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How to drive piezo atomizer?

Discussion in 'Electronic Basics' started by aerelD, Apr 4, 2008.

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  1. aerelD

    aerelD Guest

    I am in need of some help as I attempt to improve my circuit design
    skills. I am trying to reverse engineer one of those aroma dispensers
    that use the little piezo-electric atomizers and a bottle of smelly
    oil. I have measured and characterized the signal at all the nodes on
    that circuit.

    The trouble is they put that lame potted bare silicon die on the board
    so you have no idea what it's doing. I want to put on a little
    microcontroller or something and drive the atomizer for myself. The
    signal going into the power mosfet part is essentially a 3V square
    wave with maybe a 35% duty cycle. It comes out of the mosfet into a
    little transformer (which I am not understanding it's connections, but
    that may be another discussion), a big 3300uF cap and a 220uH inductor
    before going out to the atomizer.

    There is a cap, a diode and another inductor but they all seem to be
    on the input side of the silicon part - possibly just for timing and
    blocking?

    Anyway, if any of you kind and smart folks out there (does sucking up
    work in this group?) have any pointers for me I would very much
    appreciate it. It seems fairly simple, but I'm not able to completely
    recreate the final output signal. I have a function generator but I
    can't figure out how, or if it's possible, to set the duty cycle to
    something other than 50%. When I drive my circuit with the closest
    signal I can get, it doesn't get anywhere near the 150V (220v pk to
    pk) needed for the atomizer.

    Many thanks in advance.
     
  2. Chris

    Chris Guest

    The output impedance of your function generator might be limiting the
    rate of rise and fall on the signal at the MOSFET gate. Also, and
    more likely, the duty cycle is probably a very important part of the
    resonant circuit. Try using the generator output to drive the trigger
    input of an LMC555 (capable of operating at 3V) configured as a
    monostable (one shot). Use a potentiometer in series with a fixed
    resistor to allow you to tweak your duty cycle to duplicate the black
    box signal.

    http://www.national.com/mpf/LM/LMC555.html

    Reverse engineering is, after all, engineering. You need to get
    crafty. You know what's coming out of the black box. Follow Mr.
    Fields' advice and muscle out the rest of the circuit. Get it down on
    paper. It helps.

    By the way, if you post back, you might want to mention which function
    generator you're using (and whether you have a scope). Newsgroups
    can't read minds.

    And Google is your friend. Try "piezoelectric atomizer" (no quotes)
    and explore.

    Cheers
    Chris
     
  3. amdx

    amdx Guest

    What frequency is your generator set at?
    The ceramics are usually pretty high Q, so you need to be close on
    frequency.
    I don't think you need anything other than a 50% duty cycle.
    Mike
     
  4. HapticZ

    HapticZ Guest

    these are just scaled down from piezo humidifier designs. get a few of
    those schematics and like the other guys have said, as long as the ceramic
    is driven at the right freq (usually major mode, but often using harmonics)
    you can vibrate any liquid into scattered partiticles to drift off away
    into the air. i have used those cheapy peizo buzzers to perform this task
    with a little mod. most already have the circuits built into the case (and
    they are cheap)

    us navy has done extensive research on ceramic transducers, they may have
    some design unique designs for incidental information also.
     
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