Lit button on an Arduino Uno

// Lit button: a 30 mm arcade button with an LED inside. The lamp breathes
// while the button waits, goes full bright while it is held, and each press
// is counted.
//
//   button  2 -> pin 7, 1 -> GND        (the microswitch)
//           L+ -> pin 5, L- -> GND      (the lamp, a 5 V one)
//
// The two halves of the button are separate: pressing it does not light it.
// The switch is read with the pin's own pull-up, so a press reads LOW. The
// lamp has its resistor built into the holder, so a 5 V lamp goes straight
// on a pin; a red one draws about 19 mA, inside what a pin can give, and
// analogWrite() dims it with PWM.
//
// Things to try. Hold the button and let go. Then open the button's
// properties and change the color: a white or blue lamp drops more voltage
// than a red one, so on the same 5 V it is dimmer.

const int BUTTON_PIN = 7;
const int LAMP_PIN = 5;

bool wasDown = false;
unsigned long presses = 0;
unsigned long lastChange = 0;

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LAMP_PIN, OUTPUT);
  Serial.println("Lit button ready");
}

void loop() {
  bool down = digitalRead(BUTTON_PIN) == LOW;
  unsigned long now = millis();
  // A microswitch barely bounces, but 10 ms of patience costs nothing.
  if (down != wasDown && now - lastChange > 10) {
    wasDown = down;
    lastChange = now;
    if (down) {
      presses++;
      Serial.print("Press ");
      Serial.println(presses);
    }
  }
  if (wasDown) {
    analogWrite(LAMP_PIN, 255);
  } else {
    // A two second breath: up for a second, down for a second.
    int phase = (now / 4) % 500;
    int level = phase < 250 ? phase : 499 - phase;
    analogWrite(LAMP_PIN, level / 2 + 4);
  }
  delay(5);
}