Commit a9c0e645 authored by Georg Krocker's avatar Georg Krocker

Comitting the library files

parent dc6a06be
/**************************************************************************/
/*!
@file MQ135.cpp
@author G.Krocker (Mad Frog Labs)
@license GNU GPLv3
First version of an Arduino Library for the MQ135 gas sensor
TODO: Review the correction factor calculation. This currently relies on
the datasheet but the information there seems to be wrong.
@section HISTORY
v1.0 - First release
*/
/**************************************************************************/
#include "MQ135.h"
/**************************************************************************/
/*!
@brief Default constructor
@param[in] pin The analog input pin for the readout of the sensor
*/
/**************************************************************************/
MQ135::MQ135(uint8_t pin) {
_pin = pin;
}
/**************************************************************************/
/*!
@brief Get the correction factor to correct for temperature and humidity
@param[in] t The ambient air temperature
@param[in] h The relative humidity
@return The calculated correction factor
*/
/**************************************************************************/
float MQ135::getCorrectionFactor(float t, float h) {
return CORA * t * t - CORB * t + CORC - (h-33.)*CORD;
}
/**************************************************************************/
/*!
@brief Get the resistance of the sensor, ie. the measurement value
@return The sensor resistance in kOhm
*/
/**************************************************************************/
float MQ135::getResistance() {
int val = analogRead(_pin);
return ((1023./(float)val) * 5. - 1.)*RLOAD;
}
/**************************************************************************/
/*!
@brief Get the resistance of the sensor, ie. the measurement value corrected
for temp/hum
@param[in] t The ambient air temperature
@param[in] h The relative humidity
@return The corrected sensor resistance kOhm
*/
/**************************************************************************/
float MQ135::getCorrectedResistance(float t, float h) {
return getResistance()/getCorrectionFactor(t, h);
}
/**************************************************************************/
/*!
@brief Get the ppm of CO2 sensed (assuming only CO2 in the air)
@return The ppm of CO2 in the air
*/
/**************************************************************************/
float MQ135::getPPM() {
return PARA * pow((getResistance()/RZERO), -PARB);
}
/**************************************************************************/
/*!
@brief Get the ppm of CO2 sensed (assuming only CO2 in the air), corrected
for temp/hum
@param[in] t The ambient air temperature
@param[in] h The relative humidity
@return The ppm of CO2 in the air
*/
/**************************************************************************/
float MQ135::getCorrectedPPM(float t, float h) {
return PARA * pow((getCorrectedResistance(t, h)/RZERO), -PARB);
}
/**************************************************************************/
/*!
@brief Get the resistance RZero of the sensor for calibration purposes
@return The sensor resistance RZero in kOhm
*/
/**************************************************************************/
float MQ135::getRZero() {
return getResistance() * pow((ATMOCO2/PARA), (1./PARB));
}
/**************************************************************************/
/*!
@brief Get the corrected resistance RZero of the sensor for calibration
purposes
@param[in] t The ambient air temperature
@param[in] h The relative humidity
@return The corrected sensor resistance RZero in kOhm
*/
/**************************************************************************/
float MQ135::getCorrectedRZero(float t, float h) {
return getCorrectedResistance(t, h) * pow((ATMOCO2/PARA), (1./PARB));
}
/**************************************************************************/
/*!
@file MQ135.h
@author G.Krocker (Mad Frog Labs)
@license GNU GPLv3
First version of an Arduino Library for the MQ135 gas sensor
TODO: Review the correction factor calculation. This currently relies on
the datasheet but the information there seems to be wrong.
@section HISTORY
v1.0 - First release
*/
/**************************************************************************/
#ifndef MQ135_H
#define MQ135_H
#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif
/// The load resistance on the board
#define RLOAD 10.0
/// Calibration resistance at atmospheric CO2 level
#define RZERO 76.63
/// Parameters for calculating ppm of CO2 from sensor resistance
#define PARA 116.6020682
#define PARB 2.769034857
/// Parameters to model temperature and humidity dependence
#define CORA 0.00035
#define CORB 0.02718
#define CORC 1.39538
#define CORD 0.0018
/// Atmospheric CO2 level for calibration purposes
#define ATMOCO2 397.13
class MQ135 {
private:
uint8_t _pin;
public:
MQ135(uint8_t pin);
float getCorrectionFactor(float t, float h);
float getResistance();
float getCorrectedResistance(float t, float h);
float getPPM();
float getCorrectedPPM(float t, float h);
float getRZero();
float getCorrectedRZero(float t, float h);
};
#endif
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