Opto interrupter wheel

Here's a discovery yet to be confirmed with further experimentation, but worth mentioning anyway.
It seems raw fibreglass PCB material is translucent or transparent to
infra red at the frequency used by at least some opto interrupters. I couldn't figure out why my gadget, which used an interrupter made from PCB material, didn't work when the circuit worked well enough on the breadboard. When I stuck a piece of PCB between the test device, bingo! No reaction. The PCB lets too much light through.
Idea!! Instead of filing notches around the edge of the interrupter wheel, I'll etch a pattern in copper. (I guarantee the copper will stop IR light). Now I can make rigid, reasonably precise interrupter wheels with not a shonky filing job in sight.
How come I haven't read this before? Surely someone must have discovered it before me.
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Tim Polmear wrote:

shall I post the link again to the web page that will make you an image of any kind of encoder or mask you want?
http://www.bushytails.net/~randyg/encoder/encoderwheel.html
you need tweek the defaults to understand the settings. if your settings dont make sense, it wont work.
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i use laser printed designs , then use overhead transparency acetate to print on, attach to hub (or even perforated & super glued on) and i've never had a missed interrupt. cheap, accurate and easy also.
also good for linear positioning masks, can use scaling to offsett rotational/angular problems
most laser toners uses carbon black for opacity, very good for IR barrier, even red LED too!
cadware and even MS word has enough graphis edit to create these.

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Thats an interesting discovery.
I hope that your interruptor wheel invention works.
I don't know if an interrupter wheel made this way will work. I suspect that the PCB will diffuse the light too much. Diffusion may cause problems, but I expect that this depends on how big the "cogs" are on your wheel.
Good luck with it.
-- Martin Sondergaard, London.
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