# MQ-2 gas sensor: specs and pinout

> MQ-2 semiconductor (SnO2) combustible-gas sensor element on a module. The maker sheet lists high sensitivity to LPG, propane and hydrogen and use for…

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MQ-2 semiconductor (SnO2) combustible-gas sensor element on a module. The maker sheet lists high sensitivity to LPG, propane and hydrogen and use for methane and other combustible vapours.

Every value cites its sourceChip-level pinout

[Buy on Compoden](https://compoden.com/products/mq2-gas-sensor-module-for-smoke-lpg-alcohol-detection)

## Specs

| Spec | Value | Source |
|---|---|---|
| Loop voltage Vc | 24 V DC max | source Technical data table, p.1 |
| Heater voltage VH | 5.0 V +/-0.2 V, AC or DC | source Technical data table, p.1 |
| Heater resistance RH | 31 ohm +/-3 ohm (room temperature) | source Technical data table, p.1 |
| Heater power consumption PH | 900 mW max | source Technical data table, p.1 |
| Load resistance RL | Adjustable | source Technical data table, p.1 |
| Sensing resistance Rs | 2 kohm to 20 kohm (in 2000 ppm C3H8) | source Technical data table, p.1 |
| Detection concentration | 300-10000 ppm combustible gas | source Technical data table, p.1 |
| Preheat time | Over 48 hours | source Technical data table, p.1 |
| Standard test condition | 20 +/-2 C, 65% +/-5% RH, Vc 5.0 V +/-0.1 V, VH 5.0 V +/-0.1 V | source Technical data table, p.1 |

## Power

| | Value | Source |
|---|---|---|
| Supply | Heater voltage 5.0 V +/-0.2 V; heater power 900 mW max | source Technical data table, p.1 |
| Current | about 160 mA heater current at 5 V (derived: 5 V / 31 ohm RH; the sheet gives no current figure, only PH 900 mW max). Derived value, not printed in the sheet; module wiring is not documented. | source Technical data table, p.1 |

## Chip pins
These are the pins of the chip on the module, from the chip datasheet. The module's own header may label or expose them differently.

The maker sheet describes the bare MQ-2 sensor element (6 pins: 4 signal, 2 heater), not the module board. The module's header labels, regulator, comparator and load resistor are not covered by an official document, so module labels are left empty.

| Pin | Function | Voltage | Notes | Source |
|---|---|---|---|---|
| A / B (4 of the 6 sensor pins) | Sensing electrodes (signal) | | Sensor element, not the module header | source Section 'Structure and configuration', p.2; Notification 1.7, p.2 |
| H (2 of the 6 sensor pins) | Heater | | Sensor element, not the module header | source Section 'Structure and configuration', p.2; Notification 1.7, p.2 |

## Build with it
Project ideas for the MQ-2 gas sensor. Each link opens Soldr with the prompt filled in; Soldr assigns the pins, checks power and shows how to wire every part.

- [Combustible gas reading display](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20combustible%20gas%20sensor%20reading%20display%20with%20an%20Arduino%20Uno%20and%20a%2016x2%20LCD): Learning project, not a safety device. The Uno has a 5 V supply and analog inputs for the module output. The heater needs about 160 mA (derived from the heater resistance in the sheet); power the Uno from USB or a 5 V adapter rated 500 mA or more.
- [Combustible gas sensor trend display](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20combustible%20gas%20sensor%20reading%20trend%20display%20that%20draws%20the%20last%20hour%20of%20readings%20on%20a%200.96%20inch%20OLED%20with%20an%20Arduino%20Uno): Learning project, not a safety device or a gas detector. Shows the raw reading as a trend line, so you see how it changes with the air around it; no alarm or switching. The heater needs about 160 mA (derived from the heater resistance in the sheet); power the Uno from USB or a 5 V adapter rated 500 mA or more.
- [Combustible gas warm-up logger](https://app.soldr.ai/?prompt=I%20want%20to%20build%20a%20combustible%20gas%20sensor%20warm-up%20logger%20that%20prints%20readings%20to%20the%20serial%20monitor%20using%20an%20Arduino%20Uno): Learning project. Logs the slow change in reading while the sensor heats up so you can see when it settles. The sheet asks for a preheat of 48 hours, so leave it running that long before trusting the numbers. The heater needs about 160 mA (derived from the heater resistance in the sheet); power the Uno from USB or a 5 V adapter rated 500 mA or more.

## Common mistakes

- Skipping the warm-up: the sheet calls for a preheat of over 48 hours before readings are stable. ([source](https://www.pololu.com/file/0J309/MQ2.pdf))
- Applying more than the stated voltage: the sheet says a voltage higher than stipulated can damage the heater and change sensitivity; heater voltage is 5.0 V +/-0.2 V. ([source](https://www.pololu.com/file/0J309/MQ2.pdf))
- Splashing it: the sheet says sensitivity is reduced when the sensor is spattered or dipped in water. ([source](https://www.pololu.com/file/0J309/MQ2.pdf))

## Not covered by the official source

- The a hosted copy of the maker's sheet carries no maker name in its text; its content is the MQ-2 data sheet.
- Module-level supply, outputs, pin order and heater current are not documented; sheet values are for the bare sensor element.
- The sheet gives only a combustible-gas range (300-10000 ppm); no smoke figure.

## Sources

- [link](https://www.pololu.com/file/0J309/MQ2.pdf) (MQ-2 Semiconductor Sensor for Combustible Gas; a hosted copy of the maker's sheet)