const uint8_t pinGreen = 9;
const uint8_t pinRed = 12;



void setup() {
  Serial.begin(115200);
  Serial.println(F("Anti parallel LEDs"));
  Serial.print(F("L (linksom), "));
  Serial.print(F("R (rechtsom)"));
  Serial.println(F("S (stop)"));

  pinMode(pinGreen, OUTPUT);
  pinMode(pinRed, OUTPUT);
}

void loop() {
  if (Serial.available())
  {
    char ch = Serial.read();
    switch (ch)
    {
      case 'L':
      case 'l':
        digitalWrite(pinGreen, HIGH);
        digitalWrite(pinRed, LOW);
        break;
      case 'R':
      case 'r':
        digitalWrite(pinGreen, LOW);
        digitalWrite(pinRed, HIGH);
        break;
      case 'S':
      case 's':
        digitalWrite(pinGreen, LOW);
        digitalWrite(pinRed, LOW);
        break;
    }
  }
}