Converting GPS UTC time to local time zone

testclaim · February 16, 2024, 2:22pm

I apologize for my ignorance but I'm very new to programming. I have tried searching every example I can find but nothing is working. I would like for the time output from the gps to be the local timezone of EST (-5) but everything I try continues to give me UTC. Here is my code.

#include <SoftwareSerial.h>

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <LiquidCrystal_I2C.h>
#include <TimeLib.h>
#include <TinyGPSPlus.h>

byte last_second, Second, Minute, Hour, Day, Month;
int Year;


LiquidCrystal_I2C lcd(0x27, 20, 4);

// Initialize the OLED display with address 0x3C
TinyGPSPlus gps;  //defines the gps object

void setup() {
  Serial.begin(9600);   // This starts the global serial interface.  This is what is used for the majority of the functions.
  Serial3.begin(9600);  // This starts the GPS on the pin.  Anything to do with pin will be referenced as Serial3
  lcd.init();
}

void loop() {

  while (Serial3.available() > 0)
    gps.encode(Serial3.read());
  lcd.backlight();
  lcd.setCursor(1, 0);
  lcd.print("Latitude: ");
  lcd.print(gps.location.lat());
  lcd.setCursor(1, 1);
  lcd.print("Longitude: ");
  lcd.print(gps.location.lng());
  lcd.setCursor(1, 2);
  lcd.print("Time:  ");
       byte Minute = gps.time.minute();
       byte Second = gps.time.second();
       byte Hour   = gps.time.hour();
       byte Day   = gps.date.day();
       byte Month = gps.date.month();
       byte Year  = gps.date.year();
       setTime(Hour, Minute, Second, Day, Month, Year);
       adjustTime(-5);
        
  lcd.setCursor(1, 3);
  lcd.print("Date:  ");
  lcd.print(gps.date.month());
  lcd.print("/");
  lcd.print(gps.date.day());
  lcd.print("/");
  lcd.print(gps.date.year());
  Serial.println("# of Satellites " + gps.satellites.value());
  Serial.println(gps.satellites.value());
  Serial.println(gps.location.lat());
  Serial.println(Hour);
  
}

For testing, I'm just sending the hour to the serial monitor. Once it is correct, I will update the lcd output.

Any assistance would be greatly appreciated!!

odometer · February 16, 2024, 2:41pm

From my googling, it seems that adjustTime is to be in seconds, not hours.
Try:
adjustTime(-18000);

testclaim · February 16, 2024, 3:00pm

Thank you. That is what I had originally and then thought to try hours. Both were returning the UTC time.

testclaim · February 16, 2024, 3:01pm

It is like the offset is being ignored in the function

david_2018 · February 16, 2024, 3:10pm

You are printing the variable Hour that you set from the GPS, not the hour from the real-time clock maintained by the Time library.

odometer · February 16, 2024, 3:22pm

Yes, this is what is happening.
Try this instead:

Serial.println(hour());

testclaim · February 16, 2024, 3:28pm

Thank you. That is returning Hour can not be used as a function

6v6gt · February 16, 2024, 3:49pm

Do you want the time to be corrected for daylight saving time changes ?
If so, look at the TimeZone library.

gfvalvo · February 16, 2024, 3:51pm

Which Arduino board are you using?

odometer · February 16, 2024, 3:55pm

Use lowercase h for hour

testclaim · February 16, 2024, 4:05pm

Thank you. It is still returning the UTC time.

odometer · February 16, 2024, 4:06pm

What is it giving you for the year? You are trying to fit the year into a byte. A byte can only go from 0 to 255. We are in the year 2024. I don't see how the number 2024 can fit into a byte.

testclaim · February 16, 2024, 4:15pm

it is returning 2024

odometer · February 16, 2024, 4:19pm

Why are you declaring variables with these names at the top, like this

and then again declaring variables with these names here?

       byte Minute = gps.time.minute();
       byte Second = gps.time.second();
       byte Hour   = gps.time.hour();
       byte Day   = gps.date.day();
       byte Month = gps.date.month();
       byte Year  = gps.date.year();

Do you want Year to be an int or a byte?

I would remove the word byte from those lines.

Try:

#include <SoftwareSerial.h>

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <LiquidCrystal_I2C.h>
#include <TimeLib.h>
#include <TinyGPSPlus.h>

byte last_second, Second, Minute, Hour, Day, Month;
int Year;


LiquidCrystal_I2C lcd(0x27, 20, 4);

// Initialize the OLED display with address 0x3C
TinyGPSPlus gps;  //defines the gps object

void setup() {
  Serial.begin(9600);   // This starts the global serial interface.  This is what is used for the majority of the functions.
  Serial3.begin(9600);  // This starts the GPS on the pin.  Anything to do with pin will be referenced as Serial3
  lcd.init();
}

void loop() {

  while (Serial3.available() > 0)
    gps.encode(Serial3.read());
  lcd.backlight();
  lcd.setCursor(1, 0);
  lcd.print("Latitude: ");
  lcd.print(gps.location.lat());
  lcd.setCursor(1, 1);
  lcd.print("Longitude: ");
  lcd.print(gps.location.lng());
  lcd.setCursor(1, 2);
  lcd.print("Time:  ");
       Minute = gps.time.minute();
       Second = gps.time.second();
       Hour   = gps.time.hour();
       Day   = gps.date.day();
       Month = gps.date.month();
       Year  = gps.date.year();
       setTime(Hour, Minute, Second, Day, Month, Year);
       adjustTime(-18000);
        
  lcd.setCursor(1, 3);
  lcd.print("Date:  ");
  lcd.print(gps.date.month());
  lcd.print("/");
  lcd.print(gps.date.day());
  lcd.print("/");
  lcd.print(gps.date.year());
  Serial.println("# of Satellites " + gps.satellites.value());
  Serial.println(gps.satellites.value());
  Serial.println(gps.location.lat());
  Serial.println(hour());
  
}

What does this get you? If this doesn't work, I have another approach you could use.

testclaim · February 16, 2024, 4:20pm

I went back and look at everything again. If I print gps.data.year I get 2024. Serial.println(year()); will give me 2024. If I print Year, it gives 232 as that is defined as an integer. That could just be removed.

testclaim · February 16, 2024, 4:44pm

it is still giving the UTC time.

gfvalvo · February 16, 2024, 4:49pm

One more time:

odometer · February 16, 2024, 4:51pm

Try this and see if you like the results:

#include <SoftwareSerial.h>

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <LiquidCrystal_I2C.h>
#include <TimeLib.h>
#include <TinyGPSPlus.h>

byte last_second, Second, Minute, Hour, Day, Month;
int Year;


LiquidCrystal_I2C lcd(0x27, 20, 4);

// Initialize the OLED display with address 0x3C
TinyGPSPlus gps;  //defines the gps object

void setup() {
  Serial.begin(9600);   // This starts the global serial interface.  This is what is used for the majority of the functions.
  Serial3.begin(9600);  // This starts the GPS on the pin.  Anything to do with pin will be referenced as Serial3
  lcd.init();
}

void loop() {

  while (Serial3.available() > 0)
    gps.encode(Serial3.read());
  lcd.backlight();
  lcd.setCursor(1, 0);
  lcd.print("Latitude: ");
  lcd.print(gps.location.lat());
  lcd.setCursor(1, 1);
  lcd.print("Longitude: ");
  lcd.print(gps.location.lng());

  Minute = gps.time.minute();
  Second = gps.time.second();
  Hour   = gps.time.hour();
  Day   = gps.date.day();
  Month = gps.date.month();
  Year  = gps.date.year();

  // adjust for local time zone: UTC minus 5 hours
  // to avoid negative numbers in the calculation,
  // we do it by adding 19 hours and subtracting one day
  Hour += 19;
  Day--;

  // twenty-four hours make one day
  if (Hour >= 24) {
    Hour -= 24;
    Day++;
  }

  // change "zeroth" day of month to last day of previous month
  if (Day == 0) {
    Month--;
    if (Month == 0) {
      Month = 12;
      Year--;
    }
    if ((Month == 4) || (Month == 11) || (Month == 9) || (Month == 6)) {
      Day = 30;
    }
    else if (Month == 2) {
      if ((Year % 4) == 0) {
        // this will fail in the year 2100
        Day = 29;
      }
      else {
        Day = 28;
      }
    }
    else {
      Day = 31;
    }
  }

  setTime(Hour, Minute, Second, Day, Month, Year);

  lcd.setCursor(1, 2);
  lcd.print("Time:  ");
  lcd.print(Hour);
  lcd.print(":");
  if (Minute < 10) {
    lcd.print("0");
  }
  lcd.print(Minute);
  lcd.print(":");
  if (Second < 10) {
    lcd.print("0");
  }
  lcd.print(Second);
        
  lcd.setCursor(1, 3);
  lcd.print("Date:  ");
  lcd.print(Month);
  lcd.print("/");
  lcd.print(Day);
  lcd.print("/");
  lcd.print(Year);
  Serial.println("# of Satellites " + gps.satellites.value());
  Serial.println(gps.satellites.value());
  Serial.println(gps.location.lat());
  Serial.println(hour());
  
}

testclaim · February 16, 2024, 5:09pm

That worked!!!! Thank you so much!!! Now, I just have to wrap my head around the code

odometer · February 16, 2024, 5:16pm

I just did the conversion "the long way". I wanted to subtract 5 hours, but subtracting 5 could possibly result in a negative number (what if UTC hours were less than 5 when we did it?), so instead I added 19 hours, which would give the same time of day as subtracting 5 hours. Then I needed to take care of what happens if the hours end up being a number that is 24 or greater. Then the rest of the code is just to get the date right: think of what happens if adding or subtracting hours gets us into a different day.

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Converting GPS UTC time to local time zone

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