ERROR: sendNTPpacket was not declared in this scope


I am having a little trouble with the UdpNtpClient code. I have the ethernet2 shield connected to the Arduino Rev3. The chip is W5500 on the ethernet shield, so I ahd to change the code/libraries a bit to be compatible with that chip rather than the W5100. When I run my code I get an error starting with: In function’void loop()’: error ‘sendNTPpacket’ was not declared in this scope. I am confused as to what to do, I cannot figure out why I am getting this error.

UdpNtpClienterror.ino (4.71 KB)

Sorry I attached the code but this might be better:


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,

Warning: NTP Servers are subject to temporary failure or IP address change.
Plese check

if the time server used in the example didn’t work.

created 4 Sep 2010
by Michael Margolis
modified 9 Apr 2012
by Tom Igoe
modified 12 Aug 2013
by Soohwan Kim

This code is in the public domain.


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

// Enter a MAC address for your controller below.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
#if defined(WIZ550io_WITH_MACADDRESS) // Use assigned MAC address of WIZ550io
byte mac = {0x90, 0xA2, 0xDA, 0x10, 0x21, 0xCB};

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 defined(WIZ550io_WITH_MACADDRESS)
if (Ethernet.begin() == 0) {
if (Ethernet.begin(mac) == 0) {
Serial.println(“Failed to configure Ethernet using DHCP”);
// no point in carrying on, so do nothing forevermore:

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

Sorry I attached the code but this might be better:

It would have been even better if you included the code between “code tags”, which you can insert by clicking the “</>” icon in the forums editor.

I am confused as to what to do, I cannot figure out why I am getting this error.

If you are using the Arduino-IDE: Check that opening and closing curly brackets are corresponding, so that “sendNTPpacket()” is correctly declared in your code!

And if you don’t use the Arduino-IDE for compiling, move “sendNTPpacket()” function above loop() in your code or write a function prototype for it!

BTW: Why did you declare a return value “unsigned long” for the “sendNTPpacket()” function, while the function does not return any value at all?