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The MQ-2 gas sensor is widely used because of its ability to detect multiple flammable gases and smoke using a simple operating principle and minimal external circuitry. This article will discuss the MQ-2 gas sensor’s working principle, pin configuration, internal structure, hardware components, specifications, and more.
The MQ-2 gas sensor is a low-cost device used to detect flammable gases and smoke in the air. It is commonly applied in gas leakage alarms, fire detection systems, and microcontroller-based projects due to its simple design and wide availability. The sensor responds to gases such as LPG, methane, propane, hydrogen, alcohol vapor, carbon monoxide, and smoke, making it suitable for general gas and safety monitoring.
Most MQ-2 sensor modules provide both analog and digital outputs. The analog output indicates relative gas concentration, while the digital output triggers when gas levels exceed a preset threshold. A short preheating period is required to ensure stable and reliable readings.
The MQ-2 operates using a metal-oxide semiconductor (MOS) sensing mechanism. Its sensing element is made of tin dioxide (SnO₂) deposited on an aluminum-oxide ceramic substrate and heated by an internal heater. In clean air, oxygen molecules are adsorbed on the heated SnO₂ surface, capturing free electrons and increasing the sensor’s resistance.
When combustible or reducing gases are present, they react with the adsorbed oxygen and release the trapped electrons back into the sensing material. This reduces the sensor’s resistance and increases current flow, producing a measurable rise in output voltage. These voltage changes allow external circuits to detect gas presence and estimate relative gas concentration.
| Pin Label | Pin Name | Description |
| H | Heater Pin 1 | Supplies power to the internal heater element |
| H | Heater Pin 2 | Heater return pin |
| A | Electrode A | Sensing electrode (connected internally) |
| A | Electrode A | Duplicate sensing electrode |
| B | Electrode B | Output electrode (connected internally) |
| B | Electrode B | Duplicate output electrode |
| Pin No. | Pin Name | Description |
| 1 | VCC (+5V) | Power supply input |
| 2 | GND | Ground |
| 3 | DOUT | Digital output (threshold-based) |
| 4 | AOUT | Analog output (gas concentration level) |
• Clamp Ring- The clamp ring secures the metal mesh and internal parts of the sensor. It keeps the structure stable and ensures all components stay aligned during operation.
• Anti-Explosion Network (Metal Mesh) - This stainless-steel mesh prevents sparks inside the sensor from igniting flammable gases outside. It also works as a protective filter against dust and debris.
• Connecting Legs (Pins) - The pins provide electrical connections between the MQ-2 sensor and the external circuit. They include heater pins (H) and signal pins (A and B) for gas sensing output.
• Sensing Element - The sensing element is the core of the MQ-2 sensor. It changes electrical resistance when exposed to gases such as LPG, methane, or smoke, enabling gas detection.
• Aluminum Oxide (Al₂O₃) Based Ceramic - This ceramic tube supports the sensing element and heater. It offers excellent electrical insulation and can withstand high temperatures during operation.
• Tin Dioxide (SnO₂) Coating - The SnO₂ layer is the gas-sensitive material. When gas molecules interact with this coating, its conductivity changes, which the sensor converts into an electrical signal.
• Nickel-Chromium Heating Coil - The heating coil raises the temperature of the sensing element to its optimal working range. Proper heating is essential for accurate and stable gas detection.
• Platinum Wires - Platinum wires connect the sensing layer and heater to the external pins. Platinum is used because it is highly stable and resistant to heat and corrosion.
This is the main sensor that detects gases such as LPG, methane, hydrogen, and smoke. It changes resistance when gas is present, which the module converts into output signals.
This small adjustable knob lets you set how sensitive the sensor is to gas. Turning it changes the gas threshold level for the digital output.
The LM393 compares the sensor signal with the set threshold from the potentiometer. When the gas level exceeds the set limit, it triggers the digital output.
This LED turns on when the module is properly powered. It simply shows that voltage is supplied to the board.
This LED lights up when the gas concentration crosses the preset threshold. It gives a quick visual alert without needing a microcontroller.
The analog pin outputs a continuous voltage that changes based on gas concentration. It is useful for measuring relative gas levels.
The digital pin outputs HIGH or LOW depending on whether the gas level is above the set threshold. It is commonly used for alarms and simple detection.
Supplies power to the module, typically 5V. This powers both the heater and the onboard electronics.
Provides the ground reference for the module and must be connected to the system ground.
| Sensor Model | Main Gases Detected | Detection Focus | Typical Detection Range (ppm) | Operating Voltage | Heater Voltage |
| MQ-2 | Methane, LPG, Butane, Smoke | Flammable gases | 300 – 10,000 | 5V | 5V |
| MQ-3 | Alcohol, Ethanol, Smoke | Alcohol vapors | 25 – 500 | 5V | 5V |
| MQ-4 | Methane, CNG | Natural gas | 300 – 10,000 | 5V | 5V |
| MQ-5 | Natural Gas, LPG | Combustible gases | 200 – 10,000 | 5V | 5V |
| MQ-6 | LPG, Butane | Gas leakage | 300 – 10,000 | 5V | 5V |
| MQ-7 | Carbon Monoxide (CO) | Toxic gas | 20 – 2,000 | 5V | 5V |
| MQ-8 | Hydrogen | Hydrogen gas | 100 – 10,000 | 5V | 5V |
| MQ-9 | CO, Flammable gases | Mixed gases | 10 – 10,000 | 5V | 5V |
| MQ-131 | Ozone (O₃) | Air quality | 10 ppb – 2 ppm | 5V | 5V |
| MQ-135 | NH₃, Benzene, Alcohol, Smoke | Air quality | 10 – 1,000 | 5V | 5V |
| MQ-136 | Hydrogen Sulfide (H₂S) | Toxic gas | 1 – 200 | 5V | 5V |
| MQ-137 | Ammonia (NH₃) | Ammonia gas | 5 – 500 | 5V | 5V |
| MQ-138 | Benzene, Toluene, Alcohol | VOCs | 1 – 500 | 5V | 5V |
| MQ-214 | Methane, Natural Gas | Fuel gas | 300 – 10,000 | 5V | 5V |
| MQ-216 | Natural Gas, Coal Gas | Industrial gas | 300 – 10,000 | 5V | 5V |
| MQ-303A | Alcohol, Ethanol, Smoke | Alcohol vapors | 20 – 500 | 5V | 5V |
| MQ-306A | LPG, Butane | Gas leakage | 300 – 10,000 | 5V | 5V |
| MQ-307A | Carbon Monoxide | CO gas | 10 – 2,000 | 5V | 5V |
| MQ-309A | CO, Flammable gases | Mixed gases | 10 – 10,000 | 5V | 5V |
| Category | Parameter | Specification |
| General | Model No. | MQ-2 |
| Sensor Type | Semiconductor (MOS) | |
| Standard Encapsulation | Bakelite (Black Bakelite) | |
| Detection Gas | Combustible gas and smoke | |
| Target Gases | LPG, Butane, Propane, Methane, Hydrogen, Alcohol, Smoke | |
| Detection Concentration | 300 – 10,000 ppm (combustible gases) | |
| Electrical | Loop Voltage | ≤ 24 V DC |
| Heater Voltage | 5.0 V ± 0.2 V (AC or DC) | |
| Load Resistance | Adjustable | |
| Heater Resistance | 31 Ω ± 3 Ω (room temperature) | |
| Heater Power Consumption | ≤ 900 mW | |
| Typical Heater Current | ≈ 150 mA | |
| Sensing | Sensing Resistance | 2 kΩ – 20 kΩ (at 2000 ppm C₃H₈) |
| Sensitivity | Rs (air) / Rs (1000 ppm isobutane) ≥ 5 | |
| Slope | ≤ 0.6 (R₅₀₀₀ppm / R₃₀₀₀ppm CH₄) | |
| Response Time | ≤ 10 s (typical) | |
| Recovery Time | ≤ 30 s (typical) | |
| Environment | Operating Temperature | −10 °C to +50 °C |
| Storage Temperature | −20 °C to +70 °C | |
| Operating Humidity | ≤ 95% RH (non-condensing) | |
| Standard Test Conditions | 20 °C ±2 °C; 65% ±5% RH | |
| Circuit | Standard Test Circuit | Vc: 5.0 V ±0.1 V; Vh: 5.0 V ±0.1 V |
| Output Type | Analog resistance change | |
| Mechanical | Sensor Diameter | ~18 mm |
| Sensor Height | ~17 mm | |
| Pin Count | 6 pins | |
| Weight | ~5 g | |
| Other | Preheat Time | ≥ 48 hours (initial use) |
The MQ-2 gas sensor operates at a standard 5V supply, making it fully compatible with common microcontrollers such as Arduino, ESP32 (with proper interfacing), and Raspberry Pi modules. This simplifies power design and integration in DIY and embedded projects.
This sensor can detect LPG, alcohol, propane, hydrogen, carbon monoxide, and methane. Its broad sensitivity makes it suitable for gas leakage alarms, smoke detectors, and general safety monitoring where multiple combustible gases may be present.
The analog output provides a continuous voltage level that changes with gas concentration. This allows users to estimate relative gas levels and perform calibration for more precise monitoring applications.
The digital output switches HIGH or LOW when gas concentration exceeds a preset threshold. This is ideal for simple alarm systems that only require gas presence detection.
The module can provide initial readings after a short warm-up period, allowing quicker testing and demonstrations, though long-term stability improves with extended preheating.
The MQ-2 can be used as either an analog sensor for variable readings or a digital sensor for threshold-based alerts, offering flexibility for different project requirements.
An onboard potentiometer allows easy adjustment of the digital output sensitivity, enabling users to fine-tune the trigger level based on environmental conditions.
The sensor shows strong sensitivity across a wide range of combustible gases, making it effective for early gas leak detection.
The MQ-2 is particularly sensitive to LPG, propane, and hydrogen, which are common fuels in household and industrial environments.
Built with durable materials and a simple internal structure, the MQ-2 offers long operational life at a very low cost, ideal for mass deployment and educational use.
The sensor requires only minimal external components to operate, reducing circuit complexity and making it easy for beginners to use.
The MQ-2 gas sensor test circuit shows how the sensor is powered and how its gas-sensitive resistance is converted into a measurable voltage. The circuit is divided into two main parts: the heater circuit and the signal (sensing) circuit. Each part has a different role in enabling proper gas detection.
The heater circuit uses the VH supply to power the internal heater (H–H pins). This heater raises the temperature of the sensing material so that gas molecules can react with it. Without this heating, the sensor would not respond correctly to combustible gases. The heater circuit is referenced to GND, completing the power path.
The sensing circuit is formed by the internal sensing resistance (Rs, between pins A and B) and the external load resistor (RL). A supply voltage (Vc) is applied across this series combination. When gas concentration changes, the resistance of Rs changes, which causes a corresponding change in voltage across RL.
The output voltage (VRL) is measured across the load resistor RL. As gas concentration increases, Rs typically decreases, causing VRL to rise. This voltage is the usable signal that can be read by an analog input of a microcontroller or compared against a threshold for gas detection.
In the diagram, the MQ-2 gas sensor module is connected to an Arduino Uno using four basic connections: power, ground, analog output, and optional digital output. The VCC pin of the MQ-2 module is connected to the Arduino’s 5V pin, while the GND pin is connected to Arduino GND. These two connections power the sensor’s internal heater and onboard circuitry, allowing the sensor to operate correctly.
The analog output pin (A0) of the MQ-2 module is connected to one of the Arduino’s analog input pins, such as A0. This connection allows the Arduino to read a variable voltage that represents the gas concentration. As the level of combustible gas or smoke increases, the voltage on the A0 pin also changes, and the Arduino converts this voltage into a digital value using its internal ADC.
If digital detection is needed, the digital output pin (D0) can be connected to any Arduino digital input pin. The digital output is controlled by the onboard LM393 comparator and responds when gas concentration exceeds a preset threshold. This threshold is adjusted using the sensitivity potentiometer on the sensor module.
Once powered, the MQ-2 sensor requires a warm-up period so the internal heating coil can reach its working temperature. During operation, the tin dioxide (SnO₂) sensing layer changes resistance when exposed to gases such as LPG, methane, or smoke. The module converts this resistance change into an electrical signal that the Arduino continuously monitors.
By reading the analog or digital output, the Arduino can process gas concentration levels in software. Based on these readings, the system can trigger alarms, display values on a screen, or activate safety devices. This simple wiring and working principle make the MQ-2 gas sensor easy to integrate into Arduino-based gas detection and safety projects.
Catalogue
FPGA / CPLD
Memory
MOS 
MCU 
DSP
OCEP
Secondary 
Other