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High pitch sound generator

Discussion in 'Electronic Basics' started by sbl, Oct 4, 2006.

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  1. sbl

    sbl Guest


    I would like to build a home-made cat repeller, based on high pitch
    sound (18-19KHz and up)

    What's the simplest way to build such a sound generator?

  2. Bob Masta

    Bob Masta Guest

    I have my doubts about how effective it would be.
    But if you want to do some experiments before you
    commit to buying any parts, you are welcome to
    download my DaqGen freeware sound card signal
    generator. You can see what works and what doesn't,
    both with respect to frequency and speakers.
    Note that most sound cards don't go above 20 kHz,
    even though DaqGen will cheerfully generate higher
    frequencies internally... you just won't get them out
    of most cards.

    One difficulty might be knowing how well your chosen
    speaker is working at these frequencies. Might need
    a young child that still has that part of their hearing
    range to tell you what is happening.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  3. BobG

    BobG Guest

    Obviously you need a high frequrncy transducer (tweeter!). Get one of
    those Motrola peizo tweeters at radio shack or the local music store.
    And a regular old signal generator, maybe one with a burst mode or
    sweep mode...
  4. Leo Meyer

    Leo Meyer Guest

    I once bought and built an insect repellent kit based on an astable
    multivibrator. It used an earplug as a loudspeaker. The circuit is very
    simple and easy to build. And there are plenty of resources available on the
    net for astable multivibrators. Might be worth checking out.
    Probably you will need more power and a proper loudspeaker, but I think
    adding an extra transistor wouldn't be that hard.

  5. How about a 120 db speaker?


    50% of all statistics are wrong. The rest don't matter.

    Clyde Crashcup
  6. Guest

    I tried those tweeters years ago for the neighbors dog. Heathkit audio
    generator, Sansui amp. Didn't do squat but it was fun fiddling around
    with it.

  7. Johnny Boy

    Johnny Boy Guest

    Probably the simplest would be a '555 timer with a driver transistor or
    half-bridge into a piezo tweeter

    .... Johnny
  8. Guest

    My experience with dogs is that they do not respond to any sort of
    sound by itself as a repellent or deterrent to undersirable behavior.
    My bet is that cats would be the same way.

    The sound has to be strongly associated with some sort of punishment,
    i.e, the sound should probably immediately preceed the punishment or
    occur concurrently.

    Just as an example, and not necessarily a recommendation, you could for
    instance rig up a cat trap and have the sound start when the trap
    closes. If cats are like dogs, you would only need to do this once to
    permanently "train" any individual cat.
  9. Can you explain the half-bridge please.

  10. Johnny Boy

    Johnny Boy Guest

    Hello Roger,
    a simple bi-polar half-bridge would look something like

    (View in 'Courier' or 'FixedSys'):-

    +Vcc o
    o |
    | |/
    | +---| NPN
    +---+---+ | |> /|
    | | | | C +-+ |
    | '555 +----[R]---+ +---||---| | |SPKR (Piezo-Tweeter)
    | | | | +++ |
    +---+---+ | |< | \|
    | +---| PNP |
    | |\ ===
    === | GND
    GND ===

    .... Johnny
  11. Thanks. I see.

  12. sbl

    sbl Guest

    What's the effective range of such a speaker? Do you have any prefered
    tweeter model?

  13. Bob Masta

    Bob Masta Guest

    You might check for tweeters.
    They have a big selection and good prices. The problem
    with most tweeters is gettting frequency response information.
    Speaker manufacturers don't seem to use the normal -3 dB
    points to define the frequency range. I'm not sure what
    criteria they use, but I suspect that it includes a lot of hype.
    So, don't believe specs like "2000 to 25000 Hz" unless
    they specify "-3 dB", which they rarely do. Look for an
    actual curve.

    Having said all that, piezo tweeters are probably your best bet
    if you can't get better info. They tend to have extended high
    ends, though don't expect them to be flat. (Nothing is very
    flat at these high frequencies, except maybe electrostatics,
    and they have other issues.) Piezo tweeters are capacitive
    loads, with typically pretty high impedance. The efficiency
    numbers never look too good (typically low 90s for dB SPL
    at 1 watt and 1 meter) compared to dynamic drivers, but
    I think that may be because they are not measuring actual
    power input to the drive, but using an equivalent 8 ohm
    calculation with the drive voltage. However, if the actual
    (high) impedance is considered they would be much more
    efficient. (By the same token, the maximum "power" handling
    in the specs is also based upon the same fiction, so you
    aren't going to actually stuff 50 watts or whatever into any
    piezo tweeter... they just mean that it's appropriate to use
    as the tweeter with a 50 watt amp driving the overall speaker
    system with normal program material.)

    On the PartsExpress website, look under individual tweeters
    for specs. I don't recall if there are any response curves
    for piezos, but under one of them there is a PDF from CTS
    explaining all the fundamentals and how to calculate the
    crossover cap, how to use them in series and parallel, etc.

    If the underlying concept has any merit, then for good
    dispersion you might want to go with an array of piezos
    angled in different directions. You might want to buy an
    assortment of cheapo models to test, then when you find
    one you like buy a whole mess of them. They have models
    priced from under a dollar, in bulk.

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
  14. BobG

    BobG Guest

    Good answer Bob, especially if his question was about 'frequency
    range', but for some reason, I though he might be asking about
    'distance' range, like, from how far away will it annoy the cats? The
    answer to this depends on how good the cats hear, and how loud the
    noise is. I think you can put a 25V square wave into those motorola
    piezos, and at a human audible frequency like 4khz, they are too darn
    loud to listen to for more than a few seconds at arms length. Assuming
    they are still that loud at 20khz, I guess we assume they get about 6db
    quieter every time you double the distance. But to test it, you need to
    blare it into a cat about 3 feet away and see if he runs away. Then you
    need to repeat, doubling the distance each time until it becomes
    ineffective, or until you become shredded from claws.
  15. Johnny Boy

    Johnny Boy Guest

    Range is something you'll need to determine by testing. The simple
    circuit that I drew would not produce much power, so the range would not be
    great. A bit of trial and error would be needed to find the right frequency,
    too. Regarding tweeter models, I vaguely remember that a Motorola tweeter
    was recommended once for this type of application, but I can't remember what
    I should point out that I personally don't think that these things are
    very effective. From what I've heard, some people claim that they work and
    others say they don't. I've seen similar devices marketed either as
    electronic dog whistles or as 'bark stoppers'.
    .... Johnny
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