mudmin / backbit-opensource

Open Source Hardware for Vintage Computers

Open Source Hardware for Vintage Computers

Developed by BackBit (http://backbit.io)

These are some hardware devices that I use for my vintage machines. I used to sell some of these, but I no longer have the bandwidth to build these specfic items so I have made the designs open-source. Designs may have been derived from various information I scrubbed from the internet, but layouts are my own. Feel free to make your own builds, modifications, or to ask me questions about how to build.

Atari 520ST/1040ST (4MB internal upgrade)

• Details: Expands 520ST or 1040ST to maxmimum 4MB RAM.
• BOM: 2x SMT MSM5118165F-50TK, 2x SMT 0.1uF ceramic capacitors, 1x 33Ω THT resistor, 2x 66Ω THT resistor, round header pins, 16x 16P 0.3" sockets, 4x bodge wires.
• Installation: Mount sockets on main board, route bodge wires. Plug memory board into sockets.

Commodore 64/128 Diagnostic Harness: Keyboard Loopback for 128/128D/SX64

• Details: Provides a keyboard loopback for C128, C128D, and SX64 machines to peform full diagnostic tests
• Note: there are two ways to build --- a reversible C128/C128D loopback, and a SX64 loopback.
• BOM (128/128D): DB25 - male & female connectors (with screws removed), 1x #6x1/2" brass screw, E-Switch LC2259EENP DPDT switch, E-Switch 1SBLK switch cap
• BOM (SX64): DB25 - male connector with cover removed
• Instructions (128/128D): Print Keyboard128 case. Solder DB25 male connector to "DB25-M(8)" side and DB25 female connector to "DB25-M(X)/F(8)" side. Solder DPDT switch.
• Instructions (SX64): Print KeyboardSX case. Solder "SX64 enable" blob. Solder DB25 male connector (w/ cover removed) to "DB25-M(X)/F(8)" side. Attach to case with super glue, with 13-pin side closer to handle, 12-pin side away from handle.

GenAssister for (Sega Genesis joystick switcher for Commodore 64/128)

• BOM: 1x SMT ATF1502ASL-25AU44, 1x APEM MHS233 switch, 2x Amphenol LD09S13A4GX00LF DB9 port, 1x Amphenol LD09P13A4GX00LF DB9 port, 1x NE555 SOIC-8, 1x 10Kx7 resistor network, 1x 3mm Red LED, 1x 3mm Yellow LED, 1x 220R resistor, 1x 330R resistor, 1x STX-3000 TRS jack, 1x 100mA polyfuse, 1x 471 SMT capacitor, 7x 100nf SMT Capacitor, 2x 10K SMT capacitor, 1x 15K SMT capacitor.
• Installation: Program CPLD w/ ATDH1150USB programmer.

IBM PCjr (512KB sidecar expansion)

• Details: Adds 512KB, expanding total system memory to 640KB (if you already have 128KB internally).
• BOM: 1x THT AS6C4008-55PCN/PIN, 2x THT 0.1uF ceramic capacitors, 1x THT 10uF electrolytic capacitor, 1x THT 74LS151 logic chip, 2x30P 2.54mm female header.
• Installation: Plug sidecar into side of machine.

Korg 01/W LCD Fix

• Details: Adapter to fix the contrast when replacing the Korg 01/W LCD with a modern LED replacement

Plaster 64 (PLA replacement for Commodore 64)

• Details: Replaces MOS 906114 with exact equations used in original device
• CAS delay: Improves compatibility on some systems.
• KERNAL Mode: Switch allows BackBit cartridge (any maybe others) to replace KERNAL ROM.
• Private Eyes Mode: Switch sets bus high to facilitate in-circuit testing.
• BOM: SMT ATF1502ASL-25AU44, 3x 2.54mm DIP switch, 28x header pins, optional 28P socket, and parts assembled on bottom of PCB listed in parts folder.
• Instructions: PCB requires SMT assembly.
• Installation: Program CPLD w/ ATDH1150USB programmer.

PLAster 128 (PLA replacement for Commodore 128)

• Details: Replaces MOS 8721 with exact equations used in original device
• Compatibility Mode: Switch allows cartridges to work in FAST mode.
• KERNAL Mode: Switch allows BackBit cartridge (any maybe others) to replace KERNAL ROM.
• Private Eyes Mode: Switch sets bus high to facilitate in-circuit testing.
• BOM: XC9572XL-*VQG64C, 3x 2.54mm DIP switch, 48x header pins, optional 48P socket, and parts assembled on bottom of PCB listed in parts folder.
• Instructions: PCB requires SMT assembly.
• Note: There is very limited height inside the C128 and you may want to modify this design to use Flip Pins (http://oshchip.org/products/Flip-Pins_Product)
• Some research credited to: https://c128.se/posts/silicon-adventures/

Tandy Color Computer 3 (512KB internal upgrade)

• Details: Expands base model's 128KB to 512KB. Timing window is very narrow. RC delay accomodates SRAM to work in place of DRAM.
• BOM: 1x SMT IS61C25616AS-25TLI, 1x SMT ATF1502ASL-25AU44, square header pins.
• Installation: Program CPLD w/ ATDH1150USB programmer. Remove existing RAM chips, plug memory board into expansion headers. Optionally remove ceramic caps C65 and C66.

Texas Instruments TI-99/4A (32KB sidecar expansion)

• Details: Fills in the system's memory map to get the maximum non-bankswitched RAM expansion. No pass-through port in this design. Need to add JTAG header if you don't have a programmer with a socket.
• BOM: 1x SMT CY62256NLL-70SNX (SOP-28), 1x SMT ATF1502ASL-25AU44, 5x SMT 0.1uF bypass capacitors, 44P 2.54mm edge connector.
• Installation: Program CPLD w/ ATDH1150USB programmer. Plug sidecar into side of machine.
• Case: https://www.printables.com/model/301498