You don't need a computer to turn on a light in the same room. you don't even need digital electronics.
But I'm learning a whole lot of neat stuff in the process. I've spent my entire professional career in software, dealing with hardware only at a high level. So this kind of low level stuff - wiring, soldering, etc - is new to me and something I've wanted to really dive into for awhile.
The point of the exercise is not because the cats need feeding, or that I couldn't buy a programmable feeder already on the market. It's a pretext to learn a new skill and actually create something physical that I can interact with. So much of what I do every day is ephemeral - it exists and bits stored on various computers. This will be something that I can touch and see and interact with. I can look at it and say, "I made that, hardware and software."
And my cats will be happy too. :)
I'd like to find a nice big & cheap auger that could pull or push to dispense, and have a lot more control.
The other suggestion someone made was a hopper with a close-toleranced vibratory table/spout to bounce the appropriate amount out.
All this assumes you want arbitrary duration/portion dispensing, otherwise you just need N bowls, and a rotary cover that opens each at a set time (which is most commercial ones I've seen).
Mine current design will allow some level of arbitrary feeds and duration.
My current plans call for a sealed rotating drum with an opening that contains ~1/2 cup of kibbles, so each spin of the drum will dispense that much. Using door brush to seal around the bottom of the hopper and the drum to keep kibbles from escaping. The servo will rotate it from 0 to 180 and back, allowing the kibbles to fall down a small ramp and into the bowl. My concern with this design is that I may not be able to rotate the drum fast enough, but I'll see if that's an issue when I get there.
Just spin it X times for X/2 cups of kibbles. I figure 1/2 a cup is good resolution for a home project.
(Not to mention the Rube Goldberginess of needlessly using wifi when you could use a few million fewer transistors on existing wiring.)
100W * 5% * 24 Hours = 120Wh
1W * 24 Hours + 5W * 5% * 24 Hours = 30Wh
So it does depend on the duty cycle - As long as the 5W lightbulb with a 1W computer is used less than ~19 hours a day (80%) you'd still have savings:
1W * 24 Hours + 5W * 80% * 24 Hours = 120Wh