Arduino hardware serial interconnection example

hardware_serial_ino.ino

enum { LED_PIN = 13 };

void setup()
{
  pinMode(LED_PIN, OUTPUT);  
  Serial.begin(9600);
}

void loop()
{  
  if (Serial.available()) //New data arrived
  {
    char command = Serial.read();
    
    switch (command)
    {
      case '1':
        Serial.println("Hello"); 
        break;
      case '2': 
        for (int i = 1; i < 5; ++i)
        {
          digitalWrite(LED_PIN, HIGH);
          delay(50);
          digitalWrite(LED_PIN, LOW);
          delay(50);          
        }
        break;
      
      default:
        Serial.println('?');  //Not recognized commands
    }
  }  
}