>From:         Derrick Early <early@FINITE.NRL.NAVY.MIL>
>Maybe I should do this with an analog circuit. :(  I'm not sure if a 20 MHz

I also thought of implementing a DTMF decoder with the '71 (with the built
in A/D).  I soon realized that the limited ram on these chips severely
restricts the resolution of any FFT program.

You may want to use a PIC controlled bandpass filter and sweep
the pass band around.  Have the PIC output a frequency that is multiplied
by the incoming signal using a 4 quadrant multiplier.  Low pass filter the
output of the multiplier and peak detect the result.  This can serve
as the amplitude of your signal.

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