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Fix to thermistor resistance calculation. #9

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Fix to thermistor resistance calculation. #9

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37 changes: 18 additions & 19 deletions thermistor.cpp
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Original file line number Diff line number Diff line change
@@ -1,23 +1,23 @@
/**
* Copyright (c) 2014 panStamp <[email protected]>
*
*
* This file is part of the panStamp project.
*
*
* panStamp is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* any later version.
*
*
* panStamp 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 Lesser General Public License for more details.
*
*
* You should have received a copy of the GNU Lesser General Public License
* along with panStamp; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
* USA
*
*
* Author: Daniel Berenguer
* Creation date: 11/05/2014
*
Expand All @@ -39,7 +39,7 @@
#define TEMPERATURENOMINAL 25

// Number of ADC samples
#define NUMSAMPLES 5
#define NUMSAMPLES 5

// ADC resolution
#if defined(PANSTAMP_NRG) || defined(ESP_PLATFORM)
Expand All @@ -50,15 +50,15 @@
#define VERBOSE_SENSOR_ENABLED 1
/**
* THERMISTOR
*
*
* Class constructor
*
* @param adcPin Analog pin where the thermistor is connected
* @param nomRes Nominal resistance at 25 degrees Celsius
* @param bCoef beta coefficient of the thermistor
* @param serialRes Value of the serial resistor
*/
THERMISTOR::THERMISTOR(uint8_t adcPin, uint16_t nomRes, uint16_t bCoef, uint16_t serialRes)
THERMISTOR::THERMISTOR(uint8_t adcPin, uint16_t nomRes, uint16_t bCoef, uint16_t serialRes)
{
analogPin = adcPin;
nominalResistance = nomRes;
Expand Down Expand Up @@ -92,20 +92,20 @@ int THERMISTOR::read(void)
}
average /= NUMSAMPLES;

#ifdef VERBOSE_SENSOR_ENABLED
Serial.print("Average analog reading ");
#ifdef VERBOSE_SENSOR_ENABLED
Serial.print("Average analog reading ");
Serial.println(average);
#endif

// convert the value to resistance
average = ADC_RESOLUTION / average - 1;
average = serialResistance * average;
average = serialResistance / average;

#ifdef VERBOSE_SENSOR_ENABLED
Serial.print("Thermistor resistance ");
Serial.print("Thermistor resistance ");
Serial.println(average);
#endif

float steinhart;
steinhart = average / nominalResistance; // (R/Ro)
#ifdef PANSTAMP_NRG
Expand All @@ -117,13 +117,12 @@ int THERMISTOR::read(void)
steinhart += 1.0 / (TEMPERATURENOMINAL + 273.15); // + (1/To)
steinhart = 1.0 / steinhart; // Invert
steinhart -= 273.15; // convert to C

#ifdef VERBOSE_SENSOR_ENABLED
Serial.print("Temperature ");
Serial.print("Temperature ");
Serial.print(steinhart);
Serial.println(" *C");
#endif

return (int)(steinhart * 10);
}