Does it need to be a mechanical clock or would a computer display do ?
I think Lady Heather will display GPS time rather than UTC. So a raspberry
pi board (even the very oldest spec, not one of the hard-to-find ones)
would be adequate.
I realise that's different to what you asked for, but it seems as though it
gives you what you want.

On Thu, Dec 15, 2022 at 3:25 PM David G. McGaw via time-nuts <
time-nuts@lists.febo.com> wrote:

As pointed out by other people already, there are several analog wall
clocks out there that can be set by external means like NTP, GPS, etc.
In my mind they all suffer from the same flaw, which is their
functionality is restricted to advancing time in precise increments but
don't "know the time". I.e. if power goes away and comes back, you'll
have to set such clocks by hand, even though their motor function can be
influenced. What is lacking is a set of 3 absolute position rotary
encoders with 6° resolution like described at [1] which referenced [2].
Somebody^{TM} should put such a clock together. 3 such encoders, a
stepper motor with gears to arrive at 6°, the rest is just software.

-Alex OE2AHL

[1] https://www.instructables.com/Absolute-Position-Encoder-With-Single-Track-Gray-C/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6111776/

On Tue, Dec 13, 2022 at 03:09:26PM -0500, Bob Camp via time-nuts wrote:

Hi

One advantage of going straight from a GPS module to the clock is that
the setup should run through the next leap second with no operator intervention.
Having a setup that simply offsets UTC by X seconds and then feeds that
to the clock gets you into updates.

Since this is an “eyeball” measurement, anything better than milliseconds is plenty
good enough. My tired old eyes can’t detect a clock tick that is off by even 10’s
of milliseconds. Not a lot of need for sawtooth correction or fancy pps stuff.

Yes, this is a very different sort of clock and time requirement than most of what
we chat about. Running a clock at the “wrong time” will be interesting. Noticing
that it’s 18 or so seconds off should be pretty easy to do.

Bob

On 12/15/22 9:57 AM, Alexander Huemer via time-nuts wrote:

There are clocks that pulse forward with one polarity, and reset to "top
of the hour or day" with a negative pulse.  My middle school had them in
the 1970s, and it was interesting to watch the reset cycle (at noon). 
Or, to be honest, it might be some sort of "power switching" protocol.
That is, use 60 Hz to run, but some pattern of interruption sets it to a
known time.  But I remember watching the minute hand snap to 12, then
advance in discrete steps.

Some time ago I bought a NOS slave clock on eBay for about $25. It runs on
110V 60 Hz. It has a solenoid to reset time to 12:00 and all the clocks in
a building lijj my e a school would get the reset pulse at the time.

Well being ham fisted, I broke or burned out the reset solenoid, so no way
to set the time any more.

But I love this clock! So, I built an inverter and used a microcontroller
to generate a precise 60 Hz sine wave. I’m running it at 90 VAC and it’s
dead quiet. The second hand has continues movement. I wrote the code to
allow running the clock at different frequencies to simply setting the
time. E.g., running it at 59 Hz makes it lose 1 second per minute.

I get the frequency from a GPSDO. Once I set the time, it never drifts.

I spent a bunch of time fretting about power loss, and how to automatically
adjust the time afterwards, but realized I actually didn’t care because the
process of setting the time by running the clock at the wrong speed was
kinda fun.

I can’t begin to tell you how much time I’ve spent staring at this thing
while listening to WWV on the phone, and tuning it so the new minute begins
when the second hand is in the center of the black dot at the 12 position
on the dial.

I do have lights that blink if it loses power, or loses the 10 MHz
reference so I know I need to set it.

I was careful to make a very clean inverter as I didn’t want any harmonics
causing vibration in the synchronous motor.

I can post pics, but it’s just an institutional wall clock like you used to
see in schools or railway stations.

Neil

On Wed, Dec 14, 2022 at 9:11 PM Bob Camp via time-nuts <
time-nuts@lists.febo.com> wrote:

On Fri, Dec 16, 2022 at 12:49 AM Alexander Huemer via time-nuts <
time-nuts@lists.febo.com> wrote:

Yes, but mechanically is an expensive way to make a small memory. This is
why I suggested a nonvolatile ram/eeprom. It can be in the clock or in the
clock controller : the difference between those is that in the latter,
cabling faults cause memory loss.

The key point is that you align it once (at manufacture) and thereafter
writes (ticks) change both mechanical and electronic representations and
reads (on recovery) read only the electronic one. If a synchronome clock
with a capacitative impulse is used, it can probably be designed to
function even over a power failure synchronised with the tick.

The downside is difficulty of doing DST adjustments, especially autumn, But
since that's not wanted and the only correction is recovery forwards after
a power failure, it fits nicely. I don't know if you need to know that it's
stopped/recovering but a status led could show that.

Another option is to do as Alexander says and fit mechanical
feedback/readout. But it could be simplified with a top-dead-centre marker

• the extra information from encoders is nice to have, but at a cost. TDC
  wil give you an alignment check every 12 hours and can, again, indicate
  that it's uncalibrated if there have been power failures since the last
  check.

I think one of the Synchronome competitors did this using a write-only
protocol. As the hour approached, a special signal was sent that put the
clock mechanically on the exact hour and then the next pulse restarted it
from there. However you need to tolerate a short synchronising error every
hour which sounds as though it wouldn't suit your needs.

Hi

We had a system like that in one school I was at. For whatever reason, the clock in
one room always went insane at least once a week. It loved to do this in the middle of
class. Needless to say, all focus on learning went away when the clock started wildly
spinning through however many hours or minutes it though it needed to ….

Turns out they very much do still make those clocks, mechanical solenoids and all.
Slam them with some number of seconds of 24V or 110V AC on that solenoid and
they reset this or that way. Multiple systems came from all sorts of outfits and spares
still get made to match up with them.

I “discovered” that 110V signaling is something to be avoided pretty early on. I would
prefer to avoid that if I can for this project. That said, I’ll always remember the IBM clock
on the wall in 8th grade English class ….

Bob

Quite a long thread and the last post was about analog clocks that had
typically been used in schools and office buildings. Bobs request I believe
was for a clock that was analog and lived in the family room?
I used the school/office clocks for a number of years and honestly the
click thumps will drive you crazy in a quiet area. Plus they take 24 volts.
I went to the very small 14" motor clocks and have been very happy ever
since. The clocks run off a battery operated divider and osc. Nothing
magical but I hate clocks that are out of sync. There are 4 clocks across
time zones.
To wrap up also consider noise.
Good luck Bob.
Regards
Paul

On Fri, Dec 16, 2022 at 5:02 AM Tom Van Baak via time-nuts <
time-nuts@lists.febo.com> wrote:

On 2022-12-15 20:57, Lux, Jim via time-nuts wrote:

That sounds like an impulse clock that would use a DC pulse from a
master clock to pick a solenoid that operated a ratchet mechanism that
advanced the minute hand and the hour hand was gear driven off of it.  I
have an old IBM impulse clock that used a 24 VDC  pulse to advance the
minute hand.  Over the ratchet wheel there is a two way contact that is
operated by a bump on the ratchet wheel that would disconnect the normal
pulse at 1 minute before the hour.  There where both two wire and three
wire system, mine is wired for the three wire so the top normally open
contact is connected to the third wire, so with it stopped at 1 minute
to the hour, a pulse on the third wire would advance the clock on step
and the normally closed contact would close again and it would
continue.  On the two wire system there is a diode in series with   I
believe the normally open contact and the signal line so that when the
normally open is closed, it will only advance when a pulse of reverse
polarity is applied.

There was a later system that used clocks with a synchronous motor and
used signals superimposed on the AC line to synchronize the clocks. 
These clock are easy to recognize as they have a second hand where as
the impulse clocks do not.

It should also be noted that IBM did make wall clocks that that where
just normal AC clocks that where not part of a system, like the 15" one
in front of me built at the IBM Canada plant in Don Mills in the 50s and
still runs great although there is a little slop in the gears now.

I believe the impulse system was initially developed by International
Time Recorder (ITR) one of the predecessor companies that was merged  to
form CTR later renamed to IBM.  IBM would later sell it timeclock
division to Simplex that continued to produce many of the same designs.

Paul.