The variation in ON resistance has no effect until you load the ouput of
the mux. The input of a PIC A/D is a pretty high resistance, much higher
than the mux. The other concern is OFF resistance or leakage current. How
will the voltage on nonselected channels affect the selected one?
        I have used one level of 4051's with 10K pots and gotten at least 8 bit
resolution with a 16c74 (I can get a stable reading with variation only
at the "bit boundary" areas of the pot).
        To get 64 analog inputs, how about a single level of 4051's driving 8
analog inputs on the PIC?  I did this for 24 inputs.

Harold




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