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Create EU DST example #308

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Create EU DST example
J-Brinkman Oct 13, 2024
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59 changes: 59 additions & 0 deletions examples/EU DST example
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/* EU DST example */
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This deserves a few more explanations, stating for instance that:

  1. The RTC is kept in local winter time. This is not obvious at first sight, and is quite non-standard (common practice is to keep the RTC either in UTC or in local time).

  2. This code is for CET only. It can work across Europe if one is willing to accept the DST change to be one hour off.

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Very relevant suggestions.
Point 1 appears to be the key to make it a very simple procedure.
Point 2 The hour is now set to 1 and 3. This can be adapted to your local time (for instance at 2 and 4) if applicable. Therefore it is an example.
I would love to add these point to a comment in the proposed code, but have problems to find out how. (This is the very first pull request I ever do).

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This can be adapted to your local time

I believe a comment explaining how to do so would be of some value.

/* version 3: dd 14-10-2024 */
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This date format is ambiguous. Prefer the ISO date format: 2024-10-14. Or, better yet, remove the line: the history of this file is in the git repository anyways.


// The RTC is kept in local winter time (standard time). This approach is key for the simplicity of this solution.
// This code is for a DST from Last sunday in March 1:00 (am) local time until Last sunday in October 3:00 (am) local time.
// The DST time can be changed if required, by choosing a different hour in the DateTime function (4th parameter).

#include <RTClib.h> // https://github.com/adafruit/rtclib
RTC_DS3231 rtc;
//RTC_DS1307 rtc;

#define USEDST true // Use DST (true or false)

DateTime now;

DateTime dstclock(DateTime n) { // Return the given (DST adjusted) date and time according to DST settings (for extensive date and time calculations)

DateTime b, e;

b = DateTime(n.year(), 3, 31, 1, 0, 0); // Begin of DST: set on March 31 1:000 (am)
if (month(n) = 3) b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Begin of DST: adjusted to last sunday in March 1:00 (am) when actual month is March
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This doesn't compile. You mean:

Suggested change
if (month(n) = 3) b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Begin of DST: adjusted to last sunday in March 1:00 (am) when actual month is March
if (n.month() == 3) b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Begin of DST: adjusted to last sunday in March 1:00 (am) when actual month is March

e = DateTime(n.year(), 10, 31, 3, 0, 0); // End of DST: set on October 31 3:00 (am)
if (month(n) = 10) e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // End of DST: adjusted to last sunday in October 3:00 (am) when actual month is October
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Same here:

Suggested change
if (month(n) = 10) e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // End of DST: adjusted to last sunday in October 3:00 (am) when actual month is October
if (n.month() == 10) e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // End of DST: adjusted to last sunday in October 3:00 (am) when actual month is October


if (USEDST && (n > b) && (n < e)) n = n + TimeSpan(0,1,0,0); // adjust to standard time if within summertime
return n;
};

DateTime getclock() { // Retrieve the (DST adjusted) date and time

DateTime n, b, e;

n = rtc.now();
b = DateTime(n.year(), 3, 31, 1, 0, 0); // Begin of DST: set on March 31 1:000 (am)
if (month(n) = 3) b = DateTime(n.year(), 3, 31 - b.dayOfTheWeek(), 1, 0, 0); // Begin of DST: adjusted to last sunday in March 1:00 (am) when actual month is March
e = DateTime(n.year(), 10, 31, 3, 0, 0); // End of DST: set on October 31 3:00 (am)
if (month(n) = 10) e = DateTime(n.year(), 10, 31 - e.dayOfTheWeek(), 3, 0, 0); // End of DST: adjusted to last sunday in October 3:00 (am) when actual month is October

if (USEDST && (n > b) && (n < e)) n = n + TimeSpan(0,1,0,0); // adjust to standard time if within summertime
return n;
};

void setclock(DateTime n) { // if the clock is set during summertime then adjust the clock to standard time

if (USEDST && (n != dstclock(n)) n = n - TimeSpan(0,1,0,0); // if summertime then adjust to the standard time
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There are mismatched parentheses here:

Suggested change
if (USEDST && (n != dstclock(n)) n = n - TimeSpan(0,1,0,0); // if summertime then adjust to the standard time
if (USEDST && n != dstclock(n)) n = n - TimeSpan(0,1,0,0); // if summertime then adjust to the standard time

rtc.adjust(n); // Set the clock to standard time
};

void setup() {
// initialise the rtc
rtc.begin();
// if (rtc.lostPower()) setclock(DateTime(F(__DATE__), F(__TIME__))); // Set date and time for use with the DS3231 RTC
if (!rtc.isrunning()) setclock(DateTime(F(__DATE__), F(__TIME__))); // Set date and time for use with the DS1307 RTC
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This doesn't compile: the class RTC_DS3231 doesn't have a method named isrunning(). You probably want to comment-out this line and uncomment the previous one. Alternatively, comment-out the current declaration of rtc and uncomment RTC_DS1307 rtc;.

}

void loop() {
now = getclock(); // read the time from the RTC and adjust for DST or
// now = dstclock(rtc.now()); // read the time from the RTC and adjust for DST
}
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It would be nice if this example did something visible, just like all the others do. The simplest would be to initialize the serial port in setup(), then:

void loop() {
  DateTime now = getclock(); // read the time from the RTC and adjust for DST
  Serial.println(now.timestamp());
  delay(1000);
}

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This time it compiles :-) and a nice demonstration is added.

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