/* MQUnifiedsensor Library - reading an MQ9 Demonstrates the use a MQ9 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 take care, arduino A0 pin represent the analog input configured on #define pin This example code is in the public domain. */ //Include the library #include /************************Hardware Related Macros************************************/ #define Board ("Arduino UNO") #define Pin (A9) //Analog input 4 of your arduino /***********************Software Related Macros************************************/ #define Type ("MQ-9") //MQ9 #define Voltage_Resolution (5) #define ADC_Bit_Resolution (10) // For arduino UNO/MEGA/NANO #define RatioMQ9CleanAir (9.6) //RS / R0 = 60 ppm /*****************************Globals***********************************************/ //Declare Sensor MQUnifiedsensor MQ9(Board, Voltage_Resolution, ADC_Bit_Resolution, Pin, Type); void setup() { //Init the serial port communication - to debug the library Serial.begin(9600); //Init serial port //Set math model to calculate the PPM concentration and the value of constants MQ9.setRegressionMethod(1); //_PPM = a*ratio^b MQ9.setA(1000.5); MQ9.setB(-2.186); // Configurate the ecuation values to get LPG concentration /* Exponential regression: GAS | a | b LPG | 1000.5 | -2.186 CH4 | 4269.6 | -2.648 CO | 599.65 | -2.244 */ /***************************** MQ Init ********************************************/ //Remarks: Configure the pin of arduino as input. /************************************************************************************/ MQ9.init(); /* //If the RL value is different from 10K please assign your RL value with the following method: MQ9.setRL(10); */ /***************************** MQ CAlibration ********************************************/ // Explanation: // In this routine the sensor will measure the resistance of the sensor supposing before was pre-heated // and now is on clean air (Calibration conditions), and it will setup R0 value. // We recomend execute this routine only on setup or on the laboratory and save on the eeprom of your arduino // This routine not need to execute to every restart, you can load your R0 if you know the value // Acknowledgements: https://jayconsystems.com/blog/understanding-a-gas-sensor Serial.print("Calibrating please wait."); float calcR0 = 0; for(int i = 1; i<=10; i ++) { MQ9.update(); // Update data, the arduino will be read the voltage on the analog pin calcR0 += MQ9.calibrate(RatioMQ9CleanAir); Serial.print("."); } MQ9.setR0(calcR0/10); Serial.println(" done!."); if(isinf(calcR0)) {Serial.println("Warning: Conection issue founded, R0 is infite (Open circuit detected) please check your wiring and supply"); while(1);} if(calcR0 == 0){Serial.println("Warning: Conection issue founded, R0 is zero (Analog pin with short circuit to ground) please check your wiring and supply"); while(1);} /***************************** MQ CAlibration ********************************************/ MQ9.serialDebug(true); } void loop() { MQ9.update(); // Update data, the arduino will be read the voltage on the analog pin MQ9.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup MQ9.serialDebug(); // Will print the table on the serial port delay(500); //Sampling frequency }