🚀 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

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.