Tag: published design

Published twelve-chip Motorola 6800 teaching coprocessor that takes control of the Apple II bus.

This is a published construction project, not a current kit or finished product. The paper supplies a circuit diagram and tested monitor listing but no PCB layout, Gerbers, bill of materials, or explicit reuse license. A builder must recreate the board, source period logic, program a 2716 EPROM, and validate timing and bus loading.

Published 1985 Apple II coprocessor prototype with a 68020, optional 68881, 32K SRAM, and boot EPROM.

Treat this as a historical experimental build, not a safe drop-in design. The creators used custom wire-wrapped and insulation-displacement construction rather than a published PCB. Later design notes estimate roughly 1 A typical and as much as 1.5 A from +5 V even though the Apple II specifies 500 mA shared by all peripheral cards, and they identify excessive data-bus loading. A faithful build needs its own engineering review and likely a redesigned power and bus interface.

A buildable C128 and IBM CGA digital-to-analog video adapter with RGBS, RGBHV, and Commodore A/V pass-through options.

The repository publishes KiCad sources, Gerbers, a BOM, and printable cases for revision 1.3. The maker tested RGBI, composite, S-Video, audio, and GBS-Control output; revision 1.3 corrects the earlier monochrome pass-through error. This is not a scan converter. Use a compatible 15 kHz path such as GBS-Control or a suitable SCART converter. Never connect the C128 A/V power input and the external barrel power input at the same time. The maker found an ordinary SCART-to-HDMI box unstable in one 80-column game while GBS-Control remained stable.

Adds MIDI In, Out, and Thru, RS-232 communications, programmable flash, and UltiMem-compatible RAM expansion to a VIC-20.

The RETRO Innovations store exposed an Add to Cart path at USD 65 on 2026-07-28, although its current-stock field was blank. No enclosure is included. Supply a 5-pin DIN MIDI cable and use the downloadable VIC-MIDI software; the project page also publishes EAGLE 6 design files and a bill of materials.