Adopt high-quality double-panel design, with power indicator and TTL signal output indicator. With DO switch signal (TTL) output and AO analog signal output TTL output high and low level. (Can be directly connected to the microcontroller or relay module) The analog output voltage changes with the concentration. Fast response recovery feature. Has long service life and reliable stability. Electrical performance: Input voltage: DC5V Power consumption (current): 150mA DO output: TTL digital quantities 0 and 1 (0.1 and 5V) AO output: analog level signal Special reminder: After the sensor is powered on, it needs to be preheated for about 20S, and the measured data is stable. It is normal for the sensor to heat up, because there is a heating wire inside, if it is hot, it not be normal. Wiring: 1. VCC: connect to the positive pole of the power supply (5V) 2. GND: connect to the negative pole of the 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 Senso Module Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.