Medium

Gas/Smoke Sensor Alarm

An MQ-series gas sensor module detects alcohol, gas, or smoke in the air and triggers a buzzer — the same family of sensors used in commercial gas detectors.

Circuit Diagram

+9V Gas Sensor MQ-3 Module VCC (warm up first) digital OUT base R Q BC547 C → buzzer E → GND BUZZER GND Alcohol/gas vapor near the sensor → digital output HIGH → buzzer sounds

How to Build It

  1. Connect the MQ-3 gas sensor module to power (VCC/GND) — it needs a few minutes to warm up before it's stable.
  2. Connect the module's digital output to a BC547 transistor's base, through a resistor.
  3. Connect the transistor's collector to a buzzer and then to the positive rail.
  4. Connect the emitter to GND.
  5. Wait for the sensor to warm up, then expose it to alcohol vapor (e.g. hand sanitizer) — the buzzer should sound.

Bill of Materials

ProductCodeQty
Buzzer LD-BZPG-2312 1
Resistor DR47K-8/9 1
Sensor / sensor module 22132 1
Transistor (incl. IGBT) — 1
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