detect resistance changes

[rambo2_981]

I have an application that needs to sample temperature changes, and am looking at a part that supplies temperature in the form of resistance variations on one pin. I need to feed this somehow into a microprocessor. Any ideas on a simple circuit to detect the resistance? Bear with me ... I am new at this. Thanks.

[russlk]

Drive the resistance with a current source. The resultant voltage can be fed to an A/D.

[Chris Smith]

Or a unpainted volt meter, with battery, and paint in the values later?

[Calcbert]

I'll assume for now that you're using a thermistor (resistor that varies quite precisely with temperature).<p>There's two options that I could see. Using an Analog to Digital conversion like Russ Kincaid recommended is one good way if your microprocessor has that capability already. Connect the thermistor in series with another resistor of a precise value, and use them as a voltage divider, with the A/D sampling the voltage inbetween the resistors.<p>As another option, I believe you could create an astable oscillator circuit, such as with a 555 chip. The thermistor would change the rate of the generated pulses, and the microprocessor would count the pulses received within a certain period of time.<p>Either method will require careful choosing of component values and some calculation within the microprocessor.<p>A few other non-thermistor ideas:<p>The LM19 from National Semiconductor (http://www.national.com/ds/LM/LM19.pdf). This says it will change output voltage very linearly with temperature. This would be used with the A/D somewhat more easiliy than the thermistor/voltage divider.<p>You could also take a look at these digital output sensors from Maxim/Dallas at http://www.maxim-ic.com/MaximProducts/S ... ensors.htm .<p>Good luck.