Seems like you personally know him? :-) I actually made this clock so that my wife wouldn't mind a ZX81 standing in the living room :-). If it wasn't a clock, it would have ended up in the bin I guess.
The design was pretty straight forward of course but the real difficulty was to make it an accurate clock. The ZX81 frame interrupts (50Hz or 60Hz) don't come at exactly 20ms or 16.67ms intervals, in fact, without calibration routines the clock will run about 7 seconds fast every 10 minutes!! I made some calibration algorithm that could do additive calibration. Suppose you start with "roughly" 7 seconds per 10 minutes (skipping about 1 tick every 85 ticks @ 50Hz), then after say 2 hours you measured the clock runs 3 seconds slow, so you add to the previous calibration a 3/7200 correction. Then you take a measurement over 24hours and say it now runs 2 seconds fast, so you add a correction of -2/86400. If you do this, you eventually end up with a routine that can skip a tick every say 91.13579 ticks and it will (in theory) run as accurate as 1.5sec/year. Of course, not including effects of ambient temperature. I was surprised to see how active people still are with the ZX81/ TS1000, I haven't used mine for like 25 years or so. They cost peanuts on ebay. This kit is about AU$175 so including the ZX81 it is less than $225. Michel -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
