1pc MQ-135 Air Quality Sensor Hazardous Gas Detection Module

Working voltage: DC 5V

Features:

1. With signal output indication.

2. Dual signal output (analog output and TTL level output)

3. TTL output valid signal is low level. (When the output is low, the signal light is on, and it can be directly connected to the MCU)

4. The analog output voltage is 0~5V, the higher the concentration, the higher the voltage.

5. It has high sensitivity and good selectivity to carbon monoxide.

6. Long-term service life and reliable stability

Explain:

This module is MQ-135 air quality sensor, please warm up about 20S before use:

Step 1: Supply 5V DC to the module (note that the positive and negative poles are not reversed, otherwise the chip will be burnt easily).

Step 2: If you choose DOUT, TTL high and low levels, the output signal can be directly connected to the IO port of the single-chip microcomputer or an NPN transistor to drive the relay. The potentiometer RP is used here to adjust the threshold of the output level jump. The schematic diagram can be analyzed. When the sensor detects the measured gas, the voltage value of the comparator LM393 pin 2 is proportional to the concentration of the gas detected by the sensor. When the concentration value exceeds the threshold set by the potentiometer RP, The position of pin 2 of the comparator is higher than that of pin 3. At this time, pin 1 of the comparator outputs low level, the LED light is on, R3 is the current limiting resistor of the LED light, and C1 is the filter capacitor. The sensor outputs a low level. Conversely, when there is no signal, the sensor outputs a high level, which is equal to the power supply voltage.

The third step: If you choose AOUT, analog output, then you don't need to control the potentiometer, and directly connect the AOUT pin to the input terminal of AD conversion or a single-chip with AD function. According to our experience: in a normal environment, that is, in an environment where there is no gas to be measured, set the sensor output voltage as the reference voltage. At this time, the voltage at the AOUT terminal is about 1V. When the sensor detects the gas to be measured, the voltage is Increase by 0.1V, the concentration of the actual measured gas increases by 20ppm (simply put: 1ppm=1mg/kg=1mg/L=1×10-6 is commonly used to indicate gas concentration, or solution concentration.), according to this parameter. Convert the measured analog voltage value into a concentration value in the microcontroller. 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 between the output concentration and the voltage is not linear, but tends to be linear.

special reminder: