• A first run at design and challenges

    WJCarpenter • an hour ago • 0 comments

    • I already have lots of smart home doodads with Home Assistant, so I probably want to be able to integrate the solution to HA somehow.
    • There are plenty of cheap electronic scales available at various prices, but I think I can get away with something under US$20.
    • For slightly more money, there are "connected" smart scales, almost all of which use Bluetooth to talk to a companion mobile app. A Bluetooth proxy can feed that info to HA if the underlying conversation is documented or has been / can be reverse engineered.
    • The OpenScale project has already done a lot of work reverse engineering Bluetooth protocols for smart scales. They also have an example of reverse engineering a non-Bluetooth scale and sending its reports using a small add-on processor.
    • One special requirement of putting the scale under the litter box is being able to get a tare weight so we can calculate the weight of just the cat. The tare weight changes as the litter is scooped clean daily and occasionally replenished.
    • I've seen two types of triggers for electronic scales. One type requires touching a button with a toe to turn the scale on. That obviously won't work for this scenario. (Our cat is not that trainable.) The other type turns on automatically when some amount of weight is put on it. That's great for getting the gross weight of the litter box plus cat, but it doesn't help for the tare weight problem. That leads me to think I'll need to go down the path of a custom hardware interface to the scale so that I can get the tare weight when the scale is idle.
    • One of the things I don't know is how the constant weight of the litter box might affect the scale's measurement accuracy. I've got my fingers crossed that it either doesn't complicate things or any complications can easily be overcome.
    • Electronic scales are almost always battery powered, and the batteries last a long time for their normal use case. I expect that will be thrown out of whack by the extra hardware interface components. I think I'll have to either add a bunch of extra batteries or draw mains power (probably via a USB charger). I don't think either of those will be an especially big problem.