Recently people repeatedly mentioned relay computers. There is a very nice 8-bit relay computer implementation by Joe Allen. The computer looks and feels like the microprocessor trainer boards of the 70s. The CPU is implemented in 83 relays. Memory, front panel interface and serial port are implemented in a MicroChip PIC and a few ICs. This is a fully functional computer with a well thought out instruction set.
Here is a link to a YouTube video showing the relay computer in operation: https://www.youtube.com/watch?v=k1hJoalcK68 Here is the SourceForge project page: http://relaysbc.sourceforge.net/ Joe used to sell the bare PCBs with programmed MicroChip PIC on Tindie and Ebay, but it seems he no longer has any PCBs left. Here is the Tindie link: https://www.tindie.com/products/jhallen/single-board-relay-computer/ Enjoy! Tom
