Folks,
I just stumbled across something a few people might find interesting,
it might also be relevant to the water seismo discussion.
Analog Devices has a capacitance to digital converter. Basically, you
hook up your capacitive (position) sensor to an excitation output pin
and a sense input pin, and the chip puts out a 24-bit digital output.
They're claiming
from 16 to 21 useful bits at a 10+ Hz rate.  the '45, '46 are for
floating sensors (single ended or differential) where you have=20
access to both sides of the capacitor, and the '47 is for a grounded
differential sensor.

http://www.analog.com/en/prod/0%2C2877%2CAD7745%2C00.html

Hooking it up isn't completely trivial, it requires=20
knowledge of microprocessor communications (I2C).  If it works
out ok, the electronics for a non-feedback seismo might be reduced to
this chip, an 8-pin microprocessor putting the data out on
RS-232, and a few Rs and Cs.

The part numbers are AD7745-AD7747. The AD7747 is not quite in=20
production yet).

Jack

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