OptoSwitch

Jul 12, 2005 2 Replies
G

Hi All,



This is for a simple home project i'm cooking up. I need an optical component that signals high (or low..) as a beam it emits is interrupted (basically, what the had in the old elevators to open the door if somebody interrupted while it was closing). I'de rather have a retroreflector on one side to keep all the wires together so a trasmitter and receiver should be incorporated in one component controlled by a microcontroller. The distance beteeen component and retroreflector should be ~50cm-1m.



A cheap solution would be nice..



Thanks, gilad.



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A

Take a 5mm IR LED and a matching photo-diode or transistor. Put at least the receiver in a tube so that it does not pick up light directly from the LED. Drive the LED with a few kHz square wave. If you use a low duty cycle you can often drive the LED with quite a large current. Use a LM2907M or similar device to trigger on the frequency that you use to drive the LED. This way you can AC couple the Rx side amplifier, and use a high gain, since you are not interested in amplitude info.

Hope this helps

Regards Anton Erasmus

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P

Possibly even use a IrDA LED pair with this sorted already, including IR pass optical filtering to only pass the light in the IR band and not all light bands.

Paul Carpenter | paul@pcserviceselectronics.co.uk PC Services GNU H8 & mailing list info For those web sites you hate
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