This project uses sensors to monitor indoor natural gas on the basis of Arduino, and will make alarm if the natural gas leak exceeds the limit.


1.MQ-4 Natural Gas Sensor

2.Arduino Uno with Network Screening

3.Bread board

Note: you can redeem these in PCBWay, please support me by register this invited PCBWay link.

As a natural gas sensor,the MQ-4 Natural Gas Sensor is a fast and reliable sensor with a high sensitivity to natural gas and methane, also good sensitivity to propane and butane. This natural gas sensor has a long life and low cost and is widely used for gas leak detection. At the same time, two LED lights are used in the project to display the gas concentration:

Green light: it means the natural gas concentration is below the critical value.

Red light: alert! The natural gas concentration has exceeded the critical value.

The MQ-4 Arduino sensor has four pins:

1. Positive Vcc (+5V)

2. Ground GND

3. Digital output

4. Analog output

Here is the wiring diagram:

In the schematic, there are two resistors connected to the Arduino digital pins and LEDs. The resistance is 220 Ohm

Here is the code:

int pinRedLed = 11;

int pinGreenLed = 8;

int pinSensor = A5;

int THRESHOLD = 250;

void setup() {

    pinMode(pinRedLed, OUTPUT);

    pinMode(pinGreenLed, OUTPUT);

    pinMode(pinSensor, INPUT);



void loop() {

    int analogValue = analogRead(pinSensor);

    Serial.println("Val: " + analogValue);

    digitalWrite(pinGreenLed, HIGH);

    if (analogValue >= THRESHOLD) {

        digitalWrite(pinGreenLed, LOW);

        digitalWrite(pinRedLed, HIGH);


    else {

        digitalWrite(pinRedLed, LOW);




The green LED remains light up unless the natural gas concentration exceeds the threshold, the red LED will lights up.