Traffic lights with a crossing button on pin 8, on an Arduino Uno

// A pedestrian crossing: traffic lights on 3, 4 and 5, a button on 8.
//
//   pin 3 -> 220 ohm -> green LED -> GND
//   pin 4 -> 220 ohm -> yellow LED -> GND
//   pin 5 -> 220 ohm -> red LED -> GND
//   one side of the button -> 5V; the other -> pin 8, and 10k from pin 8 to GND
//
// The 10k pull-down holds pin 8 LOW while nobody presses, so the lights sit
// on green for the cars. A press joins pin 8 to 5 V, it reads HIGH, and the
// lights go yellow, then red for long enough to cross, then back to green.

const int GREEN = 3;
const int YELLOW = 4;
const int RED = 5;
const int BUTTON = 8;

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);
  pinMode(BUTTON, INPUT);
  lights(HIGH, LOW, LOW);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: green for the cars. Press the button on pin 8 to cross.");
}

void loop() {
  if (digitalRead(BUTTON) == HIGH) {
    Serial.println("button pressed: yellow, then red");
    lights(LOW, HIGH, LOW);
    delay(2000);
    lights(LOW, LOW, HIGH);
    Serial.println("red: walk");
    delay(5000);
    lights(HIGH, LOW, LOW);
    Serial.println("green for the cars again");
  }
}