GPS module - UTC/GMT to Pacific Standard Time (pst) Conversion.

Projects Programming
1

Code Novice MAC here...CODE HELP NEEDED!
Recently I inherited a gps modem salvaged from a marine plotter, so decided to try and build a gps lcd clock using an UNO and a 16X2 LED display and TinyGPS library. The project idea code is from TinyGPS | Arduiniana

Everything went together fine with code converting the UTC time to Pacific Standard Time (PST), and Pacific Daylight Time (PDT), by subtracting 8 or 7 hours respectively from the UTC time. The LCD displayed both times correctly until UTC went between 1am to 6am where it displayed negative numbers. I tried adding 24 to the UTC which corrected the low numbers, but caused all others to be too large. It looks like I need some extra conversion help. See photos and sketch attached.

Does anyone have or know code which would solve my problem?
Thanks,
Mac

TinyGPS_CLOCK_TEST1.ino (3.32 KB)

Display_OK.png

Display_Bad1.png

Display_Bad2.png

2

I use (a variant of) this library for converting between UTC and the local time zone , including daylight saving time adjustment.

3

Hi 6v6gt,
More complicated than I thought....
Looks like I have a lot more studying to do!
Thanks,
Mac
VE7DEP

PS: I remember working on 6V6GT tube equipment

4

You do not need any library to implement time zones. The native AVR GCC time.h supports time zone offsets and also supports daylight savings time.

There is not a lot more to it beyond this:

#include <time.h>
#include <locale.h>
#include <util/usa_dst.h> https://www.nongnu.org/avr-libc/user-manual/usa__dst_8h_source.html
...
  set_dst(usa_dst);
  set_zone(-5 * ONE_HOUR);
...
      tm = localtime(&timer);  //this gets the local time

for my location

5

Thanks everyone for all the advice. I decided to just add a switch for DST.
Mac