Defense Against The Dog Arts

It’s possible that it was [Matt Meerian]’s awesome pun that won us over, not his ultrasonic bicycle dog defense system, but that would be silly. [Matt] wanted an elegant solution to a common problem when riding a bicycle, dogs. While, obscenities, ammonia, water, pepper spray, and others were suggested, they all had cons that just didn’t appeal to [Matt]. He liked the idea of using C02 powered high pressure sound waves to chase the dogs away with, but decided to choose a more electronic approach.  He used a Atmel ATmega644 as the MCU, four 25kHz transmitters, and two 40kHz transmitters. When the rider sees a dog he simply flips a switch and it activates the transducers (along with, cleverly, a human audible horn so he doesn’t have to look down to know it’s working). So far [Matt] has not had a dog chase him in order to test it’s efficacy, but his cat clearly seems unaffected by the device as you can see after the break.


25 thoughts on “Defense Against The Dog Arts

  1. I hate to be negative, but I’m not holding out much hope for this working. A reasonable test might be to drag a squirrel ( Not Living ) real or stuffed, behind the bike to attract the dog to pursue. Worse case, it would amuse the dogs.

  2. Probably not the best idea to use your own pet as the test subject. Or at least do it from a distance in a manner so they can’t associate you with the pain and you loose a buddy. I was messing with one of the weapons mail carriers carry at arms length, and not pointing it to myself I pushed the button. SOB I could hear or st least experience a bit of pain. I’d think twice about using a human audible on indicator. Really don’t want the dogs associating a source of real pain to you and bicycles.

  3. I am worried, it doesn´t work. maybe the wrong frequencies and not enough power. I built such a thing times ago, but with a 555 timer at ca. 20kHz and a piezo tweeter as transducer, working at 12VDC. to get more power i added an inductance in parallel to the tweeter. before using this i often found dog poo on my lawn. now that i have this copled to a motion detector, my lawn is clean.

  4. “[Matt] wanted an elegant solution to a common problem when riding a bicycle, dogs.”

    Who has this problem? Where are there packs of feral dogs just roaming the streets? The only time I’ve ever encountered them was during urban exploration of a factory complex in Chicago’s west side.

    1. Normal, non-feral dogs attempting to chase cyclists is a pretty common problem. Most of the time they’re restrained by a leash or kept in by a fence, but sometimes they’re free to chase (in my experience, mostly in rural areas).

  5. @0xCD: I like the dead squirrel idea. it’s twisted.
    @ n0ikk: Willie is 18 years old and does not hear well. (which, I assume is age related) Sometimes he does not hear me walk up behind him. I was pretty sure he would not hear the emitters before the test on the video.
    @Hubert: It would be really nice to have some kind of profession test gear with a microphone that will work in the ultrasonic range. But, I’m sure such test gear is out of my price range. The ultrasonic emitters are rated at 92dB.

    1. Although often rated for 20KHz or so, many electret mics can detect up to 100KHz.

      Google ‘bat detectors’ since there are quite a few that do homemade stuff in that area, making simple frequency dividers and using cheap materials.

  6. I would like to use the ultrasonic beating system. It is highly directional but you don’t hear the primary sound but what is modulated on it. It sounds like it is inside your head. Teeth on bones. Once the barking starts it is the only thing they understand. Crunch pop!

  7. You’re not *repelling* dogs with this. With those tiny ultrasonic transducers, all you’re doing is producing a sound; which is not in the least bit painful, or even annoying.

    The response depends solely on the dog. The most common response is stopping in puzzlement (or sometimes fear) at the new and unfamiliar sound. That may only work a few times, as the novelty wears off. Others may ignore it immediately, or even be driven to attack.

    Speaking from experience, even with quality, high-power piezo tweeters being driven to the limit at one of the resonant peaks; it’s very difficult to produce enough ultrasonic SPL to ensure a reliable pain aversion response in dogs (or cats) at any useful distance.

    It’s better than nothing, but I wouldn’t rely on it alone.

  8. I like the dead squirrel idea, but how about taking it a step further and simply have a box of stuffed squirrels, dog treats or other interesting things on the back of the bike and a button to dispense them on the handlebar when you’re being chased?

    It would be like deploying chaff grenades, but for dogs!

    (granted, it would probably strongly reinforce the chasing behavior but it would be someone elses problem once you got away…)

  9. A Mega644 might be just a little bit of an overkill here. A Tiny45 or a few 555’s might be a more suitable solution.

    But hey! If you got a 644 just laying around with no other purpose in life – why not? ^_^

  10. If you find the right tweeters you can get more than 115dB ultrasondlevel at resonance. to get better results do not use only one static frequency but a sweep from 17kHz up to 25kHz and have a (H-) bridge output to drive the tweeter at the highest possible voltage level.

  11. maybe a sonar would work, there is a theory that the big sonar system of submarines and battleships kills these big whales. There is connection between the big war simulation of the Marines and the beaching of whales. It showed that the beached whale head are full of blood, the sonar must perforated their brains. So if you really what something effective try a sonarsystem.

  12. Sonar would definately work on dogs, I just know it. I have heard stories about how a dog’s ultrasonic rangefinding gets all confuzled in certain manufacturing areas. I’d be afraid of blowing up a dog’s sonar melon, and just getting doggy blood everywhere. I never knew that’s how they found their way around in the dark until last year.

  13. 5% Pyridine in a spray bottle will turn even the meanest dog into a whimpering tail-between-the-legs-running-away pup.

    Just don’t be down wind of the spray or you’ll retch yourself off your bike.

    I use a small squirt gun full of 25% solution when I run. Never been bit once, been chased alot. Dogs are quick learners, have a bunch that will stand and growl, but they know better now then to chase me. Makes a skunk blast seem like a gentle whiff of nice perfume.

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