#define LED RED_LED //For connection to on-board RED LED 
const int ledPin = 11; //For connection to externally wired LED on Pin 11
char ch;

void setup(){  
    
  Serial1.begin(9600); //This is to initialize Serial port 1. 
                      // Multiple serial ports (2 to be precise) are used in this setup. Serial monitor open on Serial port 0 and RX, TX serial communication open on Serial port 1.  
  } 

  
  void loop(){  
    digitalWrite(ledPin, HIGH);
    Serial1.write('H');  
    delay(800);
   Serial1.write('L');
   delay(800);  

}