Grant Searle’s web content provides detailed instructions and history behind building your own ZX80/ZX81 computer using off-the-shelf components. The page, online since 1996, features accurate schematics for building the classic machine. A major highlight is the NMI generator that, when combined with the ZX80 circuit and ZX81 ROM, creates a fully functioning ZX81 computer. The page offers in-depth information on circuit operation, PCB foil layouts, component positioning, and construction methods. Notably, the ZX80 was chosen for its simplicity and nostalgia, capturing the essence of early home microcomputers. Building your own ZX80 is a challenging project recommended for hobbyists with technical knowledge.
http://searle.x10host.com/zx80/zx80.html