In a message dated 98-01-07 11:48:01 EST, you write:

<<
 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.

 What I am currently doing is the method shown at:
 http://www.geocities.com/SiliconValley/2499/answers.html#PIC00065
 and measuring the charge time.  The times seem to vary quite a bit when the
 pot is in the same position.

 Is there a better way to get more stable readings?

 BTW I am using a 16C84 for the project.  If I can't get it to work right,
 I'll switch to the 16C71 and use the A/D converter.

 Thanks for any help

 Norm >>

Hello Norm,
I haven't looked at the URL you mentioned but I have used this method quite a
bit and it works very well.  You need to select good quality caps to prevent
drift.  Use a mylar cap.  Also experiment with the cap values.  I used a 16
bit counter instead of the usuall 8.  This steadies things up a bit.  Then you
only use the MSB of the counter for your value.  All of the drift will show up
in the LSB which you ignore.
I use this method when I need simple numeric input.  End users understand
knobs.  I made a bottled water pump for refridgerator ice makers.  The timer
on the pump was set with a simple knob.  It works great.

Dave Duley