MQ-2 Gas Sensor Symbol

The MQ-2 Gas Sensor schematic symbol. Standard-specific details are listed below where available.

Definition: The MQ-2 Gas Sensor symbol represents a resistive chemo-resistive gas detection module that responds to combustible gases, smoke, and LPG by varying its internal resistance, shown in circuit diagrams as a rectangular IC module with VCC (vcc), GND (gnd), and DO (do) pins on the left and an AO (ao) analog output pin on the right.

Also known as: MQ-2 sensor, gas sensor module, smoke sensor, LPG sensor, combustible gas detector, air quality sensor, chemo-resistive gas sensor.

What the MQ-2 Gas Sensor symbol means

The MQ-2 Gas Sensor symbol denotes an electrochemical gas detection module built around a tin oxide (SnO2) sensing element whose electrical resistance decreases when combustible gases or smoke are present. The sensor module includes the sensing element, a heating resistor, a voltage divider network, and an LM393 comparator on the PCB that produces both a digital threshold output (DO) and an analog proportional output (AO).

The four terminals — VCC (vcc) for the 5 V supply, GND (gnd) for the ground reference, DO (do) for the digital threshold output, and AO (ao) for the analog voltage proportional to gas concentration — represent the external interface pins of the module. The DO output goes low when gas concentration exceeds a threshold set by an onboard potentiometer; the AO output provides a continuous voltage ramp proportional to gas concentration for quantitative measurement.

How to identify the MQ-2 Gas Sensor symbol

The MQ-2 Gas Sensor symbol is drawn as a rectangular block labelled 'MQ-2' or 'Gas Sensor'. VCC (vcc), GND (gnd), and DO (do) pins emerge from the left edge; AO (ao) emerges from the right edge. In physical circuit representations, the symbol may show the black cylindrical sensing element cap (the sensing dome) as a distinctive circular feature on the module outline.

Function and usage boundary

The MQ-2 sensor works by heating a tin oxide (SnO2) sensing layer on a ceramic substrate to approximately 200–300 °C using a built-in resistive heater coil. At this temperature, oxygen adsorbs onto the SnO2 surface, creating a high-resistance baseline. When reducing gases such as LPG, methane, hydrogen, alcohol, smoke, or carbon monoxide contact the heated surface, the oxygen desorbs and the sensor resistance drops, increasing the output voltage from the voltage divider. The DO output from the onboard LM393 comparator goes low when this voltage exceeds a settable threshold. The AO pin provides a 0–5 V analog output proportional to gas concentration.

Standards: IEC vs ANSI

IEC 60617	Gas sensor modules such as the MQ-2 follow IEC 60079-29-1 (Gas detectors — Performance requirements for detectors for flammable gases) for performance classification. The schematic symbol follows IEC 60617 conventions for sensor modules, represented as a rectangular function block.
ANSI/IEEE 315	UL 2075 (Standard for Gas and Vapor Detectors and Sensors) covers gas sensor performance in North American practice. The MQ-2 module is commonly used in prototype and IoT devices; industrial-grade sensors for safety-critical applications must comply with relevant ATEX or UL listing requirements.
Key difference	Both IEC and ANSI represent sensor modules as labelled rectangular blocks in circuit diagrams. For safety-critical flammable gas detection (e.g., in Zone 1/2 hazardous areas), IEC 60079 series (ATEX) and UL 2075 impose performance and certification requirements that the MQ-2 does not meet; the MQ-2 is appropriate for educational, hobbyist, and non-safety-critical IoT applications.

The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.

Logical terminals

Logical ID	Editor terminal name
vcc	VCC
gnd	GND
do	DO
ao	AO

Where the MQ-2 Gas Sensor symbol is used

Residential gas leak alarms: MQ-2 sensor detects LPG or natural gas leaks above a threshold and triggers a buzzer alarm
Arduino and Raspberry Pi projects: air quality and combustible gas monitoring with serial data logging
IoT smoke detection nodes: MQ-2 AO output fed to an ADC to quantify smoke density and transmit via MQTT
Industrial pre-alarm systems (non-safety-critical): early-warning gas presence detection before dedicated safety-rated sensors
Ventilation control systems: sensor DO output activates a relay to switch on exhaust fans when gas is detected
Educational electronics labs: demonstrating resistive gas sensing principles and analog-to-digital conversion

Key facts

The MQ-2 Gas Sensor symbol represents a chemo-resistive SnO2 sensing module that detects LPG, smoke, hydrogen, propane, methane, alcohol, and carbon monoxide by resistance change.
The four terminals are VCC (vcc) at 5 V DC, GND (gnd) ground, DO (do) digital threshold output (active low), and AO (ao) analog output proportional to gas concentration.
The MQ-2 requires a preheat time of at least 20 seconds before reliable readings; full accuracy calibration requires 24–48 hours of continuous operation.
The onboard LM393 comparator generates the DO digital output by comparing the voltage-divider output against a threshold set by a potentiometer on the module PCB.
The MQ-2 is sensitive to LPG, methane, smoke, hydrogen, alcohol, and propane, but is not selective — it cannot distinguish between different gases.
Operating the MQ-2 requires approximately 150 mA heater current; microcontroller GPIO pins cannot supply this directly — a 5 V regulated supply or USB power is required.
The MQ-2 is not suitable for safety-critical or certified gas detection applications; industrial-grade detectors must comply with IEC 60079-29-1 (ATEX) or UL 2075 for use in hazardous environments.

Frequently asked questions

What does the MQ-2 gas sensor symbol mean in a circuit diagram?

The MQ-2 gas sensor symbol represents a chemo-resistive combustible gas and smoke detection module in a circuit diagram. It identifies the sensor's power supply connections (VCC, GND), its digital alarm output (DO), and its analog gas-concentration output (AO), showing how the sensor integrates with a microcontroller or alarm circuit.

What does the MQ-2 gas sensor symbol look like?

The MQ-2 gas sensor symbol looks like a labelled rectangular block with VCC (vcc), GND (gnd), and DO (do) pins on the left and AO (ao) on the right. Physical module drawings may show the cylindrical black sensing dome on top of the PCB outline.

What gases does the MQ-2 sensor detect?

The MQ-2 sensor detects a range of combustible gases and smoke, including LPG, propane, methane, hydrogen, alcohol vapour, carbon monoxide, and general smoke particles. It is not selective and cannot distinguish between different gas species — it provides a general indication of combustible gas or smoke presence.

What is the difference between the DO and AO outputs on the MQ-2 sensor?

The DO (digital output) is a threshold-triggered TTL signal from the onboard LM393 comparator that goes LOW when gas concentration exceeds the level set by the onboard potentiometer — suitable for triggering a binary alarm. The AO (analog output) provides a continuously varying voltage (0.1–4.9 V) proportional to gas concentration, allowing quantitative measurement when connected to an ADC.

How much current does the MQ-2 gas sensor consume?

The MQ-2 sensor consumes approximately 150 mA at 5 V DC due to its internal heater resistor (approximately 33 Ohms). This exceeds the current supply of most microcontroller GPIO pins, so VCC must be connected to a 5 V regulated power rail rather than to a microcontroller pin.

How long does the MQ-2 sensor need to warm up?

The MQ-2 requires at least 20 seconds of preheating after power-on before it produces reliable readings, as the internal heater must reach operating temperature. For accurate calibration-grade measurements, the sensor should operate continuously for 24–48 hours in clean air to establish a stable baseline resistance.

Is the MQ-2 suitable for certified safety gas detection?

No. The MQ-2 is intended for hobbyist, educational, and non-safety-critical IoT applications. Safety-critical combustible gas detection in buildings or industrial facilities requires sensors certified to IEC 60079-29-1 (ATEX), UL 2075, or equivalent standards, which impose performance testing, fail-safe requirements, and third-party certification that the MQ-2 does not have.

Related symbols

Physical breadboard, PCB, and panel mapping

No universal physical profile is published for this symbol yet. Create a versioned custom part from the exact manufacturer dimensions and terminal map before fabrication.

Place the MQ-2 Gas Sensor symbol directly on a wiring diagram or schematic in the free online editor — no download required.