Adopt high-quality double-panel design with power indicator and TTL signal output indicator. Features DO switch signal (TTL) output and AO analog signal output. TTL output provides high and low levels, compatible with microcontroller or relay module. Analog output voltage varies with gas concentration. Fast response and recovery. Long service life with reliable stability. Electrical specifications: Input voltage: DC 5V Power consumption: 150mA DO output: TTL digital signal (0 and 1, corresponding to 0.1V and 5V) AO output: Analog level signal Special note: After powering on, the sensor requires approximately 20 seconds of preheating for stable readings. It is normal for the sensor to generate heat during operation due to internal heating element. Wiring: 1. VCC: Connect to positive terminal of power supply (5V) 2. GND: Connect to negative terminal of power supply 3. DO: TTL switch signal output 4. AO: Analog signal output Model Number: MQ137 Type: Gas Sensor Color: Green Material: Metal Package Contents: 1 x MQ137 Ammonia Gas Sensor Module Note: Light and display differences may cause slight color variation between image and actual item. Measurement error allowed within +/- 1-3cm.