Perhaps you could put a low frequency oscillator on each board, triangle
wave at let's say 20 Hz. The oscillators can be analog, free running and
start when power is applied to the board. When the micro comes up,
sample the instantaneous voltage with one of the a/d channels (assuming
you have one). The tolerance in the oscillator parts should give enough
randomness to the frequencies that your initial reading numbers should
be quite random.
Just a thought...
Regards,
Mike M.



> Maybe you could buy good resistors of varying values and mix your own random
> selection by dumping them in a barrel and shaking them up.

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