🫁 Build Your Own Breath Monitoring System Using ESP32 and MQ Sensors

📅 By Dinesh | LearnWithDTrend Blog | 2026

🚀 Introduction

Have you ever wanted to build a simple breath monitoring system that can read gas changes from your breath and show the values on an OLED display?

In this project, I built a compact breath monitoring setup using:

• ✅ ESP32 microcontroller

• ✅ MQ3, MQ135, MQ9, and MQ2 sensors

• ✅ 128x64 OLED display

• ✅ I2C communication

• ✅ Real-time sensor reading on serial monitor and display

This project is useful for learning how gas sensors respond to breath-related changes and how sensor data can be displayed in real time.

Let’s dive in.

---

🧠 Project Concept

Here’s how the system works:

1. The ESP32 reads values from four MQ sensors.

2. Each sensor detects a different gas or air-quality pattern.

3. The data is printed on the serial monitor.

4. The same values are shown on the OLED display.

5. The system refreshes every 2 seconds for live monitoring.

This makes the project simple, interactive, and easy to demonstrate in a lab or project expo.

---

🧰 Components Used

Component	Quantity
ESP32 DevKit	1
MQ3 Sensor	1
MQ135 Sensor	1
MQ9 Sensor	1
MQ2 Sensor	1
OLED Display 128x64 (I2C)	1
Jumper Wires	As needed
Breadboard	1
USB Cable	1

---

🔌 Connections

ESP32 Pin Configuration

Component	ESP32 Pin
MQ3	GPIO 34
MQ135	GPIO 35
MQ9	GPIO 32
MQ2	GPIO 33
OLED SDA	GPIO 22
OLED SCL	GPIO 23
OLED VCC	3.3V or 5V depending on module
OLED GND	GND

Important Notes

• Use a common ground for all modules.

• The OLED in this code uses I2C address 0x3C.

• ESP32 analog pins are used for MQ sensor readings.

• MQ sensors need proper warm-up time for stable readings.

---

📟 ESP32 Code

The ESP32 reads the MQ sensor values and displays them on the OLED screen.

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

Adafruit_SSD1306 display(128, 64, &Wire, -1);

// MQ Sensor Pins
#define MQ3_PIN 34
#define MQ135_PIN 35
#define MQ9_PIN 32
#define MQ2_PIN 33

void setup() {

  Serial.begin(115200);

  Wire.begin(22,23); // SDA, SCL     

  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED not detected");
    while(true);
  }

  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);

  display.setCursor(10,20);
  display.println("Breath Analysis");
  display.setCursor(25,35);
  display.println("System Start");

  display.display();
  delay(2000);
}

void loop() {

  int mq3 = analogRead(MQ3_PIN);
  int mq135 = analogRead(MQ135_PIN);
  int mq9 = analogRead(MQ9_PIN);
  int mq2 = analogRead(MQ2_PIN);

  Serial.println("------ Sensor Readings ------");

  Serial.print("MQ3: ");
  Serial.println(mq3);

  Serial.print("MQ135: ");
  Serial.println(mq135);

  Serial.print("MQ9: ");
  Serial.println(mq9);

  Serial.print("MQ2: ");
  Serial.println(mq2);

  Serial.println("-----------------------------");

  display.clearDisplay();

  display.setCursor(0,0);
  display.println("Breath Analysis");

  display.setCursor(0,16);
  display.print("MQ3: ");
  display.println(mq3);

  display.setCursor(0,28);
  display.print("MQ135: ");
  display.println(mq135);

  display.setCursor(0,40);
  display.print("MQ9: ");
  display.println(mq9);

  display.setCursor(0,52);
  display.print("MQ2: ");
  display.println(mq2);

  display.display();

  delay(2000);
}

---

🧠 How the Code Works

1. Library Imports

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

These libraries are used to communicate with the OLED display.

• Wire.h helps with I2C communication

• Adafruit_GFX.h provides graphics functions

• Adafruit_SSD1306.h controls the OLED screen

---

2. OLED Display Setup

Adafruit_SSD1306 display(128, 64, &Wire, -1);

This creates the OLED object for a 128x64 display.

---

3. Sensor Pin Definitions

#define MQ3_PIN 34
#define MQ135_PIN 35
#define MQ9_PIN 32
#define MQ2_PIN 33

These lines assign analog input pins to each MQ sensor.

---

4. Setup Function

The setup() function runs only once when the ESP32 starts.

• Starts serial communication at 115200 baud

• Starts I2C on pins 22 and 23

• Checks whether the OLED is connected

• Shows a startup message on the screen

If the OLED is not detected, the code stops.

---

5. Loop Function

The loop() function runs continuously.

• Reads analog values from all four sensors

• Prints the values to the serial monitor

• Clears the OLED screen

• Displays all sensor readings on the OLED

• Waits 2 seconds before repeating

---

📊 Sensor Reading Logic

The MQ sensors output analog values depending on the gas concentration near the sensor.

Sensor	Purpose
MQ3	Alcohol / breath-related gas sensing
MQ135	Air quality / VOC sensing
MQ9	Carbon monoxide and combustible gas sensing
MQ2	Smoke and gas sensing

These values can change when someone exhales near the sensors.

---

🛠️ Build Process

First, I connected the MQ sensors to the ESP32 analog input pins and wired the OLED display using I2C.

Next, I uploaded the code and confirmed that the OLED started with the welcome message.

Then, I opened the serial monitor to verify that each sensor value was updating correctly.

Finally, I tested the system by breathing near the sensors and observed the changing values on both the display and the serial monitor.

---

🎮 Control / Display Features

• Real-time sensor value reading

• OLED display output

• Serial monitor output

• Simple breath-monitoring demonstration

• Easy ESP32-based hardware setup

---

📌 Important Notes

• MQ sensors need warm-up time before stable readings.

• The values are raw analog readings, not calibrated gas concentration.

• For a better project, calibration can be added later.

• Make sure the OLED I2C address matches your module.

---

🎉 Final Result

✅ Breath monitoring system built successfully
✅ ESP32 reading multiple MQ sensors
✅ OLED display showing live values
✅ Serial monitor output working
✅ Simple and effective sensor demonstration project

This project is a good example of combining gas sensors, ESP32, and OLED display in one useful embedded system.

---

❤️ Let’s Connect

This project is useful for learning:

• ESP32 programming

• Analog sensor reading

• OLED display interfacing

• I2C communication

• Real-time monitoring systems

You can use this as a blog post, mini project report, or project demonstration content for LearnWithDTrend.

LearnWithDTrend Blog Draft — ready for publishing