Thermistor Function Builder

Enter thermistor resistance at two temperatures...

Sample	Temperature	Resistance
'Cold'
'Hot'

Enter the series resistor value, (or leave it blank).
Series Resistor

Select a circuit (see diagrams below).
Thermistor on top
Thermistor on bottom

Code

float ThermistorTemperature(int adcNumber){
float reading;

	adcNumber=analogRead(adcNumber);
	reading=adcNumber;
	if(adcNumber==0) reading=0.001; // avoid a divide by zero scenario
	
	reading=10000.0*(1023.0/reading)-10000.0;
	if(reading==0.0) reading=0.00001; // avoid still another divide by zero problem
	// reading is now a resistance

	reading=4879.7/log(5000.0/reading);
	reading=373.15*reading / (reading-373.15);
	// reading is now in Kelvins

	// Celcius: Uncomment following line to return degrees C
	// reading=reading-273.15;

	// Fahrenheit: Uncomment following line to return degrees F
	// reading=(reading-273.15)*1.8+32.0;

	return reading;
}

Ranges

Parameter	Min	Max
Temperature	-37.41 degC	+440.19 degC
Resistance	10.22 Mohm	9.78 ohm
ADC @ calibrated points	16	682

Resolution: 0.13 degC
top top

bottom

Instructions

Check the resistance at two temperatures which bracket the range you are interested in.
Enter these 'calibration points' into the provided fields.
Specify F, C, or K for temperatures (default is in Kelvins).
Suffixes K or M may be used for resistance.

Enter a value for the series voltage divider resistor.
Or leave it blank, and a value will be chosen automatically (see caveat below).

Finally, indicate the circuit you will be using (see the diagrams).

After submitting the form, code will be displayed to copy and paste into your sketch.
Below the code, some info about range and resolution is given (see caveats).

Caveats
This page is meant for the casual experimenter.
A lot of factors affect accuracy, which we do not try to account for.

The min and max temperature and resistance ranges correspond to ADC limits.
These figures will not be accurate, they are meant as a guide only.
Your thermistor probably cannot withstand such temperatures anyway!

No attempt is made to produce a 'standard' value for an automatically generated series resistor.
Pick a standard resistor close to the automatic value.

The resolution shown is at the high temperature calibration point.
The resolution improves somewhat as the temperature falls.
That's simply how thermistors behave.

Send questions or comments to support at swfltek.com