How to use a 5V Relay with Arduino

INTRODUCTION

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switch mechanically, but other operating principles are also used, such as solid-state relays.

 

APPLICATIONS

Relays are used where it is necessary to control a circuit by a separate low-power signal, or where several circuits must be controlled by one signal. Relays are also used on high voltage circuits.

 

WIRING DIAGRAM

VCC –  5V

GND – GND

OUT – Digital Pin 2

 

 

 

CODE

 

const int relayPin = 2; //the base of the transistor is attached to

String comdata = "";

int lastLength = 0;


void setup()
{

  pinMode(relayPin, OUTPUT);  //initialize the LED as output
  Serial.begin(9600);  // start serial port at 9600 bps:
  while (! Serial);

  Serial.println("Please input your command to control this Lamp:");  //print message on serial monitor
}

void loop()
{

 //read string from serial monitor
  if(Serial.available()>0)    // check if data has been sent from the computer
  {  
    comdata = "";

    while (Serial.available() > 0)  
    {        
      comdata += char(Serial.read());
      delay(2);
    }

    Serial.println(comdata);
  }

    if(comdata == "on")
    {
      digitalWrite(relayPin, HIGH);//turn the lamp on
    }

    else if(comdata == "off")
    {
      digitalWrite(relayPin, LOW);//turn the lamp off
    } 

    else
    {
    Serial.println("Please input correct command !");
      delay (20000);
    }
}

END RESULT

Open the serial monitor. Type “on” to turn ON the lamp, and type “off” to turn OFF the lamp.

ADDITIONAL RESOURCES

https://www.circuitbasics.com/setting-up-a-5v-relay-on-the-arduino/

https://www.hobbyist.co.nz/?q=interfacing-relay-modules-to-arduino