int t = 100;   // one unit of time in milliseconds

void setup() {
  pinMode(13, OUTPUT);  // LED pin is OUTPUT
}

void dot() {
  //           LED on      pause                     LED off    pause
  digitalWrite(13, HIGH);  delay(1*t);  digitalWrite(13, LOW);  delay(1*t);
}

void dash() {
  digitalWrite(13, HIGH);  delay(3*t);  digitalWrite(13, LOW);  delay(1*t);
}

void letter() {
  // extra delay at end of letter
  delay(2*t); // plus one unit from end of dot/dash = 3 units
}

void word() {
  // extra delay at end of word
  delay(6*t); // plus one unit from end of dot/dash = 7 units
}

void loop() {
  dot();   dot();   dot();   letter();  // S
  dash();  dash();  dash();  letter();  // O
  dot();   dot();   dot();   word();    // S
}