Hackaday · Creativity & design

ZX81 Expansion Card Reimagined

A new project, OpenSpand, combines numerous ZX81 expansion functionalities into a single unit, addressing the cost limitations of original add-ons for 1980s users.

The original ZX81 was known for its minimal hardware, featuring a Z80 processor, 1KB of RAM, and basic interfaces. This limited its capabilities, and expansion cards were often unaffordable for users at the time.

OpenSpand, developed by [adam.klotblixt], integrates multiple desired expansions. It offers user-configurable RAM up to 64KB, SD card storage that hijacks Sinclair BASIC's LOAD and SAVE commands, high-resolution graphics, emulated sound, a joystick port, serial ports, selectable ROMs, and composite video output.

The expansion unit utilizes an RP2350 microcontroller to emulate the ZX81's original components. The microcontroller disables the onboard RAM and ROM, emulating them due to the significant power difference compared to the Z80 processor.

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