Sleigh-bell doorbell on an Arduino Uno

// Sleigh-bell doorbell: press the doorbell and a servo shakes a strap of real
// sleigh bells while a speaker plays the chorus of Jingle Bells.
//
//   doorbell   pin 2 -> button -> GND   (INPUT_PULLUP, so pressed reads LOW)
//   speaker    pin 8 -> 100 ohms -> 8 ohm speaker -> GND
//   servo      PWM -> pin 9, VCC -> 5 V, GND -> GND
//              tie a short strap of sleigh bells to the horn
//
// The servo swings the bells one way on every note and back on the next, so
// they ring in time with the tune. Real bells sound better than any speaker,
// and the tune makes it obvious it is the doorbell and not a passing sleigh.
//
// The speaker is 8 ohms, which is nearly a short across a pin, so it goes
// through 100 ohms, as in the Arduino's own melody example. For a louder bell,
// drive the speaker from a small amplifier module instead.
//
// While it plays, more presses are ignored, and it rests for a moment after,
// so a visitor leaning on the button gets one chorus, not five.
//
// On the porch: an outdoor button and its wire can pick up noise, so keep the
// run short or add a 100 nF capacitor across the button. Give the servo its
// own 5 V supply with the grounds joined.
//
// Things to try. Press the doorbell. Change TEMPO_MS for a faster jingle.
// Write in the verse as a second tune and play it on every other press.

#include <Servo.h>

const int BUTTON_PIN = 2;
const int SPEAKER_PIN = 8;
const int BELLS_PIN = 9;
const int TEMPO_MS = 180;   // one beat

const int E5 = 659, F5 = 698, G5 = 784, C5 = 523, D5 = 587;

// "Jingle bells, jingle bells, jingle all the way..." as notes and beats.
const int TUNE[] = {E5, E5, E5, E5, E5, E5, E5, G5, C5, D5, E5,
                    F5, F5, F5, F5, F5, E5, E5, E5, E5, D5, D5, E5, D5, G5};
const uint8_t BEATS[] = {1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 4,
                         1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2};
const int NOTES = sizeof(TUNE) / sizeof(TUNE[0]);

Servo bells;
unsigned int rings = 0;

void jingle() {
  rings++;
  Serial.print("Ding dong, ring ");
  Serial.println(rings);
  bool left = true;
  for (int i = 0; i < NOTES; i++) {
    int ms = BEATS[i] * TEMPO_MS;
    tone(SPEAKER_PIN, TUNE[i], ms - 30);   // a short gap keeps repeated notes apart
    bells.write(left ? 60 : 120);          // shake the bells on every note
    left = !left;
    delay(ms);
  }
  noTone(SPEAKER_PIN);
  bells.write(90);
  Serial.println("Jingle done");
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  bells.attach(BELLS_PIN);
  bells.write(90);
  Serial.println("Sleigh-bell doorbell ready");
}

void loop() {
  if (digitalRead(BUTTON_PIN) == LOW) {
    jingle();
    delay(1500);   // rest, so one long press is one chorus
  }
}