I too am curious as to how thermistors and the like are used to perform
temperature compensation.  I believe you have ventured into another one of those
black arts.

Why not use the PIC to do the work, assuming there is one?  If 8 bit resolution
is not enough, then use a 12 bit A/D.

If you want this gain to adjust linearly over temp, you will not likely get that
with a thermistor.  Your challenge is not just at two temperatures, but at all
temperatures.

Anyone out there know of a good book reference on the subject??

Chris Eddy

PDRUNEN@AOL.COM wrote:

> Hi Group,
>
> I have an op-amp circuit operating in the non-inverting mode with 36x
> amplification.  The Rf is 100k and the Rv is appr 3K.  I need to circuit to
> back down the gain at cold temperatures.
>
> At the low end of 0 deg, the gain would be 18 and at the high end 120 deg,
> the gain would be 36x, as a function of temperature.  So we would start with
> Rv near 3k and end with Rv near 6k.
>
> Is there a better method than using a thermistor for Rv?  Could a transistor
> or diode, FET or other be used to control the gain?  I could use a digital
> POT but that may be more expensive than desired.
>
> Thanks,
>
> Paul