Switches & motion
Buzzer & speaker
Turn an electrical signal into sound. A speaker moves a paper cone with a coil and a magnet; a piezo buzzer bends a ceramic disc. Either way, the frequency of the signal sets the pitch.
Pins
- Speaker
- : Two terminals, polarity matters only for keeping several speakers in step.
- Buzzer +
- : The longer leg or the one marked +. "Active" buzzers make their own tone from DC; "passive" ones need a square wave.
Piezo buzzers are flat black discs; small speakers are 8 Ω cones from 20 mm upwards.
What to look for inside
- An AC signal drives the speaker coil.
- Current in the coil makes it an electromagnet. It is pushed out and pulled back against the fixed magnet as the current reverses.
- The cone is glued to the coil, so it pushes the air in and out, sending pressure waves (sound) outward. Faster swings mean a higher pitch.
The numbers that matter
| Spec | Typical |
|---|---|
Impedance (speaker) Far too low for a GPIO pin: it needs an amplifier. | 4 Ω · 8 Ω |
Rated power More makes it louder until it distorts or burns. | 0.25 W to 3 W (small) |
Resonant frequency (piezo) Piezos are loudest at their resonance. | 2 kHz to 4 kHz |
Active / passive (buzzer) Active: apply DC and it beeps. Passive: drive it with PWM to choose the note. | — |
Where you’ll use it
- Beeps, alarms and simple tunes (PWM from a microcontroller).
- Audio output through an amplifier.
Common mistakes
- Connecting a speaker straight to a pin. 8 Ω draws far too much current.
- Giving a passive buzzer DC and wondering why it only clicks once.
Lessons that use it
Lesson 4.3’s PWM mode makes exactly the kind of square wave that drives a passive buzzer.
Go deeper
For a passive buzzer, the PWM frequency is the pitch you hear (duty ≈ 50 %).