Tom, while I used Honeywell/HyCal calibrated sensors with a voltage
output in my PIC-based weather station, I've since looked at the G-CAP
family and the related App note using a 555 Timer. I would recommend that
route since it's simple, low-cost, and you just count pulses.

   - Tom

At 03:50 PM 4/13/00 +0200, TOM THERON wrote:
>Hi all,
>
>I want to do a humidity sensing application, using either a G-Cap (General
>Eastern Instruments) or Smartec capacitive humidity sensor. There are
>diiferent ways to interface these to a micro processor, of which two are
>options for me to interface it to a 12c... Pic.  One method is to use the
>sensor as the capacitive element in a RC network for a 555 oscillator, then
>read the resultant frequency and translate it to humidity. Other is to use
>an AC bridge (excitation supplied by Pic), with some amplification  and then
>into ADC onboard Pic.
>
>The 555 option seems to me most cost effective, and easiest, but I'd like to
>hear if anybody else did the same type of experiment and what there findings
>were?
>
>Regards
>Tom Theron


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)