TimeLib & DS1307RTC

This code is focused on demonstrating how to use the TimeLib & DS1307RTC library to provide basic output without the use of delay() to implement seconds counting.   A function is also included to alternatively return a ISO 8601 datetime string.  

/*
 * TimeLib & DS1307RTC library
 * 
 * Mark Kiehl
 * 
 * Portions derived from:
 *  https://github.com/PaulStoffregen/DS1307RTC
 *  Adafruit
*/

////////////////////////////////////////////////////////////////////////
// TimeLib & DS1307RTC library
// library source: https://github.com/PaulStoffregen/DS1307RTC
// Useful info:  https://www.pjrc.com/teensy/td_libs_DS1307RTC.html
#include 
#include 
#include 
// Define a 32 bit time structure
tmElements_t tm;
int hours = 0;
int minutes = 0;
int seconds = 0;
////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////////////////////
//  ISO 8601 datetime function
//
//  time zone offset - set this to the offset in seconds to your local time
//  Eastern time zone difference is -5 hours; -5 h * (3600s/hr) = -18000
const long EST_UTC_offset = -18000L;

//  Global char variable to hold the ISO 8601 formatted datetime.  
char isoDateTime[25];

void SetIsoDateTime(long TZoffset) {
  //  Update global char variable isoDateTime with the RTC values
  //  stored in the 32 bit time structure tm (from tmElements_t).
  //  isoDateTime is a ISO 8601 formatted date/time string with the 
  //  specified time zone offset TZoffset.
  //
  //  TZ_offset = # seconds from UTC to your local time.
  //    Eastern time zone is -5 hrs; -5 h * (3600s/h) = -18000
  //
  //  https://github.com/pklaus/Arduino-Logger/blob/master/TimeNTP_UdpUpdated_SdFatLogger/TimeNTP_UdpUpdated_SdFatLogger.ino
  //
  sprintf(isoDateTime, "%4d-%02d-%02dT%02d:%02d:%02d%+05d",
     tmYearToCalendar(tm.Year), tm.Month, tm.Day, tm.Hour, tm.Minute, tm.Second, TZoffset/36 );
}
/////////////////////////////////////////////////////////////////////

void setup() {
  Serial.begin(9600);
  while (!Serial) ; // wait for serial
  delay(200);

  // Read the date & time into tm
  if (RTC.read(tm)) {
    Serial.println("DS1307RTC read successful");
  } else {
    if (RTC.chipPresent()) {
      Serial.println("The DS1307 is stopped.  Please run the SetTime");
      Serial.println();
    } else {
      Serial.println("DS1307 read error!  Please check the circuitry.");
      Serial.println();
    }
    while(true) {};
  }

  /*
  // Test setting the RTC
  tm.Hour = 21;
  //tm.Minute = 59;
  //tm.Second = 59;
  //tm.Day = 1;
  //tm.Month = 28;
  //tm.Year = 2017;
  if (!RTC.write(tm)) {
    Serial.println("RTC set/update FAILED!");
    while(true) {};
  }
  */
}

void loop() {
  
  // RTC.Read() gets the current date/time from the RTC module.
  // You need to check this result is true, otherwise you only
  // read the contents from the Time library and not what is in
  // the RTC.
  if (RTC.read(tm)) {
    // Print the time & date to the serial monitor using
    // either printDatetime() or SetIsoDateTime() 
    printDatetime();
    //OR:
    /*
    if (seconds != tm.Second) {
      seconds = tm.Second;
      SetIsoDateTime(EST_UTC_offset);
      Serial.print("ISO 8601:  "); 
      Serial.println(isoDateTime);
    } //(seconds != tm.Second)
    */
  } else {
    if (RTC.chipPresent()) {
      Serial.println("The DS1307 is stopped.  Please run the SetTime");
      Serial.println();
    } else {
      Serial.println("DS1307 read error!  Please check the circuitry.");
      Serial.println();
    }
    while(true) {};
  }

}

void printDatetime() {
  if ((hours != tm.Hour) || (minutes != tm.Minute)) {
    // Get the time from the RTC
    hours = tm.Hour;
    minutes = tm.Minute;
  } // if ((hours != tm.Hour) || (minutes != tm.Minute))
  
  if (seconds != tm.Second) {
    seconds = tm.Second;
    print2digits(hours);
    Serial.write(":");
    print2digits(minutes);
    Serial.write(":");
    print2digits(seconds);
    Serial.print(", Date (D/M/Y) = ");
    Serial.print(tm.Day);
    Serial.write('/');
    Serial.print(tm.Month);
    Serial.write('/');
    Serial.print(tmYearToCalendar(tm.Year));
    Serial.println();
  }  //(seconds != tm.Second)

}

void print2digits(int number) {
  if (number >= 0 && number < 10) {
    Serial.write('0');
  }
  Serial.print(number);
}

 

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