Instead of going with silicon-based switching (ie: transistors) this 4-bit adder uses mechanical relays. We like it for its mess of wires (don’t miss the “assembly” page which is arguably ...

[Nakazoto] built a 10-bit binary adder with relays. The build is designed from the ground up, including the PCBs, which are milled using a CNC machine. There are six boards: the input board ...