Fc-22 Gas sensor Arduino

Introduction

MQ-2, Mq2, mq22, mq-22.

Datasheet to approximate the gases

• MQ-3 https://www.sparkfun.com/datasheets/Sensors/MQ-3.pdf

Theory

Connect Vcc, GND and Analog Output to Arduino Analog A0 pin (see https://www.instructables.com/How-to-use-MQ2-Gas-Sensor-Arduino-Tutorial/). Also, there is Digital Output.

#include "MQ135.h"

MQ135 gasSensor = MQ135(A5);

int ppm = gasSensor.getPPM();

void setup() {
  Serial.begin(9600);
}

void loop() {
  float rzero = gasSensor.getRZero(); #Calibaration. Actually it takes ~24h time.
  float ppm = gasSensor.getPPM();
  Serial.println(ppm);

  delay(1000);
}

See https://github.com/Ravenneo/CO2-sensor

Calibration https://hackaday.io/project/3475-sniffing-trinket/log/12363-mq135-arduino-library

Code 1

A better code from (https://projecthub.arduino.cc/m_karim02/arduino-and-mq2-gas-sensor-f3ae33) but the MQGetGasPercentage does not work properly.

#define MQ_PIN   (0)
#define RL_VALUE (5)      //the load resistance on the board in kilo ohms
#define RO_CLEAN_AIR_FACTOR (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air) is derived from the chart in datasheet

#define CALIBRATION_SAMPLE_TIMES (50)    // the calibration 
#define CALIBRATION_SAMPLE_INTERVAL (500)   //the time interal(in milisecond) between each samples in the
#define READ_SAMPLE_INTERVAL (50)    //
#define READ_SAMPLE_TIMES (5)      //

//const int rs = 12;
 
#define GAS_LPG (0)
#define GAS_CO (1)
#define GAS_SMOKE (2)
 
float LPGCurve[3] = {2.3,0.21,-0.47}; //From the datasheet
float COCurve[3] = {2.3,0.72,-0.34}; 
float SmokeCurve[3] = {2.3,0.53,-0.44};                                                     
float Ro = 10;                 //Ro is initialized to 10 kilo ohms
   
void setup(){
  Serial.begin(9600);
  Serial.print("Calibrating...");                
  Ro = MQCalibration(MQ_PIN);     //Calibrating the sensor. Please   make sure the sensor is in clean air 
  Serial.print("Calibration is done... "); 
  Serial.print("Ro=");
  Serial.print(Ro);
  Serial.print("kohm");
  Serial.println("");
}
   
void loop(){
   Serial.print("LPG:"); 
   Serial.print("AAA ");
   Serial.print( MQRead(MQ_PIN));
   Serial.print(" ");

   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG)   );
   Serial.println( " ppm" );
   /*Serial.print("\t");   
   Serial.print("CO:");   
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
   Serial.print( " ppm" );
   Serial.print("\t");   
   Serial.print("SMOKE:"); 
   Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
   Serial.print( " ppm" );
   Serial.println("");
  */
   delay(200);
}
   
float MQResistanceCalculation(int raw_adc){
  return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
}
   
 
float MQCalibration(int mq_pin){
  int i;
  float val=0;
 
   for (i=0;i<CALIBRATION_SAMPLE_TIMES;i++) {            //take multiple samples
     val += MQResistanceCalculation(analogRead(mq_pin));
    delay(CALIBRATION_SAMPLE_INTERVAL);
   }
  val = val/CALIBRATION_SAMPLE_TIMES;  // the average value
  val = val/RO_CLEAN_AIR_FACTOR;   //yields the Ro according to the chart in the datasheet 
 
  return val; 
}
  
float MQRead(int mq_pin){
  float rs=0;
 
  for (int i=0;i<READ_SAMPLE_TIMES;i++)   {
    rs += MQResistanceCalculation(analogRead(mq_pin));
    delay(READ_SAMPLE_INTERVAL);
   }
 
  rs = rs/READ_SAMPLE_TIMES;
 
  return rs;  
}
 
int MQGetGasPercentage(float rs_ro_ratio, int gas_id){
  if ( gas_id  == GAS_LPG ) {
     return MQGetPercentage(rs_ro_ratio, LPGCurve);
  } else if ( gas_id == GAS_CO ) {
     return MQGetPercentage(rs_ro_ratio, COCurve);
   } else if ( gas_id == GAS_SMOKE ) {
     return MQGetPercentage(rs_ro_ratio, SmokeCurve);
   }    
 
  return 0;
}
   
int  MQGetPercentage(float rs_ro_ratio, float *pcurve){
  return (pow(10,(   ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}