The MQ-131 is an ozone (O₃) gas sensor used for air quality monitoring. It detects ozone concentrations
across a wide range. The sensor offers an analog output and supports TTL/SWD interfaces, making it suitable
for integration into environmental monitoring systems, air purifiers, and industrial applications requiring
ozone level detection. It can also detect chlorine (Cl₂) and nitrogen dioxide (NO₂).
The CJMCU-131 module features two MQ-131 sensors—one capable of operating at low concentrations
(10–1000 ppb) and the other at high concentrations
(10–1000 ppm), thus expanding the possibilities for
detecting and identifying ozone gas.
| Threshold Type | Concentration | Description / Action |
|---|---|---|
| Normal Range | ≤ 180 µg/m³ | Acceptable air quality. No health concern for the general population. |
| Information Threshold | ≥ 180 µg/m³ | Authorities must inform the public; sensitive groups should reduce outdoor activity. |
| Alarm Threshold | ≥ 240 µg/m³ | High risk. General population should avoid heavy outdoor activity; emergency measures may be initiated. |
| Target Value | 120 µg/m³ (8-hour average) | EU target value: should not be exceeded more than 25 days per year. |
| Limit for Vegetation | 180 µg/m³ (AOT40 index) | Threshold for protection of crops and ecosystems during the growing season. |
The sensitive compound of the MQ-131 sensor is SnO₂, which provides low conductivity in the presence of clean air. In the presence of ozone (O₃), chlorine (Cl₂) or nitrogen dioxide NO₂, the conductivity of the sensor becomes greater, increasing the increase in the concentration of the gas. The conversion of the output signal, based on the concentration of the detected gas, is entrusted to a simple circuit, and the voltage output allows a simplified connection with discrete microcontrollers, PLC systems or development kits such as Raspberry and Arduino.
| Detection range: |
10–1000 ppb (low concentration version) 10–1000 ppm (high concentration version) |
|---|---|
| Operating voltage: | 5 VDC |
| Output voltage: | 5 VDC |
| Load resistance (adjustable): | 500kΩ |
| Response time: | ≤1 s (preheating 3–5 minutes) |
| Typical Current: |
Heater: ~90 mA Signal circuit: ~10 mA Total (approx.): ~100 mA |
| Operating humidity: | 95% RH |
| Operating temperature: | -30°C to +70°C |
| Lifetime: | >5 years |
| Dimensions: | 65 x 45 x 28.5 mm |
| Used microcontroller: |
STM8S003F3P6 from STMicroelectronics Core: STM8 8-bit RISC processor Clock Frequency: Up to 16 MHz Flash Memory: 8 KB RAM: 1 KB EEPROM: 128 bytes |
📄 MQ-131 datasheet (Low Concentration) (561 kB)
📄 MQ-131 datasheet (High Concentration) (723 kB)
📄 MQ-131 schematic (67 kB)
📄 STM8S003F3 datasheet (1542 kB)
| Pin Name | Function |
|---|---|
| OUTL | Low-level digital output |
| OUTH | High-level digital output |
| Pin Name | Function |
| GND | Ground |
| RST | Reset |
| SWI | Serial Wire Interface |
| VCC | Power supply |
| Pin Name | Function |
| GND | Ground |
| URX | Receive serial data (UART receive pin) |
| UTX | Transmit serial data (UART transmit pin) |
| VCC | Power supply |
#define PIN_OUTL A0
#define PIN_OUTH A1
void setup() {
pinMode(PIN_OUTL, INPUT);
pinMode(PIN_OUTH, INPUT);
Serial.begin(9600);
}
void loop() {
Serial.println(String(analogRead(PIN_OUTL))+","+String(analogRead(PIN_OUTH)));
delay(100);
}