🚀 go-pugleaf

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