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Loud Piezo Buzzer for Timer

Discussion in 'Electronic Basics' started by RobZ, Nov 15, 2006.

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  1. RobZ

    RobZ Guest

    Hi all,
    as the result of a dare, I am trying to build a shooting Timer. ( a
    timer that responds to the sound of a firearm being fired and records
    the times thereof).

    The timing is done by an ATMEL micro.
    the Start signal (from the Atmel) is a .5sec pulse.
    I have been using this to switch on a transitor to connect the 9V
    battery directy to the Piezo buzzer.
    this works fine except the volume/db of the buzzer is far to low. the
    Buzzer is rated 85Db with a supply voltage of 24V,
    another problem is that a buzzer of less than .25 Sec is too quick
    can any one assist in pointing me in the right direction re the
    a) Will a voltage doubler circuit (diode/capacitor network) work in
    this instance?
    b) must this "increased voltage" be stored in a capacitor before being
    able to be used ?
    c) if so, how do i connect it up to "release" the stored voltage -
    similiar to flash trigger , connecting to ground?
    d) given a 9v supply and a 5v trigger, could someone supply me a rough
    schematic ?
    e) the circuits i have been looking at (via google) typically use a 555
    as an oscilator but they produce 200-300Volts!
    am i on the right track here?
    any Response is appreciated
  2. Chris

    Chris Guest

    Hi, Rob. One at a time:

    a) Using a 555 as a voltage doubler will pump your 9V battery supply
    up to 18V, It should definitely work to increase your piezo beeper

    b) Any voltage doubler uses an output cap to store the energy. The
    bigger the output cap, the more energy is stored. Your piezo isn't a
    high current load (probably less than 20mA DC), though, so an enormous
    storage cap shouldn't be much of a consideration.

    c-e) The basic 555 voltage doubler circuit is at this link:

    It should work exactly as shown in the link (555 driving 1N4002s and
    220uF caps). Your hookup diagram should look soomething like this
    (view in fixed font or M$ Notepad):

    | BZ1
    | |.-.| +18V
    | || || |
    | .-|| ||---'
    | | || ||
    | | |'-'|
    | |
    | From ___ |/
    | uC >-|___|-o-| 2N3904
    | 2.2K | |>
    | .-. |
    | 2.2K| | |
    | | | ===
    | '-' GND
    | |
    | ===
    | GND
    (created by AACircuit v1.28.6 beta 04/19/05

    With the higher voltage and full voltage turn on, your beeper should
    start up right away -- .25 seconds is plenty long for the beeper's
    internal oscillator to start up and give you a good tone.

    I hope this has been of use. Feel free to post again with more

    Good luck
  3. This concept has a problem. The piezo buzzer is essentially
    a capacitor that looses energy into mechanical distortion
    when its state of charge changes. Replace it with a
    capacitor, in the above circuit, and it becomes pretty clear
    that there is no path for current (after the first pulse)
    through the transistor's collector. This circuit will
    produce a single tick when activated.

    It is not even a good idea to apply pulsating DC to a piezo.
    They last longest with AC, only.
  4. RobZ

    RobZ Guest

    Thanks Chris, Will give it a go!
    ps. sorry about the delay, somehow google did not inform me of a reply
    to topic?
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