Buzzers and tone()

Learning Goals 5 min

By the end of this lesson you will be able to:

1. Wire a piezo buzzer to digital pin D8 and GND on the breadboard — your first component that needs no current-limiting resistor.
2. Use tone(pin, frequencyHz, durationMs) to make the buzzer play a single note for a given length of time, and noTone(pin) to silence it on demand.
3. Pick a frequency in hertz and predict whether the note will sound higher or lower than the previous one — and explain the rule in one sentence.

Warm-Up 10 min

For thirteen lessons everything you've built has communicated through light — onboard LED, external LEDs, three LEDs in a row. Today your circuit gets a voice.

Quick-fire puzzle

Wei Jie names three everyday beeps:

• the high-pitched "tweet" of a smoke alarm
• the cheerful "ding" of a microwave timer
• the low "thunk" of a refrigerator door warning

1. What is physically moving inside each of these devices to make the air carry the sound to your ear?
2. Why does the smoke alarm sound higher than the fridge warning? What is the physical difference between the two sounds?
3. If you could control how fast that physical thing moves, what would you have control over?

New Concept 20 min

The big idea — make a pin flip on and off fast enough to be heard

From L01-08 you know that digitalWrite can set a pin to HIGH or LOW. Now imagine doing that 440 times per second — every 2.27 ms the pin flips. Connect that pin to a piezo crystal and the crystal flexes back and forth 440 times per second. Air gets pushed 440 times per second. Your ear hears musical A — the same note an orchestra tunes to.

Doing this by hand with digitalWrite and tiny delays is painful. Arduino gives you one built-in function that does the flipping for you — tone().

The piezo buzzer

The piezo buzzer in your kit is a small black disc with two legs sticking out the bottom. It has:

• Two pins, like an LED — one for the signal, one for GND.
• No required polarity for most small piezos in starter kits — they work either way round. (Larger industrial ones have a + mark; respect it if present.)
• No current-limiting resistor needed. Piezos are "capacitive" — they barely draw any current at all. Wire them directly to the pin.

Frequency and pitch

• Frequency is the number of times something repeats per second. Measured in hertz (Hz).
• 1 Hz = once per second (like a slow heartbeat).
• 1 000 Hz (1 kHz) = a thousand times per second (an alarm clock).
• Human hearing covers about 20 Hz to 20 000 Hz. Below or above that range and you can't hear it at all.
• Higher frequency = higher pitch. 1000 Hz is shrill; 200 Hz is a low rumble.

A handful of musical-note frequencies

Musical notes have standard frequencies you can call by name. The most useful for today:

The new functions

Important: tone() is non-blocking

tone(8, 440, 500) starts the tone and immediately returns. The chip plays in the background and silences itself 500 ms later. If you want your sketch to wait while the note plays, you must follow up with a delay().

tone(8, 440, 500);  // Start A4 for 500 ms. Returns immediately.
delay(500);          // Wait 500 ms so the note finishes playing.

Today's wiring — just the buzzer, no LEDs

To keep today's focus on the new component, we temporarily unplug the three LEDs from L01-10. Just the piezo buzzer on pin 8.

Why it matters

Once you can make sound, your circuits can communicate: alarms, alerts, melodies, error tones. Every doorbell, microwave, oven timer, smoke alarm, mobile phone notification — they all go back to a pin and a tone() call.

Worked Example 20 min

Goal: build the buzzer circuit, then write a sketch that beeps musical A (440 Hz) once a second.

The wiring

The same circuit as a schematic

Take a moment to read the abstract view of what you just built. Only two component-like symbols sit between D8 at the top and GND at the bottom — and one of them is the piezo itself, drawn as the standard "speaker trapezoid".

The sketch

const int BUZZER_PIN = 8;

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  tone(BUZZER_PIN, 440, 500);
  delay(1000);
}

Expected behaviour

• Beep at musical A (440 Hz) for half a second.
• Silence for half a second.
• Repeat forever.

If the buzzer is completely silent, check that one of its legs is at B12 (signal column) and the other at B13 (GND column). On small piezos polarity rarely matters, but a leg in the wrong column means no circuit.

Why is delay(1000) after a tone(…, …, 500)?

The third argument tells the chip when to stop the tone, but it does not pause the sketch. If we wrote tone(BUZZER_PIN, 440, 500); tone(BUZZER_PIN, 880, 500); with nothing in between, the second call would immediately overwrite the first and we'd never hear the A. The delay after each tone is what makes the sketch wait for the note to finish.

Try It Yourself 20 min

Three small mutations. For each one, predict on paper whether the note will sound higher or lower than the worked example, then upload to check.

const int BUZZER_PIN = 8;

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  tone(BUZZER_PIN, 523, 500);
  delay(1000);
}

const int BUZZER_PIN = 8;

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  tone(BUZZER_PIN, 100,  200);  delay(220);
  tone(BUZZER_PIN, 800,  200);  delay(220);
  tone(BUZZER_PIN, 2000, 200);  delay(220);
  delay(500);
}

const int BUZZER_PIN = 8;
const int NOTE_C4 = 262;
const int NOTE_D4 = 294;
const int NOTE_E4 = 330;

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  tone(BUZZER_PIN, NOTE_C4, 300);  delay(350);
  tone(BUZZER_PIN, NOTE_D4, 300);  delay(350);
  tone(BUZZER_PIN, NOTE_E4, 300);  delay(350);
  delay(1000);
}

Mini-Challenge 15 min

Play the opening of "Twinkle Twinkle Little Star"

Use the named-note approach from the 🔴 stretch task and a beep() helper from L01-12 to play the recognisable first phrase: do do so so la la so — that's C C G G A A G in note-name form. The last G is held twice as long as the rest.

Your task:

1. At the top of the sketch, declare named constants for NOTE_C4, NOTE_G4 and NOTE_A4 with their frequencies.
2. Write a beep(frequencyHz, durationMs) helper that calls tone() with the right pin, waits the duration, then waits a tiny extra gap (50 ms) so neighbouring notes don't blur together.
3. In loop(), call beep() seven times to play the phrase, with the last note twice the length of the first six.
4. End the loop with a 1-second pause before the phrase repeats.

It works if:

• A classmate can recognise the tune from the first three notes.
• Each note sits cleanly on its own — no slurring into the next one.
• Your loop() body uses only beep() and delay(). No raw tone() or noTone() calls.

const int BUZZER_PIN = 8;
const int NOTE_C4 = 262;
const int NOTE_G4 = 392;
const int NOTE_A4 = 440;

void beep(int frequencyHz, int durationMs) {
  tone(BUZZER_PIN, frequencyHz, durationMs);
  delay(durationMs + 50);
}

void setup() {
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop() {
  beep(NOTE_C4, 300);
  beep(NOTE_C4, 300);
  beep(NOTE_G4, 300);
  beep(NOTE_G4, 300);
  beep(NOTE_A4, 300);
  beep(NOTE_A4, 300);
  beep(NOTE_G4, 600);
  delay(1000);
}

Recap 5 min

A piezo buzzer turns electrical pulses into vibration, and vibration into sound. tone(pin, frequencyHz, durationMs) tells the Arduino to flip a pin on and off at a given frequency for a given length of time. Higher frequency = higher pitch. noTone(pin) stops a tone that's still playing. The hardware does the fast-flipping; you only write the music.

Piezo buzzer

A small disc-shaped component containing a piezoelectric crystal. The crystal flexes when voltage is applied; pulsing the voltage rapidly makes it vibrate audibly. Two pins; no current-limiting resistor needed.

Frequency

How many times a signal repeats per second. Measured in hertz (Hz). 1000 Hz = a thousand times per second.

Pitch

How high or low a sound is, as perceived by the ear. Higher frequency = higher pitch.

tone(pin, frequencyHz, durationMs)

Play a square-wave tone at frequencyHz on pin for durationMs milliseconds. Non-blocking — pair it with a delay() if you want the sketch to wait.

noTone(pin)

Stop any tone currently playing on the pin.

Hertz (Hz)

The unit of frequency — once per second. Named after Heinrich Hertz, the physicist who proved electromagnetic waves exist.

Homework 5 min

Build a doorbell. Write a sketch that plays a classic two-note doorbell sound — "ding-dong" — once every 4 seconds. The "ding" is higher than the "dong".

1. Pick two frequencies. A common doorbell uses about E5 (659 Hz) for the ding and C5 (523 Hz) for the dong. Or pick your own.
2. Give each frequency a named constant at the top of the sketch.
3. Write a beep() helper like the one from class.
4. In loop(), beep the ding (≈ 400 ms), beep the dong (≈ 600 ms), then delay(4000) before the next ring.

Also: a reflection question on paper.

• Look at your kit's piezo. Now look at the speaker on a phone or laptop. Both make sound. What is the same about how they work, and what is different? (Hint: think about size, range of frequencies, and what each is good at.) ____

Bring back next class:

• The saved .ino file (call it doorbell).
• A short phone video (10–15 seconds) with the audio on so we can hear the ding-dong.
• Your reflection answer on a notebook page.

Heads up for next class: in L01-15 "Musical Doorbell" we re-plug the three LEDs from L01-10 alongside today's buzzer, add a push button, and combine all of it into a project that flashes lights and plays a tune when someone presses the button. Keep your kit handy.