Real-time clock with Arduino

// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
#include <Wire.h>
#include "RTClib.h"

#if defined(ARDUINO_ARCH_SAMD)
// for Zero, output on USB Serial console, remove line below if using programming port to program the Zero!
   #define Serial SerialUSB
#endif

RTC_DS1307 rtc;

char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

void setup () {

#ifndef ESP8266
  while (!Serial); // for Leonardo/Micro/Zero
#endif

  Serial.begin(9600);
  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1);
  }

  if (! rtc.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    //rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
    // This line sets the RTC with an explicit date & time, for example to set
    // January 21, 2014 at 3am you would call:
    rtc.adjust(DateTime(2019, 06, 27, 16, 43, 0));
  }
}

void loop () {
    DateTime now = rtc.now();
    
    Serial.print(now.year(), DEC);
    Serial.print('/');
    Serial.print(now.month(), DEC);
    Serial.print('/');
    Serial.print(now.day(), DEC);
    Serial.print(" (");
    Serial.print(daysOfTheWeek[now.dayOfTheWeek()]);
    Serial.print(") ");
    Serial.print(now.hour(), DEC);
    Serial.print(':');
    Serial.print(now.minute(), DEC);
    Serial.print(':');
    Serial.print(now.second(), DEC);
    Serial.println();
    
 
    delay(3000);
}

// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
#include <Wire.h>
#include "RTClib.h"
#include <avr/sleep.h>//this AVR library contains the methods that controls the sleep modes
#define interruptPin 2 //Pin we are going to use to wake up the Arduino

RTC_DS1307 rtc;

char daysOfTheWeek[7][12] = {"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"};

void setup () {
  pinMode(LED_BUILTIN, OUTPUT); //We use the led on pin 13 to indecate when Arduino is asleep
  pinMode(interruptPin, INPUT_PULLUP); //Set pin d2 to input using the built-in pullup resistor
  digitalWrite(LED_BUILTIN, HIGH); //turn built-in LED on
  Serial.begin(9600);
  if (! rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1);
  }

  if (! rtc.isrunning()) {
    Serial.println("RTC is NOT running!");
    // following line sets the RTC to the date & time this sketch was compiled
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
    // This line sets the RTC with an explicit date & time, for example to set
    // January 21, 2014 at 3am you would call:
    //rtc.adjust(DateTime(2019, 06, 27, 20, 30, 0));
  }
}

void loop () {
  DateTime now = rtc.now();
  Serial.print(now.hour(), DEC);
  Serial.print(':');
  Serial.print(now.minute(), DEC);
  Serial.print(':');
  Serial.print(now.second(), DEC);
  Serial.println(); 
  if (now.hour() == 20) {
    delay(5000); //wait 5 seconds before going to sleep
    Going_To_Sleep();
  }
}

void Going_To_Sleep() {
  sleep_enable();//Enabling sleep mode
  attachInterrupt(0, wakeUp, LOW);//attaching a interrupt to pin d2
  set_sleep_mode(SLEEP_MODE_PWR_DOWN);//Setting the sleep mode, in our case full sleep
  digitalWrite(LED_BUILTIN, LOW); //turn LED off
  delay(1000); //wait a second to allow the led to be turned off before going to sleep
  sleep_cpu();//activating sleep mode
  Serial.println("just woke up!");//next line of code executed after the interrupt
  digitalWrite(LED_BUILTIN, HIGH); //turn LED on
}

void wakeUp() {
  Serial.println("Interrrupt Fired");//Print message to serial monitor
  sleep_disable();//Disable sleep mode
  detachInterrupt(0); //Removes the interrupt from pin 2;
}