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Looking for small, cheap, ultrasonic transducers.  Do the systems that use two, (Transmitter & Receiver) give better range/performance than those that use the same transducer for both T & R?  I want to detect a human at about 25 feet.  -- Thanks for any and all info.

Hmmm 25ft is really far for a sensor . . .

These are the best transducers I can find at 18ft

This one claims 35 ft
You will need to buy a transducer to go with that.

What I think would be better for you is a PIR that they use in buglar systems

My best recommendation is buying one of these motion sensors, and hacking them for the output.

Many of them have a built in light/alarm sound that turns on only when it detects motion. Just connect your circuit to the light/speaker wiring.

If you decide to do this, feel free to post pics and other info here when you can!

Thanks, Admin.  --  I was using IR, however I now want to determine whether they are coming or going.  By using ultrasonics I have Doppler information that I donít have otherwise.


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