My code is:
/*
* Inputs ADC Value from Thermistor and outputs Temperature in Celsius
* requires: include <math.h>
* Utilizes the Steinhart-Hart Thermistor Equation:
* Temperature in Kelvin = 1 / {A + B[ln(R)] + C[ln(R)]3}
* where A = 0.001129148, B = 0.000234125 and C = 8.76741E-08
*
* These coefficients seem to work fairly universally, which is a bit of a
* surprise.
*
* Schematic:
* [Ground] -- [10k-pad-resistor] -- | -- [thermistor] --[Vcc (5 or 3.3v)]
* |
* Analog Pin 0
*
* In case it isn't obvious (as it wasn't to me until I thought about it), the analog ports
* measure the voltage between 0v -> Vcc which for an Arduino is a nominal 5v, but for (say)
* a JeeNode, is a nominal 3.3v.
*
* The resistance calculation uses the ratio of the two resistors, so the voltage
* specified above is really only required for the debugging that is commented out below
*
* Resistance = PadResistor * (1024/ADC -1)
*
* I have used this successfully with some CH Pipe Sensors (http://www.atcsemitec.co.uk/pdfdocs/ch.pdf)
* which be obtained from http://www.rapidonline.co.uk.
*
*/
#include <math.h>
#define ThermistorPIN 0 // Analog Pin 0
float vcc = 5.00; // only used for display purposes, if used
// set to the measured Vcc.
float pad = 10000; // balance/pad resistor value, set this to
// the measured resistance of your pad resistor
float thermr = 10000; // thermistor nominal resistance
float Thermistor(int RawADC) {
long Resistance;
float Temp; // Dual-Purpose variable to save space.
Resistance=pad*((1024.0 / RawADC) - 1);
Temp = log(Resistance); // Saving the Log(resistance) so not to calculate it 4 times later
Temp = 1 / (0.001129148 + (0.000234125 * Temp) + (0.0000000876741 * Temp * Temp * Temp));
Temp = Temp - 273.15; // Convert Kelvin to Celsius
// BEGIN- Remove these lines for the function not to display anything
//Serial.print("ADC: ");
//Serial.print(RawADC);
//Serial.print("/1024"); // Print out RAW ADC Number
//Serial.print(", vcc: ");
//Serial.print(vcc,2);
//Serial.print(", pad: ");
//Serial.print(pad/1000,3);
//Serial.print(" Kohms, Volts: ");
//Serial.print(((RawADC*vcc)/1024.0),3);
//Serial.print(", Resistance: ");
//Serial.print(Resistance);
//Serial.print(" ohms, ");
// END- Remove these lines for the function not to display anything
// Uncomment this line for the function to return Fahrenheit instead.
//temp = (Temp * 9.0)/ 5.0 + 32.0; // Convert to Fahrenheit
return Temp; // Return the Temperature
}
void setup() {
Serial.begin(9200);
}
void loop() {
float temp;
temp=Thermistor(analogRead(ThermistorPIN)); // read ADC and convert it to Celsius
Serial.print("Celsius: ");
Serial.println(temp,1); // display Celsius
temp = (temp * 9.0)/ 5.0 + 32.0; // converts to Fahrenheit
Serial.print("Fahrenheit: ");
Serial.println(temp,1); // display Fahrenheit
Serial.println("");
delay(5000); // Delay a bit...
}
I took it form the Arduino reference site.
The Temp is 17.5 DEG C
Reading is -12.1 DEGC
What is wrong?
The pad resistor is 10K
The Thermistor is the one from the RadioShack Sidekick basic kit for arduino. And says 503 on it.
3 wires .. two or power and one is signal. LM35 outputs 10mV/°C and LM34 outputs 10mV/°F