optimizations

lib/MQ135New/MQ135New.cpp

@@ -4,21 +4,25 @@ MQ135::MQ135(uint8_t pin) {
   _pin = pin;
 }
 
-double MQ135::getRS() {
-    double voltage = getVoltage();
-    double RS = (double)((double)(VIn * RL) / voltage) - RL;
-    return RS;
+double MQ135::getVoltage() {
+    return (double)analogRead(_pin) * VStep;
 }
 
-double MQ135::getVoltage() {
-    int value = analogRead(_pin);
-    double voltage = (double)(value * VIn) / (double)(Resolution - 1);
-    return voltage;
+double MQ135::getResistance() {
+    double voltage = getVoltage();
+    double rs = ((VIn * RL) / voltage) - RL;
+    if (rs < 0) {
+        rs = 0;
+    }
+    return rs;
 }
 
 double MQ135::getPPM(float a, float b) {
-    double ratio = getRS() / R0;
+    double ratio = getResistance() / R0;
     double ppm = a * pow(ratio, b);
+    if (ppm < 0) {
+        ppm = 0;
+    }
     return ppm;
 }
 
@@ -47,10 +51,15 @@ double MQ135::getTolueno() {
 }
 
 float MQ135::getR0() {
-    double r0 = getRS() / 3.6;
+    double r0 = getResistance() / 3.6;
     return r0;
 }
 
+double MQ135::getR0By(float ppm, float a, float b) {
+    double tmp = (log10(ppm / a) / b) - log10(RL);
+    return pow(10, tmp);
+}
+
 void MQ135::setR0(float r0) {
     R0 = r0;
 }

lib/MQ135New/MQ135New.h

@@ -9,23 +9,28 @@
 
 #define ATMOCO2 397.13
 
+const double VStep = (double)VIn / (Resolution - 1);
+
 class MQ135 {
  private:
   uint8_t _pin;
   float R0;
-  double getPPM(float a, float b);
 
  public:
   MQ135(uint8_t pin);
+  float getR0();
+  double getR0By(float ppm, float a, float b);
+  void setR0(float r0);
+  
+  double getVoltage();
+  double getResistance();
+  double getPPM(float a, float b);
+
   double getAcetona();
   double getAlcohol();
   double getCO();
   double getCO2();
   double getNH4();
   double getTolueno();
-  float getR0();
-  void setR0(float r0);
-  double getRS();
-  double getVoltage();
 };
 #endif

src/main.cpp

@@ -1,5 +1,5 @@
 #include <Arduino.h>
-#include <MQ135New.h>
+#include "MQ135New.h"
 
 #define PIN_MQ135 A0
 #define PIN_LED_GREEN DD2
@@ -22,12 +22,17 @@ void printValues(float ppm, float temp, float humidity);
 
 void loop() {
   float value = co2_sensor.getCO2();
+  Serial.print("co2: ");
   Serial.println(value);
-  Serial.print("rs: ");
-  Serial.println(co2_sensor.getRS());
+  Serial.print("resistance: ");
+  Serial.println(co2_sensor.getResistance());
   Serial.print("voltage: ");
   Serial.println(co2_sensor.getVoltage());
-  delay(500);
+  Serial.print("r01: ");
+  Serial.println(co2_sensor.getR0());
+  Serial.print("r02: ");
+  Serial.println(co2_sensor.getR0By(1, 110.47, -2.862));
+  delay(2000);
   // if (count >= maxCount || count < 0) {
   //   float temp = bme.readTemperature();
   //   float humidity = bme.readHumidity();