Seconds out of sync with blink

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3 months 1 day ago #10433 by MikeS

davideos wrote: Although I don't have specs for this particular one I purchased, I found that the expected accuracy (at least from one internet site's perspective) is 0.5%. Mine is actually better than that at 0.22%. So I don't think my crystal is bad. Even a more precise oscillator is going to be off and will eventually show a sign of re syncing.

Are you sure? That would be a really, really terrible crystal. 50 ppm (0.005%) is more likely, although 20 ppm is very common. Ceramic (not crystal) resonators are more like 0.5%, but that's not what your classic kit was designed to use.

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3 months 1 day ago #10434 by davideos
I'm pretty sure what I have is a resonator although advertised as a crystal oscillator. I think that's what I received in my original kit as well, but I'm not 100% certain; but I have seen it exhibit the same behavior.

It is relatively easy to see if your "crystal" is keeping up. Just look at the right-most seconds digit as the separator/blink LED or Neon is increasing in intensity. Note if it is odd or even. Check again sometime later. Mine will change odd-even or even-odd every 7-8 minutes. The longer the time between, the better the accuracy of the clock source.

It isn't any big deal anyway.

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3 months 1 day ago #10435 by Ian
Replied by Ian on topic Seconds out of sync with blink
OK, there are two things going on here, but I think they are both back to the fact that the crystal is bad.

Seconds out of sync:
We're running the separators from the millis() counter so that we can do the fade. USUALLY the seconds and the millis don't drift, but if they do, you will see the separators and the seconds diverge. If the crystal is really crap, you'll notice this. If it's only a bit crap, you should not really notice it. If it's a problem, I can do a software change to sync the millis to the second change. I never obsessed about it, but that's just me. Now you've made me notice it, I suppose I'll end up changing it... ;)

Stutter at the minute change
Once per minute we read the RTC and then we're re-sync the millis used internally to count all the seconds up from 1 to 59. In the space of a minute, it's hard that there is a noticeable drift. It's only 60 seconds, but the crystal you have seems to be so crap that it's drifting by a good portion of a second in the 60 it went "unattended".

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3 months 1 day ago #10436 by davideos
I'm pretty sure what I have is a resonator with pretty low precision. However, it isn't every minute that a correction occurs...once every 7-8 minutes...which turns out to be about 0.22% accuracy, which is within spec for a resonator. I'll need to buy a crystal from a more reliable source....but it isn't so bad that I need to do this immediately.

I got my RTC from ebay/china and I had expected that to not be very good, but it hasn't lost a second in even the 2 weeks I've had it running. I think I got lucky there.

As for the "seconds out of sync", I haven't seen that occur again since I updated the firmware from v55 to v56.

Bottom line, it seems to be working quite well. I suppose if I want to watch the clock every second, I might be disappointed. Anyway, I purchased 3 more PCBs, so I must be quite happy with it :)

Thanks.

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2 months 2 weeks ago #10440 by Phil_Mod3
Not 100% on topic, but:
I'd prefer to have separator neons/leds in sync with seconds. I changed the code for the separators in a way that they are on for one second and off for another second, without any fading. With that, the out of sync is much more conspicuous and really anoying. In my adapted code, performOncePerSecondProcessing() is now triggered by a change of second() and not by millis().

Thanks
Phil

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1 day 21 hours ago #10641 by Ian
Replied by Ian on topic Seconds out of sync with blink
Ty did this on the firmware versions for the Numitron clock: It's a simple fix. I will backport it soon.

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