Circuit Break Podcast #420: The Mega IIe: A Vintage Computing Adventure with James Lewis

Podcast Title: The Mega IIe: A Vintage Computing Adventure with James Lewis

Release Date: 2024-03-05

Episode: #420

We dive into the intricate world of vintage computing with James Lewis, aka the Bald Engineer, who takes us through the journey of constructing a functional computer based on the Apple II GS’s Mega II chip. He shares his nostalgic connection to the Apple II series, revered for its open design and pioneering hardware engineering. Our conversation spans the detailed architecture and challenges of his Mega IIe project, from initial concepts to the complexities of integrating modern microcontrollers like the RP2040 during pandemic component shortages. Tune in for a fascinating journey from the past to the future, bridging vintage computing with modern technology!

Podcast Audio:

Podcast Notes:

:rotating_light:**Contest Announcement** :rotating_light:: Introducing a new Circuit Break contest! This contest is themed around building food-related electronic projects. We’re offering over $5,000 in cash prizes, themed trophies, and free prototyping from MacroFab. The deadline to submit is March 31st, 2024. Thanks to Mouser Electronics for sponsoring the contest prizes!

Discussion Highlights

  • The Mega IIe Project: James built a functional computer around the Mega II chip from the Apple II GS, containing the logic of previous generations of Apple II computers.
  • Nostalgia for the Apple II: James shares his personal connection to the Apple II, and explains why the Apple II is revered in the vintage computing space, particularly for its open design and hardware engineering aspects.
  • Technical Deep Dive into the Apple II and Mega IIe: James dives into how Apple II’s open design compares to other computers of its era such as the Commodore.
  • Bit Preserve Project: His GitHub project, Bit Preserve, is where people can contribute redrawn vintage computer schematics in KiCad.
  • Architecture and Development of the Mega IIe: James outlines the evolution of the Mega IIe project from a simple breakout board idea to a complex design involving multiple boards, fly wires, and the use of modern microcontrollers like the RP2040 due to component shortages during the lockdown period.
  • Debugging Challenges: Difficulties encountered when integrating components and understanding undocumented features, such as the keyboard signals and slot communications.
  • Design Approach (Rev 2): A backplane system where individual blocks of the Apple II design were isolated into separate cards, allowing systematic troubleshooting and incremental progress, which significantly facilitated debugging.
  • Video Signal Processing: Explored the challenges and solutions in handling video output, particularly transitioning from composite video to digital video using the Mega II chip’s RGB output.
  • Rev 3 Development: The transition from a modular backplane system (Rev 2) to a single board computer (Rev 3), consolidating all functions and addressing issues like power supply design.
  • Future Directions and Learning: Reflects on the initial underestimation of the project’s complexity and duration and discusses potential next steps, including the possibility of a shift in focus towards modern technology areas like machine learning for edge devices.

Relevant Links

Here are some pictures I mentioned.

Rev 1 “Booting”

Rev 2 with Digital Discovery attached

Rev 3 PCB w/ SMPS (rev 2)

That rev 1 is even more of a glorious mess then I even imagined it would be!


And, remember, it passed the Apple IIe ROM’s built-in self-test. Somehow!

@baldengineer James, in regards to potential documents buried in Apple’s internal archives. Admittedly I am unfamiliar with the internal machinations of huge companies, especially one like Apple. But it doesn’t seem unreasonable to at least ask if such documents exist and if so, could they be released. I might see how something like the source code for very old OS or applications might still be held very close to the best and unfit for public consumption. But one could reasonably think that a data sheet for a long-obscure custom IC would be far less worrisome.

Is there any way you (or your inside friend) could formally request that this internal archive be at least searched to see whether such a data sheet exists at all? The mere fact that the datasheet does or does not exist shouldn’t itself be a sensitive matter at all. Whether such a data sheet could be released if found, now that’s another matter. But it seems on the surface that just asking “does it exist in your internal archives” shouldn’t be a big deal. But I realize big companies don’t always operate logically.

Great work!

As with any large organization, it isn’t clear who to contact.

And with Apple, the layers of obscurity are extreme.

My contacts (more than the one I vaguely referred to) are unwilling to risk their jobs by upsetting the wrong person/manager/group by asking questions about a silly project,

So, I will respect that.

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Understand. I can’t imagine working in an environment where just asking such a question would be perceived as risking your job. Hope this is just an Apple thing and not an industry trend.