EP#420: The Mega IIe: A Vintage Computing Adventure with James Lewis

Circuit Break - A MacroFab Podcast

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!

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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:

• Bit Preserve (Vintage Schematics in KiCad)
• 1st Video: Mega II video: Getting it to boot
• KansasFest 2022 Talk (before Rev 3 worked)
• 2nd Video: Getting to the first done
• Mega IIe Github
• Mega IIe Twitch Archive (hundreds of hours of content!)
• Circuit Break #411: Entropy rules everything with James Lewis
  • Reliability and component aging effects
• Circuit Break #222: Turning It On - New Design Checklists with James Lewis
  • Testing and validating PCB assembly design
• Circuit Break #141: James joins us to talk about ceramic capacitors

About MacroFab:

This show is brought to you by MacroFab, which provides a platform for electronics manufacturing services (EMS), hardware development, designing and prototyping for individuals, startups, and businesses. Key MacroFab services include PCB (Printed Circuit Board) fabrication, assembly, and testing. Customers can use MacroFab's platform to upload their PCB designs, select components, and specify manufacturing requirements.

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