Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor

Kit purchase

Looking for parts? Check out our all-in-one kits below — packed with components, beginner-friendly guides, and tons of fun.

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Name	Includes Arduino board	PURCHASE LINK
Ultimate Sensor Kit	Arduino Uno R4 Minima	BUY
Universal Maker Sensor Kit	×	BUY

Course Introduction

This Arduino project simulates a basic gas leak detection system using an MQ-2 gas sensor, a red LED, and a buzzer.

The sensor continuously monitors gas concentration. If the reading exceeds a set threshold, the buzzer sounds and the LED blinks to indicate danger.

Otherwise, the system remains silent and the LED stays off.

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

Please follow the steps in the tutorial below to complete the binding and setup of Arduino Cloud and the Arduino WiFi board.
1.4 Arduino IoT Cloud

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	1	BUY
7	MQ-2 Gas Sensor Module	1	BUY
8	1kΩ resistor	1	BUY

Wiring

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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 9 on the Arduino.
GND: Connect to breadboard’s negative power bus.
VCC: Connect to breadboard’s red power bus.

LED
Connect the LED anode to 6 on the Arduino, and the cathode to a 1kΩ resistor, then to the negative power bus on the breadboard.

Create a New IoT Project
After configuring the Arduino Cloud and the Arduino WiFi board, follow the steps below to complete the Arduino Cloud project setup

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Edit Value

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Follow the steps below to configure the dashboard.
1.Create New Dashboard

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2.Add Widgets

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3.Link Variable

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4.Remember to click Done

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After completing the above configuration, return to the Things page and open the sketch.

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When you have completed the configuration of the Things and Dashboard, as well as the connection and network setup of the Arduino WiFi board, the thingProperties.h and Sketch Secrets files will be generated automatically. If Sketch Secrets is not generated, please manually enter the connected SSID and OPTIONAL_PASS

Copy this code into Arduino Cloud.

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Don’t forget to select the board(Arduino UNO R4 WIFI) and the correct port before clicking the Upload button.

#include <I2C_RTC.h>
#include "thingProperties.h"
#include <math.h>  // Use pow for gamma boost

// ========== Hardware pins (modifiable if needed) ==========
const uint8_t PIN_GAS_AO     = A0; // Gas sensor analog output
const uint8_t PIN_BUZZER     = 9;  // Buzzer
const uint8_t LED_ALARM_PIN  = 6;  // Alarm LED (with 220~330Ω resistor)
// Active buzzer: HIGH = sound; Passive buzzer: use tone() to generate sound
const bool BUZZER_ACTIVE_TYPE = true; // true = active; false = passive
// ==========================================================

// UNO R4 (Renesas) uses 12-bit ADC; ignored if board does not support
#if defined(ARDUINO_ARCH_RENESAS)
  static const int ADC_MAX = 4095;  // 12-bit
#else
  static const int ADC_MAX = 1023;  // 10-bit
#endif

// Sampling and refresh
const unsigned long SAMPLE_INTERVAL_MS = 50;    // Sampling period
const unsigned long UI_PUSH_INTERVAL_MS = 500;  // Push period to cloud
const unsigned long BLINK_INTERVAL_MS   = 200;  // Alarm blinking rhythm

// Filtering
float filteredRaw = 0.0f;           // First-order low-pass filter
const float ALPHA = 0.15f;          // 0~1, larger = more responsive, smaller = smoother

// Adaptive/safety parameters (for percentage mapping)
const int   MIN_SPAN          = 50;     // Minimum mapping span to avoid small denominator
const float INIT_SPAN_GUESS   = 200.0f; // Initial span guess
const float LOW_FOLLOW_ALPHA  = 0.02f;  // Low-end following (slow)
const float HIGH_EXPAND_ALPHA = 0.30f;  // High-end expansion (fast)
const float LINEAR_GAIN       = 1.8f;   // Linear gain: larger = more sensitive
const double GAMMA            = 0.65;   // Gamma <1 enhances low end, >1 compresses low end

// Timers
unsigned long tSample = 0, tPush = 0, tBlink = 0;

// Local alarm state (corresponds to alarmActive)
bool alarmOn = false;

void setup() {
  Serial.begin(115200);
  delay(300);

  pinMode(PIN_BUZZER, OUTPUT);
  pinMode(LED_ALARM_PIN, OUTPUT);
  digitalWrite(PIN_BUZZER, LOW);
  digitalWrite(LED_ALARM_PIN, LOW);

#if defined(ARDUINO_ARCH_RENESAS)
  analogReadResolution(12); // UNO R4 WiFi
#endif

  // IoT Cloud
  initProperties();
  ArduinoCloud.begin(ArduinoIoTPreferredConnection);
  setDebugMessageLevel(2);
  ArduinoCloud.printDebugInfo();

  // Default threshold (prevents zero when not set from cloud)
  if (threshold <= 0 || threshold > 100) threshold = 30;

  // Initialize filter to avoid "jump" at startup
  int raw = analogRead(PIN_GAS_AO);
  filteredRaw = raw;
  gasPercent  = toPercent(filteredRaw);
  alarmActive = false;

  tSample = tPush = tBlink = millis();

  Serial.print("ADC_MAX="); Serial.println(ADC_MAX);
}

void loop() {
  ArduinoCloud.update();

  unsigned long now = millis();

  // 1) Sampling + filtering (non-blocking)
  if (now - tSample >= SAMPLE_INTERVAL_MS) {
    tSample = now;
    int raw = analogRead(PIN_GAS_AO);
    filteredRaw = ALPHA * raw + (1.0f - ALPHA) * filteredRaw;

    // 2) Calculate percentage and perform threshold check
    float percent = toPercent(filteredRaw);
    bool shouldAlarm = (percent >= (float)constrain(threshold, 0, 100));

    // 3) When alarm state changes, reset blink rhythm
    if (shouldAlarm != alarmOn) {
      alarmOn = shouldAlarm;
      alarmActive = alarmOn; // Sync to cloud
      tBlink = now;
      // Immediately unify output (avoid waiting until next blink)
      applyOutputs(alarmOn, /*blinkPhase*/true);
    }

    // 4) Push values to cloud periodically (rate-limited)
    if (now - tPush >= UI_PUSH_INTERVAL_MS) {
      tPush = now;
      gasPercent = percent;
    }
  }

  // 5) Buzzer/LED blinking rhythm during alarm (non-blocking)
  if (alarmOn && (millis() - tBlink >= BLINK_INTERVAL_MS)) {
    tBlink = millis();
    static bool phase = false;
    phase = !phase;
    applyOutputs(true, phase);
  }
  // Keep off when not alarming
  if (!alarmOn) {
    applyOutputs(false, false);
  }
}

// ---------- Utility functions ----------
// Adaptive two-point + gain/gamma boost: weak leak rises noticeably, strong leak closer to 100%
float toPercent(float raw) {
  static bool  init = false;
  static float low  = 0.0f;   // Environmental baseline (≈0%)
  static float high = 0.0f;   // Recent high value (≈100%)

  if (!init) {
    low  = raw;
    high = raw + INIT_SPAN_GUESS;
    if (high > ADC_MAX) high = (float)ADC_MAX;
    if (high <= low + MIN_SPAN) high = low + MIN_SPAN;
    init = true;
  }

  // Low endpoint: slowly follow environmental decreases
  if (raw < low)  low  = (1.0f - LOW_FOLLOW_ALPHA) * low  + LOW_FOLLOW_ALPHA * raw;
  // High endpoint: quickly expand to new highs
  if (raw > high) high = (1.0f - HIGH_EXPAND_ALPHA) * high + HIGH_EXPAND_ALPHA * raw;

  // Prevent interval from being too small
  if (high <= low + MIN_SPAN) high = low + MIN_SPAN;
  if (high > ADC_MAX) high = (float)ADC_MAX;

  // Normalize to 0..1
  float x = (raw - low) / (high - low);
  if (x < 0.0f) x = 0.0f;
  if (x > 1.0f) x = 1.0f;

  // Linear gain
  x *= LINEAR_GAIN;
  if (x > 1.0f) x = 1.0f;

  // Gamma boost (<1 enhances low range)
  double boosted = pow((double)x, GAMMA);
  float p = (float)(boosted * 100.0);

  if (p < 0.0f)   p = 0.0f;
  if (p > 100.0f) p = 100.0f;
  return p;
}

void applyOutputs(bool alarm, bool blinkPhase) {
  if (alarm) {
    // LED blinking
    digitalWrite(LED_ALARM_PIN, blinkPhase ? HIGH : LOW);
    // Buzzer
    if (BUZZER_ACTIVE_TYPE) {
      digitalWrite(PIN_BUZZER, blinkPhase ? HIGH : LOW);
    } else {
      if (blinkPhase) tone(PIN_BUZZER, 2000); // 2kHz
      else            noTone(PIN_BUZZER);
    }
  } else {
    digitalWrite(LED_ALARM_PIN, LOW);
    if (BUZZER_ACTIVE_TYPE) digitalWrite(PIN_BUZZER, LOW);
    else noTone(PIN_BUZZER);
  }
}

// ---------- Cloud property callbacks ----------
void onThresholdChange() {
  threshold = constrain(threshold, 0, 100);
  Serial.print("Threshold set to "); Serial.println(threshold);
}

void onAlarmActiveChange() {}

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Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor

Kit purchase

Course Introduction

Required Components

Wiring

Common Connections:

Arduino Project

Arduino Gas Leak Detector with MQ-2 Sensor

Kit purchase

Course Introduction

Required Components

Wiring

Common Connections:

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