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Using piezoelectric to power a laser diode?

Discussion in 'Electronic Basics' started by [email protected], Jan 27, 2006.

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  1. Guest

    Hi,

    I'm a complete novice/noob to electronics.

    I have a little project i'm working on, and would like to use a
    piezoelectric power source to run a small visible laser diode for a
    short duration (20-200ms). Does this seem feasible? The biggest
    problem, from what i can tell, is the output voltage of the piezo is
    likely to be much greater than the 2-3V i need to run the diode. The
    other problem i'm having is actually finding suppliers of piezo devices
    that would be suitable for this...all i can find are accelerometers and
    strain gauges.

    Any thoughts? The energy source will be a sharp blow from a small
    spring-loaded lever.

    Thanks!
     
  2. Phil Allison

    Phil Allison Guest


    ** The laser diode is attached to a mouse trap - right ?

    When the mouse sets it off - the mouse gets a blast of laser light in the
    eye.

    You will soon get yourself 3 blind mice.

    Nice one - boob.




    ............ Phil
     
  3. Pooh Bear

    Pooh Bear Guest

    And for how long do you expect a sharp blow from a hammer to illuminate
    this led ?

    Graham
     
  4. John Fields

    John Fields Guest

    ---
    That won't work.

    Try this:

    Vcc Vcc
    | |
    [10K] [100K] +-------+
    | | |__ |
    +------[0.1µF]--+------|--O|TR OUT|O---[R]--+
    |- |A | | | |A
    [PIEZO] [1N4148] +---|TH | [LASER]
    |+ | | |_ | |
    GND GND +--O|D | GND
    | +-------+
    [1.5µF] 555
    |
    GND

    1.5µF will get you a 200ms pulse out of the laser and 0.15µF will
    get you 20ms.

    Or this:

    +-----+
    +------|~ +|----+-----+
    | | | |+ |A
    [PIEZO] | | [C] [LASER]
    | | | | |
    +------|~ -|----+-----+
    +-----+
    FWB

    You'll have to determine the value of C experimentally. Start with
    something like 10µF and work down until the laser flashes.

    It worked for me with a plain old red LED and the piezo element from
    a barbecue lighter, which you might be able to adapt for your use.
     
  5. John Fields

    John Fields Guest

    ---
    Oops...

    The 1N4148 _cathode_ should be connectedto the 10k resistor:


    Vcc Vcc
    | |
    [10K] [100K] +-------+
    | | |__ |
    +------[0.1µF]--+------|--O|TR OUT|O---[R]--+
    |- |K | | | |A
    [PIEZO] [1N4148] +---|TH | [LASER]
    |+ | | |_ | |
    GND GND +--O|D | GND
    | +-------+
    [1.5µF] 555
    |
    GND
     
  6. Guest

    John,

    All i can say is holy cow! I didn't expect schematics!!! I'll have to
    give that a try!

    The illumination just has to be long enough for the human eye to detect
    it, which i'm assuming is going to be a function of brightness, but at
    5mW i'm assuming 20-50ms is plenty..(my 200 upper end range is on the
    long side)...lots of assuming though, eh?

    I do like the mousetrap idea, though... If you can't smash em, blind
    em. :)

    Thanks again!!!!
     

  7. You're aiming a 5mW laser at a human eye?
     
  8. Stef Mientki

    Stef Mientki Guest

    You can easily see a 1 usec puls from a normal (high efficiency) white
    LED, at 100 mA.
    Stef
     
  9. Guest

    Nooooooooo. I thought i fixed that part of my post...sorry. I'm just
    basically building a laser pointer for a little personal project. The
    piezo power idea came from the desire to make it as compact as
    possible, with the longest shelf life i can muster. In addition, the
    chassis that this is mounted in will be moving kind of vigorously, so i
    want to capture, in essence, a 'flash' that a person can see through
    persistence of vision...rather than a continuous beam which would
    rapidly become ambigous due to aforementioned motion.

    The laser will, under almost any conceivable circumstance, be aimed at
    a wall or 'calibrated' paper area so we can see how much the chassis
    has deflected.

    The application would be analagous to setting a similar device in the
    head of a golf club. The laser is parallel with the club face, and
    'flashes' upon impact with the ball. The position of the flash
    relative to the alignment of the tee with the player will detect how
    much slice or hook is in the swing.

    Bad example, but it gives you an idea of what i'm trying to achieve.
    That's good info, thank you. I wasn't sure how much of a duration i
    would need for it to be effective. I'm assuming the laser diode would
    essentially have the same characteristics...the shorter the pulse, the
    better.

    John, if you're still hanging around...one quick question regarding the
    schematics you wrote up. In the onces with Vcc, is that an external
    power supply, and the piezo is just used to switch?



    Thanks everyone for your replies!!!
     
  10. John Fields

    John Fields Guest

    ---
    Yes. Taking a look at it and adding the power and ground pins for
    the chip _and_ fixing an error:

    Vcc Vcc Vcc Vcc
    | |K | |
    [10K] [1N4148] [100K] +-------+
    | | Rt| |__ |
    +--[0.1µF]--+------+-------|---O|TR OUT|O---[R]--+
    |- |K | | | |A
    [PIEZO] [1N4148] +----|TH | [LASER]
    |+ | | |_ | |
    GND GND +---O|D | GND
    Ct| +-------+
    [1.5µF] | 555
    | |
    GND GND

    Here's what happens:

    When you whack the piezo a high voltage pulse will be generated
    which would kill the chip, the 1N4148 diodes are in there to clamp
    the positive peak of the piezo voltage to roughly Vcc + 0.7V and the
    negative peak to about -0.7V.

    The side (end?) of the piezo which generates the initial low-going
    pulse (which is what the 555 wants to see) is connected to the 555's
    TRIGGER- input, which will drive its output high for the time
    determined by:


    t = 1.5RtCt

    In this case,

    t = 1.5 * 0.1E-6R * 1.5E-6F = 0.225 seconds

    which about what you asked for for long pulse. You can easily make
    the pulse narrower by decreasing the capacitance of Ct or the
    resistance of Rt, but I'd leave Rt alone and go for a smaller
    capacitor.

    One caveat about the input pulse is that it needs to be narrower
    than the output pulse, (a 555 peculiarity) or the output pulse will
    be as wide as the input pulse, which may be wider than you want. If
    that happens, a possible solution would be to load down the piezo
    with a resistor wired across it, or to diddle with the value of the
    10k resistor and/or the value of the 0.1µF cap. Either way, the
    value would have to be determined experimentally, and if that got to
    be too tricky, then you could use a different one-shot and not have
    to worry about it. Something like an HC123 or an HC4538 would work,
    but you'd probably have to add a transistor to drive the laser
    diode.

    If you're looking for a nice, sharp, short pulse, then I recommend
    that you _don't_ use the bridge-cap scheme since it'll smear the
    pulse and you wont have nice edges.
     
  11. Guest

    Thank you for the explanation! I'm learning stuff every day!

    I guess the only issue is that i'm trying to use the output from the
    piezo to directly power the laser, so i don't need an external power
    source...kind of like the FBR + C(ap?) diagram you had at the bottom of
    your previous email. I think i'm going to order up some parts for
    both...if the cap+bridge is too sloppy, i'll go with the other. I'm
    sure a few watch batteries would power the diode for years given the
    usage i'm going for.

    Thanks again for all of your help!!! I've been surfing forums for the
    last few years, and forgot just how great USENET still is.

    Take care!!

    Bob
     
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