const int ledpin = LED_BUILTIN; 
const int dot_duration = 300;
String sequence = "LSSSP";
unsigned int sequence_pos = 0;

void setup() {
  pinMode(ledpin, OUTPUT);
}

void loop() {
  if (sequence[sequence_pos] == 'S') {
    digitalWrite(ledpin, HIGH);
    delay(dot_duration);
    digitalWrite(ledpin, LOW);
    delay(dot_duration);
  }
  else if (sequence[sequence_pos] == 'L') {
    digitalWrite(ledpin, HIGH);
    delay(3*dot_duration);
    digitalWrite(ledpin, LOW);
    delay(dot_duration);
  }
  else if (sequence[sequence_pos] == 'P') {
    digitalWrite(ledpin, LOW);
    delay(3*dot_duration);
  }

  sequence_pos++;
  if (sequence_pos > sequence.length()) {
    sequence_pos = 0;
  }

}