When you create a device you probably need to know the correct time, on wifi device the resonably choiche is to use Internet to get time via NTP.
The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use. NTP was designed by David L. Mills of the University of Delaware. (cit. wiki)
NTPClient Library
The Arduino IDE have a library very simple to use NTPClient.
You can download It directly from Arduino IDE --> Manage Libraries.
I add directly the example code, in this article I try to explain by comment on code, because the code is very simple.
/*
* Simple NTP client
* https://mischianti.org/
*
* The MIT License (MIT)
* written by Renzo Mischianti <www.mischianti.org>
*/
#include <NTPClient.h>
// change next line to use with another board/shield
#include <ESP8266WiFi.h>
//#include <WiFi.h> // for WiFi shield
//#include <WiFi101.h> // for WiFi 101 shield or MKR1000
#include <WiFiUdp.h>
const char *ssid = "<SSID>";
const char *password = "<PASSWORD>";
WiFiUDP ntpUDP;
// By default 'pool.ntp.org' is used with 60 seconds update interval and
// no offset
// NTPClient timeClient(ntpUDP);
// You can specify the time server pool and the offset, (in seconds)
// additionaly you can specify the update interval (in milliseconds).
int GTMOffset = 1;
NTPClient timeClient(ntpUDP, "europe.pool.ntp.org", GTMOffset*60*60, 60000);
void setup(){
Serial.begin(115200);
WiFi.begin(ssid, password);
while ( WiFi.status() != WL_CONNECTED ) {
delay ( 500 );
Serial.print ( "." );
}
timeClient.begin();
}
void loop() {
// I'm going to update time from internet
timeClient.update();
// Print the updated time
Serial.println(timeClient.getFormattedTime());
delay(1000);
}
Now your arduino or esp became a clock.
Time library
This example have some limitation, to update the date you must call service, a simple way to update less time the date you can use Time library. This Arduino library use internal clock as a normal clock that after you adjust It via NTP is a normal clock.
You can find the library here GitHub.
But I show you a simple example.
/*
* Simple NTP client
* https://mischianti.org/
*
* The MIT License (MIT)
* written by Renzo Mischianti <www.mischianti.org>
*/
const char *ssid = "<SSID>";
const char *password = "<PASSWORD>";
#include <NTPClient.h>
// change next line to use with another board/shield
#include <ESP8266WiFi.h>
//#include <WiFi.h> // for WiFi shield
//#include <WiFi101.h> // for WiFi 101 shield or MKR1000
#include <WiFiUdp.h>
#include <TimeLib.h>
#include <time.h>
/**
* Input time in epoch format and return tm time format
* by Renzo Mischianti <www.mischianti.org>
*/
static tm getDateTimeByParams(long time){
struct tm *newtime;
const time_t tim = time;
newtime = localtime(&tim);
return *newtime;
}
/**
* Input tm time format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getDateTimeStringByParams(tm *newtime, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
char buffer[30];
strftime(buffer, 30, pattern, newtime);
return buffer;
}
/**
* Input time in epoch format format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getEpochStringByParams(long time, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
// struct tm *newtime;
tm newtime;
newtime = getDateTimeByParams(time);
return getDateTimeStringByParams(&newtime, pattern);
}
WiFiUDP ntpUDP;
// By default 'pool.ntp.org' is used with 60 seconds update interval and
// no offset
// NTPClient timeClient(ntpUDP);
// You can specify the time server pool and the offset, (in seconds)
// additionaly you can specify the update interval (in milliseconds).
int GTMOffset = 1;
NTPClient timeClient(ntpUDP, "europe.pool.ntp.org", GTMOffset*60*60, 60*60*1000);
void setup(){
Serial.begin(115200);
WiFi.begin(ssid, password);
while ( WiFi.status() != WL_CONNECTED ) {
delay ( 500 );
Serial.print ( "." );
}
timeClient.begin();
delay ( 1000 );
if (timeClient.update()){
Serial.print ( "Adjust local clock" );
unsigned long epoch = timeClient.getEpochTime();
// HERE I'M UPDATE LOCAL CLOCK
setTime(epoch);
}else{
Serial.print ( "NTP Update not WORK!!" );
}
}
void loop() {
// Here I print time from local clock
Serial.println(getEpochStringByParams(now()));
delay(1000);
}
As you can see I create some simple function to parse and format the date, very usefully for me.
/**
* Input time in epoch format and return tm time format
* by Renzo Mischianti <www.mischianti.org>
*/
static tm getDateTimeByParams(long time){
struct tm *newtime;
const time_t tim = time;
newtime = localtime(&tim);
return *newtime;
}
/**
* Input tm time format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getDateTimeStringByParams(tm *newtime, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
char buffer[30];
strftime(buffer, 30, pattern, newtime);
return buffer;
}
/**
* Input time in epoch format format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getEpochStringByParams(long time, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
// struct tm *newtime;
tm newtime;
newtime = getDateTimeByParams(time);
return getDateTimeStringByParams(&newtime, pattern);
}
You must pay attention to line 20, there you can choiche if you want UTC time, by set GTMOffset to 0 or if you want set your area GTM offset.
I live in Italy so I’m going to set GTM+1 and I set the last parameter to 60000 the update interval in milliseconds, this protocol use UDP as you can see, and you must choiche an NTP server.
But this is not sufficient, some zone have DST (Daylight saving time), so you must calculate the offset change, in the summer time Italy put another hour to the offset (so we are going formally in GTM+2), but a lot of country for energy saving purpose use DST.
But calculate that dynamic offset is very tedious, but exist a library that do It for you.
Timezone library
To manage DST you can use Timezone library.
You can download It directly from Arduino IDE --> Manage Libraries.
The usage is not so simple, but with the example, you can understand It.
First you must configure your DST, there is an example with some configuration that you can use as starting point.
// Australia Eastern Time Zone (Sydney, Melbourne)
TimeChangeRule aEDT = {"AEDT", First, Sun, Oct, 2, 660}; // UTC + 11 hours
TimeChangeRule aEST = {"AEST", First, Sun, Apr, 3, 600}; // UTC + 10 hours
Timezone ausET(aEDT, aEST);
// Moscow Standard Time (MSK, does not observe DST)
TimeChangeRule msk = {"MSK", Last, Sun, Mar, 1, 180};
Timezone tzMSK(msk);
// Central European Time (Frankfurt, Paris)
TimeChangeRule CEST = {"CEST", Last, Sun, Mar, 2, 120}; // Central European Summer Time
TimeChangeRule CET = {"CET ", Last, Sun, Oct, 3, 60}; // Central European Standard Time
Timezone CE(CEST, CET);
// United Kingdom (London, Belfast)
TimeChangeRule BST = {"BST", Last, Sun, Mar, 1, 60}; // British Summer Time
TimeChangeRule GMT = {"GMT", Last, Sun, Oct, 2, 0}; // Standard Time
Timezone UK(BST, GMT);
// UTC
TimeChangeRule utcRule = {"UTC", Last, Sun, Mar, 1, 0}; // UTC
Timezone UTC(utcRule);
// US Eastern Time Zone (New York, Detroit)
TimeChangeRule usEDT = {"EDT", Second, Sun, Mar, 2, -240}; // Eastern Daylight Time = UTC - 4 hours
TimeChangeRule usEST = {"EST", First, Sun, Nov, 2, -300}; // Eastern Standard Time = UTC - 5 hours
Timezone usET(usEDT, usEST);
// US Central Time Zone (Chicago, Houston)
TimeChangeRule usCDT = {"CDT", Second, Sun, Mar, 2, -300};
TimeChangeRule usCST = {"CST", First, Sun, Nov, 2, -360};
Timezone usCT(usCDT, usCST);
// US Mountain Time Zone (Denver, Salt Lake City)
TimeChangeRule usMDT = {"MDT", Second, Sun, Mar, 2, -360};
TimeChangeRule usMST = {"MST", First, Sun, Nov, 2, -420};
Timezone usMT(usMDT, usMST);
// Arizona is US Mountain Time Zone but does not use DST
Timezone usAZ(usMST);
// US Pacific Time Zone (Las Vegas, Los Angeles)
TimeChangeRule usPDT = {"PDT", Second, Sun, Mar, 2, -420};
TimeChangeRule usPST = {"PST", First, Sun, Nov, 2, -480};
Timezone usPT(usPDT, usPST);
In my case I must set CET and CEST parameter (line 10), and I’m going to modify original NTP example.
/*
* Simple NTP client
* https://mischianti.org/
*
* The MIT License (MIT)
* written by Renzo Mischianti <www.mischianti.org>
*/
const char *ssid = "<YOURSSID>";
const char *password = "<YOURPASSWD>";
#include <NTPClient.h>
// change next line to use with another board/shield
#include <ESP8266WiFi.h>
//#include <WiFi.h> // for WiFi shield
//#include <WiFi101.h> // for WiFi 101 shield or MKR1000
#include <WiFiUdp.h>
#include <TimeLib.h>
#include <time.h>
#include <Timezone.h> // https://github.com/JChristensen/Timezone
/**
* Input time in epoch format and return tm time format
* by Renzo Mischianti <www.mischianti.org>
*/
static tm getDateTimeByParams(long time){
struct tm *newtime;
const time_t tim = time;
newtime = localtime(&tim);
return *newtime;
}
/**
* Input tm time format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getDateTimeStringByParams(tm *newtime, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
char buffer[30];
strftime(buffer, 30, pattern, newtime);
return buffer;
}
/**
* Input time in epoch format format and return String with format pattern
* by Renzo Mischianti <www.mischianti.org>
*/
static String getEpochStringByParams(long time, char* pattern = (char *)"%d/%m/%Y %H:%M:%S"){
// struct tm *newtime;
tm newtime;
newtime = getDateTimeByParams(time);
return getDateTimeStringByParams(&newtime, pattern);
}
WiFiUDP ntpUDP;
// By default 'pool.ntp.org' is used with 60 seconds update interval and
// no offset
// NTPClient timeClient(ntpUDP);
// You can specify the time server pool and the offset, (in seconds)
// additionaly you can specify the update interval (in milliseconds).
int GTMOffset = 0; // SET TO UTC TIME
NTPClient timeClient(ntpUDP, "europe.pool.ntp.org", GTMOffset*60*60, 60*60*1000);
// Central European Time (Frankfurt, Paris)
TimeChangeRule CEST = {"CEST", Last, Sun, Mar, 2, 120}; // Central European Summer Time
TimeChangeRule CET = {"CET ", Last, Sun, Oct, 3, 60}; // Central European Standard Time
Timezone CE(CEST, CET);
void setup(){
Serial.begin(115200);
WiFi.begin(ssid, password);
while ( WiFi.status() != WL_CONNECTED ) {
delay ( 500 );
Serial.print ( "." );
}
timeClient.begin();
delay ( 1000 );
if (timeClient.update()){
Serial.print ( "Adjust local clock" );
unsigned long epoch = timeClient.getEpochTime();
setTime(epoch);
}else{
Serial.print ( "NTP Update not WORK!!" );
}
}
void loop() {
// I print the time from local clock but first I check DST
// to add hours if needed
Serial.println(getEpochStringByParams(CE.toLocal(now())));
delay(1000);
}
Now you have your time with DST correctly set.