Simon Pettersson Has Finally Found a Use for Sweden's Failed Teleguide Terminals: Retro Gaming

Maker Simon Pettersson has brought new life to a near-forgotten relic of Swedish telecommunications history, the failed Teleguide terminal — turning it into a Raspberry Pi-powered all-in-one with mechanical keyboard and original monochrome cathode-ray tube (CRT) display.

"This is a Teleguide, or rather it was a Teleguide; a complete flop of a project from the Swedish state telecom operator, released in 1991," Pettersson explains of the device around which he has built his machine. "They pushed around 10,000 units and a lot of them still sit in storage in unopened boxes around the country, so I got this one for myself, new in unbroken packaging with Styrofoam and spiders and everything."

Televerket, the Swedish telecoms operator, launched an experimental version of the Teleguide network, developed in partnership with IBM and Esselte, in 1988, and released the consumer variant in 1991 in the hope of following in the footsteps of the highly successful French Minitel service. The Teleguide, stylized "TeleGuide" on the machine proper, packed an Intel 8051-based communications terminal into a plastic housing along with a 10" monochrome CRT display — and the design even included a handset on the top of the housing, so you could use it as a standard telephone too. Based on the Loewe Multitel, the gadget even included a smart-card reader with dedicated microcontroller and neat magnetic ejection mechanism — but rollout was halted after around six months, when someone at Televerket crunched the numbers and realized the network would have to be run at a drastic loss.

The closure of the Teleguide network in 1993 was no barrier to Pettersson's project, as the internals have been replaced with a Raspberry Pi single-board computer. Making use of the terminal's stock monitor, though, proved awkward: "The monitor does not follow any standard composite or VGA mode," the maker explains. "Instead it runs at roughly 18.75kHz horizontal and ~57Hz vertical sync, which is just far enough from standard timings to be annoying."

Being unable to use the Raspberry Pi's composite video output as a result, Pettersson had to design an adapter board — taking a signal from the machine's DPI parallel RGB video output, available via the 40-pin general-purpose input/output (GPIO) header, with a software driver using lookup tables to mix the RGB video into a grayscale signal. That worked for the Raspberry Pi 3 originally used in the project, but not the more powerful Raspberry Pi 5 Pettersson introduced as an upgrade — requiring a new driver that adds a missing RGB565 output mode and a redesigned adapter board, taking the form of a full analog front-end (AFE) to perform in hardware what the Raspberry Pi 3 was doing in software.

More information is available in Pettersson's Reddit post; the maker has released KiCad project files for the video adapter boards on Google Drive under an unspecified license, though a link to the patched video driver was not working at the time of writing.