How to make Arduino sync time from internet

Hello, I have an Arduino and Ethernet shield. I want to make it sync time from internet. I think the candidate solution is call a web service API, and the web service returns the time data (a unsigned int32 data is OK for me). Does anybody know which timer server should I connect to? And what is the request and response data format?

Regards, Jeffrey

If you search around the forum for NTP you'll find a very good working example on how to synchronize time through the web (I have a bookmark on my other computer :( ). You may have to adjust the time to your local parallel and find an NTP server somewhere that can do this.

On the right side, you can choose a time server close to you.

Have fun.

if you want to sync a DS1307 -

Thank you guys. I extract an example from the discussion here (,51003.0.html).

I paste my code below. Hope it helps to somebody who wants it.

#include <Time.h>
#include <SPI.h>
#include <Ethernet.h>
#include <Udp.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = {  192, 168, 1, 44 }; // set the IP address to an unused address on your network

unsigned int localPort = 8888;	// local port to listen for UDP packets

byte timeServer[]  = { 192, 43, 244, 18}; //

const int NTP_PACKET_SIZE= 48; // NTP time stamp is in the first 48 bytes of the message

byte packetBuffer[ NTP_PACKET_SIZE]; //buffer to hold incoming and outgoing packets

time_t prevDisplay = 0; // when the digital clock was displayed

void digitalClockDisplay();
void printDigits(int digits);

unsigned long getNtpTime();
unsigned long sendNTPpacket(byte *address);

void setup()
	// start Ethernet and UDP
	Serial.println("waiting for sync");

	setSyncInterval(15); // sync every 15 seconds

	while(timeStatus()== timeNotSet)
		; // wait until the time is set by the sync provider

	Serial.println("Sync successfully");

void loop()

	if( now() != prevDisplay) //update the display only if the time has changed
		prevDisplay = now();

void digitalClockDisplay(){
	// digital clock display of the time
	Serial.print(" ");

void printDigits(int digits){
	// utility function for digital clock display: prints preceding colon and leading 0
	if(digits < 10)

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

unsigned long getNtpTime()
	Serial.println("Sending time sync request to NTP server.");
	sendNTPpacket(timeServer); // send an NTP packet to a time server

	unsigned long startMillis = millis();
	int tryCounter = 1;
	while( millis() - startMillis < 1000)  // wait up to one second for the response
	{  // wait to see if a reply is available
		if ( Udp.available() )
			Udp.readPacket(packetBuffer,NTP_PACKET_SIZE);  // read the packet into the buffer

			//the timestamp starts at byte 40 of the received packet and is four bytes,
			// or two words, long. First, esxtract the two words:
			unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
			unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);
			// combine the four bytes (two words) into a long integer
			// this is NTP time (seconds since Jan 1 1900):
			unsigned long secsSince1900 = highWord << 16 | lowWord;
			// now convert NTP time into Arduino Time format:
			// Time starts on Jan 1 1970. In seconds, that's 2208988800:
			const unsigned long seventyYears = 2208988800UL;
			// subtract seventy years:
			unsigned long epoch = secsSince1900 - seventyYears;

			Serial.println("Time sync successfully.");

			return epoch;

		Serial.print("No date data available. Try counter: .");

	Serial.println("Time sync failed.");

	return 0;   // return 0 if unable to get the time

// send an NTP request to the time server at the given address
unsigned long sendNTPpacket(byte *address)
	// set all bytes in the buffer to 0
	memset(packetBuffer, 0, NTP_PACKET_SIZE);
	// Initialize values needed to form NTP request
	// (see URL above for details on the packets)
	packetBuffer[0] = 0b11100011;   // LI, Version, Mode
	packetBuffer[1] = 0;     // Stratum, or type of clock
	packetBuffer[2] = 6;     // Polling Interval
	packetBuffer[3] = 0xEC;  // Peer Clock Precision
	// 8 bytes of zero for Root Delay & Root Dispersion
	packetBuffer[12]  = 49;
	packetBuffer[13]  = 0x4E;
	packetBuffer[14]  = 49;
	packetBuffer[15]  = 52;

	// all NTP fields have been given values, now
	// you can send a packet requesting a timestamp:
	Udp.sendPacket( packetBuffer,NTP_PACKET_SIZE,  address, 123); //NTP requests are to port 123

you are using a very complicate way to display time !

use :

#include <stdio.h>

and then :

char timeToDisplay[20];

sprintf(timeToDisplay, “%02d:%02d:%02d %02d-%02d-%02d”, hour(), minute(), second(), year(), month(), day());


That’s all !

Hi, all I just want to share what I found on Internet. the Code for Arduino. It works. The offset of time zone. Choose the correct number for your local. Arduino library: Time.h

Enjoy it!!!!