Thread: IR Detection
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berkeman
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Aug17-10, 12:06 PM
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Quote Quote by Wetmelon View Post
Hey experts! I've designed an infrared detection circuit to drive a motor, but I need the circuit and my math checked. I tried 5Spice, but I can't get my head around it. Circuit image attached.

Do you know about how far I would be able to detect someone crossing in front of the light? I need 10-20 feet. Even farther would be great!

Edit: I should also mention that the TIP41C transistors are the correct components, but I am only using what Eagle had in its library for the other components, so they are not necessarily to spec.
You're not really adding any gain to the IR Rx diode -- it would be better to use a photocurrent-to-voltage converter stage with an opamp. Also, for best real-world IR TX-->Rx performance, you should modulate the IR transmission and demodulate at the RX stage, to help reject DC IR and AC Mains (60Hz, 120Hz) interference.

You might be able to use Passive IR (PIR) sensing instead, if you are just looking for the motion of people / warm objects.