Gas & Air Quality
Interfacing MQ 3 Gas & Air Quality with Arduino Uno
What is the MQ 3?
MQ 3 practical reference
Tuned specifically for detecting alcohol vapor concentration, frequently used in breathalyzer-style hobby projects. The MQ-3 is a metal-oxide semiconductor gas sensor whose surface resistance changes in the presence of ethanol vapor, producing an analog output that increases with alcohol concentration — like other MQ-series sensors it needs a warm-up period and isn't lab-calibrated, so it's best suited for relative/comparative alcohol-detection demos rather than legally-relevant breathalyzer readings.
Key specifications
- Sensor type: MQ-3 metal-oxide semiconductor (MOS) gas sensor, tuned for alcohol vapor
- Operating voltage: 5 V DC (heater circuit + sensing circuit both typically run at 5V)
- Detection range: ~0.05-10 mg/L alcohol vapor concentration
- Warm-up time: Requires several minutes (some sources recommend 24-48 hours for first-use burn-in) of heater warm-up before stable readings
- Output: Analog voltage proportional to alcohol vapor concentration, plus a digital threshold output (DO) on breakout modules with an onboard comparator
- Sensitivity adjustment: Onboard potentiometer sets the digital-output trigger threshold
- Interface: 1 analog pin (AO) + 1 digital pin (DO, breakout-dependent)
Pinout and connection notes
Like all MQ-series sensors, allow several minutes of warm-up after power-on before trusting readings, since the internal heater element needs time to reach a stable operating temperature; results also drift with humidity and temperature, so treat readings as relative/comparative rather than a precisely calibrated measurement, and never rely on this sensor for legal or medical breath-alcohol determinations.
- VCC: Power, 5V DC (powers both the internal heater and sensing circuit)
- GND: Ground
- AO: Analog output — voltage proportional to alcohol vapor concentration
- DO: Digital output — threshold-triggered HIGH/LOW based on the onboard potentiometer setting
Integration checklist
- Confirm the exact part number and breakout-board revision.
- Verify supply voltage, current demand, logic levels, and signal direction against the datasheet.
- Check controller pin assignments and bus address or interface mode against the example code.
- Power up with external loads disconnected, then test signals before full integration.
- If readings or communication fail, check power and ground first, then pin mapping, interface settings, and library initialization.
Troubleshooting and reproducibility
Record the board used, wiring, library/version, supply arrangement, and measured behavior. Use the selected board-specific wiring example as the source of truth. Never assume visually similar modules share identical voltage tolerance or pin order.
Setting Up MQ 3 with Arduino Uno
Wiring
| Component pin | Arduino Uno pin | Note |
|---|---|---|
| VCC | 5V | |
| GND | GND | |
| AO | A0 | Analog voltage output — rises with detected alcohol vapor concentration |
| DO | D2 (optional) | Digital threshold trigger; trip point set by the onboard potentiometer |
Swipe sideways to see every column →
- MQ-3 needs several minutes of heater warm-up before readings settle, and the baseline keeps drifting for the first day or two of total run time — don't trust a reading taken right after power-up.
- This is not a calibrated breathalyzer. Treat the output as "rising/falling," not an accurate BAC number, and never use it for anything safety-critical or legal.
- The onboard potentiometer only sets the DO threshold — it doesn't calibrate the analog reading.
Related Components
A3144
Digital Hall-effect switch for contactless magnetic detection
ACS712
Measure AC or DC current with an analog Hall-effect sensor
MQ 2
Detects LPG, smoke, and combustible gases — the standard gas sensor for safety projects.
MQ 7
Dedicated CO sensor for indoor safety monitors and air-quality projects.
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