> What is the best way to read a POT without using an A/D converter?  I need
> to generate values between 0 and 128 from the reading.  It also needs to be
> repeatable i.e. when the POT is not moved, the same number is generated.
> The time limit for reading is not too critical, maybe 250 msec or less.
> Idealy it should not need "calibration" so that multiple units would behave
> the same.

The charge-based RC method can work okay, but there are some caveats to be
aware of:

[1] If the capacitor is not discharged thoroughly before each reading, the
    latent charge will cause errors.

[2] If VDD is not stable, or if there are pins switching near the RC circuit
    these factors will cause errors.

[3] The pot value should be relatively small, but should have a resistor
    in series to ensure that the resistance is never zero.  The cap value
    should be moderately big to compensate for the small R, and the leads
    between the PIC and the pot should be as short as practical.

[4] Software hysteresis can work wonders at cleaning up noisy pot signals.

[5] If noise is still a problem, voltage-based pot-measurement schemes are
    much more reliable and repeatable than RC-based ones.  You may either
    use a 16C71, or you may use one of several tricks with a 16C622 or else
    a normal PIC plus external comparator.