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Comment by SamBam | Hacker News Reader

I've been wanting for quite some time to build a device with a camera that could recognize my cat on the counter and turn on a servo that would release a jet of compressed air. It looks like I could actually use this for that.

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I’ve been debating doing this too. I’m not too worried about the cat detection but haven’t got a clue how to programmatically release compressed air? Wouldn’t it be as easy just to play the sound of compressed air through a speaker? My dumb cat wouldn’t be able to tell the difference.

An MCU with an attached relay module that is connected to a DC solenoid controlling a valve should do the trick.

There are probably a few kinks to work out that will come up in practice!

Number one kink that prevents me from building such contraptions: how to ensure it doesn't catch fire and burn the house down?

Use high quality relays purchased from Digikey or another distributor (should be $10-30 in single quantities for AC mains) and put thermal fuses on the mains side of the relay (I generally put several, each going to different parts that are at risk of shorting). Slather everything but the heatsinks (add some if necessary) with fire retardant epoxy, carefully pushing the thermal fuse into the epoxy until it makes contact and pushes out most of the epoxy under the fuse.

Burning down the house isn’t even an issue for me. USB relay throws 24VDC from a UL-approved power supply that opens the valve. The noise from the air compressor OTOH....

Simple! You just rig up another contraption with to a gite extinguisher

Found the Krynnian gnome

I was thinking just fixing a servo motor with a short arm right above a regular can of compressed air. Unsure if it will be as simple as in my head.

If you can position the camera so that only the "counter" is visible from it, a much easier option is to use the pre-trained yolov4.

https://gist.github.com/YashasSamaga/e2b19a6807a13046e399f4b... (download links for yolov4.weights is at https://github.com/AlexeyAB/darknet)

Using this, you will be able to detect if a cat is present in your image.

Add a random delay 0-60 sec delay for the jet air. This would create a fear and whenever she would sit there will think about jet of air coming any moment of time and now you can remove the machine after 1 month when your cat is trained.

Yup. I also seem to remember studies showing that if the reward/punishment is given randomly, it strengthens the Pavlovian response.

I plan (if I ever do this) to program a decay over time, starting at 100% chance/zero seconds, and moving to lower chance and higher random time interval.

Militarizing Your Backyard with Python: Computer Vision and the Squirrel Hordes

https://www.youtube.com/watch?v=QPgqfnKG_T4

you could do that with openCV years ago

I think the point he is trying to make is that this tool seems to make it easier to the point he is willing to put in the effort/time.

Exactly. Minus the job and kids, I'd love to have the time to learn all the tools I need for all the dozens of projects in my head. But if this makes it easier, it greatly increases the chance of the project actually happening. (And heck, I still have to work out how I'll actually send the signal to the servo...)

You only need something like 30 lines of code to do it with openCV

Unless you have some feature detection for cats, I don't see how you can discern whether it is a cat or someone's arm.

Check out the oss project [autofocus](https://github.com/uptake/autofocus) used by the Chicago zoo to operate camera traps. Could be useful for you too!

omg please make this project haha I love this - we'll make it a project highlight on our twitter @lobe_ai! And be a hit on our subreddit https://reddit.com/r/lobe

There are commercial "puffers" that work by presence, no need for OpenCV

But they puff for any motion, like, if you get in the way.

Tried that. It hit us far too often.

The cat invades the same counter space where we cook and do, well, everything.

I would love to see a video of that!

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