Mq-135 air quality sensor mq135 harmful gas detection module

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MQ-135Brief introduction of sensors：
The gas sensing material used in mq135 gas sensor is SnO2 with low conductivity in clean air. When there is polluted gas in the environment, the conductivity of the sensor increases with the concentration of polluted gas in the air. Using a simple circuit, the change of conductivity can be converted into the output signal corresponding to the gas concentration.
Mq135 sensor has high sensitivity to ammonia, sulfide and benzene vapor, and is also ideal for monitoring smoke and other harmful gases. The sensor can detect a variety of harmful gases and is a low-cost sensor suitable for a variety of applications.

Module application:
It is suitable for the detection of harmful gases such as ammonia, aromatic compounds, sulfide, benzene vapor, smoke and so on. The test concentration range of gas sensor is 10 to 1000ppm
Module features:
1. High quality double panel design, with power indication and TTL signal output indication;
2. It has do switch signal (TTL) output and AO analog signal output;
3. TTL output valid signal is low level（ When the output level is low, the signal light is on, which can be directly connected to the MCU or relay module.)
4. The higher the concentration is, the higher the voltage is.
5. It has good sensitivity for air quality and harmful gas detection.
6. There are four screw holes for easy positioning;
7. Product dimensions: 32 (L) * 20 (W) * 22 (H)
8. It has long service life and reliable stability
9. Fast response and recovery characteristics

Electrical performance:
Input voltage: DC5V, power consumption (current): 150mA
Do output: TTL digital quantity 0 and 1 (0.1 and 5V)
Ao output: 0.1-0.3v (relatively pollution-free), maximum concentration voltage about 4V
Special reminder: after the sensor is powered on, it needs to be preheated for about 20s before the measured data is stable. The heating of the sensor is a normal phenomenon, because there is an electric heating wire inside, if it is hot, it is abnormal.
Connection mode:

1. VCC: connected to positive pole of power supply (5V)
2. GND: connected to negative pole of power supply
3. Do: TTL switch signal output
4. Ao: analog signal output
Test procedure:
Implementation function: This version of supporting test program
Chip: AT89S52
Crystal oscillator: 11.0592Mhz
Baud rate: 9600
Compilation environment: Keil