read GPS NMEA data to get UTC

getUTCfromGPS.ino

//
// GPS clock
// UTCdata get from NMEA $GPGGA field $2
//
// for Arduino Leonardo / Seeeduino Lite(3.3V)

void setup() {
  Serial1.begin(9600); // GPS port
  while(!Serial1) delay(10);
  
  Serial.begin(9600); // Console
  while(!Serial) delay(10);

}

int hh,mm,ss ;
const int TD = 9;

void loop() {
  if (Serial1.available()) {
    String nmea = Serial1.readStringUntil('\n');
    String nmeames = nmea.substring(0,6); // $GP***
    if ( nmeames.equals("$GPGGA") ) { // get UTC
      String shh = nmea.substring(7,9);
      String smm = nmea.substring(9,11);
      String sss = nmea.substring(11,13);
      // Serial.println(shh + smm + sss);
      hh = (shh.toInt() + TD)%24; // Timezone offset+
      mm = smm.toInt();
      ss = sss.toInt();
      Serial.print(hh);
      Serial.print(":");
      Serial.print(mm);
      Serial.print(":");
      Serial.println(ss);
    }
  }

//  if (Serial1.available()) Serial.write(Serial1.read());
//  if (Serial.available()) Serial1.write(Serial.read());
}