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Salvage It! BY JULIAN EDGAR The good bits inside flatbed scanners! It’s not hard to obtain a computer flatbed scanner for nothing – they’re a frequent discard that can be found at garage sales, kerbside rubbish collections and the tip. But what use can be made of the parts inside? Despite first appearances, quite a lot. Pulling a scanner apart is easy: most models just clip together and can be separated by the judicious use of a screwdriver. Inside you’ll find a moving carriage on which the cold cathode fluorescent lamp (CCFL), focusing lens and charge coupled device (CCD) image sensor are mounted. In addition, the carriage contains two or three mirrors to reflect the image to the lens. The carriage is driven by a geareddown stepper motor that operates a toothed belt. There’s usually also a position sensor to detect when the carriage is in its “start” position and, of course, the necessary image processing circuitry. So getting the bits is easy – but what can you do with them? The CCFL The Cold Cathode Fluorescent Light (CCFL) is run by a high voltage (HV) power supply which produces several hundred volts. Warning – it’s high enough to give you a nasty shock Many scanners use small stepper motors integrated into a reduction gear train. These make excellent hand-cranked generators (complete with a ~1:16 step-up ratio) or they can be used conventionally in a host of projects. siliconchip.com.au or burn your skin! In fact, given the right circumstances, a shock could be fatal. Salvaging this part of the system is very easy – in most scanners, the HV power supply is mounted close to the CCFL on the carriage or alternatively, is mounted remotely and is connected to the CCFL via some HV wires. The HV power supply is a separate circuit board and contains a transformer, inductor, a few capacitors and some transistors. The power supply is fed by either two or three wires. When there is a pair, you’ll normally find that they are red and black – red for positive, black for negative. Observing the polarity, connect a variable voltage power supply to these wires and slowly wind up the voltage. The CCFL will first light at anywhere from 4.5–21V but note that the HV power supply itself delivers several hundred volts to the lamp. If the original input voltage is unknown, don’t go up any more than a few volts over the “light-up” voltage of the CCFL. A 3-wire power supply also includes a “control” input (in addition to the red and black wires). If power is applied via the red and black wires, supplying this control input with a small voltage (eg, 1V) will cause the CCFL to light. CCFLs have some major advantages over other lighting sources. First, the tubes are extremely thin – 2.5mm is common. Second, they provide a diffuse light, usually with good colour rendition. And third, they are quite bright but at the same time remain cool! However, you must remember that the tubes are also fragile – where possible, they should be supported in exactly the same way as they were in the scanner carriage. Remember also that the power supply should be housed in a plastic case and the lamp August 2006  117 All flatbed scanners contain a Cold Cathode Fluorescent Light (CCFL) and its accompanying high-voltage power supply. It’s very easy to make these work separately from the scanner, to provide a free (or very low-cost) 2-3W fluorescent tube that can be powered by low-voltage DC! connections must be well insulated and away from probing fingers. Scanner CCFLs are typically rated at 2-3W and are ideal for use in model railway layouts (where they can provide concealed factory and station lighting), for low voltage lighting (eg, in a caravan or solar home) and for instrument and gauge lighting. Front Housing The front of the scanner consists of a flat sheet of high-quality glass mounted in a plastic housing. And that’s it – most times, the electronics, carriage and motor are all in the bottom half of the scanner. So what use is this top half? Well, it isn’t an electronic application but if the housing is placed over a shallow tray that’s been filled with soil, you get an ideal device for germinating seeds. Want some other uses? The front housing can also be used to protect solar cells that aren’t already under glass, or you can make a picture frame that matches the glass size. When I was a kid, I made a solar pie warmer that used a front glass sheet very similar in size to a typical flat bed scanner’s glass panel – so there’s another use. In short, wherever you need a precut, zero cost small sheet of good quality glass, here it is! Why on earth would you throw it away? Stepper Motor Scanners use stepper motors that are attached to compact reduction gears. Unlike many discarded consumer goods from which you can obtain steppers, the scanner stepper and its gear train often comprise a standalone, easily removable assembly. So if you want a small stepper (they’re typically 25–35mm in diameter) that’s integrated with a ~16:1 reduction drive and forms an assembly that’s only about Rat It Before You Chuck It! Whenever you throw away an old TV (or VCR or washing machine or dishwasher or printer) do you always think that surely there must be some good salvageable components inside? Well, this column is for you! (And it’s also for people without a lot of dough.) Each month we’ll use bits and pieces sourced from discards, sometimes in mini-projects and other times as an ideas smorgasbord. And you can contribute as well. If you have a use for specific parts which can 118  Silicon Chip easily be salvaged from goods commonly being thrown away, we’d love to hear from you. Perhaps you use the pressure switch from a washing machine to control a pump. Or maybe you have a use for the highquality bearings from VCR heads. Or perhaps you’ve found how the guts of a cassette player can be easily turned into a metal detector. (Well, we made the last one up but you get the idea . . .) If you have some practical ideas, write in and tell us! 70 x 50 x 40mm, reach for the nearest discarded scanner. To drive these motors, you’ll need a stepper motor control circuit. Of course, the scanner already incorporated this but it’s easiest to use new circuitry to achieve the control you want – eg, the Stepper Motor Controller kit described in the May 2002 issue of SILICON CHIP. Alternatively, you can apply physical effort to rotate the output shaft and so generate power! The 16:1 reduction ratio then becomes a 1:16 step-up ratio. By adding a crank handle to the output cog (this is easy because this cog originally needed clearance to drive the belt and so always stands proud), you can take advantage of the gear train to turn the stepper motor at an easilyachievable 1500 RPM! The resulting power produced is enough to charge a battery or run a white LED. For more on using stepper motors as alternators, see “Our Fantastic HumanPowered LED Torches” in the February 2004 issue of SILICON CHIP. The benefit of taking this approach over using a larger, direct-driven stepper is that a very compact generator or hand-cranked torch can be built. The disadvantage is that the plastic gear train may have a short life. Miscellaneous Don’t forget the other bits and pieces inside the scanner. I always salvage the chrome-plated steel bar on which the carriage rides (and it runs in bronze bushes, no less!). These bars are typisiliconchip.com.au contain a variety of pre-focusing lenses – and curved mirrors – but it’s the lens closest to the image sensor that’s the “good ‘un”. Often only about 8mm dia­ meter by 10mm long, these typically have a focal length of just of 15mm and make for extremely effective close-up hand lenses. They’re not super bright but they’re of excellent quality and provide huge magnification. They’re just the thing for inspecting solder joints or checking just how dull the ends of those supposedly sharp multimeter probes are! Finally, most scanners are powered by plugpacks and many people throw these away at the same time as they’re getting rid of the scanner. It’s worth keeping – you can never have too many different plugpacks on the shelf. Conclusion Here’s a use out of left field. A scanner cover makes the ideal top half for a small seed germinator. Alternatively, the glass can be used to cover solar cells, in small solar projects or even in a picture frame! cally 8mm in diameter and if you have a metal turning lathe and/or a set of thread-cutting dies, are excellent raw material for all sorts of projects. You’ll also find front-faced mirrors (that is, the reflected light doesn’t have to pass through the glass) and Halleffect position sensors. I’ve nearly forgotten one of the gems – the final focusing lens. Scanners Not interested in free low-voltage fluorescent lighting? Or seed germination boxes? Or geared stepper motors? Or hand-cranked generators? Or a compact, high-magnification hand lens? Or salvaging another plugpack without cost? That’s OK – just be sure you give any old scanners that you have to someone SC who can make use of them! From the publishers of SILICON CHIP PERFORMANCE ELECTRONICS FOR CARS NOT A REPRINT: More than 160 pages of new and exciting projects never published before – all designed to get top performance from your car. FASCINATING ARTICLES: 7 chapters explaining your car – engine management, car electronics systems, etc ADVANCED PROJECTS: You’ll build controllers for turbo boost, nitrous, fuel injection and much more! We explain the why as well as the how to! Available direct from the Publisher ($22.50 inc postage): Silicon Chip Publications, PO Box 139, Collaroy NSW 2097. Ph (02) 9939 3295; Fax (02) 9939 2648; email silchip<at>siliconchip.com.au or via our website: www.siliconchip.com.au siliconchip.com.au August 2006  119