AVR Guardian filters out dogs

Cats and dogs can get along quite nicely when they are raised up together. The problem with this type of arrangement tends to be keeping dogs out of the cat box and away from the cat food. [Ryan Meuth] tried out a simple electronic barrier to keep the dog away. It uses an IR transmitter and receiver to shine a beam of invisible light across the doorway to his cat room. In the demo after the break you’ll see that he took steps to make sure the cats don’t set off the alarm. The beam of light is set high enough that their bodies don’t get in the way, and the firmware measures the amount of time the beam was broken in order to avoid false positives caused by the cats’ tails. If the dog does try to get into the room it will break the beam and set off a high-pitched alarm sound.

It’s interesting that the dog doesn’t like the sound but the cat’s don’t seem to be scared of it. Also, we’ve got a less-than-ferocious feline that would love to chew on the cord that connects the two modules. Still, it’s a solution that works for [Ryan] and could be incorporated into an automatic feeder to keep the dog away from feedings while you’re out of the house.


  1. The Cageybee says:

    Aawww. Lovely cats and dog.
    Poor dog was hanging his head as if he’d done something wrong.

    The Cageybee

  2. Hotwired2689 says:

    better not teach him how to crawl XD

  3. Cynyr says:

    a mirror and a carefully aligned emitter/detector would make this a cordless system would mean no cord across the floor.

  4. Hirudinea says:

    It reminds me of a chastity belt, because it protects a … anyway, its a clever design, if you can hide the cord, but what if the dog figures out jumping over or crawling under it?

  5. Taylor Alexander says:

    I’ve always wanted to get my animals chipped (RFID chip embedded in their neck for if they get lost. this is common and i should do that anyway) and then build a reader that can tell which animal is which, for this kind of thing.

    I have a couple kittens and an older cat. They always eat eachothers food and then puke it up on my floor. I’d like to build a box that only let the right ones in it to eat.

  6. sPiTfIrE-K1LL says:

    Easier solution: get rid of the stupid cat.

  7. anonymous says:


    This is the internet, we like cats. Please leave.

  8. Concino says:

    You don’t need to “carefully align” a mirror if you use a Retro Reflector (Corner Reflector or Cat’s eye reflector). It makes the installation quite simple.

  9. Anonymous says:

    “but the cat’s don’t seem to be scared of it’

    Plural’s don’t need apostrophe’s.

  10. walt says:

    I needed this when I had a cat. My dog loves eating cat food and cat poop out of the box.

  11. Ilias says:

    @Hirudinea: Maybe he’ll learn how to walk sideways too.

  12. Drone says:

    Proximity shock collar via RFID. My Girlfriend wears one.

  13. Spork says:

    Where can I get the schematics? Also does your home have some sort of path from the bedroom to the kitchen that she’s allowed to follow?

  14. Tachikoma says:

    What about GPS-based path enforcement to do the shopping?

  15. sPiTfIrE-K1LL says:

    @anon: then the internet is inferior and must be destroyed. Please replace your head with a trashcan.

  16. Myke says:

    @Drone: I pretty sure those aren’t RFID. You fail.

  17. @sPiTfIrE-K1LL



  18. robomonkey says:

    Petsafe radio fence would work even better. A couple of good jolts for fido and he’ll avoid that room like the plague.

  19. blackman says:

    are uControllers making people forget about electronics?

    This is a fairly simple problem, which could have easily been accomplished with a few transistors and a 555.

    Not that this is a bad thing, it opens up a lot of potential for expansion, but it just seems overkill at the moment.

    I really hope electronics as I know it doesent die off as a result of uC’s.

    I do love them, but when they are used to their potential.

  20. redbeard says:

    Or, more reasonably, RFID in the dogs collar. Then it doesn’t matter if the dog crawls, jumps, or walks erect.

  21. Richard says:

    how long before the dog learns to run though the sensor, so as not to set it off?

  22. chango says:

    @blackman Yes. Also, duct tape has all but replaced the art of welding and Twinkies have thinned the ranks of skilled bakers.

  23. SelfSilent says:


    The internet has been powered by cats since for years. A far more simple solution would to put the dog outside where it should be.

  24. walt says:

    great idea. i would use two receivers so i could tell which way the obstructing object was traveling. kinda how a two channel incremental sensor works. why would i want this? what if fido somehow ninjas his way past the alarm system then can’t get back out? if the owner is away for too long, fido would have to live off of cat food. if the owner was away for the weekend, fido would have to eat the cat poop. and, if the owner went on vacation, fido would have to survive on a diet of cats! oh the humanity!

  25. Paul says:
  26. pff says:


    > ‘girlfriend’

    enjoy your hand.

  27. Trollicus says:

    My cat is bigger than both the dogs. I need a better method, I’m thinking RFID.

  28. Rick says:

    Here is a lower tech solution that I recommend and use to keep my dog out of the bathroom with the kitty litter:

    It is a “hook and screw”, “window hook”, or “safety gate hook” that is long enough to let the cat through but not the dog.

    Make sure that either the hook is high enough that the dog cannot reach it or opt for the safety version.

  29. Patrick says:

    Wow, that’s an awesome pet hack. I’m not smart enough to figure something like that out.

    We would just have to use our Havahart Wireless fence indoors if we ever got a cat, but I’m not planning on that happening any time soon.

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