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.

 

Seperate transducers give far better performance, a transmit one should be series resonant, and a receive one should be parallel resonant. Using a single transducer comprimises one or both requirements.

Have you considered PIR sensors instead?, they replaced ultrasonic sensors years ago in burglar alarms.

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Thanks, Nigel. 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.

 

OK, 25m though is pushing things!.

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