MQ-139 MQ139 Freon Gas Sensor Probe, Gas Sensor Module,Freon Gas Detection Module High sensitivity    Product Description:    1: Wide range of applications    2: With signal output indicator light    3: With mounting holes for easy fixed installation    4: High sensitivity    5: Long service life        Parameter:    1. Dimensions: 35mm X21mm X28mm length X width X height    2. Working voltage: DC 5V        Features:    1. With signal output indicator light;    2. Dual signal output (analog output and TTL level output);    3. The TTL output valid signal is low level; (the signal light is on when the output low level, can be connected to the IO port of the microcontroller)    4. The analog output increases with the concentration, the higher the concentration, the higher the voltage;    High sensitivity to ozone gas (detection concentration range 10-1000ppm)    6. It has a long service life and reliable stability;    7. Quick response and recovery features;    8. With mounting holes, it is convenient for fixed installation;    9. The probe can be plugged and unplugged, which is convenient for testing.        Packing list:    1*MQ139 Freon gas sensor