[Tutorial] Extracting sensor data from MQ9 Gas Sensor with ESP32

1. Devices

• ESP32

• MQ9 Gas Sensor

• some jumper wires or four pins cable

2. Upload the code below to your Arduino IDE project

• Basic Example: extract the raw data

#include "Arduino.h"

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

void loop() {
    float sensor_volt;
    float sensorValue;

    sensorValue = analogRead(A0);
    sensor_volt = sensorValue/1024*5.0;

    Serial.print("sensor_volt = ");
    Serial.print(sensor_volt);
    Serial.println("V");
    delay(1000);
}

•  So if you want to make the data more accurate? we can use the code below to get the mean of observations and take it as the reference value. Attention, you should put your sensor in a space with clean air.

#include "Arduino.h"

void setup() {

    Serial.begin(9600);

}

void loop() {

    float sensor_volt;

    float RS_air; //  Get the value of RS via in a clear air

    float R0;  // Get the value of R0 via in LPG

    float sensorValue;

    /*--- Get a average data by testing 100 times ---*/

    for(int x = 0 ; x < 100 ; x++)

    {

        sensorValue = sensorValue + analogRead(A0);

    }

    sensorValue = sensorValue/100.0;

    /*-----------------------------------------------*/

    sensor_volt = sensorValue/1024*5.0;

    RS_air = (5.0-sensor_volt)/sensor_volt; // omit *RL

    R0 = RS_air/9.9; // The ratio of RS/R0 is 9.9 in LPG gas from Graph (Found using WebPlotDigitizer)

    Serial.print("sensor_volt = ");

    Serial.print(sensor_volt);

    Serial.println("V");

    Serial.print("R0 = ");

    Serial.println(R0);

    delay(1000);

}

• Use the record obtaining from experiment above to help you get a more accurate air quality value.

#include "Arduino.h"

void setup() {

    Serial.begin(9600);

}

void loop() {

    float sensor_volt;

    float RS_gas; // Get value of RS in a GAS

    float ratio; // Get ratio RS_GAS/RS_air

    int sensorValue = analogRead(A0);

    sensor_volt=(float)sensorValue/1024*5.0;

    RS_gas = (5.0-sensor_volt)/sensor_volt; // omit *RL

          /*-Replace the name "R0" with the value of R0 in the demo of First Test -*/

    ratio = RS_gas/R0;  // ratio = RS/R0

          /*-----------------------------------------------------------------------*/

    Serial.print("sensor_volt = ");

    Serial.println(sensor_volt);

    Serial.print("RS_ratio = ");

    Serial.println(RS_gas);

    Serial.print("Rs/R0 = ");

    Serial.println(ratio);

    Serial.print("\n\n");

    delay(1000);

}

3. Output