> So I have a board that I designed with a 10K thermistor, but its feeding =
a 3.3V
> micro (and that is fixed...cant change this part).=A0 They have come back=
 and asked
> for a better resolution.
>=20
> Now a thermistor, it simply generates a voltage as a divider with a sourc=
e impedance
> of course. =A0As the temperature changes, the voltage that is generated a=
cross it
> changes, and the resolution of what you can measure is going to be depend=
ent on the
> source voltage as well as the ADC resolution.
>=20
> So the ONLY way to get better resolution is to be able to increase the so=
urce
> voltage from 3.3V to 5V or use a higher resolution ADC.=A0 Now for either=
 case, the
> micro thats reading this is 3.3V, so using 5V is out of the question.
>=20
> Sorta thinking....using a PIC running at 5V to read the thermistor, and t=
hen either
> using a PWM output (with RC filter) to regenerate a voltage of controlled=
 steps over
> the temperature range they want to measure (pretty sure its 0 to 100F) fo=
r the ADC
> in their part to measure.
>=20
> Any=A0 other possible clever ideas?

Microchip have an app note where they obtain quite high resolution measurin=
g a thermocouple, by having the ADC 'window' on a range of the total voltag=
e swing. They adjust the window point using the PWM output to set the base =
end of the window. Maybe you could use a similar method to achieve what you=
 want. Look for AN1306 on the Microchip web site.




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