Don't shoot the nuclear weapons
The Saturday was a Legends of Tomorrow-esque setup with the players travelling through time to chase down a temporal conspiracy. So we had a Victorian military demonstration, 70s CND protest and 23rd Century spaceship launch in one story line.
Games like this often need props and I volunteered to make something. As part of the 70s section I ended up putting together a 'suitcase nuke', the sort of thing beloved of 90s action movies. The game organiser built a WWI tank and replica of the HG Wells time machine out of wood, carpet roll tube, random household junk and Correx sheet. I got the easy job.
This prop is a big pile of old-school Arduino stuff: a matrix keyboard, hand-wired LEDs for the 'plutonium core' and a 32x8 LED matrix driven by MAX7219 chips to show the countdown timer on. All housed in an equipment case a friend gave to me and accessorised with some 3D printing. It was a bit last minute and I made a deliberate effort to use up a bunch of stuff that was sitting in my storage boxes. The only thing I spent money on was a sheet of MDF and some spray paint.
It does the LED countdown thing and if you unscrew the display it conforms to the "help I'm being disarmed" trope of the counter speeding up, but you can quite easily switch it off.
It was quite a simple from a technical perspective but good fun in the game and there's plenty of scope for it to be re-used.