I've simplified my sonar unit, and switched to cheaper parts.

The schematic is at http://www.hamjudo.com/sonar with some notes on the
code.

The circuit now runs off of a single 5 volt supply, uses a PIC16F84, a
pair of ultrasonic transducers ($2.50/pair), a couple capacitors, and a
few resistors.  No op amps, no comparators, no transistors, not even a
diode, all the active stuff is in the PIC.

[My apologies if this hits the list twice.  I sent it 10 hours ago,
the list server didn't acknowledge it, but I've got that turned on,
"repro" is also turned on.  Also, no hits to the web page, last time
I posted on this topic, there were hits within minutes.  I know my
schematic is ugly, but you can't tell till you look at the URL.]

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