Air Quality MQ-135 Gas Detection Sensor

Introduction of MQ-135 sensor:
The gas-sensitive material used in the MQ135 gas sensor is tin dioxide (SnO2) with low conductivity in clean air. When the sensor is stored in the environment
When polluting gas, the conductivity of the sensor increases as the concentration of polluting gas in the air increases. Use a simple circuit to change the conductivity
Conversion into an output signal corresponding to the gas concentration.
The MQ135 sensor is highly sensitive to ammonia, sulfide, and benzene vapors, and is ideal for monitoring smoke and other harmful effects. This sensor is detectable
It is a low-cost sensor suitable for a variety of applications, measuring a variety of harmful gases.
Module application:
Harmful gas detection device for home and environment, suitable for the detection of harmful gases such as ammonia, aromatic compounds, sulfides, benzene-based steam, smoke, etc. Gas sensor test concentration range: 10 to 1000ppm

Module instructions:
Explanation: Please preheat about 20S before use
The first step: supply 5V DC power to the module (note that the positive and negative poles are not reversed, otherwise the chip will be easily burned).
Step 2: If you select DO, TTL high and low level output terminals, the output signal can be directly connected to the IO port of the single-chip computer or to the relay module. The potentiometer is used here to adjust the threshold of the output level jump.
The third step: If you choose AO, analog output, then you do n°Øt need to control the potentiometer. Just connect the AO pin to the input terminal of AD conversion or a single-chip microcomputer with AD function. According to our experience: In a normal environment, that is, an environment without measured gas, set the output voltage of the sensor to the reference voltage. At this time, the voltage at the AO terminal is about 1V. When the sensor detects the measured gas, the voltage per Increase 0.1V, the actual measured gas concentration increases by 200ppm (simply put: 1ppm = 1mg / kg = 1mg / L = 1 °¡ 10-6 is often used to indicate gas concentration, or solution concentration.), According to this parameter Convert the measured analog voltage value into concentration value in the single chip microcomputer. Note: If you are using it as a precision instrument, please purchase a standard calibration instrument on the market, otherwise there will be errors, because the ratio of the relationship between the output concentration and the voltage is not nonlinear, but tends to be linear.
Special reminder: After the sensor is energized, it needs to preheat about 20S, the measured data is stable, the sensor heating is normal, because there are heating wires inside, if the hand is hot, it will not be normal.