MQ-135 Gas Sensor

The MQ135 gas sensor uses tin dioxide (SnO2), a gas-sensitive material with low conductivity in clean air. When pollutants are present in the sensor's environment, the sensor's conductivity increases with the concentration of those pollutants. A simple circuit converts this conductivity change into an output signal corresponding to the gas concentration.

The MQ135 sensor is highly sensitive to ammonia, sulfides, and benzene vapors, and is also ideal for monitoring smoke and other harmful gases. This sensor can detect a variety of harmful gases and is a low-cost sensor suitable for various applications.

Module Applications: Harmful gas detection devices for homes and environments, suitable for detecting harmful gases such as ammonia, aromatic compounds, sulfides, benzene vapors, and smoke. Gas sensitive element test concentration range: 10 to 1000 ppm.

Module Features:
1. High-quality double-sided panel design with power indicator and TTL signal output indicator;
2. DO switch signal (TTL) output and AO analog signal output;
3. TTL output valid signal is low level. (The indicator light illuminates when the output is low, allowing direct connection to a microcontroller or relay module.)
4. Analog output: 0~5V voltage; higher concentration results in higher voltage.
5. Good sensitivity for air quality and harmful gas detection.
6. Four screw holes for easy positioning.
7. Product dimensions: 32mm (L) * 22mm (W) * 27mm (H)
8. Long service life and reliable stability.
9. Fast response and recovery characteristics.
10. Operating voltage: 5V

Module Instructions:
Explanation: Please warm up for approximately 20 seconds before use.

Step 1: Supply 5V DC power to the module (note: do not reverse the positive and negative terminals, otherwise the chip may be damaged).

Step 2: If selecting the DO, TTL high/low level output terminals, the output signal can be directly connected to the microcontroller's I/O port or a relay module. The potentiometer is used here to adjust the output level transition threshold.

Step 3: If you select AO (Analog Output), then you don't need to worry about the potentiometer. Simply connect the AO pin to the input of the AD converter or a microcontroller with AD functionality. Based on our experience: In a normal environment (i.e., without the gas being measured), set the sensor output voltage to a reference voltage. In this case, the voltage at the AO pin will be around 1V. When the sensor detects the gas being measured, for every 0.1V increase in voltage, the actual concentration of the gas increases by 200ppm (simply put: 1ppm = 1mg/kg = 1mg/L = 1×10⁻⁶, commonly used to express gas concentration or solution concentration). Based on this parameter, the measured analog voltage value can be converted to a concentration value in the microcontroller. Note: If you are using it for precision instruments, please purchase a standard calibration instrument from the market; otherwise, there will be errors because the ratio of output concentration to voltage is not linear but tends to be linear.

Special Reminder: After the sensor is powered on, it needs to warm up for about 20 seconds for the measured data to stabilize. Sensor heating is normal because it contains an internal heating wire; however, if it becomes too hot to touch, it is abnormal.

Technical Parameters

1. Heating Voltage: 5±0.2V (AC·DC)

2. Operating Current: 150mA

3. Circuit Voltage: ≤DC15V (Maximum DC15V)

4. Load Resistance: 1K (Adjustable)

5. Detection Concentration Range: 100-20000ppm (Varies depending on gas concentration)

6. Voltage in Clean Air: ≤1.5V

7. Sensitivity: ≥3%

8. Response Time: ≤1S (3-5 minutes preheating)

9. Reply Time: ≤30S

10. Component Power Consumption: ≤0.9W

11. Operating Temperature: -10~50℃ (Nominal Temperature 20℃)

12. Operating Humidity: 95%RH (Nominal Humidity 65%RH)

13. Service Life: 5 years

14. Dimensions: 35mm×22mm×25mm