>
> Hi, I heard somebody did use PIC direcly measure the capacitance by get
 discharg
> e
> time. Is there other more accurate way to directly measure capacitance ? I try
 t
> o
> interface PIC directly to the capacitance sensor (it changes from 60pF to
 70pF).
> Thanks for your help.
>
> Gu
>
 No problem. Thats how I read a PC joystick in my servo controller. Charge
the cap through the pot on the joystick and see how long it takes to go high,
flip the port & discharge it, repeat. I was dealing with 1-100k & 50nf, but
that shouldn't matter too much just work out the TC of some RC network until
the variation meets you resolution requirement. A 555 solution is of course
trivial, and probably easier given that your only an order of magnitude above
the C of the pin itself.

----------------------------------------------------------------------------
Rick Farmer           gt5876b@prism.gatech.edu  `85 CB700SC  AMA# 482666
3510 Buford Hwy K-6   85k miles and 10 years of merciless abuse and it still
Atlanta, Ga. 30329    lives, but then again a spare engine (or two) helps.