MQ-136 Hydrogen Sulfide (H2S) Gas Sensor Module - Analog & TTL Output

The module's logic circuit operates on 5V DC. The sensor's internal heater also requires a separate 5V DC (±0.1V) supply, which can be AC or DC, to bring the SnO2 sensing element to its optimal operating temperature for accurate detection.

Connect the module's VCC and GND to Arduino's 5V and GND. The analog output pin connects to an Arduino analog input (e.g., A0) to read the 0-5V concentration signal. The digital TTL output pin connects to a digital input pin; it goes LOW when the gas concentration exceeds the threshold set by the onboard potentiometer.

Calibration involves adjusting the blue potentiometer on the module to set the digital trigger threshold. Expose the sensor to a known concentration of H2S gas (or use a calibrated source) and adjust the pot until the digital output switches state (LED turns on) at the desired concentration level. The analog output provides a continuous voltage for more precise measurement.

The MQ-136 is specifically sensitized for Hydrogen Sulfide (H2S) with high selectivity. While it may show some cross-sensitivity to other combustible gases like liquefied petroleum gas (LPG), natural gas, and city gas, its primary and most reliable detection is for H2S, which is critical for safety applications.