ESP32 - Gas Sensor Relay

In this tutorial, We will explore the utilization of the ESP32 along with a gas sensor and relay to trigger the activation of a fan or siren upon detecting various potentially hazardous gases such as LPG, smoke, alcohol, propane, hydrogen, methane, carbon monoxide, and other flammable substances.

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×USB Cable Type-C
1×MQ2 Gas Sensor
1×Jumper Wires
1×(Optional) 12V Cooling Fan
1×(Optional) 12V Alarm Siren Horn
1×(Optional) 12V Power Adapter
1×(Optional) DC Power Jack
1×(Recommended) ESP32 Screw Terminal Adapter

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
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Introduction to Relay and MQ2 Gas Sensor

Unfamiliar with relay and MQ2 Gas Sensor, including their pinouts, functionality, and programming? Explore comprehensive tutorials on these topics below:

Wiring Diagram

ESP32 MQ2 Gas Sensor Relay Wiring Diagram

This image is created using Fritzing. Click to enlarge image

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

ESP32 Code

/* * This ESP32 code is created by * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit */ #define DO_PIN 14 // The ESP32 pin GPIO14 connected to DO pin of the MQ2 sensor #define RELAY_PIN 18 // The ESP32 pin GPIO18 connected to relay void setup() { // initialize serial communication Serial.begin(9600); // initialize the ESP32's pin as an input pinMode(DO_PIN, INPUT); pinMode(RELAY_PIN, OUTPUT); Serial.println("Warming up the MQ2 sensor"); delay(20000); // wait for the MQ2 to warm up } void loop() { int gasState = digitalRead(DO_PIN); if (gasState == HIGH) { Serial.println("The gas is NOT present"); digitalWrite(RELAY_PIN, LOW); // turn off } else { Serial.println("The gas is present"); digitalWrite(RELAY_PIN, HIGH); // turn on } }

Quick Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Do the wiring as above image.
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
  • Connect ESP32 to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to ESP32
Arduino IDE Upload Code
  • Move your hand in front of sensor
  • See the change of relay's state

Code Explanation

Read the line-by-line explanation in comment lines of source code!

Video Tutorial

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