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Total newbie question:

Discussion in 'Electronic Basics' started by Blarg, May 26, 2004.

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  1. Blarg

    Blarg Guest

    How do I get a piezo-electric buzzer to make an audible sound? I've heard
    that I need an IC circuit to
    'drive' the buzzer, but I can't seem to find out what an IC driver circuit
    consists of.

    I'm trying to make a super compact circuit that will make a sound at low
    (1.5-3.5v DC) voltage.
     
  2. Soeren

    Soeren Guest

    Hi,

    The term "buzzer" is normally used for those which contains the driver
    and only needs a supply voltage. They can be found with working voltages
    down to 1.5V.

    If a driver is needed, you only have a raw piezo disk, which must be
    driven by an oscillator - preferably one with a transformer coupled
    output, if you want it to be loud when run from a low voltage.


    --
    Regards,
    Soeren

    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:http://www.elektronikteknolog.dk/cgi-bin/SPEED/>
     
  3. Zwox

    Zwox Guest

    How do I get a piezo-electric buzzer to make an audible sound? I've heard
    With a piezo buzzer you should only need to connect the buzzer to a DC
    source to hear an audible tone. Try connecting your buzzer to a single AA
    battery and find out. It's different if what you have is a piezo-electric
    transducer, in which case you will indeed need an oscillator.

    Zwox
     
  4. CFoley1064

    CFoley1064 Guest

    Subject: Total newbie question:
    Hi, Blarg. The smallest piezo beepers don't have drivers built in. They're
    just piezoelectric disks, to which you have to apply an AC voltage at the
    appropriate frequency to get them to beep. The piezo elements will output a
    voltage if they're flexed, and will flex if you apply a voltage. Since sound
    requires a "back-and-forth" flexing, you need an AC voltage.

    I'd suggest getting a beeper with the drivers built-in. That'll probably be
    the smallest solution, even though their package will be somewhat larger.
    However, if you've got a few gates of a 74HC14 to spare, this will work down to
    3VDC or so (view in fixed font or M$ Notepad):

    Piezo Element Driver
    ___
    .--|___|--.
    Control | 33K |
    Signal | | .-.
    ___ | |\ | || || /|
    o-|<-|___|-o -| >O---o-------|| ||-----O< |--.
    3.3K | |/ | || || \| |
    1N914 --- | || || |
    ---.1uF | '-' |
    | | |
    | '-----------------------'
    ===
    GND


    The first schmitt triggered inverter acts like an oscillator, and the second
    inverts that output to drive the other side of the piezo element. It won't
    work very well for larger elements, because they have larger capacitance, which
    strains the HC14 output FETs and leads to reliability problems. You're driving
    a capacitance here. It will work fairly well, however, for *small* piezo
    elements. Note that when one side of the element has 3V across it, the other
    side has 0V. When the oscillator changes states, the voltages are reversed.
    Voilla, AC. The control signal input swamps out the oscillator feedback when
    it's low, and lets it oscillate when it's high. If you don't need control,
    just omit the 3.3K resistor and the diode, and it will beep when you power it
    up.

    You might have to tweak the R value a little to get the desired frequency, but
    this will get you started, anyway.

    Good luck
    Chris
     
  5. I like CFoley's solution. You can also drive it with a 555, which
    might give you slightly better control and predictability for the
    frequency. There are circuits all over the internet for this, so just
    go look around. A 555 at radio shack is about a buck.

    Regards,
    Bob Monsen
     
  6. Blarg

    Blarg Guest

    Thanks to all. Cfoley, your solution seems elegant, but is way over my
    head. I also must ask, what is a 555? Some type of
    oscillator circuit?
    My circuit needn't be controlled beyond on and off. A continuous tone is
    fine.
    Here's the tricky part: The whole thing, including battery, must weigh
    under 2 grams.

    Again, thanks to all who responded!
     
  7. Soeren

    Soeren Guest

    Hi,


    Then your best bet is an astable multivibrator made from a couple of SMD
    transistors, driven from the tiniest button cell, but getting below 2 grams
    will be tricky still.

    With the piezos terminals driven from the collectors, you should be able to
    get a (not very loud) sound.


    --
    Regards,
    Soeren

    * If it puzzles you dear... Reverse engineer *
    New forum: <URL:http://www.ElektronikTeknolog.dk/cgi-bin/SPEED/>
     
  8. Rich Grise

    Rich Grise Guest

    For the absolute minimum, see if you can get a 3-lead transducer -
    the 3rd lead is a feedback lead, so it, one transistor, and two
    resistors make an oscillator. I don't know exactly what the
    element is technically called, but someone here probably does.

    Good Luck!
    Rich
     
  9. CFoley1064

    CFoley1064 Guest

    Subject: Re: Total newbie question:
    Hi, Rich. Paradoxically, these 3-lead devices are called "self-drive" beepers.
    You need a transistor and a couple of resistors to get gain for the feedback
    to create self-sustaining oscillations. Here's an example:

    http://www.murata.com/catalog/p37/es0041.pdf

    Good luck
    Chris
     
  10. A 555 is a timer IC, which also makes a pretty good oscillator, given
    a couple of resistors and a capacitor. You can use it to create the
    "A/C" waveform you'll need to drive your little piezo thingy. I have a
    'get up and move' circuit that makes me get up and push a button
    across the room every 20 minutes (So I'll stretch my back, I have back
    problems.) It uses a 555 to drive a piezo thingy, and a timing
    cap/resistor to delay the buzzer from going on for 20 minutes using
    the reset pin on the 555.

    FYI, I suspect you won't be able to get a battery that is as light as
    2 grams. I'd rethink the specs. Take a look at the battery specs on
    www.duracell.com for some clues about battery size.

    I'll send you a schematic for the nag circuit if you want.

    Regards,
    Bob Monsen
     
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