things to investigate, try, and learn from, like quests but smaller

how to number buildings on streets with one sequence across all streets? probably a space-filling curve

detailed analysis of subset shuffling algorithms

how many distinct languages for DFAs of a given size?

find real, popular programming languages that are primitve recursive, or perhaps are so after excluding some obscure features, of which jq seems a candidate

USB port, HDMI port, etc on a laptop that can switch between server/client mode, so that you could reuse the keyboard, trackpad, display, etc in a laptop as USB peripherals on another device

do circles always project to ellipses?

why the plastic slip in that light trinket?

how do rotary encoders work?
bounded-range potentiometres are easy, abs-rotation encoders (lose direction) are easy
one approach: turn a permanent magnet next to a coil next to an ammetre (Lenz's law)

derive magnetism from relativistic electricity

any hazards in excessively looking at polarised light?

polarisers and liquid crystal for solid-state window shades