> >Could some one please tell me how to measure capacitance
> >using a PIC. Can  I power-up the probes for a very short time
> >(few u secs) and measure the resistancs with out polarising?
> >
> >I have seen some discussion on measuring Conductivity using
> >a PIC in early August. I would like to use a similar setup to
> >measure water table depth.


Jagath,

If you are trying to measure conductance, ignore this message.

If you are really trying to measure capacitance, there are two good
ways to go about it with a PIC.  I've had a lot of luck with applyang
a variant of APP NOTE AN512.  The app note is designed to measure
resistance by charging through a known capacitance and then checking
the time to trigger a schmidt trigger input on TMR0.  You can also
measure a capacitance by charging it through a known resistance.  I
had to go through a whole lot of calibration and noise reduction
techniques, though.  Capacitors and leads are also antennae, and
antannae slurp up noise.

My code ended up using some fuzzy techniques to "weight" each reading
and add up the wieghts over a certain time period.  Since then I've
learned how to use median filters, and that's how I'd approach it
today.

I'd show you the actual code, but it's patent pending and also
probably not totally appropriate to your task.
Best Regards,

Lawrence Lile