void setup()
{
  pinMode(13, OUTPUT);
  Serial.begin(9600);
}
char a; // stores incoming character from other device
void loop()
{
  if (Serial.available())
  {
    a = (Serial.read());

    if (a == '1')
    {
      Serial.print("12345");
      digitalWrite(13, HIGH);
    }
    if (a == '2')
    {
      Serial.print("12345");
      digitalWrite(13, LOW);
    }
  }
}