MQ-2 Gas & Smoke Sensor

Sensing Principle

The MQ-2 sensor relies on a tin dioxide (SnO₂) sensitive layer with low conductivity in clean air. In the presence of combustible gases (LPG, propane, methane, hydrogen, smoke), conductivity rises proportionally to gas concentration.

Firmware Calibration & Calculation

The firmware uses MQUnifiedsensor configured for 3.3V supply and 12-bit ADC resolution:

MQUnifiedsensor MQ2("ESP-32", 3.3, 12, PIN_GAS_SENSOR, "MQ-2");
MQ2.init();
MQ2.setVCC(3.3);
MQ2.setRegressionMethod(1); // Exponential regression
MQ2.setA(574.25); 
MQ2.setB(-2.222);
MQ2.setR0(10.0);

Concentration is calculated using exponential power regression:

PPM = A * (R_s / R_0) ^ B

• A: 574.25
• B: -2.222
• Baseline Sensor Resistance (R₀): 10.0 kΩ