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Relay Module

An electrically controlled mechanical switch that allows an Arduino to safely control high-power loads like motors and lights.

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5V Relay

The relay module acts as an electrically controlled switch. It contains a coil that, when energized, magnetically pulls a switch contact. This completely isolates the low-power Arduino circuitry from the high-power load circuit.

ActuatorsSwitchIsolation

Overview

A relay has two sides:

• Low Power Side (Input): Connected to the Arduino. It takes a small 5V logic signal to energize the coil.
• High Power Side (Output): Connected to the load (e.g., a lamp or motor). It acts as a mechanical switch capable of handling high voltage/current (like 250VAC at 10A).

By default, many relay modules are Active LOW, meaning the relay energizes (turns ON) when the IN pin is pulled to GND (LOW).

Pin Reference

Pin	Type	Description
VCC	power	Relay coil power. Connect to 5V.
GND	power	Ground. Connect to Arduino GND.
IN	digital	Control signal. Connect to Arduino digital pin.
NC	passive	Normally Closed. Connected to COM when relay is OFF.
COM	passive	Common terminal. Power source for the load connects here.
NO	passive	Normally Open. Connected to COM when relay is ON.

Configurable Attributes

Attribute	Type	Default	Description
triggerLevel	string	"low"	Set to "low" for Active-LOW, or "high" for Active-HIGH trigger.
state	string	"off"	Initial simulated mechanical state ("off" or "on").

Wiring Diagram

Connect the Relay Module to the Arduino to control high-power loads safely.

Example Arduino Code

This code assumes an Active-LOW relay module.

const int relayPin = 7;

void setup() {
  pinMode(relayPin, OUTPUT);
  // Active LOW: HIGH = relay OFF (safe default on startup)
  digitalWrite(relayPin, HIGH);
}

void loop() {
  // Turn Relay ON
  digitalWrite(relayPin, LOW);
  delay(2000);
  
  // Turn Relay OFF
  digitalWrite(relayPin, HIGH);
  delay(2000);
}

Simulation Notes

• In OpenHW Studio, right-click the relay during simulation to toggle between Active LOW and Active HIGH trigger modes dynamically.

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