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MQ135 MQ-135 Air Quality Gas Sensor

K-TECHNICS
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KSh400.00

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The MQ-135 Gas Sensor is a low-cost, semiconductor-based metal oxide sensor designed primarily for monitoring indoor air quality. It utilizes a Tin Dioxide (SnO₂) sensing element, which exhibits low electrical conductivity in clean air. When exposed to target pollutants, its conductivity increases proportionally to the concentration of the gas.
Technical Specifications
  • Operating Voltage: 5V ± 0.1V AC or DC
  • Current Consumption: Approximately 150mA
  • Heater Resistance: 33 Ω ± 5% at room temperature
  • Heating Consumption: ≤ 800mW
  • Detection Range: 10 to 1000 ppm (Parts Per Million)
Target Gases & Sensitivity
The MQ-135 is a broad-spectrum sensor, meaning it reacts to multiple gases rather than isolating just one. It displays its highest sensitivity to:
  • Ammonia (NH₃)
  • Benzene (C₆H₆) and Toluene
  • Sulfide vapors
  • Carbon Dioxide (CO₂)
  • Alcohol vapors and Smoke
Module Pinout & Dual Outputs
Most commercial versions of the MQ-135 come mounted on a breakout board with four interface pins:
  • VCC: Power input (5V)
  • GND: Ground connection
  • AOUT (Analog Output): Outputs a continuous 0V to 5V signal. The voltage rises alongside increases in gas concentration, making it ideal for microcontrollers with ADCs to log precise trends.
  • DOUT (Digital Output): Transmits a TTL-logic level (High/Low). An onboard potentiometer allows you to adjust the threshold limit. If gas levels rise past this limit, the digital pin shifts to a low level and illuminates an onboard LED.
Critical Usage Notes
  • Preheating Requirement: The sensor relies on an internal Ni-Cr heating element. For basic daily use, it needs a warm-up period of 5 minutes to stabilize. For first-time setups or precise data logging, a burn-in period of 24 to 48 hours is mandatory according to the technical documentation.
  • Cross-Sensitivity & Calibration: Because it responds to many gases simultaneously, it cannot inherently distinguish between CO₂ and alcohol vapor on its own. For accurate Parts-Per-Million (PPM) values, you must calibrate the sensor in clean air (R₀ baseline).

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