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SteinhartHart.cpp
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SteinhartHart.cpp
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/**
* SteinhartHart.cpp - Library for interacting with NTC thermistors
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "SteinhartHart.h"
#include <math.h>
/**
* Returns the temperature in kelvin for the given resistance value
* using the Steinhart-Hart polynom.
*/
double SteinhartHart::steinhartHart(double r)
{
double log_r = log(r);
double log_r3 = log_r * log_r * log_r;
return 1.0 / (_a + _b * log_r + _c * log_r3);
}
double SteinhartHart::getTempKelvin()
{
double adc_raw = analogRead(_reading_pin);
double voltage = adc_raw / 1024 * V_IN;
double resistance = ((1024 * _resistance / adc_raw) - _resistance);
// Account for dissipation factor K
return steinhartHart(resistance) - voltage * voltage / (K * _resistance);
}
double SteinhartHart::getTempCelsius()
{
return getTempKelvin() - 273.15;
}
double SteinhartHart::getTempFahrenheit()
{
return getTempCelsius() * 9/5 + 32;
}