Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!swrinde!elroy.jpl.nasa.gov!usc!samsung!uakari.primate.wisc.edu!umriscc!mcs213j.cs.umr.edu!robf From: robf@mcs213j.cs.umr.edu (Rob Fugina) Newsgroups: sci.electronics Subject: Sidereal Time Clock Message-ID: <1833@umriscc.isc.umr.edu> Date: 12 Dec 90 19:31:36 GMT References: Sender: news@umriscc.isc.umr.edu Distribution: sci.electronics Organization: University of Missouri - Rolla Lines: 32 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 to campus for one of my EE labs). From there, I can use 7400-series chips to do the logic. BCD counters for both digits of the hour, and for the ones digits of the minutes and seconds. What do they make as far as divide-by-6 counters? I would need these for the tens digits of the minutes and seconds. The outputs of the counters would go to 7-segment decoders. Next is how to set it. I figured I could, for each digit, put a momentary switch directly to the digit's clock line, which would advance that digit. Special attention would have to be taken to make sure they flip to 0 correctly. A spst switch could enable/disable these switches. B Power supply...how easy is it to make it AC line powered, with a battery backup? This I'm not so worried about, but I'd like advice on whether it would be better powered by AC line or by battery...i.e., how long do you think the battery would last? The whole thing would be made up of a 555, 6 counters, 6 BCD-to-7 seg decoders, and 6 LED digits. Oh, and I nearly forgot...the most complicated part will be using logic gates to reset 0 at the right time...I'm looking at two 24-input NAND gates or something similar. Advice, please! Rob Fugina robf@cs.umr.edu