🧪 Introduction to MQ3 Sensor

   

4

The MQ3 Gas Sensor is a chemical gas detection sensor mainly used to detect:

• Alcohol vapor

• Ethanol

• Smoke

• Flammable gases (low sensitivity)

It is widely used in:

• Breath analyzers

• Industrial gas safety systems

• Laboratory monitoring

• Smart safety projects

🧠 Full Form of MQ

MQ sensors are a series of gas sensors.

“MQ” does not officially stand for a full form — it is a model series name used by manufacturers.

Different MQ models detect different gases.

📊 Types of MQ Sensors Available

Here are common MQ series sensors:

In this module, we are using:

👉 MQ3 – Alcohol Gas Detection

🔬 Working Principle of MQ3

The MQ3 sensor works based on:

🔥 Metal Oxide Semiconductor (MOS) Technology

Inside the sensor:

• There is a heating element

• There is a sensing material (SnO₂ – Tin Dioxide)

How it works:

1️⃣ Heater warms the sensing layer
2️⃣ Clean air → High resistance
3️⃣ Alcohol gas present → Resistance decreases
4️⃣ Output voltage changes
5️⃣ ESP32 reads voltage change

So basically:

Gas concentration ↑
Resistance ↓
Output voltage ↑

⚙ Internal Structure

Main parts inside MQ3:

• Heating Coil

• Sensing Layer (SnO₂)

• Electrodes

• Protective mesh

The heating coil keeps temperature around 300°C for proper reaction.

🔌 MQ3 Module Pin Description

Most MQ3 modules have 4 pins:

🔹 AO (Analog Output)

• Gives continuous voltage value

• Used to measure gas concentration level

• Best for ESP32 projects

🔹 DO (Digital Output)

• HIGH or LOW signal

• Triggered when gas crosses threshold

• Adjustable using onboard potentiometer

📈 Sensitivity of MQ3

• High sensitivity to alcohol

• Moderate sensitivity to smoke

• Low sensitivity to LPG

Best use:

Alcohol gas detection system

⏳ Warm-Up Time

Important:

MQ3 requires:

⏱ 24–48 hours initial burn-in (recommended)
⏱ 30–60 seconds warm-up before readings

This stabilizes sensor output.

⚠ Safety Precautions

When testing:

• Do NOT expose directly to high flame

• Use small alcohol vapor source

• Ensure ventilation

• Avoid continuous high gas exposure

🧠 Why We Use MQ3 with ESP32?

• ESP32 has ADC (Analog-to-Digital Converter)

• Can read analog voltage easily

• Can connect to WiFi/Bluetooth for IoT

• Can trigger buzzer or alerts

🎓 Learning Outcomes of Lesson 10.0

Students will understand:

• What is gas sensor

• Different types of MQ sensors

• How MQ3 works

• Analog vs Digital output

• Safety handling