Time zone and day light saving time


Timezones and daylight saving time (DST) must/should be accounted for if the weather station is to show current time/date and hours/days ahead correctly. It is not easy to program because countries, territories and states:

  • do not necessarily have time offsets as integral number of hours from UTC/GMT (ref. i.e. this overview)
  • sometimes make adjustments that are announced just days or weeks ahead of the change (!)

politics-cutback-government_cutback-budget_cut-clock_change-time_zone-cman255l

A lot of info can be found at timeanddate.com and/or thetimenow.com.
An updated list when daylight saving occur worldwide for 2014 can be found here. There you can also find detailed information about each DST (i.e. first half of 2014). There are also api’s available for current local times, time zones, public holidays and observances worldwide, daylight saving time (DST), international calling codes, rise/set times for sun and moon, etc.

In some countries, i.e. Norway, DST is called “summer time”. When DST is not observed, it is called standard time, normal time or winter time.

The prototype software uses

    • The standard arduino Time library for time formatting etc.
    • The Timezone library  by JChristensen to convert Universal Coordinated Time (UTC) to the correct local time, whether it is daylight saving time (DST). It is compatible with the Time library.

These libraries can be used together and can fetch time from Real Time Clock (RTC),Internet NTP time service, GPS time data, DCF77 radio signal, and Serial time messages from a computer.

My weatherstation prototype fetches time from a RTC and has hardcoded DST and timezone for Norway.

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