Over-Engineered Cat Door Makes Purrfect Sense

On paper, pet doors are pretty great. You don’t have to keep letting the cat in and out, and there should be fewer scratches on the door overall. Unfortunately, your average pet door is indiscriminate, and will let any old creature waltz right in. Well, [Jeremiah] was tired of uninvited critters, so he built a motorized door with a built-in bouncer. Now, only animals with pre-approved BLE tags can get in.

The bouncer is a Raspi 3 running Node-RED, which scans continuously for BLE advertisements from the cats’ collars. [Jeremiah] settled on Tile tags because they’re reliable and cat-proof. The first version used an Arduino and RFID tags for the cats, but they had to get too close to the door to trigger it.

We love [Jeremiah]’s choice of door actuator, a 12V retractable car antenna. [Jeremiah] uses the antenna itself to lift and lower the removable lockout panel that comes with the door. He removed the circuit that retracts the antenna when power is lost, so that power outages don’t become free-for-alls for shelter-seeking animals.

There’s also a nice feature for slow creatures—the door won’t close until 15 seconds after the last BLE ad, so they cats won’t ever have to Indiana Jones it through the opening. Magnetic switches currently limit the door travel at the top and bottom, though [Jeremiah] will eventually replace them with standard switches. Paw at the break until you get a walk-through video.

Cats will be cats, and the ones that go outside will probably rack up a body count. Here’s a cat door that looks for victims clenched between cat jaws and starts a 15-minute lockout period.

Thanks for the tip, [baldpower].

21 thoughts on “Over-Engineered Cat Door Makes Purrfect Sense

  1. purrty clever. BLE has an antenna distance of >100 m, I think. I wonder if he limited the antenna reception somehow to make sure that it doesn’t start working when the cat is still really far away.

  2. The hardest part of these hacks is getting your freaking cat to use them. Mine would rather try to get in via the roof than use her normal flap cat door. I think she suspected it was a trap. She never trusted us.

  3. Love the use of the car antenna. Very clever. When I have an idea, I usually head for Digikey and McMaster and am often dissuaded by some of the component prices. This is a great example of repurposing (more) inexpensive and commonly available parts.

  4. Of course, over engineering is always my preferred solution, but you can also buy cat doors which use the RFID tags that most pets these days have, in order to unlock. They’re somewhat pricey, but using the tag that your cat probably already has is a neat solution imo.
    Of course, first you have to program them, which involves catching your cat, and shoving it through the cat flap. For some cats this is trivial, for others, well, lets just say your next hack might have to be scratch-proof arms.

  5. We had one of the commercial ones for a while. It was loaded with issues: The door was raised and lowered with a wire rope (string?) which had a tendency to jam/fray/break and it always happened at the worst time, like with a pet half way in or out; The door was “some assembly” with pretty rudimentary instructions, including some wiring, such a limit sensors’; The door had a marked tendency to “false” and raise when the pet was not near enough.

    My Labrador got hit by the door a couple of times when the wire broke (which happened WAY too often) and began to refuse to use it. One of our little dogs got stuck half way out when the door did not open all the way. Small amounts of snow would prevent the door from opening.

    The company, which I can’t find any more, provided me with several sets of the wire rope, but replacing it meant disassembling the thing and threading the wire through pullies, and winding the right number of turns around the capstan, and if you got the wrong number, good luck.

    The company sent me a full replacement one time, which never worked because the “door down” limit sensor wire got trapped in the frame and shorted, causing the door to continuously cycle up and down. When I repaired it myself, it would go up and stop just fine, but when it went down it slammed to a stop at the bottom (see above about winding the right number of turns.)

    After the third door, I finally gave up and asked them to replace it with a plain old flap, but initially they refused to refund the difference because it had been too long.

    The dogs are quite happy with the flap.

  6. I was expecting “meow” as my password or cat wicker image recognition, but this may be simpler. Does BLE report distance and uniqueness in the client server setup? This hack makes me want to move to the burbs and get a cat.

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