Adopt high-quality double-panel design, with indicator and TTL signal output indicator.With DO switch signal (TTL) output and AO analog signal outputTTL 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 consumption (current): 150mADO output: TTL digital quantities 0 and 1 (0.1 and 5V)AO output: analog level signalSpecial 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 will not be normal.Wiring:1. VCC: connect to the positive pole of the supply (5V)2. GND: connect to the negative pole of the supply3. DO: TTL switch signal output4. AO: analog signal outputModel Number: MQ137Type: Gas Sensorcolor:GreenMaterial:MetalPackage Contents:1 x MQ137 Ammonia Gas Senso ModuleOnly 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.