/* MQUnifiedsensor Library - reading an MQ309 Demonstrates the use a MQ309 sensor. Library originally added 01 may 2019 by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez Added example modified 23 May 2019 by Miguel Califa Updated library usage modified 26 March 2020 by Miguel Califa Wiring: https://github.com/miguel5612/MQSensorsLib_Docs/blob/master/static/img/MQ_Arduino.PNG Please make sure arduino A0 pin represents the analog input configured on #define pin This example code is in the public domain. */ //Include the library #include //Definitions #define placa "Arduino UNO" #define Voltage_Resolution 5 #define pin A0 //Analog input 0 of your arduino #define type "MQ-309" //MQ309 #define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO #define RatioMQ309CleanAir 11 //RS / R0 = 11 ppm #define PWMPin 5 // Pin connected to mosfet //Declare Sensor MQUnifiedsensor MQ309(placa, Voltage_Resolution, ADC_Bit_Resolution, pin, type); unsigned long oldTime = 0; void setup() { //Init the serial port communication - to debug the library Serial.begin(9600); //Init serial port pinMode(PWMPin, OUTPUT); //Set math model to calculate the PPM concentration and the value of constants MQ309.setRegressionMethod(1); //_PPM = a*ratio^b MQ309.setA(1000000); MQ309.setB(-4.01); // Configure the equation to calculate CO concentration value /* Exponential regression: GAS | a | b H2 | 1532.9 | -1.951 CH4 | 980.24 | -1.68 CO | 1000000 | -4.01 ALCOHOL | 473622 | -3.647 */ /***************************** MQ Init ********************************************/ //Remarks: Configure the pin of arduino as input. /************************************************************************************/ MQ309.init(); /* //If the RL value is different from 10K please assign your RL value with the following method: MQ309.setRL(10); */ /***************************** MQ CAlibration ********************************************/ // Explanation: // In this routine the sensor will measure the resistance of the sensor supposedly before being pre-heated // and on clean air (Calibration conditions), setting up R0 value. // We recomend executing this routine only on setup in laboratory conditions. // This routine does not need to be executed on each restart, you can load your R0 value from eeprom. // Acknowledgements: https://jayconsystems.com/blog/understanding-a-gas-sensor Serial.print("Calibrating please wait."); float calcR0 = 0; for(int i = 1; i<=10; i ++) { MQ309.update(); // Update data, the arduino will read the voltage from the analog pin calcR0 += MQ309.calibrate(RatioMQ309CleanAir); Serial.print("."); } MQ309.setR0(calcR0/10); Serial.println(" done!."); if(isinf(calcR0)) {Serial.println("Warning: Conection issue, R0 is infinite (Open circuit detected) please check your wiring and supply"); while(1);} if(calcR0 == 0){Serial.println("Warning: Conection issue found, R0 is zero (Analog pin shorts to ground) please check your wiring and supply"); while(1);} /***************************** MQ CAlibration ********************************************/ MQ309.serialDebug(true); } void loop() { // 60s cycle oldTime = millis(); while(millis() - oldTime <= (30*1000)) { // VH 0.9 Volts analogWrite(5, 2); // 255 is 100%, 2.295 is aprox 0.9% of Duty cycle for 60s MQ309.update(); // Update data, the arduino will read the voltage from the analog pin MQ309.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup MQ309.serialDebug(); // Will print the table on the serial port delay(500); //Sampling frequency } // 90s cycle oldTime = millis(); while(millis() - oldTime <= (120*1000)) { // VL 0.2 Volts analogWrite(5, 1); // 255 is 100%, 0.51 is aprox 0.2% of Duty cycle for 120s MQ309.update(); // Update data, the arduino will read the voltage from the analog pin MQ309.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup MQ309.serialDebug(); // Will print the table on the serial port delay(500); //Sampling frequency } // Total: 30 + 120s = 2.5 minutes. }