Timex Sinclair User Group Meeting — December 5, 2022

David, Adam Trionfo, Jeff Burrell, Jeff K, Paul, Tim, Stuart, Ryan Gray, Carl Miles, Keith, Robert Opalko, Brian

Adam opened with a digital-archaeology win: he pulled a basic Qbert off one of the recently-archived TS2068 floppy-disk images using the TOMATO command-line utility, dumped it to a TAP, converted to WAV, and got it loading on a real 2068 — after Johnny Red repaired the program's LOAD * references (originally aimed at a disk system, case-sensitive, with no fallback) so it ran from tape. That led into a wider discussion of the LOAD * hook in the 2068 ROM, how Interface 1 / disk systems trap the error-restart vector to handle their own commands, and why the 64-column "64COL" program on the same disk was so slow (almost certainly drawing characters in high-res from BASIC rather than using a fast machine-code mode like Tasword/Taswide, MScript or the 64-column routine in Larry Kenny's LKDOS).

Jeff Burrell reported progress on his FPGA-based advanced-2068 effort: video routines ported to the new Affinity FPGA, plug-in daughter boards for the 2068 just arrived, and the design now incorporates a Raspberry Pi Pico W as a WiFi+CF-storage front-end (BOM up from about $5 to $6). He also walked through FPGA pricing — ~$12 for the part, ~$2 for the config ROM, with ~20K gates and ~128K of internal RAM, enough to host an entire 2068 plus a VGA ULA. Disk routines are the next port. Tim mentioned that his TS2068-aware fork of zmakebas had a user submit hundreds of lines of code and feature requests, and Ryan raised the long-standing problem of keyword tokens inside strings/REMs not round-tripping through listbasic-style converters.

David walked through his new blog post on replacing the TS2068's troublesome internal switching regulator with one of the tiny dual 5V/12V buck modules Carl had previously flagged, motivated by Frederico's help request on the list. Carl explained why the 2068 swap is more involved than the 1000 or Spectrum equivalent: the switching regulator chip also contains the op-amp that drives the speaker, so you have to disable the switcher's power input while keeping the op-amp alive — and dropping in a higher-current 12V regulator (replacing the marginal 78L12) plus a dedicated linear 5V feed to the SCLD measurably cleans up video. David agreed to redo the project with a proper before/after video showing both picture and audio. Other site updates: scans of Fred Nazelbauer's Syncware News material and Greg Harder's TS1000 high-res-graphics extensions (the Wilf Rigter approach using an 8K RAM card in the ROM gap).

Stuart gave a long update on two ZX81 sub-projects: his USB-keyboard adapter (Arduino Pro Micro, custom PCB) — the hardware is finalized and now works reliably after fresh Pro Micros from China, but the firmware still needs proper shift-combo handling and the EightyOne emulator currently won't accept its keystrokes; and an 8255-on-breadboard educational rig aimed at giving Arduino/Pi hobbyists a reason to drag a ZX81 back out of the attic, with snap-in LED/button modules to make I/O experiments approachable. Tim shared his ZX81 keyboard-ribbon repair recipe (thin slivers of conductive aluminium tape over cracks, reinforced with Kapton — more responsive than replacement membranes). Brian was live-archiving a cassette into Audacity during the call and demonstrated loading it in Fuse. The group debated cassette-deck quality for archiving (modern transports are mediocre; old Pioneer Elite decks have digital S/PDIF out; Carl swore by the Timex 2020), and David revealed he's had his TS2068 ROM disassembly (~500 pages) printed via Amazon as a working reference. Next meeting: Sunday December 18th at 2pm.

Highlights

Adam + Johnny Red recover a basic Qbert from an archived TS2068 disk image and load it on real hardware via TOMATO → TAP → WAV
Jeff Burrell's FPGA-2068 board boots video on the new Affinity FPGA; Pi Pico W added for WiFi + CF storage
David publishes a TS2068 power-supply swap using Carl's tiny 5V/12V buck modules; Carl explains why the SCLD/op-amp tangle makes it tricky
Stuart's ZX81 USB-keyboard adapter hardware is finalized; firmware still fights the EightyOne emulator's keystroke handling
Tim's ZX81 keyboard-ribbon fix: conductive aluminium-tape slivers reinforced with Kapton, reportedly better than replacement membranes

Projects discussed: Library Tape Archiving Process · FPGA "Advanced 2068" Topics: Tape & library archiving (TAP/TZX) · Hardware projects & new boards · Spectrum emulation & software · Repair & restoration · Video upgrades (composite, RGB, HDMI) · TS2068 / TC2068

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