Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!jaytee!vergil!gsteckel From: gsteckel@vergil.East.Sun.COM (Geoff Steckel - Sun BOS Hardware) Newsgroups: sci.electronics Subject: Re: Sidereal Time Clock Message-ID: <3607@jaytee.East.Sun.COM> Date: 12 Dec 90 21:19:07 GMT References: <1833@umriscc.isc.umr.edu> Sender: news@East.Sun.COM Reply-To: gsteckel@east.sun.com (Geoff Steckel - Sun BOS Hardware) Distribution: na Organization: Omnivore Technology, Newton, Mass. (617)969-3448 Lines: 27 In article <1833@umriscc.isc.umr.edu> robf@mcs213j.cs.umr.edu (Rob Fugina) writes: >My roommate just asked me to design a clock for him. It's for astronomical >purposes. Relatively simple, really, but I need a little advice and some >chip numbers. > >The clock has to count from 00:00:00 to 23:56:03, then reset back to zero. >I figured it would be easy enough to design an oscillator with a 555 to >100Hz, calibrated with a 15-turn pot and an oscilloscope (I'll take it I recommend: use a 32768 Hz crystal and a National Semi crystal-to-1-Hz chip, then run it through 4000 series CMOS for the dividers. Result: a LOT more accurate than a 555. I think you would find the 555 completely unusable for timekeeping, unless you wanted to reset it twice daily. I don't have my parts manuals here or I'd recommend chips. You can get programmable divide-by-n chips and n-to-7 segment decoders in CMOS. You can then run the whole mess off 3 alkaline batteries. Be sure to connect EVERY LAST input to +V or ground! CMOS behaves VERY unpredictably with floating inputs. If you use a LCD display, it will run all the time with less than 1 mA drain. They are available from Digi-Key, among others. Just a quick sketch. Hope this helps. geoff steckel (gwes@wjh12.harvard.EDU) (...!husc6!wjh12!omnivore!gws) Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line. This posting is entirely the author's responsibility.