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Mystery Thermistor A B C coefficients (Steinhart-hart model)
/*
* http://arduino.cc/playground/ComponentLib/Thermistor2
*
* 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 = (1024 * PadResistance/ADC) - PadResistor
*
* 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 3 // Analog Pin 0
float vcc = 4.96; // only used for display purposes, if used
// set to the measured Vcc.
float pad = 9880; // balance/pad resistor value, set this to
// the measured resistance of your pad resistor
float thermr = 4120; // thermistor nominal resistance
float Thermistor(int RawADC) {
long Resistance;
float Temp; // Dual-Purpose variable to save space.
Resistance=((1024 * pad / RawADC) - pad);
Temp = log(Resistance); // Saving the Log(resistance) so not to calculate it 4 times later
Temp = 1 / (0.0018990381 + (0.00012651185 * Temp) + (0.00000064511266 * 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(115200);
}
void loop() {
float temp;
temp=Thermistor(analogRead(ThermistorPIN)); // read ADC and convert it to Celsius
Serial.print("Celsius: ");
Serial.print(temp,1); // display Celsius
//temp = (temp * 9.0)/ 5.0 + 32.0; // converts to Fahrenheit
//Serial.print(", Fahrenheit: ");
//Serial.print(temp,1); // display Fahrenheit
Serial.println("");
delay(1000); // Delay a bit...
}
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