MQ135.h

Go to the documentation of this file.

#pragma once
#include "../Common.h"
#include "GasSensor.h"
 
namespace RumPi
{
    class MQ135 : public GasSensor
    {
    protected:
        //For details about the parameters below, see:
        //http://davidegironi.blogspot.com/2014/01/cheap-co2-meter-using-mq135-sensor-with.html
        //https://hackaday.io/project/3475-sniffing-trinket/log/12363-mq135-arduino-library
        //Parameters for calculating ppm of CO2 from sensor resistance
        //These were obtained using power regression based on the graph data.
        //Use constexpr here for double/float value compile time initialization (non integral types)
        static constexpr double PARA = 116.6020682;
        static constexpr double PARB = 2.769034857;
 
        //Parameters to model temperature and humidity dependence.
        //These are used to correct the PPM calculations based on the current temperature and humidity.
        static constexpr double CORA = 0.00035;
        static constexpr double CORB = 0.02718;
        static constexpr double CORC = 1.39538;
        static constexpr double CORD = 0.0018;
        static constexpr double CORE = -0.003333333;
        static constexpr double CORF = -0.001923077;
        static constexpr double CORG = 1.130128205;
 
        //Atmospheric CO2 level for calibration purposes,
        //from "Globally averaged marine surface monthly mean data"
        //available at https://gml.noaa.gov/ccgg/trends/gl_data.html
        static constexpr double ATMOCO2 = 419.51; // Global CO2 June 2023
 
        double myAtmosphericCO2PPMConstant;
 
        double myCurrentTemperatureInC;
 
        double myCurrentHumidityPercent;
 
    public:
        MQ135();
 
        MQ135(IAnalogDigitalConverterComponent* analogToDigitalConverter, const unsigned int& analogToDigitalConverterIndex, const unsigned int& digitalOutputPinNumber);
 
        MQ135(IAnalogDigitalConverterComponent* analogToDigitalConverter, const unsigned int& analogToDigitalConverterIndex);
 
        MQ135(const unsigned int& digitalOutputPinNumber);
 
        virtual ~MQ135();
 
        void Initialize() override;
 
        double ReadGasValue() const override;
 
        double CalculateR0() override;
 
        double CalculateResistance() const;
 
        double CalculatePPM() const;
 
        double CalculateCorrectedR0(double temperatureInC, double humidityPercent);
 
        double CalculateCorrectionFactor(double temperatureInC, double humidityPercent) const;
 
        double CalculateCorrectedResistance(double temperatureInC, double humidityPercent) const;
 
        double CalculateCorrectedPPM(double temperatureInC, double humidityPercent) const;
 
        std::string ToString() const override;
 
        double GetCurrentTemperatureInC() const;
 
        double GetCurrentHumidityPercent() const;
 
        void SetCurrentTemperatureInC(double currentTemperatureInC);
 
        void SetCurrentHumidityPercent(double currentHumidityPercent);
 
    };
} // namespace RumPi