LED alarm clocks all lose accuracy over time

I have 3 Intelli-Time LED alarm clocks around the house, just like the one here:

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I initially bought these due to them keeping time when the power goes off and auto resetting for DST. There is a problem, however. Each of the clocks becomes inaccurate over time. If I set them all manually to the same time, within a few months, each one will be off by 3-5 minutes.

So I ask, what is the problem and is there any way to repair it?

Thanks in advance, Bill

Reply to
Bill Proms
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027a2.html

same

I've always put this down to hash on the mains being interpreted as extra cycles by the clock monitoring input. The supply companies contractually have to correct the mains frequency so an exact number of cycles per day (50/60)x60x60x24, but at any instant can be above or below the nominal frequency.

Reply to
N_Cook

[...]

Anyhow in continental Europe the 50Hz is very accurate due to the large high voltage net, which must be synchronized to all generators in all connected power plants.

I doubt but don`t know if GB is power connected to the continent. So their frequency shift is possibly much larger due to less coupled generators.

Same I think in the US where AFAIK not all powerplants are connected to a great (one?) power net.

On load the generator/turbine set slows down a little, so frequency goes down. On load dump they accelerate a little (less or more) depending on the amongth of all coupled generators and the accuracy of the net controll.

So the frequeny of 50/60Hz line varies, but in continental Europe the

50Hz varies much lesser than in all other countries.

Saludos Wolfgang

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Reply to
Wolfgang Allinger

You didn't mention if there had been actual power interruptions during the period you are measuring. Most inexpensive clocks use the power line frequency to keep time when they have power, but use a cheap oscillator when the power is off. I have one that keeps very good time normally, but during a power outage, it runs very fast (gains 5 minutes per hour). That is good in that the alarm goes off in time for me to get up and go to work, but I always have to reset the time after a power outage. Some of your clocks might be close while others are way off but only during a power outage.

Pat

Reply to
Pat

Yes, there are power interruptions and surges on occasion, but the former LED clocks I had never lost time over periods of years.

As a possible replacement, I have considered an atomic LED clock, but these appear to be next to impossible to come by for some reason. I see LCD atomic clocks everywhere, but most or all have to have the backlight pressed to see the time in dim conditions.

Bill

Reply to
Bill Proms

Barring the possibility that your powerline frequency is erratic, I'm inclined to accept Mr Cook's explanation -- that these clocks have poor powerline filtering, and spikes get through to trip the counter. You might try putting a ferrite choke on the line.

The LED clock has become uncommon, if only because it doesn't lend itself to cordless operation. I keep one in the bedroom for those occasions when I need a loud alarm, but it's not atomically controlled.

This one looks interesting. It //claims// to always display the correct time and adjust for DST -- which would require access to a stable time source.

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You might look for atomic clocks using vacuum-fluorescent displays.

Reply to
William Sommerwerck

Several problems and combination of problems.

  1. Noise on the power lines triggering added pulses. This will make the clock run fast.
  2. Internal free running oscillator is off frequency.
  3. Crappy design.

I once modified a vacuum fluorescent alarm clock to keep accurate time. I opened the device, figured out what chip was used, looked at the data sheet, and replaced the crappy RC oscillator with a 32KHz clock crystal. When the AC power disappears, the display goes blank and the internal 9v battery runs the clock. The problem is that the battery drain was so high that it would kill the 9V battery in about 6 hrs. There was also no charging circuit. So, I replaced the 9V battery with 4ea AA NiCd batteries (the clock chip would still run on about 6VDC), and added a crude trickle charger.

These daze, there are alarm clocks that use a WWVB 60Khz receiver to keep accurate time. I have one of these. When the power dies, the piece of junk still has a crappy RC oscillator. The 9V battery runs down in about 12 hrs (progress, I guess), and still doesn't have an internal recharger for the 9V battery. The way it works is really bizarre. If the power dies in the morning, the clock drifts around (usually slows down) all day because the receiver can't hear the 60KHz signal until late at night. After midnight, the clock hears the WWVB signal, and sets the clock to the correct time. Not great, but functional. Meanwhile, the 9V battery is half way discharged. The next time the power dies for an extended period, the battery usually runs down to near zero. When the power then returns, the clock doesn't drift around, but displays the dreaded flashing 12:00AM. I can either set it manually, or wait until after midnight for WWVH to do it for me. So much for progress.

How Accurate is a Radio Controlled Clock?

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Reply to
Jeff Liebermann

to

correct time

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This is an interesting monitor of UK mains frequency, especially when its breaktime on commercial TV carrying football or some opium of the people soap-opera

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But cycles summed over a day has to be spot on. I want to know when the utility companies will give away "intelligent" fridges rather than CFL , that only come on when this frequency is high

All the LED clocks I've ever had experience of always gain , never loose time, maybe only a minute a quarter , but only gaining. So my assumption its due to mains hash

Reply to
N_Cook

The world's first clock-radio with an all-electronic digital clock -- a GE, which I still have, 40 years after I bought it (!!!) -- used a nicad-powered oscillator running at ~ 60Hz to keep the timer going. I don't think it ran more than about 10 minutes.

Reply to
William Sommerwerck

You probably won't find an LED or vacuum fluorescent WWVB atomic clock. The problem is RFI/EMI from the high power of the LED display will produce enough RF hash to prevent the WWVB receiver from functioning. I accidentally produced this problem when I put my LED alarm clock too close to my LCD weather station. The weather station has a WWVB receiver to set the time, but it never seemed to work. When daylight savings time came and went, but the weather station didn't change time, I decided to investigate. A portable AM radio near the LED clock confirmed the RFI/EMI problem. Physically seperating the devices by about 3 meters was sufficient to allow the WWVB receiver to operate normally.

When I Google for "LED Atomic Clock", I get plenty of hits, all showing LCD displays. However, there are many clocks that have LCD displays, but also have an LED projector that displays the time on the ceiling. However, this single digit display is NOT multiplexed, and therefore generates no RFI/EMI hash.

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Reply to
Jeff Liebermann

I think I remember seeing those. Todays version will last about a year before something blows or it falls apart. Progress?

Way back in college daze (1960's), one of my friends was trying to devise a method of running a motor drive electric clock during power outages. I designed a line sync blocking oscillator, that ran in sync with the 60Hz power line frequency when that was present, but ran off battery power at roughly 60Hz when that disappeared. To get sufficient power to run the clock, it had two 2N3055 transistors playing push-pull oscillator to a small power transformer. It was big, noisy, and ugly, but worked quite well. Keeping the wet cell battery charged was the major challenge. We were thinking of manufacturing these, but was talked out of the idea by someone with more marketing sense than us.

The analog wall clocks in high skool were all wired to central time controller. Curious as to how it worked, I dragged an oscilloscope into the main hallway to clip onto the only accessible wires I could find. Every 15 minutes, a sync pulse would appear on the line, resetting the clocks to the nearest 15 minutes. Every hour, two pulses would reset the clocks to the nearest hour. At noon and midnight, 5 pulses would reset the clocks to midnight. Unfortunately, gathering this intelligence required almost constant monitoring, which attract too much attention. I was caught before I could make the clocks run backwards. Not a great start for my first attempt at hacking.

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Jeff Liebermann     jeffl@cruzio.com
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Reply to
Jeff Liebermann

In the UK we have MSF60 (60kHz time signal) and Europe the DCF 70, so far I've yet to see a compatible clock with LED display.

My solution is to have a mains synchronised LED clock sitting next to a MSF60 LCD clock - then simply adjust the LED clock whenever it gets a minute or 2 out of step.

It might be possible to test the spikes causing extra clock cycles theory by gutting a small PC PSU box that has filtered mains inlet and adding more capacitors and MOV or sidac spike protection.

The mains "in spec" frequency is actually an average - at peak demand its allowed to be slow, and catches up at off peak times when they can run the generators a little faster with little energy expenditure.

Depending what time of day you check the time; a mains sync clock can be slow, fast or just right.

Reply to
Ian Field

I doubt if any use power line for sync. Most have battery backup. Crystals jump frequency from time to time.

Greg

Reply to
gregz

There's a classic "Carl and Jerry" story about this. The scholl clocks aren't keeping good time, and -- for no obvious reason -- they run faster when it's raining.

It turns out that the janitor's vacuum cleaner put out a lot of line noise, and even more when it was sucking up water.

Reply to
William Sommerwerck

It's because the US is trying to get rid of those broadcasts. With GPS they are obsolete.

Geoff.

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Reply to
Geoffrey S. Mendelson

The real answer which has yet to be rolled out to consumers is to use NTP (networked time protcol) self correcting clocks. They basically are are cheap router with a single ethernet and wifi interfaces, and a display. All of them already run NTP, it's a matter of adding the time display, changing the setup to limit them to things needed to connect to the internet and set the clock and repackaging them.

Figure a consumer price for the cheap ones of around $25-$30 and another $10 for self setting GPS one.

Geoff.

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Geoffrey S. Mendelson,  N3OWJ/4X1GM/KBUH7245/KBUW5379
In 1969 the US could put a man on the moon, now teenagers just howl at it. :-(
Reply to
Geoffrey S. Mendelson

GE,

nicad-powered

ran

I used to "wind-up" my father by stopping the synchronus-motor clock and with a bit of backwards pressure on the seconds hand , while turning the power back on , the clock would go backwards

Reply to
N_Cook

I beg to differ. The cost of a GPS disciplined oscillator or clock in a consumer product is prohibitive. Running continuously, GPS is a major power drain. GPS doesn't work well indoors. There are huge number of products that currently use 60KHz time sync that will go dark if the US pulls the plug on WWVH and WWVB. That's not going to happen. Quite the contrary, there are plans to add a US east coast transmitter. See:

under "Service Improvement Plans".

Incidentally, I'm building my own 10MHz GPSDO for running my test eqipment and ham junk. It's NOT a trivial or inexpensive exercise:

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Jeff Liebermann     jeffl@cruzio.com
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Reply to
Jeff Liebermann

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

was that a 32KHz crystal,or a 32KHz ceramic resonator? I suspect it's the latter.that would explain the poor freq.stability. You can trim up an XTAL oscillator.

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Reply to
Jim Yanik

Even one I bought recently uses mains sync, but it has a battery & crystal divider backup to cover outages.

The mains frequency varies depending on peak demand/off peak, but long term its average has less drift than the cheap crystal oscillator they're going to put in a radio alarm clock.

Reply to
Ian Field

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