The MQ-9 is a gas sensor specifically designed to detect carbon monoxide (CO) and flammable gases such as LPG, methane, propane. It is widely used in safety systems, gas leak detectors, and industrial monitoring devices. 🔹 Details and Explanation 1. Main Features Type: CO and flammable gas sensor Gases Detected: Carbon Monoxide (CO), LPG, methane, propane, and other combustible gases Operating Voltage: 5V DC Current Consumption: ~150 mA Output: Analog (AO): Voltage proportional to gas concentration Digital (DO): HIGH/LOW signal based on threshold set by onboard potentiometer Detection Range: Carbon Monoxide (CO): 10 ppm – 1000 ppm Methane / LPG: 100 ppm – 10,000 ppm 2. Working Principle The MQ-9 sensor contains a heating element and a metal oxide semiconductor layer (SnO₂). In clean air → resistance of SnO₂ is high. When target gases are present → resistance decreases → higher current flow. The sensor is designed to operate in dual heating cycles: Low temperature → detects CO. High temperature → detects flammable gases like methane and LPG. This makes it versatile for detecting both toxic and combustible gases. 3. Pin Configuration (MQ-9 Module) VCC → +5V supply GND → Ground DO → Digital output (1 = gas detected, 0 = no gas) AO → Analog output (proportional to gas concentration) 4. Applications Carbon monoxide detectors Gas leak detection in homes and industries Fire detection systems Automotive exhaust monitoring IoT-based gas safety systems 5. Important Notes Requires preheating/burn-in time (24–48 hours) for accurate readings. Best accuracy is achieved after a few minutes of heating before measurement. Should be calibrated in a controlled environment for precise ppm detection.