From b57b22fdea226576c734f9a3344d1c39e4d91d74 Mon Sep 17 00:00:00 2001
From: GrafZeppelin <grafzeppelin@gamlo.de>
Date: Mon, 5 Apr 2021 16:10:16 +0200
Subject: [PATCH] init

---
 MQ135.cpp | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 MQ135.h   | 66 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 149 insertions(+)
 create mode 100644 MQ135.cpp
 create mode 100644 MQ135.h

diff --git a/MQ135.cpp b/MQ135.cpp
new file mode 100644
index 0000000..ef235f7
--- /dev/null
+++ b/MQ135.cpp
@@ -0,0 +1,83 @@
+#include "MQ135.h"
+
+MQ135::MQ135(uint8_t pin) {
+  this->pin = pin;
+  pinMode(pin, INPUT);
+}
+
+double MQ135::getVoltage() {
+    return (double)analogRead(pin) * VStep;
+}
+
+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 = getResistance() / 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;
+    double ppm = pow(10, ppm_log);
+    if (ppm < 0) {
+        ppm = 0;
+    }
+    return ppm;
+}
+
+double MQ135::getAcetona() {
+    return getPPM(34.668, -3.369);
+}
+
+double MQ135::getAlcohol() {
+    return getPPM(77.255, -3.18);
+}
+
+double MQ135::getCO2() {
+    // return getPPMLinear(-0.3525, 0.7142) + ATMOCO2;
+    return getPPM(110.47, -2.862) + ATMOCO2;
+}
+
+double MQ135::getCO() {
+    return getPPM(605.18, -3.937);
+}
+
+double MQ135::getNH4() {
+    return getPPM(102.2, -2.473);
+}
+
+double MQ135::getTolueno() {
+    return getPPM(44.947, -3.445);
+}
+
+float MQ135::getR0() {
+    double r0 = getResistance() / 3.6;
+    return r0;
+}
+
+double MQ135::getR0ByCO2Level(float ppm) {
+    if (ppm > ATMOCO2) {
+        ppm -= ATMOCO2;
+    }
+    else {
+        return NAN;
+    }
+    double tmp = -(log10(ppm / 110.47) / -2.862) + log10(getResistance());
+    return pow(10, tmp);
+}
+
+void MQ135::setR0(float r0) {
+    R0 = r0;
+}
diff --git a/MQ135.h b/MQ135.h
new file mode 100644
index 0000000..4f3d0fe
--- /dev/null
+++ b/MQ135.h
@@ -0,0 +1,66 @@
+#ifndef MQ135New_H
+#define MQ135New_H
+
+#include "Arduino.h"
+
+/// Resistor on Sensor in kΩ
+#define RL 10
+
+/// Voltage on Sensor in V
+#define VIn 5
+
+/// Board analog Input Resolution
+/// Default: 2^10
+#define Resolution 1024
+
+/// CO2 Level in Atmosphere
+#define ATMOCO2 397.13
+
+/// Helper to calculate Voltage from Input
+/// Voltage = input * Vin / (Resolution - 1)
+const double VStep = (double)VIn / (Resolution - 1);
+
+class MQ135 {
+ private:
+  /// input pin
+  uint8_t pin;
+  /// calibration Resistance
+  float R0;
+
+ public:
+  /// Constructor with analog input Pin
+  MQ135(uint8_t pin);
+  /// Get R0 in default conditions for calibration purposes.
+  /// Assume CO2 Level is the default Atmospheric Level (~400ppm)
+  float getR0();
+  /// Get R0 in custom conditions for calibration purposes.
+  /// Can be used, if you know the current CO2 Level.
+  double getR0ByCO2Level(float ppm);
+  /// Set R0 Value for calibration.
+  void setR0(float r0);
+  
+  /// Gets the resolved sensor voltage
+  double getVoltage();
+  /// Calculates the Resistance of the Sensor
+  double getResistance();
+  /// Calculates ppm on a exponential curve
+  /// (Different Gases have different curves)
+  double getPPM(float a, float b);
+  /// 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();
+  /// Gets ppm of Alcohol in Air
+  double getAlcohol();
+  /// Gets ppm of CO in Air
+  double getCO();
+  /// Gets ppm of CO2 in Air
+  double getCO2();
+  /// Gets ppm of NH4 in Air
+  double getNH4();
+  /// Gets ppm of Tolueno in Air (CH3)
+  double getTolueno();
+};
+#endif