At 12.12 2012.02.08, you wrote:
>
>
>> -----Original Message-----
>> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
>> Of alan smith
>> Sent: 07 February 2012 20:37
>> To: Microcontroller discussion list - Public.
>> Subject: [EE] increasing sensitivity of a thermistor
>>=20
>> hi group..me again
>>=20
>> I want to bounce something off the members.
>>=20
>>=20
>> So I have a board that I designed with a 10K
>> thermistor, but its feeding a 3.3V micro (and that is fixed...cant chang=
e
>> this
>> part).  They have come back and asked for
>> a better resolution.
>>=20
>> 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 a=
s
>> well
>> as the ADC resolution.
>>=20
>> 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.
>>=20
>> 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.
>>=20
>> Any  other possible clever ideas?
>
>If you have (or can introduce) at least 0.5LSB's worth of noise into=20
>the thermistor circuit you can simply oversample to gain increased=20
>resolution e.g. sample 4 times to gain one extra bit, 16 times to gain=20
>2 extra bits etc.

Delta-Sigma cleverness. :)

--=20
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