This is a basic Arduino Demo project for my Android app in Play Store. Bluetooth Switches: Arduino 26 Relay Controller The aim is to explain how to interact with the app

1. First Upload this Code to Arduino

   char ch;
   int LED_1 = 3;
   int LED_2 = 4;
   int LED_3 = 5;
   int LED_4 = 6;
   int LED_5 = 7;
   int LED_6 = 8;
   int LED_7 = 9;
   int LED_8 = 10;
   int LED_9 = 11;
   int LED_10 = 12;
   
   
   
   void setup() {
     // put your setup code here, to run once:
    Serial.begin(9600);
    pinMode(LED_1,OUTPUT);
    pinMode(LED_2,OUTPUT);
    pinMode(LED_3,OUTPUT);
    pinMode(LED_4,OUTPUT);
    pinMode(LED_5,OUTPUT);
    pinMode(LED_6,OUTPUT);
    pinMode(LED_7,OUTPUT);
    pinMode(LED_8,OUTPUT);
    pinMode(LED_9,OUTPUT);
    pinMode(LED_10,OUTPUT);
   
   }
   
   void loop() {
     // put your main code here, to run repeatedly:
   
   if(Serial.available()){
       ch = Serial.read();
       Serial.write(ch);
       doWork(ch);
     }
   }
   
   void doWork(char ch){
     switch(ch){
       case 'A': //code for switch 1 turned on
                 digitalWrite(LED_1,HIGH);
                 break;
       case 'a': //code for switch 1 turned off
                 digitalWrite(LED_1,LOW);
                 break;
       case 'B': //code for switch 2 turned on
                 digitalWrite(LED_2,HIGH);
                 break;
       case 'b': //code for switch 2 turned off
                 digitalWrite(LED_2,LOW);
                 break;
       case 'C': //code for switch 3 turned on
                 digitalWrite(LED_3,HIGH);
                 break;
       case 'c': //code for switch 3 turned off
                 digitalWrite(LED_3,LOW);
                 break;
       case 'D': //code for switch 4 turned on
                 digitalWrite(LED_4,HIGH);
                 break;
       case 'd': //code for switch 4 turned off
                 digitalWrite(LED_4,LOW);
                 break;      
       case 'E': //code for switch 5 turned on
                 digitalWrite(LED_5,HIGH);
                 break;
       case 'e': //code for switch 5 turned off
                 digitalWrite(LED_5,LOW);
                 break;
       case 'F': //code for switch 6 turned on
                 digitalWrite(LED_6,HIGH);
                 break;
      case 'f':  //code for switch 6 turned off
                 digitalWrite(LED_6,LOW);
                 break;
      case 'G':  //code for switch 7 turned on
                 digitalWrite(LED_7,HIGH);
                 break;
      case 'g':  //code for switch 7 turned off
                 digitalWrite(LED_7,LOW);
                 break;
      case 'H':  //code for switch 8 turned on
                 digitalWrite(LED_8,HIGH);
                 break;
      case 'h':  //code for switch 8 turned off
                 digitalWrite(LED_8,LOW);
                 break;
      case 'I':  //code for switch 9 turned on
                 digitalWrite(LED_9,HIGH);
                 break;
       case 'i': //code for switch 9 turned off
                 digitalWrite(LED_9,LOW);
                 break;
      case 'J':  //code for switch 10 turned on
                 digitalWrite(LED_10,HIGH);
                 break;
      case 'j':  //code for switch 10 turned off
                 digitalWrite(LED_10,LOW);
                 break;
      // Similarly for others
     }
   }

2. Then make the circuit as shown here

   

   Don't connect HC 05 when you are uploading code to Arduino as you may get errors

3. Pair the module with your phone

   The pairing code will be 1234 or 0000

4. Download and Use the App

   Play Store Link