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Hmm, what to write...
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  Reply # 1450120 14-Dec-2015 13:34
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I use a Sony projector clock that projects the time on the ceiling. It is very geeky  (Yep battery backup as well)




Matthew


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  Reply # 1450121 14-Dec-2015 13:35
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This has happened to me when a GSM phone was right beside a cheap alarm clock.




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  Reply # 1450137 14-Dec-2015 13:57
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mdooher:
Aredwood:
gzt: Mains frequency would never be reliable enough. The clock will use an xco and presumably a component or interface of that has failed in this instance.


Actually the mains frequency is surprisingly accurate. As every time it goes lower than 49.5Hz or higher than 50.5Hz, Transpower issue an Excursion Notice. Some months none have been issued. Which means that the mains frequency have varied by less than 1Hz for that entire month. Which means my old digital clock has no problem keeping time despite only using the mains as it's reference.


I have an old "Railway Clock" with a synchronous motor and sweep second hand. It keeps perfect time for this very reason.



In practice the analog motor design is subject to much less interference than digital.

Also in digital if a manufacturer leaves out simple xco im guessing they will skimp on everything else needed to create stability in the alternative mains freq driven design for good measure.

+1 for old analog mains clocks. Many have the added virtue of stopping when power fails and require manual restart - preserving the exact time of the first power failure. : )

Edit: format paragraph breaks

Hmm, what to write...
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  Reply # 1450138 14-Dec-2015 13:59
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gzt:
mdooher:
Aredwood:
gzt: Mains frequency would never be reliable enough. The clock will use an xco and presumably a component or interface of that has failed in this instance.


Actually the mains frequency is surprisingly accurate. As every time it goes lower than 49.5Hz or higher than 50.5Hz, Transpower issue an Excursion Notice. Some months none have been issued. Which means that the mains frequency have varied by less than 1Hz for that entire month. Which means my old digital clock has no problem keeping time despite only using the mains as it's reference.


I have an old "Railway Clock" with a synchronous motor and sweep second hand. It keeps perfect time for this very reason.



In practice the analog motor design is subject to much less interference than digital. Also if a manufacturer leaves out simple xco im guessing they will skimp on everything else needed to create stability in the alternative mains freq driven design for good measure.

+1 for old analog mains clocks. Many have the added virtue of stopping when power fails and require manual restart. Therefore preserving the exact time of the first power failure : ).


I LOVE that part..




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  Reply # 1450145 14-Dec-2015 14:03
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gzt:
In practice the analog motor design is subject to much less interference than digital.

Also in digital if a manufacturer leaves out simple xco im guessing they will skimp on everything else needed to create stability in the alternative mains freq driven design for good measure.

+1 for old analog mains clocks. Many have the added virtue of stopping when power fails and require manual restart - preserving the exact time of the first power failure

Edit: format paragraph breaks


Mains reference for the LED bedside type clocks has been the norm for over 40 years. The only oscillator is the backup one to keep it running on the 9v battery during an outage. Its normally not very good at all




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  Reply # 1450179 14-Dec-2015 15:01
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Ok I am still amazed. Also googled for quartz led alarm. Nothing : ).

Considering a very cheap digital watch is accurate, maybe it is time for some enterprising xtal manufactuer to update the reference designs so OEM's can stamp 'Quartz' on their mains alarm clocks.

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  Reply # 1450188 14-Dec-2015 15:11
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Why would they when they have a more accurate time source available from the wall? Quartz watches seem to be out a few seconds a month. LED alarm clocks are locked to the power which is controled to be exact when referenced to accurate time sources. There may be a few seconds drift during the day that is caught up at night, but it will never be out over a month.




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  Reply # 1450199 14-Dec-2015 15:27
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Only because there are cases where the mains freq design fails. Other than that I agree, no reason to change.



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  Reply # 1461513 5-Jan-2016 11:55
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In the end I went with another $10 no brand Warehouse alarm clock (exactly the same as the Transonic model, but no longer named Transonic)
Even put in the same 9V battery and connected to the same power slot - 2 weeks later, no issues

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  Reply # 1462018 5-Jan-2016 22:37
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gzt: Ok I am still amazed. Also googled for quartz led alarm. Nothing : ).

Considering a very cheap digital watch is accurate, maybe it is time for some enterprising xtal manufactuer to update the reference designs so OEM's can stamp 'Quartz' on their mains alarm clocks.



Problem is digital watch circuits are based on 4000 series logic ICs.  Which would be sensitive to interference. Not an issue for something that is in a metal case and runs off a battery. But would need a well designed power supply circuit and good shielding to work properly using the mains. Wouldn't trust a cheap alarm clock to have that.

Also the mains is used to multiplex the display. further simplifying the design. Those cheap mains clocks don't contain much else apart from a centre tapped transformer, the display and 1 IC that does all time related functions. 

It wouldn't be that hard to mod one of those alarm clocks to into a Nixie tube clock. Or some other custom digital clock.





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