MQSensorsLib/examples/ESP8266/ESP8266.ino

// This is an example of implementation using ESP8266
// Never connect the sensor direct to the ESP8266, sensor high level is 5V
// ADC of ESP8266 high level is 3.3
// To connect use a voltage divisor, where 5V will 3v3 on the middle point like
// this {{URL}}

/*
  MQUnifiedsensor Library - reading an MQSensor using ESP8266 board

  For this example wi will demonstrates the use a MQ3 sensor.
  Library originally added 01 may 2019
  by Miguel A Califa, Yersson Carrillo, Ghiordy Contreras, Mario Rodriguez
 
  Added ESP8266 example 
  29.03.2020
  Wiring:
  https://github.com/miguel5612/MQSensorsLib_Docs/blob/master/static/img/MQ_ESP8266.PNG

 This example code is in the public domain.

*/

//Include the library
#include <MQUnifiedsensor.h>
/************************Hardware Related Macros************************************/
#define         Board                   ("Arduino UNO")
#define         Pin                     (A0)  //Analog input 3 of your arduino
/***********************Software Related Macros************************************/
#define         Type                    ("MQ-3") //MQ3
#define         Voltage_Resolution      (3.3) // 3V3 <- IMPORTANT
#define         ADC_Bit_Resolution      (10) // For arduino UNO/MEGA/NANO
#define         RatioMQ3CleanAir        (60)
/*****************************Globals***********************************************/
MQUnifiedsensor MQ3(Board, Voltage_Resolution, ADC_Bit_Resolution, Pin, Type);
/*****************************Globals***********************************************/

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
  MQ3.setRegressionMethod(1); //_PPM =  a*ratio^b
  MQ3.setA(4.8387); MQ3.setB(-2.68); // Configurate the ecuation values to get Benzene concentration
  /*
    Exponential regression:
  Gas    | a      | b
  LPG    | 44771  | -3.245
  CH4    | 2*10^31| 19.01
  CO     | 521853 | -3.821
  Alcohol| 0.3934 | -1.504
  Benzene| 4.8387 | -2.68
  Hexane | 7585.3 | -2.849
  */

  /*****************************  MQ Init ********************************************/ 
  //Remarks: Configure the pin of arduino as input.
  /************************************************************************************/ 
  MQ3.init(); 
 
  /* 
    //If the RL value is different from 10K please assign your RL value with the following method:
    MQ3.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 ++)
  {
    MQ3.update(); // Update data, the arduino will be read the voltage on the analog pin
    calcR0 += MQ3.calibrate(RatioMQ3CleanAir);
    Serial.print(".");
  }
  MQ3.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 ********************************************/ 
  MQ3.serialDebug(true);
}

void loop() {
  MQ3.update(); // Update data, the arduino will be read the voltage on the analog pin
  MQ3.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup
  MQ3.serialDebug(); // Will print the table on the serial port
  delay(500); //Sampling frequency
}