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Driving a Piezo speaker

Discussion in 'General Electronics Discussion' started by eldavid0000, Sep 24, 2011.

  1. eldavid0000

    eldavid0000

    3
    0
    Sep 24, 2011
    I have a waterproof piezo speaker from Murata (http://www.murata.com/products/catalog/pdf/p83e.pdf) that I would like to drive, however I have no experience in driving piezo type speakers. The resonance frequency is 1400 Hz, the capacitance is 09. microfarads, and the maximum sinusoidal voltage is 5V RMS. I plan to control it off of my Arduino One - should I just use the 5V supply from this? Is there any other information that I should use when attempting this? I've worked with piezoelectric actuators before, and they worked at much much higher voltages ...

    Thanks very much
     
  2. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Are you intending to drive it with sine or square? Yes, you can use the 5V. Try to Google 'driving piezo'. You mean 0.9μF, which is quite a lot, you'll need a good driver.
     
  3. eldavid0000

    eldavid0000

    3
    0
    Sep 24, 2011
    I'm planning to drive it using a square wave (probably using a 5V digital PWM signal off of my arduino microcontroller). The I/O pins provide 40mA current according to the spec sheet.

    I'm surprised that the speaker is rated for use at 5V (so small). I also wonder how the volume is controlled on a piezo, since the expansion or in this case bimorph bending is voltage dependent. I'd like to get it up to the max dB of ~90, so I need to figure out how much current the amp needs to provide.... if current is what dictates volume.
     
  4. Resqueline

    Resqueline

    2,848
    1
    Jul 31, 2009
    Note that capacitors (& piezo speakers) draws higher currents at higher frequencies. This one (0.9uF) has an impedance of only 8.84 ohms at 20kHz (sine). Driver needs to be lo-Z.
    The steep flanks of square waves causes very high currents to pass into the capacitance, so driving it with an unfiltered 44kHz PWM for example is not a good idea.
    If by PWM you just mean square waves inside the audio range you could use a dual CMOS driver, for example an ISL55111. It's good for 100mA continous, 3.5A peak current.
    The idea is to connect the speaker between two outputs being in anti-phase. The 55111 has one straight and one inverted channel. It may dissipate as much as 0.9W at 20kHz.
    You could also use a dual inverting driver, connecting them in series instead. This also creates a full-bridge driver. The CMOS drivers are only to be used with square waves.

    The high capacitance and small size of that speaker indicates the piezo element is very thin, thus the low voltage rating. Yes, current pretty much goes hand-in-hand with volume.
     

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