On 07-Feb-12 21:36, alan smith wrote:
> hi group..me again
>
> I want to bounce something off the members.
>
>
> 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).  They have come back and asked for
> a better resolution.
>
> Now a thermistor, it simply generates a voltage
> as a divider with a source impedance of course.  As the temperature chang=
es, the voltage that
> is
> generated across it changes, and the resolution
> of what you can measure is going to be dependent on the source voltage as=
 well
> as the ADC resolution.
>
> So the ONLY way to get better resolution is to
> be able to increase the source voltage from 3.3V to 5V or use a higher
> resolution ADC.  Now for either case, the
> micro thats reading this is 3.3V, so using 5V is out of the question.
>
> Sorta thinking....using a PIC running at 5V to
> read the thermistor, and then either using a PWM output (with RC filter) =
to regenerate
> a voltage of controlled steps over the temperature range they want to mea=
sure
> (pretty sure its 0 to 100F) for the ADC in their part to measure.
>
> Any  other possible clever ideas?
>
>

What about using a constant current source?
What other higher voltages (or negative) are available? What is the=20
resolution now and what is required? What are the resistances at 0 and=20
100 degrees F?

Djula
--=20
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