add correction calculations

MQ135.cpp

@@ -9,6 +9,10 @@ double MQ135::getVoltage() {
     return (double)analogRead(pin) * VStep;
 }
 
+double MQ135::getCorrectionFactor(float temparature, float humidity) {
+    return (CorrA * pow(temparature, 3) + CorrB * pow(temparature, 2) - CorrC * temparature + CorrD - (CorrE * humidity - CorrE * 33));
+}
+
 double MQ135::getResistance() {
     double voltage = getVoltage();
     double rs = ((VIn * RL) / voltage) - RL;
@@ -18,6 +22,10 @@ double MQ135::getResistance() {
     return rs;
 }
 
+double MQ135::getCorrectedResistance(float temparature, float humidity) {
+    return getResistance() / getCorrectionFactor(temparature, humidity);
+}
+
 double MQ135::getPPM(float a, float b) {
     double ratio = getResistance() / R0;
     double ppm = a * pow(ratio, b);
@@ -27,6 +35,15 @@ double MQ135::getPPM(float a, float b) {
     return ppm;
 }
 
+double MQ135::getCorrectedPPM(float a, float b, float temparature, float humidity) {
+    double ratio = getCorrectedResistance(temparature, humidity) / R0;
+    double ppm = a * pow(ratio, b);
+    if (ppm < 0) {
+        ppm = 0;
+    }
+    return ppm;
+}
+
 double MQ135::getPPMLinear(float a, float b) {
     double ratio = getResistance() / R0;
     double ppm_log = (log10(ratio) - b) / a;
@@ -41,32 +58,61 @@ double MQ135::getAcetona() {
     return getPPM(34.668, -3.369);
 }
 
+double MQ135::getCorrectedAcetona(float temparature, float humidity) {
+    return getCorrectedPPM(34.668, -3.369, temparature, humidity);
+}
+
 double MQ135::getAlcohol() {
     return getPPM(77.255, -3.18);
 }
 
+double MQ135::getCorrectedAlcohol(float temparature, float humidity) {
+    return getCorrectedPPM(77.255, -3.18, temparature, humidity);
+}
+
 double MQ135::getCO2() {
     // return getPPMLinear(-0.3525, 0.7142) + ATMOCO2;
     return getPPM(110.47, -2.862) + ATMOCO2;
 }
 
+double MQ135::getCorrectedCO2(float temparature, float humidity) {
+    return getCorrectedPPM(110.47, -2.862, temparature, humidity) + ATMOCO2;
+}
+
 double MQ135::getCO() {
     return getPPM(605.18, -3.937);
 }
 
+double MQ135::getCorrectedCO(float temparature, float humidity) {
+    return getCorrectedPPM(605.18, -3.937, temparature, humidity);
+}
+
 double MQ135::getNH4() {
     return getPPM(102.2, -2.473);
 }
 
+double MQ135::getCorrectedNH4(float temparature, float humidity) {
+    return getCorrectedPPM(102.2, -2.473, temparature, humidity);
+}
+
 double MQ135::getTolueno() {
     return getPPM(44.947, -3.445);
 }
 
+double MQ135::getCorrectedTolueno(float temparature, float humidity) {
+    return getCorrectedPPM(44.947, -3.445, temparature, humidity);
+}
+
 float MQ135::getR0() {
     double r0 = getResistance() / 3.6;
     return r0;
 }
 
+float MQ135::getCorrectedR0(float temparature, float humidity) {
+    double r0 = getCorrectedResistance(temparature, humidity) / 3.6;
+    return r0;
+}
+
 double MQ135::getR0ByCO2Level(float ppm) {
     if (ppm > ATMOCO2) {
         ppm -= ATMOCO2;
@@ -78,6 +124,17 @@ double MQ135::getR0ByCO2Level(float ppm) {
     return pow(10, tmp);
 }
 
+double MQ135::getCorrectedR0ByCO2Level(float ppm, float temparature, float humidity) {
+    if (ppm > ATMOCO2) {
+        ppm -= ATMOCO2;
+    }
+    else {
+        return NAN;
+    }
+    double tmp = -(log10(ppm / 110.47) / -2.862) + log10(getCorrectedResistance(temparature, humidity));
+    return pow(10, tmp);
+}
+
 void MQ135::setR0(float r0) {
     R0 = r0;
 }

MQ135.h

@@ -16,6 +16,13 @@
 /// CO2 Level in Atmosphere
 #define ATMOCO2 397.13
 
+//Correction Values
+#define CorrA -0.000002469136
+#define CorrB 0.00048148148
+#define CorrC 0.0274074074
+#define CorrD 1.37530864197
+#define CorrE 0.0019230769
+
 /// Helper to calculate Voltage from Input
 /// Voltage = input * Vin / (Resolution - 1)
 const double VStep = (double)VIn / (Resolution - 1);
@@ -33,34 +40,48 @@ class MQ135 {
   /// Get R0 in default conditions for calibration purposes.
   /// Assume CO2 Level is the default Atmospheric Level (~400ppm)
   float getR0();
+  float getCorrectedR0(float temparature, float humidity);
   /// Get R0 in custom conditions for calibration purposes.
   /// Can be used, if you know the current CO2 Level.
   double getR0ByCO2Level(float ppm);
+  double getCorrectedR0ByCO2Level(float ppm, float temparature, float humidity);
   /// Set R0 Value for calibration.
   void setR0(float r0);
-  
+
   /// Gets the resolved sensor voltage
   double getVoltage();
+
+  /// Calculate Correction Factor depending on temparature and humidity
+  double getCorrectionFactor(float temparature, float humidity);
+  
   /// Calculates the Resistance of the Sensor
   double getResistance();
+  double getCorrectedResistance(float temparature, float humidity);
   /// Calculates ppm on a exponential curve
   /// (Different Gases have different curves)
   double getPPM(float a, float b);
+  double getCorrectedPPM(float a, float b, float temparature, float humidity);
   /// Calculates ppm on a linear curve
   /// (Different Gases have different curves)
   double getPPMLinear(float a, float b);
 
   /// Gets ppm of Acetona in Air (C3H6O)
   double getAcetona();
+  double getCorrectedAcetona(float temparature, float humidity);
   /// Gets ppm of Alcohol in Air
   double getAlcohol();
+  double getCorrectedAlcohol(float temparature, float humidity);
   /// Gets ppm of CO in Air
   double getCO();
+  double getCorrectedCO(float temparature, float humidit);
   /// Gets ppm of CO2 in Air
   double getCO2();
+  double getCorrectedCO2(float temparature, float humidit);
   /// Gets ppm of NH4 in Air
   double getNH4();
+  double getCorrectedNH4(float temparature, float humidit);
   /// Gets ppm of Tolueno in Air (CH3)
   double getTolueno();
+  double getCorrectedTolueno(float temparature, float humidit);
 };
 #endif