The MQ-2 is a metal-oxide semiconductor gas sensor that detects combustible gases including LPG, propane, methane, alcohol, hydrogen, smoke, and CO. An integrated heater raises the sensing element to ~300 °C for activation.
| IC / Sensing | SnO₂ metal-oxide (MQ-2) |
| Supply voltage | 5 V |
| Heater power | 0.9 W |
| Warmup time | 20 s (pre-heat 24 h recommended) |
| Detection gases | LPG, CO, Smoke, CH₄, H₂, Alcohol |
| Analog output | 0 – VCC |
| Digital threshold | Preset via potentiometer |
| Operating temp | −10 to +50 °C |
The SnO₂ semiconductor surface adsorbs oxygen in clean air, creating a depletion layer that raises resistance. When reducing gases (CO, hydrocarbons) contact the surface, they react with adsorbed oxygen, releasing electrons and lowering resistance. Lower resistance → higher analog output voltage.
Cannot distinguish between gas types — cross-sensitive to alcohol, humidity, temperature. Requires pre-heating (24 h for stable baseline). Sensor degrades over years of exposure. High humidity causes false positives. Not suitable for precise concentration measurement without calibration gas.