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Turn ON OFF LEDs using Arduino and GSM Module


This article will help us to understand to turn ON/OFF LEDs using ARDUINO based on messages received by GSM Module. Before starting this, reader should have basic understanding about serial interface and its communication between GSM Module and ARDUINO.

Required Components:

  2. 8 to 10 Jumper Male and Female Pins
  3. Bread Board
  4. GSM Module and Working SIM to receive messages
  5. LED Light

Interface between Components:

In this project, GSM Module sends messages to ARDUINO which will TURN ON/OFF LED based incoming messages.

Instead of LEDs (5V), we can control AC appliances using relay connecting with ARDUINO (but Extra care should be taken when dealing with 240V, please don't attempt if you are not confident). I will do share a separate article on this.

Message Format:

I have used below format to Turn ON/OFF LEDs.

1.    @Light On#

2.    @Light Off#

Circuit Design: (using LEDs)

Arduino and GSM Module

ARDUINO Source Code:

Given below the code to Turn ON/OFF LEDs. Copy and Paste it in ARDUINO Code explorer and burn the code in ARDUINO by selecting required COM Port. Then Send Message from Sender Mobile as mentioned above.

String inputString = "";         // a string to hold incoming data

boolean stringComplete = false;  // whether the string is complete

String incomingString ="";

int startIndex = 0;

int endIndex = 0;

int led1 = 4;

void setup() {

  // initialize serial:


   // prepare the digital output pins

   pinMode(led1, OUTPUT);

   // initially all are off

   digitalWrite(led1, LOW);


  // reserve 200 bytes for the inputString:


  //--Start: Send SMS --



  //Serial.print("AT+CMGD=1,4\r");  // Deletes all SMS saved in SIM memory


  Serial.println("DEL ALL\"");



  Serial.print("AT+CMGS=\"+91XXXXXXXXXX\"\r");    //Number to which you want to send the sms


  Serial.print("Test SMS - It Started Working1..\r");   //The text of the message to be sent






  //--End: SMS--


void loop() {

  // print the string when a newline arrives:

  if (stringComplete && inputString!="") {



    if(inputString=="@light on#")


      digitalWrite(led1, HIGH); 


    else if(inputString=="@light off#")


      digitalWrite(led1, LOW); 



   Serial.println("DEL ALL\""); // To Delete Messages from SIM Memory


  // clear the string:

   inputString = "";

   stringComplete = false;



void serialEvent() 


   if(stringComplete == false)


        incomingString = Serial.readString();



          startIndex = incomingString.indexOf("@");

          endIndex = incomingString.indexOf("#");

          if(startIndex>0 && endIndex>0)


             inputString = incomingString.substring(startIndex,endIndex+1);

             stringComplete = true;




That’s all, Follow the steps to Turn ON/OFF LEDs.

1.    Burn the ARDUINO code into ARDUINO.

2.    Make sure you have connected GSM Module and ARDUINO along with LED.

3.    Make sure the SIM present in GSM Module is working.

4.    Send Message from your mobile.

By replacing LEDs, we can use Relays to connect to turn ON/OFF electrical house appliances (Extra care should be taken when dealing with 240V, please don't attempt if you are not confident). I will do share a separate article on this.

Hope this article gave an idea on how to work with arduino and GSM Module. Thanks for reading this article.
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Raj Kumar
Total Posts 24
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Work like charm!! Thanks.
the above code is not working to on led and off by recieving sms from gsm module 900
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