of equal illuminance. These lines are called isolux contours and a typical isolux diagram is shown in Fig.4. Basically, it is a diagram of the “pool of light” found beneath outside street lights – the one so beloved of writers of detective fiction! Such a diagram is useful when designing the lighting system of a car park, for example. The pattern of illu­minance shown by the diagram can be clearly seen in the photo­graph of the McDonald’s car park (above), Mailbag : ctd from p.3 Fig.4: an isolux diagram shows lines of equal illuminance, as would be found beneath a single light illuminating a car park, for example. (Pritchard, D. Lighting). detection point) has already entered the “over charge” mode. This, he points out, is not desirable for long battery life. He also mentions that it is desirable to utilise some form of alternate charge and discharge, especially if one is charging at the fast charge rate; ie 1C. I must mention at this stage that I have had one of Horst Reuter’s fast chargers and have found that it has done wonders for cells and batteries which had become marginal for a variety of reasons and it is fast reaching the point where it has just about paid for itself. I would be very interested to hear your views on the points which I have raised. I do look forward to reading the many interesting articles which appear in SILICON CHIP each month. M. Fraer, New Zealand. Comment: the licensed technology used by Smart FastChargers does appear to be effective. What more can we say? TENS electrodes not easy to obtain The colour distribution of a light source can be directly exam­ined with a spectrometer, which uses a prism to split the light into its different colours. which is illuminated mainly by a single light source. Colour temperature An object at any temperature will emit radiation. At low temperatures, the wavelengths of the radiation are mostly in the infrared region and so cannot be seen. However, if the tempera­ture of the object is increased, that object (eg, a piece of steel) will start to glow (ie, it begins emitting radiation that can be seen). The temperature of the object can be measured in degrees Kelvin (K), which is its temperature in degrees Celsius plus 273.15. The radiation properties of a hypothetical so-called black body radiator mean that it will be red at 1000°K, I am writing to let you know of an experience that I have just had with your TENS kit, that you might want to pass on to your readers. I had a friend who wanted one made so I decided to purchase a kitset. The kitsets themselves are very hard to find. I had to ring around several Dick Smith Electronics stores before locating one. The kit itself is great. It is the electrodes that are the real problem. Your article states that the electrodes are available from most chemists. Unfortunately, that may not be entirely accurate. I tried over eight chemists in Sydney, none of whom had stocked them for at least six months. Only one chemist was able to provide details of where to get them. They can be bought from Masters Medical, 8 Palmer St, Parramatta, NSW 2150. Phone 02 9890 1711. They are about $15-$20 for a pair. J. Cowan, No address supplied. November 1997  7 colour temper­ atures, the perceived colour of different light sources varies relatively little. Daylight has a colour temperature of about 5500°K, while an incandescent light bulb is around 2800°K. Fluores­cent tubes are available with colour temperatures ranging from 2900-6500°K. Unlike the eye, however, camera film is very much affected by differing colour temperatures. Photos taken under 1500°K light­ ing will have a red cast, under 3000°K a yellowish cast and under 12,000°K a blue cast. Colour rendering Photos taken under different lighting clearly show the effect of varying colour temperature. This photo has a strong yellow cast and was taken under incandescent tungsten halogen lighting with a colour temperature of about 3000°K. Fig.5: (1) low pressure sodium lamp; (2) incandescent lamp; (3) high pressure mercury vapour lamp. The appearance of colours when illuminated by a lamp depends on the distribution of the wave­lengths of light emitted by the lamp. Under a sodium lamp, every­thing is yellow! (Pritchard, D. Lighting). yellow near 3000°K, white near 5000°K, blueish white near 10,000°K and pale blue near 30,000°K. This means that the colour of a light source can be specified in terms of its colour temperature. This is the temperature 8  Silicon Chip to which a blackbody radiator would have to be heated to match the colour of the light source. Electric lights have widely varying colour temperatures but because your eyes are very tolerant of differing Colour rendering refers to the appearance of an object when it is illuminated by the light source under consideration. Light sources of similar colour temperature can have completely differ­ e nt wavelength compositions and so can provide great differences in colour rendering. Fig.5 shows the spectra (mix of wavelengths) of various lamps. The low pressure sodium lamp (1) produces light at just a single wavelength and so the lamp reveals only that colour. Line 2 shows the spectrum of a incandescent lamp, which has an output that covers all wavelengths fairly evenly – although there is an emphasis on red. A high pressure mercury vapour lamp (3) has a mixture of some ‘lines’ (high outputs at specific wavelengths) mixed with a continuous background spectrum and a band of energy at the red end. Of these light sources, the incandescent lamp gives the best colour rendering, followed by the high pressure mercury lamp and then the low pressure sodium lamp. Colour rendering is measured on a colour rendering index (expressed as Ra) scale of 1-100, where 100 provides the best colour rendering. The Ra scale for a lamp is based on the illumi­ nated appearance of 14 different colour chips. These colours include saturated red, yellow, green and blue; and colours ap­proximating the (white) human skin and green foliage. The scale is based on the average colour shift that occurs when changing from the test to the reference illuminant. The colour rendering of incandescent lights is very good at 99Ra, while fluorescent lights vary from 85-90Ra. That’s all for this month. Next month, we will look at incandescent SC lamps. Tweak your PC’s interface with Microsoft’s PowerToys This handy collection of utilities from Microsoft lets you enhance your Windows 95 interface – By Greg Swain. If you don’t already have them, the Microsoft PowerToys provide some handy user interface enhancements for Windows 95. These enhancements were developed by Microsoft’s Win95 team and you can download them from the Microsoft web site. If you don’t have access to the Internet, the Power­Toys are often included on the CD-ROMs that come with some computer magazines. Tweak UI is perhaps the handiest utility in the PowerToys range. Tweak UI stands for “tweak user interface” and when you install the PowerToys, the Tweak UI icon is automatically in­stalled into the Control Panel group. To quote Microsoft, “Tweak UI is a handy control panel for ‘Type A’ personalities”. Among other things, it can be used to quickly change the boot parameters, including whether or not to automatically start the graphic user interface or stop at the DOS prompt. You can also select an option to automatically display the boot menu and you can choose the length of time that the boot menu is displayed (Fig.2). Fig.2: TweakUI makes it easy to alter the boot parameters. This machine is set to show the boot menu for 10 seconds before booting into Windows. Fig.3: this menu lets you change (or delete) the shortcut arrow and can eliminate that pesky “Shortcut to” preface when you create a shortcut. Fig.1: the TweakUI icon is installed in the Control Panel group when you install the PowerToys. This saves you from having to manually edit the MSDOS.SYS file. Tweak UI also lets you change the appearance of your short­cuts (you can have a smaller arrow or even get rid of the arrow completely) and can eliminate that pesky “Shortcut to” phrase when you create a shortcut (Fig.3). It also lets you set mouse sensitivi­ty and speed and can prevent drive icons from appearing in My Computer. Another handy PowerToy is the “Cabfile” viewer. For those unfamiliar with the term, the Windows 95 program files are stored on the CD-ROM (or floppies) as compressed files in “cabs”. A “cab” consists of a number of compressed files and, on the CDROM, is generally about 2.0Mb in size. Normally, you can’t use the Explorer to see inside these cab files but with this Power­Toy, Explorer treats the cab files as though they were ordinary folders so that you can see the individual files. You can then extract a file from a cab folder simply by dragging it to another folder. There’s lots more to Tweak UI and also quite a few other useful Power­ Toys, including QuickRes for on-the-fly changes to screen settings (resolution and bit depth) and FlexiCD for con­ trolling audio CDs. The best way to learn about them is to get hold of a copy SC and install it on your system. November 1997  9 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.dse.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.dse.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.dse.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.dse.com.au Replacing foam speaker surrounds . . . just follow this step-by-step procedure Perished foam speaker surrounds are a common problem for hifi enthusiasts. Unfortunately, replacement drivers are often unavailable or are expensive. Here’s a simple step-by-step fix to get things going again. By BILL HENDRY This article is in response to a letter published on page 91 of the August 1997 issue, concerning the replacement of per­ished foam loudspeaker surrounds. Although the answer includes appropriate references to the perils of DIY repairs, the process certainly isn’t as onerous or as mysterious as one might infer. I’ve been repairing speakers suffering from this complaint for six or 14  Silicon Chip seven years now. Although it’s not my professional area, I’ve developed techniques that return the speakers – from 4-inch midranges to 15-inch woofers – to virtually as-new condi­ tion. None has failed in this time and owners I’ve spoken to since have reported normal operation. As has now become common know­ l edge, foam-type surrounds, even if “tropic proofed,” deteriorate quite quickly. Some become a soggy mess in just two years, particularly in my area, Mackay, on the Central Queensland coast. The most durable compounds ap­pear to be rubber (1215 years) and impregnated cloth, the latter used on some good Australian speakers. My technique is well suited to the dedicated home enthu­ siast. It’s inexpensive but does require patience and dexterity. It can be used with all cone materials and the assembly appears to retain its fundamental free-air resonance. However, the four to six hours of work required may not be justified for low-end, plug-in replacement drivers. The step-by-step procedure is as follows: Step 1: check the speaker care- fully to ascertain that the cone is in good condition and that the voice-coil is intact. You should also check that there’s nothing in the air-gap to impede normal movement and that the rear suspension “spider” is in good shape. There’s no need to cut away the dust cap – in fact, doing so could damage the (now unstable) voice-coil assembly. Step 2: clean the chassis and cone edge thoroughly, remov­ing all traces of the perished material and any glue. Some models may have dress rings or segments which can be carefully removed and later reinstalled if necessary (although they are usually only cosmetic). I use a hobby knife to scrape away the material but I haven’t experimented with sol­vents. On a pair of AR 25s that I recently refurbished, the ring of surround material remaining on the edge of the cardboard cone was best removed by carefully pulling it away from the surface towards the edge. This has the effect of also removing a thin layer from the cone material which can later be stabilised by the application of a painted layer of PVA glue (eg, Aquad­ here). Other situations may require the careful scraping away of decomposed residue. Inspect the underside of the cone edge to confirm a stable surface that’s necessary for the next step. All traces of the perished material have been removed from the chassis and cone edge of this driver, which is now ready to accept its new felt roll surround. Note the four dress ring segments which have been removed intact – these can later be replaced if desired. Step 3:: obtain an appropriate piece of (black) felt from a haberdashery shop. You may not be able to specify density or thickness but the operation doesn’t appear to be grade specific. At this point, determine whether you’d prefer to mount the felt surround replacement on the underside or the upper (visible) side of the cone. (On my last job, a 6-inch Bose Studiocraft midrange, the rear of the chassis was fully enclosed, necessitating attach­ment of the surround to the upper side). Generally, underside mounting results in a more presentable appearance, allowing for a very neat “dressing” of the join. The felt rings have been glued to the cones of the drivers shown here but not yet to the chassis. Note that, in each case, the felt has been glued to the underside of the cone but it can also be glued to the top of the cone if necessary. overlap around the edge of the cone when the felt is in place. The outside of the felt should overlap the edge of the speaker chassis by about 10mm (this will be trimmed later). You can use a template such as a saucepan lid or a bowl to mark out the felt, which can then be cut using a hobby knife or a pair of scissors. Step 4: (delete if you choose Step Step 5: run a bead of PVA glue 7). If the edge of the felt is going to be visible (ie; attached to the upper side of the cone), cut a hole in the felt that’s 10-12mm less than the diameter of the cone. This will provide a 5-6mm around the edge of the cone and smooth it neatly to produce a band 5-6mm wide. This done, do the same to the inside edge of the felt ring out to the point of overlap. Step 6: place the felt ring central- ly onto the cone and press it carefully onto the surface. Work the leading edge so that the felt appears “chamfered” at the line of contact with the cone. Paper wedges (eg, loosely crumpled tissues) placed between the cone and the basket will help to keep the cone stable during this procedure. Step 7: (delete if you chose Step 4): if the edge of the felt is to be attached on the underside, cut out a circle in the felt using a compass, a dressmaker’s white pencil and November 1997  15 not allow runs to dribble down the sup­ports towards the spider during this procedure. Step 11: this step is critical. Gen- Once the felt has been glued to the chassis, it can be trimmed by running a sharp hobby knife around the inside of the lip. scissors. Neatness isn’t so important in this case, and you won’t need to spend time hunting for a template of the right dimension. Apply glue to the appropriate edges as described in Step 5 above. It can be frustrating working through the rear of the chassis, so an artist’s brush can be a help. Step 8: carefully manoeuvre the felt ring over the cone and bring the mating surfaces together. Now, working from the back, make sure that the felt ring is centrally located and work the contact area to optimise adhesion. 16  Silicon Chip Step 9: run a thin bead of glue around the cone at its junction with the felt ring. At this stage leave the PVA to dry completely. Step 10: lay the speaker on its magnet. You now have the inner edge of the felt ring attached to the cone and the outer edge overlapping the chassis by about 10mm. Lift the skirt of the felt ring to expose the flat area on the outer edge of the basket and, using a small brush, paint a generous film of glue onto the entire flat surface. Do tly place an upturned glass centrally on the cone (over the dustcap), with sufficient weight to depress the cone to its maximum backward excursion position. This will be indicated by either the former contacting the back of the magnet assembly or the rear suspension spider being stretched to its limit (be careful not to deform it perma­nently, though). Carefully wiggle the glass up and down and from side to side to make absolutely sure that the voice-coil is centred in the air-gap. It may be necessary to “play” with the assembly to become aware of the tolerances. Step 12: gently move your hands around the edge of the speaker, working the felt evenly onto the glued surface. This done, use a blunt table knife to create a sharp corner in the felt at the point where the lip is flanged forward. Step 13: remove the glass and check that the assembly moves freely Below: the lefthand speaker in this photo has been finished, except for the mounting holes and the optional dress ring segments. Note the “roll” in the felt between the edge of the cone and where the felt attaches to the frame. to its natural rest position. In so doing, the felt will bulge or dome to form the roll necessary for normal cone travel. Allow the glue to dry. Step 14: run a hobby knife around the inside of the lip to create a neat invisible edge at the flange. This done, gently lift the cone by applying equal equal pressure to both sides and check that the whole assembly is axially free but radially secure; ie, the cone should move backwards and forwards easily but should not move from side to side. Step 15: make mounting holes in the felt to align with the holes in the chassis flange. This can be neatly achieved by first gently pushing a hot soldering iron tip right through the felt from the rear at each flange hole position to create a pilot hole. The holes can then be finished by pushing the soldering iron tip through from the front. Step 16: at this stage, it’s time to decide whether you want to replace the dress ring segments. The finished speaker looks quite acceptable without them and, in any case, they may have been damaged during removal. If you do decide to fit them, glue them onto the surface of the felt using a thin layer of PVA but don’t let the glue contact the roll. Turn the speaker face down so that its weight is on the dress segments during drying. Step 17: apply a generous quantity of grease to the felt. Do not use engine grease; instead, use a high-temperature, waterproof compound (eg, Bel-Ray marine grade). This is applied to the felt surround with a fairly stiff-bristled brush, so that the grease is worked well into the fibres (do the whole surround if there’s no dress ring). This has the necessary effect of clogging the air-gaps between the fibres but allows the surround to retain its flexibility. It also discourag­es creatures from making a meal of the felt. If some deformation of the roll occurs during this process, reform it by gently running the handle end of the brush around the underside of the felt. The result is an attractive, fairly New Foam Surrounds For AR Speakers On page 91 in the August 1997 issue, G. E. of Armidale, NSW asks about new foam surrounds for AR speakers. I cannot entirely agree with your answer. I have had more than 20 speakers fitted with new surrounds, some over 20 years old, and in no instance has there ever been a problem with the cones themselves. More than half my repaired units have been AR (I am a huge fan) and I still own and use five AR pairs. The best pair are 24-year-old AR3a’s which are quite superb and compare easily with anything costing up to $5000. In New Zealand, a cone surround job for a pair of 12-inch drivers costs about $NZ120 (approximately $A100), while new sur­rounds for 8-inch drivers cost about $NZ85 ($A70). For that cost, the units are inspected (cones, suspension and chassis), fitted with new surrounds and the voice coil as- uniform surface that looks quite professional. The speaker is now ready for use. It’s a good idea to feed a very low-frequency sinewave (say 10-20Hz) at low voltage into the voice-coil to check that the cone moves freely before the system is reassembled and played at high volume levels. Final notes A few final points are worth noting: (1) You may feel inclined to paint the entire surface of the (cardboard) cone with PVA to: (a) freshen the appearance, (b) stiffen it, and (c) minimise “grease-creep” across the cone. I don’t normally do this to a diaphragm in good condition, in case it significantly alters the cone’s mass. (2) You might consider coating the surround of a new speaker with the abovementioned grease, even if it has been tropic-proofed. I did this with a 10-inch Etone subwoofer foam surround and there’s been little change in its appearance after seven years. (3) Although I’ve never noticed a problem, you might feel more confident using a non-water based glue, thereby obviating poten­tial corrosion of the metal parts. During the devel- sembly checked for cor­rect alignment. They are also fitted with a new spider suspension and dust cap if necessary, tested and guaranteed. This is excel­ lent value and the situation is probably similar in Australia. AR have always been masters of acoustic suspension speak­ ers, so cabinet size, cone size and air tightness are critical. Your correspondent should stress this to the repairer. Of course, if he can buy new drivers at reasonable cost, then that is a simpler solution. Depending on age, correct drivers may be difficult to obtain. The Australian agent for AR is WC Wedderspoon Pty Ltd, 3 Ford St, Greenacre, NSW 2190. Phone (02) 9642 3993. If your correspondent requires any help or would like to communicate with me I would be happy to oblige, as an AR enthu­siast. J. Calkin, Takapuna, NZ. opmental stages of this technique, I used contact glue but there’s no room for error – the mating surfaces have to be positioned exactly. (4) Often the gasket that seals the speaker to the baffle board is damaged, disintegrated or missing. To overcome this problem, I use the Bel-Ray grease to form a continuous ridge at the edge of the baffle-board cutout. The refitted speaker then provides an automatic seal which, if necessary, can easily be broken if the driver needs to be removed. Finally, please note that although the technique described here generally gives good results, it doesn’t restore a driver to its exact original specifications. That’s because the compliance of the felt used to make the repair will differ from the compliance of the original foam surround. The method of attachment will also have some effect on the free-air resonance of the repaired speak­ er, although its sensitivity will probably be much the same as before. In the end, it’s up to you. If you don’t want to fork out big dollars for new drivers, then you’ve got nothing to loose and you will probably be quite happy with the end result. SC November 1997  17 Heavy duty 10A 240VAC Motor Speed Controller 18  Silicon Chip T HIS NEW SPEED CONTROLLER can be used with power tools rated up to 10 amps and will give smooth control from zero to full speed. Use it to control the speed of electric drills, routers, circular saws, lawn edgers and other appliances with universal brush-type motors. Design by JOHN CLARKE Our last Drill Speed Controller, published in September & November 1992, has been extremely popular and has been used in a host of applications, some of them far beyond what we ever envis­aged. But while it is still a valid design, it does have shortcomings. The first of these is that the maximum speed attainable from the motor is considerably reduced. So for an electric drill which normally runs at say 3000 rpm, the maximum speed might be reduced to around 2200 rpm. This is inevitable with an SCR (silicon controlled rectifier) since the controller circuit effectively half-wave rectifies the 240VAC mains sinewave to give a maximum output voltage of around 160 volts RMS. Result: reduced speed and power capability. The second drawback has to do with low speed control. While the 1992 circuit does allow your drill or other appliance to run at quite low speeds, the result leaves much to be desired. There isn’t much torque available and the speed regulation is poor. This means that if you’re operating your drill at a low speed and you put a reasonable load on it, its speed will drop right away or it may stall completely. Worse, the motor will tend to “cog”. This is caused by erratic firing of the SCR (Triac) so that the motor gets inter­mittent bursts of power. An electric drill that is cogging badly is virtually useless and the only cure is to increase the speed setting which rather defeats the purpose if you want to operate at low speed. The new SILICON CHIP Motor Speed Controller overcomes these drawbacks. The design does away with traditional phase control circuitry and uses switchmode power supply techniques to produce an outstanding controller for universal brush-type motors. By the way, before we go further we should point out that virtually all power tools and appliances use so-called universal motors. These are series wound motors with brushes. We’ll have more to say on this point later in the article. Why use a speed control anyway? Well, why not? Most power tools will do a better job if they have a speed control. For example, electric drills should be slowed down when using larger drill bits; they make a cleaner cut. Similarly, it is useful to be able Features •  Control from zero to maximum speed •  Good speed regulation under load •  Smooth low speed operation •  Freedom from cogging •  Can power appliances rated up to 2400W •  Overcurrent limiting •  Fuse protection •  Earthed diecast case •  Interference suppression included What Motors Can Be Controlled? We’ve noted elsewhere in this article that virtually all power tools and appliances use so-called universal motors. These are series wound motors with brushes. But how do you make sure that your power tool or appliance is a universal motor and not an induction motor. Induction motors must not be used with this speed controller. In many power tools you can easily identify that the motor has brushes and a commutator – you see sparking from the brushes and that settles the matter. But if you can’t see the brushes, you can also get a clue from the nameplate or the in­struction booklet. OK, so how do you identify an induction motor? Most induc­tion motors used in domestic appliances will be 2-pole or 4-pole and always operate at a fixed speed which is typically 2850 rpm for a 2-pole or 1440 rpm for a 4-pole unit. The speed will on the name plate. Bench grinders typically use 2-pole induction motors. November 1997  19 ciples. Having said that, we had better explain what we mean by phase control before we can illustrate the benefits of the new circuitry. Phase control Fig.1: these waveforms illustrate the operation of a typical phase-controlled SCR when a motor is driven at a slow speed. The full sinewave is the 50Hz AC mains voltage, while the chopped waveform is the voltage applied to the motor. Its RMS value is 147V. Fig.2: chopped waveforms from an SCR speed control at high and low settings. At the high setting (lower trace) the motor has 164V applied to it while at the low setting (upper trace) the motor has 144V applied. If the motor is to run at full speed, it would need to be fed with both the positive and negative halfcycles of the 50Hz mains waveform. to slow down routers, jigsaws and even circular saws when cutting some materials, particularly plastics. The same applies to sanding and polishing tools and even electric 20  Silicon Chip whipper snippers are less likely to snap their lines when slowed down. As mentioned above, the new design does not use phase con­trolled circuitry but uses switchmode prin- Phase control refers to a method of triggering a Triac or SCR (silicon controlled rectifier) at various times during each half-cycle of the 240VAC mains waveform. If the Triac is trig­ gered early in each half-cycle, the power applied to the load is high and if it is triggered late in each half-cycle, the power level is low. The term “phase control” comes about because the timing of the trigger pulses is varied with respect to the phase of the mains sinewave. The oscilloscope waveform of Fig.1 shows the chopped wave­form from a phase controlled SCR when a motor is driven at a slow speed. The full sinewave is the 50Hz AC mains voltage, while the chopped waveform is the voltage applied to the motor. Its RMS value is 147V. Fig.2 shows the chopped waveform from an SCR speed control at high and low settings. At the high setting (lower trace) the motor has 164V applied to it while at the low setting (upper trace) the motor has 144V applied. Note that these examples show only the positive half of the mains waveform being used, as is the normal case with a phase controlled SCR circuit. If the motor is to run at full speed, it would need to be fed with both the positive and negative half-cycles of the 50Hz mains waveform. Normally this is not possible with an SCR circuit and while it is possible with a Triac, it is difficult to achieve without a complex circuit. (We should note that full-wave control circuits are used in some washing machines using the Plessey TDA1085 power control IC. This uses tachometric feedback for a wide range of speeds from a series-wound motor.) Another big problem with conventional phase controlled circuits is that the trigger pulse applied to the Triac or SCR is very short and if this corresponds with the time when the brushes hit an open-circuit portion of the commutator, no current will flow and consequently, the motor will miss out on a whole cycle of the mains waveform. This problem is more critical at low speed settings and is one of the reasons for the “cogging” behaviour referred to earlier. Speed regulation In theory, most phase controlled SCR speed control circuits incorporate a form of feedback which is designed to maintain the speed of the motor under load. When the motor is loaded, the back EMF (electromotive force) produced by the motor drops and the circuit compensates by triggering the SCR earlier in the mains cycle. This helps to drive the motor at the original speed. In practice though, the back-EMF generated by most series motors when the SCR is not conducting is low or nonexistent or it is produced too late after the end of each half-cycle to have a worthwhile effect on the circuit triggering in the next half-cycle. So while the theory says good motor speed regulation should be obtained, in practice, it doesn’t happen in many cases. Pulse width modulation The new SILICON CHIP speed control circuit uses Pulse Width Modulation (PWM) and a different feedback method for speed regu­lation which solves the above problems associated with phase control. Fig.3 and Fig.4 shows the voltage waveforms applied to the motor at high and low speed settings. What happens is that we rectify the mains voltage and then chop it up with a high voltage IGBT (Insulated Gate Bipolar Transistor) at a switching rate of about 1.2kHz. For the high speed setting the pulses applied to the motor are relatively wide (Fig.3) while at the low speed setting, the pulses are very narrow (Fig.4). Note that there are 12 pulses during each and every mains half-cycle so that the motor does not miss out on large blocks of current because of erratic triggering. This means that the motor operates very smoothly over the whole of its speed range. The speed regulation does not rely upon motor back-EMF. Instead it monitors the current through the motor and adjusts the pulse width to maintain the motor speed. Block diagram Fig.5 shows the basic circuit arrangement of the Motor Speed Controller. The 240VAC input waveform is fed through a filter and full wave Fig.3 (top) and Fig.4 (above) show the voltage waveforms applied to the motor at high and low speed settings. The rectified mains voltage is chopped up with a high voltage IGBT (Insulated Gate Bipolar Transistor) at a switching rate of about 1.2kHz. For the high speed setting the pulses applied to the motor are relatively wide (Fig.3) while at the low speed setting, the pulses are very narrow (Fig.4). Note that there are 12 pulses during each and every mains half-cycle so that the motor does not miss out on large blocks of current because of erratic triggering. This means that the motor operates very smoothly over the whole of its speed range. rectified. The resulting positive-going waveform is fed to one side of the motor, while the other motor terminal is switched on and off via transistor Q1. A triangle (ramp) waveform is generated using IC1b and this is ap- plied to comparator IC1a where it is compared with the voltage level from VR1, the speed control potentiometer. If the speed voltage is high relative to the triangle wave­ form, then the comparator will produce wide pulses November 1997  21 Fig.5: the basic circuit arrangement of the Motor Speed Controll­er. The 240VAC input is full-wave rectified and fed to one side of the motor, while the other motor terminal is switched on and off via IGBT Q1. Q1 is controlled by a conventional PWM circuit involving IC1, IC2 & IC3. at its output; a lower speed voltage will reduce the pulse width. This can be seen in the scope waveforms of Fig.6. The triangle waveform at the top is compared to the speed voltage, the horizontal voltage intersecting the triangle wave. The resulting lower trace is the pulse width modulation signal from the comparator. The comparator output is fed to the gate driver (IC2) which then drives the high voltage IGBT (Q1). Diode D1 is a fast recovery diode to conduct the motor current when Q1 is switched off while a snubber across Q1 prev­ents excessive voltage excursions on Q1. Resistor R1 monitors the current flow through the motor when Q1 is on and the resulting voltage generated is sampled by IC4, whenever Q1 is on. IC3a amplifies the voltage from R1 and applies it to the speed pot. Thus an increase in motor current, as the motor slows down, leads to an increase in the output from IC3a to increase the speed setting from VR1 and this results in an increase in the voltage applied to the motor. Yes, this is a positive feedback system and too much positive feedback is not good so the amount of feedback is fairly critical to optimum circuit operation. IC3b also monitors the voltage produced from R1 via IC4 and compares it against a reference voltage. If the voltage from R1 exceeds the reference threshold, IC3b’s output goes low and reduces the speed pot voltage via diode D2. This reduces the voltage applied to the motor and provides current limiting. Circuit description Fig.6: These waveforms show the interaction of the triangle waveform and the speed voltage. The triangle waveform at the top is compared to the speed voltage, the horizontal voltage inter­secting the triangle wave. The resulting lower trace is the pulse width modulation signal from the comparator. The comparator output is fed to the gate driver IC2 which then drives the high voltage IGBT. 22  Silicon Chip The circuit for the Motor Speed Controller is shown in Fig.7. It comprises four ICs, several diodes, resistors and capacitors plus the high voltage IGBT, Q1. IC1b is the triangle waveform generator and it is essen­tially an oscillator whereby the .018µF capacitor at pin 5 is charged and discharged via the 33kΩ resistor connected to the output at pin 12. The triangle or ramp waveform across the ca­pacitor has an amplitude of about 5V peak-to-peak. Comparator IC1a compares the triangle waveform at pin 10 with the speed voltage at pin 9, as set by VR1. VR1 is the centre portion of a voltage divider with a 1kΩ resistor connect­ing Fig.7: the circuit uses a 32A 1200V avalanche-protected IGBT (insulated gate bipolar transistor) as the switching element to the load. It is switched at 1.2kHz; ie, 12 times in each half-cycle of the 50Hz 240VAC mains supply. to the +15V rail and an 8.2kΩ resistor to 0V. The speed voltage from VR1 is filtered with a 47µF capacitor to prevent any sudden changes in level and this voltage is monitored by the inverting input (pin 9) of IC1a via a 1kΩ resistor. The 1MΩ resistor between pin 9 and the pin 7 output provides positive feed­back to give a small amount of hysteresis in the comparator action. This is to prevent “hunting” in the comparator output when changing levels. The pin 7 output of IC1a drives buffers IC2a and IC2e. IC2a drives three paralleled buffers, IC2b, 2c & 2d, which provide a high current capability to charge and discharge the gate of the high voltage IGBT Q1. The gate is protected from excessive Warning! (1) The entire circuit of this motor speed controller floats at 240VAC and is potentially lethal. Do not build it unless you know exactly what you are doing. DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS PLUGGED INTO A MAINS OUTLET and do not operate the circuit outside its metal case. (2) This circuit is not suitable for induction motors or shaded pole motors used in fans – see panel. drive voltage with ZD2, a 15V zener diode. Normally the circuit should have no way of providing excessive gate drive however we blew a number of devices during the development process when attempting to monitor gate drive levels with an oscilloscope. So the 15V zener has been included for insurance. Three circuit features combine to ensure that the IGBT can safely switch high levels of current through the motor load. First, there is a snubber network comprising an 82Ω resistor and .01µF capacitor connected in series across the IGBT’s source and drain and second, there is the fast recovery diode D1. Third, there is a 275VAC metal oxide varistor (MOV) connected across the output of the bridge rectifier. These measures combine to damp any spike voltages which would otherwise occur every time the IGBT switched off. Finally, the specified IGBT is a November 1997  23 The lid of the case must be independently earthed by running an extra lead from a solder lug to the earth terminal on the mains socket – see Fig.8. Fit the earth solder lug mounting screws with washers and locknuts so that they cannot possibly come adrift. Siemens BUP213 1200V 32A avalanche-protected device. We do not recommend substitution of lower rated devices. During the development of this project we ended up with quite a graveyard of IGBTs and Mosfets which should have been up to the task but were found wanting. Current monitoring R1 is a used to monitor the current flow through the motor and IGBT Q1. The voltage developed across R1 is fed through a low pass filter consisting of a 10kΩ resistor and .001µF capacitor to one side of a 4066 analog switch, IC4. This is the sample and hold cir24  Silicon Chip cuit and IC4 is switched on to sample the voltage across R1 each time the IGBT is switched on. Hence, IC4’s gate signal comes from comparator IC1a and is buffered by IC2e. The sampled signal from R1 is held in the .047µF capacitor at pin 4 of IC4. The sampled voltage from IC4 is fed to two op amps, IC3a & IC3b. IC3a amplifies the voltage by about 53 when VR1 is set to maximum and 3.2 when set to minimum. IC3a acts to vary the DC level fed to comparator IC1a from VR1 and thereby compensates for speed variations in the motor. IC3b acts as a comparator, comparing the sampled voltage from R1 with a reference voltage at its pin 3. If the current through R1 is excessive, the output of IC3b goes low and pulls pin 9 of IC1a low via diode D2 and a 470Ω resistor. This has the effect of greatly reducing the motor drive voltage. Power for the circuit is derived directly from the 240VAC mains. Fuse F1 protects against shorts while the .01µF capacitor in conjunction with L1 & L2 prevents switching artefacts from the IGBT and motor being radiated by the mains wiring. BR1 is a bridge rectifier with a 600V 35A rating. BR1 provides the circuit with the positive full-wave rectified mains voltage and this is lightly filtered using a 0.1µF 250VAC capaci­tor. Power for the low voltage circuitry is derived via two series 4.7kΩ 5W resistors, diode D3 and the 15V zener diode ZD1. A 22µF capacitor across Table 1: Capacitor Codes ❏ ❏ ❏ ❏ ❏ ❏ Value IEC Code EIA Code 0.1µF   100n   104 .047µF   47n  473 .018µF   18n  183 .01µF   10n  103 .001µF   1n0  102 the 15V zener smooths the DC while diode D3 prevents the capacitor from discharging when the mains voltage falls to below 15V every half cycle. The result is a regulated 15V supply. Construction The Motor Speed Controller is constructed on a PC board which is coded 10311971 and measures 112 x 144mm. It is housed in a diecast case measuring 171 x 121 x 55mm. The PC board has circular cutouts to suit the case. By the way, we do not recom­mend a sheet metal case for this project. Since all the circuitry inside is at 240VAC mains potential, it is important that the case is strong and rigid. The complete wiring diagram is shown in Fig.8. THE EARTHING DETAILS OF THE CASE ARE MOST IMPORTANT SINCE THE IGBT, FAST RECOVERY DIODE D1 AND POTENTIOMETER VR1 ARE ALL AT MAINS POTENTIAL YET ARE ATTACHED TO THE CASE. If the mica washers or the insulation of the potentiometer were to break down, the case would be live (ie, at 240VAC) if it was not properly earthed. For this reason, the case lid must also be sepa­rately earthed, as shown in Fig.8 because otherwise the lid could be live if the potentiometer broke down and the lid was not actually attached to the case. Begin construction by checking the PC board against the published pattern in Fig.11. There should not be any shorts or breaks between tracks. If there are, repair these as necessary. If the cutouts in the sides of the PC board have not been made, they should be done before any components are soldered on. A large semicircular cutout is required on both the long sides of the board, as well as notches to clear the vertical slot channels in the sides of the case. Also you will need to round off the corners of the board. Make sure Parts List 1 PC board, code 10311971, 112 x 144mm 1 metal diecast case, 171 x 121 x 55mm 1 front panel label, 100 x 70mm 1 Neosid iron powdered core, 17742-22 (L1,L2) 1 GPO mains power point (Clipsal NO.16N or equivalent) 1 10A mains cord and plug 1 cordgrip grommet 3 solder lugs 1 10kΩ linear potentiometer (VR1) 1 500kΩ horizontal trimpot (VR2) 1 knob 2 3AG (or 2AG) PC mount fuse clips 1 10A 3AG fast blow fuse (or 2AG), (F1) 2 3mm x 10mm screws, nuts & star washers 4 4mm x 15mm screws, nuts and star washers plus two locknuts 7 small cable ties 2 TO-218 mica insulating washers OR 1 SIL-PAD 400 washer 2 TO-220 mica insulating washers OR 1 SIL-PAD 400 washer 2 insulating bushes 1 500mm length of blue 10A mains wire 1 150mm length of brown 10A mains wire 1 1.5m length of 1mm enamelled copper wire 1 1m length of 0.8mm enamelled copper wire 1 140mm length of 0.8mm tinned copper wire 1 26mm length of 15mm ID heatshrink tubing 9 PC stakes the PC board fits into the case before starting assembly. You can start the board assembly by inserting the PC stakes and the links now and then the resistors, using the accompanying table for the colour codes. The two 5W resistors should be in­serted so that they stand several millimetres above the PC board to allow cooling since each will be dissipating about 2.7W and will run hot. When inserting diode D2 and the zeners, take care with their orientation and be sure to place each type in its correct place. Install the ICs, taking Semiconductors 1 LM319 dual comparator (IC1) 1 4050 hex CMOS buffers (IC2) 1 LM358 dual op amp (IC3) 1 4066 quad CMOS analog switch (IC4) 1 Siemens BUP213 32A 1200V IGBT (Q1) 1 STTA3006P SOD93 30A 600V fast recovery diode (D1) 1 1N914, 1N4148 signal diode (D2) 1 1N4004 1A 400V diode (D3) 1 15V 1W zener diodes (ZD1) 1 15V 400mW zener diode (ZD2) 1 36MB60A 35A 600V bridge rectifier (BR1) 1 S14K275 275VAC metal oxide varistor (MOV) Capacitors 1 47µF 16VW PC electrolytic 1 22µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 2 0.1µF 63V MKT polyester 1 0.1µF 250VAC X2 class MKT polyester 1 .047µF 63V MKT polyester 1 .018µF 63V MKT polyester 2 .01µF 250VAC X2 class MKT polyester 1 .001µF 63V MKT polyester Resistors (0.25W, 1%) 1 2.2MΩ 2 4.7kΩ 1 1MΩ 2 4.7kΩ 5W 1 470kΩ 1W 2 1kΩ 4 100kΩ 1 470Ω 1 33kΩ 1 390Ω 1 22kΩ 1 82Ω 1W 4 10kΩ 1 10Ω 1 8.2kΩ care to orient them as shown on Fig.8. D1 and Q1 are oriented with the metal flange towards the edge of the PC board and are located as high as possible with their leads extending about 1mm below the PC board. The capacitors can be installed next. The accompanying capacitor table shows the various codes which may be used to indicate the capacitance values. The electrolytic capacitors must be oriented with the correct polarity. L1 & L2 are wound on a single Neosid toroidal core as shown in Fig.9. Make sure that there are an equal November 1997  25 Fig.8: the complete wiring diagram of the Motor Speed Controller. Note that the case and lid must be separately earthed, as shown here. Note also that all parts of the circuit, including the terminals of VR1, float at 240VAC. number of turns on each winding and that they are wound in the directions as shown. Insert the wire ends into the PC board holes and secure the toroid with two cable ties. The wire ends can be soldered to the PC board using a hot soldering iron to strip the self-fluxing insulation on the wire. 26  Silicon Chip The current monitoring resistor is made from a 1m length of 0.8mm enamelled copper wire which is wound onto a 10mm former (3/8"). This may be a drill bit, pen or a wooden dowel. Wind on about 26 turns then remove the former and secure the coil with insulation tape so that each winding touches the adjacent one. Bend the wire ends outward and place a 26mm length of heatshrink tubing over the coil and shrink it down with a hot air gun. Re-bend the wire ends and secure in place into the PC board mount­ing holes. The bridge rectifier (BR1) is attached Fig.10: mounting details for the IGBT (Q1) and the fast recovery diode (D1). Fig.9: winding details for the input filter choke. Note that L1 and L2 are wound so that their flux cancels in the toroid core. must be bent so that the metal flange of each device is in contact with the case sides. Remove the PC board and drill out these holes plus holes for the cordgrip grommet and the earth lug screw. Deburr the holes for D1 and Q1 must be deburred with a larger drill to prevent punch-through of the insulating washers. Attach the PC board to the case with the supplied screws (yes, they do come with the case) and secure D1 and Q1 to the case with a screw, nut, insulating washer and insulating bush. The arrangement for this is shown in Fig.10. If you use mica washers apply a smear of heatsink compound to the mating surfaces before assembly and use two for each device, to prevent flash-over. Silicone heatsink washers do not require heat­sink compound and if the 3.5kV-rated SIL-PAD 400 types are used, one is enough for each device. to the PC board with the (-) and adjacent AC terminal sitting over and soldered to PC stakes. The other AC terminal and the positive (+) terminal are wired to the PC board pins using 10A 250VAC-rated hookup wire. Fuse F1 is mounted in fuse clips which attach to the PC board as shown. We have catered for both 2AG and 3AG sizes. Clip the fuse into the clips first, insert them into the PC board and solder in position. Mounting the hardware Insert the PC board into the case and mark the mounting hole positions for diode D1, IGBT Q1 and bridge rectifier BR1. Note that the leads for D1 and Q1 After mounting, check that the metal tabs of the devices are indeed isolated from the case by measuring the resistance with a multi­meter. The bridge rectifier (BR1) is secured to the case with a 4mm screw, nut and star washer. It does not require an insulating washer between its body and the case. Mark out and drill the case lid for the mains socket and potentiometer. Attach the mains socket with the 4mm screws and nuts and secure the pot after the stick-on front panel label has been affixed. Solder the Active and Neutral wires of the power cord to the stakes on the PC board and secure the cord with a cordgrip grommet. The earth connection on the mains socket should be run to a solder lug using green/yellow mains wire. Similarly, solder the earth wire from Table 2: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  1 ❏  4 ❏  1 ❏  1 ❏  4 ❏  1 ❏  2 ❏  2 ❏  1 ❏  1 ❏  1 ❏  1 ❏  1 Value 2.2MΩ 1MΩ 470kΩ 100kΩ 33kΩ 22kΩ 10kΩ 8.2kΩ 4.7kΩ 1kΩ 470Ω 390Ω 82Ω 10Ω 1Ω 4-Band Code (1%) red red green brown brown black green brown yellow violet yellow brown brown black yellow brown orange orange orange brown red red orange brown black red orange brown grey red red brown yellow violet red brown brown black red brown yellow violet brown brown orange white brown brown grey red black black brown black black brown brown black gold gold 5-Band Code (1%) red red black yellow brown brown black black yellow brown yellow violet black orange brown brown black black orange brown orange orange black red brown red red black red brown black black red brown grey red black brown brown yellow violet black brown brown brown black black brown brown yellow violet black black brown orange white black black brown n/a brown black black gold brown brown black black silver brown November 1997  27 the mains cord to a solder lug and connect both solder lugs to the case using a screw, nut and star washer. An additional locknut should then be fitted so that the earth lugs can not possibly come loose. Note that the case lid should also be earthed, via a third solder lug, with a wire connected to the earth terminal on the mains socket. Wire up the potentiometer using 250VAC-rated hookup wire. Secure the wiring with cable ties. Testing Fig.11: check your PC board by comparing it with this full-size etching pattern before installing any of the parts. MOTOR SPEED CONTROLLER WARNING! Internal circuit floats at 240VAC SLOW FAST SUITABLE FOR SERIES MOTORS RATED UP TO 10A <at> 240VAC OR 2400W. Fig.12: this full-size front panel artwork can be used as a drilling template for the front-panel speed control. 28  Silicon Chip Before you power up the circuit, set trimpot VR2 to the mid-position – this setting should give good performance with most motors. This done, check all of your wiring very carefully against the circuit of Fig.7 and the wiring dia­ gram of Fig.8. Use your multimeter to check that there is no leakage between the Active and Neutral wires of the power cord and the case. Also check that the case and lid are connected to the earth pin of the power cord. The lid should be screwed to the case. The safest and best way to test the circuit operation is to connect a load. This may be an ordinary incandescent lamp with a rating of between (say) 40W and 100W. Apply power and check that you can vary the brightness of the lamp from zero up to full brilliance. If that checks out OK, connect up a drill or other power tool and check that you can vary its speed over the full range. If so, your project is complete but some motors may require adjustment of VR2 for best speed regulation. In practice, if VR2 is adjusted too far anticlockwise, the motor will tend to be overcompensated when loaded and will actually speed up. It may even hunt back and forth between a fast and slow speed. Back off the adjustment for VR2 for best results. This must be done on a trial and error basis, with the plug removed from the mains outlet before each adjustment. Replace the lid before reapplying power. If you are using a drill for example, at fairly low speed, the motor should not slow down by much as you put a reasonable load on it. Troubleshooting If the speed controller did not work when you applied power, it’s time to don your troubleshooting hat. Note that all of the circuit is connected to the 240VAC mains supply Silicon Chip Binders REAL VALUE AT $11.95 PLUS P &P These binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. The holes in the side of the case for D1 and Q1 must be deburred using an oversize drill to prevent punch-through of the insulating washers. After the devices have been mounted, use your multimeter (set to a low ohms range) to confirm that their metal tabs are indeed correctly isolated from the case. should be able to vary the voltage at pin 7 of IC1a by winding the speed pot up and down. The same effect should be observed at the gate of the IGBT. If you have an oscilloscope you should be able to observe the waveforms shown in Fig.6. Should you wish to monitor any of the other waveforms il­lustrated in this article, the circuit will need to be powered from 240VAC again and will then be completely live. If you connect an oscilloscope under these conditions, you cannot con­nect the earth terminal of the probe to any part of the circuit. In fact, the only really safe way to monitor waveforms in the circuit when it is powered is to use an oscilloscope with fully floating differential inputs. Two final points: if you are using this controller with a high power tool such as a large circular saw or 2HP router, it will not give the same kick when starting. Because of the current limiting, the motor will take a few seconds to come up to full speed. To use the appliance at full speed, it is better not connect the Speed Controller at all. Finally, note that this unit is not suitable for use with devices such as 2400W heaters which will draw 10A SC continuously. ★  80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $A3 p&p in Australia; or $A11.95 plus $A8 p&p in NZ & PNG. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form  and is potentially lethal. This includes the tabs of D1 and Q1, the terminals of potentiometer VR1 and all other parts. Do not touch any part of the circuit when it is plugged into a mains outlet. Always remove the plug from the mains outlet before touching any part of the circuit. If you wish to work on or measure voltages in any part of the circuit, connect it via an isolating trans­former. Failing that, you can at least check that there is ap­proximately 15V present in the circuit by connecting a multimeter across the zener diode ZD1. If you wish to check the circuit operation in detail, you should power it from a low voltage power supply set to provide 14V. At 15V, you run the risk of blowing zener diode ZD1. Note that the unit must not be plugged into 240VAC if the low voltage part of the circuit is to be separately powered. Assuming that you are powering the unit from a 14V power supply, you can use your multimeter to check that +14V is present at pin 11 of IC1, pin 1 of IC2, pin 8 of IC3 and pin 14 of IC4. You can also check the circuit operation by measuring the average DC levels around the circuit. For example, if the circuit is working correctly, you ★  Hold up to 14 issues Enclosed is my cheque/money order for $________ or please debit my ❏ Bankcard  ❏  Visa   ❏ Mastercard Card No: ________________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ November 1997  29 SERVICEMAN'S LOG From soap to Teletext It takes all sorts of people and their problems to make a serviceman’s world. For one of my customers, a misbehaving VCR assumed the proportions of a major life threatening emergency. One won­ders how they would react to the real thing. Mrs Proby likes – no, that word is too soft – loves, even adores, her soaps (situation comedies for the uninitiated). She lives for them; is addicted to them. In between watching and recording them, she somehow makes time for her family. But, inevitably, disaster struck; the video recorder wouldn’t work. It was a real emergency and it had to be fixed immediately. The recorder was a Sony SLVX50AS and, on examination, the 30  Silicon Chip problem was worse than she could possibly have imagined – the recorder had had the audacity to actually chew up some of her beloved tapes and they were ruined! I did my best to calm her and tried to sound sincere as I pointed out that worse things can happen in life. But she was inconsolable. Eventually, I managed to convince her that I would do my best to fix it as soon as possible. Afraid of what might happen if I didn’t apply immediate first aid, I rushed it into the operating theatre and opened it. She had given me her most precious tape to examine but unfor­tunately it was in a real mess and beyond repair. Fortunately, I did have a manual for the machine and I have reproduced a couple of diagrams from it, particularly the section “VHS Mechanical Adjustment Manual ll”, which should help the reader follow the story. Seized bearing The reason for the damage became obvious when a dummy tape was run. The RVS guide (No.8) – the reverse search arm – had almost seized on its bearing and wouldn’t free the tape to re­tract into its housing on eject. I hoped I could free this with­ out removing it, as this would save time because it would not then require re- Fig.1: portion of the deck around the capstan/pinch roller area in the Sony SLV-X50AS VCR. The RSV guide is partially obscured and shown dotted. alignment. And I was in luck – after a squirt of CRC and some wiggling, the arm moved freely. After cleaning up any excess CRC with alcohol, the tape went in and out perfectly. I cleaned the heads and tape path and initially thought that that was the end of it; that I had scored an easy one. But I was wrong. On tape play there was considerable curl on the lower edge of the tape, just after the pinch roller, and the tape was being mutilated as it went into the cassette. I removed the pinch roller, cleaned and roughened the rub­ber, and tried again. It was still no good so I fitted a new pinch roller assembly. This improved the situation enormously but the tape was still curling a little on the RVS guide. There was nothing for it – I would have to remove, clean and realign this guide according to the instructions on page 25 of the manual. The gist of this adjustment is the need to move both the RVS guide (No.8) and guide No.7 up or down until the tape tracks with both guides and with the nearby ACE head assembly. This adjustment is by means of height adjuster nuts, one for each guide. The No.7 guide appeared to be correct, so I concentrated on the RVS guide. Unfortunately, the only adjustment setting which brought the alignment close to correct was to have the nut screwed hard down. This not only failed to cure the problem but it Fig.2: side view of the RVS (reverse search) arm, showing its relationship to guide roller No.7 in the Sony SLV-X50AS. Note the adjuster nuts. meant that, on eject, the arm jammed on a gear just below it. There was only one thing for it. I had to replace the arm – but where could I get one in a hurry? This part does not usually need to be replaced. After ringing around, I found a colleague who had one and would let me have it in view of the emergency. I dashed into the ambulance and shot around to pick up the donor organ. Secondhand shop My colleague, Jim, is the senior technician at a busy sec­ ondhand shop. He spends his days growing white hair from refur­bishing TV sets and video recorders, which they purchase from all and sundry. He was in a talkative mood when I arrived and was muttering rude words about two cranky TV sets which had defied all his efforts to repair them. It had got to the stage where he was fed up and was planning to send them off to auction. A cursory glance show­ ed them to be low-cost generic TV sets made in China but both were modern and looked good. I stu­pidly volunteered to have a look at them if he would care to stick them in the back of the “ambulance”. I then shot back to the operating theatre and transplanted the new part into the Sony vide recorder. This time, realigning the arm produced the desired effect, the tape now running through the guides perfectly. I carefully examined the old arm and pinch roller but could not detect any imperfections. The arm, which is a chrome-plated steel rod embed­ded in a diecast aluminium block, didn’t look the slightest degree bent or distorted. However, it only needs a minute change to cause problems like these. Anyway, I pronounced that the patient would live and so undoubtedly would Mrs Proby. But I did issue her with a prescrip­tion of sorts, advising her to purchase some new tapes and ditch the old ones (if she can bring November 1997  31 Serviceman’s Log – continued herself to do it). Anyway, she thanked me most profusely; I thought she was going to call me Doctor but she didn’t. Jim’s TV sets When things were quieter, I decided to have a go at Jim’s TV sets. The first was a 51cm Palsonic 5138 with remote control, twin speakers, and Fast Text – the Palsonic version of Teletext. The fault ticket read, “No picture, no sound”. Jim thought that the fault lay in the Teletext section but he didn’t have a circuit diagram. So my first step was to order a manual from N & G Enterprises. The second set was an Aiko Super­ vision VST 60, model 2801, as sold by Cumberland TV. This was also dead and so I ordered a manual for this as well. A week later I received photocopied circuits for both mod­els. The Palsonic circuit looked very similar to a Chinese chas­sis used in Teac and some other sets. At switch on, the LED on the front 32  Silicon Chip panel lit up and a telltale 15,625kHz whistle suggested that the line output stage was working. The remote control had no effect but turning up the screen control (G2) gave a full-screen faint blank raster. With no sound or picture, I started by measuring the vari­ous voltage rails. Most are not marked on the circuit but in any case, they seemed a little high. Shrunk heatshrink on an electro­lytic capacitor in the power supply (C514, 47µF/50V) pointed to the likely culprit and I immediate replaced it to prevent further damage. I was now getting 130V, 20V, 16V and 8V on the various rails which seemed reasonable but there was no 16V on pin 3 of connector XT01 on the main board, which mates with XT01 on the Teletext board. This feeds NT01, a 12V IC regulator on the Tele­text board. Following the 16V rail back from pin 1 of XT101 on the main board, I ran into a 10Ω 1W resistor (R536) which is not marked on the circuit diagram. This resistor was open circuit. Replacing it restored the sound but there was still no picture or onscreen displays. The voltages on the CRT socket didn’t provide much help, except that the cathodes were higher than expected. I reached for the CRO probe, planning to trace the lumi­nance (Y) signal through to the picture tube. However, this was not as straightforward as in most sets. Whereas most Teletext decoders are designed as plug-in optional extras and the set will work without them, this set diverts the colour difference and luminance signals through the decoder. Also, the circuit is somewhat misleading as to what plug fits into what socket. I was able to trace the Y signal into the Teletext card at connector XT03 (pin 1) but nothing seemed to be coming out on XT02; or rather, on a Y pin adjacent to XT02. From there, the path goes to X401 on the CRT board. This confirmed that the decoder could not be bypassed and so would have to be fixed. However, I didn’t fancy rushing in and replacing suspect ICs, particularly as they cost, on average, about $30 each. It was time for some help. I phoned N & G Enterprises and was informed that the decoder gave very few problems – the only thing they were aware of was the 27MHz crystal. I checked this and could find nothing wrong but I removed a lot of black gunk that had been coated over its pins. A red herring By now, this line of attack was looking like a red herring. I went back to the CRT socket and followed up on my earlier observation that the tube cathode voltages appeared to be high. It didn’t take long to discover that there was no voltage on the bases of video drive transistors V402, V405 and V409, although voltage was present on their emitters. The base bias is supplied via R403, a 120kΩ resistor connected to the 180V rail, and this resistor was very high. Replacing it restored the picture com­pletely. So problem solved but one part of this investigation has me puzzled. When checking with the CRO, I could swear I saw lumi­nance and colour difference signals going into the Teletext board but nothing coming out to the CRT board. But now there were Fig.3: the CRT board in the Palsonic 5138, showing the three video driver transistors, V402, V405 and V409. signals coming out of the board after I had replaced R403. I can see no correlation between the failure of R403 and the lack of signal into X401 from the decoder. I even removed R403 and re­checked with the CRO and there was still plenty of signal. And by what process had I concluded that it was the Tele­text card that was faulty? Well, in hindsight, I cannot explain it. Jim had voiced the thought that it might be in the Teletext section, so perhaps I had allowed this to lead me astray. The remote control needed a new rubber keypad and after alignment, the picture was good and all “Fast Text” functions checked out OK. Destructive overload Jim’s second set filled me with dread when I found that the power supply had suffered a severe destructive overload and a wide range of parts had been affected. Some parts, apparently damaged, had been replaced, some had been partially disconnected, and some were missing altogether. I refitted the disconnected parts and replaced all the missing ones. Then I disconnected it from the main chassis, substituted a 100W globe as a load on the 136V rail, and removed fuse FU502 in this line. I applied 240V AC power via a 200W globe and a Variac, connected meters everywhere and switched on. The 200W globe lit to full brilliance immediately, indicating a short circuit. Switching transistor V501 and diode VD504 in the bridge were both short circuit and were replaced. When I switched it on again, the power supply started to squeal as I turned the Variac up to around 100V and was obviously under stress. There was no output. I examined the circuit very closely. All the small electro­lytics had been replaced and so had R509, a 56kΩ resistor coming off the positive rail from the bridge. All the high value resis­ tors measured OK. The small transistors had all been replaced with substitutes but even the discovery that transistor V503, part of a Darlington pair, was fitted the wrong way around didn’t solve the problem. With the CRO connected, the waveform on the collector of V501 consisted of a series of positive spikes, suggesting that the mark space ratio was indicating a heavy load. I didn’t twig to the significance of this immediately and put it down to the low input (100V) to which I had set the Variac. To cut a long story short, I replaced V504, C519, C521, V505, VD513 and many more parts around this area before the penny dropped. There was no ringing in the waveform indicating, on the one hand, that there were no shorted turns in the chopper trans­ former (T503) but that there was a short circuit somewhere across the secondary. All the diodes measured OK out of circuit but there was something wrong around diode VD518 and it didn’t take long to find that C525, a 470µF 200V electrolytic across pins 19 & 21 of T503, was short circuit. Replacing this and turning up the Variac restored everything. Now for the acid test – I reconnected the main chassis to the power supply, replaced fuse FU502 and switched on. Unfortunately, it still wouldn’t work. A quick check soon showed that there was 136V on the collector of V303, the horizon­tal output transistor, but nothing on the collector of V302 which drives it. The reason for this wasn’t hard to find – the primary winding of transformer T301, which couples these together, was open, probably due to corrosion from the black gunk all around it. Ordering and fitting a replacement transformer fixed the final problem and the set burst into life at last. Jim was pleas­antly surprised and I think only he fully appreciated the time I spent going up so many blind alleys before tracking down the various SC faults. November 1997  33 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 Silicon Chip Bookshop Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 383 pages, in hard cover at $55.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $75.00. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $55.00. Digital Audio & Compact Disc Technology Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $69.00. Power Electronics Handbook Components, Circuits & Applica­tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Surface Mount Technology By Rudolph Strauss. First pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $95.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. This just has to be the best refer­ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semi­-custom electronics & data communications. 63 chapters, soft cover at $125.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order  ❏ Bankcard  ❏ Visa Card  ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return 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. tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $55.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is a very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $49.95. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. NOW IN STOCK First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. ✓ Title o o o o o o o o o o Price Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A November 1997  37 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Single supply version of LM3876/LM3886 modules The LM3876 50W amplifier module published in March 1994 and the stereo 60W/ channel LM3886 amplifier module published in February 1995 have proved to be very popular and reliable. Howev­er, a number of readers restoring older amplifiers have asked about the possibility of producing single supply versions. The reason for this that most solid state commercial amplifiers produced before about 1980 used single rail amplifiers. The method for running any amplifier module of this sort from a single supply rail is to provide a voltage divider to produce a half-supply input bias, a lower impedance “half supply” reference for the normal amplifier input ground and a large electrolytic capacitor at the output to block the resulting half-DC supply from the loudspeaker. Square wave pulse generator Originally designed as part of a calibration circuit for EMI noise Changing the Neon Tube Modulator A number of readers have asked us how to modify the Neon Tube Modulator which was published in the May 1997 issue so that the bass notes actually cause the neon tube to light. This is the opposite modulation to the existing circuit. The simplest solution is to replace Q2, the BD140 control tran38  Silicon Chip The revised circuit shows the LM­ 3886 but the same circuit components can be used with the LM3876. A voltage divider con­sisting of 91kΩ and 100kΩ resistors provides a nominal “half supply” to bias the non-inverting input (pin 10) via a 75kΩ resistor. Also fed from this voltage divider is emitter follower Q1 which provides the ground reference at pin 7. While it may be possible to install the additional input bias components on the PC board, the 4700µF output coupling capacitor will probably need to be mounted off the board. SILICON CHIP spectrum measurements, this circuit should prove useful as a general purpose square wave generator. It generates square wave output signals at a calibrated frequency select­able from 0.5Hz to 100kHz in 1-2-5 steps. The frequency at each step is variable (uncalibrated) over a range of approximately 5:1, giving a total frequency range from 0.5Hz to over 500kHz (around 700kHz in the prototype). The frequency stability appears to be better than 0.5% at any calibrated position, although this has not been tested over the full operating temperature range. IC1 and associated components form a square wave oscillator operating in the range from 200kHz to over 1MHz. This is divided by counters IC2 and IC3 by one of eight selectable ratios in a 1-2-5 sequence as set by diode matrix D1-D17 and switch S2. The fre­quency is further divided by IC5 by 2 or 2024, depending upon sistor, with a BD139 and swap the emitter and collector leads. With this modification the time that the tube is illumi­ nated may not be long enough. This on-time can be lengthened by increasing the 150kΩ resistor, the increase being directly pro­portional to the resistor value. If necessary the 0.1µF capacitor from pin 6 of IC1 can also be increased to 0.22µF or 0.47µF. SILICON CHIP the output selected by S1b. IC4b-IC4d pass the selected frequency to output buffer IC6. As shown, there are two outputs: (1) a low impedance 50Ω output and (2) a high impedance 600Ω output, both providing 12V peak-to-peak with no load. Typically, one output might be used as the “main” output while the other might be used as a reference for an oscilloscope display or fed to a frequency counter. If desired, an adjustable attenuator could be provided between the output buffer (IC6) and either of the output sockets. The output frequency is calibrated in either “Hz” or “kHz”, depending on the setting of switch S1. Variable capacitor C2 is used to adjust the frequency in the “kHz” range to compensate for the fact that the division ratios obtainable with IC5 at the selected outputs are not in an exact 1000:1 ratio. To calibrate, first set S1 to “Hz” and S2 to “100”. Set VR1 to its minimum frequency position and adjust VR2 for an output frequency of 100.0Hz. Next, set S1 to the “kHz” position and adjust C2 for an output frequency of 100.0kHz. H. Nacinovich, Gulgong, NSW. ($60) November 1997  39 This Cable and Wiring Tester has a row of four LEDs to indicate the condition of a pair of wires: open circuit, short, reversed and good. A diode is hooked across the far end of the wire pair to assist the test which is done automatically as soon as you press the button. By LEON WILLIAMS Here’s an easy to build and simple to use tester that will prove indispensable to anyone involved in the installation or maintenance of cables or wiring systems. Small enough to carry in a pocket, the tester employs four LEDs to speedily indicate the health of a pair of wires. Tracing faults in cables, especially those in large build­ings can be very difficult if you are working on your own. If you have a partner and some form of communication, you can use a multimeter set to measure resistance at your end while you get your partner to apply a short circuit and then remove it. With the short removed the meter should show an infinite resistance, and with the short applied a low resistance. This is obviously difficult on your own, as you would have to travel between ends to place the short and remove it in bet­ween taking readings 40  Silicon Chip with the meter. Thankfully there’s an easier way. Diode testing A technique that has been used for a long time to test cable pairs is to place a diode across the A and B wires of the pair at the remote end. When a meter is placed across the pair at the local end, a low resistance will be obtained with the meter leads connected one way and a very high (ideally infinite) re­ sistance with the leads reversed. This happens because the diode only passes current in one direction; ie, when the anode is more positive than the cathode by about 0.7V. A big advantage of the diode test is that fault conditions such as a short or open circuit can be diagnosed quickly. If a pair has a short circuit somewhere along its length, a low re­sistance will be seen when the meter is connected either way. Conversely an open circuit will show an infinite resistance with the meter connected either way. The diode test will also show a reversed pair; ie, where the A and B wires get crossed along the way, as the low resist­ ance/high resistance results will be opposite to those for a good pair. This goes to prove that the best ideas are sometimes the simplest. Fig.1 illustrates the four common pair combinations and the results obtained. Easy to use Carrying around an expensive multimeter, continuously turn­ing it on and off and reversing the leads to test pairs is tedi­ous. With the Cable and Wiring tester all you have to do is connect the two test leads to the pair under test and press the Test button. The tester will automatically test the pair and display the result on one of four LEDs. The orange LED (O) will flash to indicate an open circuit and the yellow LED (S) will flash if the pair is short circuit. A pair that is reversed will cause the red LED (R) to flash, while a pair that is in good condition will cause the green LED (G) to flash. Of course you will need to connect the diode at the other end of the pair you are testing. Circuit description The Cable and Wiring tester works just like the manual diode testing shown in Fig.1 but it does it automatically in two phases before it displays the result. I will refer to these as phase 1 and phase 2. Fig.2 shows the circuit. An oscillator is formed with IC2c, one section of a 40106 hex Schmitt trigger inverter, a 330kΩ resistor and a 0.22µF capacitor. It produces a square wave output with a frequency of about 20Hz. IC2d, a 100kΩ resistor and a 0.1µF capacitor form a delay circuit. The output at pin 10 of IC2d is a delayed and inverted replica of the output from IC2c. The reason for the delay circuit is to separate the sample and display pulses from the unstable periods when the analog switches are swapping the Fig.1: this series of the diagrams illustrates the method of testing a cable pair with a multimeter and a diode connected to the far end. The Cable and Wiring Tester runs through these tests automatically. polarity of the line. The oscillator controls the overall operation of the tester and when its output is low, it is in phase 1, and when its output is high, it is in phase 2. In phase 1, analog switch IC1a connects wire A of the pair to pin 1 of IC2a, while IC1b connects wire B to ground. If the pair is good (ie, not reversed) and the diode is connected Fig.2: the Cable and Wiring Tester works by alternately applying DC voltage to a cable pair in one direction and then the other. The four possible conditions are indicated by the LEDs. November 1997  41 Fig.3 (left): the component layout for the PC board. Take care to ensure that all polarised parts are correctly orientated. Fig.4 (below): this is the actual size artwork for the PC board. ent on the wires being tested, most likely in the form of static charges, each input is protected with a series 680Ω resistor and a 9.1V zener diode. A .001µF capacitor is also connected between the two inputs to shunt any RF signals that might otherwise be picked up by the wires under test. The tester operates from a standard 9V battery which should last quite a long time. Note that the Test switch is also the power switch and is connected in the negative supply lead instead of the positive supply lead as is normal practice. This was done simply because it made the PC board layout easier. Construction with its cathode to wire A, no current will flow through this circuit and pin 1 of IC2a will be pulled high by the 4.7kΩ resistor. If the pair is short circuit or the diode is connected in reverse, current will flow and pin 1 of IC2a will be pulled to ground. Assuming that all is well, pin 2 of IC2a will be low. IC2f, a 33kΩ resistor and a 0.1µF capacitor form a mono­ stable which produces a narrow negative pulse when the output of IC2d goes high, which is only within phase 1. The negative pulse from IC2f closes analog switch IC1c and charges the 0.22µF “memory” capacitor connected to pin 12 of IC1c to the voltage present at pin 2 of IC2a. When the pulse ends, the gate opens but the charge on the capacitor remains as the only discharge path is via the very high input impedance of inverter IC2b. The high output of IC2b is applied directly to the B input of the 4028 BCD-to-decimal decod­er IC3. During phase 2 the states of IC1a & IC1b are reversed and wire A is connected to ground while wire B is connected to pin 1 of IC2a. With a good pair, current will flow through 42  Silicon Chip the circuit and pin 1 of IC2a will be pulled to ground. The output (pin 2) of IC2a is connected directly to the A input of IC3. IC2e, a 0.1µF capacitor and a 100kΩ resistor form a monostable which produces a positive-going pulse when the output of IC2d goes low, which is only during phase 2. This pulse is applied to the C input of IC3 and effectively becomes an enable input, as with this input low none of the LEDs can be selected. One of the LEDs will be turned on when the C input is high, depending on the state of the A and B inputs. Note that the D input is permanently connected to ground. With a good pair, both A and B will be high. The LEDs are only turned on for the period of the pulse from IC2e which has the added benefit that the current drain from the batteries is less than if a LED was on constantly. In summary, the result of phase 1 is stored in the memory capacitor until the result of phase 2 is available, at which point they are both applied to the decoder and the respective LED is turned on. Since high voltages could be pres- The Cable and Wiring Tester is mounted in a small plastic case with a row of four LEDs and a pushbutton on top. At one end is a 3.5mm jack socket to enable connection to a pair of wires. Pressing the button flashes one of the four LEDs depending in the test condition: Open (Orange); Short (Yellow); Reversed (Red); and Good (green). All the components apart from the test socket are mounted on a single-sided PC board. Fig.3 shows the wiring diagram. Begin construction by soldering in the five tinned copper wire links, ensuring that they are straight and lay flat on the board. Follow this with the resistors, the zener diodes and the PC stakes. Next, solder in the capacitors, remembering that the 22µF capacitor is polarised and must be inserted the right way. The integrated circuits can be installed next, ensuring that they are in the correct way. These are CMOS types and can be destroyed by static electricity, so earth yourself and take care not to handle them too much. The LEDs are installed with the top of each LED 25mm above the PC board. They should protrude slightly from the lid of the case when it is fitted. Similarly, the pushbutton switch is installed in a vertical position by soldering its tags to two PC stakes. Again, the switch should be at the correct height with the case closed. Install the PC board in the bottom case half with four self-tapping screws. If you find it won’t sit properly, you can lightly file the edge of the board or cut out the small plastic tabs inside the edge of the case. Drill a hole in the centre of the top endplate and mount the 3.5mm test socket. Place the two The four LEDs and the pushbutton switch are stood off the board so that they protrude through the lid of the case. end plates in the slots on the bottom half of the case. The bottom half has four holes for the case mounting screws while the top half has threaded brass inserts. Solder two wires from the socket to the PC stakes on the PC board. Now solder in the battery clip and trim the length of the wires so that they sit neatly with the battery positioned as shown in the photographs. You may find it necessary to cut off some of the plastic tabs on the inside of the top half to clear the battery clip when the two halves are screwed together. Drill the four holes for the LEDs and for the test switch in the top half of the case. The positions for these can be quite easily found by firstly making measurements with a ruler and then mark­ing with a pencil before drilling. The test lead is made from a short length of figure-8 cable. The type used in the prototype was coloured red and black. I soldered the red A wire to the centre pin of the 3.5mm plug and the Parts List 1 PC board, code 04411971, 51 x 88mm 1 plastic case, 120 x 60 x 30mm 1 3.5mm mono phono socket 1 3.5mm mono phono plug 2 small black alligator clips 2 small red alligator clips 1 normally open pushbutton switch 6 PC stakes 1 9 volt battery clip 4 No. 4 x 6mm self-tapper screws 1 5mm red LED (LED1) 1 5mm yellow LED (LED2) 1 5mm orange LED (LED3) 1 5mm green LED (LED4) Semiconductors 1 4053 triple analog selector (IC1) 1 40106 or 74C14 hex Schmitt trigger (IC2) 1 4028 BCD-to-decimal decoder (IC3) 2 9.1V 1W zener diodes (ZD1,ZD2) 1 1N4004 diode (remote test diode) Resistors (0.25W, 1%) 1 330kΩ 1 4.7kΩ 2 100kΩ 6 680Ω 1 33kΩ Capacitors 1 22µF 16VW electrolytic 2 0.22µF MKT polyester 3 0.1µF MKT polyester 1 .01µF MKT polyester 1 .001µF MKT polyester Miscellaneous Tinned copper wire, hookup wire, figure-8 cable, small piece of scrap stripboard, heatshrink tubing Resistor Colour Codes ❏ No. ❏  1 ❏  2 ❏  1 ❏  1 ❏  6 Value 330kΩ 100kΩ 33kΩ 4.7kΩ 680Ω 4-Band Code (1%) orange orange yellow brown brown black yellow brown orange orange orange brown yellow violet red brown blue grey brown brown 5-Band Code (1%) orange orange black orange brown brown black black orange brown orange orange black red brown yellow violet black brown brown blue grey black black brown November 1997  43 to­gether. Now clip the tester leads to the diode leads, with the red A wire clips connected together and the black B wire clips connected together. Press the Test button and verify that the “G” LED flashes. Now reverse the connection to the diode leads, press the Test button and check that the “R” LED flashes. Once you are happy with the testing, screw the case together with the four screws supplied, checking that the drilled holes line up with the LEDs and switch without placing stress on them. Using the tester The basic operation of the tester should be quite apparent. Simply connect the diode to the remote end with the red clip connected to the A wire, the tester to the local end with the red clip connected to the A wire, press the Test button and monitor the LEDs. Multiple wire cables Another view of the prototype Cable & Wiring Tester. Power comes from an internal 9V battery. black B wire to the ground pin. To finish the lead, solder a red alligator clip to the red wire and a black alligator clip to the black wire. The diode assembly can be made next. It simply comprises a diode soldered to a length of figure-8 cable as before. Its anode is soldered to the black wire and the cathode to the red wire. I used a scrap piece of strip board to give the assembly some mechanical strength and then covered it with heatshrink sleeving to prevent accidental shorting. The red alligator clip is sol­dered to the red wire and the black alligator clip to the black 44  Silicon Chip wire. Finally, fit a good 9V battery into the case. Testing With the assembly complete, press the test switch briefly and check that the “O” LED flashes at about 20Hz. If it does, you can proceed with the rest of the testing. If it doesn’t work, have a good look at the assembly again and check it for construction errors. Plug the test lead into the socket and connect the two alligator clips together. Press the Test button and check that the “S” LED flashes to indicate that the wires are shorted So far this article has referred to just testing a pair of wires, such as those in a telephone cable or Local Area Network (LAN) cabling. However, the tester can be used to test cables with multiple wires even if they are not paired. The simplest way is to select one of the wires as a common A wire and then progress through the other wires as a second B wire. If you are working on cable that has, for example three pairs, you might construct a multiple diode lead with three diodes and six leads so that you could check all the pairs at one time. Some cabling systems use a special socket to terminate a multiple pair cable. An example of this is an RJ45 socket used in modern building cabling where four pairs provide computer and telephone connections at one socket. A plug could be adapted to hold four diodes and plugged into the remote socket while the tester could be plugged into a mating socket at the local end. A switch would need to be incorporated in the tester leads to select the pair to be tested. Finally the tester can be used as a general continuity tester to test diodes, speakers, audio/video cables, etc. The tester will indicate a short circuit with about 2kΩ or less placed across the test leads but this will vary from unit to unit and is dependent mainly on the character­istics SC of the ICs used. 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 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia November 1997  53 By RICK WALTERS Regulated Supply For Darkroom Lamps Don’t let variations in the mains supply ruin your photographic prints. This regulated power supply will keep the halogen lamp in your enlarger at its correct colour temperature. Maintaining an enlarger lamp at its correct colour tempera­ture is important when doing darkroom work, especially if you expect to obtain consistent results. In particular, the colour temperature of the lamp is critical for colour prints, although you can often get away with small variations for black and white prints. 54  Silicon Chip Unfortunately, many a darkroom session can be made frus­trating by small variations in the lamp output due in turn to variations in the mains supply. These variations are quite normal and can be due, for example, to heaters or air-conditioners cycling on and off or to some other cause. When this occurs, the lamp output changes and this affects both its colour temperature and exposure times. To overcome this problem, some readers have asked us to design a mains stabiliser but these are expensive and impractical for the hobbyist to con­struct. This Halogen Lamp Supply will effectively do the same job at a fraction of the cost. It provides a well-regulated 12V supply for the halogen lamp in the enlarger and varies its output by just 2mV for mains input voltages ranging from 195VAC to 280VAC. The unit is also very easy to operate. The front panel carries just a mains rocker switch, a power indicator LED and a toggle switch to turn the lamp on and off. Alternatively, the enlarger lamp can be turned on and off via a remote switch con­nected to a terminal block on the rear panel. Fig.1: the circuit is based on a TL494 PWM controller (IC1). This controls the output voltage by varying its output pulse width at pins 9 and 10. The circuit (see Fig.1) is basically a regulated 12V power supply capable of supplying up to 10A. It uses a mains transform­er to feed a full-wave bridge rectifier and this then supplies an unregulated filtered DC voltage to a switching regulator circuit. In this type of regulator, the output switching devices (power Mosfes) are either on or off and so their losses are quite low. In fact, the bridge rectifier gets much hotter than the output devices. Circuit details Let’s now take a look at the circuit in greater detail. As shown in Fig.1, the primary of the transformer is protected by a 3A slow-blow fuse which has been specified to handle the high inrush current. The two 18V secondary windings of the transformer are con­nected in parallel to provide the required current and these feed the bridge rectifier. This in turn supplies the rectified DC to two 4700µF filter capacitors which are both needed to cope with the high ripple current. They are followed by a 15A fuse which is only included to provide output short circuit protection. The output of the fuse is fed directly to one side of the lamp and to REG1, a 12V regulator which supplies a stable voltage to the rest of the circuit. We could probably have omitted the regulator as IC1 has its own inbuilt reference but as we are looking for a rock steady output, we decided to include it. The heart of the circuit is IC1, a TL494 pulse width modu­ lation (PWM) controller. Inside this device is an on-board oscil­lator, a reference regulator, two error amplifiers, several com­parators and a pair of output driver transistors. You can find out more about this device by referring to the Motor Speed Con­troller article in the June 1997 issue (a block diagram of the device was published on page 28). In simple terms, the TL494 PWM controller operates as fol­ lows. Its oscillator runs at 20kHz (as set by the RC components on pins 5 & 6) and it produces a pulse train at its outputs at this frequency. The width of the pulses is varied (ie, pulse width modulated) and the ratio of the “on” time to the “off” time controls the voltage applied to the load which in this case is the enlarger lamp. A fraction of the output voltage is fed to one input of one of the error amplifiers (pin 2 of A1), while the other input (pin 1) is connected to a reference voltage. If the output voltage rises slightly, the error amplifier senses this change and alters the output on-off ratio to bring the output voltage back to the required level. This is done by reducing the “on” time at the device out­puts (pins 9 & 10). The converse applies for a falling output voltage. Pins 9 & 10 of IC1 are simply the emitters of the two output transistors, November 1997  55 This close-up view shows the assembled PC board with one Mosfet fitted. Note that the board was modified after this photo was taken and some parts shown here have been deleted from the final design. connected here in parallel. Their collectors at pins 8 & 11 are connected to a +12V supply rail derived from 3-terminal regulator REG1. This means that the internal transis­tors operate as emitter followers and each time they turn on, they pull the bases of Q1 & Q2 to +12V. As a result, the emitters of Q1 & Q2 which are wired as complementary emitter followers, together with the gates of Q3 & Q4, swing from 0V to +12V. This means that the gate drive signal is limited to this voltage. Q1 and Q2 are included for another 56  Silicon Chip reason and that is to rapidly charge and discharge the gate capacitances of the Mosfets each time they turn on and off. This improves the switching action of the Mosfets; ie, it speeds up their turn-on and turn-off times and thereby reduces their power dissipation. Each time the Mosfets turn on (ie, when Q1 & Q2 turn on), current flows through them and the lamp to ground. The switching regulator (IC1) then acts to ensure that the average output voltage applied to the lamp is 12V. In order to control the output voltage precisely, the TL494 monitors both sides of the lamp. The filtered output from the bridge rectifier is monitored via 20kΩ and 2.2kΩ voltage divider resistors (R3 & R4), the output of which goes to pin 1 of com­parator A1. The voltage on the other side (at the drains of the Mosfets) is sensed via R1 & R2 (18kΩ and 4.7kΩ) and the sampled voltage fed via a 47kΩ resistor to pin 2 (the other input of com­parator A1). In addition, a voltage is tapped off the +5V reference by VR1 and fed through a second 47kΩ resistor to pin 2. This trimpot is used to set the output voltage. To understand how this works, it’s important to realise that the voltage on pin 2 is always equal to the voltage on pin 1, since these two pins are the inputs of an op amp. This means that if the wiper of VR1 is wound down towards 0V, the voltage at the junction of R1 & R2 must increase so that the pin 2 voltage remains the same as the voltage on pin 1. Conversely, if the wiper of VR1 is wound towards +5V, the voltage at the junction of R1 & R2 goes down to maintain the voltage on pin 2. What happens is that the TL494 varies its output pulse width so that its pin 2 voltage matches its pin 1 voltage. In practice, of course, VR1 is set to a fixed value and so the TL494 maintains a constant average voltage on the drains of the Mosfets and thus across the lamp. Note that the reference voltage for pin 1 of IC1 has been derived from the unregulated DC supply rail. This has been done so that the circuit automatically compensates for mains voltage variations. If the mains voltage varies, then so does the unregu­lated DC supply rail and thus the voltage on pin 1. As a result, the TL494 varies its output pulse width to bring the pin 2 vol­tage into line and keep the average lamp voltage constant. Slow start circuit Switches S2 (local) and S3 (remote) are used to turn the lamp on or off. They work in conjunction with a slow start cir­cuit which has been included to prolong the life of the lamp. If both switches are off, the 1µF capacitor between pins 4 & 14 of IC1 will be discharged due to the 4.7kΩ resistor and diode D1. The voltage on the inhibit pin (pin 4) will thus be equal to the REF voltage on pin 14 (5V) and there will be no output from the TL494. Conversely, when one of the switch­ es is closed, the 1µF capacitor charges via the 100kΩ resistor in parallel with D1. During this time, the voltage on the inhibit pin gradually falls and the output pulse width from the TL494 steadily increases. This means that the lamp voltage rises steadily to 12V, thereby providing a soft start. Construction Most of the parts are accommodated on a PC board coded 10107971 and measuring 145 x 102mm. Before commencing the assem­bly, check the board carefully against the published pattern to ensure that there are no etching defects. Fig.2 shows where all the parts go. No particular order need be followed when assembling the board but it’s best to start with the smaller parts first (resistors, trimpot, diodes and low-value capacitors). Table 1 shows the resistor colour codes but it’s also a good idea to check the resistor values on a digital multimeter. Take care to ensure that the correct transistor is in­stalled at each location and that its orientation is correct. We used an IC socket for the TL494 but this can be considered op­tional. It too must be correctly orientated, as must D1 and the electrolytic capacitors. PC stakes are used for the external connections to the local and remote switches and to LED1. Do not use PC stakes for the other wiring connections though – these points carry heavy currents and the leads should be soldered directly to the PC board. Although the circuit diagram (Fig.1) shows two Mosfets in parallel, one should be sufficient for lamp loads up to about 5A (ie, for lamps rated up to 60W). This Mosfet can be mounted Fig.2: take care to ensure that all polarised components are correctly orientated when building the PC board. You can use just one Mosfet for lamp loads up to about 60W. in either the Q3 or Q4 position and should be fitted with a small U-shaped heatsink (see photo of prototype). If the lamp is rated at more than 60W, then the second Mosfet should also be installed. Note that it will be necessary to splay the fins on one of the heatsinks slightly, so that the second heatsink can be fitted to its Mosfet. Make sure that the metal tabs of the Mosfets go towards IC1. The metal tab of REG1 Table 1: Resistor Colour Codes ❏ No. ❏  1 ❏  1 ❏  2 ❏  1 ❏  1 ❏  1 ❏  2 ❏  2 ❏  1 ❏  2 Value 1MΩ 100kΩ 47kΩ 20kΩ 18kΩ 10kΩ 4.7kΩ 2.2kΩ 1kΩ 4.7Ω 4-Band Code (1%) brown black green brown brown black yellow brown yellow violet orange brown red black orange brown brown grey orange brown brown black orange brown yellow violet red brown red red red brown brown black red 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 black black red brown brown grey black red brown brown black black red brown yellow violet black brown brown red red black brown brown brown black black brown brown yellow violet black silver brown November 1997  57 Fig.3: be sure to use mains-rated cable for all wiring to fuse F1, the mains terminal block, switch S1 and for the earth connection to S2. LED1 and the wiring to it can be omitted if you use a neon-illuminated mains rocker switch. faces in the opposite direc­tion. Now install the two large 4700µF electrolytic capacitors and fit the bridge rectifier and the chassis-mount fuseholder. These last two items are bolted to the PC board using machine screws and nuts. Orient the bridge rectifier so that its “+” and “-” terminals are located as shown and note that a Powerfin heatsink (normally drilled for a TO-3 transistor) goes between it and the PC board. 58  Silicon Chip Smear heatsink compound over the bottom of the bridge rectifier before bolting it down. You can use one of the existing TO-3 mounting holes, which means that the bridge rectifier will sit slightly off-centre. The PC board assembly can now be completed by installing the wiring to the fuseholder and to the “+” and “-” terminals of the bridge rectifier (BR1). Use heavy duty 10A cable for this job. We used automotive-style spade connectors to terminate the leads on the bridge rectifier and fuseholder terminals. Two more heavy-duty cables, each about 180mm long, should also be soldered to points 3 and 4 on the PC board. Use a red lead for the point 3 connection and a black lead to point 4 (these are the output leads for the lamp and are later run to a terminal block mounted on the rear panel). Drilling the case A standard plastic instrument case with plastic front and rear panels is used to house the circuitry. Fig.3 shows the layout inside the case. As can be seen, the power transformer (T1) is mounted on an aluminium baseplate and this is secured, along with the PC board, to integral standoffs on the base of the case using self-tapping screws. The first step is to mark out and drill the necessary holes in the baseplate. You will need four mounting holes for the case standoffs, a mounting hole in the rear lefthand corner to secure the earth solder lugs, and a mounting hole in the centre to take the power transformer bolt. The hole locations for the standoffs can be easily marked out by first marking the tops of the standoffs with a felt pen and then carefully pressing the aluminium plate onto them. This done, the holes can all be centre punched and drilled to 3mm. By the way, the aluminium baseplate allows the mains wiring and the circuit to be correctly earthed. As such, it is an im­portant safety measure and must not be deleted. When drilling is complete, deburr all the holes and secure the two earth solder lugs in position using a machine screw, washer and nut. An additional locknut should then be fitted so that the earth lugs can not come loose. This done, secure the transformer to the baseplate, then fasten the baseplate to the case standoffs using four self-tapping screws. Note that the transformer is secured using a large bolt, two rubber washers and a large metal washer. One of the rubber washers sits under the transformer, while the second sits under the metal washer at the top. The front and rear panels can now be drilled to accept the various hardware items. The front panel requires a rectangular cutout for the mains switch (S1), plus holes for the power indi­cator LED and toggle switch S2. If you use a mains switch with a neon illuminated rocker, the power indicator LED can be omitted. The cutout for the mains switch can be made by drilling a series of small holes around the inside edge of the cutout area and then knocking out the centre piece. The edges should then be cleaned up using a file and the cutout carefully enlarged until the mains switch just fits. Make sure that the switch is a tight fit and that it cannot accidentally fall out. Moving now to the rear panel, you Parts List 1 PC board, code 10107971, 145 x 102mm 1 160VA toroidal power transformer with two 18V secondaries; Jaycar MT-2113, Altronics M4055 or equivalent 1 plastic case, 200 x 160 x 70mm 1 panel-mount 3AG fuseholder 1 3A 3AG fuse (F1) 1 chassis-mount 3AG fuseholder; Altronics Cat. S6010 or equiv. 1 15A 3AG fuse (F2) 1 3-way mains terminal block 1 4-way mains terminal block 1 mains switch with plastic rocker; Jaycar Cat. SK-0984 or SK0985 (illuminated) 1 mains lead with moulded 3-pin plug 1 miniature toggle switch 1 Powerfin heatsink (DSE Cat. H-3400 or equiv). 1 semi-mini heatsink (DSE Cat. H-3404 or equiv). 3 solder lugs 1 piece of aluminium, 130 x 90 x 1.6mm 1 5kΩ horizontal PC-mount trimpot (VR1) Semiconductors 1 TL494CN switching regulator controller (IC1) will require mounting holes for the cordgrip grommet, the fuseholder and the 4-way terminal strip. The locations of these components can be gauged from the photographs and from Fig.3. Note that the mains cord hole should be carefully profiled to match the cordgrip grommet. Final wiring The hardware items can now all be mounted in the case, ready for wiring – see Fig.3. Note that the mains terminal strip is secured to one of the case standoffs using a self-tapping screw. Exercise extreme care when installing the mains wiring, as your safety depends on it. In particular, make sure that the mains cord is securely anchored by the cordgrip grommet on the rear panel and cannot be pulled out. The Active (brown) lead from the 1 BC639 NPN power transistor (Q1) 1 BC640 PNP power transistor (Q2) 1 or 2 MTP75N05 Mosfets (Q3,Q4) – see text 1 7812 regulator (REG1) 1 1N914 small signal diode (D1) 1 400V 25A bridge rectifier (BR1) 1 red LED and mounting bezel (LED1) (not needed if mains switch has neon-illuminated rocker) Capacitors 2 4700µF 25WV PC electrolytic 3 100µF 25WV PC electrolytic 1 1µF 16VW PC electrolytic 3 0.1µF MKT polyester 1 .0068µF MKT polyester Resistors (0.25W, 1%) 1 1MΩ 1 10kΩ 1 100kΩ 2 4.7kΩ 2 47kΩ 2 2.2kΩ 1 20kΩ 1 1kΩ 1 18kΩ 2 4.7Ω Miscellaneous Heatshrink tubing, red and black heavy-duty hookup wire, light-duty figure-8 cable, mains-rated cable (brown, blue & green/yellow) mains cord goes directly to fuse F1, the Neutral (Blue) lead goes to the mains terminal block, and the Earth lead is soldered to one of the earth lugs on the baseplate. Additional mains-rated leads are then run from the fuse and terminal block to the mains switch (S1). The terminals of the fuseholder and mains switch should be covered with heatshrink tubing to prevent accidental contact with the mains. This involves slipping a length of heatshrink tubing over all the leads before they are soldered to the terminals. After soldering, the heatshrink tubing is pushed over the fuse­holder and mains switch bodies and shrunk using a hot-air gun. The two orange wires from the transformer are the primary leads and these go to the mains terminal block, as shown. The low-voltage secondary November 1997  59 The power transformer is mounted on an aluminium plate which must be securely earthed. Sleeve all exposed terminals on the mains switch and fuse with heatshrink tubing to prevent accidental contact with the mains. leads are much thicker. Twist the red and pink leads together and terminate their ends in a spade terminal. This done, do the same for the white and yellow leads, then connect the transformer secondaries to the AC terminals on the bridge rectifier. Finally, complete the wiring to LED 1, switch S2 and to the rear-panel terminal strip. Note that a solder lug goes over S2’s collar and that an earth lead (mains rated) is run from this collar back to an earth solder lug on the baseplate. This earths the metal parts of the switch body, including the toggle actua­tor. Testing Before switching on, go back over the wiring carefully and check that all is correct. This done, wind VR1 fully clockwise apply power and check 60  Silicon Chip SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. SMART ® FASTCHARGERS Brings you advanced technology at affordable prices Fig.4: check your PC board against this full-size etching pattern before installing the parts. REMOTE SWITCH TO LAMP (12V) FUSE 3A 240VAC Fig.5 (above & right): these two labels can be affixed to the rear panel above the terminal block and next to the mains fuse. Disconnect mains plug from wall outlet before removing fuse As featured in ‘Silicon Chip’ Jan. ’96 This REFLEX® charger charges single cells or battery packs from 1.2V to 13.2V and 110mAh to 7Ah. VERY FAST CHARGING. Standard batteries in maximum 1 hour, fast charge batteries in max. 15 minutes AVOID THE WELL KNOWN MEMORY EFFECT. the voltages at various points on the circuit. You should get about +27V at the output of the bridge rectifier, +2.7V on pin 1 of IC1, +5V on pin 14 and +12V on pin 12 (ie, the output of REG1). If all these voltages are correct, connect a 12V test lamp and a voltmeter across the output terminals and carefully wind VR1 up until you get 12V. You should now be able to measure about 2.4V at the wiper of VR1 and 3.0V at the junction of R1 and R2 although your unit may vary slightly from these figures. Finally, the output voltage should be reset when the enlarger lamp is connected, to make sure it is correct. That’s it – you can now tackle your darkroom printing jobs without being affected by annoying variations in the SC lamp output. NO NEED TO DISCHARGE. Just top up. This saves time and also extends the life of the batteries. SAVE MONEY. Restore most Nicads with memory effect to remaining capacity and rejuvenate many 0V worn-out Nicads EXTEND THE LIFE OF YOUR BATTERIES Recharge them up to 3000 times. DESIGNED AND MADE IN AUSTRALIA 12V-24V Converters, P. supplies and dedicated, fully automatic chargers for industrial applications are also available. For a FREE detailed technical description please Ph: (03) 6492 1368 or Fax: (03) 6492 1329 2567 Wilmot Rd, Devenport, TAS 7310 November 1997  61 Does your doorbell just go ding dong or worse, don’t you have any doorbell at all? Either way, you can improve your whole lifestyle by building and installing this musical doorbell. It plays a sequence of nine notes each time someone presses the button. Design by BOB FLYNN Musical come clean. Maybe A building this musical doorbell might not make a huge difference to LRIGHT, WE’LL your lifestyle but then again maybe it might. One of the visitors to your home might be so impressed by your unique doorbell that they might offer you a partnership in a huge new electronics venture. You never know . . . The new doorbell uses just three cheap ICs and three tran­sistors in the circuit. There are two good ol’ reliable 62  Silicon Chip oorbell D CMOS 555 timers, a 4017 counter and not much else. We are presenting this project just as a PC board, knowing that you will want to make your own arrangements as far as the case and loudspeaker are concerned. The unit will play virtually any tune of up to nine notes although there is a proviso which we will come to later. Let’s have a look at the circuit of Fig.1. There are two separate 555 oscillators and a 4017 decade counter. What happens is that the first 555 oscillator (IC1) produces the clock pulses for counter IC2. IC2 then counts from 0 to 8 and then stops on the tenth clock pulse. The whole circuit waits until the next time the door bell button is pressed but we’re getting a little ahead of ourselves. Each output of the 4017 counter is used to produce a sepa­rate frequency from the second 555 timer, IC3. This then drives an amplifier stage consist- Fig.1: IC2 is the heart of the circuit and its nine outputs cause IC3 to produce nine different notes as it counts through. ing of two transistors, Q2 & Q3, which drive the loudspeaker. How it works Now let’s have a more detailed look at how the circuit works. IC1 is a conventional 555 timer circuit with its output frequency variable between about 1.3Hz and 5.5Hz, depending on the setting of the 2MΩ trimpot VR1. The only unusual feature of the circuit of IC1 is the con­nection to pin 4. In normal free-running 555 oscillator circuits, pin 4 is tied to the positive supply rail but in this case we use pin 4 to start and stop oscillation. The output pulses from pin 3 of IC1 are fed to the clock input of IC2 and each of its outputs from Q0-Q8 goes high in turn for the duration of a clock pulse. Each 4017 output is fed via a diode and two resistors (R1 & R2) to pin 7 of IC3. Depend­ing on the values of R1 & R2 connected to each 4017 output, IC3 can then generate a different note in a nine-note sequence. On the tenth clock pulse, the Q9 output of IC2 goes high and this pulls the clock enable pin 13 high and also pulls the base of transistor Q1 high. The combination of these two events effectively stops IC2 on the tenth count and ensures that when pushbutton S1 is pressed, the pin 3 output of IC1 immediately goes high to give a full first count in the nine count sequence from IC2. IC3 generates the nine notes. The frequency of each note is determined by the sum of the resistance of resistors R1 & R2, the 51kΩ resistor between pins 6 & 7 and the .01µF capacitor at pins 2 & 6. Table 1 shows the values to provide one octave of notes including sharps and flats. The overall pitch of all the notes can be shifted up or down by the tune control, trimpot VR2. This takes advantage of the fact that you can shift the upper and lower thresholds of the 555 timer with an adjustable voltage divider connected to pin 5. The pin 3 output of IC3 drives a rud­ i­ mentary amplifier stage consisting of complementary emitter followers Q2 & Q3. These in turn drive the 8Ω loudspeaker via a 220µF coupling capacitor and a 27Ω current limiting resistor. Since the output waveform is essentially a pulse train, the complementary amplifier stage can operate in class-B and do without such niceties as quiescent current. By the way, the output from pin 3 of IC3 has a varying duty cycle, depending on the frequency, since the resistor between pins 6 & 7 is constant at 51kΩ while resistors R1 & R2 are varied. Construction As noted above, we are presenting this project just as a PC board, knowing that you will want to make your own arrangements as far as the case and loudspeaker are concerned. The PC board measures 129 x 79mm and is coded 11211971. Fig.2 shows the com­ponent overlay. After checking the PC board for any etching defects or undrilled holes, November 1997  63 Fig.2: the component overlay for the PC board. You will need to select the values for R1 & R2 from Table 1. Fig.3: here is the full-size etching pattern for the PC board. install the PC stakes for the supply, loudspeak­er and pushbutton connections. This done, install the wire links, the diode and the resistors. It is a good idea to check each resistor value with your multimeter before you install it. Ah, now what values should you use for R1 & R2? Table 1 shows the values for various notes so if you have a favourite few bars of music you can determine the notes you want and pick the resistors accordingly. But there is 64  Silicon Chip one little drawback to be noted. Since the 4017 counts from one to nine in a continuous sequence, the notes are produced in the same sequence, with no gaps in between. This does not present a problem if all adjacent notes in the sequence are different but if you have two adjacent notes which are the same you do have a problem. Instead of having two separate notes you will just get one long note. The only way of overcoming this, short of adding extra gates to provide a short break between each note, is to leave a one-note gap between two identical notes. This means that your tune will be shortened to eight notes and you will then need to omit the diode and resistors R1 & R2 for that note position. Going back the circuit of Fig.1 for a moment, that is why the diode and the resistors associated with the Q4 Parts List 1 PC board, code 11211971, 129 x 79mm 6 PC stakes 1 momentary contact pushbutton switch (S1) 1 6V or 9V battery or DC plugpack (see text) 1 8Ω loudspeaker 1 2MΩ trimpot (VR1) 1 2kΩ trimpot (VR2) This musical doorbell can be arranged to play a nine-note sequence each time you press the pushbutton. Make sure that all parts are correctly oriented. output of IC2 have the note “Omit”. The circuit actually shows the note se­quence for “Westminster Chimes” and since the fourth and fifth notes are both C, we’ve had to omit the resistors and diode for the Q4 output of IC2. So this long-winded explanation makes the point: if you have a tune with two adjacent notes the same, you will need to leave gap (in time) otherwise you will get one note the same. The obvious alternative to this Table 1 Semiconductors 2 7555 timers (IC1, IC3) 1 4017 decade counter (IC2) 1 BC547 NPN transistor (Q1) 1 BC337 NPN transistor (Q2) 1 BC327 PNP transistor (Q3) 9 1N914, 1N4148 small signal diodes (D1-D9) 1 1N4004 silicon diode (D10) dilemma is to choose a tune which does not present this problem. Having inserted all the resistors, you can now finish the board assembly, taking care to ensure that all the semiconductors and electrolytic capacitors are inserted the correct way around. Capacitors 1 220µF 16VW PC electrolytic 2 100µF 16VW PC electrolytic 1 0.33µF MKT polyester 1 0.15µF MKT polyester 3 0.1µF MKT polyester 2 .01µF MKT polyester 1 .0033 MKT polyester Testing Resistors (0.25W, 1%) 1 560kΩ 1 15kΩ 2 100kΩ 2 10kΩ 1 56kΩ 1 27Ω 1 22kΩ Values for R1 & R2 depend on desired notes – see Table 1. To test the finished board, you will need a 9V battery or DC power supply, an 8Ω loudspeaker and a pushbutton. If all your work is correct, the board should run through its sequence of notes as soon as the supply is connected and then fall silent. After that, nothing should happen until you push the button and then the note sequence should be produced. If the circuit does not work as it should you can check the operation of each stage with your multimeter. For example, the output at pin 3 of IC1 should pulse up and down at around two or three times per second if trimpot VR1 is at its mid setting. You can check this with your multimeter set to read DC. Similarly, you can check that each of the outputs of IC2 go high in turn and so on. Options You have several options for powering the circuit. First, you can use a 9V battery but ideally this should employ six C or D cells to obtain long battery life. If you use a 9V (Eveready 216 size), the battery will not last long. You could also use a 6V lantern battery but then the 27Ω resistor in series with the loudspeaker should be reduced to 18Ω. Alternatively you could power the circuit with a 6V or 9V DC plugpack, bearing in mind that their operating voltage will typically be around 50% more; ie, 9V and 13V, respectively. Do not use a 12V DC plugpack because the output voltage will be too lightly loaded for this circuit. You would run the risk of blowing the chips as the plugpack voltage is likely to be as high as 17V. Finally, if you do use a DC plugpack instead of a battery, you can save a little money by using ordinary 555s instead of 7555s. Their current drain will be a lot higher but that does not SC matter with a plugpack. November 1997  65 RADIO CONTROL BY BOB YOUNG How does a servo work? This month we take a look at the principles underlying the operation of servos designed for use with R/C systems. You move the stick on your transmitter and the servo moves to a new position. Why? We shall find out. in a high level of interchangeability. Fig.2 shows an exploded view of a typical servo. Item 19 is the potentiometer which in this servo is a replaceable ceramic element which screws into a housing moulded into the servo case. Modern servos use a miniature sealed potentiometer. Pulse width modulation Not only is the design of the typical R/C servo an elegant example of modern mass production but the system whereby six, seven or more channels of data are modulated onto the radio carrier is elegant as well. It is here that the great mystery begins for the average electronics buff. Just what is the system of modulation and how does it result in such precise clockwise (CW) and counter-clock-wise (CCW) control of an electric motor? The basic servo is best defined as a closed loop, error cancelling system in which some of the output is fed back into the input in such a way that the system automatically seeks to come to rest in a state of zero error. In this null or neutral position it should draw negligible current. Fig.1 is the block diagram of such a system. A typical modern R/C servo has the following components: a plastic housing and gear train, electric motor, feedback poten­tiometer and a servo amp­lifier. The feedback potentiometer is mechanically linked to the servo output arm either directly or indirectly via a gear train. The indirect drive servo minimises the vibrational wear on the potentiometer but is more expensive. A three-pin plug is fitted as standard to most servos, resulting Fig.1: block diagram of a typical servo motor. A posi­tive-going input pulse is compared with an internally generated negative going reference pulse in the error amplifier and used to drive the motor. 66  Silicon Chip The input signal to the servo amplifier is a variable width pulse and it is here that the magic begins. The position of the servo output arm is slaved (or proportional) to the width of this input pulse. Thus it can be described as a pulse width modulation (PWM) system. Modern PWM systems have a virtually universal standard positive input pulse of 3-5V amplitude with a neutral of 1.5ms and varying between 1-2ms. The repetition rate of this pulse (Frame Rate) is typically between 14-25ms (70Hz to 40Hz) de­pending upon the number of channels transmitted. Don’t worry if this terminology is all Greek to you at the moment. We will explain it. The diagram of Fig.3 shows typical input pulse parameters. This pulse signal comes from the decoder which produces separate pulse signals for each servo. We will discuss encoders and decod­ers next month. While the basic elements of the modern servos differ little from their early counterparts, the same cannot be said about the servo amplifier which is now just an integrated circuit with a few external components, taking up little space inside the servo case. Example circuit As the modern IC servo amplifier is difficult to analyse, it is easier for us to look at a discrete servo amplifier devel­oped before the IC took over. Fig.4 shows the circuit of an old Silvertone servo. RV is the feedback potentiometer which is coupled to the motor. A positive-going pulse of 4.8V amplitude is fed from the receiver decoder into the base of transistor Q1 which operates as an emitter follower. The pulse signal appears across R1 in the same phase but with the base/emitter voltage drop of about 0.6V subtracted. This positive-going pulse is then fed via R6 to the summing junction and via capacitor C2 and R2 to the input of IC1, a UL914 dual OR gate. IC1 is configured as a one-shot multivibrator with a time constant set by C3, R3 and RV. This one-shot generates a nega­tive-going reference pulse of about 4.2V amplitude which is then fed via R7 to the summing junction R8, R9, C4, C5. The values of R5, R6 and R7 are chosen to deliver pulses of equal amplitude but opposite phase to the summing junction. R5 along with C1 also forms the supply decoupling network for the one-shot IC1. Timing diagrams Now we need to look at some timing diagrams which show how the input pulse and the reference pulse are summed to produce a drive signal to the servo motor. Fig.5 shows the first condition. The top trace (a) is the positive-going input pulse while the second trace (b) is the negative-going reference pulse. When these two pulses are applied to the summing junction the result is trace (c). As you can see, the pulses have exactly cancelled out since they have equal amplitude and duration. The result is zero output, the condition required for neutral or rest position. Fig.6 shows the conditions for clockwise drive (CW) of the servo motor. Here the positive pulse (a) is of longer duration than the negative reference pulse (b). The output of the summing junction is a positive pulse, the duration of which equals the difference between the input (positive) and reference generator (negative) pulses. This positive pulse is transferred to the bases of Q2 and Q3 via capacitors C4 and C5. As Q2 is a PNP transistor it will not respond to this Fig.2: exploded view of a typical servo. Item 19 is the poten­tiometer which in this servo is a replaceable ceramic element which screws into a housing moulded into the servo case. Modern servos use a miniature sealed potentiometer. November 1997  67 Fig.3: typical input pulse parameters for an R/C servo. This pulse signal comes from the decoder which produces separate pulse signals for each servo. positive-going pulse but NPN transistor Q3 will. Capacitor C6 is a pulse stretcher and provides smoothing until the next pulse arrives 20ms later. The drive circuit for the motor is unusual in that it is the old centre-tapped 4.8V system (four wire system). Modern IC servo amplifiers use a bridge drive circuit which will give bidirectional drive from a single 4.8V battery (three wire sys­tem). With Q3 now conducting, transistors Q5 & Q7 will also con­duct and drive the motor in a clockwise direction. When we have the conditions shown in Fig.7, where the input pulse is shorter the than the reference pulse, the output of the summing junction Fig.4 (below): the circuit of an old Silvertone servo using discrete components. RV is the feedback potentiometer built into the servo mechanics. It adjusts the reference pulse width as the motor is driven to the desired position. 68  Silicon Chip is a negative pulse (c). This causes transistors Q2, Q4 & Q6 to conduct, driving the motor in the counter clockwise direction. Feedback seeks the neutral Now we come to the clever part. The feedback potentiometer RV is connected to the output shaft of the servo mechanics and is wired in such a manner that the servo motor always moves to reduce the error (difference) signal to zero by changing the width of the reference generator pulse. You can visualise this happening. Say, we have the condi­tion shown in the waveforms of Fig.7 and the input pulse is wider than the reference pulse. The motor will be driven clockwise and at the same time the setting of RV changes to widen the reference pulse. This narrows the pulse from the summing junction until ultimately the input pulse and reference pulse cancel each other exactly and the result is zero output to the motor. The servo is now in the null or neutral position and will stay that way until the input pulse changes. The same thing happens when we have the conditions shown in Fig.8. Here the input pulse is narrower than the reference pulse and the motor is driven anticlockwise. This changes the setting of RV to reduce the duration of the reference pulse until again, the input pulse cancels out the reference pulse and the motor arrives at the neutral position. To sum up, if the input pulse is narrow, the servo will move until the reference pulse is also narrow. If the input pulse is wide, the servo will move until the reference pulse is equally wide. Relating this back to the beginning of the article when we said that the neutral pulse width is typically 1.5ms, this means that when the input pulse width is also 1.5ms, the servo seeks the neutral or null position which is usually in the centre of its travel. If the input pulse is 2ms wide, the servo will move clock­ wise. If the input pulse is 1ms wide, the servo will move anticlockwise. Servo phasing In case you are wondering how to work out the correct sense for the potentiometer wiring let me tell you a simple way. You wire the positive and negative leads to the two outside tabs on the pot and the wiper to the lead coming from R14. When you plug the servo in, if it races down to Damping R4 is the main damping resistor, advancing or retarding the reference pulse generator slightly according to the direction of rotation. In this way the motor drive can be shut down just before the null point is reached, allowing the servo to coast smoothly to a stop at the correct position. In a feedback system there are three types of damping conditions possible: under-damped, over-damped and dead-beat. An under-damped servo will swing past the neutral point and then kick back past neutral and kick back again in increasingly small oscillations until the zero error point is reached. An over-damped servo will shut down well before the zero error point is reached and slowly creep back to neutral. The dead-beat servo will come straight back to the correct neutral with no over or undershoot. By adjusting R4 the correct amount of ref- SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________  Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ one end of the throw, tearing the teeth off the output gears, you know you got it wrong. You then reverse either the two outside wires on the pot or reverse the two motor wires but not both and the servo operates normally. These days the servo manufacturers usually wire the motor and pot leads directly into the amplifier PC board and servo reversing is no longer possible. Servo repairing is no longer possible or cost effective in most cases, thereby increasing the pressure on transmitter designers to provide servo reversing at the transmitter end. To tidy up the remaining parts of the amplifier descrip­tion, R14 is the feedback voltage set resistor, setting the throw of the servo. The higher the value of R14, the more travel re­quired before sufficient control voltage was available to null the error. R3 will also provide throw adjustment. Throw is de­fined as the amount of angular displacement on the output arm for any given pulse width variation. D1 is an isolation diode. R8, R9 & R10 also act as base tie-down resistors for thermal stability. R13 is a current limiting resistor. Capacitors C7 & C8 are connected from each motor termi­ nal to the case. These capacitors must be mounted on the servo motor and form the noise suppression network for the motor. R15 prevents both sides of the amplifier switching on simultaneously. November 1997  69 Fig.5: the top trace (a) is the positive-going input pulse while the second trace (b) is the negative-going reference pulse. When these two pulses are applied to the summing junction the result is zero output (c), the condition required for neutral or rest position. Fig.6: conditions for clockwise drive (CW) of the servo motor. Here the positive pulse (a) is of longer duration than the nega­tive reference pulse (b). The output of the summing junction is a positive pulse, the duration of which equals the difference between the input (positive) and reference generator (negative) pulses. Fig.7: conditions for CCW drive. The input pulse is shorter the than the reference pulse, so the output of the summing junction is a negative pulse (c) which drives the motor anticlockwise. erence generator adjustment may be achieved. A slightly under-damped servo (one kickback) is the best compromise for heavily loaded servos. Setting the damping on any servo 70  Silicon Chip is the most difficult part of the servo design. The problem begins with the pulse stretching network and encompasses such factors as servo power, slew rate, operational load, dead band This is a Silvertone servo, circa 1973, showing the double deck amplifier board complete with 11 transistors. Also visible is the drive motor and feedback potentiometer. and most importantly the minimum impulse power of the servo amplifier. The dead band is the notch that the servo comes to rest in. If this notch is too wide, then centring inaccuracies occur; if too narrow, the servo chatters away because it cannot find a spot to come to rest. This results in excess current being drawn by the servo, overheating of the amplifier and brush wear on the motor. The minimum impulse power of the amplifier is the ability of the amplifier to obtain the maximum torque from the motor on the minimum error pulse. The higher the minimum impulse power the better the resolution of the servo and the less demands on the damping network. As you can imagine, if the servo is over-damped and it shuts down too early it must rely on the minimum impulse power to creep it back to the correct neutral. If the servo is heavily loaded and with too high a dead band, then the servo may sit just short of the correct neutral, introducing a control error which is annoying to the operator of the model. Worse still the servo is drawing excessive current, reducing battery life and overheating the transistors. Four or more servos doing this could reduce battery life to half and possibly result in a crash. So there you have it! Now you should have good understand­ing of the theory of servo operation. Just coincidentally, next month’s Circuit Notebook will include a servo based on a windscreen wiper motor. The operating principles are the same. Next month we will look at how the input pulse arrives via a remote SC or local link. BARGAIN CORNER See our WEB SITE or “Poll” (02) 9570 7910 for BARGAIN CORNER and NEW PRODUCTS. The WEB SITE has much, much more information and a catalogue. Many more items than the following sample of our “BARGAIN CORNER”. Note that we have LIMITED STOCK of some of the items. 109701.USED GEARED 24V DC MOTORS, metal gears and gear casing, very STRONG!. Approx 28RPM<at>24V, 14RPM<at>12V, starts turning at a few volts, 0.12A <at> 12V N/L, 0.16A <at> 24V N/L, motor itself is 40mm dia., 60mm long: $20. 109702. 115Vac “MUFFIN” FANS, new, 50/60Hz, 0.20A, shaded pole motor, metal frame, plastic blade, 40mm thickness: $4. 109714. INDUCTIVE PROXIMITY SWITCHES, LINK NO30MB-2AL, 30mm dia., 90mm long, two wire, 40 to 250Vac, 0.5A: $5 ea. 99710. CAR CIGARETTE LIGHTER LEADS, good quality, new, fused plug with 2A fuse, curly cord that stretches to 3 metres, terminated in 2.1mm DC plug: 3 for $5. 99711. CAR CIGARETTE LIGHTER LEADS, good quality, new, fused plug with 8A fuse, heavy duty 1.5m long 18 A.W.G. (8A rating) cable, terminated in 2.1mm DC plug: 3 for $7. 99712. UNIDIRECTIONAL ELECTRET MICROPHONE, good quality, fitted with alligator clamp for use as lapel mic and 2.8m long shielded cable terminated in jack plug: $4 ea. 99713. WIRING LOOMS, new, contains 3m each of yellow and blue stranded (0.5mm square C.S.A.) cable, 4m each of red and black heavy duty (1.5mm square C.S.A) stranded cable, also includes some automotive fuses/holders and matching spade connectors: 5 lots (70m wire) for $9. 99715. CAR COMMUNICATIONS SPEAKER IN BOX, parcel shelf mounting bracket, swivel mount, speaker is 4-ohm, 3W nom, 5W max, 50mm diameter, 1.5m cable terminated in jack plug: $6 ea. 99717. MYSTERY BOX OF ELECTRONICS, something to do with hands free phone equipment for cars, 85 x 30 x 120mm plastic box, most bits are surface mount but there are two useful power MOSFETs that could be recovered from the PCB inside, IRF9530 (P-channel, case: TO-220AB, 100V, 0.30-ohm on-resistance, 12A max) & IRF530 (N-channel, 100V, 0.16ohm, 14A): 2 boxes for $4. 79716. PCB WITH SEVEN SEGMENT DISPLAYS: PCBs from poker machines, have 5 x 7.6mm (digit height) and 4 x 20mm 7 segment LED displays which are soldered to the board : 2 boards for $6. 79717. VALVES: 6J6, 6J7, 6AV6, 6D4; new, any mixture of 10 for $20. QUANTITY 79748. HEWLETT PACKARD SWITCH MODE POWER SUPPLY- WORLDWIDE, works at any voltage 100 to 240Vac, 10.6V / 1.32A DC out, used, in plastic box 115 x 70 x 30mm with lead and DC plug. $10 79784. USED TO3 DEVICES: 1kg bag (Approx 80) of used TO3 devices, mostly transistors, some voltage regulators/ diodes/mosfets, wide variety, badly stored, most have bent pins: 1kg bag for $6. COLOUR MONITOR New 12V DC-1A 6" colour monitor, ready for enclosing, no box, just the tube and driver PCBs, digital RGB inputs (CGA?), we may have more information: $65. CALLER ID See the phone no. of your incoming calls displayed on a LCD screen while the telephone is ringing. Has 80 call memory, dialler etc. We should have an approved unit available during the month of publication. Price will be around $50! 650nm VISIBLE LASER POINTER KIT YES, NEW 650nM kit!!! Very bright! Complete laser pointer that works from 3-4V DC. Includes 650nm/5mW laser diode, new handheld case 125 x 39 x 25mm, adjustable collimator lens, PCB battery holder: $30. DISCO LASER LIGHT SHOW PACK The above 5mW/650nm kit plus our AUTOMATIC LASER LIGHT SHOW: $99. 650nm LASER POINTER SPECIAL Light weight (2 x AAA) pen sized pointer with 5mW/650nm laser diode, 140mm long, 18mm diameter: $55. 650nm LASER MODULE Our new module is fitted with a 650nM laser diode! Very small, 35mm long, 10mm diameter, 3 to 4.5V operation: $50. DC MOTOR SPEED CONTROL- EXPERIMENTERS PACK One 20A motor speed controller kit (similar to SC June 97) $18, plus two small new 12VDC motors (40mm dia., 40mm length) plus one used car windscreen wiper motor (which have internal gear reduction) for: $32. VISIBLE LASER DIODE MODULE KIT This kit has the same circuit as our “visible laser diode kit” but has a smaller printed circuit board that allows it to be fitted into a piece of tubing. Dimensions of the board are less than 25mm wide and 50mm long. 650nm/5mW laser diode. 3V operation $29. THREE STAGE IMAGE INTENSIFIER TUBES Back in stock. Make a high resolution night scope that will work in starlight! Three tubes plus the inverter kit plus a suitable eyepiece. The housing and the front lens are not supplied: $250. 32mm AUDIO AMPLIFIER: An LM386 based $9 audio power amplifier which can directly drive a speaker - needs the 32mm preamplifier. WHAT IS 32mm? All boards are 32mm, so you can house these kits in a plastic 32mm joiner: cheap plumbing part. COMPUTER POWER SUPPLY New PCB assembly only, 45 x 108 x 200mm, 120/230V AC IN, +5V-6A/12V-1A/-12V-1A/-5V-1A OUT. Circuit provided, RU approval. Modern design. Not for the inexperienced! Be quick: $16 ea. or 4 for $56. WOOFER STOPPER MkII Works on dogs and most animals, ref SC Feb 96. PCB and all on-board components, transformer, electret mic & horn piezo tweeter: ON SPECIAL $33, extra tweeters (drives 4): $7 ea. Approved 13.8V/1A DC plugpack (PP6) $10. SUPER BRIGHT BLUE LEDS BY FAR THE BRIGHTEST BLUE EVER OFFERED, super bright at 400mCd: $1.50 ea. or 10 for $10. 5mm LEDS AT SUPER PRICES 1Cd red: 10 for $4 300mCd green: $1.10 ea. or 10 for $7 (make white light by mixing the output of red green and blue) 3Cd red: $1.10 ea. or 10 for $7 3Cd yellow (small torch!) also available in 3mm: 10 for $9 Super bright flashing LEDs: $1.50 ea. or 10 for $10 PC POCKET SAMPLER KIT Ref EA Aug 96. Data logger/sampler, connects to PC parallel port, samples over a 0-2V or 0-20V range at intervals of one/ hour to one/100us. Monitor battery charging, make a 5kHz scope etc! Kit includes on-board components, PCB, plastic box and software (3.5" disk): (K90) $30. BOSSMAN ELECTRONICS This new company is a subsidiary of OATLEY ELECTRONICS, for the purpose of giving TAX EXEMPT PRICES to entitled organisations. The product range will that will be included on this list will increase rapidly. For enquiries call BOSSMAN ELECTRONICS on 02 9584 3562 or fax 02 9584 1031. NEW SEMICONDUCTOR BARGAINS 2SK2175 - MOSFETS 15A, TO220, 60V, 30W: 10 for $15, CA3140 - MOSFET input op amp : 5 for $5, TL494 - switchmode power supply IC : 5 for $5, NE555 - timer IC : 10 for $5, ICL7106 - LCD display driver : $5, ICL7107 - LED display driver: $5, IRFZ44 MOSFETS 60V,0.028-ohm on resistance,50A: 10 for $30 C8050 and C8550 transistors: 20 for $5, CMOS ICs 4001/11/13/16/17/20/24/28/40/46/6 0/66/69/93: Any mixture 10 for $8. 12V/7Ah GEL BATTERY BARGAIN Fresh stock standard plus one GEL/LEAD-ACID BATTERY CHARGER for $30. HELIUM NEON LASER BARGAINS Large 2-3mW He-Ne laser head plus a compact potted US made laser power supply. The head plugs into the supply, and two wires are connected to 240V mains. Needs 3-6V/5mA DC to enable: $100. Also 5mW tubes plus a 12V inverter kit: $80. USED ARGON - ION LASER HEADS The cheapest way to get a BLUE-GREEN LASER beam! A power supply design for these is based on a transformer with 80V <at> 10A and 3V <at> 20A secondaries. Ring or Email for more information. Head only: $250. AUDIO - VIDEO MONITOR Compact high resolution 5" screen B/W audio and video monitor. Has two way audio, built in microphone, audio amplifier, speaker and pushbutton “talk” switch. Needs a pre-amplifier and microphone for remote audio monitoring (our 32mm audio preamplifier is ideal). Has two camera inputs to allow manual or auto switching (adjustable speed) between each camera. Needs 12V DC 1A (our switched mode supply is ideal), size 160 x 190 x 150mm, has audio and video outputs for connecting to a VCR etc. Monitor and 6-way mini input connector only $125. BEST “VALUE FOR MONEY” CCD CAMERA The best “value for money” CCD camera on the market! Tiny CCD camera, 0.1 lux, IR responsive, high resolution. This camera has a metal lens housing (not plastic) and performs better than many cheaper models. The pinhole lensed version of this camera is also available for the same price: $105. KITS FOR CCD CAMERA SECURITY New INTERFACE KIT FOR TIME LAPSE RECORDING: now has relay contact outputs! Can be directly connected to a VCR or via a learning remote control: $25 for PCB and all on-board components, used PIR to suit: $12. 32mm 10 LED IR ILLUMINATOR new IR (880nm) LEDs have an output about equal to our old 42 LED IR illuminator: $14. 32mm AUDIO PREAMPLIFIER. An $8 kit that produces a “line level” signal from an electret microphone, connect the output to our . . . UHF VIDEO TRANSMITTER ($30) or $20 when bought with the camera for a complete Audio-Video link. MASTHEAD AMPLIFIER KIT Our famous MAR-6 based masthead amplifier. 2-section PCB (so power supply section can be indoors) and components kit (KO3) $15. Suitable plugpack (PP2): $6 Weatherproof box: (HB4) $2.50. Box for power supply: (HB1) $2.50 Rabbit-ears antenna (RF2) $7 (MAR-6 available separately). NICAD CHARGER & DISCHARGER High quality commercial 7.2V Nicad charger and discharger PCB assembly only. Switched mode design professional, fully assembled and tested fast NICAD battery charger and discharger PCB assembly. Switch mode circuit, surfaced mounted on a double-sided PCB. Nominal unregulated input 13.7V DC, 900mA charge current. Appears to use voltage slope detection for charge terminating, also has a timer (4060) to terminate the charge. We supply a thermistor for temperature sensing. For fast-charging 7.2V AA nicads. Basic information provided, Incredible pricing: $9 ea. or 3 for $21. VERY EFFICIENT WHITE LIGHT - LCD DISPLAY New “second grade” (few missing pixels) Sharp 640 x 480 LCD display (LM64P722). Features a very efficient long life cold cathode BL fluorescent lamp (5mm diam., 150mm long), very easy to remove! Produces useful white light at only about 1-3W AC input! Removing the display will reveal a very uniformly lit backplane with an overall size of 150 x 200mm. Complete display plus BL inverter kit: (Needs 12V-150mA): $17. Data sheets (11pages) for a similar display: $2. NICAD BATTERY SPECIAL New 1.2V-400mAhr cells wired in packs of 6, each pack has a thermal cutout switch, each cell is 16 x 45 x 5mm, as used in mobile phones, 5 packs (30 batteries) for: $10. SOLAR REGULATOR Ref: EA Nov/Dec 94 (intelligent battery charger). Efficiently charge 12-24V batteries from solar panels but can also be used with simple car battery chargers to prevent overcharging. Extremely high efficiency due to the very efficient MOSFET switch and Shottky isolation diode. We now offer a 7.5A or 15A kit: $26/$29 (K09). MORE KITS Geiger counter: $40, Breath tester: $40, 12V DC inverter for driving compact fluoro lamps plus one CFL lamp: $35, Music box: $11, Ding dong doorbell: $3.50, Siren using a 10cm speaker: $14, Electric fence using used car coil: $25 AMPLIFIER - PREAMPLIFIER AND MORE! A professional mostly SM PCB that contains a 5W amplifier based on a TDA1905 IC and a separate audio preamplifier section. We also provide a prewired high quality unidirectional electret microphone that has a wind filter and a mounting clip. A small speaker and basic hook up information is also included. Appears to have been designed for a communications system. Great for many applications including a two way intercom (2 required) that does not require switching! Available at less than the cost of the electret microphone: $15 ea., 2 for $24. OATLEY ELECTRONICS PO Box 89, Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: oatley<at>world.net WEB SITE: http://www.ozemail.com.au/~oatley Major cards with phone and fax orders, P&P typically $6. November 1997  71 Making old ships go faster Photo: Blohm + Voss GmbH A new marine propulsion system using an ABB motor and generator has boosted the speed of three rebuilt US container ships from 18 to 21 knots. Instead of “power take off” (PTO), it makes use of the “power take in” (PTI) concept to transmit 4000kW to the ships’ main shafts. Vessels (ACV). Ten years later, speed has become the dominating factor for these vessels, with large container capacities given only a second priority. The most obvious way to increase the speed of the ships was to reduce their length and to equip each of them with a new forebody and afterbody plus a new propulsion plant. However, that idea was rejected as being eco­nomically inviable. Three US container ships were recently upgraded at the Hamburg shipyard of Blohm + Voss GmbH by shortening the vessels and installing a new marine propulsion system. The reasons for the modifications to the three vessels were straightforward. Operators of container ships have had to adjust to a vastly changed economic situation in recent years. The need today is for faster, smaller container vessels with a capacity of 2500 to 6000 TEU (equivalent unit for 20-foot containers) and able to travel at a speed SL-31 – a brand new concept 72  Silicon Chip of at least 21 knots. Recognising this trend, the SeaLand Division of CSX Corpo­ ration in the USA began looking for ways to modernise its large and relatively slow container ships. These were built in Korea in the early 1980s for United States Lines (USL). The vessels, which when new were among the most economical container ships in service, originally had a storage capacity of approximately 3900 TEU and a speed of 18 knots. USL operated the ships as Atlantic Class The shipyard and shipowner eventually agreed on a complete­ ly new concept. The project name that was chosen was SL-31 (SL stands for Sea-Land, 3 for 3000 TEU and 1 for 21 knots). It proposed a reduction in the length of the ACV container ships by three hatch groups (bringing their length down from 279 metres to 248 metres), a more streamlined forebody and a higher power rating for the propeller. Extensive calculations and tests were carried out by the shipyard at the HSVA marine test insti­ tute in Hamburg to make sure that a speed of 21 knots would actually be achieved. An increase in the drive power rating would be necessary, as would modifications to the shape of the fore­body. The changes that had to be made to the body of the ship called for precision work. For example, during the removal of the midbody, a flamecut with a length of 330m had to be made in one operation and with an accuracy that would ensure that no re­machining of the storage structures would be necessary after the forebody and afterbody had been floated back together again. In addition, the electrical power connections between the two halves of the ship, involving about 350 cables and large numbers of pipes, had to be separated. After the midbody had been cut out and temporary bulkheads had been fitted, the forebody and the midbody were floated and pulled out of the dock by tugs. After this, the forebody was moved to within about 300mm of the afterbody. The dock was then floated again and the forebody pushed up against the afterbody, aligned, tacked and welded in place. The most critical part of this operation was the manoeuvring and alignment of the two halves. Very high precision was necessary, as a deviation of just a few millimetres from the original longitudinal axis would translate into a loss of speed. Optical measuring equipment was used to ensure a perfect fit. It is worth remembering that the Photo: Blohm + Voss GmbH The “Sea-Land Pride” in Dock 10 after the forebody had been cut away and with the midbody being prepared for removal. The photo on the facing page shows the ship after conversion. Next to it, on the left, is the “Sea-Land Value”. parts being manoeuvred weighed several thousand tonnes and that they had to be moved by tugs to precise positions in the dock. This part of the moderni­sation alone was a considerable achievement on the part of the shipyard. Increasing the drive power A new approach was also necessary for the upgrade of the propulsion systems. The installed machines, Sulzer 7 RLB 90 engines, were rated at 20,590kW (100%) and 18,530kW (90%). In order to run the ships at 21 knots without modifying the ves- sels, it would have been necessary to increase the engine power to about 30,000kW. By streamlining the forebody through hydrodynamic improve­ ments, an initial power saving of 3700kW could be achieved. Also the reduction in length by three hatch groups reduced the ships’ frictional resistance, allowing a further saving of 1500kW (or 5200kW in total). This meant that, to achieve the required speed of 21 knots, an additional 38004000kW would have to be fed into the propeller shaft system. To raise the drive power rating to the a b Fig.1: ACV container ship conversion based on the SL-31 concept: (a) forebody cut away and midbody removed; (b) short­ened ship with new forebody. November 1997  73 Photo: Blohm + Voss GmbH This photo shows the new, more streamlined forebody being fitted to the “SeaLand Pride”. 2 n = 102 min-1 New propeller 1 3 4 5 6 7 8 Fig.2: design of the new marine propulsion system with booster motor: (1) Sulzer diesel engine, 20,588kW; (2) Controllable-pitch propeller; (3) Gearing; (4) Booster motor, 4000kW; (5) Switch­board, 6.6kV; (6) Wartsila diesel engine, 4860kW; (7) Generator, 4374kW; (8) To bow thruster, 1800kW. 2940 7700 2860 1 ø 620 2 Fig.3: shaft arrangement for the booster motor and tunnel gear­ing: (1) Booster motor; (2) Tunnel gearing. 74  Silicon Chip required level, Blohm + Voss GmbH developed a new, unconventional concept that “reverses” the standard shaft generator system commonly in use. Previously, electrical power has been fed into the onboard power system from the main machine by means of a gear system with an attached generator. The new drive makes use of the “power take in” instead of “power take off” concept (Fig.2). In this method, 4000kW is transmitted via a 6.6kV electric motor to the main drive shaft by means of tunnel gearing which is flanged via a Vulcan coupling to the flywheel of the main machine (see Fig.3). The electric motor is fed with 4860kW (100%) or 4374kW (90%) from an additional Wartsila-Diesel generator set with a 6MVA alternator. The high-voltage switchgear and diesel-generator set are installed in a new engine room on the main deck. Many new, innovative control features were required to link the slow-speed main machine to the electric motor via the tunnel gearing. The power is transmitted to the water by a new controllable pitch propeller with a diameter of 7.1 metres. This propeller can absorb up to 24,400kW which is also the maximum power transmitted to the shaft. Although the new propeller is 0.5m smaller in diameter than the original unit, its special shape enables it to produce 20% more power. Using the machine data as a basis, the propeller power was calculated to be 19,160kW. Tests with a draught of 10m and a speed of 21 knots showed the power demand to be 18,639kW, giving a safety margin of 521kW. After converting this extra power into speed, the maximum predicted speed possible is 21.2 knots. Booster drive system As with many seemingly simple solutions, it was the small details that caused the main problems. A slow-speed diesel engine with oscillating torque had never before been combined with a constant-torque electric motor on a propeller shaft. To protect the electric motor and gearing system from the vibrations caused by the main machine, tunnel gearing was chosen. This transmits the electric motor power via a multi-disc clutch to the gear system and then via a Vulcan coupling direct to the flywheel of the main machine and the propeller shaft. The energy flow in the shaft is shown in Fig.4. To enable the two different systems to be used together, new automatic controls had to be developed for the drive system. These had to be completely reliable in every operating mode. This problem alone presented a major challenge, especially in view of the limited time that was available for the development work. For this particular application, a new digital control system was installed. The new main-machine/booster system was rigorously tested by the US Coast Guard (USCG) and the American Bureau of Shipping (ABS) with the help of Failure Mode Effective Analysis (FMEA). This involved a run-through of all possible service profiles, both in the dock and at sea, to ensure the safety and reliability of the booster system. The new electrical auxiliary system for the booster in­stallation receives its power from the booster diesel-generator set via a 6600/480V, 500kVA transformer. Photo: Blohm + Voss GmbH The new booster generator is used to feed an additional 4000kW (before losses) to the main drive shaft. 87 kW Electrical loss Self-supporting system 400 kW Booster drives bow thruster Since the booster diesel-generator is not required for docking man­oeuvres or when the ships are in port, it can also be used to drive the newly installed ABB bow thruster. Thus, the booster diesel-generator has two tasks in that it supplies: (1). additional energy for the main drive (PTI); and (2). drive power for the bow thruster. The diesel-generator set supplies power to a 6.6kV substa­tion with load feeders to the booster motor, the bow thruster and an auxiliary transformer. For this project, the Marine, Oil and Gas Industry Division of ABB Indust­ rie­technik AG supplied the electrical booster plant, the electrical equipment for the bow thruster and all of the cabling for the electrical systems. During the conversion, it was necessary, among other things, to shorten all of the cables to the forebody. This involved cutting a 40m-long section out of approximately 350 cables and then reconnecting the cables using heatshrink joints. This work was carried out in close collabora­tion with the shipyard and the suppliers of the other systems to ensure full compliance with ABS and USCG regulations. 80 kW Electrical loss Booster motor 4000 kW 159 kW Gear loss 210 kW Shaft loss Alternator Wärtsilä6000 kVA Diesel engine 12R 32 4860 kW Main engine Sulzer 7 RLB 90 20,588 kW Gearing 3822 kW 24,410 kW 20,588 kW Sea margin 3184 kW Fig.4: energy flow in the propeller shaft. Sea trials with the first ship to be completed, the Sea-Land Pride (formerly Galveston Bay), were carried out in the summer of 1994 and underscored the success of the project. The vessel, which had been running with a speed of 18 knots, achieved 19 knots without the booster system and almost 22 knots with it. In the same year, its two sister ships, Sea-Land Value and Ra­leigh Bay, were also handed over to the customer after successful SC conversions. Acknowledgement: this article has been adapted from an article that appeared in the March 1997 issue of ABB Review, published by Asea Brown Boveri Ltd. November 1997  75 VINTAGE RADIO By JOHN HILL The 4-valve Airzone superhet During the 1930s era, large TRF receivers in huge cabi­nets were very popular and remained that way for some time. However, the depression years saw many changes in radio manufac­ture and these hard times spawned a variety of smaller and cheap­ er receivers. Making a successful low-cost radio meant cutting back and although the 5-valve receiver was the accepted norm of the day, some manufacturers produced 4-valvers – something that was not all that practical at the time. While quite reasonable 4-valve receivers were common in the 1940s and 1950s, their predecessors of the early 1930s were sadly lacking in performance. Neverthe­less, the 4-valve super­hets were considerably better than their TRF counterparts. The 4-valve Airzone This month’s story is about an early Airzone 4-valve mantel style superhet of about 1933 vintage. It was bought in a fairly sad state of repair and although a few whispers (whimpers) came forth from the loudspeaker, one could not really say that the set was working. The Airzone’s valve line up is as follows: 80 rectifier, 57 autodyne mixer, 58 intermediate frequency amplifier and 59 output pentode, the latter used as a combined anode bend detector and output stage. The Airzone has an intermediate frequency of 465kHz, which means that the 3-gang tuning capacitor The budget-priced Airzone has no dial escutcheon. Instead, it features two routed grooves around a heartshaped peephole dial aperture. 76  Silicon Chip The Airzone 4-valve superhet, circa 1933. A semi-gloss lacquer treatment seemed appropriate for the age of the receiver. The speaker grille cloth was reversed so that its clean side showed through the front of the cabinet. This trick is well worth remembering if you are restoring an old receiver. and bandpass filter used on early super­ hets with 175kHz IFs were not required. That in itself would amount to a worthwhile reduction in production costs. Anode bend detection had been used in radio receivers for some time and was the current trend when the Airzone was made. However, using this method of detection on the output valve was a departure from the normal practice of putting the detector ahead of the output stage. Anode bend problems Using the output valve as an anode bend detector creates a number of problems. First, because the valve is biased to work near cut off, its plate current is considerably reduced. This means that the set requires an output transformer with a much higher than normal primary impedance, otherwise its output power will be well down compared to that from a conventional class-A output stage. Second, because of the reduced plate current, there is insufficient current flowing through the field coil to adequately energise the speaker magnet, if a standard 2kΩ field resist­ance is used. This speaker problem was overcome by employing a tapped high resistance winding. Other 4-valve receiv­ers did use standard speakers but the circuit was designed to bleed off sufficient high tension current to energise the field. It wasn’t until diode detection came into general use that the output valve was used as a conventional output stage in these early 4-valve superhet receivers. When diode detection was used, the diodes were usually enclosed in the IF amplifier valve. The old 6B7 and type 55 valves had built-in diodes and were much used during the mid-1930s. But let’s return to the old Airzone. Budget market This receiver was undoubtedly aimed at the budget end of the market. Its manufacture was so cost-effective that the lightweight plywood cabinet has no dial escutcheon and relies on a routed shape in the front panel to substitute for this common embellishment. Most receivers of that era had either a pressed brass or moulded bakelite escutcheon but not the old Airzone! The dial pointer takes the form of This view shows the front of the chassis after the restoration work had been completed. This rear view shows the chassis inside the cabinet. The old receiver cleaned up quite well, despite its initial condition. a heart-shaped peephole cut into the front panel. If a radio manufacturer was to survive in the early 1930s he had to trim costs in every way imaginable. Airzone successfully did this and was still making radios well into the post-war period. The speaker is the original Magnavox 150D, a 6-inch (150mm) electrodynamic type with a tapped field winding. The field wind­ing has an impedance of 6kΩ and is tapped at 3.5kΩ. The original high-impedance output transformer was still attached to the speaker. Fortunately, both the tapped field and the output transform­ e r were still in working order. As might be expected, these somewhat rare items are difficult to find and expensive to buy or have rewound. The IF transformers are mounted November 1997  77 – wet type was replaced with a new 10µF 500V unit. The wirewound voltage divider and cathode bias resistors are unusual in that they are wound like a bunched filament in a light globe, thus making very compact units. Also of unusual design is the type 59 output pentode in that it has two cathodes and a suppressor grid that connects to a separate base pin. Even with one heater out of action, the old 59 will still work reasonably well. While most other pentodes have the suppressor grid connected internally to the cathode and use a 6-pin base, the 59 has a pin connection for the suppressor and a large 7-pin base. Anode bend detector All the bias resistors in the old Airzone are wirewound. on top of the chassis in large aluminium cans and are adjusted by trimmer capacitors. The aerial and oscillator coils are also mounted in large aluminium cans. These are underneath the chassis and occupy approximately one third of the available space below. They hinder access to some of the valve sockets and wiring. The high tension setup is unusual in that the voltages are extremely high (460V at the rectifier) and only one filter ca­pacitor, an 8µF electrolytic on the input side of the field winding, is used. The original – and defunct The type 59 output pentode has a large 7-pin base which gives the suppressor its own pin connection. The output/detector has a very high cathode resistor of around 4kΩ, which operates the valve near its cutoff point. This is necessary for a valve operating as an anode bend detector. When set up in this manner there will be pulses of anode current during positive half-cycles at the control grid and little or no current during negative half-cycles. Thus, the valve rectifies or detects the radio frequency signal applied to its control grid. Inserting a milliamp meter in the output valve’s cathode connection was an interesting experiment. Total valve current varied between 6-10mA, depending on the signal strength at the control grid. If set up as a normal class-A output stage, a 59 would pass about 44mA. The cathode bias voltage is around 40V. Another point worth mentioning is the fact that, because of the low current flow, the valve does not operate at a very high temperature. One can grasp it firmly without being burnt. Even the rectifier works much cooler but is still too hot to hold for long. Plate voltages throughout the Air­ zone are extremely high, with 320V on the 57, 350V on the 58 and 360V on the 59. I guess that’s one way of squeezing out that extra performance. Repairs A great deal of the under-chassis space is taken up by the aerial and oscillator coils. These units restrict access to several valve sockets, making voltage checks quite difficult. 78  Silicon Chip The repairs involved replacing the paper capacitors and the previously mentioned 8µF electrolytic. Due to the high tension supply being so elevated, 630V capacitors were used throughout as some would be stressed at close to 500V potentials during the warm-up period. Vintage Radio Repairs Sales Valves Books Spare Parts See the specialists * Stock constantly changing. * Top prices paid for good quality vintage wireless and audio amps. * Friendly, reliable expert service. Call in or send SSAE for our current catalogue The power cord and speaker leads share a common grommet. The speaker has no plug and is wired directly into the circuit. RESURRECTION RADIO 242 Chapel Street (PO Box 2029) PRAHRAN, VIC 3181 Tel (03) 9510 4486 Fax (03) 9529 5639 The answers! to 260,000 questions, ALL in one book! This view shows the 80 rectifier and the 59 output detector. Note also the large IF transformer and the single wet type elec­trolytic capacitor. The cabinet required the usual re-gluing treatment and was refinished in semi-gloss. The speaker grille cloth was dirty but otherwise in reasonable condition. Turning it back to front soon solved that problem. All things considered, the old 4-valve superhet Airzone is a fairly unusual receiver when compared to the 4-valvers that followed in the diode detection era. While it was originally marketed as an economy model, it is nevertheless a very collect­ible item today – particularly as it is housed in a “Cathedral” style cabinet and retains SC its original speaker setup. The largest range of replacement semiconductors in the industry! Call now to get your new NTE cross reference book for just $25. Stewart Electronic Components P/L P.O. Box 281 Oakleigh 3166 phone (03)9543-3733 fax (03)9543-7238 November 1997  79 COMPUTER BITS BY JASON COLE Relocating your CD-ROM drive Windows 95 works well but how do you correct the problem of adding a new hard disc drive that wants to live where the CD-ROM currently lives? Hard disc drives (HDDs) have dramatically increased in size in the last couple of years, while prices have gone the other way. The only problem is that when you buy your new HDD, it generally becomes the secondary or D: drive while the older unit is kept as the C: drive (so that you don’t have to reinstall the operating system). This is fine except that your CD-ROM is now assigned the next drive letter along the chain which is E:. Of course, if the CD-ROM had been assigned a higher drive letter such as R: in the first place, then all would be well. It would retain its drive assignment when extra hard disc drives were added and the problem simply would not arise. But why is it a problem if your CDROM is shuffled from D: to E: when a new HDD is added? The answer is that Fig.1: right click My Computer, then click Properties and select the Device Manager tab to bring up this dialog box. 80  Silicon Chip any program that was originally installed from the CD-ROM, and which refers back to the CD-ROM while it is running, will no longer work. When it’s time to load that wonderful game called “LightHouse” (or whatever), it will go to the drive assignment where it thinks the CD-ROM is and find the new hard disc drive instead. And that means no fancy graphics or anything else. In short, “it ain’t gonna work mate”. One way to correct this problem is to reinstall all the CD-ROM based software. However, this might not work out too well. Any patches will also have to be reinstalled and this can be time consuming and troublesome with some of the older software packages. A more elegant way to solve the Fig.2: double-click the CD-ROM option so that it expands to show the currently installed CD-ROM drive. Fig.3 (left): selecting the CD-ROM drive, then clicking Properties and selecting the Settings tab brings up this dialog box. The current drive assignment is shown towards the bottom and you can change it by clicking the down arrows and selecting a new assignment (eg, R:). Fig.4: you launch the Registry Editor by clicking Start, Run and typing regedit on the Open line. problem is to change all pointers to the old D: drive to the new CD-ROM assignment. This is done by delving into the subterranean depths of the Registry. Now I know that I have warned about the dangers of delving into the Registry in the past but there are times when it is neces­sary. Back it up Now remember, the Registry is really, really important to the correct operation of Windows 95. For this reason, make a backup of it first so that you can restore it if you make a mistake. The Computer Bits column in the September 1997 issue tells you how to make Registry backups. Also, make sure Windows 95 is working correctly in the first place. It’s pointless fixing the brakes if the wheels are square! Before starting, I have found that it’s best if the CD-ROM is changed to another drive assignment before you install the second hard disc drive. To do this in Windows 95, just follow these simple steps: (1). Right click on My Computer (on the desktop) and select Properties to bring up the Systems Properties box. (2) Click the Device Manager tab to bring up the dialog box shown in Fig.5 (below): this is the window that appears when you launch the Registry Editor. Be sure to back the registry up first before making any changes, as the registry is vital to the operation of Windows 95. November 1997  81 Fig.6: you can search for all occurrences of D: in the Registry by pressing CTRL F to bring up the Find dialog box. Fig.1, then Double click on the CDROM option. The CD-ROM option will expand to show your currently installed CD-ROM (Fig.2). (3) Click once on your CD-ROM and then click the Properties button. A new box will open and you should now click the Settings tab to bring up a box similar to that shown in Fig.3. (4) Towards the bottom of this box, you will see a section which shows the current CD-ROM drive assignment and just below that some settings for reserving a drive letter. At this stage, the latter will probably have no assignment selected. To select an assignment, click on NORBITON SYSTEMS NS_PC101 card for XT/AT/PCs allows access to 48 I/O lines. There are 5 groups (0 to 4) available on a de-facto industrial standard 50-way ribbon cable used in STEbus and VMEbus 19" rack mount control systems. The board uses 2 x 8255 ICs. Multiple boards can be used if more I/O lines are required. NS_LED PCB gives visual access to five groups (0 to 4) of the NS_PC1OX. There is a total of 40 status LEDs. The board offers a 25-way “D” type female socket. The lines are driven by 74244 ICs & configured as a parallel printer port. This socket gives access to printer port kits, eg, stepper motors, LCDs, direct digital synthesis. NS_16_8 PCB is a system conditioning card with 16 optically isolated inputs set-up for either 12V or 24V operation. The board provides 8 single pole, double throw relays with 10 Amp contact rating. For brochure write to: Reply Paid 68 82  Silicon Chip the Start Drive Letter down arrow. A list of available assignments will now appear. Select a new assignment (R: is always a good drive letter assign­ ment for a CD-ROM drive) and the End Drive Letter will automati­cally select R: as well. (5) Click OK to close the dialog box and save the new as­signment, then click OK on the Device Manager box to close it. You will now be prompted to reset your computer so that the new changes will work. Let’s hack the Registry Now that we’ve assigned a new drive letter to the CD-ROM, let’s KITS & CARDS NS_DC_DC is a step down converter with an input range 11 to 35V DC and an output of 5 volts DC at 5 Amps, with an output ripple of approx 150mV. There is an IN/OUT 50-way connector isolating the 5V and 12V+ &12V- rails of the PC power supply. This segregates PC’s power when working on prototypes. NSDC_DC1 module used with NS_DC_DC & NSDC_DC4 converters is a 5V to 12V(+/-) step- up converter. The board utilises 743 switch mode IC with 2 x 12V regulators, with output ripple of approx 200mV. NS_UTIL1 prototyping board has 1580 bread board holes access to any 3 groups (0 to 4) on the 50-way cable pinout. Power is available from the 50-way cable format 5 volts at 2 Amps & 12V+ 12V- at 1 Amp. There is provision for array resistors with either a ground or positive common connection. NORBITON SYSTEMS PO Box 687 Rockingham WA 6968 open the Registry Editor. There is no shortcut to the Registry Editor on the Taskbar, so we must launch it using the Run command. To do this, click the Start button, select Run, type Regedit and press return (Fig.4) The Registry Editor will load and you see a window just like that shown in Fig.5. Now select (highlight) My Computer and press Ctrl F for the search engine. A window like that shown in Fig.6 will pop up and you should then type in D: and click the Find Next button. It will now go through the Registry and find any occurrence of D:. Be careful, because it will also find other values that match this criterion such as Dword: It is wise not to set the search up so that it only matches the whole string because it can miss some setup options. Search­ing for D: should locate both D: and D:/, as well as D:/progra~1 and so on. This sounds easy and it actually is. All you really have to do is think about what you are changing. In order to make the actual changes, you utilise the right click option Protect Your Valuable Issues Silicon Chip Binders REAL VALUE AT $11.95 PLUS P &P ★  Heavy board covers with 2-tone green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A11.95 plus $A3 p&p each (NZ $A8 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. Fig.7: each time you find an old drive assignment (ie, D:), right click on the name and then click Modify so that you can make the necessary changes to the Data. on the mouse. Each time you find an old drive as­signment, you right click on the Name and then left click on Modify so that you can make the necessary changes to the Data. To change the Name (should that also be incorrect), you select the Rename option – see Fig.7. Do not make any other changes except to the drive assign­ment, as changing the path will cause problems that can only be corrected by reinstalling the affected software. Once you have made the necessary changes, click the Find Next button (or press F3) to automatically search for the next occurrence of D:. Once all the changes have been made, you can then check for any missed assignments by highlighting “My Comput­er” and pressing F3 to initiate a complete new search from the top. This may take a while to do as the Registry can be quite large. When all is done, check it out by loading your favourite CD-ROM based game and see if it works. Most programs should run fine but remember to check out your System.ini and Win. ini files for programs that were written for Windows 3.x and edit any path entries accordingly. You should also inspect any .ini files that are specific to those programs and edit these if necessary. If a program still refuses to work, then reinstall it and everything should be OK. Saved game points should still be there as will all your important documents. The changes we have made only affect the programs themselves SC and not your saved data. Tip: Send Files Straight To The Recycle Bin; Do Not Click “Yes” To Confirm Sick of clicking “yes” in the confirmation box that pops up each time you press the delete key or drag files to the Recycle Bin? Then turn it off. To do this, right-click the Recycle Bin and click Proper­ties from the resulting drop-down menu to bring up the dialog box shown in Fig.8. Now clear the “Display Delete Confirmation Box” option and click OK to close the box. Now when you delete files, they will go straight to the Recycle Bin. Don’t worry about deleting the wrong stuff because it is all in the Recycle Bin and can be retrieved if necessary until the bin is cleared. You will still be prompted if you want to delete an appli­ cations (*.exe) file, however. This is because application files are considered more important than others. By the way, you can also use the Recycle Bin Properties dialog box to set the maximum size of the Recycle Bin (as a percentage of disc size). If you have two hard disc drives, you can either use the same percentage for both or set them independently. November 1997  83 SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. SILICON CHIP This page is blank because it contained advertising which is now out of date and the page has been removed to prevent misunderstandings. 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. BassBox software: where do you get it? I was really interested in the Bass Barrel subwoofer de­ scribed in the August 1997 issue of SILICON CHIP. In particular, I’m interested in the BassBox software. Can you tell me who distributes it in Australia and how much is it? (P. T., Ruther­ford, NSW). • The distributor for BassBox software is Earthquake Audio, PO Box 226, Balgowlah, NSW 2116. Phone (02) 9949 8071; fax (02) 9949 8073. We reviewed the BassBox 5.1 software in the June 1996 issue of SILICON CHIP. Back issues are available at $7 each including postage. By the way, we have had a number of enquiries wanting to know if we have published a subwoofer amplifier and the answer is no. But we did publish a subwoofer controller in the December 1995 issue (as mentioned in the article) and that could be teamed with virtually any power amplifier. On the other hand, if you wish to use the Bass Barrel in a Dolby Pro-Logic Sur- Pros & cons of high voltage transistor I am writing with an enquiry about the High Energy Ignition described in the May & June 1988 issues of SILICON CHIP. Is it possible to use a standard 2N3055 power transistor instead of the very expensive MJ10012? The current rating is nowhere near that of the MJ10012, however, from what I can work out, the current through the primary circuit never comes anywhere near this, probably more like 1A rather than the 15A of the MJ10012. The back EMF may be a problem however more of the zeners should alleviate this problem. Also to increase the spark duration can I round Sound system, you don’t need a subwoofer controller. Just hook the subwoofer power amplifier’s input to the subwoofer output on the decoder (or Dolby receiver) and you’re ready to go. While we are on the subject, some readers have discussed the Bass Barrel with hifi dealers and have been told that it would be not satisfactory because it was not an “active” system. In fact, when the Bass Barrel is teamed with its own power ampli­fier, it is an “active” system. Stabilising a 12V supply My house is on a 12V DC system and wherever possible every­thing runs on 12V except power tools, for which I use an invert­er. The problem arises with items like a laptop computer. Now it is possible to use the inverter with the 240VAC adaptor but at the lower loads of a laptop, say 20-30W, the use of a moderately large inverter (660W) at such a low load is inefficient. In effect, the consumption at the just change capacitor C1? (A. M., Bays­water, Vic). • The 2N3055 is completely unsuitable for an ignition system. The peak current through the coil can be expected to be around 5A while the peak voltage is limited to 300V by the four 75V zener diodes. These conditions are far in excess of what can be handled by a 2N3055. We understand that the MJ10012 is normally fairly expensive but you can presently buy it from Rod Irving Electron­ics at $7.95. We do not recommend that you modify the circuit in an attempt to increase the spark duration. This is a function of energy storage in the coil and since the circuit has dwell extension, no effective increase in duration can be ob­tained. TOROIDAL POWER TRANSFORMERS Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 battery system is a lot higher than the 20-odd watts of the laptop. I do have an old Toshiba 286 which fortunately runs off 12V DC. However, whilst at first glance it seems my troubles are over, in reality they’re not. The battery bank voltage can fluc­ tuate throughout the day and night. By day as the battery comes up to charge, the voltage may reach 13V. And at night as lights and the laptop drain the system, the voltage begins to fall. It is not unusual for the system to crash and keyed-in text is lost if not stored on the hard disc. The problem is therefore twofold, to produce a variable DC voltage in the range 12-24V DC, and second, to achieve a stable supply. Can you help? (R. O., Witten­oom, WA). • To stabilise your 12V supply, we suggest you try the 2A SLA battery charger published in the July 1996 issue. It may be advisable to connect a 1000µF 16VW capacitor at the output as well. Expansion in amplifier heatsink I am very enthusiastic about your new 500W amplifier as described in November 1997  89 Fig.1: this modified circuit of the High Energy Ignition System is suitable for use with cars that have a positive earth electrical system. The changes are to the trigger circuit. High energy ignition for an old Jaguar I have constructed and installed four of your High Energy Ignition kits with great success and satisfaction. They really are all they are cracked up to be. A friend of mine with a 1947 Mark IV Jaguar asked me if I could fit one to his car, which has (+) positive earth. Is this possible? If not, would it be possi­ble to modify the the August, September & October 1997 issues. I have purchased all 28 bipolar transistors and am currently sourcing the other components. I may be wrong (please forgive me if I am) but to have the 14 bipolars terminated so close to the PC board and secured to such a long heatsink, I feel that at above 80°C the thermal expansion of the heatsink may want to place the bipolar transistors at a greater pitch (and something has to give) and damage the solder joints to the PC board or the transistors themselves. Just a thought, but should the full length of transistor legs be used or perhaps flying leads to the transistors? (L. L., Carrum Downs, Vic). • The potential problem lies in the differing coefficients of expansion of the aluminium heatsink and the copper laminate of the PC board. The 90  Silicon Chip kit in some way? (P. T., Vaucluse, NSW). • We assume that the car in question has a 12V battery and the existing ignition system does not have a ballast resistor. This should be the case for an English car of that vintage. That being the case, it should be a straightforward matter to adapt the circuit of the High Energy Ignition system. In effect, the posi­tive side of the circuit goes to the case, to match the car’s electri- practical temperature range to be considered is about 70°C, say from 15°C ambient to about 85°C, by which temperature the thermal cutout should have operated to disconnect the load. If you then take the difference between the coefficients of expansion of aluminium and the PC board and allow for quite effective heat transfer via the transistor leads to the PC board, the differences in expansion for the worst case tran­sistor (at the extreme ends of the heatsink) should be no more than about .07mm. Given that the transistors have single hole mounting which does allow for some movement, we are inclined to the view that there is not a problem. Of course, if readers are concerned, they can increase the lead length of the transistors to allow for a little more compliance. cal system, and the negative supply comes from the igni­tion switch. However, the points themselves do present a problem because they pull the points input high, instead of low, as for a nega­tive-chassis car. The solution is to add a PNP transistor to invert the points switching signal. The accompanying circuit (Fig.1) should do the job. The extra components can be fitted on the existing PC board; there is vacant position for a transistor. We strongly recommend against increasing the lead length by using flying leads as it might result in supersonic oscillation. Drift in the FM Stereo Transmitter I need your help please with the FM Stereo Transmitter, as described in the October 1988 issue of SILICON CHIP. The problem is that it “drifts” off station, either over a period of five minutes or an hour or simply after switching off and then back on again. I then have to readjust either the L1 or L2 slug or both. When I first switched on and check­ ed the voltage across pins 3 & 15 and then started adjusting the slugs (with a plastic screwdriver), I found that “breathing” on the 1.5 turns of copper wire would upset the adjustment. I then “fixed” the turns with a dab of nail polish. L1 is very touchy; L2 takes maybe only 1/16 turn to reset. As I only need to “transmit” over about three metres I used the single wire antenna but even so it works well over 20 metres. (K. C., Balgownie, NSW). • The drift in frequency of transmission is probably due to the capacitance change of the tuning capacitors with temperature. Make sure that the 47pF capacitors across L1 and L2, the 15pF capacitors on pins 9 and 10 and the 4.7pF capacitor at pin 10 are NPO types. These will be labelled “NPO” or with a black dot. NPO stands for “Negative Positive Zero”. This means that the tempera­ ture coefficient of capacitance is zero for the normal operating temperature range. You can expect to affect the tuning when the antenna is held with your finger and thumb. This is because it alters the capacitance of the tuned circuit. Using a transducer with the speed control I am interested in using the 12-24V Motor Speed Controller featured in the June 1997 issue of SILICON CHIP. However, I wish to use the output from a MAP sensor in a car to control the speed of a 12V fan. The MAP sensor has an output range of zero to 5V and I wish to obtain full fan speed when the MAP sensor output is 5V. Furthermore, I would like to introduce an adjustable offset, so that the MAP sensor might produce a voltage of say, 1.5V, before the fan operated. Can this wish list be achieved or is it all a dream? (G. B., Unley, SA). • While we did not make provision for this sort of application it turns out to be relatively easy to do and just by adding one resistor. By connecting a Don’t overdrive the Bass Barrel I intend to construct the Bass Barrel Subwoofer from the August 1997 issue but I need further information. Firstly, what is the power requirement to drive this unit? Also what is the maximum (safe) power the unit can handle? Can you recommend a suitable amplifier kit? What passive low-pass filter could be used in place of the active one briefly alluded to in the arti­ cle? Thank you. (G. P., NT). • The specified woofers have a maximum rated power input of 75W and since they are in parallel, the Bass Barrel would have a nominal maximum input power of 150W. However, we do not think it would be safe to drive them at these high levels for anything more than a brief interval otherwise you run the risk 68kΩ resistor from your transducer to the pin 2 of IC1, the motor will have 12V applied to it, as set by VR1, for an input of 5V from the transducer. Furthermore, the initial offset will be 1.5V, so the effective input range is from 1.5V to 5V. By changing the resistor to 100kΩ, the offset can be re­duced to 0.3V and if you reduced the resistor to 47kΩ, the offset is increased to 2.5V. Notes & Errata Flexible Interface Card, July 1997; Stepper Motor Con­ troller, August 1997; and PC Card For Two Stepper Motors, Septem­ber 1997: in the circuit of each of these boards the resistor from pin 4 of IC1 is shown going to ground. This is how the PC boards of blowing them. In fact, we have heard of a number of instances where people have done just that. Note that this unit was originally designed for cars and is also suitable for small lounge rooms but if you use it in a large room and wind up the wick, you are bound to pay the penalty. A suitable amplifier module would be the 125/175W design featured in the April 1996 issue. This could be teamed with the subwoofer controller featured in the December 1995 issue of SILICON CHIP but remember our warning about winding up the wick. An alternative amplifier would be the 50W unit described in March 1994. Alternatively, if you intend using the Bass Barrel in a Dolby Surround system, you could use the Dolby subwoofer output to drive the Bass Barrel amplifier. will be supplied. The resistor should go to the +5V sup­ply, which is pin 16 of IC1. On each board it is quite simple to move the ground end of the resistor to the positive supply after drilling one hole. If you are only using a single board this may not be a problem, although we do suggest that you move the 10kΩ resistor so that it is wired between pins 4 and 16. The problem shows up when you are using several cards with different addresses on the same printer port and start changing these addresses. Low Dropout 5V Regulator, Circuit Notebook, October 1997: This circuit has the emitter and collector of Q1 reversed. The emitter should go to the +9V supply and the collector should SC connect to the 5V output. 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. November 1997  91 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; The Snowy Mountains Hydro Scheme. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band Transmitter. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. June 1990: Multi-Sector Home Burglar Alarm; Build A LowNoise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Build a Turnstile Antenna For Weather Satellite Reception. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; Guide Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. ORDER FORM Please send me the following back issues: _____________________________________________________________________ _______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ Enclosed is my cheque/money order for $­______or please debit my:  ❏ Bankcard  ❏ Visa Card  ❏ Master Card Signature ___________________________ Card expiry date_____ /______ Name ______________________________ Phone No (___) ____________ PLEASE PRINT Street ______________________________________________________ Suburb/town _______________________________ Postcode ___________ 92  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A8 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503. ✂ Card No. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; A Windows-Based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags – How They Work. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Nicad Zapper; Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. October 1994: How Dolby Surround Sound Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Build A Temperature Controlled Soldering Station; Electronic Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford – A Pesky Electronic Cricket; Cruise Control – How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Pre­a mp­lifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 50 Watt Per Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: FM Radio Trainer, Pt.1; Photographic Timer For Dark­rooms; Balanced Microphone Preamp. & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. May 1995: What To Do When the Battery On Your PC’s Mother­b oard Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; LowCost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Build A Reliable Door Minder (Uses Pressure Sensing); Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­v erter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. March 1996: Programmable Electronic Ignition System; Zener Diode Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1996: VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Using An Auto­ transformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter Calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Computer Problems: Sorting Out What’s At Fault; Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Model Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; Simple Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; Installing A PC-Compatible Floppy Drive In An Amiga 500; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. June 1997: Tuning Up Your Hard Disc Drive; PC-Controlled Thermometer/Thermostat; Colour TV Pattern Generator, Pt.1; Build An Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor; Fail-Safe Module For The Throttle Servo; Cathode Ray Oscilloscopes, Pt.10. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Simple Square/Triangle Waveform Generator; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers; How Holden’s Electronic Control Unit works, Pt.1. August 1997: The Bass Barrel Subwoofer; 500 Watt Audio Power Amplifier Module; A TENs Unit For Pain Relief; Addressable PC Card For Stepper Motor Control; Remote Controlled Gates For Your Home; How Holden’s Electronic Control Unit Works, Pt.2. September 1997: Multi-Spark Capacitor Discharge Ignition; 500W Audio Power Amplifier, Pt.2; A Video Security System For Your Home; PC Card For Controlling Two Stepper Motors; HiFi On A Budget; Win95, MSDOS.SYS & The Registry. October 1997: Build A 5-Digit Tachometer; Add Central Locking To Your Car; PC-Controlled 6-Channel Voltmeter; The Flickering Flame Stage Prop; 500W Audio Power Amplifier, Pt.3; Customising The Windows 95 Start Menu PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc for $10 including p&p. November 1997  93 ISSN 1030-2662 10 9 771030 266001 Subscribe today by phoning (02) 9979 5644 & quoting your credit card number, or fill in the form below & fax it to (02) 9979 6503. ❏ New subscription – month to start­­___________________________  ❏ Renewal – Sub. No._______________ RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia    ❏ $A99    ❏ $A54 Australia with binder(s)**    ❏ $A123   ❏ $A66 **1 binder with 1-year subscription; 2 binders with 2-year subscription Your Name________________________________________________ (PLEASE PRINT) Fax to (02) 9979 6503 or mail coupon to: Silicon Chip Publications PO Box 139 Collaroy 2097 Signature Address__________________________________________________ ______________________________ _______________________________________Postcode__________ Card expiry date________/________ Card No. Bankcard, Visa Card or MasterCard only, or cheque MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. CLASSIFIED ADVERTISING RATES FOR SALE Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. $59 VIDEO CAMERAS! TOP QUALI T Y M O D U L E S O N LY ! $ 5 9 1 2 MONTHS WARRANTY! Also 400 Line 0.05 lux 32mm x 32mm Modules with SONY CCD Image Sensor ONLY $99. These have Japanese Optical GLASS (not plastic) Lens Elements, Lightweight Trouble-Free FRP Lens Hold­e rs. Accessories: 14 Lenses 2.1 -12mm, MicroFine Zero Backlash Focus, Infra-Red Cut, Pass & Polarising Filters, IR Illuminators, 50-210 LED Kits & 74mW LEDs. Our Range of Modules & Cameras include 380570 Line Resolution, 0.2-0.05 lux sensitivity, 50+dB Signal: Noise Ratio, TOP QUALITY Image Sensors from SONY, SHARP & SAMSUNG, 28mm x 28mm PCBs & Digital Signal Processing Colour Cameras. COLOUR MODULES 420 Line, 1 lux, MicroFine Focus, 7 Acc Lenses ONLY $379. PCI Video Capture Cards $199. DISCRETE 36mm SQUARE & DOME CEILING Cameras ONLY $99. Baluns 100/75 ohm use Telephone or LAN cables for Video ONLY $15. Our RANGE of CCTV Equipment includes:- Monitors, Switchers, Quads, Wireless Trans­m itters, CCTV-TV Ant Interface Modules, Single Cable Power-up-Coax System, Camera Housings & Brackets, MULTI-RECORD PROCESSORS use one VCR to Record/Playback NINE FULL-FRAME FULL-RESOLUTION images, Automatic Iris Japanese Lenses ONLY $79. Many items are UNIQUE & unobtainable elsewhere. Before you buy, ask for our Illustrated Detailed Price List with Application Notes. Allth­ings Sales & Services 08 9349 9413 Fax 08 9344 5905. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & 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. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________  Bankcard    Visa Card    Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ VARIABLE VOLTAGE TRANSFORMER 0-260V, rotary control, new 10 amp, $350.00. Kiwi Electronics 03 9762 2688. DONTRONICS can be found at: http://www.dontronics.com November 1997  95 MicroZed Computers Advertising Index BASIC STAMPS & PIC Tools Altronics................................. 34-36 Scott Edwards Electronics kits in stock, including Counterfeit Stamp Our specialty is easy to learn, easy to use sophisticated CPU based controllers & peripherals, with support Daycom.......................................79 Dick Smith Electronics........... 10-13 PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (02) 6772 2777 – may time out to Mobile 014 036775 Fax (02 6772 8987 Harbuch Electronics....................91 http://www.microzed.com.au/~microzed Credit cards OK. Send two 45c stamps for info Instant PCBs................................99 Silicon Chip Floppy Index Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Inter­ net: http://www.grantronics.com.au MicroZed new Web page address: http://www.microzed.com.au/~microzed LOGGING AND GRAPH options available for DS1620 and PCVOLTMETER. Mr Softmark, PO Box 1609, Hornsby, NSW 2077. Ph/fax (02) 9482 1565. HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at: http://www.onekw.co.nz/ PCBs MADE, ONE OR MANY. Low prices, hobbyists welcome. Sesame Electronics, Ph/Fax (02) 9554 9760. sesame<at>nettrade.com.au 20 SPEAKERS 15 Watt, 4 10 Watt, 2 long horn, 2 short horn with drivers, 800 mtr cable, 4 amplifiers, mixer: $400 the lot (02) 6458 3663. 300 Watt inverter $100, 700 Watt motor generator $700. 96  Silicon Chip 68HC11 & 68HC05 DEVELOPMENT SYSTEMS: Oztechnics, PO Box 38, Illawong, NSW 2234. Phone (02) 9541 0310, fax (02) 9541 0734. http://www.oztechnics.com.au/ Jaycar ............................IFC, 45-52 Rola Australia..............................96 MicroZed Computers...................96 Norbiton Systems........................82 Oatley Electronics........................71 Resurrection Radio......................79 PIC COMPILERS and programmers (the best ones) are available from Micro­­Zed. Rod Irving Electronics .......... 84-88 CHRISTMAS LIGHTS controller gear (as seen in EA) available from Micro­ Zed. Silicon Chip Back Issues....... 92-93 $239 COLOUR VIDEO CAMERAS $239 with uP DIGITAL SIGNAL PROCESSING for Superb Colour Rendition & Long Term Stability. Cigarette Pack size Modules $239 (320 + line), $369 (450 + line, Cameras $319 (320 +), $419 (450 +). Up to 437 664 Element CCDs 752 (H) x 582 (V) for EXTRA HIGH RESOLUTION IMAGES. Options include 8 CHARACTER TITLE GENERATOR, Automatic or Manual White Balance One-Push, 3200, 4600 & 5600K to ensure correct colour balance with various light sources. TWO Back Light Compensation Patterns for difficult lighting situations. Automatic 1/100 000 or Manual Electronic Shutter 1/50, 1/100 Flickerless, 1/250, 1/500, 1/1 000 & 1/10 000. Composite & S-VIDEO outputs. VIDEO & DC Automatic Iris Lens DRIVE outputs. Automatic Black Balance. Also a Wide Range of Lenses from 2.1mm FL. Before you buy Ask for our Illustrated Detailed Price List with FULL SPECIFICATIONS & Application Notes. Allthings Sales & Services, Ph 08 9349 9413 Fax 08 9344 5905. Silicon Chip Binders/Wallcht....OBC Scan Audio..................................61 Silicon Chip Bookshop.................37 Silicon Chip Software..................69 Silicon Chip Subscriptions...........94 Smart Fastchargers.....................61 Zoom Magazine.........................IBC _____________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: •  RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. •  Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. MicroZed has 8-pin 6 I/O (up to 4 I/O can be A>D) 12C672 at $5 ea, $6.10 incl S/t. Quartz window version $25 + S/t.