Dr. Scott Baker Builds an ATtiny85-Powered Keyboard Converter to Bring a Tandy 1000 Back to Life

Vintage computing enthusiast Dr. Scott Baker has published a guide to converting PS/2 keyboards for use with classic Tandy 1000 IBM-compatible microcomputers — bringing new life to otherwise keyboardless Tandy systems.

"A Tandy 1000 was the second computer that I owned, the first was a Tandy CoCo," Baker writes. "Owning computers is fun, but modifying computers is even funner, so I set about to modify the Tandy 1000.

"A few modifications were necessary — for example, I didn’t yet own a Tandy keyboard, so I had to make myself an adapter to use a PS/2 keyboard on the Tandy 1000. In this post I’m going to document the keyboard adapter, in case other keyboardless Tandy 1000 owners could use the resources in getting their Tandy 1000 up and running."

Baker's initial attempt at converting a PS/2 keyboard — a standard created for IBM's Personal System/2 range of personal computers, the first of which released a full three years after the first Tandy 1000 rolled off the production line — was thwarted by a simple mistake: "I actually started by building the Tandy-PS/2 adapter over at kbdbabel.org," Baker admits, "only to realize after I finished assembling it that the adapter allowed you to use a Tandy Keyboard on a PS/2. I wanted to do the exact opposite."

The solution: a custom design, borrowing from the opposite-conversion schematic and with a single ATtiny85 microcontroller at its heart. " It was a bit of a challenge dealing with two things," Baker notes. "The backslash and tilde keys. On the Tandy 1000 these are mapped to the numeric keypad, but on a PS/2 keyboard these two characters have their own unique keys. At first this sounds like a straightforward mapping, but keep in mind that if the SHIFT key or the NUMLOCK is active, then it would cause the Tandy’s numeric keypad to output a number instead of a symbol. So you have to fuss with the shift state and make sure shift is correct when sending the scancode to the Tandy.

"The pause/break key. I absolutely hate this damn thing every time I encounter it in a PS/2 project. It sends an 8-byte scancode (sometimes; depends on what modifiers you have pushed) that you have to trap and decode and make the right thing happen. Hate it. Don’t know why IBM inflicted the pause/break key or the printscr key on us."

Full details of the build, complete with schematic, can be found on Baker's website; Gerbers, Eagle files, and the source code are available on the SB Electronics GitHub repository.