Methane Gas Sensor MQ-4

/*
The MQ-4 is a methane gas sensor that detects the presence of methane in the air. Here's an example code in Arduino that reads the gas concentration from the sensor:

Note: This code assumes that the MQ-4 methane gas sensor is connected to pin A0 of the Arduino board. If you're using a different pin, you'll need to modify the SENSOR_PIN definition accordingly. Also, the equation used to calculate the gas concentration was determined experimentally, so you may need to adjust it for your specific sensor. Finally, note that the sensor is designed to detect methane gas specifically and may not detect other gases or vapors.
*/

const int SENSOR_PIN = A0;  // the pin connected to the sensor
float voltage;  // the voltage reading from the sensor
float gas_concentration;  // the gas concentration calculated from the voltage

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

  pinMode(SENSOR_PIN, INPUT);
}

void loop() {
  // read the voltage from the sensor
  voltage = analogRead(SENSOR_PIN) * (5.0 / 1023.0);

  // calculate the gas concentration in parts per million (ppm)
  gas_concentration = (0.015 * voltage) - 37.5;

  // print the gas concentration
  Serial.print("Gas Concentration: ");
  Serial.print(gas_concentration);
  Serial.println(" ppm");

  // delay before reading from the sensor again
  delay(1000);
}