Crosswalk on an Arduino Uno

// Crosswalk: a traffic light module, a button for walkers and a piezo that
// beeps while it is safe to cross.
//
//   pins 13, 12, 11  the module's R, Y and G (its resistors are on the board)
//   GND              the module's GND, to a ground symbol
//   pin 2            the button, to ground (INPUT_PULLUP: pressed reads LOW)
//   pin 8            the piezo; its other leg to ground
//
// The light runs on its own: green for the cars, yellow, then red while the
// walkers cross with the piezo beeping, faster at the end. A press of the
// button during the green cuts it short, so nobody waits the whole cycle.

const int RED_PIN = 13;
const int YELLOW_PIN = 12;
const int GREEN_PIN = 11;
const int BUTTON = 2;
const int PIEZO = 8;

const unsigned long GREEN_MS = 8000;
const unsigned long SHORT_GREEN_MS = 1500;
const unsigned long YELLOW_MS = 2000;
const int WALK_BEEPS = 16;
const int HURRY_BEEPS = 12;

void lights(bool red, bool yellow, bool green) {
  digitalWrite(RED_PIN, red ? HIGH : LOW);
  digitalWrite(YELLOW_PIN, yellow ? HIGH : LOW);
  digitalWrite(GREEN_PIN, green ? HIGH : LOW);
}

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: crosswalk");
  pinMode(RED_PIN, OUTPUT);
  pinMode(YELLOW_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BUTTON, INPUT_PULLUP);
  pinMode(PIEZO, OUTPUT);
}

// Green for the cars until the time is up, or a walker presses the button.
void green() {
  lights(false, false, true);
  Serial.println("cars: green");
  unsigned long start = millis();
  unsigned long limit = GREEN_MS;
  while (millis() - start < limit) {
    if (digitalRead(BUTTON) == LOW && limit == GREEN_MS) {
      Serial.println("button: walk soon");
      limit = millis() - start + SHORT_GREEN_MS;
    }
    delay(10);
  }
}

void loop() {
  green();
  lights(false, true, false);
  Serial.println("cars: yellow");
  delay(YELLOW_MS);

  lights(true, false, false);
  Serial.println("cars: red, walk");
  for (int i = 0; i < WALK_BEEPS; i++) {
    tone(PIEZO, 2000, 50);
    delay(250);
  }
  Serial.println("hurry");
  for (int i = 0; i < HURRY_BEEPS; i++) {
    tone(PIEZO, 2500, 30);
    delay(100);
  }
}