/*
  Modified Blink Program
  Sends out the SOS distress signal in Morse code. This distress signal is 
  originally established for maritime use but is now used internationally. 
  In the language of Morse code, the letter “S” is three short dots and 
  the letter “O” is three longer dashes. 
  This program will blink a LED ON rapidly for 3 times then slowly for 3 times repeatedly.
  modified 21 March 2020
  by Ting Kok Eng
*/
int LED = 4;
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED, OUTPUT);
}

// the loop function runs over and over again forever
void loop() {
  /* The code below produced Long Blink for the morse code letter "O" */
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for a half second
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for a second
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);               // wait for a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for a half second

/* The code below produced Short Blink for the morse code letter "S" */
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(400);                // wait for half a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for half a second
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(400);                // wait for half a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for half a second
  digitalWrite(LED, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(400);                // wait for half a second
  digitalWrite(LED, LOW);    // turn the LED off by making the voltage LOW
  delay(200);                // wait for half a second
}