The MQ-136 is a sulfur dioxide (SO₂) gas sensor designed to detect SO₂ gas concentrations in the environment. Since sulfur dioxide is a harmful and toxic gas produced mainly from burning fossil fuels, industrial emissions, and volcanic activity, this sensor is often used in environmental monitoring, industrial safety, and air quality systems. 🔹 Details and Explanation 1. Main Features Type: Sulfur Dioxide (SO₂) gas sensor Gas Detected: SO₂ (Sulfur dioxide), with slight sensitivity to H₂S and other sulfur-based gases Operating Voltage: 5V DC Current Consumption: ~150 mA (due to internal heater) Output: Analog (AO): Continuous voltage proportional to SO₂ concentration Digital (DO): HIGH/LOW signal based on threshold set via onboard potentiometer Detection Range: 1 ppm – 200 ppm SO₂ 2. Working Principle Built with a heating element and a metal oxide semiconductor layer (SnO₂). In clean air → the resistance of SnO₂ is high. When exposed to SO₂ gas → resistance decreases → current flow increases. The change in resistance is converted into a voltage signal. AO pin provides analog readings proportional to SO₂ levels. DO pin outputs HIGH/LOW depending on whether SO₂ exceeds the set threshold. 3. Pin Configuration (MQ-136 Module) VCC → +5V supply GND → Ground DO → Digital output (1 = SO₂ detected above threshold, 0 = normal) AO → Analog output (SO₂ concentration level) 4. Applications Environmental monitoring (air pollution detection) Industrial safety systems (factories, refineries, power plants) Gas leakage detection in chemical plants IoT-based smart air quality systems Early warning systems in areas near volcanoes or heavy industry 5. Important Notes Requires burn-in time (24–48 hours) for stable and accurate readings. Works best after a few minutes of heating during each use. Should be calibrated in known SO₂ concentrations for precise ppm measurement. Not a substitute for certified industrial-grade gas detectors but excellent for prototyping and monitoring projects.