Sławek Zegar's CA80 Is an RCBus-Compatible Clone of Stanisław Gardynik's 1980s Polish Kit Computer

Maker and vintage electronics enthusiast Sławek Zegar has designed a functional clone of a classic of Polish home computing, the Zilog Z80-based MIK CA80 — a multi-board RCBus design with flash storage and a display and keyboard from an upcycled calculator.

"When I was a teenager, the CA80 computer was created. Under the supervision of my teacher, I made my first copy of it. I only had the motherboard, and I drew the display in the same way as technical drawings — with ink. In the early 1980s, [the CA80] was the only option to have your own computer," Zegar recalls. "At school we used an even older SA80, constructed by the same engineer: Stanisław Gardynik."

Gardynik's SA80 and CA80 designs were built for those unfamiliar with both computing and electronics, and centered around the VEB Mikroelektronik "Karl Marx" Erfurt U880 — an East German clone of the Zilog Z80. MIK's kit-form version of the CA80 went on sale in 1984 with booklets designed to guide the reader through the assembly and core electronics and computing concepts — while a 1990s re-release placed the device in a calculator-like housing with dedicated keypad and display.

"I designed the CA80 [clone] from scratch," Zegar writes. "Initially, I used SMD, but I changed the assumptions and adapted the project to RCBus [as used on the RC2014]. I used the Z80-MBC2 project and with its help I developed an additional data loader. I also made an additional mass memory module that stores programs in flash memory. The data format is compatible with that recorded on the tape recorder. LCD 2004 modules and a touch keyboard were also created. I also have a VFD [Vacuum Fluorescent] display and a keyboard from an old calculator."

Rather than keep the device to himself, though, Zegar has released the design files and source code under the permissive MIT license — allowing others to build their own CA80 compatible. "All programs written for CA80 in accordance with Mr. Stanisław Gardynik's recommendations should work," Zegar says. "In the minimum version, 2kB EPROM and 2kB RAM are enough, but it is optimal to use the full 64kB RAM."

More information is available in Zegar's Hackaday.io page, while the project's source files are available on GitHub; a deeper dive into the project is available on Zegar's blog, in Polish.