Track Your Cat’s Weight Through This Internet-Connected Litter Box

A wooden platform for a litter box

With feline obesity on the rise, keeping track of your cat’s weight is an important part of keeping them healthy. However, a weighing session can be anything from a routine job to a painful procedure, depending on your cat’s temperament. [Andy]’s cat Ellie is one of those who dislike being weighed, so in order to track her weight without drama [Andy] got creative and built an internet-connected weighing platform for her litter box.

The platform consists of two pieces of MDF held apart by two load cells, which are hooked up to an ESP8266. The ESP reads out the load cells and reports its findings to the Adafruit IO platform through its WiFi connection, sending updates to [Andy] whenever litter box use has been detected. The cat’s weight can be simply calculated by subtracting the weight of the unused litter box from the weight measured when it’s in use.

A smartphone pop-up message from an IoT litter boxGetting reliable readings from the load cells was a bit of a challenge, since the measured weight fluctuated wildly as Ellie moved around the litter box. A combination of waiting for the readings to settle and using timeouts to discard the effect of brief movements resulted in reasonably stable measurements. The resolution was even good enough to measure the difference in litter weight before and after use. We’re not sure what’s the practical value of knowing how much your cat poops each time, but if the data is there you might as well log it.

[Andy] also imagines smart-home features of the IoT litter box: for example, he could run an air purifier or send in the Roomba after heavy usage. This is not even the first internet-connected litter box we’ve featured; we’ve seen one connected to the Thingspeak platform, as well as one that sends poop alerts through Twitter. If you’re not around to clean up the mess, an automatic fume extractor might come in handy.

26 thoughts on “Track Your Cat’s Weight Through This Internet-Connected Litter Box

  1. Ooo, she’s a big girl! I have a question though, after he changes the litter how does he tare the weight (set it to zero)? As for knowing how much she “deposits” in the litter can be an indication of health problems, for instance if she uses the box multiple times but doesn’t poop she may be constipated or be having urinary tract problems, this stuff is good to know. One more thing, my vet used to weigh cats by simply weighing himself, picking the cat up in his arms, weighing both of them and doing the math, easy method if you need to weigh your cat really.

    1. Hi,

      I set the litter to automatically tare when not in use. The sensors are subject to drifting somewhat over time so I needed to correct for that. If a small weight is added or removed from the litter, but not enough that it could be a cat, it zeros the scale after a couple of seconds. That way after cleaning / raking it resets itself.

      I also added a timeout, so if a larger weight is added (like replacing the whole litter bed) if it sees no movement after a while it concludes it’s not a cat and tares to that new value.

      The pick up and weigh method is a system I’ve used with other cats, but Ellie is extremely nervous. She’s learned to trust me, but really hates being picked up. While it’s possible to just sort of grab her, it’s not a nice experience for her, so I try and avoid doing it too often.


      1. Oh, automatic taring, I should have known considering the quality of the build.

        “but Ellie is extremely nervous.”

        OK, it’s better not to stress her out if she’s nervous. I’ve got to day this is a really cool, I’d buy one if I had a cat right now, nice job (and nice cat, she’s a big girl but cute.)

  2. If you’re one of those people who likes programming the microcontrollers and hate the construction, or feel useless at it… you might consider adapting a Wii Fit board, which I still frequently see around at used/thrift stores. Then you just have to hook up to the cells in that by expedient means, find a space to glue your board inside there and set the litterbox on top of it.

    1. Oh, there’s been work done on Wii Controllers to use them with anything that speaks Bluetooth, so maybe you don’t necessarily have to mod a Wii Fit balance board, only use a bluetooth aware gizmo to snarf the data. Might need to be making a dummy battery and wall adapter for it. With stock hardware though I think some means of making sure it stays on will be required.

        1. Long ago, I wrote some code for my university because they needed the Wii balance board to chat with Matlab or Octave. Unfortunately, I wrote it on their computer and the library we modified seems to have disappeared.

          The changes, though, were not much. If you can get your device scanning Bluetooth frequencies, you are very close. If you adapt n existing library, (like those found here ) then be aware that the Balance Board did have a different range of MAC addresses than regular wiimote, or that it can be identified by the “friendly name” field in the HID packet.

          For how to handle the raw bits :

          Some libraries also limit use of the Wiimote reports an unknown attachment (the board is conceptually a wiimote with a specialized nunchuck) so make sure the library isn’t throwing out a valid device because the ID in register 0xa400fe is unexpected.

  3. On the subject of wee controllers, the weight measurement does not distinguish between #1, #2 and kicked-out litter so it’s not clear what it is that you are measuring. A good amount of litter gets kicked out onto the floor even with a cover, and they track litter out between their toes. Some cats bolt out of the litter box like it’s a 100 yard dash and the litter goes everywhere! We have a special mat in front of the litter box that supposedly helps get it out of their toes, and it’s pretty horrifying how much it collects.

    If you want to weigh your cat, get a baby scale. It only takes a second and the cat probably needs some attention anyway.

    1. Well, you know that the weight has stabilized at a value, whatever the breakdown of that mass is. And you can then recognize the magnitude of the disturbance created by the addition of cat.

      Few people would find precise data about the weight of the type of their pets leavings, or how many grams of litter were carelessly ejected from the box by your overzealous feline. but tracking your pet’s weight and adjusting feeding quantity and schedule makes you a better pet owner.

      You’re right that the system can’t tell you those things, but I question why anyone cares about them. The important data is there for accurate collection. Products on the market use the same technique for measuring and logging weights, even for multiple cat households.

      1. Depending on the sample rate of the load cells, and looking in the noise band, it should be possible to distinguish between single plops (#2) and fast waterjet-like vibrations (#1). With enough samples should be possible to train a neural network to classify what is the content of the gift.

  4. “We’re not sure what’s the practical value of knowing how much your cat poops each time, but if the data is there you might as well log it“

    The root cause of many privacy disasters.

  5. If your cat’s output (liquid and solid) increases a lot, it may have diabetes.
    It’s the body’s way of trying to get rid of excess sugar in the blood.
    The cat will also eat & drink more than usual.

  6. Or you could just put a cardboard box on a scale and wait for your cat to jump in the box, which he or she will invariable do. Subtract the weight of the box and you have an accurate measurement, no sensor-building, coding text notifications or adjusting for movement/poop weight needed.

    Almost every cat-related issue can be solved with boxes.

    Cat won’t leave you alone while you work and insists on sitting on the keyboard or blocking your view of the monitor? Put a box beside the computer, close enough so your cat gets the proximity to you she wants, and you can reach over and scratch her head occasionally.

    Cat drives you crazy at night and interrupts your sleep, but won’t stop meowing and scratching at the door if you kick him out of the bedroom? Put a box on the night stand with a towel or blanket inside.

    Cat won’t get out of your way while you sweep or mop the floor? Put a box down and toss a treat or two inside.

    1. The desk cardboard box truck has made working from home 100x better for me. Grace hops up, gets brushed in my morning stand-up, and goes to her box for a nap.

  7. I bought a PetKit Cura X, one of their “used” models that was steeply discounted and almost certainly a 30-day-guarabtee returned unit from a pet owner with cats that were terrified of the new spinning bathroom automation… Understandably so.

    But for my cats it has been excellent. It even has a mesh nebulizer and reservoir of “purifying liquid” that it fogs into the waste collection bin after cleaning cycle to attempt to sanitize the litter waste.

    I haven’t had to scoop the box once since buying it. The collection tray requires emptying and trash bag replacement twice a week with two cats. Their special bags are not offensively overpriced. It works with any litter type as long as it clumps. It actually has cut litter consumption in half, because the waste has much less time to soak in and contaminate otherwise clean litter around it.

    It recently has had app and firmware updates that have allowed it to identify which cat is using it, by their weight. And tracks, plots their weight change over longer time periods. It has been pretty reliable.

    I don’t like the smell of their “purifying liquid” so I don’t buy the refills. I did add a nearly silent ducted 110V “muffin fan” extractor to maintain a slight airflow into the litter tray and then put the window. 3D printed duct adapters for into the existing handle opening at the upper rear of the unit. I ought to upload them for others to use, the extractor fan seems to work really well. I never smell the litterbox, even though it’s in the living room.

    1. God forbid it should also clean the litter if there was a raccoon or ferret present. Where’s the machine learning cuda cores to visually verify it IS a cat!!! :-D

  8. You don’t exactly get the cats weight. You get the cat’s weight plus the offering to the litterbox. Next time it get in the box you should have an idea of it’s weight and you could figure out the weight of the last offering. I think you have wayyy to much time on your hands..

    1. Actually, if you can constantly track the a amount your cat urinates and defecates as well as it’s weight, you can recognize the first signs of illness before it becomes critical and get treatment before it’s too late.

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