#define redled 5
#define yellowled 18
#define greenled 19

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  pinMode(redled, OUTPUT);
  pinMode(yellowled, OUTPUT);
  pinMode(greenled, OUTPUT);
}

void loop() {
  digitalWrite(redled, HIGH);
  digitalWrite(yellowled, LOW);
  digitalWrite(greenled, LOW);

  delay(2000); // this speeds up the simulation
  
  digitalWrite(redled, LOW);
  digitalWrite(yellowled, HIGH);
  digitalWrite(greenled, LOW);

  delay(2000); // this speeds up the simulation
  
  digitalWrite(redled, LOW);
  digitalWrite(yellowled, LOW);
  digitalWrite(greenled, HIGH);

  delay(2000); // this speeds up the simulation
}