Garmin vivofit 4 losing time (possible on digital watches?) - Page 1
Forum section: electronics / general

author: edy
author_rank: Super Contributor
timestamp: September 08, 2019, 05:12:58 pm
content: I have a Garmin vivofit 4 that is probably about 6-7 months old now. I'm assuming the battery is going. But my stupid question is, how can a digital watch lose time with low battery? I never experienced this with any of my other digital watches (Casio, Timex). I always assumed the crystal in there keeps constant frequency and low battery would result in display fade and just shutting off eventually. I've never experienced a digital watch running slow with normal LCD contrast. It would always run normal and fade out. Is the Vivofit4 using some other method for keeping time that is susceptible to losing time or does this happen with all digital watches (and perhaps I didn't notice because they use way less power)? The vivofit4 is designed to last about 1 year before you need to change the internal battery, whereas my Casio or Timex last 5-10 years.

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 08, 2019, 05:46:04 pm
content: Googling this finds a lot of others with the same problem, I'd contact Garmin (for a replacement?).

author: edy
author_rank: Super Contributor
timestamp: September 08, 2019, 05:54:42 pm
content: Yes thank you, I have seen the posts of others finding a similar issue. Garmin's stock answer seems to be to keep Syncing your device daily (which resets the time to the phone) and changing the battery. My more basic question is related to the design of the watch... that is, how does it keep time? Is it a basic electronic design decision that makes the watch have voltage-dependent clock speed? Do crystal-based circuits have this issue when voltage starts to drop? Does Garmin prioritize LCD contrast to keeping the clock circuit working accurately or perhaps figures that being synced often it didn't care to design in very accurate time?

author: PA0PBZ
author_rank: Super Contributor
timestamp: September 08, 2019, 06:03:24 pm
content: That is a fair question and I'd say yes, according to your findings the oscillator frequency is voltage depended, also because they say to replace the battery. I agree that it seems a bit of a weird design choice but all evidence points to the fact. Try changing the batteries and see what happens, they are not that expensive.

author: edy
author_rank: Super Contributor
timestamp: September 08, 2019, 06:14:33 pm
content: Garmin has an answer on their website regarding vivofit and vivofit2, which I guess applies also to vivofit4... involving changing the battery and applying Vaseline to each side of the battery to prevent battery "wear"?I don't get it?!? And I quote...https://support.garmin.com/en-CA/?faq=4CAZECSpgg2qNuVBhn9gX5QuoteWhat does the Vaseline do? Are they worried about corrosion and possible oxides forming which decrease voltage or is the Vaseline layer itself acting as a small resistive element to reduce current draw, thereby prolonging the battery life?!? The official explanation talks about battery "wear" which seems fairly ambiguous and still doesn't explain why a digital device which I assume would use a quartz crystal would lose time, and why a thin film of Vaseline is considered a solution?

author: amyk
author_rank: Super Contributor
timestamp: September 08, 2019, 07:16:33 pm
content: That's because "dielectric grease" would be too technical for most users to understand. I think what's happening is that dissimilar metals between the battery and contacts are causing corrosion.

author: edy
author_rank: Super Contributor
timestamp: September 08, 2019, 07:29:35 pm
content: Quote from: amyk on September 08, 2019, 07:16:33 pmWould this require the ingress of moisture or can it happen on a dry contact between 2 dissimilar metals? Also wouldn't dielectric grease or vaseline act as an insulator and introduce additional resistance to the contact? From online usage and descriptions we find the following:QuoteNow I realize for the purposes of the Garmin battery we are talking a very thin coating and the effects are probably negligible but again, even this doesn't seem to address why the underlying circuit loses time unless the oscillator frequency is voltage-dependent. Not sure if quartz circuits suffer the same effects, but a 555-timer type circuit I assume would.

author: amyk
author_rank: Super Contributor
timestamp: September 09, 2019, 12:14:10 pm
content: Yes, it requires moisture --- which is what the dielectric grease keeps out.The grease itself is an insulator, but the wiping action of the contacting surfaces removes it from the actual contact while maintaining a barrier to moisture around. I'm not sure where that paragraph suggesting to not apply it to the contacts came from, because that's the way I've always used dielectric grease and it hasn't been a problem.On such a lower-power device the crystal is going to be driven atverylow power, so any sagging power rail may cause it to be slightly intermittent when running.