I have cheaply modified a commercial trackball to operate with a touch-switch rather than a button (which requires pressing). I can now use a computer four or five times longer than before, and it has proved to be a real boon. I've created a web page which gives details of the modification, and wondered if it might be of some use to others.
The page of instructions is:
and someone with a little electronics experience should be able to make one.
Thanks!
Phil
I'm quite impressed by that.
Hi, Phil. That's a really good idea for people with Repetitive Stress Injuries.
Possibly I could make a couple of suggestions? First, there's a small error in the schematic -- TP2 isn't connected to GND as shown in the schematic. Your Veroboard diagram shows that TP2 is actually open.
Since you're fairly tight on space, I'd like to make a couple of suggestions which might help make your project smaller, and also make it a little harder to short out.
Since you only need one normally open relay contact, I'd go with a 5V DIP reed relay with built-in protection diode (Maplin FX88V, =A32.29 ea.) This relay has a 500 ohm coil, so you'll only need to drive 10mA with your transistor. That means you can lose the chain of 3 transistors, and replace them with one NPN darlington. Try one BC517 (Maplin N52AH, =A30.14 in stock).
You really do need at least one (and possibly a couple) of extra components to avoid shorting out the +5V and save the transistor. If you've got a few 1/8W resistors and a pF cap lurking around in your junkbox, you might want to try this (view in fixed font or M$ Notepad):
| | +5V | o----o-------------o--. | | | | RY1 | | | | | .-. V C| | | |10K - C| | | | | C| | '-' | | | | '--o | TP1 | | | o----' .----o | | | | TP2 |/ Q1 | | o----o---o-----| BC517| | | | |> | | .-. | | |/ | | | --- '--| | 3.3Meg| | --- |>
| '-' |220pF | | | | | | GND | | | | o----o---o------------' | (created by AACircuit v1.28.6 beta 04/19/05
If you're really pressed for space, the 10K resistor is the most important for safe operation, and the 220pF cap is second (it'll help with the 50/60Hz buzz). The 3.3Meg is helpful to ballast the base. If you've got "room to spare", add another 10K resistor between TP2 and the tranny base/resistor/cap node.
Again, great idea.
Cheers Chris
TA!
Thanks - yes, and I've swapped TP1/2 on the diagrams!
FABULOUS! THANKS!
MANY thanks for the help. Will alter webpage soon.
Phil
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