Cambridge-1 is a 4-bit homebrew 7400-based CPU
Richard of ARITH-MATIC had the idea to build a 4-bit computer based on 7400 series ICs (like the 74HC273, 74HC193, and 74HC125), but other responsibilities got in the way of this becoming a reality for quite some time. Finally, with the Retro Computer Festival at the Centre for Computing History in Cambridge, England held earlier this month, he went ahead and started the project in hopes of creating a working CPU in under 30 days.
The resulting homebrew computer is known as the ‘Cambridge-1,’ comprised mostly of 7400 series ICs, wiring, and an SRAM chip for storage carefully arranged on a set of breadboards. In addition to the other components, an Arduino Micro is also implemented. While not technically a retro device, the Arduino allowed him to “change the control logic on-the fly,” and gave him the flexibility to finish the project in his compressed time scale.