I'm getting a range of 10 feet using a single comparator from an LM339.
The output of the LM339 is digital.  I'm not good at analog, so I
converted to digital as simply as I could.

The ultrasonic transducer is Mouser Electronics part number 251-1603.

I'll post the schematic and more notes at http://www.hamjudo.com/sonar

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paulh@hamjudo.com  http://www.hamjudo.com
The April 97 WebSight magazine describes me as "(presumably) normal".