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Need ultrasonic sound

Discussion in 'Electronic Basics' started by Ken, Apr 27, 2004.

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  1. Ken

    Ken Guest

    I have a pest repeller that can drive an external speaker. It has
    three separate settings: rodents, birds and dogs. I want to repel
    rodents (squirrels in my attic, to be precise).

    Where can I find a speaker that will not cost an arm and a leg that
    will put out a strong, modulated ultrasonic signal? My guess is we
    are talking 5 watts at and around 35 kHz.

    In the alternative, where can I find a piezo buzzer that will put out
    a big 35 kHz sound when DC is applied?

    (to reply via email
    remove "zz" from address)
  2. Bob Masta

    Bob Masta Guest

    Ultrasonic signals are commonly used as stimuli
    for auditory experiments with rodents. We used to
    use piezo horn tweeters, those plastic jobs about
    3-4 inches across. They were made by Motorola,
    and we bought them at Radio Shack.

    Note that you will not get anything like flat
    frequency response. We measured the response
    (a trick in itself at these frequencies) and tried to
    work in the "hottest" regions. But they were
    cheap and fairly powerful. (Flat response
    pretty much requires electrostatic drivers. These
    are not only really expensive, but because they
    have a big, flat radiating surface they tend to
    beam the sound in a tight pattern.)

    Note, however, that all these "pest repeller"
    gadgets are long on extravagant claims and
    really short on hard evidence. I've never heard
    of an independent study that shows they work.

    Hope this helps!

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
  3. Any observations on their effectiveness as dog detterents/calmers, as
    in the Dazer?

    I'm still thinking of getting one, following my failure to build an
    effective equivalent. My design is shown at
    and I was quite pleased with it initially because its audible setting
    (one way of the 2-way switch) gave an ear-splitting sound with a fresh
    pair of PP3 NiMH batteries. I therefore (rashly) assumed its
    ultrasonic setting would have a suitable effect on any savage dogs I
    encountered while walking in remote areas.

    Happily, unlike the previous year in Tuscany, I had no cause to use it
    in anger when I took it on a walking holiday in Poland in 2002. But
    curiosity had to be satisfied, so I discretely tried it as I strolled
    through the crowded streets of Zakopane. No visible effect on the
    unwitting victims whatsoever. Even a poodle at 2 metres apparently
    remained unaware of it. In fact, I convinced myself after a
    few such abortive experiments that it was broken or that the batteries
    had failed. But switching fleetingly to the 'human' setting made that
    look very unlikely.

    I reckon it's just too low-powered. Which is why I'm keen to hear from
    any Dazer users. On that walking holiday in Tuscany (when I was
    attacked by two dogs, prompting the project originally), another
    member of the group demonstrated the Dazer to me (on a barking
    Alsatian behind gates). It definitely calmed it down and made it back
    off, so its design is clearly superior to mine. Almost certainly down
    to power output, I assume.

    Terry Pinnell
    Hobbyist, West Sussex, UK
  4. Soeren

    Soeren Guest

    Hi Terry,

    Which frequency was it ?

    Years ago I made a small ultrasounder from a piezo-disk (about 2kHz
    natural resonance) which was very ineffective in terms of power output,
    but my parents dog (in lieu of a real ginnea-pig) nevertheless reacted
    with a surprised listening attitude (if you know what I mean).

    About what level ?

    Perhaps you tested on a deaf dog ;)

    I guess anything around a couple of Watts woud be plenty, if used
    efficiently (the right piezo-tweeter and the right frequency being the
    main concerns).

    The non-electronic solution would be a small can of mace to ensure your
    hiking enjoyment :)
  5. I guess you didn't look at the circuit? As stated in the notes, it's a
    swept range 24 - 30 kHz.
    As per notes, 15V pk-pk into the piezo tweeter. Power? Wish I knew.
    The tweeter impedance is specified as 1k at 1 kHz and 20 ohms at 40
    kHz. So suppose it's say an average of 40 ohms at my output
    frequencies. Then, unless I've slipped somewhere, approximating with
    ((Vrms)^2)/R implies a very low power of about 700mW. Which would
    explain the pathetic results. But using the same calculation, the
    power output of the human-audible signal would be at a greatly *lower*
    level, of the order of 60 mW! That just doesn't square with the
    ear-splitting shriek I actually hear. Resonance effects presumably
    account for some of this? But how would you determine the power
    Regrettably illegal in UK, and probably in rest of EU by now <g>.
  6. Soeren

    Soeren Guest

    Hi Terry,

    Yes. Sorry for my laziness, but I am looking at it now :)

    A linear regression on these numbers says 270 to 422 Ohms (at your
    frequency range). In reality, the curve will not be all that linear, but
    at least it gives a clue.

    I guess it is just a _drawing_ error that pin 2 is connected to pin 7 ?

    The RMS of a 15V_pp 50% squarewave is 7V5, 7V5^2/40 is 1W4 (at least in
    my country ;)

    With 270 to 422 Ohms however, yeilds only 133mW to 208mW, so I am not
    all that surprised of your results.

    I think resonance is accountable for the major part of the difference.
    Most piezo disks of around 1½" diameter I have played around with has
    had their resonance around 2kHz, what is the diameter of your tweeter ?
    There are tweeters with good as well as bad hi freq. responce (and
    luckily the cheaper ones might be better for your purpose although they
    might be a bit shreaky when used for hi-fi.

    To get a real blast from a piezo, you need to increase the V_pp fed to
    it. A Hi-Q LC-circuit in resonance at the frequency you want, should
    enable you to get some real power, 5W to 6W should be reasonably easy to
    It will rule out the sweep, of course, but perhaps an intermittent tone
    of a single frequency is just as effective (test with low power a couple
    of dogs for the best frequency).

    Sure, but so is letting your mongrels attack people ;)

    Anyway, nobody will find out until you are attacked, so which duo you
    prefer... Hospital or a fine ?

    Besides, it might give you peace of mind, as being attacked by dogs can
    give you a real fobia towards those filthy bastards ;) (been there
    myself as a kid)... But... unprovoked dog attacks are _extremely_ rare,
    so perhaps you could get some advice from an animal psykologist about
    behaviour around dogs. In most cases of threatening dogs, a bit of
    understanding of their mind is a very good help...

    By nature, dogs want to dominate, not kill, so if you are not able to
    dominate them, submissive behaviour will get you minimal damage (so lomg
    as we are not talking of a trained dog gone whacko), at least a couple
    of scientists studying animal behavour have verified it the hard way, by
    lying on their back and letting the dog _pretend_ to bite their throat
    (they must have huge balls to do that, personally I would rather kick
    the dogs than test mine that way ;)

    Hope you get a solution you are comfortable with, so you can hike
    without worrying :)
  7. Can't put my hands on the specs now, but I recall it was heavily
    skewed, so my figure would be much closer than yours.
    No, it's your optician's error - pin 2 is correctly connected to pin
    I think it was closer to a sine than a square wave. But let's
    compromise on say 1W for 40 ohms, and correspondingly less for higher
    impedances. Anyway, bottom line is that it was plainly inadequate in
    As you can estimate from the 3.5mm jack socket in the picture I
    provided, that's pretty well full size (on a 17" display), so I
    suppose tweeter was about 6 cm diameter.
    FWIW, here's the audible output.
    Assuming my 40 ohm guess is about right, and that wave is somewhere
    between square and sine, that would probably mean a voltage supply of
    around 45-50V, compared with my present 18V (2 X PP3). Seems
    impractical. A DC-DC step-up converter would add complexity and reduce
    Thanks. Meanwhile, I've taken the line of least resistance, and
    ordered a Dazer from the site I mentioned <g>.
  8. Soeren

    Soeren Guest

    Hi Terry,

    I just complained to my optician, but he also claims that pin 2 is
    connected to pin 7 - on the right 555 in the drawing :)
    (Or to pin 6 through an 82k if you like).

    <URL:> works
    Hard to judge the actual sound pressure from a recording, but I guess it
    would annoy a dog as weel as a person ?

    No step-up is needed.
    The piezo is a capacitor, so all you would have to add, is a coil with a
    +---+ <--- *NOT* connected to Vcc !
    | |
    ) |
    L1a ) |
    Out ) O
    from O--* Piezo Tweeter.
    555 ) O
    L1b ) |
    ) |
    | |
    Gnd O---+---+

    The value of the coil will have to be calculated to get resonance at the
    frequency you want and from the piezos capacity at that frequency.
    The Q of the coil and the impedance of the piezo will determine the
    voltage you get.

    Yeah, outsourcing is the key ;)
  9. Apologies to you and your optician - I checked only the left 555!
    Thanks. I'll try that soon.
    Now I need to scour the neighbourhood for unwitting strays, or lie in
    wait for the regular dog-walkers...<g>
  10. Soeren

    Soeren Guest

    Hi Terry,

    You are welcome :)

    Place it behind a hedge and use a PIR-sensor to trigger it for a few
    seconds when someone walks by. If you see a lot of people hanging after
    stampeeding dogs, you know you have a winner :)
  11. I opened up my Dazer. It includes a miniature transfomer; presumably
    an audio-type, but the only identification I can see is the number
    '2145'. The very simple PCB has a couple of 'KSP2222A' transistors,
    which I'm guessing are equivalent to 2N2222A, and a TIP110 medium
    power transistor. There's also a small 94V zener. The piezo tweeter
    itself is only 1" diameter, and the markings I can see are
    'MASSA-HINGH' and 'TR89...'

    The contrast in power with my own DIY circuit is apparent from this
    shot of the output waveform, which shows a frequency of about 25 kHz
    and a pk-pk amplitude of 85V.

    Anyone care to suggest the likely circuit approach from all that? I'm
    guessing a two-transistor multivibrator drives the transformer primary
    via the power transistor, with output from the secondary to the
    tweeter. Would the zener be directly across that?

    And, given the pk-pk of 85V, what other factors would be needed to
    estimate the actual output power please?
  12. Use an inductor and a power mosfet to kick the voltage up. put your
    transducer in parallel with the inductor.

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