MQ-135 is an air quality sensor in MOS technology and detects a wide range of substances such as ammoina, sulfide, benzene, smoke, and other gases.
One especially important gas to evaluate air quality is not detected: CO2. Even though the datasheet claims that CO2 is part of the detected gases, this sensor type can only indirectly detect it, and sensitivity towards CO2 does not seem to be particularly high.
Overview
MQ-135 is an analog sensor that returns a voltage reading representing the overall gas concentration of all detectable gases.
| Parameter | Value |
|---|---|
| Voltage | 5V |
| Heater Current | <950mW |
| Sensitivity (ppm) | ammonia 10-300, benzene 10-1000, ethanol 10-300 |
| Preheat Time | >24h |
| Gas sensing | SnO2 |
Pins
The raw sensor has six pins:
| Pin | Description |
|---|---|
| H/H | apply 5V AC or DC |
| AA/BB | apply up to 24V DC in series with a load resistor, and measure voltage drop |
Typically, the sensor is mounted on a breakout board with these pins:
| Pin | Description |
|---|---|
| AO | analog out: measured sensor voltage |
| DO | digital out: high when threshold is exceeded |
| GND | Ground |
| VCC | 5V |
The threshold for the digital output (DO) can be set with a potentiometer.
Materials
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(content created Jul 16, 2024)