OptoSwitch?

You need matching LED/photodiode. For what you're doing, the wavelength will not matter much, so long as you pick a pair that are well-tuned to each other. If you're in a hurry, Radio Shack probably has some, or you can order online from Digi-Key. You have a wide variety of choices for the circuit. To get started, you could use the photodiode as an inline-switch feeding into the base of BJT that is biased to turn on when the photodiode is illuminated and off when it is not. It's generally a good idea to use lenses on the transmitter and receiver for maximum range and reliability, especially if you're going to go with a simple ON/OFF circuit. With modulation/amplification/detection, you get longer ranges, but at I wouldn't bother for the distances you're looking at.

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-Chaud Lapin-

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If he wants to get rid of ambient infrared sensitivity he\'ll need to
use a modulated signal.  It\'s simple enough, a single IRLED pulsed
with a 50% duty cycle, 40kHz signal, and a 40kHz receiver.  DigiKey
has both available from Sharp, and the reflector could be something as
simple as a strip of aluminum foil, shiny side out, or as complex as a
corner cube reflector.

Why not just get a set of the devices used to keep garage doors from closing on someone. They do just what you want and will work.

Dan

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Dan Hollands

1120 S Creek Dr Webster NY 14580 585-872-2606 snipped-for-privacy@USSailing.net