>1)  I want an audio-input tach.  I need to hear what speed the motor is
>turning at in my boats while they're on the water.  I know I'll probably
>see harmonics and secondary tones, but Scott Dattalo can probably help with
>filtering those out.
>


Thinking about this makes me wonder if the "Doppler Effect" would screw up
your results??  You know, like when a passing train blows it's whistle and
the frequency of the whistle goes down as the train gets further away and
vice versa.  If the distance between your microphone and the sound source
never changed, this probably wouldn't happen.

Wouldn't it be more accurate and easy to make a tachometer for the boat that
would send it's results to you via RF???

Just some thoughts   :o)

Barry