A couple of weekends ago I found myself in conversation with Jon, my brother-in-law, a vintage game systems collector and proud owner of an Action 52 cartridge, about NES controllers—specifically, how all eight buttons can be crammed down only seven controller pins (a trivial setup would require nine). I just happened to know most of the mechanism already and gave him the surprisingly simple rundown. I got curious about the parts I didn’t know, so here’s a digest of my research.