MIKE ROSS wrote in a message to Roy J. Tellason:

 MR> "Roy J. Tellason" wrote to "ROBERT SAYRE" (15
Dec 02  12:05:52) 
 MR> --- on the topic of "digital clocks"

 RJT> I know that with the old-style analog clocks setups in a building like
 RJT> a school or large office typically included much more than simply
 RJT> providing power to the clock.  They would also run additional wires to
 RJT> allow for setting the clocks and synchronizing them to all be running
 RJT> at the exact same time.  (Which reminds me of the one in the lunchroom
 RJT> at work,  which had a dual-faced clock hanging from the ceiling,  one
 RJT> side of which proceeded to run backwards at an accelerated pace,
 RJT> after a thunderstorm...  :-)

 RJT> It doesn't strike me as too likely that you could take a lot of the
 RJT> clock chips that are out there these days and interface them by
 RJT> looking at what the display output lines were doing.  This gets
 RJT> further complicated by there being big differences between outputs
 RJT> that were designed for LED and LCD displays.
 RJT> I wonder how you'd do something of this sort?  Probably easiest would
 RJT> be to "throw a microprocessor at it"...

 MR> Maybe not. I'd make the individual clocks dumb and not much more
 MR> than a simple display. 

An n-bit shift register?  Say,  32 bits if we want four digits?  Yeah,  if
you don't want to do decoding locally,  or multiplexing.  That would be
about as simple as I could figure it.

 MR> A central clock would only send digit data serially to all the 
 MR> displays daisy-chained down the wire. No need to set anything and 
 MR> only 1 wire plus ground is all that would be required.

This reminds me of a story that appeared in a *real* early Byte magazine, 
where the author (who was also editor at that time,  Carl Helmers) talked
about how absurd the wiring could get for pipe organs,  and suggested
something similar.  I think his setup was shift registers and latches.

 MR> I would even try to integrated it all with the fire alarm system 
 MR> and intercom to save on copper. I think they do something like 
 MR> this in subways.

Fire (and other) alarms are something else I'd like to explore a bit,  as
well as intercoms.  I started to sit down and design an alarm system at one
point,  back when I had my shop.  All of the doors were equipped with reed
switches,  and the few windows there never got treated before we closed up.
 I have some rough sketches somewhere but never actually built the thing. 
Logic was nice to use in that setup,  a bit of cmos and you can do all
sorts of stuff.

I remember an intercome that was at one place I worked at.  The
"slave" end was just a speaker,  maybe with a coupling cap,  I'm
not sure any more.  The "call" button just shorted across the
line.  The other end was live all the time,  but unless you had it actively
set it didn't do much,  though it did respond with a noise when somebody
hit that button.  Not too bad for only two wires.  I also vaguely recall
assorted other setups in magazine articles,  way back when.  I don't have
most of those magazines any more,  unfortunately.  One that I can still
recall had some outrageous number of wires running between stations,  of
which there couldn't have been more than 3,  and some really bizarre
switching,  all mechanical.  The basic stuff is pretty straightforward,  in
that you need some amplification and speakers and such,  but for a
multi-stationed setup that can be all over a house and that'd be flexible
I'm not sure how I'd proceed.  Maybe kick some stuff around in here,  there
seem to be some pretty creative folk in here... 

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