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 and recovery feature. Has long service life and reliable stability. Electrical performance: Input voltage: DC 5V 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 20 seconds. The measured data will then stabilize. It is normal for the sensor to heat up, as there is a heating wire inside. If it does not heat up, it is not functioning properly. 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 Sensor Module Only the above package content; other products are not included. Note: Lighting and different displays may cause the color of the item in the picture to appear slightly different from the real thing. Measurement allowed error is +/- 1-3 cm.