MQSensorsLib/examples/MQ-9-ALL/MQ-9-ALL.ino

/*
  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 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 <MQUnifiedsensor.h>
/************************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
 
  
  /*****************************  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 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 ++)
  {
    MQ9.update(); // Update data, the arduino will read the voltage from the analog pin
    calcR0 += MQ9.calibrate(RatioMQ9CleanAir);
    Serial.print(".");
  }
  MQ9.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 ********************************************/ 
  Serial.println("** Values from MQ-9 ****");
  Serial.println("|    LPG   |  CH4 |   CO  |");  
}

void loop() {
  MQ9.update(); // Update data, the arduino will read the voltage from the analog pin
  /*
  Exponential regression:
  GAS     | a      | b
  LPG     | 1000.5 | -2.186
  CH4     | 4269.6 | -2.648
  CO      | 599.65 | -2.244
  */

  MQ9.setA(1000.5); MQ9.setB(-2.186); // Configure the equation to to calculate LPG concentration
  float LPG = MQ9.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ9.setA(4269.6); MQ9.setB(-2.648); // Configure the equation to to calculate LPG concentration
  float CH4 = MQ9.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  MQ9.setA(599.65); MQ9.setB(-2.244); // Configure the equation to to calculate LPG concentration
  float CO = MQ9.readSensor(); // Sensor will read PPM concentration using the model, a and b values set previously or from the setup

  Serial.print("|    "); Serial.print(LPG);
  Serial.print("    |    "); Serial.print(CH4);
  Serial.print("    |    "); Serial.print(CO); 
  Serial.println("    |");

  delay(500); //Sampling frequency
}