MQSensorsLib/examples/MQ-135-ALL/MQ-135-ALL.ino

/*
  MQUnifiedsensor Library - reading an MQ135

  Demonstrates the use a MQ135 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-135" //MQ135
#define ADC_Bit_Resolution 10 // For arduino UNO/MEGA/NANO
#define RatioMQ135CleanAir 3.6//RS / R0 = 3.6 ppm  
//#define calibration_button 13 //Pin to calibrate your sensor

//Declare Sensor
MQUnifiedsensor MQ135(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
  MQ135.setRegressionMethod(1); //_PPM =  a*ratio^b
  
  /*****************************  MQ Init ********************************************/ 
  //Remarks: Configure the pin of arduino as input.
  /************************************************************************************/ 
  MQ135.init(); 
  /* 
    //If the RL value is different from 10K please assign your RL value with the following method:
    MQ135.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 ++)
  {
    MQ135.update(); // Update data, the arduino will be read the voltage on the analog pin
    calcR0 += MQ135.calibrate(RatioMQ135CleanAir);
    Serial.print(".");
  }
  MQ135.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 ********************************************/ 
  Serial.println("** Lectures from MQ-135 ****");
  Serial.println("|    CO   |  Alcohol |   CO2  |  Tolueno  |  NH4  |  Acteona  |");  
}

void loop() {
  MQ135.update(); // Update data, the arduino will be read the voltage on the analog pin

  MQ135.setA(605.18); MQ135.setB(-3.937); // Configurate the ecuation values to get CO concentration
  float CO = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  MQ135.setA(77.255); MQ135.setB(-3.18); // Configurate the ecuation values to get Alcohol concentration
  float Alcohol = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  MQ135.setA(110.47); MQ135.setB(-2.862); // Configurate the ecuation values to get CO2 concentration
  float CO2 = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  MQ135.setA(44.947); MQ135.setB(-3.445); // Configurate the ecuation values to get Tolueno concentration
  float Tolueno = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  MQ135.setA(102.2 ); MQ135.setB(-2.473); // Configurate the ecuation values to get NH4 concentration
  float NH4 = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  MQ135.setA(34.668); MQ135.setB(-3.369); // Configurate the ecuation values to get Acetona concentration
  float Acetona = MQ135.readSensor(); // Sensor will read PPM concentration using the model and a and b values setted before or in the setup

  Serial.print("|   "); Serial.print(CO); 
  Serial.print("   |   "); Serial.print(Alcohol);
  // Note: 200 Offset for CO2 source: https://github.com/miguel5612/MQSensorsLib/issues/29
  /*
  Motivation:
  We have added 200 PPM because when the library is calibrated it assumes the current state of the
  air as 0 PPM, and it is considered today that the CO2 present in the atmosphere is around 400 PPM.
  https://www.lavanguardia.com/natural/20190514/462242832581/concentracion-dioxido-cabono-co2-atmosfera-bate-record-historia-humanidad.html
  */
  Serial.print("   |   "); Serial.print(CO2 + 400); 
  Serial.print("   |   "); Serial.print(Tolueno); 
  Serial.print("   |   "); Serial.print(NH4); 
  Serial.print("   |   "); Serial.print(Acetona);
  Serial.println("   |"); 
  /*
    Exponential regression:
  GAS      | a      | b
  CO       | 605.18 | -3.937  
  Alcohol  | 77.255 | -3.18 
  CO2      | 110.47 | -2.862
  Tolueno  | 44.947 | -3.445
  NH4      | 102.2  | -2.473
  Acetona  | 34.668 | -3.369
  */

  delay(500); //Sampling frequency
}