How do RTC ics handle daylight savings time?

Thread Starter

Razor Concepts

Joined Oct 7, 2008
212
I was just wondering, as DST is coming up, how would the dedicated RTC ICs (like DS3231) handle daylight savings time? Is there internal circuitry that says if the time is X, subtract/add an hour?
 

kubeek

Joined Sep 20, 2005
5,622
Especially when DST is different in each country a and the laws keep changing. Adding or substracting 3600 form your UTC time seems simpler than making the device universal.
 

SgtWookie

Joined Jul 17, 2007
22,210
I have an "atomic clock" hanging on the wall. It has a built-in daylight savings time adjustment, but since they started moving the date, the clock is an hour off for several weeks around the DST change (it's an hour slow right now).
 

Wendy

Joined Mar 24, 2008
21,906
Hmmm, must be a data channel in there somewhere, mine was before the new rules, but changes on schedule.
 

crutschow

Joined Mar 14, 2008
23,500
I have an "atomic clock" hanging on the wall. It has a built-in daylight savings time adjustment, but since they started moving the date, the clock is an hour off for several weeks around the DST change (it's an hour slow right now).
Your clock must be in a room with marginal reception of the "atomic" signal. Mine all change on the Sunday morning of the switch-over, right on schedule. The time change is broadcast at that time so it is always in sync with whatever the official change-over date is.

I do have an older non-atomic clock though that has the built-in old change date and it is also off for several weeks until it reaches the old date, just as yours does.
 

magnet18

Joined Dec 22, 2010
1,227
I remember those automatic clocks used to be a pain in Indiana, since we didn't switch. The clocks would change, but the time didn't :p

Personally, I would rather not switch.
 

MrChips

Joined Oct 2, 2009
19,383
Some RTC chips contain embedded MCU in order to handle day of week, leap years and DST. The problem is, as others have pointed out, these chips become out of date quickly because each country changes the rules.
Writing the code for this is not difficult and I have done all of the above for a data logger using MC146805 many years ago.
 
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