🚀 go-pugleaf

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
>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


 Why 23:56:03?   Doesn't sidereal time use 24 hours and just lose 4 min/day?
 Boy, I've kinda forgotten.  At any rate, Astronomy magazine had an 
 article on how to convert a Radio Shack 24 Hr alarm clock (digital) to
 sidereal time.  It just added a couple run-of-the-mill counter chips
 to change the 60 Hz count input the right amount.  I don't have the
 date but try 1988 +1/-2 years.
 Ken