Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor V4

Course Introduction

This Arduino project uses an MQ-2 gas sensor, LEDs, and a buzzer to detect gas concentration in real time.

Note

If this is your first time working with an Arduino project, we recommend downloading and reviewing the basic materials first.

1.1 Install Arduino IDE(Important)
1.2 Introduction of Arduino IDE

Required Components

In this project, we need the following components:

SN	COMPONENT INTRODUCTION	QUANTITY	PURCHASE LINK
1	Arduino UNO R4 WIFI	1	BUY
2	USB Type-C cable	1	×
3	Breadboard	1	BUY
4	Wires	Several	BUY
5	Buzzer Modudle	1	BUY
6	LED	Several	BUY
7	MQ-2 Gas Sensor Module	1	BUY
8	1kΩ resistor	Several	BUY

Wiring

4.png__PID:f5aa7d59-5476-4857-b48d-755b5225c4ae

Common Connections:

MQ-2 Gas Sensor Module
A0: Connect to A0 on the Arduino.
GND: Connect to breadboard’s negative power bus.
VCC: Connect to breadboard’s red power bus.

Buzzer Modudle
I/O: Connect to 2 on the Arduino.
GND: Connect to breadboard’s negative power bus.
VCC: Connect to breadboard’s red power bus.

LED
Connect the LEDs cathode to the negative power bus on the breadboard, and the LEDs anode to 1kΩ resistor then to 4 to 11 on the Arduino.

Writing the Code

Note
You can copy this code into Arduino IDE.
Don’t forget to select the board(Arduino UNO R4 Minima) and the correct port before clicking the Upload button.

// -------- Pin definitions --------
#define PIN_SMOKE  A0    // MQ-2 smoke sensor
#define PIN_BUZZER 2     // Buzzer

int ledPins[] = {4, 5, 6, 7, 8, 9, 10, 11}; // LED bar
const int LED_COUNT = 8;

// -------- Thresholds --------
#define LED_START_TH 50     // LED starts lighting
#define LED_STEP     50     // One LED per 50
#define WARN_TH      100    // Warning threshold
#define ALARM_TH     300    // Alarm threshold (same as traffic light project)

// -------- Setup --------
void setup() {
  pinMode(PIN_BUZZER, OUTPUT);

  for (int i = 0; i < LED_COUNT; i++) {
    pinMode(ledPins[i], OUTPUT);
    digitalWrite(ledPins[i], LOW);
  }

  Serial.begin(9600);
}

// -------- Main loop --------
void loop() {
  int smokeValue = analogRead(PIN_SMOKE); // Read smoke value

  ledBarDisplay(smokeValue);              // LED display
  buzzerService(smokeValue);              // Buzzer (same behavior as before)

  Serial.print("Smoke value: ");
  Serial.println(smokeValue);
}

// -------- LED bar display --------
// 50  -> D11
// 100 -> D11, D10
// 150 -> D11, D10, D9 ...
void ledBarDisplay(int value) {
  int ledCount = 0;

  if (value >= LED_START_TH) {
    ledCount = (value - LED_START_TH) / LED_STEP + 1;
  }

  if (ledCount > LED_COUNT) {
    ledCount = LED_COUNT;
  }

  // Light LEDs from D11 to D4
  for (int i = 0; i < LED_COUNT; i++) {
    int index = LED_COUNT - 1 - i;
    digitalWrite(ledPins[index], (i < ledCount) ? HIGH : LOW);
  }
}

// -------- Buzzer behavior --------
// WARN  (100–299): short beep every 1 second (same as yellow)
// ALERT (>=300): fast alarm beep (same as red)
void buzzerService(int value) {
  unsigned long now = millis();

  // -------- ALERT mode --------
  if (value >= ALARM_TH) {
    const unsigned long period = 250;
    unsigned long phase = now % period;

    if (phase < 120) {
      tone(PIN_BUZZER, 2000);   // Alarm ON
    } else {
      noTone(PIN_BUZZER);       // Alarm OFF
    }
    return;
  }

  // -------- WARN mode --------
  if (value >= WARN_TH) {
    const unsigned long period = 1000;
    unsigned long phase = now % period;

    if (phase < 80) {
      tone(PIN_BUZZER, 1200);   // Short reminder beep
    } else {
      noTone(PIN_BUZZER);
    }
    return;
  }

  // -------- SAFE mode --------
  noTone(PIN_BUZZER);
}

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Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor V4

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor V4

Course Introduction

Required Components

Wiring

Common Connections:

Writing the Code

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