Jim Shortz Reinvents the Game of Simon, with the Aid of an Intel SDK-85 1970s Single-Board Computer
Having found an old Intel 8085 demonstrator at a ham meet, Shortz set about designing a daughterboard for a classic memory game.
Tinkerer and vintage technology enthusiast Jim Shortz has built a home-brew implementation of classic 1970s memory game Simon — using a period-appropriate Intel SDK-85 development kit, bought at a ham meet.
"A few weeks ago, I found an Intel SDK-85 Single Board Computer [SBC] at a ham-fest," Shortz explains. "I am a sucker for anything with a keypad and 7 segment displays. Having had a Heathkit ET-1 disappear in front of me, I made sure to act on this one as quickly as possible. I didn't even know what it was, but I knew I needed it. It's an Intel 8085 hardware/software development kit from the late 1970s. It's aimed at the hobbyist/education market. It sports a fine manual, generous 36 GPIO [General-Purpose Input/Output] ports and a meager 256 BYTES of RAM."
The Intel System Development Kit 85 (SDK-85) was released in 1976 as the successor to the SDK-80, replacing the latter's Intel 8080 processor with an Intel 8085. In addition to a newer processor running at a higher clock speed — 3MHz to 2MHz on the SDK-80 — the SDK-85 offered an on-board six-digit display, input keyboard, and support for 512B of RAM and up to 4kB of ROM. The device served as a demonstration of the 8085's capabilities — which, apparently, includes the ability to play a game of Simon.
"I looked for a problem space that was well matched to the SDK-85 and its obvious emphasis on hardware integration. The answer became obvious - recreate the legendary Simon electronic game from 1978," Shortz explains, referring to Ralph Baer and Howard Morrison's iconic sound-and-color-matching handheld gizmo, programmed by Lenny Cope.
"This is where alternative history took over. I imagine myself as a lowly hobbyist inventor in my basement. I could afford an SDK-85, but no teletype, and certainly not a 'real' computer. I would do this with the books, graph paper, pencils, and my trusty HP calculator."
What followed was painstaking reverse-engineering of the handheld, purely from video recordings — with no physical version of the game to hand — aided by a few concessions to build what Shortz admits is a "simplified version of the game," including the loss of selectable difficulty levels.
"I decided on a detached daughter board that would house the 4 push button switches, lights, and speaker," Shortz explains of his implementation of Simon's hardware, having decided to leave the vintage SDK-85 in original condition. "The daughter board connects to the SDK-85 using a ribbon cable into an IDC header I installed on the port 0/1 connector. The switches I had on-hand were panel-mount type, so I drilled through the board to mount them — another reason to keep these on a daughter board."
"The board was wire wrapped on a hot Saturday afternoon and does not represent my best work," Shortz adds. "I completed the board in its entirety before getting to work on the software. I wrote the code out on graph paper using a mechanical pencil. The mnemonics started near the middle of the page. This left room to put the addresses and hex bytes on the left hand side of the page, just like an assembler program's listing file would use."
Shortz' full project write-up is available on Hackaday.io, though he readily admits that "the [Intel] 8085 would be a horribly expensive choice for a consumer product with millions of units."