Photo: Justine Haupt (Sky’s Edge)Haupt’s original rotary cellphone was created with an open source design that allowed anyone to build their own, with firmware, build notes, and even the 3D ...

The trickier part was getting the original bells to work — in North America, it takes up to 90 VAC to get a phone’s ringer going, which is quite a bit more than the lowly Arduino can handle.