Seeking for a wall clock

On a sunny day (Fri, 19 Nov 2021 19:48:21 +0100) it happened "Carlos E.R." <robin snipped-for-privacy@es.invalid wrote in snipped-for-privacy@Telcontar.valinor:

Yes I did:

Much simpler is use GPS time:

it can also measure radiation and tracks location....

If you get a 30$ GPS module and connect it to a raspberry the C code to get the time from it and add time offset for CET is in

raspberry will normally sync its system time automaticaly from the internet if connected to it, you do not normally need GPS. So maybe for you a simple raspberry and LCD display?

And my cellphone gets its time from the phone network.

An alternative would be a sundial.

There are schematics around, at least for WWW and WWWH (60 kHz), which can be changed for 77.5 kHz. You'll need to place the reception antenna far enough to prevent feedback and oscillation of the unit.

If you find a clock, please tell us. I'm 1540 km from Mainflingen, but opposite direction compared to you (Helsinki, Finland).

A small Pi system (or one of the many similar SOCs) would almost certainly be the way to go. You could have it time-sync in either of two ways:

(1) Over the Internet, via NTP. The necessary NTP software is almost certainly available in the standard Pi software repo.

(2) Using GPS - buy a cheap GSP module, wire it to a cheap USB-to-serial adapter, and plug it into the Pi's USB port. The GPS-management program "gpsd" plays pretty well as a time source for either ntpd or Chrony.

For the time display, you have all sorts of options... use a small text-only or graphic LCD, or connect a larger display screen to the Pi and write an X Window display application.

I don't know of kitted versions for any of the above, though.

My home network uses Chrony to talk to NTP servers as a secondary time reference, and has a GSP module as the primary. I have no practical need to have my home network time-sync'ed to better than a millisecond with "standard time", but I do it anyway :-)

It's probably not beyond the realm of possibility to make some sort of DCF transmitter, driven from a Pi or a home PC which uses NTP or GPS.

A cheap modern XO clock should be stable to a few PPM.

Replace the batteries and set it every 6 months.

Yeah, well, that's what I use, a plain analog clock, Xtall controlled. Still, goes of more than a minute by the time I have to adjust summer/winter time again. I want improvement :-)

Yes, I use NTP on my computers, that's why I said "sync over WiFi". That's a minor problem, compared to setting up a Pi with a suitable display (I have never played with a Pi).

Yep.

That would be another idea...

I feared that :-(

Ok! :-)

>

But prices go up. A complete kitchen clock with DCF can be 20€. Plus the time to build all those.

LOL. With a repeater to show inside the kitchen :-D

A decent quartz crystal clock should be good to a few tens of seconds a month at most. There is something wrong if it runs out more than that.

The only thing I have with a similar fault is a Meade LX200 where they failed to put the right load around the RTC xtal and it gains about 30s a month. They solved this design error by adding GPS sync to the next generation rather than adding the right capacitors to the load network!

These days it is very hard to find a quartz crystal based clock that doesn't keep good time although I expect if you try hard enough you can. Wrist watches do even better since they are thermally regulated by us.

My antique 400 day torsion pendulum clock is good to seconds a week provided I keep the ambient temperature reasonably stable. It has a couple of small counter weights on the main block that tweak the moment of inertia and null out the first order thermal expansion.

Specs are normally up to 4 seconds off per day, thus easily a minute a month; thus by the time I have to adjust summer/winter time, they are easily 5 minutes off.

And I hate having to adjust summer/winter time.

I also have 2 "automatic" DCF clocks, radio adjusted, and they don't work.

So I specifically want clocks that adjust via Internet, NTP protocol, nothing else is valid for me. That's my question, please. Wall clocks for kitchen or elsewhere that sync using WiFi.

It's pretty easy to make an analog 77.5 KHz amplifier repeater to increase the allowed distance to the transmitter at Mainflingen. There are some necessary tricks. First, use tuned ferrite-rods for both repeater receive and repeater transmit antennas. The bandwidth is maybe 10 Hz Second, space them at least ten meters apart. Third, make them perpendicular to one another. Forth, shield everything, so no electrostatic coupling.

The repeater input rod is oriented for maximum reception from Mainflingen. The repeater output rod is perpendicular, and the clock is nearby, with its rod parallel to the repeater output rod.

Joe Gwinn

It may have a trimmer cap inside. And probably a 32768 Hz crystal. You could potentially trim it.

Hum. Too complicated, unless someone sells a prepared kit. It has been decades since I do anything of the sort.

On Friday, 19 November 2021 at 18:32:11 UTC-8, Carlos E.R. wrote: ...

... You don't need a Raspberry Pi to synchronize with NTP.

Here is a design using an ESP8266 programmed in the Arduino IDE.

kw

An off-the-shelf solution is the venerable Chumby

which is kinda open-source and somewhat supported, with Sony and other manufacturers sometimes supporting the hardware. A NNTP clock is the base application for these.

There is usually a trimmer on the back or in the case so you adjust it to be within about 2ppm if you have the patience. A little wheel with a legend along the lines of "- <-> +" though sometimes just an exposed screwhead. I assume here that the clock will be indoors and not subject to violent changes in temperature.

Buy better ones then.

It is an ideal DIY electronics project if you you must have one.

All of the cheap xtal clock mechanisms I have ever seen have an adjuster on the back. The odd one does it digitally calibrated at manufacture against a reference second by tweaking the length of a second every now and then to compensate up or down by a few ppm. Long term average over a whole number of days can be made very good indeed this way.

On a sunny day (Sat, 20 Nov 2021 10:50:17 +0000) it happened Martin Brown <'''newspam'''@nonad.co.uk> wrote in <snajtm$1nb9$ snipped-for-privacy@gioia.aioe.org>:

It is interesting to know that the clock on my microwave oven (make Whirlpool), that I think uses 50Hz mains, stays to within seconds over a long time, Same for my Sony radio clock. Few years ago there was a minutes long error due to 50Hz drift between power stations.. and it showed, You realy do not normally need any more accuracy, but until the politiCsians stop the summer / winter time crap you have have to adjust those things twice a year. I am all for UTC everywhere worldwide. Just a matter of getting used to locally, but much easier globally, and no clock change stress.

Long term mains frequency is effectively locked back to atomic clocks.

They have to keep the long term average within very tight bounds and so typically run the frequency faster overnight when loads are lighter (the older mechanical systems tend to do this slightly anyway). It used to annoy astronomers back in the day when many drives were ac mains synchronous motors (and they would run fast by ~1% at night).

Today everything is dc servo based and autoguided so it is irrelevant.

At higher latitudes the clock changes sort of make sense.