Problem: Thermistor readings are inaccurate. These problems are not from the Steinhart-Hart equation but from either the voltage divider circuit, the analog read or how we are determining resistance.
If we utilize this equation to determine the resistance of my thermistor I do not get an accurate resistance.
Rt = R * ( 1023.0 / (float) Vo - 1.0 ) (RT is thermistor/divider top, Vo holds the data from analog read, R is the divider bottom and is defined as float 82000.00 which matches the 82 k? resistor in Rbottom)
(Note that our Vin is = 5V, not the 9V shown in the diag.)
I've read countless PDFs and websites regarding thermistors, voltage dividers, the arduino and their use. However my group and I must be missing something. We've taken our Temp/Resistance readings from 0C - 37.77C. This range is for testing the sensors, intended range will be between 37C - 148C. Here is the chart we've created: https://docs.google.com/spreadsheet/ccc?key=0AroU4BiUyB-odFRKclFHQlVjX0Eycy00NTRZd0lNSlE
Utilzing this calc http://www.thinksrs.com/support/Therm%20Calc/NTCCalibrator/NTCcalculator.htm we have come up with the following Steinhart-Hart coefficients: A= -1.531358897e-3, B= 4.353291903e-4, C= -2.488687432e-7.
Most of our work has come from [PDF]: http://web.cecs.pdx.edu/~gerry/class/EAS199B/howto/thermistorArduino/thermistorArduino.pdf
Any help would be GREATLY appreciated.
//EDIT Code for this project may be found on github. https://github.com/znorris/LazySmoker