This tutorial explains how to use a low-trigger single-channel 5V relay module with Arduino. A relay allows you to control high-voltage or high-current devices using the low voltage logic of a microcontroller like the Arduino.

The tutorial walks through relay working principles, pinouts, wiring connections, and a demonstration using an actual electrical load. The provided code and wiring diagram are available below this article

🔍 What Is a Relay?

A relay is an electrically controlled switch. In this tutorial, we are working with a low-trigger relay, which activates when the signal pin receives 0V (LOW).

This module contains:

• A magnetic coil (controlled by Arduino)

• A switching mechanism (which connects or disconnects AC/DC loads)

• A transistor for driving the coil

• Three terminal screws: COM (common), NO (normally open), and NC (normally closed)

When the signal pin goes LOW, the coil is energized and the relay switches from its default state to its active state, allowing current to pass to the load.

⚙️ Wiring the Relay to Arduino

Connect the relay to the Arduino as follows:

• VCC → 5V

• GND → GND

• IN (Signal) → Digital pin (e.g., D2)

For the load:

• Connect one end of your light, fan, or device to the NO or NC terminal

• 
  

💻 Code Explanation – Low-Trigger Relay Control

This simple Arduino sketch toggles a low-trigger 5V relay module ON and OFF in 500ms intervals. A low-trigger relay is activated when the input pin receives a LOW signal (0V), and deactivated with a HIGH signal (5V).

1. Define Relay Pin

cppCopyEditint relayPin = 8; // define output pin for relay

• Pin D8 on the Arduino is designated as the output control for the relay module.

2. Setup Function

cppCopyEditvoid setup() {
  pinMode(relayPin, OUTPUT); // define pin 8 as output
}

• The pinMode() function configures relayPin as an output to allow the Arduino to control it.

3. Loop Function

cppCopyEditvoid loop() {
  digitalWrite(relayPin, LOW);  // turn the relay ON (active LOW)
  delay(500);                   // wait for 500 milliseconds
  digitalWrite(relayPin, HIGH); // turn the relay OFF
  delay(500);                   // wait for 500 milliseconds
}

• digitalWrite(relayPin, LOW): Sends a LOW signal to the relay, which activates it. This closes the internal switch, powering the connected device (lamp, motor, etc.).

• delay(500): Holds the relay in its current state for 500 milliseconds.

• digitalWrite(relayPin, HIGH): Sends a HIGH signal to the relay, deactivating it (switch opens).

• The loop continuously repeats this ON/OFF toggling every 1 second.

🔧 Note: If you're using a high-trigger relay, reverse the logic—use HIGH to turn ON and LOW to turn OFF.

This sketch is ideal for testing relays, blinking lamps, or triggering any AC/DC load in timed intervals.

🎬 Video Chapters

• 00:00 – Introduction

• 00:52 – Relay Hardware Explained

• 03:33 – Wiring Explained

• 04:42 – Code Explained

• 06:10 – Demonstration

📥 Download Section

You’ll find the Arduino code and wiring diagrams available for download below. This project is a building block for controlling home appliances or implementing safety shut-off mechanisms in DIY electronics.