File content as of revision 0:964a928b323e:

#include "mbed.h"
#include "Air.h"

Air::Air (PinName 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 Air::getCorrectionFactor(float t, float h) {
  return CORA * (double)t * t - (double)CORB * t + CORC - ((double)h-33.)*CORD;
}

/**************************************************************************/
/*!
@brief  Get the correction factor to correct for temperature and humidity
a
@return The sensor resistance in kOhm
*/
/**************************************************************************/
float Air::getResistance() {
  double val = _pin.read();
  return ((1023./(double)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 Air::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 Air::getPPM() {
  return PARA * pow(((double)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 Air::getCorrectedPPM(float t, float h) {
  return PARA * pow(((double)getCorrectedResistance(t, h)/RZERO), -PARB);
}

/**************************************************************************/
/*!
@brief  Get the resistance RZero of the sensor for calibration purposes

@return The sensor resistance RZero in kOhm
*/
/**************************************************************************/
float Air::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 Air::getCorrectedRZero(float t, float h) {
  return getCorrectedResistance(t, h) * pow((ATMOCO2/PARA), (1./PARB));
}