I've often wondered about using a "plate" type
variable capacitor as a rotary angle sensor.
The problem is the low pF of the things, but
you can get around this by making an oscillator
using a CMOS inverter with the cap, then feed this
high-freq signal into the PIC to trigger the
counter in external mode. Obviously use the counter
prescaler or interrupt etc to reduce the freq of
the input signal and compare to the PIC clock
speed. Apart from the external inverter, the
system uses very low hardware or software count
and should give very high resolution. :o)
-Roman


Jim wrote:
>
>    "Weeelll, with 0.82 pF * (cm^2/mm) in air you
>     better come up with a"
>
> ... bridge or other means to 'self calibrate'.
>
> This is using a PIC - correct?
>
> I can envision several worakable scenarios - including
> the use of multiple fingers cut or 'sandwiched' together
> (fabricated) from dielectric material and in a crude
> 'bridge' fashion as well.

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body