MQ2

mQ2 is commonly used as shorthand for the MQ-2 gas sensor, a member of the MQ-series of metal oxide semiconductor (MOS) sensors. The term mQ2 is a less formal spelling that appears in informal writing and on some hobbyist boards; the official designation is MQ-2. These sensors are widely used in low-cost gas leak and smoke detectors because they are inexpensive and easy to interface with microcontrollers.

Principle of operation and sensing characteristics: The MQ-2 sensor contains a heated tin oxide (SnO2) film. In clean air, the film presents a relatively high resistance. When exposed to certain reducing gases—such as LPG, propane, methane, other hydrocarbons, and to some extent smoke—the resistance drops. This resistance change is typically read as an analog voltage through a load resistor in a voltage divider; many breakout boards also offer a digital output via a comparator. The sensor responds to a broad range of gases, which makes it versatile but not highly selective. Environmental factors like humidity and temperature can influence readings and long-term drift is common.

Construction and integration: The bare sensor is housed in a small ceramic body with heater elements that require a stable supply (commonly 5V, though some boards support 3.3V). The load resistor, often in the range of 20 kΩ to 47 kΩ, determines the sensitivity and output range. For hobbyist projects, the MQ-2 is typically wired to Vcc, ground, and analog (and sometimes digital) outputs on a microcontroller such as an Arduino or Raspberry Pi.

Applications and limitations: MQ-2 modules are popular for DIY gas leak detectors, air-quality monitors, and safety alarms. They are inexpensive and easy to use but require careful calibration, awareness of cross-sensitivity, and regular maintenance due to drift and environmental effects.