Traffic lights on pins 3, 4 and 5, on an Arduino Uno

// Traffic lights: green, yellow and red on pins 3, 4 and 5.
//
//   pin 3 -> 220 ohm -> green LED -> GND
//   pin 4 -> 220 ohm -> yellow LED -> GND
//   pin 5 -> 220 ohm -> red LED -> GND
//
// One function sets all three lights at once, so each step of the cycle is
// one line: which lamps are on, and for how long.

const int GREEN = 3;
const int YELLOW = 4;
const int RED = 5;

void lights(int green, int yellow, int red) {
  digitalWrite(GREEN, green);
  digitalWrite(YELLOW, yellow);
  digitalWrite(RED, red);
}

void setup() {
  pinMode(GREEN, OUTPUT);
  pinMode(YELLOW, OUTPUT);
  pinMode(RED, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: traffic lights on pins 3, 4 and 5");
}

void loop() {
  Serial.println("green");
  lights(HIGH, LOW, LOW);
  delay(5000);
  Serial.println("yellow");
  lights(LOW, HIGH, LOW);
  delay(2000);
  Serial.println("red");
  lights(LOW, LOW, HIGH);
  delay(5000);
}