Super accurate time on a Raspberry Pi.

MartyS

For any time nerds out there:

After seeing some videos about people creating super accurate clocks with special GPS modules I had to try it out for myself, being a bit of a clock enthusiast…

Got a 2 pack of GPS modules from Amazon that have pulse per second (PPS) pins on them for less than $20.

After soldering on the connector to a module and hooking it up to an RPi 5 it took about half an hour messing with software to get the Pi to use the PPS signal to sync the clock to within 100ns of UTC.

That was fun but temporary, since I have a Pi 3B+ running all the time feeding Flightaware, I figured I’d put the module on there and use that Pi as the NTP server for my network. 2nd time setting it up went much faster.

So now the piaware server is also an NTP server:

Since that pi is using wifi I hooked up the 2nd module back onto the Pi 5 over Ethernet and did a comparison, the wifi does degrade the sync by a hundred or so microseconds, but that’s still better than the milliseconds using NTP over the internet.

I then went down the rabbit hole of trying to get the GPS module and an RTC to interface with an Arduino, that took many days of messing around but I did get it to work. Maybe someday I’ll get around to building a really big LED clock now that I have an Arduino setup that can set it’s own time as long as it get a GPS signal.

Anyway, a week messing with this stuff has satisfied my clock obsession for a while. Watched a video of someone repairing a vintage HP atomic clock and realized those are out there for sale, this was way cheaper than that…

Somewhat-Reticent

If it suddenly gets erratic, would that be an early warning sign?

telcodad

There was a similar discussion in this previous thread: https://broadbandbulletin.com/d/2518-government-cuts-wwvb-on-the-chopping-block-again/13

Thane_Bitter

MartyS Curious Marc? He does get his hands on a lot of interesting technology of the past, I think he has gotten his hands on a few atomic clocks including an HP made one. Those clocks uses consumable parts, they are not cheap and are also as old as the instrument.

I am sure there are companies selling souped up pi’s as time servers at high costs. They likely have costly external clocks (better than the onboard chip) and might include RF as well as GPS, but the key thing is whatever their time clock is that they would record the difference between the true time (GPS) and their own clock so it can be corrected. Web interface with this sort of thing as well as the time would be nice, more so if an external display with clock could be tacked on.

All that is above my Pi skill set but it’s possible.

egeezer

This stuff is fascinating. While the time server setup is fascinating, the FlightAware feedback system looks like a great project.

MacLeech

Thane_Bitter I am sure there are companies selling souped up pi’s as time servers at high costs.

Something like these:
https://www.microchip.com/en-us/products/clock-and-timing/systems/ptp-grandmaster-clocks
https://www.oscilloquartz.com/en/products-and-services/ptp-grandmasters-and-ntp-server-clocks
https://www.mobatime.com/product-category/ptp-ieee-1588-systems/ptp-grandmaster-clock/

MartyS

egeezer This stuff is fascinating. While the time server setup is fascinating, the FlightAware feedback system looks like a great project.

Since I didn’t want to put an antenna on the roof I have one in the attic, and the fun part was trying out different designs.

The one up there now is a coaxial made from sections of copper tubing with 3D printed spacers to thread the wires down the middle of the sections of tubing. Been so long I can’t remember if it’s half wave sections or ¼.

I had previously tried aluminum tubing with press fit connections for the wires, but the heat of the attic was too much for that, with copper I was able to solder the wires on and it has lasted 5 or 6 years up there.

MartyS

I also feed ADS-B Exchange, here’s what my antenna is seeing right now:

https://globe.adsbexchange.com/?feed=V96qYlU0nF7Q

That link should be good for a while, only changes if I have to reinstall the software on the Pi.

Thane_Bitter

MacLeech That sort of thing but just not at that price tag, I bet some of those use heated oven oscillators for increased stability. Precision = price. I have seen smaller units ₁₀₀₀-2000 USD range which offer most of those but use GPS and are less accurate but still very adequate for home lab time services.

Microsemi should be noted as they have built an atomic clock on a chip (or chips, its a large module but still microsized compared to cesium tube units though I don’t think it’s included with those units.

What would be great if there was a standard link that every clock make in the last 20 years could use so that everything could synch up, who doesn’t hate it when the stove says its 5:59, the microwave says its 6:01, and somewhere buried in an AV rack forgotten a VCR blinks 12:00.

Somewhat-Reticent

Thane_Bitter who doesn’t hate it when

a brief power outage means re-setting so many time displays ?

Thane_Bitter

Somewhat-Reticent Yeah, most kitchens will have two or more clocks, stove microwave, coffee machine etc. and then there is the DST which most appliances do not take into account and require manual interaction.

MartyS

After a power outage I only have 3 clocks that need to be reset because most of my many clocks are spring or battery powered. But because I do have so many clocks the DST changes take a while, just about every room has at least one clock and then there are the watches. You would think my 2024 car would automatically change but nope, it sets the time automatically but for DST there is a menu item you have to manually check or uncheck if DST is in effect or not.