ESP32 MQ-2 Gas Leak Monitor

ESP32-based gas and smoke monitoring system using an MQ-2 sensor, SSD1306 OLED display, LEDs, and buzzer with multi-state alert logic.

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Overview

The ESP32 MQ-2 Gas Leak Monitor is an embedded environmental safety monitoring system designed to detect gas and smoke concentration levels in real time.

The system continuously reads analog values from an MQ-2 gas sensor and evaluates environmental conditions using a three-state alert model:

• SAFE
• WARNING
• DANGER

Measured gas levels are displayed on an SSD1306 OLED display, while LEDs and a buzzer provide immediate visual and audible feedback.

This project demonstrates practical applications of:

• Analog sensor interfacing
• ADC measurements
• OLED display communication
• Real-time monitoring
• State-machine design
• Embedded firmware development

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Features

• Real-time gas monitoring
• MQ-2 gas sensor integration
• SSD1306 OLED display interface
• Three-level safety indication
• Green LED for SAFE state
• Orange LED for WARNING state
• Blue LED for DANGER state
• High-tone buzzer alarm
• Serial Monitor debugging output
• Clean and documented firmware
• ESP32 compatible

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Hardware Components

Component	Quantity
ESP32 Development Board	1
MQ-2 Gas Sensor Module	1
SSD1306 OLED Display (128×64 I2C)	1
Green LED	1
Orange LED	1
Blue LED	1
Active / Passive Buzzer	1
220Ω Resistors	3
Breadboard / Jumper Wires	Several

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Pin Configuration

MQ-2 Gas Sensor

MQ-2 Pin	ESP32 Pin
VCC	VIN (5V)
GND	GND
AO	GPIO34

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OLED Display

OLED Pin	ESP32 Pin
VCC	3.3V
GND	GND
SDA	GPIO21
SCL	GPIO22

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LEDs

LED	ESP32 GPIO
Green LED	GPIO15
Orange LED	GPIO2
Blue LED	GPIO4

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Buzzer

Buzzer	ESP32 GPIO
Positive (+)	GPIO14
Negative (-)	GND

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System States

The monitoring system uses a simple finite-state approach.

SAFE State

Condition:

Gas Value < 300

Outputs:

Green LED : ON Orange LED : OFF Blue LED : OFF Buzzer : OFF OLED : SAFE

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WARNING State

Condition:

300 ≤ Gas Value < 500

Outputs:

Green LED : OFF Orange LED : ON Blue LED : OFF Buzzer : OFF OLED : WARNING

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DANGER State

Condition:

Gas Value ≥ 500

Outputs:

Green LED : OFF Orange LED : OFF Blue LED : ON Buzzer : ON OLED : DANGER

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How It Works

Step 1 – System Initialization

The ESP32 initializes:

• OLED display
• MQ-2 gas sensor
• LEDs
• Buzzer

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Step 2 – Sensor Warm-Up

The MQ-2 contains an internal heating element.

During startup the OLED displays:

MQ-2 GAS MONITOR

Sensor Warming Please Wait...

The sensor is allowed to stabilize before monitoring begins.

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Step 3 – Gas Measurement

The ESP32 continuously reads the analog output of the MQ-2 sensor.

gasValue = analogRead(MQ2_PIN);

The ADC converts sensor voltage into a digital value.

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Step 4 – State Evaluation

The firmware compares the measured value against predefined thresholds.

SAFE WARNING DANGER

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Step 5 – User Feedback

The OLED updates the gas concentration and system status.

LEDs indicate the current safety level.

The buzzer activates when dangerous gas concentrations are detected.

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Step 6 – Continuous Monitoring

The monitoring process repeats indefinitely.

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Example OLED Output

SAFE

MQ-2 GAS MONITOR

Gas: 223

STATUS: SAFE

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WARNING

MQ-2 GAS MONITOR

Gas: 387

STATUS: WARNING

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DANGER

MQ-2 GAS MONITOR

Gas: 645

STATUS: DANGER ``

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Wiring Diagram

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Circuit Diagram

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OLED Display Preview

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Demo Video

Watch the project in action:

docs/demo.mp4

or

Demo

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Software Requirements

Arduino IDE

Recommended:

Arduino IDE 2.x

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ESP32 Board Package

Install the ESP32 board package from Arduino Boards Manager.

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Required Libraries

Install the following libraries using Arduino Library Manager:

Adafruit GFX Library Adafruit SSD1306 Library Wire Library

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Open Project

Open:

src/ESP32_MQ2_Gas_Leak_Monitor.ino

in Arduino IDE.

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Select Board

Tools → Board → ESP32 Dev Module

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Upload Firmware

Connect ESP32 via USB and upload the sketch.

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Open Serial Monitor

115200 Baud

Observe live gas readings.

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Calibration

MQ-2 sensors vary between modules and environments.

Before deployment:

1. Power the sensor.
2. Allow warm-up time.
3. Observe readings in clean air.
4. Record the average value.
5. Adjust thresholds if necessary.

Example:

Clean Air: 190 - 250

Warning: 300 - 500

Danger:

500

The thresholds used in this project were calibrated using actual sensor measurements.

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## Project Structure


ESP32-MQ2-Gas-Leak-Monitor
│
├── docs
│   ├── wiring.png
│   ├── circuit_diagram.png
│   ├── oled_active.png
│   └── demo.mp4
│
├── src
│   └── ESP32_MQ2_Gas_Leak_Monitor.ino
│
├── LICENSE
│
└── README.md


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## Educational Objectives

This project demonstrates:

- Analog-to-Digital Conversion (ADC)
- Sensor calibration
- Embedded state machines
- OLED display programming
- Real-time monitoring systems
- Embedded alarm systems
- GPIO control
- Safety monitoring applications

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## Future Improvements

Potential upgrades include:

- Wi-Fi notifications
- MQTT integration
- Mobile alerts
- Cloud dashboard
- Data logging
- SD card storage
- Historical gas graphs
- FreeRTOS implementation
- Multi-sensor integration
- Automatic calibration

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## Repository Topics


esp32
arduino
iot
embedded-systems
mq2
gas-sensor
smoke-detector
oled-display
ssd1306
environment-monitoring
embedded-firmware
safety-system
real-time-monitoring


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## Author

**Milad Mohseni**

Embedded Systems & IoT Engineer

Areas of Interest:

- Embedded Systems
- ESP32 Development
- IoT Applications
- Sensor Interfacing
- Firmware Development
- Real-Time Monitoring Systems

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## License

This project is licensed under the MIT License.

See the LICENSE file for more information.