Another approach, though I am sure PETA and fish lovers would call me evil, buy another fish if this one happens to die while I am on vacation. For the cost of the various hardware and time, a lot of replacement goldfish could be bought.
Given the relative complexity of the system, it seems that there could be some alternative approaches that would be simpler and more reliable, and probably take up less space. For monitoring the temperature, a thermometer stuck to the far side of the tank could allow temperature checking as part of the video monitoring procedure. And with the price of cameras being quite low, multiple cameras would eliminate the need to have a moving platform and all of that control and drive hardware. The automatic feeder would still be a challenge and I can't offer much of a suggestion without understanding a lot more about how it is supposed to function.
Of course I realize that the whole project is designed to be an interesting writeup and so it had to include the various systems. But sometimes there is a simpler and more reliable way to do things, often without needing to include an Arduino.
I wonder if the people who built the Toyota Highlander aquarium (which we wrote about recently) need an automatic fish feeder. Seems like a natural for a bunch of fish sitting around a tank at a trade show.,
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