The most unhinged video wall, made out of Chromebooks • Hacker News Board

Re: The most unhinged video wall, made out of Chromebooks

#61

Post by simondotau » Sun, Mar 02, 2025, 11:38 PM UTC

varun_ch wrote: post #44

simondotau wrote: post #39

Earlier quoted context omitted.

I feel like this deserves a deep dive of its own. Were the clocks drifting substantially over a reasonable time period between syncs (e.g. 24 hours)? Was SNTP not acting reliably? Did they try hosting a local time server?

Did not get the chance to try much at! We just observed that clocks could be synchronized, but the next time we checked they would no longer be. I agree that this is definitely something that could also be interesting to look into in the future.

Was the sync issue observed before or after replacing ChromeOS with a raw Linux distro? I believe ChromeOS has a number of issues with time sync.

Re: The most unhinged video wall, made out of Chromebooks

#62

Post by incanus77 » Sun, Mar 02, 2025, 11:39 PM UTC

Love to see this repurposing. My first experience with Chromebooks was after a workshop at Teardown '23 here in Portland, where I attended a session on using the MrChromebox stuff. I eventually ended up using the knowledge to encase Chromebooks in custom-built cabinets for use as display screens and GPIO interfaces for a science festival educational exhibit on electromagnetism and speakers.

https://justinmiller.io/projects/catchthewave/

The machines are rugged (the spec I use is "able to be dropped on concrete from waist high and to have a full soda dumped in the keyboard") and once running Linux, fast and light. And I got them for $50 a piece!

Re: The most unhinged video wall, made out of Chromebooks

#63

Post by crote » Mon, Mar 03, 2025, 2:45 AM UTC

01HNNWZ0MV43FF wrote: post #41

simondotau wrote: post #39

Earlier quoted context omitted.

I feel like this deserves a deep dive of its own. Were the clocks drifting substantially over a reasonable time period between syncs (e.g. 24 hours)? Was SNTP not acting reliably? Did they try hosting a local time server?

I was on an IoT project once and surprised to find that when blocked from ntp, PC clocks drift pretty quick. A couple milliseconds per day would not surprise me. It looked to me like the fleet did consistently fall behind, which seems like thoughtful design - syncing would always cause them to skip ahead and never rewind time

Accurate timekeeping is hard. Computers generally don't need long-term clock stability, so nobody is going to invest a lot of money into it. Why bother putting expensive timekeeping hardware in a machine to avoid clock drift when you can also just sync from ntp once a day?

If anything, I'd consider "milliseconds per day" to be extremely good. Regular crystal oscillators have an error of 20 PPM or so, which means a worst-case drift of ~2 seconds per day.

Re: The most unhinged video wall, made out of Chromebooks

#64

Post by _kb » Fri, Mar 07, 2025, 9:00 PM UTC

greggman25 wrote: post #42

preinheimer wrote: post #33

Earlier quoted context omitted.

The author tried, but the clocks wouldn’t stay in sync. It’s in a sidenote expandable section. > Unfortunately, these Chromebooks could not reliably keep track of time within milliseconds of each other, so this method didn't work for us.

I don't know if syncing the videos would work because of playback issues over time but the aquarium pages sync their clocks every second just asking the server the time (demo time not wall time) over web-sockets and then subtracting 1/2 of the time it took to get a response. I suspect the technique works better for time based animations than video since video require seeking to change the time.

PTP [1] is a common approach to time sync in these scenarios. It provides sub-microsecond accuracy for when working on a LAN. This is used behind most products, software, and protocol suites in the real-time media space.

[1]: https://networklessons.com/ip-services/introduction-to-preci...