Tiny 3D-Printed DEC VT-102 Hides a Fully-Functional, ESP32-Powered PDP-11 Minicomputer

A tiny screen and a 3D-printed chassis brings some of Digital's fondest-remembered hardware up to date — and down in scale.

Gareth Halfacree
3 years agoRetro Tech / 3D Printing

Jeroen "Sprite_tm" Domburg has been working on a build with a difference: It's an ultra-compact replica of a Digital DEC VT-102 terminal, emulating a PDP-11 running 2.11BSD — all on the top of an Espressif ESP32 microcontroller.

"The thing that attracted me to the PDP11 is that the PDP line in general always has been a family of 'hackers' machines,'" Sprite_tm explains. "Its members were cheap enough to allow people to do fun stuff on, and for instance the first computer game, SpaceWar!, was written on a PDP1. It wouldn't be the last game written on a PDP machine, though: Apart from the aforementioned arcade games, all the way in Russia on a cloned PDP-11, Russian software engineer Alexey Pajitnov wrote a certain title called 'Tetris,' which later was spread all over the world."

Scaled for a doll's house, this VT-102 hides a functional PDP-11. (📹: Jeroen "Sprite_tm" Domburg)

"Nowadays, through the miracle of emulation, we can still enjoy the historical PDP-11 software. The go-to PDP-11 emulator is SIMH, which seems to run on most POSIX'y OSses. The ESP32, with ESP-IDF, has fairly decent POSIX compatibility, so why not give porting the emulator over a try?"

The software porting process, which included having to remove the ability to dynamically reconfigure the emulated PDP-11 and various unnecessary peripherals and debugging functionality, was tricky but ultimately successful — proven by running the original PDP-11 version of Tetris. Next came work on porting 2.11BSD and its TCP/IP networking stack — connected to the outside world via the ESP32's Wi-Fi radio and the ESP-NETIF abstraction layer.

Finally, Sprite_tm needed to make the project look good - so created a custom housing using a resin-based 3D printer. "I thought that for a device that's mostly there for its looks and interactivity, perhaps I'd house it in one of the things users would mostly look at it: An age-appropriate serial terminal," he notes. "I decided to pick the DEC VT-100 here (actually specifically the more common DEC VT-102) as it has a very nice industrial look and is easily recognizable."

"Additionally, actually hiding the entire PDP-11 into that terminal wasn't without precedent: the VT-100 range was designed to be expanded, and e.g. the VT-103 could incorporate a small PDP-11 system. In the case of the miniaturized PDP-11 I was building, the VT-100 would give me ample room to put in the logic board and some more."

The full write-up is available on SpritesMods.com, while the source code, PCB design files, and case models have been released on GitHub under an unspecified license.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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