Self setting clock

Discussion in 'General Electronics Chat' started by Jaguarjoe, Jul 3, 2010.

  1. Jaguarjoe

    Thread Starter Active Member

    Apr 7, 2010
    I have a self setting digital alarm clock. After a power failure, when power is restored, the clock is supposed to automatically set itself to the correct time.
    Mine is 14 minutes fast- IOW, when it comes back on it will be offset by 14 minutes.
    Does anyone know how these work?
    Any ideas on getting rid of the extra 14 minutes?
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    The only self-setting clock that I have receives (radio) signals from WWVB. That is, if I place it close to a window so that the radio signals can get to it. It actually adjusts itself every night; an icon that looks like a radio tower shows up to confirm that it has received the signal. If yours works that way, it will automatically set itself to the correct time overnight; your 14 minutes will be gone.

    There may be other ways a clock can set itself, but I don't know what they are short of being connected to the internet.
    Last edited: Jul 3, 2010
  3. retched

    AAC Fanatic!

    Dec 5, 2009
    There are a few types of "self-setting" clocks. One uses the GPS or CELL or radio signals to get the time, and others simply use a battery backup and a uC to make the setting process "look cool".

    I have an Emerson Technologies "self-setting" clock. It is the back-up battery type.

    There is a way to set them to correct them. As I found out years ago when George W. Bush changed daylight-savings-time. I had not realized that my clock would not "learn" the new DST changes, so now I have to set it 4 times a year.

    Once when it is DST+
    Once when it USED to be DST+ To set it back to the proper time
    Once when it is DST-
    Once more when it USED to be DST- to set it forward to the proper time.

    No fun. But it does look cool when the power goes out and it clocks up to the proper time.

    So a google search for the manual for your particular model and you should be set. (No pun intended ;) )
  4. bertus


    Apr 5, 2008
  5. Upaj Os

    New Member

    Oct 6, 2015
    The U.S. Congress is the proper entity to blame for this mess.
  6. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Put a GPS in it. My Garmin even knows the geographic boundaries of the states, and therefore changes from MST to MDT automatically when I fly north across the AZ to Utah border. It is accurate to a fraction of a sec.
  7. WBahn


    Mar 31, 2012
    Does it now the proper boundaries for the portions of states that do/don't recognize DST?

    I don't know if any of the GPS systems responded correctly after the change in the DST law (what I call the Y4X law, meaning that we have a Y2K event 4X a year) went into effect or if they have to be updated. I didn't get my first unit until sometime shortly after the law took effect.
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    It has an aviation data base, so it knows about geographic boundaries, obstructions, radio towers, mountain peaks, terrain contours, the locations of navaids, runways, airways, controlled airspace boundaries, etc. I periodically pay to have the data base updated, so changes in laws about who obeys DST is automatic... (just $).
  9. GopherT

    AAC Fanatic!

    Nov 23, 2012
    You need to download a copy of Back To The Future and buy a Delorean.
  10. WBahn


    Mar 31, 2012
    I had a similar clock and when I first got it I managed to get it off by four minutes. It stayed that way for months. I tried everything I could think of, including unplugging it for two weeks while I was out of town. There was a pair of buttons supposedly to increase or decrease the time, but they weren't responsive -- until one day they were and so I set the clock, but was off by a minute. When I tried to correct that a few days later, the buttons were unresponsive again. Never did figure out what was going on.
  11. user8192

    New Member

    Nov 9, 2011
    If it is one of those "atomic clocks" built for the North American market, it uses the NIST 60 kHz radio signal from WWVB in Fort Collins, Colorado, based on NIST's atomic clocks. The signal is weak and prone to interference, and generally best received in the wee hours of the night when nearby electrical equipment is turned off and propagation conditions are best. According to instructions you'll find online from companies such as Oregon Scientific and Lacrosse, even after you find a good location in the house to place such a clock, it can take up to five days for one to fully synchronize with WWVB. I have a digital "atomic" wall clock that never could get the signal after a week in the location where I intended to hang it, so I had to try another until it worked. If the battery dies, my clock starts seeking the WWVB signal as soon as a fresh battery is inserted, any time of day, and I have witnessed it synchronizing even in daylight, but once it has synchronized, it only turns on the radio receiver up to five times each night on the hour for 10 minutes, starting at midnight, to conserve battery power. If it manages to synchronize between 12:00 a.m. and 12:10 a.m., it won't activate the receiver again until the next night.

    Another popular technology for self-setting clocks is called Autoset, also known as "Insta-Set", "SmartSet", "Intelli-Time", and possibly other monikers used by vendors such as Elgin, Emerson, Equity, Jensen, Seth Thomas, Sony, Timex, etc. These use a microchip with a lithium battery backup to maintain the time, using an accurate quartz crystal as a reference. The clock would initially be set at the factory and all the owner had to do was plug it into an outlet, perhaps just selecting the time zone. The early Autoset clocks had the Standard Time and Daylight Saving Time dates fixed in hardware, but after the "Energy Policy Act of 2005" was passed, manufacturers revised the chip, allowing clock owners to change the "spring forward" and "fall back" dates in accordance with the whims of the United States Congress. The lithium battery in such clocks has an expected lifetime of about five years, and if your clock is well over that age, the battery may be getting run down, causing the microchip to lose time rapidly during even brief power outages. If that's the case, replacing the battery could cure the problem. In some Autoset clocks the lithium battery can readily be changed, but in others some soldering might be involved. Unless the manufacturer specifically provided a way of accessing the battery with no tools, they may have intended that the clock be discarded after five to seven years. The main advantage of Autoset clocks is that they work in places where WWVB, GPS or cell phone repeater radio time signals are unusable, such as deep inside a steel-and-concrete building or in a cellar.

    If your clock is starting up with the wrong time, you should be able to set it manually with the buttons, but if the buttons don't work, it probably means that the switch contacts are contaminated with dust or oxidation. If it is feasible to do so, you could try disassembling the clock and cleaning the switch contacts with a cotton swab (e.g., "Q-Tip") saturated with something like pure methanol ("shellac thinner"), but if not, toss the clock and get another one.
  12. #12


    Nov 30, 2010
    Ah yes, a major improvement in reliability made feasible by modern technology.

    [/sarc off]
  13. WBahn


    Mar 31, 2012
    What does an "accurate quarts crystal" mean in this context?

    If the time is set at the factory and the clock intended to last for five years, then what level of accuracy is required?

    If it achieves 1 ppm then after five years it could be nearly three minutes off. For practical purposes, that is probably good enough. But if I'm buying a clock that is claiming to be so accurate that it never needs to be set, I'm not gonna be happy with that at all -- I'm gonna want it to be within a few seconds at most, which would require something closer to 10 ppb.

    How expensive are crystal oscillators that can achieve sub-ppm performance over a period of several years?