View source for Arduino: RTC DS1302 NTP Sync

// time ntp RTC DS1302 set

#include <Time.h>
#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <DS1302.h>

// Init the DS1302
// DS1302 rtc([CE/RST], [I/O], [CLOCK]);
DS1302 rtc(8, 7, 6);

// Ethernet library configuration
byte mac[] = { 0x24, 0x7B, 0xA2, 0x4A, 0x52, 0x10 };
IPAddress timeServer(128, 138, 140, 44 ); // time.nist.gov

unsigned int localPort = 8888;
const int NTP_PACKET_SIZE= 48;     
byte packetBuffer[NTP_PACKET_SIZE]; 
EthernetUDP Udp;                   

void setup() {
  // Set the clock to run-mode, and disable the write protection
  rtc.halt(false);
  rtc.writeProtect(false);

  // Setup Communication
  Serial.begin(9600);
  Ethernet.begin(mac);
  Udp.begin(localPort);


  Serial.print("get time");
  setSyncInterval(10); // Set seconds between re-sync
  getNtpTime;

  // The following lines can be commented out to use the values already stored in the DS1302
  rtc.setDOW(WEDNESDAY);        // Set Day-of-Week to MONDAY
  // rtc.setTime(13, 0, 0);     // Set the time to 12:00:00 (24hr format)
  rtc.setDate(30, 5, 2018);   // Set the date to Feb 2, 2016
}

void loop() {
  setSyncProvider(getNtpTime);

  rtc.setTime(hour()+7, minute(), second());

  // Send Day-of-Week
  Serial.print(rtc.getDOWStr());
  Serial.print(" ");
  
  // Send date
  Serial.print(rtc.getDateStr());
  Serial.print(" -- ");
 
  // Send time
  Serial.println(rtc.getTimeStr());
  
  getNtpTime;
  // delay(1000);
} 

/*-------- NTP code ----------*/

unsigned long getNtpTime()
{
  sendNTPpacket(timeServer); // send an NTP packet to a time server
    delay(500);
   
    if ( Udp.parsePacket() ) {
     Udp.read(packetBuffer,NTP_PACKET_SIZE);
     unsigned long hi = word(packetBuffer[40], packetBuffer[41]);
     unsigned long low = word(packetBuffer[42], packetBuffer[43]);
     unsigned long secsSince1900 = hi << 16 | low; 
     const unsigned long seventyYears = 2208988800UL;     
     unsigned long epoch = secsSince1900 - seventyYears;
     return epoch;
  }
  return 0; // return 0 if unable to get the time
}

unsigned long sendNTPpacket(IPAddress& address)
{
  memset(packetBuffer, 0, NTP_PACKET_SIZE);  // set all bytes in the buffer to 0

  // Initialize values needed to form NTP request
  packetBuffer[0] = B11100011;   // LI, Version, Mode
  packetBuffer[1] = 0;     // Stratum
  packetBuffer[2] = 6;     // Max Interval between messages in seconds
  packetBuffer[3] = 0xEC;  // Clock Precision
  // bytes 4 - 11 are for Root Delay and Dispersion and were set to 0 by memset
  packetBuffer[12]  = 49;  // four-byte reference ID identifying
  packetBuffer[13]  = 0x4E;
  packetBuffer[14]  = 49;
  packetBuffer[15]  = 52;

  // send the packet requesting a timestamp:
  Udp.beginPacket(address, 123); //NTP requests are to port 123
  Udp.write(packetBuffer,NTP_PACKET_SIZE);
  Udp.endPacket();
}