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Transducers

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Robo:
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.

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

These are the best transducers I can find at 18ft
http://www.acroname.com/robotics/parts/R241-SRF10.html
http://www.acroname.com/robotics/parts/R145-SRF08.html

This one claims 35 ft
http://www.acroname.com/robotics/parts/R11-6500.html
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
http://home.howstuffworks.com/question238.htm

My best recommendation is buying one of these motion sensors, and hacking them for the output.
http://froogle.google.com/froogle?sourceid=navclient&ie=UTF-8&rls=DGUS,DGUS:2006-11,DGUS:en&q=passive%20human%20motion%20detector&sa=N&tab=wf

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!

Robo:
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 don’t have otherwise.

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