Bluetooth-Arduino module from BuildCircuit

BTmodule.ino

void setup() {
  // initialize serial communication:
  Serial.begin(38400);// this can be different for your Bluetooth module. It can be 9600 also.
  // initialize the LED pins:
  for (int thisPin = 2; thisPin < 13; thisPin++) {
    pinMode(thisPin, OUTPUT);
  }
}

void loop() {
  // read the sensor:
  if (Serial.available() > 0) {
    int inByte = Serial.read();
    // do something different depending on the character received.
    // The switch statement expects single number values for each case; in this
    // example, though, you're using single quotes to tell the controller to get
    // the ASCII value for the character. For example 'a' = 97, 'b' = 98,
    // and so forth:

    switch (inByte) {
      case '1':// when the app sends 1
        digitalWrite(2, HIGH);
        delay(1000);
        digitalWrite(2, LOW);
        break;
        
      case '2':// when the app sends 2
        digitalWrite(4, HIGH);
        delay(1000);
        digitalWrite(4, LOW);
        break;
        
      case '3':// when the app sends 3
        digitalWrite(6, HIGH);
        delay(1000);
        digitalWrite(6, LOW);
        break;
        
      case '4':// when the app sends 4
        digitalWrite(8, HIGH);
        delay(1000);
        digitalWrite(8, LOW);
        break;

        //likewise, you can find an app that can send digits from 1 to 12. 
      
      default:
        // turn all the LEDs off:
        for (int thisPin = 2; thisPin < 13; thisPin++) {
          digitalWrite(thisPin, LOW);
        }
    }
  }
}