I'm exploring the inside of my favorite device, a Japanese electronic dictionary. It runs on AAA batteries and has two screens (one for writing and one for viewing), speakers/headphone jack, a USB connector and an SD card slot.

There's a peculiar component I can't identify. It looks like two plates of metal glued together with a lead from each plate. The simplicity of it makes me think it's a capacitor; however, I've never encountered a capacitor that looks like this, and the huge footprint seems like a waste for a simple capacitor.

Here's a picture of the side of the PCB with the unidentified component. The leads on the top left lead to a keyboard PCB and on the ones on the right lead to the screen. The unidentified component is below the two blobs.

PCB with unknown component

Here's a closeup of the component:

Closeup of unknown component

In case it helps (or is interesting!), here's the other side of the PCB:

Opposite side of PCB


1 Answer 1


That is a piezoelectric buzzer:

enter image description here

Photo from the linked Wikipedia article.

  • 4
    \$\begingroup\$ It's actually a piezoelectric "transducer" or "element". A buzzer contains an oscillator of some kind, so you apply a (typically DC) power supply and it emits a tone. An element (like this) converts applied voltage to mechanical movement, so needs to be driven with an AC signal to produce a noise. \$\endgroup\$
    – rolinger
    Sep 21, 2020 at 15:24
  • 1
    \$\begingroup\$ It may be worth noting that while often used as an emitter/sink for electrical current, it can also be a source, and (in the same way an electric motor is a generator) is interchangeably a pickup or emitter. Load cells are sometimes (often?) piezoelectric \$\endgroup\$ Sep 21, 2020 at 17:41
  • \$\begingroup\$ I guess that's what the "p" stands for on the soldering pads :) Thanks for the help. Can you tell me what might be the advantage of having a piezo buzzer in there? The device already has speakers and it can even play mp3 files. \$\endgroup\$
    – Nate Glenn
    Sep 21, 2020 at 20:03
  • 1
    \$\begingroup\$ @NateGlenn the device can issue a beep, using less power and faster than intialising the whole MP3 decoder, DAC, and amplifier, The buzzer also doesn't require external speakers to be on and with the volume level up. Also the buzzer could be quite piercing/attention-getting compared to the MP3 playback. Nothing says "WAKE UP NOW" like a sharp >BEEP-BEEP< compared to a song playing, which is quite ignorable (like my morning phone alarm) \$\endgroup\$
    – Criggie
    Sep 21, 2020 at 20:27

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