The Z80 8-bit microprocessor designed by Zilog and launched in July 1976 has just turned 50 years old last month. The Z80 was widely used in home computers (TRS-80, ZX Spectrum, Amstrad CPC, Coleco Adam, MSX), video game consoles (ColecoVision, Sega Master System, Game Boy, Game Gear), CP/M systems (CompuPro, Kaypro, Heathkit/Zenith, Osborne) and many arcade machines.

Ever since I saw Grant Searle's CP/M on a breadboard, I've always wanted to design and build my own homebrew Z80 computer. Unfortunately I knew nothing about the Z80 microprocessor, or designing a homebrew computer, or PCB design, and my basic electronics knowledge and soldering skills were rusty having not used them since college. I have been reading up, watching YouTube tutorials, learning KiCad and hoarding obsolete parts, and now after the Z80 microprocessor's 50th year anniversary, I think it's time I finally complete the design and build of this computer.

The question I have been asked often is why another Z80 homebrew computer?

• For nostalgia, my first computer was a ZX Spectrum.
• To re-live the homebrew microcomputer revolution with a Z80, BASIC and CP/M.
• To re-live the 8-bit gaming revolution as ColecoVision, SG-1000 and MSX all have a similar simple design that can be built using off-the-shelf components.

Being a total noob, the goals for this Z80 SBC are:

• Start with the simplest established circuit that runs BASIC and CP/M: Grant Searle's CP/M on breadboard.
• Extend it to support 512K banked RAM and 512K banked ROM and make it compatible with RomWBW.
• Limit design to 100mmx100mm 2-layer PCB with through-the-hole components for easy production.
• Provide expandability with a RCBus expansion bus to leverage the many RCBus designs available online.
• ???
• Profit?

This build log will document my journey from creating a simple Z80 tester to a full-blown homebrew Z80 computer running BASIC and CP/M.