OptoSwitch?

Question

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 itemits is interrupted (basically, what the had in the old elevators toopen the door if somebody interrupted while it was closing). I'derather have a retroreflector on one side to keep all the wires togetherso a trasmitter and receiver should be incorporated in one componentcontrolled by a microcontroller. The distance beteeen component andretroreflector should be ~50cm-1m.A cheap solution would be nice..Thanks,gilad.

Le Chaud Lapin · Accepted Answer

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-

John Fields · Answer

---If he wants to get rid of ambient infrared sensitivity he'll need touse a modulated signal.  It's simple enough, a single IRLED pulsedwith a 50% duty cycle, 40kHz signal, and a 40kHz receiver.  DigiKeyhas both available from Sharp, and the reflector could be something assimple as a strip of aluminum foil, shiny side out, or as complex as acorner cube reflector. -- John FieldsProfessional Circuit Designer

Dan Hollands · Answer

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-- Dan Hollands1120 S Creek DrWebster NY 14580585-872-2606

OptoSwitch?

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