A good month ago I was contemplating what to build next...
I had just finished building an 8-bit CPU on a breadboard - thanks to Ben Eater's amazing teaching skills - and figured I could step it up a notch.
That's when I came across the other Ben's (Heckendorn) videos on him building an Apple 1 on a piece of perf board and my new goal had been set: to build myself an Apple 1.
I started by researching the resources Ben Heck had left behind, which was mainly based on Briel Computers' Apple 1 Replica project.
During that research I began creating a new circuit diagram for my own build.
Starting a new circuit from scratch really helped me understand every aspect of the computer. That and troubleshooting it with my oscilloscope and logic analyzer once I put everything on a prototype board.
Once the prototype was functional, I decided to produce one (inefficient) PCB to verify my circuit diagram was correct.
The result of that first PCB (revision 0) can be found in the gallery; it's a rather large board, but works exactly as I hoped!
What I have so far:
- 6502 CPU with 6821 PIA, 8 KB (EEP)ROM and 32 KB RAM
- ROM containing BASIC, Krusader and WozMonitor
- Firmware running on an Arduino that provides serial communication between the computer and an external terminal client (PuTTY, for example)
- The firmware mimics Apple 1 visual representation (only uppercase, blinking "@" as cursor)
I intentionally started with a board that does the bear minimum; run 6502 code and provide serial communication.
The idea is that the computer is expanded in the future by adding boards on top of the main board using the expansion header.
What I have planned for this project:
- Produce a smaller PCB that is easy to fit into a casing.
- Create one or more expansion boards, for example to provide an interface for a monitor and keyboard so the computer can run standalone.
- Create a modular casing from laser cut pieces. Modular in the sense that it can fit just the main board, but the casing itself can be expanded (using interlocking tabs) once expansion boards are added.
- And most importantly: release the computer as DIY kit, in different variations!