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Getting the Good Parts from Scanners!

Useful parts for nothing

by Julian Edgar

Click on pics to view larger images


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 hard rubbish collections and the tip. But what use can be made of the parts inside?

Despite first appearances, quite a lot.

Pulling the 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 moved by a geared-down stepper motor that operates a toothed belt to which the carriage is attached. Image processing circuitry is included, as is (usually) a position sensor to detect when the carriage is at its ‘start’ position.

So getting the bits is easy – but what uses can you put them to?

CCFL

Click for larger image

The Cold Cathode Fluorescent Light (CCFL) is run by a high voltage (HV) power supply. (It’s important to realise that it’s high enough in voltage to give you a shock or burn your skin!) 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. If the original input voltage is unknown, go up only a few volts over the ‘light-up’ voltage of the CCFL.

In the case of three wire power supplies, in addition to the red and black wires there’ll be a ‘control’ input. With power connected via the red and black wires, supplying this control input with a small voltage (eg 1V) will cause the CCFL to light.

Scanner CCFLs have a measured power of 2-3W.

The 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. Finally, they are quite bright!

However, you must remember that the tubes are also fragile – where possible, they should be supported in the same way as they were in the scanner carriage and you cannot expect them to be anywhere near as rugged as LEDs. Also remember that in use, the power supply must be well insulated away from probing fingers.

Click for larger image

Ex-scanner CCFLs are ideal in model railway layouts (where they can provide concealed factory and station lighting), for low voltage lighting (eg in a caravan or solar home), or for instrument and gauge lighting. At Zero Cost High Tech Interior Lamp we used an ex-scanner CCFL as a new boot-light, a job it did brilliantly (pun intended!).

Front Housing

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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, if the housing is placed over a shallow tray that’s been filled with soil, an ideal device for germinating seeds is formed.

Want some other uses? The front housing can also be used to provide a layer of protection for 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 pre-cut, zero cost small sheet of good quality glass, here it is! Why on earth would you throw it away?

Stepper Motor

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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 wherever 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 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 – electronic kits are available that can do this.

But you don’t need to electronically drive the stepper - instead you can apply physical effort to rotate the output shaft and so generate power!

The 16:1 reduction ratio then becomes a 16:1 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 easily-achievable 1500 rpm!

The power produced is enough to charge a battery or run a white LED. 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. (And the disadvantage is that the plastic gear-train will have a finite life.)

Miscellaneous

Also, 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 typically 8mm in diameter and if you have a metal turning lathe and/or a set of thread-cutting dies, make an 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 Hall-effect position sensors.

And I nearly forget one of the gems – the final focusing lens.

Scanners 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 diameter by 10mm long, these very short focal length lenses (eg. a focal length of 15mm) make for extremely effective close-up hand lenses. They’re not super bright, but they’re of excellent quality and provide huge magnification.

Finally, most scanners that you’ll find discarded are powered by plugpacks – and many people throw these away at the same time as they’re getting rid of the scanner. And you can never have too many different voltage/current plugpacks on the shelf…

Conclusion

Perhaps you’re not interested in free, high efficacy, compact low voltage fluorescent lighting. Or maybe seed germination boxes leave you cold. Or perhaps you can’t think of any uses for geared stepper motors or hand-cranked generators. A compact, high magnification hand lens? Well, it bores you. Having a range of different plugpacks available without cost? Who cares!

And all that’s OK – just make sure you give any old scanners that you find to someone who doesn’t share your ideas!

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