Real time clock from Ntc server

Real time clock from NTP server

This example shows you how to use the UDP (User Datagram Protocol) communication to get the real time clock from Network Time Protocol (NTP) server. 
NTP is the protocol used to synchronize the clocks of computers and of electronics devices connected on internet with a margin of 10 milliseconds and 
an accuracy of 200 microseconds in optimal conditions.


  • Arduino board
  • Arduino Ethernet Shield 2


Arduino Ethernet 2 Shield 
Mount your Ethenet shield 2 on an Arduino board and connect it to the network using the Ethernet cable.


The first operation of this sketch is to include the "SPI.h", "Ethernet2.h" and "EthernetUdp2.h" libraries and to indicate the MAC address of the Shield. 
Also it is defined the local port for udp communication. 
In the setup function is initialized the Serial communication and the UDP. 
Instead in the loop block is made the request to NTP server, after it is processed the answer and finally it is shown all on serial monitor.

The complete code and its detailed description are shown down.

You need the "SPI.h", "Ethernet2.h" and "EthernetUdp2.h" libraries to use this sketch and you need to change the network settings in the sketch to correspond to your network.

Udp NTP Client
Get the time from a Network Time Protocol (NTP) time server
Demonstrates use of UDP sendPacket and ReceivePacket
For more on NTP time servers and the messages needed to communicate with them,
created 4 Sep 2010
by Michael Margolis
modified 9 Apr 2012
by Tom Igoe
This code is in the public domain.
#include <SPI.h>
#include <Ethernet2.h>
#include <EthernetUdp2.h>
// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = {
0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED
unsigned int localPort = 8888;       // local port to listen for UDP packets
char timeServer[] = ""; // NTP server
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
// A UDP instance to let us send and receive packets over UDP
EthernetUDP Udp;
void setup()
// Open serial communications and wait for port to open:
while (!Serial) {
  ; // wait for serial port to connect. Needed for Leonardo only
// start Ethernet and UDP
if (Ethernet.begin(mac) == 0) {
  Serial.println("Failed to configure Ethernet using DHCP");
  // no point in carrying on, so do nothing forevermore:
  for (;;)
void loop()
sendNTPpacket(timeServer); // send an NTP packet to a time server
// wait to see if a reply is available
if ( Udp.parsePacket() ) {
  // We've received a packet, read the data from it, 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;
  Serial.print("Seconds since Jan 1 1900 = " );
  // now convert NTP time into everyday time:
  Serial.print("Unix time = ");
  // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
  const unsigned long seventyYears = 2208988800UL;
  // subtract seventy years:
  unsigned long epoch = secsSince1900 - seventyYears;
  // print Unix time:
  // print the hour, minute and second:
  Serial.print("The UTC time is ");       // UTC is the time at Greenwich Meridian (GMT)
  Serial.print((epoch % 86400L) / 3600); // print the hour (86400 equals secs per day)
  if ( ((epoch % 3600) / 60) < 10 ) {
    // In the first 10 minutes of each hour, we'll want a leading '0'
  Serial.print((epoch % 3600) / 60); // print the minute (3600 equals secs per minute)
  if ( (epoch % 60) < 10 ) {
    // In the first 10 seconds of each minute, we'll want a leading '0'
  Serial.println(epoch % 60); // print the second
// wait ten seconds before asking for the time again
// send an NTP request to the time server at the given address
unsigned long sendNTPpacket(char* 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.beginPacket(address, 123); //NTP requests are to port 123
Udp.write(packetBuffer, NTP_PACKET_SIZE);