Arduino/libraries/Rtc_by_Makuna/examples/DS1307_Simple/DS1307_Simple.ino

// CONNECTIONS:
// DS1307 SDA --> SDA
// DS1307 SCL --> SCL
// DS1307 VCC --> 5v
// DS1307 GND --> GND

/* for software wire use below
#include <SoftwareWire.h>  // must be included here so that Arduino library object file references work
#include <RtcDS1307.h>

SoftwareWire myWire(SDA, SCL);
RtcDS1307<SoftwareWire> Rtc(myWire);
 for software wire use above */

/* for normal hardware wire use below */
#include <Wire.h> // must be included here so that Arduino library object file references work
#include <RtcDS1307.h>
RtcDS1307<TwoWire> Rtc(Wire);
/* for normal hardware wire use above */

// handy routine to return true if there was an error
// but it will also print out an error message with the given topic
bool wasError(const char* errorTopic = "")
{
    uint8_t error = Rtc.LastError();
    if (error != 0)
    {
        // we have a communications error
        // see https://www.arduino.cc/reference/en/language/functions/communication/wire/endtransmission/
        // for what the number means
        Serial.print("[");
        Serial.print(errorTopic);
        Serial.print("] WIRE communications error (");
        Serial.print(error);
        Serial.print(") : ");

        switch (error)
        {
        case Rtc_Wire_Error_None:
            Serial.println("(none?!)");
            break;
        case Rtc_Wire_Error_TxBufferOverflow:
            Serial.println("transmit buffer overflow");
            break;
        case Rtc_Wire_Error_NoAddressableDevice:
            Serial.println("no device responded");
            break;
        case Rtc_Wire_Error_UnsupportedRequest:
            Serial.println("device doesn't support request");
            break;
        case Rtc_Wire_Error_Unspecific:
            Serial.println("unspecified error");
            break;
        case Rtc_Wire_Error_CommunicationTimeout:
            Serial.println("communications timed out");
            break;
        }
        return true;
    }
    return false;
}


void setup () 
{
    Serial.begin(115200);

    Serial.print("compiled: ");
    Serial.print(__DATE__);
    Serial.println(__TIME__);

    //--------RTC SETUP ------------
    // if you are using ESP-01 then uncomment the line below to reset the pins to
    // the available pins for SDA, SCL
    // Rtc.Begin(0, 2); // due to limited pins, use pin 0 and 2 for SDA, SCL
    
    Rtc.Begin();
#if defined(WIRE_HAS_TIMEOUT)
    Wire.setWireTimeout(3000 /* us */, true /* reset_on_timeout */);
#endif

    RtcDateTime compiled = RtcDateTime(__DATE__, __TIME__);
    printDateTime(compiled);
    Serial.println();

    if (!Rtc.IsDateTimeValid()) 
    {
        if (!wasError("setup IsDateTimeValid"))
        {
            // Common Causes:
            //    1) first time you ran and the device wasn't running yet
            //    2) the battery on the device is low or even missing

            Serial.println("RTC lost confidence in the DateTime!");
            // following line sets the RTC to the date & time this sketch was compiled
            // it will also reset the valid flag internally unless the Rtc device is
            // having an issue

            Rtc.SetDateTime(compiled);
        }
    }

    if (!Rtc.GetIsRunning())
    {
        if (!wasError("setup GetIsRunning"))
        {
            Serial.println("RTC was not actively running, starting now");
            Rtc.SetIsRunning(true);
        }
    }

    RtcDateTime now = Rtc.GetDateTime();
    if (!wasError("setup GetDateTime"))
    {
        if (now < compiled)
        {
            Serial.println("RTC is older than compile time, updating DateTime");
            Rtc.SetDateTime(compiled);
        }
        else if (now > compiled)
        {
            Serial.println("RTC is newer than compile time, this is expected");
        }
        else if (now == compiled)
        {
            Serial.println("RTC is the same as compile time, while not expected all is still fine");
        }
    }

    // never assume the Rtc was last configured by you, so
    // just clear them to your needed state
    Rtc.SetSquareWavePin(DS1307SquareWaveOut_Low); 
    wasError("setup SetSquareWavePin");
}

void loop () 
{
    if (!Rtc.IsDateTimeValid()) 
    {
        if (!wasError("loop IsDateTimeValid"))
        {
            // Common Causes:
            //    1) the battery on the device is low or even missing and the power line was disconnected
            Serial.println("RTC lost confidence in the DateTime!");
        }
    }

    RtcDateTime now = Rtc.GetDateTime();
    if (!wasError("loop GetDateTime"))
    {
        printDateTime(now);
        Serial.println();
    }

    delay(10000); // ten seconds
}

#define countof(a) (sizeof(a) / sizeof(a[0]))

void printDateTime(const RtcDateTime& dt)
{
    char datestring[26];

    snprintf_P(datestring, 
            countof(datestring),
            PSTR("%02u/%02u/%04u %02u:%02u:%02u"),
            dt.Month(),
            dt.Day(),
            dt.Year(),
            dt.Hour(),
            dt.Minute(),
            dt.Second() );
    Serial.print(datestring);
}