Hi,
The problem with these voltage divider schemes is that you will only be
able to use a comparatively small fraction of the ADC range thereby
limiting your measurement resolution.  Adding additional "parallel (in
the Thevenin sense)" resistors to the network without scaling the
network to compensate will only make the problem worse.  The voltage
non-linearity of these resistive networks may actually turn out to be a
benefit if the sensor changes its resistance in an exponential or
pseudo-exponential fashion (as in a thermistor) as the resistive divider
will (sort of) compensate in the reverse direction.

In order to provide a good solution to the problem we need to know more
about the sensor characteristics and the required measurement resolution
and accuracy.  Tell us more.

Best regards,
Dave

Pic Dude wrote:
>
> For simplicity, could you not form a voltage divider
> w/2 fixed resistors, and the large variable resistor
> to be measured placed in parallel across one of the
> fixed resistors?  Of course you now need some math
> since the voltage measured at the AD port is no longer
> linearly proportional to the variable resistance.
>

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