Description
🌫️ MQ135 Air Quality Gas Sensor
The MQ135 is a popular air quality sensor designed to detect a wide range of gases, including:
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Ammonia (NH₃)
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Sulfur compounds
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Benzene
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Smoke
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Carbon dioxide (CO₂)
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Alcohols
It’s widely used in air quality monitoring, gas leakage detection, and smart environmental sensing.
⚙️ Key Specifications
| Feature | Details |
|---|---|
| Supply Voltage | 5V DC |
| Current Consumption | 150 mA (typical, during heater operation) |
| Sensing Range | 10 – 1000 ppm (for specific gases) |
| Preheat Time | ≥ 24 hours for accurate results |
| Output | Analog voltage + Digital out (with comparator board) |
| Sensitivity | High sensitivity to NH₃, NOₓ, alcohol, benzene, smoke |
| Operating Temp | -10°C to 50°C |
| Size (module) | Approx. 32mm x 20mm (varies by breakout board) |
📦 Variants
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Raw sensor (just the MQ135)
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Module with breakout board (includes potentiometer, comparator IC like LM393, and digital/analog outputs)
🔌 Typical Connections
| Pin | Function |
|---|---|
| VCC | 5V power input |
| GND | Ground |
| AOUT | Analog output (0–5V) |
| DOUT | Digital output (threshold adjustable) |
🧪 Applications
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Indoor air quality monitoring
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Smart homes (detecting poor ventilation or pollution)
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Industrial safety systems
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DIY environmental sensor stations (e.g., with Arduino or ESP32)
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CO₂ estimation (approximate, not highly accurate)
📌 Notes
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Needs a burn-in period (up to 24 hours) to stabilize readings.
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Not suitable for precision CO₂ detection (use NDIR sensors for that).
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Best used to detect general air quality trends rather than exact concentrations.
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