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Hi
I have achieved a Produal Teat ntc 20 that is a termistor that is 20k when its 25 degree celcius, by putting a 20k resistor on the other side of a voltage divider, i can get a reading of about 10-40 degrees (according to data sheet). but is it possible to expand the measuring area somehow? aka use other resisistors to increase the voltage divider?

may be a simple soulution, but i'm tired, and my head is not working optimal =P
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Is a termistor the main part of a Terminator?
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The table shows resistance going from 609Ω at 120°C to 1,659,082 at -50°C.  You should be able to measure the whole range by using the thermistor as part of a voltage divider and measuring the voltage.  Since you didn't say, I'll assume your 20K resistor is used as a pull-up (connecting the pin to +5) and the thermistor is used as a pull-down (connecting the pin to ground).

float voltageAcrossThermistor = (analogRead(A0) * 5.0) / 1024.0;
float resistanceOfThermistor = 5.0/voltageAcrossThermistor * 20000 - 20000;

Then you can use a linear interpolation of the Temperature/Resistance table to get the temperature from the resistance.
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Sigh...

Ok. Take a look at:
http://www.arduino.cc/playground/ComponentLib/Thermistor
http://www.arduino.cc/playground/ComponentLib/Thermistor2

Learn how to find this kind of stuff by using Google advanced search: http://www.google.com/advanced_search  and in the "site or domain:" field put "arduino.cc"..  Then your search terms. Try "thermistor"  smiley

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