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