Marechiare wrote:
> He didn't say the frequency is constant.

Actually he started by asking about measuring individual pulses.  I am
really skeptical that is going to work.

> Thus he could vary the
> frequency of the sine during the mesarument, get the analog difference
> signal, digitize it, and then using math, based on many points,
> calculate the frequency of ZERO PHASE SHIFT.

It's a little unclear what you are saying, but using multiple frequencies
and measuring the phase delay of each relative to some reference is probably
the best way to measure distance via sound.

> ... generated by 100 mHz DAC.

Huh?  100 millihertz is way way too low for the tiny systems the OP was
describing.  Think of the size of the transducers you'd need to get any
meaningful amount of air to move when one cycle takes 10 seconds.


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