![]() I would advise to store the DST flag somewhere in non volatile memory, in case you need to unplug your arduino. If (dow = 7 & mo = 10 & d >= 25 & h = 3 & DST=1)Īs you may be using different libraries the command 'setclockto 2 am' is just a place holder for your specific routine to set your RTC to 2 am. Therefore our check at the end of daylight saving will be as follows: Anyway, we have the following variables read from our RTCĭST is a flag we set when DST starts and that we clear at the end of DST to avoid that the program starts correcting the time for a full hour and even getting in an endless loop when we set the clock back.Īs October has 31 days, we know that the last Sunday will always fall from the 25th to the 31st. Some people like to start the week on Sunday, but that is just a matter of taste. As you set these yourself lets agree that you have set the day of week such that Monday is day 1 and Sunday is day 7. Let's agree that you have an RTC that will keep the "day of week" (as the DS1307 and the DS3231 do). Lets put that in a program for Western Europe, which means that the switch times are 2 and 3 am (that is 1:00 UTC) But there is a simpler way, in which you don’t even have to count. So what to do? Well you could of course determine if the first day starts on Friday, Saturday or Sunday and if so, count to 5 and otherwise count to 4. If for instance October starts on a Friday, Saturday or Sunday, it has 5 Sundays. Well, a month has four Sundays right? Wrong. October, but at the LAST Sunday of the month. In the EU the switch isn’t made at the first, second, third or fourth Sunday in March resp. Obviously you also need to set a flag to do the clock correction only once. When you arrived at the required Sunday check the time and if it is say 2 am, advance the clock an hour (=set it to 3) if DST has to start, or wait till 3 am and reset the clock hours to '2'. ![]() UTC itself is not an abbreviation but a compromise between the French abbreviation "TUC" and the English "CUT" ( Temps Universel Coordonné resp Coordinated Universal Time).Ĭatering for your local daylight savings program is usually quite easy: Let your program check for the proper month and then count the number of Sundays (the change is usually on a Sunday). In practice UTC is equal to GMT (Greenwich Mean Time). In the EU the hour to switch is at 01:00 UTC. The EU of course has a guideline on it that determines the daylight saving time to start on the last Sunday of March and to end on the last Sunday of October. The USA has daylight saving time from the 2nd Sunday of March till the first Sunday of November. Newfoundland en Nunavut have their own rule and many of the northern territories do not have daylight saving time In Canada it largely depends on where you live, some states follow the United states. In Australia daylight saving time is a matter of the states and territories but in general daylight saving time is between the first sunday in oktober and the first Sunday in April (remember, it is down under) Though one could of course reset the RTC chip manually twice a year but that is tedious, especially while it can easily be solved with a few lines of code.ĭifferent parts of the world have different rules for when the daylight saving time takes place and many countries of course have no daylight saving: It only makes sense (if at all) to do it between the tropics and the Arctic circles, so in fact between the tropic of Cancer and the Arctic circle and the tropic of Capricorn and the Antarctic circle. Obviously that would be quite hard as there are different DST conditions all over the world One thing they do not do is to automatically switch between standard time and daylight saving time (DST). They keep time very well (but I prefer the DS3231) and there are a hoist of libraries available for them. You all had to reset your clocks, but what about your microcontroller? Many programs on the arduino and other microcontrollers keep time and do that with one of the popular RTC chips such as the DS1307 or the DS3231. Just this past weekend Europe has started the Daylight Saving Time.
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