Why can't clocks be just a bit smarter? - Page 1
Forum section: electronics / projects

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 13, 2023, 10:26:18 am
content: I have an indoor-outdoor thermometer that I set up about a year ago. It has a built-in clock as part of the display. It has lost about 10 minutes over that year. I just set it to the correct time by advancing it by 10 minutes.Why can't the clock learn something from that experience? If the clock is running slow by 10 minutes a year, setting it should "educate" the clock, so that it corrects its rate to compensate for the inaccuracy. That doesn't sound like an insurmountable engineering challenge to me.

author: Jackster
author_rank: Frequent Contributor
timestamp: November 13, 2023, 10:34:16 am
content: If a clock is unable to keep time accurately, it would also not be able to keep an accurate compensation for its own inaccuracy..

author: Dan123456
author_rank: Regular Contributor
timestamp: November 13, 2023, 10:36:49 am
content: I reckon it all comes down to costThey could… but then they would need to spend the extra 5c… and charge you an extra $50 for the productMaybe there are technical challenges too but I’ll wait to see what others have to say on that side

author: DimitriP
author_rank: Super Contributor
timestamp: November 13, 2023, 10:38:22 am
content: The clock is not dumb, it's broken.

author: Psi
author_rank: Super Contributor
timestamp: November 13, 2023, 10:41:16 am
content: Quote from: Connecteur on November 13, 2023, 10:26:18 amMany could, old mechanical clocks often had an adjustment lever inside that you could move if the watch was running fast or slow to correct it.Digital clocks could be designed to add or subtract a tick after n ticks. but then they would need an UI so the user could configure that.

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2023, 10:43:43 am
content: 10 minutes a year is about 20ppm average over the year, which will be varying with the temperature. Since the unit measures its own temperature constantly it has the information needed to correct for that varying temperature, and a quick precision check of the manufacturing tolerance of the crystal during production testing would allow that to be corrected too. If the crystal's aging characteristics are not too severe you could correct that clock to maybe 2ppm or so with a little software. The question for the manufacturer is can they get any extra revenue from the extra effort put it to calibrate the clock? Probably not. Its hard to market accuracy like that.

author: Siwastaja
author_rank: Super Contributor
timestamp: November 13, 2023, 11:08:42 am
content: You could only compensate for fixed error, but there are sources for errors that are not fixed, these are called "drift" in engineering speak.For fixed error, it would be far easier to calibrate that out at the factory instead of adding a user interface and have user do it. Absolute lowest tier cheapest products obviously do neither.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 13, 2023, 11:14:34 am
content: It is smart. It's got you adjusting it.

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2023, 11:30:57 am
content: Quote from: Siwastaja on November 13, 2023, 11:08:42 amA 32kHz clock crystal (almost universal in clocks) oscillator drifts for 2 key reasons - temperature and crystal ageing. The ageing part is hard to compensate for, but the temperature part is easy to reduce by at least an order of magnitude with a temperature measurement, and the application of a quadratic correction curve. While that curve varies a little from sample to sample of crystal, using the mean of a batch of curves in the software works very well.

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2023, 11:56:34 am
content: I'd say that's on par for a cheap clock. Most people alter the clock twice a year for daylight savings time, so it's not an issue.I have a weather station with a radio controlled clock. I believe it receives a low frequency singal (68kHz if I recall correctly) which is broadcast from Cumbria, in north-west England. It adjusts itself automatically and never loses or gains time.

author: wraper
author_rank: Unknown
timestamp: November 13, 2023, 12:10:05 pm
content: These made in Belarus watches that barely changed since production started in USSR sometime in 80's have such adjustment.https://technochas.ru/?page=katalog&subpage=naruchnijeManual in RussianYou check inaccuracy over longer time period, then calculate how much adjustment it needs per day and set the value.

author: newbrain
author_rank: Super Contributor
timestamp: November 13, 2023, 01:17:01 pm
content: Quote from: coppice on November 13, 2023, 11:30:57 amovenized, constant temperature solutions, possibly with a large thermal mass and sophisticated feedback mechanism - they call it "wrist watches".

author: coppice
author_rank: Super Contributor
timestamp: November 13, 2023, 01:24:08 pm
content: Quote from: newbrain on November 13, 2023, 01:17:01 pmYeah, leave a digital watch in a draw and it doesn't keep very good time at all. A lot of timing applications work well because the temperature is not allowed to go wild. A clock in a lounge wall versus the same clock in a shed may have very different accuracies.

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: November 13, 2023, 02:03:47 pm
content: This reminds me of the idea for installing "spin up" motors on aircraft landing gear.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: November 13, 2023, 03:19:13 pm
content: I remember the entirely mechanical clock in my dad's Buick. It actually did adjust itself a bit faster or slower when you reset the time every now and then. Most of my clocks are WWVB clocks now. I keep one like this in the lab-https://airwatches.com/index.php/la-crosse-technology-ws-8117u-it-al-atomic-wall-clock-with-indoor-outdoor-temperature.htmland a big dial one in the computer room.

author: wraper
author_rank: Unknown
timestamp: November 13, 2023, 03:29:31 pm
content: Quote from: coppice on November 13, 2023, 01:24:08 pmThe major reason for clocks/watches running at a wrong speed is not that oscillator frequency drifts but that it was not factory tuned at all. That particular Belarus watch has +/-6.3 seconds/day adjustment range and <0.5 s/day @ 23±2°С spec after adjustment. I had such watch in my childhood and it was pretty good at keeping correct time. Order of magnitude better than most of the "quartz" clocks.

author: xrunner
author_rank: Super Contributor
timestamp: November 13, 2023, 03:42:58 pm
content: Quote from: Connecteur on November 13, 2023, 10:26:18 amLOL it isn't "insurmountable" - it's been surmounted long ago. Get an "atomic" which reads WWVB 60 kHz signals, hang it on the wall, and you've got one that's a bit smarter ...

author: Siwastaja
author_rank: Super Contributor
timestamp: November 13, 2023, 03:55:33 pm
content: The problem with user calibration is that it's prone to go wrong. If you make it automated like the OP suggests:previous change a year ago -> detect 2-minute change -> deduce error of 2 minutes per year, compensatethen what if the user set the clock originally 2 minutes wrong and was now setting it to correct time? Now the clock compensates for an error which didn't exist.You can mitigate this by making the calibration process more explicit to the user (wraper's example), but then it needs to be carefully explained in the manual and many people would still get it wrong.Factory-calibration of initial tolerance error, plus temperature measurement and compensation would be, in the end, simple to implement and would never go wrong like end-user calibration. This still leaves some aging-related drift but it's already pretty small.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 13, 2023, 04:07:56 pm
content: Think of the fun when a naive compensation routine adjusts for the one hour 'error' of a DST change, or a power outage of indeterminate length. Solving these problems requires a user interface, and a user sophisticated enough to know how long the clock has been running since the last adjustment.As mentioned before the right answer is for the clock to periodically reset itself via an independent source. Either a national time broadcast (which is disappearing or just as bad, changing formats in some locations) or wifi to the internet.

author: wraper
author_rank: Unknown
timestamp: November 13, 2023, 05:00:48 pm
content: Quote from: Siwastaja on November 13, 2023, 03:55:33 pmHowever user calibration can be done for nearly free on the chip level. Factory calibration would be much more expensive to implement. Adding analog stuff would require quite a bit more advanced electronics. And running it from 1.5V battery would be problematic too.

author: Bud
author_rank: Super Contributor
timestamp: November 13, 2023, 05:50:50 pm
content: It is a goddamn clock radio FFS, not a chronometer, what do you want from it. Should it also auto-adjust winter time change for you?

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2023, 06:08:34 pm
content: My reasonable-price LaCrosse weather station with "atomic clock" control from NIST works well.The only problem is that on the two days per year where legal time changes from Daylight Saving to Standard Time and back, the automatic change is made not at 2 AM (legal changeover), but at the following midnight.I remember wall clocks that received a pulse by telegraph at the top of each hour that forced the minute hand to top-dead-center: the mechanism itself had to be stable for only an hour.https://www.kensclockclinic.com/docs/model-1900s-white-paper/The astronomy observatory at my undergraduate college (Carleton College in Northfield, Minnesota) has a mechanism given them by the Great Northern Railway (now part of the Burlington Northern Santa Fe Railroad).For decades thereafter, the college sold time service to rail companies in the center of the US.While still there, I stumbled onto some documentation about litigation between the College and the US Naval Observatory about business rights to time services.

author: coromonadalix
author_rank: Super Contributor
timestamp: November 13, 2023, 06:09:37 pm
content: just find an gps synchronized clock ??

author: bd139
author_rank: Super Contributor
timestamp: November 13, 2023, 07:48:09 pm
content: This thread is just fucking retarded.£12 ex VAThttps://www.tlc-direct.co.uk/Products/CKRC10S.htmlMost countries have some variant of that.

author: mansaxel
author_rank: Super Contributor
timestamp: November 13, 2023, 08:01:52 pm
content: Quote from: wraper on November 13, 2023, 12:10:05 pmAlmost all mechanical watches can be nudged thusly, be they manual or automatic winding.These days, you (if you're a watch tinkerer) forego the long time base calculation, and instead buy a special calculating frequency counter with a microphone on its input, then place the movement on it, and let it listen for a while. After a few seconds, it has figured out the clock frequency, usually between 5 and 8 ticks per second, and then it will start comparing the ticks heard to its internal reference. After some more time, usually less than a minute, it will plot a graph of the movements behaviour together with a prognosis on accuracy. There will be reports on how fast/slow it goes and if the movement jitters, all of which is important data for the continued troubleshooting or simply regulation of the watch.

author: floobydust
author_rank: Super Contributor
timestamp: November 13, 2023, 08:21:57 pm
content: Quote from: bd139 on November 13, 2023, 07:48:09 pmNot entirely retarded- 32kHz watch crystals and their parabolic tempco have been around for many decades. Very few people here know WTF N750 means. It's a lost art.I have a Casio Japan watch, it has a trimmer cap but the ~15°C temperature change between on my arm or the nightstand makes any watch challenged to not drift.Atomic (radio-controlled) clock's signal isWWVBfrom Boulder Colorado 60kHz. I thought SMPS EMI was really making them not work well. Couple thousand km away. WWV 10MHz is a challenge to pick up, for both coverage varies with weather and time of day. Did it sync? Stupid VLF receivers will not save the world.I find GPS a little power piggy and signal won't make it through metal roofing or solar-tinted windows.So far, for stand-alone clocks the DS3231 does great although moving time back and forth for DST is a PITA.So clocksaredumb in 2023.

author: bd139
author_rank: Super Contributor
timestamp: November 13, 2023, 08:28:16 pm
content: Oh noes! Look at the one on your phone or computer thenI literally haven't had to set a clock for the last decade. I occasionally take a Casio F91W out if I'm going somewhere exotic but I don't care about second or even minute precision over time as it's for approximation and pacing.

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2023, 08:32:38 pm
content: My $24 "atomic clock" receiver for WWVB is about 1 meter from my desktop computer and monitor, which have smps.From Chicago to Colorado is about 1600 km.The clock is wall mounted on the first floor of a two-story brick house, and has a clear indicator of when it is sync'ed.It works.Try parsing the original title: "Why can't clocks be just a bit smarter?", as opposed to "Why is my clock not smart enough?"

author: xrunner
author_rank: Super Contributor
timestamp: November 13, 2023, 08:35:02 pm
content: Quote from: bd139 on November 13, 2023, 08:28:16 pmI still got two that lose time when a power outage happens, nor do they keep up with daylight savings time changes. They are the microwave and the built-in oven.I said f*ck it to the microwave clock years ago who cares? I just let it show a ":" with no numbers.The oven? Just to remind me of the good old daze I do set it now and then.

author: magic
author_rank: Super Contributor
timestamp: November 13, 2023, 08:40:12 pm
content: They make 32kHz TCXOs so you can upgrade your clockhttps://www.analog.com/media/en/technical-documentation/data-sheets/DS32KHZ.pdf

author: bd139
author_rank: Super Contributor
timestamp: November 13, 2023, 08:40:48 pm
content: Quote from: TimFox on November 13, 2023, 08:32:38 pmtl;dr:https://xyproblem.info/

author: bd139
author_rank: Super Contributor
timestamp: November 13, 2023, 08:45:11 pm
content: Quote from: xrunner on November 13, 2023, 08:35:02 pmYeah I've got an oven too. Current time ... whatever-o-clock!

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 13, 2023, 09:23:14 pm
content: Quote from: Connecteur on November 13, 2023, 10:26:18 amYou are correct, it's not 'an insurmountable engineering challenge' at all.A smarter question, is does it make financial/business sense ?Original RTCs are simple chain counters in a low power CMOS process. A clock only needs to count to 24hrs.So you are asking to add counters to track last-set time for hundreds of days, then you need maths ability to divide the two numbers, to calculate and then apply a assumed correction.What about a dying battery ? The counter will likely continue as the voltage falls, and frequency drifts further, then it will lose counts and get garbage in the registers.Now, a manual set gives nonsense for the correction, and customers phone to complain...See the problems yet ?What parts does this indoor-outdoor thermometer use ? If it is a flash MCU, you could create new firmware...

author: mwb1100
author_rank: Frequent Contributor
timestamp: November 13, 2023, 09:28:58 pm
content: This thread reminds me of a spoof ad (SNL?) from way back for a VCR clock repair kit. The kit contained a strip of electrician's tape.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 13, 2023, 09:29:50 pm
content: Even just 1 ppm of drift, which is already a pretty decent oscillator, will be 31 s per year. If you're not ready to spend ridiculous amounts of money for an atomic clock, just synchronize it automatically using whatever is most practical for your use case (GPS clock, NTP, DCF-77 if your'e in Europe, etc.) It works and is much more practical than trying to be smart.

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2023, 09:47:34 pm
content: Price for "atomic clock":My vendor in US has such clocks (using WWVB) starting at about $25 list price (cheaper through retailers):https://www.lacrossetechnology.com/collections/atomic-time#/sort:ss_price:ascHow much do similar units cost in Europe?My exact model seems to have been discontinued: it included an indoor temperature sensor and a wireless outdoor temperature sensor .(I had to add their optional outdoor shield enclosure to get reasonable outdoor temperature readings.)Of course, a real cesium primary atomic clock is a bit expensive: thousands of USD.

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2023, 09:48:36 pm
content: Quote from: mwb1100 on November 13, 2023, 09:28:58 pmSNL also had a spoof ad for a digital-readout wristwatch (LEDs) that required three hands to enable the time display.

author: SiliconWizard
author_rank: Super Contributor
timestamp: November 13, 2023, 10:01:37 pm
content: Quote from: TimFox on November 13, 2023, 09:47:34 pmThese clocks use the WWVB signal, which is a US equivalent to our DCF-77 that I mentioned. Prices are equivalent. The receivers are pretty cheap. (Don't know about WWVB, but over here, the DCF-77 signal has been harder and harder to receive cleanly the past few years, due to too many interferences everywhere. It's just AM...)https://en.wikipedia.org/wiki/WWVB

author: TimFox
author_rank: Super Contributor
timestamp: November 13, 2023, 10:17:06 pm
content: That Wiki article has a lot of detail about the phase-modulated encoding used along with the AM.I was truly amazed when American politics thought of defunding WWVB (and short-wave WWV), since "atomic time" timepieces (watches and clocks) are so popular in the US (> 50 million in use), but cooler heads prevailed.The 20 kHz station WWVL was shut down in 1972.

author: TonyStewart
author_rank: Contributor
timestamp: November 14, 2023, 01:52:08 am
content: You would have to know how much of tolerance and stability with temperature and aging. Although most are the parabolic tempco, you have 20 ppm of cumulative error and if the temperature was the same as a year ago, then you have no reference to correct the seasonal error.As stated the solution takes more than a simple 20 ppm correction to make a significant improvement.

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 14, 2023, 02:40:56 am
content: Quote from: TonyStewart on November 14, 2023, 01:52:08 amI disagree that you would have to know any of that. The circuit could simply use the amount of time difference over the running time, and simply adjust the running rate accordingly. It doesn't need to be any more complicated than that.

author: DTJ
author_rank: Super Contributor
timestamp: November 14, 2023, 03:00:34 am
content: Quote from: Jackster on November 13, 2023, 10:34:16 amSure but buy adjusting it once and it learning from the period between adjustments and the amount of adjustment you have 'calibrated' it.It won't be perfect but it will be a *lot* better than no adaptive adjustment.

author: TimFox
author_rank: Super Contributor
timestamp: November 14, 2023, 03:47:40 am
content: A parable, from personal history:A professor of mine, who was from Germany, was giving an elementary lecture on electron optics.He wrote an equation on the board, which obviously had a solution in the form of a sine function, and asked how to solve it.A theoretically-minded student in the front row said to find the Green's function.The professor replied, "you could also put your pants on with tongs".

author: mansaxel
author_rank: Super Contributor
timestamp: November 14, 2023, 06:51:31 am
content: Quote from: Connecteur on November 14, 2023, 02:40:56 amAlready that will be complicated. How do you know that those 20ppm weren't all gained or lost in the last 5 days? Or in other words;Your simplistic model contains a feedback loop length that is way too long. You do not know if your clock has drift (steady change in one direction), wander (here: slow oscillations around an average) or jitters (fast variations). Or a combination of the three!In addition to a reference clock, you need to sample more often than once a year in order to catch variation. Only when the characteristic of the movement is known can you lower sample rate.NTP, radio controlled clocks, GNSS derived time, et c will all fix this to levels of accuracy my grandfather could only dream about. Ok, he repaired typewriters, so probably did not care about the SI definition of the second, but you get my drift (sic.).So, get one of those. There are no easy solutions to most hard problems, but fortunately there are lots of people who have packaged the hard solutions in easy bite-size chunks at an attractive price.

author: zapta
author_rank: Super Contributor
timestamp: November 14, 2023, 07:48:11 am
content: if every year it deviates exactly the same, this is a very accurate clock.

author: magic
author_rank: Super Contributor
timestamp: November 14, 2023, 08:04:36 am
content: Quote from: Connecteur on November 14, 2023, 02:40:56 amAnd a load of reasons has been given already why this will never work in practice.OK, maybe after 10 years the clock could actually gain some confidence that it understand what's going on, but by that time the owner will have already thrown it out...

author: Siwastaja
author_rank: Super Contributor
timestamp: November 14, 2023, 08:17:53 am
content: Quote from: Connecteur on November 14, 2023, 02:40:56 amWhy do you make a thread if you don't read the replies? I addressed specifically why your suggested procedure does not work in my earlier post: if user originally sets the clock wrong, which would be completely normal in absence of perfect reference, then this calculation would be wrong. For end-user calibration, a more explicit procedure where the user knows they are making an adjustment, as shown by wraper, is less prone to go wrong.

author: wraper
author_rank: Unknown
timestamp: November 14, 2023, 10:15:50 am
content: Quote from: Siwastaja on November 14, 2023, 08:17:53 amThe major problem I see is how are you supposed to enter the difference? Setting a new correct time down to a second? Good luck with that on a first try. Then how do you confirm that this time you actually entered correctly? Entering a number of how much time must shift? Then you need to calculate yourself anyway.

author: Smokey
author_rank: Super Contributor
timestamp: November 14, 2023, 10:46:08 am
content: You guys are all wrong. That clock kept absolutely perfect time.What you missed was that during that year, someone stole your clock and took it for a joy ride at the speed of light, then put it back.

author: coppice
author_rank: Super Contributor
timestamp: November 14, 2023, 01:55:24 pm
content: Quote from: Smokey on November 14, 2023, 10:46:08 amIf that happened he would remember the anal probing. All encounters with aliens travelling at the speed of light leave a strong memory of the anal probing.

author: TonyStewart
author_rank: Contributor
timestamp: November 14, 2023, 04:06:39 pm
content: You can tweak the capacitance on your CPU RTC crystal if you like.https://www.fountainware.com/download/TimeCalibrator/TimeCalib.exestay in sync within 10 ms all the time !

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 15, 2023, 04:15:18 pm
content: Quote from: wraper on November 14, 2023, 10:15:50 amI had a mechanical clock that used a similar principle and it worked. If you wound it up one day, and it was 10 minutes fast the next day, the very act of setting it back 10 minutes, adjusted the rate by slowing it 10 minutes per day. After a few settings, it was keeping nearly perfect time.It would seem to be a simpler engineering problem to make a digital clock work that way.It's not that I don't read replies that say I'm wrong, I just disagree with them.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 15, 2023, 06:07:09 pm
content: Quote from: Connecteur on November 15, 2023, 04:15:18 pmI had such mechanical clocks also, and I think you are missing the key point. Initial errors in such clocks were minutes per day or more (ten in your example). That is a large enough error that an implicit assumption of how long it has been since an adjustment is going to give an improved result. And the time is short enough that seasonal factors like temperature are not involved. The minor tweak of making the actual correction a fraction of the 'computed" value assures convergence. The untrimmed error on quartz clocks is measured in minutes per year and is over an interval long enough to bring several different unknowns into the problem. Those simple algorithms are much less effective and either result in very slow convergence on a good average value or actual divergent behavior. The benefits of a clock whose accuracy slowly improves over a decade or two of adjustments apparently isn't worth the effort for vendors and users alike.It doesn't matter what the system is, as you pursue more and more decimal points of accuracy the problem gets more complicated. In some cases the complication is hidden in a huge amount of work that has been done fabricating the device. Quartz time keeping crystals are a case in point. The concept is fundamentally simple. But look into the details of making these things. The good news is that because of all that work several orders of magnitude of accuracy have been obtained. The bad news is that taking it further requires esoterica such as temperature control, mechanical stresses on leads, stray capacitance and many other fun things.

author: floobydust
author_rank: Super Contributor
timestamp: November 16, 2023, 02:22:29 am
content: How accurate a mechanical clock keeps time despite the main spring being wound up or not, would be interesting.Another unexpected variable is the RTC operating voltage. Had a power outage for a few hours and running off battery, a few calibrated clocks I have drifted off frequency. From 5V to 3V.So it's ambient temperature, system voltage, and aging that need to be accounted for. And spring tension lol.

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 16, 2023, 04:51:40 am
content: Quote from: CatalinaWOW on November 15, 2023, 06:07:09 pmI don't think so. One of my digital clocks loses a minute per month consistently, and has done so for the last 10 years. Unfortunately there is no fine-tuning, as there was once on mechanical clocks. If I adjusted it to the correct time, it should be able to figure out how much time it loses in a month, or however frequently I reset the time. Unfortunately no one seems to have been able to engineer such a simple solution.

author: 5U4GB
author_rank: Super Contributor
timestamp: November 16, 2023, 07:18:10 am
content: Quote from: Jackster on November 13, 2023, 10:34:16 amAlso known as "asking the drunk whether he's drunk".

author: 5U4GB
author_rank: Super Contributor
timestamp: November 16, 2023, 07:22:58 am
content: Quote from: Conrad Hoffman on November 13, 2023, 03:19:13 pmSeiko makes beautiful analog clocks under the name Space Link that are GPS-sync'ed. They're pretty impressive, you tell them your time zone and when DST starts and stops and that's it. Downside is that they're a bit expensive to get from Japan, like many cool Japanese things they don't seem to be sold much outside of there.

author: mansaxel
author_rank: Super Contributor
timestamp: November 16, 2023, 12:17:49 pm
content: Quote from: Connecteur on November 16, 2023, 04:51:40 amThere is such a system. Dave Millsntpdhas provisions for a "drift file", a record the ntp daemon keeps of the corrections it has had to apply to the system clock in order to stay in sync with its peers and servers. Over enough long time, this, in theory, and given enough high quality (as in stable, with excellent low-PDV symmetrical network connection, et c) peers, and a stable enough local reference oscillator, an otherwise pretty modest clock could tune itself pretty close. In practice, the clocks in computers are too cheap for this to work in an insular mode unless the holdover time is short.In the practical end, then, ntp clocks are much more stable when talking to others, which sort of devaluates the drift file concept. We have better ways, and we should use them.

author: CaptDon
author_rank: Super Contributor
timestamp: November 16, 2023, 03:43:13 pm
content: There were many digital clocks years ago that used a 3.58MHz 'color crystal' and they kept terrible time as there is no accurate divisor to produce 1p.p.s. and the crystals couldn't be 'pulled' far enough to work correctly. Your self correcting digital clock would also have to measure the time 'between corrections' and how far you corrected it to derive a 'correction factor' to then be applied. Far to much to ask from an economical clock. Fantastically cheap very accurate clocks that use no external reference are easy to find. My little 'single AA powered' travel alarm clock is probably good to about 1 minute per year and cost under $10 U.S.D. If you have a clock that is inaccurate it is trash and its best duty would be target practice!! Far more rewarding watching it blown to bits than constantly resetting it!!! I could sell you my 'one off' 9 digit Nixie display rubidium clock from General Dynamics : Electronics which says it was made by Geo Space Corporation. It shows + and - on far left then 3 digits of days, 2 digits of hours, 2 digits of minutes and 2 digits of seconds. It uses long life large nixies and I turn off the nixie high voltage to preserve their life. It also outputs parallel TTL level BCD data for all digits! The cable to the remote display would make a horse jealous. AND it never needs tweaking. (B.T.W., none of the manufacturers listed on the label ever recall making it even though it has a model and serial and says it was made 8/31/65.

author: floobydust
author_rank: Super Contributor
timestamp: November 17, 2023, 04:05:39 am
content: Quote from: CaptDon on November 16, 2023, 03:43:13 pmThe MM5369 did it, you don't divide down to 50/50 duty cycle waveform. I have 3.579545MHz crystal massive HC-6U can and 50 years old doing fine paired with the IC.Or doing it with a PIC 12C508AN4_008 An Enhanced MM5369 - 60Hz Generator

author: CaptDon
author_rank: Super Contributor
timestamp: November 17, 2023, 01:36:05 pm
content: I do remember as another poster stated an automotive clock from around 1964/5 that in the owner manual said if it was running fast set it backwards at least one full revolution of the hour hand, do the opposite if running fast. Apparently cranking the adjustment button also somehow effected the mainspring adjuster? It was a 'ticking' clock with a solenoid impulse winder that you could hear 'kick' about every 10 minutes. Old cars (1960's vintage) had the best clocks (some even with the tachometer included) and the most sensitive A.M. radios that were fantastic to use downstream of a shortwave 'converter' back in the days of Swiss Radio International, Radio Norway, B.B.C., V.O.A. and even Radio Moscow. There used to be really interesting stuff on international broadcasts!!! (and great music)

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 17, 2023, 04:00:06 pm
content: It seems sad that after all this time, no one has perfected the digital clock by making it self-adjust for accuracy.Apparently it was "job done" over 40 years ago, and very little improvement was done since.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 17, 2023, 05:00:22 pm
content: Quote from: Connecteur on November 17, 2023, 04:00:06 pmWhat you are sad about is that you represent what seems to be a very small market.What you seem to want is a cheap clock that after some number of manual adjustments doesn't need to be adjusted again. Or at least needs adjusted very rarely thereafter. And one that is guaranteed to meet that requirement in every unit sold.The market has provided cheap clocks that usually only require adjustment after several months or even years, somewhat more expensive clocks that don't require adjustment at all because they adjust themselves via a radio signal or the internet, and expensive clocks that are so accurate that they don't need adjustment over human time scales.Your cheap clock is defective, an outlier that provides accuracy far lower than is typical for the breed. But these are sold by the millions (probably tens of millions and possibly hundreds of millions) and at prices such that the cost increment for switches, sensors, backup batteries and whatever other paraphernalia required to implement a self correction algorithm would be an issue. So the tradeoff for manufacturers addressing this market is between customer dissatisfaction with some tiny fraction of their output and the loss of sales to other manufacturers with slightly lower costs. I don't know how common defects of the magnitude of your clock occur, but my personal experience suggests that it is a four sigma or more event.If this is important to you the solution is rather easy. Make your own. A clock that self corrects could easily be implemented in an Arduino. A few evenings of effort and you would have the perfect solution for you, which isn't apparently something that the market is clamoring for. It may take the rest of your life to determine if you have really met your expectations. Presumably the interval between required adjustments will decline over time. But what interval is satisfactory to you? Bi-annual? Once a year (common for the cheap digital clocks)? Every decade?

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 17, 2023, 06:06:03 pm
content: I think the market would be huge for a self-calibrating clock.How many of us are frustrated by electronic clocks that drift off time constantly?Nearly everyone I'd say. The fascination with a clock regulated by a quartz crystal should have worn off after nearly 60 years.Synchronizing it to an external signal seems like a lazy shortcut to me.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 17, 2023, 06:06:34 pm
content: Quote from: Connecteur on November 17, 2023, 04:00:06 pmYes and no.There are a huge number of choices now, around ‘getting the time’, as well as a lot more choices in resonator performance.What has changed little, is the very bottom end, where the tuning fork crystals still do the work.Many products bundle a ‘clock for free’ because marketing decides that helps the feature list.There are huge numbers of clocks never set, or ignored.

author: TimFox
author_rank: Super Contributor
timestamp: November 17, 2023, 06:07:23 pm
content: External synchronization works well, and does not need intervention by the owner.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 17, 2023, 06:12:04 pm
content: Quote from: Connecteur on November 17, 2023, 06:06:03 pmThen go for it !I think you meant to say ‘user calibrated’ clock, or even ‘user who can find the manual calibrated clock’You may also need to revisit the meaning of ‘calibrate’

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 17, 2023, 06:13:28 pm
content: Quote from: TimFox on November 17, 2023, 06:07:23 pmMost of our clocks do not have any cost-effective way to receive an external signal. Nearly everything nowadays has a clock, and most of them are not very accurate. A self-calibrating circuit would cost little or nothing extra to incorporate.

author: TimFox
author_rank: Super Contributor
timestamp: November 17, 2023, 06:27:56 pm
content: Quote from: Connecteur on November 17, 2023, 06:13:28 pmA quick Google for "cheap atomic clock" finds available simple clocks for $5.00 US.(Of course, "atomic" here means synchronized to WWVB in US, or VLF stations in other countries.)Walmart has many for less than $15.00 US.Therefore, we see thatmanyclocks have a cost-effective way to be synchronized to an external signal.Those who need high accuracy have many choices already.

author: coppice
author_rank: Super Contributor
timestamp: November 17, 2023, 06:38:48 pm
content: Quote from: TimFox on November 17, 2023, 06:27:56 pmOvens with wifi usually set their clock from the internet now. However, for years high end ovens have had MCUs in them to run fancy timers. A cheapy RF front end and a little code could have made most of them work from the 60kHz beacons, and most ovens are in an open enough location to receive the signal clearly. I've never seen one do that, though. Connected to the mains, you don't have to worry about an oven gaining or losing, unless you are in an area with flaky power, but going out at the wrong time 2 mornings a year because you forgot about daylight savings, and rely on the oven clock while eating breakfast is a nuisance.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 17, 2023, 07:04:33 pm
content: Quote from: Connecteur on November 17, 2023, 06:13:28 pmYou are badly mis-using the term self-calibrate.What you propose is a user applied correction, that the clock somehow learns from, but how should the clock learn ?This graph below is what you fight against - the real world :so a user correction, is not enough information, as the smart clock really needs to know the historic average temperature, and the likely upcoming temperature.Once the clock knows all that, it does not need the user anymore, you have just 'invented' the TCXO.

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 17, 2023, 09:22:57 pm
content: I'm no engineer, but it seems like a simple calculation to determine the error as the difference between the clock's time, and the corrected time, and divide that error over the running time since last set. It's hard to believe that all the engineering managers since digital clocks began, forbade anyone to incorporate such into the design.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: November 17, 2023, 09:30:09 pm
content: Quote from: Connecteur on November 17, 2023, 09:22:57 pmGo ahead, and build what you are sure will sell.- but before that, you might like to find an engineer, to explainwhythat curve I gave, matters.

author: MarkT
author_rank: Frequent Contributor
timestamp: November 18, 2023, 10:09:55 am
content: The whole premise of the thread is suspect - the original device was a thermometer. Someone decided it was good to add a clock to a thermometer, then it got implemented poorly, turning what was probably a perfectly good thermometer into a flawed product for no reason!If they wanted to show the daily maximum and minimum temperature that can be done smartly without requiring high accuracy timing or trying to show the time, just log the time regularly into a buffer that holds the last 24-ish hours of data.Creeping featuritis...

author: xrunner
author_rank: Super Contributor
timestamp: November 18, 2023, 12:51:31 pm
content: I think we've all gotten too anal with accurate time (me included), what with GPS clocks and all that.Really, for daily life just get a cheap clock with hour and minute hands, specificallyNOsecond hand. Set it to the approximate time with your eye and use it for daily living. If it's off even by two minutes either way is it going to matter all that much? All you need to know is, is it abut lunch time, is it close to when I need to leave for my appointment?I don't even need a clock to tell me to fix lunch, my cat knows, somehow, he really seems to know what time lunch time is.

author: Connecteur
author_rank: Frequent Contributor
timestamp: November 23, 2023, 04:42:12 pm
content: I can't help but be disappointed that such a simple and useful innovation has escaped nearly all the greatest minds in the circuit engineering world.