Electronics
I was once, at one time, aspiring to be an electrical engineer. Then I discovered analog circuit analysis. While I avoid the analog world to the best of my ability, sometimes there's fun to be had crossing from analog to digital and back. Here's that stuff.
Old is new again, but not. But also new. Clock stuff.
The sun is good for more than just the continuing misadventures of the human race. It's also good for powering neat stuff.