David, here are a few suggestions for a solution to your problem with
harmonics:

1)  Use a dual speed PLL to initially lock onto the strong fundamental
    in 'fast' tracking mode and then automatically switch to 'slow' mode
    to stay locked onto the decaying fundamental (decrease capture
    range). The 'fast' speed would be optimized to lock onto the
    fundamental quickly and the 'slow' speed would be fast enough to
    track tuning variations but too slow to 'jump' over to a harmonic.
    The fundamental could then be measured by coupling the vco to the
    pic.

2)  Use zero crossing detection. It has the unique property of allways
    digitizing the lowest frequency, even if its not the strongest.
    A well designed front end, and possibly threshold tracking to
    maintain sensitivity could be used to extend its range.

3)  Use a switched capacitor filter with external clock input configured
    as a 'comb' filter. Lock on to the fundamental and feed it into the
    filter's clock, thereby attenuating its harmonics. Something
    creative would need to be done here to aquire the fundamental in the
    first place.

4)  Use the pic to implement an FIR or IIR filter.

5)  Use the pic to integrate its measurement of frequency and then use
    that to detect the rate-of-change. If the rate of change (slope)
    exceeds a pre-set value then we know the detection circuitry has
    switched from the fundamental to a harmonic. At that point in time
    divide the new frequency measurement by the fundamental to calculate
    the harmonic factor and use that factor in subsequent calculations.
    This idea would work best if the signal were processed first by a
    PLL to lock onto a single spectral component. In fact, you could use
    the lock detection circuitry of the PLL to detect when the
    switchover to a harminic occurs.

6)  Can you tell if a note is sharp or flat from its harmonic as well as
    from its fundamental? If so, then use a PLL front end to purify the
    spectrum (one frequency at a time) and do your function on the VCO
    signal.

7)  Use an analog input and implement a PLL in pic firmware, using a
    combination of the above ideas.

I really know absolutely nothing about music, but I hope these ideas are
usefull, or stimulate the formulation of new ones.

Regards, Dana Frank Raymond - Foxtrot Systems Ltd.
Internet: dana.raymond@canrem.com. Compuserve: 73362,3052