The MQ-135 gas sensor uses tin dioxide (SnO2) as its sensitive material, which has low conductivity in clean air. When the sensor is exposed to target gases, its conductivity increases with the concentration of combustible gases in the air. Different concentrations result in different resistance values, and a simple circuit can convert the change in conductivity into an output signal corresponding to the gas concentration. The MQ-135 sensor is highly sensitive to ammonia, sulfides, and benzene vapors, making it ideal for monitoring smoke and other harmful gases. It is a low-cost sensor suitable for various applications, such as household and environmentally harmful gas detection devices, and is ideal for detecting gases like ammonia, aromatic compounds, sulfides, benzene vapors, and smoke. The sensor includes an M3 mounting hole, uses a wide-voltage LM393 comparator for clean signals, good waveforms, and strong driving capability exceeding 15mA, with an adjustable precision potentiometer to set sensitivity. Parameters Operating Voltage: 5VDC Power Consumption (Current): 150mA Output Type: Analog and Digital Output Instructions Connect VCC and GND, and the module's power indicator light will turn on. Before use, allow the power to warm up for at least 2 minutes. It is normal for the sensor to feel slightly warm due to the internal heating element; however, if it feels too hot to touch, it may indicate an issue. When there is no sensitive gas influence or when the gas concentration does not exceed the set threshold, the digital interface DO output will be at a high level, and the analog interface A0 voltage will be approximately 0V. When the gas concentration exceeds the set threshold, the digital interface D0 will output a low level, the digital indicator light will turn on, and the voltage at the analog interface A0 will gradually increase with the gas concentration. AO output: 0.1-0.3V (relative to a non-polluted environment), with a maximum voltage of around 4V at high concentrations. Adjusting the potentiometer clockwise increases the sensitivity (only for TTL output). The digital output D0 can be directly connected to a microcontroller, which can detect high and low levels to monitor environmental gases. The digital output DO can also directly drive a relay module, creating a gas switch, or an active buzzer module, forming a gas alarm. The analog output AO can be connected to an AD module, allowing for approximate gas concentration readings through AD conversion. Note: Ensure correct wiring! Reversing the positive and negative connections can damage the module's electronic components. The sensitivity of the sensor probe is non-linear, so the analog output voltage does not have a linear relationship with the gas concentration. This module does not provide an analog output voltage-to-concentration curve; please use a standard instrument for actual measurements. The concentration may vary depending on the distance from the gas source. A 5.1-ohm resistor in series with the sensor’s heating circuit protects the heating wire from surge damage during cold start-up.
