So the title really should be a bit longer: “QR codes on a laptop from 1989 with 256k RAM and no native graphics support” – but that doesn’t sound quite so snappy 😉
The laptop in question is my Psion MC400 – a marvel of engineering and industrial design, conceived in the mid-1980s and cursed by not having “PC compatibility”. Even though it had a multi-tasking GUI-based OS, touch pad and SSDs and would run for 40+ hours on a pack of AA batteries it was overpriced, unloved and had little software available for it. But for me it was love at first sight.
So back to 2026, or 2021 more precisely, when I first got the old lump of technology “connected to the internet” with the help of an attached Pi (of course). I created software on the MC400 to interface with the Pi that allowed it to send tweets (when twitter wasn’t a cesspit), send emails and I had it syncing screenshots to Google drive and producing a bitly shortened link to the image.
I recently read on some online forum somewhere some other retro-computer nerds talking about using QR codes as a way to retrieve info from old machines that weren’t easily networked and it got me thinking…
So, disclaimer: the MC400’s 7MHz 8086 CPU doesn’t have the muscle (not without some serious x86 assembler genius) to generate the code (Reed-Solomon error correction and masking) so the actual QR code generation is done by standard python libraries on the Pi (of course, again) – it creates the code from the last bitly link to a screenshot, draws the matrix using the Psion’s “block character” (CHR$(219) or 0xDB) and whitespace and writes the matrix to a file as a single stream. This file is then copied to the MC which uses its built-in OPL to open the file, read the stream 1 row at a time and print to screen. Turned out not bad at all.
In all its glory – below is the OPL on the MC that detects a screenshot has been created (Ctrl-Psion-Shift-S on the Psion) then copies it to the Pi for conversion to PNG, syncing to Gdrive, then waits for QRDATA.BIN to be generated and opens/prints the QR data/code 😉
REMREM Move any LOC::M:\SCREEN.PIC screen dumpsREM to an attached computer for processingREMREM v0.0.01 21/09/2021 @zedstarrREM v0.0.02 18/02/2026 ADDED QR-CODE GENREMPROC Main: local l% SCREEN 80,35 WHILE 1 PRINT DATIM$,"Auto conversion to PNG & cloud sync of screenshots" PRINT DATIM$,"Waiting for LOC::M:\SCREEN.PIC..." DO REM check every 10s PAUSE 200 UNTIL EXIST("LOC::M:\SCREEN.PIC") PRINT DATIM$,"Found LOC::M:\SCREEN.PIC" REM Wait until dumping is truly finished PAUSE 100 REM If link not connected the re-check every minute ONERR borked:: l%=EXIST("REM::C:\MCLINK.EXE") borked:: ONERR OFF IF l% PRINT DATIM$,"Copying to REM::C:\IMAGE\INBOX\SCREEN.PIC" TRAP COPY "LOC::M:\SCREEN.PIC","REM::C:\IMAGE\INBOX\SCREEN.PIC" IF ERR Showerr:(ERR) GET RETURN ELSE PRINT DATIM$,"Deleting LOC::M:\SCREEN.PIC" TRAP DELETE "LOC::M:\SCREEN.PIC" IF ERR Showerr:(ERR) GET RETURN ENDIF PRINT DATIM$,"Waiting for REM::C:\IMAGE\OUTBOX\QRDATA.BIN..." DO REM check every 2s PAUSE 40 UNTIL EXIST ("REM::C:\IMAGE\OUTBOX\QRDATA.BIN") TRAP COPY "REM::C:\IMAGE\OUTBOX\QRDATA.BIN","LOC::M:\QRDATA.BIN" IF ERR Showerr:(ERR) GET RETURN ELSE FASTQR: ENDIF ENDIF ELSE PRINT DATIM$,"Waiting for LINK..." PRINT " Error: ",ERR,ERR$(ERR) PAUSE 1000 ENDIF PAUSE 20 ENDWHENDPPROC Showerr:(val%) PRINT "Error: ",val%,err$(val%) GETENDPPROC FASTQR: LOCAL h%, status%, line$(70), y% LOCAL width% REM 33 modules * 2 characters per module = 66 width% = 66 CURSOR OFF CLS status% = IOOPEN(h%, "LOC::M:\QRDATA.BIN", 0) IF status% < 0 : PRINT "File Error" : GET : RETURN : ENDIF PRINT DATIM$,"QR code for last screenshot:" y% = 1 DO REM Read the pre-formatted line (66 bytes) status% = IOREAD(h%, ADDR(line$) + 1, width%) IF status% < width% : BREAK : ENDIF REM Set the string length byte for OPL POKEB ADDR(line$), width% REM Move to row and print the whole string at once AT 10, y%+1 PRINT line$; y% = y% + 1 UNTIL y% > 29 REM Yes, that's 4 lines too short but it's whitespace/border anyway... IOCLOSE(h%) AT 20, 33 : PRINT "Ready to scan... (Press any key to continue)"; GET CLSENDP
Room 7609 