Formaldehyde Sensor Module Gas Detection Sensor MQ138 MQ-138 Aldehydes And Ketones Alcohols Gas Sensor   Features:   1: Wide range of applications   2: Small appearance   3: Long service life   4: Fast response time   5: With mounting holes for easy permanent installation         Product Description:   1. The module comes with MQ138 gas sensor and circuit, easy to plug in and use, just connect the power supply and the module can be connected with the microcontroller.   2. Working voltage: DC 5V   3. Comes with power and digital signal LED indicators.   4.2-channel signal output (analog output, TTL level output).   5. TTL output valid signal is low level; (low output signal light, can be connected to the IO port of the microcontroller)   The analog output increases with the concentration, the higher the voltage, the higher the concentration, the higher the sensitivity of aldehydes, alcohols, ketones, and aromatic compounds.   6. Has long life and reliable stability.   7. Quick response feature.   8. With mounting holes for easy permanent installation.   9. Main chip: LM393, formaldehyde sensing probe   10. Dimensions: 35mm x 21mm x 28mm         Packing list:   1*Sensor Module