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TSU Meeting MONDAY — July 6, 2026

David Stevenson, Joe, John, Ryan, Charlie

This Monday session featured guest David Stevenson, a ZX81/TS1000 developer from Australia. He traced his path from building a Raspberry Pi–based ZX81 emulator box with an Arduino keyboard interface to the full-size external keyboard he sold, which works both on a real ZX81 and as a USB keyboard for emulators. He then talked about his hardware projects, including an I/O expansion board that can drive a Dallas real-time clock. His games came next: Tut-Tut started as a fast BASIC maze game for the Spectrum, was rewritten in C (z88dk) for the ZX81 and released through Cronosoft, and has since been ported to the Jupiter Ace, RC2014, Commodore PET and VIC-20. Minosis Kenosis followed as a sequel.

Most of the hour went to his new ZX81 Xevious conversion. David explained how it was built: a scrolling map buffer plus two swapped display files (triple buffering, about 3K of RAM). Background tiles are 4×3 characters and sprites 3×3, and level data is run-length-encoded at about one byte per tile so the game fits in a 16K machine. Game timing follows the frame counter, with display files swapped every 8 frames on PAL and a slower rate for NTSC. The bullet logic borrows ideas from the Spectrum game Lightforce. He tests in EightyOne and on a Minstrel 3. The game was demoed on screen, along with a colour version for the Chroma 81 made by Kelly Murta. It has had about 400 itch.io downloads, and a PET port with TFW8b's Dave is planned next.

Joe showed vintage machines sent to him to get ready for the Chicago Vintage Computer Festival. One heavily modified TS1000 has a 555-based composite video mod, extra-key and keyboard-beeper circuitry, and an LM3915 bar-graph tape-loading indicator. It also has a three-row keyboard where a toggle switch makes the top row act as either 1–0 or Q–P. Another machine has a hand-painted keyboard and a Christmas-tree-bulb power light. Joe 3D-printed a replacement space bar for it. The group connected the extra-key circuitry to published TS2068 projects that added extra keys, such as an Escape key for terminal programs.

John reported that he got two of Asa Gordon's BASIC programs, which had been damaged by OCR errors, working again and posted the fixed versions. The third needs a data file that hasn't turned up. John also turns out to be a contributor to the EightyOne emulator, working with Paul Farrow on AY sound and speech support. He described features like WAV-based loading and saving to real hardware and ZX81 video-signal annotations. Ryan closed with photos from the National Videogame Museum in Frisco, Texas. The next meeting is Sunday, July 19, and the group floated a celebration for its 127th/128th meeting.

Highlights

  • Guest David Stevenson walked through how his ZX81 Xevious works: triple-buffered display files and RLE-packed levels, all in 16K
  • Tut-Tut's history: a BASIC Spectrum game, rewritten in C for the ZX81, then ported to the Jupiter Ace, RC2014, PET and VIC-20; next up is a PET port of Xevious
  • Joe is reverse-engineering a heavily modified TS1000 (composite mod, extra keys, LM3915 load meter) for the Chicago Vintage Computer Festival
  • John fixed the OCR errors in Asa Gordon's BASIC programs and posted two working versions
  • John contributes to the EightyOne emulator (AY sound, speech, WAV load/save to real hardware)

Topics: TS1000 / ZX81 / TS1500 · Games · Spectrum emulation & software · Hardware projects & new boards · Repair & restoration · User group meetings & events

Summary generated from the meeting recording; the full transcript is kept in the group's private archive.