Network Time Protocol (NTP) Client

In this example, you will use your WiFi Shield 101 with your Arduino Zero board, or a MKR1000 board, to query a Network Time Protocol (NTP) server. In this way, your board can get the time from the Internet.

Hardware Required

  • Arduino WiFi Shield 101

  • Arduino Zero board


  • MKR1000


Digital pin 7 is used as a handshake pin between the WiFi Shield 101 and the board, and should not be used.

You should have access to a 802.11b/g wireless network that connects to the internet for this example. You will need to change the network settings in the sketch to correspond to your particular networks SSID.


image developed using Fritzing. For more circuit examples, see the Fritzing project page

In the above image, the Arduino Zero board would be stacked below the WiFi shield.



 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 <WiFi101.h>
#include <WiFiUdp.h>

int status = WL_IDLE_STATUS;
#include "arduino_secrets.h"
///////please enter your sensitive data in the Secret tab/arduino_secrets.h
char ssid[] = SECRET_SSID;        // your network SSID (name)
char pass[] = SECRET_PASS;    // your network password (use for WPA, or use as key for WEP)
int keyIndex = 0;            // your network key Index number (needed only for WEP)

unsigned int localPort = 2390;      // local port to listen for UDP packets

IPAddress timeServer(129, 6, 15, 28); // 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

WiFiUDP Udp;

void setup()

  // Open serial communications and wait for port to open:


  while (!Serial) {

    ; // wait for serial port to connect. Needed for native USB port only


  // check for the presence of the shield:

  if (WiFi.status() == WL_NO_SHIELD) {

    Serial.println("WiFi shield not present");

    // don't continue:

    while (true);


  // attempt to connect to WiFi network:

  while ( status != WL_CONNECTED) {

    Serial.print("Attempting to connect to SSID: ");


    // Connect to WPA/WPA2 network. Change this line if using open or WEP network:

    status = WiFi.begin(ssid, pass);

    // wait 10 seconds for connection:



  Serial.println("Connected to wifi");


  Serial.println("\nStarting connection to server...");


void loop()

  sendNTPpacket(timeServer); // send an NTP packet to a time server

  // wait to see if a reply is available


  if ( Udp.parsePacket() ) {

    Serial.println("packet received");

    // 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(IPAddress& 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);




void printWiFiStatus() {

  // print the SSID of the network you're attached to:

  Serial.print("SSID: ");


  // print your WiFi shield's IP address:

  IPAddress ip = WiFi.localIP();

  Serial.print("IP Address: ");


  // print the received signal strength:

  long rssi = WiFi.RSSI();

  Serial.print("signal strength (RSSI):");


  Serial.println(" dBm");

See Also:

Last revision 2016/04/16 by SM