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From: squishy@casbah.acns.nwu.edu (Shishin Yamada)
Newsgroups: sci.electronics
Subject: Re: Sidereal Time Clock
Summary: Fix to Previous Post
Keywords: Sidereal Time Clock, Time, Clock
Message-ID: <2372@casbah.acns.nwu.edu>
Date: 30 Dec 90 10:43:24 GMT
References: <1990Dec29.102106.5881@cerritos.edu> <37391@cup.portal.com>
Distribution: na
Organization: Northwestern University
Lines: 26

Dave and others who noticed:
     Sorry, I am new to the newsgroup and did not mean to mess up with an
echo. I also goofed in the fact that the clock runs SLOWER not FASTER. The
gist of the post should have been:
     Using a digital clock that obtains it's timing pulses from the 60Hz
line, which is typically sent into a wave-shaped to produce a cleaner
square wave output of 60Hz. You would want to skip a pulse every 14,400
pulse. This clock would count a normal 240 seconds, then count 61/60th of a
second. This correction would thus make the clock count to 23:56:00 in a 24
hour day. The maximum error (assuming the AC line is OK) is 1/60th of a
second off actual sidereal time in 14,400 ticks. Or a relative error of 1
part in 14,400 which is equal to a relative error of 0.0069444% (percent).
I would think that error would be acceptable, considering it corrects
itself every four minutes. One possible counter for this would be two
divide-by-ten serial counters in series, then sequential logic to determine
if the result is equal to 144 decimal.
     One possible binary clock circuit driven by an AC line is given in the
January 1991 issue of Popular Electronics. It could be modified with
appropriate logic circuits.
     Once again, sorry to all for the screwed up info in my first (ever)
post. Best of luck with your project!

*************************************************************************
Shishin "SQUISH" Yamada             * Undergrad Senior, Electrical Engineering
BitNet: Squishy@Casbah.ACNS.NWU.EDU * Northwestern University, Evanston IL
**************************************************************************