Sol-20

Manufactured By: Processor Technology

Designed By: Lee Felsenstein

Release Date: 1976

The Sol-20 was an interesting machine. It was introduced in July 1976, appearing on the cover of Popular Electronics magazine. With its 8080 microprocessor and S-100 bus, it had more in common with the Altair 8800s and IMSAI 8080s of the day, than it did with the Apple and Commodore computers that were soon to follow, despite looking more like the latter.

I distinctly remember seeing a Sol-20 in the wild. It would have been the fall of 1977 or perhaps the summer of 1978. I had just started at the University of Waterloo and was visiting my cousin in Toronto. While walking along Queen Street we passed a small computer store and the Sol was prominently displayed in the front window. What a great looking machine with it's bright blue case and walnut sides, but at roughly $1650 (CAD) it was out of my poor student price range.

Because only 12,000 were ever produced, Sol-20s are virtually unobtainable today, so my only recourse was to build one. Talk about delayed gratification.

I planned to make a full size reproduction that will be as authentic looking as possible, with beautiful walnut sides for sure. I chose to 3D print the blue panels instead of using sheet metal so the build will be accessible to more people should they decide to make one.

For the keyboard I was in touch with Dave from osiweb.org who has designed a complete replacement keyboard for the Sol-20 using modern Cherry key switches.

From the Unified Retro Keyboard Project:

The keyboard is not a replica of the original. It doesn't use the same capacitive circuit or keys. But it does have exactly the same layout with the same functionality, including the 3 LEDs (UPPER CASE, SHIFT LOCK, LOCAL) and 3 outputs (RESET, BREAK, LOCAL). It uses cherry MX or Futaba MD-4PCs keys. Neither has quite the same feel as the capacitive keys, but the Futaba keys approach the travel of the keytronic switches, and do have a nice feel.

So I ordered the kit for the Futaba MD-4PCs keys.

On the inside I decided to emulate the Sol-20 hardware on a Raspberry Pi 4. While detailed schematics and board layouts for the machine exist, the cost of reproducing a Sol-20 PCB and populating it with "vintage" parts would be prohibitive.

When I started I hadn't decided what to do for a monitor. Certainly a CRT of some sort would be ideal, but in the end I could not find a suitable TV or monitor so I ended up designing one to look like a CRT but with an LCD display.

I learned so much about the Sol-20 while making this reproduction. More than I would have known had I been able to purchase one back in the late 70s for sure. Such a great personal computer. A stepping stone between the S-100 bus era and the Apple, Commodore, and TRS-80s that followed.