Piezo element (passive)
A passive piezo disc: the other half of the buzzer pair, with no oscillator built in. It sings whatever frequency you drive it at.
Where the active buzzer makes its one note off plain DC, a
passive piezo does nothing at all with a steady voltage. It needs a square wave, the
way tone() produces one, and a 440 Hz drive gives an A.
Pins
| Pin | What it does |
|---|---|
1 |
One leg. |
2 |
The other leg. |
Properties
None.
What the model gets right
The part watches the voltage across its two legs and times the transitions, with hysteresis so a slow edge or a noisy net cannot count twice; the gap between one rise and the next is the note's period, and the probe reports its frequency in hertz. Driven differentially, as an H-bridge would, it reads the same way, because what it is watching is the difference between the legs. Silence for long enough reads back as 0 Hz.
What it does not model
No capacitance (a real element is roughly 10 nF and loads the pin driving it; this one is high impedance on both legs) and no loudness. The probe is a frequency, not a volume.
It is a frequency counter rather than an acoustic model. The hysteresis is 1.0 V to go one way and 0.4 V to come back, which are round numbers rather than a real element's thresholds, and they are absolute volts: a 3.3 V board's square wave crosses them and a 200 mV signal never does, however loud a real disc would be. Anything faster than 40 kHz is rejected as noise rather than reported, and 60 ms with no edge reads as silence, so a note shorter than that never gets a frequency at all. There is no resonance (a real disc is loudest near 4 kHz and nearly silent an octave away), no mechanical ring-down, no harmonics and no waveform: a sine and a square at the same rate read identically.
Common mistakes
Wiring it expecting a buzzer's plain-DC behavior. A passive piezo stays silent on
a steady voltage no matter how it is polarized; it needs a driven square wave from
tone() or an oscillator.
See it in action
Metronome, Reaction timer and Morse sender all drive a passive piezo with
tone(). Open them at /templates.