On Tue, Feb 7, 2012 at 3:36 PM, alan smith <micro_eng2@yahoo.com> 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
> changes, 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
> measure
> (pretty sure its 0 to 100F) for the ADC in their part to measure.
>
> Any  other possible clever ideas?


Are you sure the accuracy and repeatability of your existing circuit better
the resolution that you're being asked to provide?

Out of interest, is this an R25 thermistor? What's the beta value?

Thx.

-m


>
--=20
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