Active and Passive Buzzers

Two buzzers, near enough identical to look at, and they behave completely differently. Knowing which one is in your hand saves an afternoon.

An active buzzer has an oscillator built in. Give it 5 V and it makes its own noise — one fixed pitch, usually around 2 kHz. digitalWrite(HIGH) is all it needs. You cannot change the note, and that is the point: it is a component for alerting, not for music.

A passive buzzer has no oscillator. It is a piezo disc that flexes once each time the voltage changes. Hold it HIGH and you get a single faint click, then silence. To make a sound you must flip the pin thousands of times a second — and tone() does exactly that.

So the note comes from who is doing the flipping. The active buzzer flips itself. The passive one waits for you.

Telling them apart on the bench: turn them over. A passive buzzer shows its green circuit board underneath. An active one is sealed with a sticker or a black pad, is usually slightly taller, and often has a + marked on top — it cares which way round it goes.

Unplug the USB cable before you build. Both buzzers wire up the same way, so build it once and swap the component.

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Which buzzer is which?

	Active buzzer	Passive buzzer (piezo)
Oscillator inside	yes	no
digitalWrite(HIGH)	sings, one fixed pitch	one faint click
Needs tone()	no	yes
Can change pitch	no	yes
Polarised	usually, + marked	no
Underside	sealed with a sticker	green circuit board visible
Good for	alarms, alerts, reversing beeps	melodies, doorbells, games

→ Buzzers and tone() — how a piezo crystal actually makes a sound, and what a frequency is. → Musical Doorbell — a full build using tone() with an LED.

The note table

Frequencies are in hertz. Round numbers are fine — nobody will hear one hertz.

Note	Hz	Note	Hz	Note	Hz
C4	262	C5	523	C6	1047
D4	294	D5	587	D6	1175
E4	330	E5	659	E6	1319
F4	349	F5	698	F6	1397
G4	392	G5	784	G6	1568
A4	440	A5	880	A6	1760
B4	494	B5	988	B6	1976

The 4, 5 and 6 are octaves. Double the frequency and you get the same note one octave higher: A4 is 440, A5 is 880, A6 is 1760. C4 is middle C.

Happy Birthday.

Press button A and the passive buzzer plays the whole tune. The LED blinks on each note.

The melody, in order:

Bar	Notes
1	G4 G4 A4 G4 C5 B4
2	G4 G4 A4 G4 D5 C5
3	G4 G4 G5 E5 C5 B4 A4
4	F5 F5 E5 C5 D5 C5

As frequencies:

392, 392, 440, 392, 523, 494 392, 392, 440, 392, 587, 523 392, 392, 784, 659, 523, 494, 440 698, 698, 659, 523, 587, 523

Timing that sounds right: most notes 300 ms, but the last note of every bar 600 ms. Leave a 50 ms gap of noTone() between notes or the repeated G4s run together into one long note.

Think about it: that is 25 notes. Written as 25 tone() calls and 25 delay() calls, the sketch is 50 lines and changing the speed means editing 25 numbers. Two arrays — one of frequencies, one of lengths — and a for loop would play it in six. You are ready for arrays.

Topics you need for this one: → Arrays — two lists, one of frequencies and one of lengths. → The for Loop — walking both lists together, so 25 notes cost six lines rather than fifty. → if, else if and else — reading the button that starts the tune.