[HN Gopher] Raspberry Pi Nixie Atomic Clock
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Raspberry Pi Nixie Atomic Clock
Author : geerlingguy
Score : 81 points
Date : 2021-09-07 06:16 UTC (1 days ago)
(HTM) web link (github.com)
(TXT) w3m dump (github.com)
| freedomben wrote:
| Confirmation bias struck me and I read this as "Raspberry Pi
| Nixie Alarm Clock" and now I'm disappointed. I really need an
| alarm clock and would love to build one out of a pi. I see a ton
| of blog posts and stuff. Has anyone actually done that and could
| recommend?
| LCoder wrote:
| I'm actually starting this right now with my two teenage kids
| who are interested in going to college for CS. We are using an
| esp32 instead of a Raspberry Pi, but I'm having them work
| through all the hardware and software requirements to get sound
| (I2S) output, display, WiFi, etc.
|
| My end goal is to have them create a backend api server for
| syncing data to the alarm clock, and then a mobile app so they
| can change settings remotely. I figure it is a good learning
| project for them to touch a lot of disciplines (hardware,
| embedded firmware, circuit design and layout, 3d modeling, web
| services, mobile apps) to see what they gravitate towards.
| beervirus wrote:
| Why not just use NTP to get time data from someone else's (more
| accurate) atomic clock?
| willis936 wrote:
| NTP isn't going to beat a GPSDO by any metric, especially when
| the LO is Rb.
| jrockway wrote:
| NTP is really not that good. I'm looking at "chronyc sources"
| on my GPS-disciplined clock, and relative to GPS time, the NTP
| sources are +/- 100s of milliseconds off. I'm sure most of this
| is the flakiness intrinsic in a consumer-grade ISP, but even
| after measuring them over a long period of time they tend to
| drift at about 1 part per million. (That's a second off every
| 12 days.) Comparatively, a tuned TXCO connected to the same
| clock is about 0.009 parts per million off, and many would
| consider that unacceptable.
|
| GPS is actually an extremely good time reference. On the
| ground, you can be sure of the time to about 50ns, and the
| internal clocks on the satellites are kept synchronized to UTC
| time. (Which variant of UTC depends on the satellite
| constellation. The US uses the US Naval Observatory for GPS;
| China has their own version of UTC for BeiDou, etc.)
| geerlingguy wrote:
| I'm guessing this is more of a fun project than serious--the
| display on the nixie tubes won't refresh quickly enough to
| demonstrate the rubidium oscillator's ability to hold
| nanoseconds of time.
|
| But in the case of potentially _also_ using this board as a
| Stratum 1 clock (it has GPS /GNSS built in...), why would it
| not be as accurate as pretty much any other clock that serves
| up NTP time?
|
| It would surely be a lot more accurate than any sync via NTP
| going over the public internet.
| willis936 wrote:
| You _could_ push nixies down from +200 us to roughly + /- 5
| us with a current sense circuit feeding a tracking circuit
| (either a hardware PLL or digital DLL) with feedback from the
| PPS gen circuit.
|
| Most of the inaccuracy of nixie displays (that are done
| properly and conventionally) is that the nixies require a few
| hundred us to build up enough charge to ionize the gas. If
| you send your HV trigger out before the actual start of
| second then you can account for the static part of this
| offset.
|
| Reducing the random part would be... a trick. Low and
| constant temperature would be a decent starting point.
|
| My next ideas are based around taking out the feedback loop
| and replacing it with static offsets based on an empirical
| model. Taking measurements of the nixie state transition
| delay (ie 1 to 2 takes a different amount of time than 2 to
| 3) would provide useful information. You could take
| temperature measurements and induce temperature over a range
| and build a matrix of the nixie state transition delay
| measurements.
| at_a_remove wrote:
| I have seen a few alternatives, but are there any nixie
| replacements which have the features of a nixie (elegantly-shaped
| lettering, warm glow, solid stroke as opposed to dots) without
| the voltage issues and rarity? Lixie seems to have stopped
| producing, etc.
| anfractuosity wrote:
| I guess it sounds like you're looking for an alternative
| technology? but in case you haven't seen them, these folks make
| them - https://www.daliborfarny.com/
| newman314 wrote:
| I was just looking at these this AM. They are $$$$ but so
| beautiful.
| scrumper wrote:
| They have a very interesting project of a clock custom built
| for NASA to calibrate high speed cameras. Apparently these
| tubes can switch 100,000 times a second and their lack of any
| flicker makes them well suited to this purpose:
| https://www.daliborfarny.com/project/calibration-display-
| for...
|
| I've worked with vacuum tubes a bit in audio amplifiers, but
| this seems wild, honestly. Does anyone know how Nixie tubes
| can manage such a feat? 100,000 times a second? It's
| incredible.
| tyingq wrote:
| Someone tried edge lit acrylic:
| https://hackaday.io/project/165079-lixie-ii-the-newnixie-for...
|
| What appears to be a commercialized version:
| https://www.banggood.com/Geekcreit-Pseudo-Glow-Tube-Clock-DI...
| willis936 wrote:
| This has to be my favorite thing in a while.
|
| I've been doing small hobby iterations of gps nixie clocks for a
| decade. I'm using a pi in my latest iteration, but man this
| project really goes the distance. It does everything I want to do
| in my most ambitious vision of the project and then goes another
| 50% further. Really excellent stuff.
| geerlingguy wrote:
| When I was working on testing Facebook's PCIe Time Card on my Pi
| CM4 last week (it has GNSS and a rubidium atomic clock built in),
| I found out about this project, and thought it looked amazing!
| cyberge99 wrote:
| My first thought when I saw the headline was that it was one of
| your projects building upon the RTC unit you have.
| jrockway wrote:
| This is a great project! I was expecting a run-of-the-mill GPSDO,
| but this is way better.
|
| I've been looking for more time sources to add to my own GPS
| clock: https://github.com/jrockway/beaglebone-gps-clock (which is
| one of those boring ones that everyone has).
|
| I have been thinking about buying a rubidium oscillator from eBay
| for fun, but basically anticipated the problem the author had --
| they have been mistreated for years before finally landing on
| eBay, and aren't any good. GPS is my only frequency reference, so
| I wouldn't really be able to fix it; I'm at the mercy of my very
| obstructed view of the sky.
|
| I'd like to be able to measure how badly out of sync I get when I
| fall down from 16 satellites to 4 satellite throughout the day. I
| can sort of intuit that from the data I get right now (I send
| "chronyc sourcestats" to influxdb every 30 seconds, and you can
| see that when the GPS signal gets bad, the frequency error in my
| system clock also gets bad.), but I'd like to measure it
| conclusively. Will probably spend a bunch of money on the problem
| and become even more unsure which way is up ;)
|
| The link to the "time to digital converter":
| https://www.ti.com/lit/ds/symlink/tdc7200.pdf is very
| interesting, and I totally forgot that I should be measuring AC
| powerline cycles to see how they're doing relative to GPS.
|
| (In the past, I also incorporated a WWVB receiver, but get such a
| terrible signal in New York that I didn't get any usable data out
| of it. I then dropped the ceramic antenna and that was the end of
| that project. I have since realized that I can buy a phase-
| modulation receiver inside of a clock, throw away the clock, and
| try that, however. Ordering one right now, actually! Thanks HN!)
| barrettotte wrote:
| This is the kind of stuff I love to see; an absolute mad man
| nirav72 wrote:
| I've been wanting to build a Raspberry Pi controlled Nixie clock
| - but instead of a Atomic Clock, I'm going just use a USB GPS
| dongle. Also set it up as a NTP server for machines on my home
| network.
| magicalhippo wrote:
| I'm working on just that. The GSP NTP server is handled by a
| different Pi, but makes little difference. I used Chrony and
| it's working like a charm[1].
|
| I'm settling for a regular RTC[2] rather than an atomic clock
| for the fallback though.
|
| Designing the PCB's is taking a bit of time though, me being
| rather new and Nixie tubes being 170V does slow things down a
| bit.
|
| [1]: https://news.ycombinator.com/item?id=28372861
|
| [2]: https://www.nxp.com/products/peripherals-and-logic/signal-
| ch...
| Raineer wrote:
| I've had a Pi GPS clock running for 6 years now, it's
| fantastic. It's not only an NTP server for my house but it's
| been contributing to pool.ntp.org for the duration as well. I
| adore it.
|
| Mine was built with a much older version of this board - https:
| //store.uputronics.com/index.php?route=product/product.... I
| like using the HAT as a dedicated solution instead of the USB
| route.
| sowbug wrote:
| Good luck with the project. Are you adding the GPS component as
| a hobby challenge? If it's going to be an NTP server, then it
| could also be an NTP client.
| nirav72 wrote:
| Its more of a hobby project. Have a spare Rpi 3b and Usb GPS
| dongle from another project. Plus, saw some cool projects on
| the nixie sub. Figured, it would make a nice looking retro
| clock in my home office. The USB dongle is a big finicky. So
| if I can't get that to work - then I might just make it into
| a NTP client and let it sync up with a public server. Nothing
| on my LAN or homelab is mission critical where I need that
| level of time accuracy.
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(page generated 2021-09-08 23:00 UTC)