Calculating Daylight Saving Time

[Heckler]

I don't understand your tables... Column c,d,e are years? If there are, what years?

The seven columns represent ANY year. Since in any given year, the first day of March or November could be a Sun, Mon, Tue, etc. I had to account for that fact that there are 7 POSSIBLE starting days for each month.

The reason I also show Sun=1, Mon=2, etc., is so I could ask "less than" or "greater than" questions.

I wanted this to be a universal calculation for USA.

The code will only apply for these rules...

At present, daylight saving time in the United States
begins at 2:00 a.m. on the second Sunday of March and
ends at 2:00 a.m. on the first Sunday of November

If you are in another part of the world where you have different rules (or no DST at all) then obviously this would not apply.

[MichelJasmin]

Heckler don't you get your time sync from NTP? Do you have the day of week?

If so:

Delta = Date - 7

IF Month=3 AND Day=Sunday AND (Delta>0 OR Delta<8) Then DST!

By the way thank you for the ESPBasic code! Got some ideas...

[enigma]

Hi All
I've used this for many years, works for Europe and I suppose could be adapted for USA. DST Europe changes in March or October, last weekend of the month. The routine calculates the date in the respective month that the change occurs on.
DSTStart holds the start date for DST
DSTEnd holds the end date for DST
Year holds the year in this format e.g 2016

DSTCheck:
DSTStart = (31 - (((5*Year)/4)+ 4) mod 7)
DSTEnd = (31 - (((5*Year/4)) + 1) mod 7)
Return

That's it, Pete

[pedja089]

Can you explain how did you get this formulas?
I was searching whole net few years ago, and best I could think is to type dates for whole century find pattern, and put it in lookup table.
EDIT:
Heckler,
Just found this
http://delphiforfun.org/programs/mat...cs/dstcalc.htm
Basically what Enigma wrote, but it have calculation for US.

[richard]

thanks enigma

that's very neat and tidy
for australia
#au DSTEnd 1st sunday in april = (7- (((5*Year/4)) + 4) % 7)
#au DSTStart 1st sunday in october = (7- (((5*Year/4)) + 5) % 7)

[Heckler]

@MichelJasmin

yes I do use NTP as the starting point of my calculation and I do get the date in the following format...
Thu Jan 01 00:00:00 1970

But your example would (I believe) only work if I happened to check the time on the actual day that the DST or STD time began and only be persistent if I kept track of whether DST or STD was in effect.
However in my case I may power up the clock say on March 12 or any other day of the year and need to determine the current DST/STD status.
I could probably use your example and then check to see if the current date was before or after that date.

@Enigma (Pete)

So how do you translate this bit of code into PICbasic??

DSTStart = (31 - (((5*Year)/4)+ 4) mod 7)

Does MOD 7 mean Y= X // 7 (in your example is MOD the same as the remainder?)

At this point I think I am going to give my code a spin and see how it performs.
but great discussion
Thanks all

[enigma]

Hi Heckler


So how do you translate this bit of code into PICbasic??
DSTStart = (31 - (((5*Year)/4)+ 4) mod 7)

The whole subroutine is cut directly from my PBP program and will work as is. If you want to check it write it as a small program, set Year word variable to 2016 and debug out the start and end dates.
Cheers Pete

[Heckler]

@Pete,

I'll give it a try.
I scanned through my PBP3 manual and could not find "MOD" anywhere. It doesn't show in the reserved word list either.

From the link that Pedja089 posted...

USA starting in 2007, extended DST to
begin on the 2nd Sunday in March (Day of month = 14 - (1+Y*5/4) mod 7)
and end on the 1st Sunday in November (Day of month = 7 - (1 + 5*Y/4) mod 7).

For Europe...
DST begins on the last Sunday in March (Day of month = 31 - (4+ 5*Y/4 ) mod 7)
and ends on the last Sunday in October (Day of month = 31 - (1 + 5*Y/4) mod 7)