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Piezo buzzer drivin' — Parallax Forums

Piezo buzzer drivin'

Wuerfel_21Wuerfel_21 Posts: 5,052
in Propeller 2

Just thought that it would be really funny to play some obnoxiously tinny audio out of one of these motherboard piezo buzzers. They conveniently fit right onto a normal pin header...

It does infact work, but even if I drive it differential across two DAC pins (124R_3V vs 75R_2V seems to make no major difference), it's kind of disappointingly quiet.

How do PC motherboards drive these to make them obnoxiously loud? Might be using that 12V juice...

Comments

  • JonnyMacJonnyMac Posts: 9,102

    For a laser tag accessory, I use an N-FET to drive it with the other side connected directly to the battery (~7v). I don't know about PC motherboards.

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2022-07-16 22:09

    Here are a couple things you can do to increase loudness:

    1. Add a series inductor to your piezo circuit. This will increase the drive voltage to the device.

    2. Create a resonance chamber around the piezo device. This will allow standing waves within the chamber to build up and enhance the transfer of energy to the air. I used this technique with the Parallax SoundPAL. The resonator was made of shrink tubing:

    image

    -Phil

  • Wuerfel_21Wuerfel_21 Posts: 5,052

    @JonnyMac said:
    For a laser tag accessory, I use an N-FET to drive it with the other side connected directly to the battery (~7v). I don't know about PC motherboards.

    That works? I thought these are capacitor-like devices (which would need to be driven back up?)

  • JonnyMacJonnyMac Posts: 9,102
    edited 2022-07-16 22:44

    I checked with the piezo vendor and they said it was okay to drive single-ended with a square wave. Ultimately, though, we went with a model with an internal driver that simply needs on-off control. We don't need to control frequency, we just need the box to beep.

  • Wuerfel_21Wuerfel_21 Posts: 5,052

    Huh. Only have FETs laying around though, which IIRC aren't terribly great at amplifying analog signals. Oh well.

  • Wuerfel_21Wuerfel_21 Posts: 5,052
    edited 2022-07-16 22:51

    ...

    I did however figure out that raising the amplitudes being output by a factor of 6 doesn't really cause major distortion. Maybe I just can't hear how distorted it is through the tiny buzzer, but that gets it up to usable volume levels, though still rather quiet.

  • roglohrogloh Posts: 5,786
    edited 2022-07-17 00:53

    @Wuerfel_21 said:
    I did however figure out that raising the amplitudes being output by a factor of 6 doesn't really cause major distortion. Maybe I just can't hear how distorted it is through the tiny buzzer, but that gets it up to usable volume levels, though still rather quiet.

    If you sweep slowly through the frequency range you might find some spots where it resonates loudly. I had some that liked around 2kHz (and became piercingly loud).

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514

    BTW, when I designed the SoundPAL, I did not use a piezo transducer but, rather, a miniature magnetic speaker. It was driven from an nMOSFET. With the resonator attached, it was quite loud.

    -Phil

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