MQSensorsLib/examples/MQ-7/MQ-7.ino

/*
  MQUnifiedsensor Library - reading an MQ7

  Demonstrates the use a MQ7 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 <MQUnifiedsensor.h>

//Definitions
#define placa "Arduino UNO"
#define Voltage_Resolution 5
#define pin A0 //Analog input 0 of your arduino
#define type "MQ-7" //MQ7
#define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO
#define RatioMQ7CleanAir 27.5 //RS / R0 = 27.5 ppm 
//#define calibration_button 13 //Pin to calibrate your sensor

//Declare Sensor
MQUnifiedsensor MQ7(placa, 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
  MQ7.setRegressionMethod(1); //_PPM =  a*ratio^b
  MQ7.setA(99.042); MQ7.setB(-1.518); // Configurate the ecuation values to get CO concentration

  /*
    Exponential regression:
  GAS     | a      | b
  H2      | 69.014  | -1.374
  LPG     | 700000000 | -7.703
  CH4     | 60000000000000 | -10.54
  CO      | 99.042 | -1.518
  Alcohol | 40000000000000000 | -12.35
  */
  
  /*****************************  MQ Init ********************************************/ 
  //Remarks: Configure the pin of arduino as input.
  /************************************************************************************/ 
  MQ7.init(); 
  /* 
    //If the RL value is different from 10K please assign your RL value with the following method:
    MQ7.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 ++)
  {
    MQ7.update(); // Update data, the arduino will be read the voltage on the analog pin
    calcR0 += MQ7.calibrate(RatioMQ7CleanAir);
    Serial.print(".");
  }
  MQ7.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 ********************************************/ 
  MQ7.serialDebug(true);
}

void loop() {
  MQ7.update(); // Update data, the arduino will be read the voltage on the analog pin
  MQ7.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup
  MQ7.serialDebug(); // Will print the table on the serial port
  delay(500); //Sampling frequency
}