> I wonder if you really need a special clock? Can't you adjust a normal > spring driven clock to run fast (or is it slow?) by about 1/3 of a percent > (one day per year)? This should be within the range of adjustment.
Chris, When you mention 1/3 percent, you're thinking sidereal time, which is a completely different concept, and much easier to implement than equation of time. Sidereal time is simply a calendar-day independent, fixed (2730 ppm) frequency offset. I already have PIC chips that do this; see PD28 under www.leapsecond.com/pic/picdiv.htm or read the comments in the source code at: http://www.leapsecond.com/pic/src/pd28.asm Solar time, on the other hand, is continuously variable in rate (and phase) throughout the whole year. A microprocessor implementation of solar time also needs to know calendar date, time, and longitude. A 4800 baud GPS NMEA stream input would be a convenient way to obtain this information. Without using floating point or trig functions, a tiny PIC implementation would probably use a 365 entry lookup table to adjust the output tick rate on a per-day basis. A more capable Arduino or RPi might allow one to accurate calculate EOT directly from planetary motion equations, avoiding hard-coded tables altogether. /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
