DIY Touch Screen

[Steve Morgan <steve@xxxxxxx>]

Folks,

Continuing the monitor theme, has anyone got any thoughts on
constructing a touch screen to retrofit to a standard (CRT or LCD)
monitor.

I'm sure I've seen before units that use an array of infra-red
emitter/receiver pairs but I've got no idea where.

So the question is, what's the scope for coming up with our own?

The idea is this... a bezel that fits on the front of an existing
monitor with a row of IR LED's along X & Y axes with corresponding IR
photodiodes opposite (say, 16x16 giving 256 crosspoints). If you can
minimise the spread from the emitters, I would have thought that a
fairly simple microcontroller-based module could handle the scanning.
The thing I'm not sure about is that issue of minimising the spread. An
IR LED has a spread of about 60 degrees, if I remember rightly. Thus I
would expect to several photodiodes to detect the signal from each of
the emitters. How about simply recessing the emitters? If a different
modulation where used for each emitter/receiver pair, would that help?
What about reflections?

Any ideas, suggestions, other issues?

I quite like the idea of bits of 2x2" timber glued to the front of all
my monitors!!

Steve




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