MQ-4 Methane Sensor Circuit Arduino

 
const int AOUTpin=0;//the AOUT pin of the methane sensor goes into analog pin A0 of the arduino
const int DOUTpin=8;//the DOUT pin of the methane sensor goes into digital pin D8 of the arduino
const int ledPin=9;//the anode of the LED connects to digital pin D13 of the arduino
 
int limit=0;
int value;
 
void setup() {
  Serial.begin(115200);//sets the baud rate
  pinMode(DOUTpin, INPUT);//sets the pin as an input to the arduino
  pinMode(ledPin, OUTPUT);//sets the pin as an output of the arduino
}
 
void loop()
{
  value= analogRead(AOUTpin);//reads the analaog value from the methane sensor's AOUT pin
  limit= digitalRead(DOUTpin);//reads the digital value from the methane sensor's DOUT pin
  Serial.print(" Methane value: ");
  Serial.println(value);//prints the methane value
  Serial.print("Limit: ");
  Serial.print(limit);//prints the limit reached as either LOW or HIGH (above or underneath)
  delay(100);
  if (limit == HIGH){
    digitalWrite(ledPin, LOW);//if limit has been reached, LED turns on as status indicator
  }else{
    digitalWrite(ledPin, HIGH);//if threshold not reached, LED remains off
  }
}

References