Revision 0:964a928b323e, committed 2015-04-14

Comitter:

Guillaume31

Date:

Tue Apr 14 11:36:17 2015 +0000

Commit message:

AirQualityClick on A0 on Nucleo-F411RE

Changed in this revision

diff -r 000000000000 -r 964a928b323e Air.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Air.cpp	Tue Apr 14 11:36:17 2015 +0000
@@ -0,0 +1,98 @@
+#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));
+}

diff -r 000000000000 -r 964a928b323e Air.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Air.h	Tue Apr 14 11:36:17 2015 +0000
@@ -0,0 +1,36 @@
+#ifndef AIR
+#define AIR
+
+#include "mbed.h"
+
+/// 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 Air {
+ private:
+    AnalogIn _pin;
+ public:
+    Air (PinName 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