You MIGHT be able to come up with a function that does the correction,
then do the calculation on the fly. I use Curve Expert to fit data to
curves. For my thermistor based cow thermometer, the curve was not pretty.
So, I took data points from the thermistor manufacturer (every 1 degree C)
and had the PIC do linear interpolation between these values. The circuit
uses a 16 bit ADC. The thermistor goes to ground with a pull-up (0.1%
resistor) to the ADC reference (so reference errors cancel). I used a
spreadsheet starting with the resistance for each degree C. The next
column had the calculated voltage for the voltage divider for each degree
C. The next column had the expected ADC value for each degree C. Another
column had calculated degrees F for each degree C. The PIC got three
tables (actually, arrays, since I wrote this in C). The raw ADC value does
a table lookup in the ADC array and calculates what fraction of the step
to the next value is needed to get the exact value. The same entry in the
F or C table is used, then linearly interpolated up to the correct value.
Works nicely!

Harold

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