MakerNTP - A Low Cost Arduino Mega2560 GPS-based Stratum 1 NTP Server

My homebrew low locst (not more than 120 USD for retail) MakerNTP is now in operation for about one month without any problem in my home environment. The features of MakerNTP are:

Protocol: SNTP V4
Performance: 40 requests/second
Ethernet Port: 1
Default IP: 192.168.1.123
Power Supply: 9V (recommended) / 5V (USB)
Enclosure: ABS
Application: home automation, security surveillance ......

NOTE: Most SNTP clients will generally sync your system time to within 100 milliseconds of the correct time - often within 10 milliseconds. Of course, the accuracy is highly dependent on the accuracy of the server that it is connecting to.

Photos

NTP Server Synchronized DS1307 RTC Analog Data Logger

This sketch combine analog sensor data logger on Aug. 15, 2013 and NTP server synchronized DS1307 RTC using TimeAlarm library on Aug. 17, 2013.

The shetch use fixed IP, so DHCP server is not needed in the local area network.

Because the RTC is synchronized with NTP server, so the data logger keeps the time within 5 seconds. The NTP sync may fail sometimes depending on the network conditions.

Sketch

/*
 * NTPSynchronizedAnalogDataLogger.ino
 *
 * This sketch calls alarm functions at 7:30 am and at 7:30 pm (19:30)
 * and sync DS1307, Arduino system time 
 *
 * At startup the system time read from DS1307, then both sync with NTP 
 */

#include <Wire.h>
#include <Time.h>
#include <DS1307RTC.h>
#include <TimeAlarms.h>
#include <SPI.h>
#include <Ethernet.h>
#include <EthernetUdp.h>
#include <SD.h>
#define analogSensorStart 3 // sensor connect to A3
#define analogSensorEnd 3 // sensor connect to A3

// Enter a MAC address for your controller bellow.
// Newer Ethernet shields have a MAC address printed on a sticker on the shield
byte mac[] = {0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED};
byte ip[] = {192, 168, 1, 177};
unsigned int localPort = 8888; // local port to listen for UDP packets
IPAddress timeServer(140, 112, 2, 188); // ntp2.ntu.edu.tw 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;
// timeZoneOffset = (Time Zone) * 3600L eg. (+8) * 3600L = 28800L for Taipei, Taiwan
const long timeZoneOffset = 28800L; 
// sync to NTP server every "ntpSyncTime" seconds, set to 1 hour or more to be reasonable
unsigned long ntpSyncTime = 21600;
// adjust the sync latency with computer NTP client in seconds 
unsigned int syncLatency = 2;

// sd card variables
File file; // test file
const uint8_t SD_CS = 4; // SD chip select
String file_name = ""; // file name should not prefix with "prefix_word"
char fn[] = "MMDDHHMM.CSV";
int i=0;
int displayAtSecond = 0;
time_t t;

//------------------------------------------------------------------------------
// call back for file timestamps 
void dateTime(uint16_t* date, uint16_t* time) {
  time_t timeStamp = now();

  // return date using FAT_DATE macro to format fields
  *date = FAT_DATE(year(timeStamp), month(timeStamp), day(timeStamp));

  // return time using FAT_TIME macro to format fields
  *time = FAT_TIME(hour(timeStamp), minute(timeStamp), second(timeStamp));
} 
//------------------------------------------------------------------------------

void setup()
{
  Serial.begin(9600);
  Wire.begin();
  setSyncProvider(RTC.get); // the function to get the time from the RTC
  if (timeStatus() != timeSet)
    Serial.println("Unable to sync with the RTC");
  else
    Serial.println("RTC has set the system time");
  // set date time callback function
  SdFile::dateTimeCallback(dateTime);  
  // display RTC time
  Serial.print(year());
  Serial.print('-');
  Serial.print(month());
  Serial.print('-');
  Serial.print(day());
  Serial.print(' ');
  Serial.print(hour());
  Serial.print(':');
  Serial.print(minute());
  Serial.print(':');
  Serial.print(second());
  Serial.println(" --- RTC Time");
  // create the alarms 
  Alarm.alarmRepeat(7,30,0, ntpSyncDS1307);  // 7:30am every day
  Alarm.alarmRepeat(19,30,0, ntpSyncDS1307);  // 7:30pm every day 
  
  // start Ethernet and UDP
  Ethernet.begin(mac, ip);
  Udp.begin(localPort); 
  // Serial.println("connect to ntp server");
  ntpSyncDS1307();
  
  // process file name string
  t = now();
  if (month(t) < 10) {
      file_name = String(file_name + '0' + String(month(t), DEC));
    }
    else {
    file_name = String(file_name +String(month(t), DEC));
    }
  if (day(t) < 10) {
      file_name = String(file_name + '0' + String(day(t), DEC));
    }
    else {
    file_name = String(file_name +String(day(t), DEC));
    }
  if (hour(t) < 10) {
      file_name = String(file_name + '0' + String(hour(t), DEC));
    }
    else {
    file_name = String(file_name +String(hour(t), DEC));
    }
  if (minute(t) < 10) {
      file_name = String(file_name + '0' + String(minute(t), DEC));
    }
    else {
    file_name = String(file_name +String(minute(t), DEC));
    }

  file_name = String(file_name + ".CSV");

  for (i=0;i<=file_name.length();i++) {
    fn[i] = file_name.charAt(i);
  }
  Serial.print("File Name: ");
  Serial.println(fn);
  pinMode(10, OUTPUT);
  digitalWrite(10, HIGH);
  if (!SD.begin(SD_CS)) {
    Serial.println("SD failed");
    // while(1);
  }
}

void loop(){
  t = now();
  if (displayAtSecond != second(t)) {
    analogSensorDataLogger();
    displayAtSecond = second(t);
  }
  Alarm.delay(100); // wait 1/10 second between cycles
}

// functions to be called when an alarm triggers:
void ntpSyncDS1307() {
  sendNTPpacket(timeServer); // send an NTP packet to a time server
  // wait to see if a replay is available
  delay(1000);
  if (Udp.parsePacket()) {
    // We've received a packet, read the data from it
    Udp.read(packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer
    // the timstamp starts at byte 40 of the received packet and is four bytes,
    // or two words, long. First, extract 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 everyday time:
    // Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
    const unsigned long seventyYears = 2208988800L;
    // substract seventy years:
    unsigned long epoch = secsSince1900 - seventyYears + timeZoneOffset + syncLatency;
    setTime(epoch);
    RTC.set(epoch);
    // output time and "Sync OK" message every sync 
    Serial.print(year());
    Serial.print('-');
    Serial.print(month());
    Serial.print('-');
    Serial.print(day());
    Serial.print(' ');
    Serial.print(hour());
    Serial.print(':');
    Serial.print(minute());
    Serial.print(':');
    Serial.print(second());
    Serial.print(' ');
    Serial.println("Sync OK");
  }
}

// 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 clodk
  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);
  Udp.write(packetBuffer, NTP_PACKET_SIZE);
  Udp.endPacket();
}

void analogSensorDataLogger() { 
  String data_string = "";
  data_string = String(year(t), DEC);
  data_string += "/";
  if (month(t) < 10) {
      data_string = String(data_string + '0' + String(month(t), DEC));
    }
    else {
    data_string = String(data_string +String(month(t), DEC));
    }
  data_string += "/";
  if (day(t) < 10) {
      data_string = String(data_string + '0' + String(day(t), DEC));
    }
    else {
    data_string = String(data_string +String(day(t), DEC));
    }
  data_string += " ";
  if (hour(t) < 10) {
      data_string = String(data_string + '0' + String(hour(t), DEC));
    }
    else {
    data_string = String(data_string +String(hour(t), DEC));
    }
  data_string += ":";
  if (minute(t) < 10) {
      data_string = String(data_string + '0' + String(minute(t), DEC));
    }
    else {
    data_string = String(data_string +String(minute(t), DEC));
    }
  data_string += ":";  
  if (second(t) < 10) {
      data_string = String(data_string + '0' + String(second(t), DEC));
    }
    else {
    data_string = String(data_string +String(second(t), DEC));
    }
  data_string += ",";

  //read sensor value from A0-A3 and append to the string
  for (int analogPin = analogSensorStart; analogPin <= analogSensorEnd; analogPin++)
    {
    int sensor = analogRead(analogPin);
    data_string += String(sensor);
    if (analogPin < analogSensorEnd) {
      data_string += ",";
      }
    }
  
  file = SD.open(fn, FILE_WRITE);
  if (file) {
    file.println(data_string);
    file.close();
    Serial.println(data_string);
    }
    else {
      Serial.print("error opening ");
      Serial.println(fn);
    }
}

Analog Sensor Data Logger

Create data file name:MMDDhhmm.CSV where M means month, D means day, h means hour and m means minute respectively. Once the reset on Arduino board is pressed, a new logger file is created.

An altenative is to use a DS1307 RTC shield (such as RTC Sensor Shield) and a SD shield.

This is the new version of the post on May 01, 2012 with the difference of using Time.h library.

Pin Used

Analog pin 3 is used for LM35 temperature sensor.
Analog pins 4 and 5 are used for I2C protocol implemented by Maxim DS1307.
Digital pins 10, 11, 12, 13 are used for SPI protocol to save data file to micro SD card.

Time.h Download

http://playground.arduino.cc//Code/Time

Sketch

// File Name: AnalogDataLoggerTimeLibrary.ino
// The sketch works on Arduino IDE 1.05
#include <SD.h>
#include <Wire.h>
#include <Time.h>
#include <DS1307RTC.h>
#define analogSensorStart 3
#define analogSensorEnd 3

File file; // test file
const uint8_t SD_CS = 10; // SD chip select
String file_name = ""; // file name should not prefix with "prefix_word"
char fn[] = "MMDDHHMM.CSV";
int i=0;
int displayAtSecond = 0;
time_t t;

//------------------------------------------------------------------------------
// call back for file timestamps 
void dateTime(uint16_t* date, uint16_t* time) {
  time_t timeStamp = now();

  // return date using FAT_DATE macro to format fields
  *date = FAT_DATE(year(timeStamp), month(timeStamp), day(timeStamp));

  // return time using FAT_TIME macro to format fields
  *time = FAT_TIME(hour(timeStamp), minute(timeStamp), second(timeStamp));
} 
//------------------------------------------------------------------------------
void setup() {
  Serial.begin(9600);
  Wire.begin();
  setSyncProvider(RTC.get); // the function to get the time from the RTC
  if (timeStatus() != timeSet)
    Serial.println("Unable to sync with the RTC");
    else
    Serial.println("RTC has set the system time");
    
  // set date time callback function
  SdFile::dateTimeCallback(dateTime);

  t = now();
  if (month(t) < 10) {
      file_name = String(file_name + '0' + String(month(t), DEC));
    }
    else {
    file_name = String(file_name +String(month(t), DEC));
    }
  if (day(t) < 10) {
      file_name = String(file_name + '0' + String(day(t), DEC));
    }
    else {
    file_name = String(file_name +String(day(t), DEC));
    }
  if (hour(t) < 10) {
      file_name = String(file_name + '0' + String(hour(t), DEC));
    }
    else {
    file_name = String(file_name +String(hour(t), DEC));
    }
  if (minute(t) < 10) {
      file_name = String(file_name + '0' + String(minute(t), DEC));
    }
    else {
    file_name = String(file_name +String(minute(t), DEC));
    }

  file_name = String(file_name + ".CSV");

  for (i=0;i<=file_name.length();i++) {
    fn[i] = file_name.charAt(i);
  }

  if (!SD.begin(SD_CS)) {
    Serial.println("SD failed");
    while(1);
  }
  Serial.print("File Name: ");
  Serial.println(fn);
}
//------------------------------------------------------------------------------
void loop()
{
  t = now();
  if (displayAtSecond != second(t)) {
    analogSensorDataLogger();
    displayAtSecond = second(t);
  }
}

void analogSensorDataLogger() { 
  String data_string = "";
  data_string = String(year(t), DEC);
  data_string += "/";
  if (month(t) < 10) {
      data_string = String(data_string + '0' + String(month(t), DEC));
    }
    else {
    data_string = String(data_string +String(month(t), DEC));
    }
  data_string += "/";
  if (day(t) < 10) {
      data_string = String(data_string + '0' + String(day(t), DEC));
    }
    else {
    data_string = String(data_string +String(day(t), DEC));
    }
  data_string += " ";
  if (hour(t) < 10) {
      data_string = String(data_string + '0' + String(hour(t), DEC));
    }
    else {
    data_string = String(data_string +String(hour(t), DEC));
    }
  data_string += ":";
  if (minute(t) < 10) {
      data_string = String(data_string + '0' + String(minute(t), DEC));
    }
    else {
    data_string = String(data_string +String(minute(t), DEC));
    }
  data_string += ":";  
  if (second(t) < 10) {
      data_string = String(data_string + '0' + String(second(t), DEC));
    }
    else {
    data_string = String(data_string +String(second(t), DEC));
    }
  data_string += ",";

  //read sensor value from A0-A3 and append to the string
  for (int analogPin = analogSensorStart; analogPin <= analogSensorEnd; analogPin++)
    {
    int sensor = analogRead(analogPin);
    data_string += String(sensor);
    if (analogPin < analogSensorEnd) {
      data_string += ",";
      }
    }
  
  file = SD.open(fn, FILE_WRITE);
  if (file) {
    file.println(data_string);
    file.close();
    Serial.println(data_string);
    }
    else {
      Serial.print("error opening ");
      Serial.println(fn);
    }
}

LCD Display Date, Time, Weekday From DS1307 And Temperature From LM35

Date and time is useful for many applications. Most visitors to my blog search for rtc stuff. The following sketch show a simple application using a LCD shield, a RTC Sensor shield and a LM35 temperature sensor to display date, time, weekday, and environmental temperature. To use the sketch, you need to download the Time library.

The sketch is a new version of the sketches post on Jun. 3, 2012 and May. 3, 2013 using Time.h library and showing weekday.

Output

Sketch

 /*
 * TimeRTC.pde
 * example code illustrating Time library with Real Time Clock.
 * the sketch works on Arduino IDE 1.05
 * 1) modified by Befun Hung on Jul. 28, 2013 
 *    changing the sequence to year, month, day, hour, minute, second
 *    adding the day of week
 *    almost same function as sketch on May 1, 2012
 * 2) modified by Befun Hung on Jul. 29, 2013
 *    change display device to LCD Shield
 *    adding temperature readout from LM35
 *    the sketch does not contain delay() in the loop section 
 */

#include <Time.h>  
#include <Wire.h>  
#include <DS1307RTC.h>  // a basic DS1307 library that returns time as a time_t
#include <LiquidCrystal.h>
LiquidCrystal lcd(8,9,4,5,6,7);

char *dayOfWeek[] = {"", "SUN", "MON", "TUE", "WED", "THU", "FRI", "SAT"};
int potPin = 3; // change potPin value to 0, 1, 2 for A0, A1, A2 respectly
float temperature = 0;
int displayAtSecond;

void setup()  {
  lcd.begin(16,2);
  lcd.print("*cheaphousetek*");
  lcd.setCursor(0,1);
  setSyncProvider(RTC.get);   // the function to get the time from the RTC
  if(timeStatus()!= timeSet) 
     lcd.print("Unable to sync");
  else
     lcd.print("Sync system time ");
  displayAtSecond = second();
  delay(2000);
  lcd.clear();
}

void loop()
{
  if (displayAtSecond != second()) { 
  digitalClockDisplay(); 
  displayAtSecond = second(); 
  }
}

void printTenths(long value) {
  // prints a value of 123 as 12.3
  lcd.setCursor(10,1);
  lcd.print(value / 10);
  lcd.setCursor(12,1);
  lcd.print('.');
  lcd.setCursor(13,1);
  lcd.print(value % 10);
}

void digitalClockDisplay(){
  // digital clock display of the time
  int span = 10;
  long aRead = 0;
  unsigned long temp;
  
  lcd.setCursor(0,0);
  lcd.print(year());
  lcd.print('-');
  if (month() < 10) {
    lcd.print('0');
  }
  lcd.print(month());
  lcd.print('-');
  if (day() < 10) {
    lcd.print('0');
  }
  lcd.print(day());
  lcd.print(' ');
  lcd.setCursor(11,0);
  lcd.print(dayOfWeek[weekday()]);
  lcd.setCursor(0,1);
  if (hour() < 10) {
    lcd.print('0');
  }
  lcd.print(hour());
  lcd.print(':');
  if (minute() < 10) {
    lcd.print('0');
  }
  lcd.print(minute());
  lcd.print(':');
  if (second() < 10) {
    lcd.print('0');
  }
  lcd.print(second());
  lcd.print(' ');
  for (int i=0;i<span;i++) {
    aRead = aRead + analogRead(potPin);
  }
  temperature = (aRead / span * 500.0 / 1024.0); // for other analog sensor change the constants
  printTenths(long (temperature * 10));
  lcd.setCursor(14,1);
  lcd.print(char(223));
  lcd.setCursor(15,1);
  lcd.print('C');
}

Display Date and Time In Arduino Serial Monitor Using Time.h

First, Download Time.h from the following link.
http://playground.arduino.cc/uploads/Code/Time.zip

Read usage of Time.h library.
http://playground.arduino.cc/Code/time

The function is almost same as the sketch post on May 1, 2012, except adding displaying the day of week.

Pins Used

Analog pins 4.and 5 are used for I2C protocol implemented by Maxim DS1307.

Serial Monitor Output

Sketch

/*
 * TimeRTC.pde
 * example code illustrating Time library with Real Time Clock.
 * the sketch works on Arduino IDE 1.05
 * modified by Befun Horng on Jul. 28, 2013
 * changing the sequence to year, month, day, hour, minute, second
 * adding the day of week
 * almost same function as sketch on May 1, 2012
 */

#include <Time.h>
#include <Wire.h>
#include <DS1307RTC.h>  // a basic DS1307 library that returns time as a time_t
char *dayOfWeek[] = {"", "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
void setup()  {
  Serial.begin(9600);
  setSyncProvider(RTC.get);   // the function to get the time from the RTC
  if(timeStatus()!= timeSet)
     Serial.println("Unable to sync with the RTC");
  else
     Serial.println("RTC has set the system time");    
}

void loop()
{
   digitalClockDisplay();
   delay(1000);
}

void digitalClockDisplay(){
  // digital clock display of the time
  Serial.print(year());
  Serial.print("-");
  if (month() < 10) {
    Serial.print('0');
  }
  Serial.print(month());
  Serial.print("-");
  if (day() < 10) {
    Serial.print('0');
  }
  Serial.print(day());
  Serial.print(" ");
  Serial.print(dayOfWeek[weekday()]);
  Serial.print(' ');
  if (hour() < 10) {
    Serial.print('0');
  }
  Serial.print(hour());
  Serial.print(':');
  if (minute() < 10) {
    Serial.print('0');
  }
  Serial.print(minute());
  Serial.print(':');
  if (second() < 10) {
    Serial.print('0');
  }
  Serial.print(second());
  Serial.println();
}

LCD Displaying Date, Time From DS1307 And Temperature From LM35

Date and time is useful for many applications. Most visitors to my blog search for rtc stuff. The following sketch show a simple application using a LCD shield, a RTC Sensor shield and a LM35 temperature sensor to display date, time and enviromnental temperature. To use the sketch, you need to download the RTClib library.

There is a new version using Time.h library and showing weekday.

Output:

Sketch:

// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
// 2010-02-04 <jcw@equi4.com> http://opensource.org/licenses/mit-license.php
// $Id: ds1307.pde 4773 2010-02-04 14:09:18Z jcw $
// Added LCD display and LM35 temperature function by Befun Hung 2011-10-13
// Take out displayDateTime procedure from loop() by Befun Hung 2013-05-03
// The sketch works on Arduino IDE 0022

#include <Wire.h>
#include <RTClib.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

RTC_DS1307 RTC;
// change potPin value to 0, 1, 2 for A0, A1, A2 respectly
int potPin = 3;
float temperature = 0;

void setup () {
    Serial.begin(9600);
    Wire.begin();
    RTC.begin();
    lcd.begin(16, 2);
    lcd.print("*cheaphousetek*");
    delay(5000);
    lcd.clear();
    
    // following line sets the RTC to the date & time this sketch was compiled
    // RTC.adjust(DateTime(__DATE__, __TIME__));
}

void loop() {
  displayDateTime();
}

void printTenths(long value) {
  // prints a value of 123 as 12.3
  Serial.print(value / 10);
  Serial.print('.');
  Serial.print(value % 10);
  Serial.println();
  lcd.setCursor(10, 1);
  lcd.print(value / 10);
  lcd.setCursor(12, 1);
  lcd.print('.');
  lcd.setCursor(13, 1);
  lcd.print(value % 10);
}

void displayDateTime() {
    DateTime now = RTC.now();
    int span = 10;
    long aRead = 0;
    unsigned long tmp;
      
    tmp = now.year();
    Serial.print(now.year(), DEC);
    lcd.setCursor(0, 0);
    lcd.print(tmp);
    Serial.print('/');
    lcd.setCursor(4, 0);
    lcd.print("-");
    
    tmp = now.month();
    if (now.month() < 10) {
      Serial.print('0');
      Serial.print(now.month(), DEC);
      lcd.setCursor(5, 0);
      lcd.print('0');
      lcd.setCursor(6, 0);
      lcd.print(tmp);
    }
    else {
      Serial.print(now.month(), DEC);
      lcd.setCursor(5, 0);
      lcd.print(tmp);
    }
    Serial.print('/');
    lcd.setCursor(7, 0);
    lcd.print('-');
    
    tmp = now.day();
    if (now.day() < 10) {
      Serial.print('0');
      Serial.print(now.day());
      lcd.setCursor(8, 0);
      lcd.print('0');
      lcd.setCursor(9, 0);
      lcd.print(tmp);
    }
    else {
      Serial.print(now.day(), DEC);
      lcd.setCursor(8, 0);
      lcd.print(tmp);
    }
    Serial.print(' ');
    
    tmp = now.hour();
    if (now.hour() < 10) {
      Serial.print('0');
      Serial.print(now.hour(), DEC);
      lcd.setCursor(0, 1);
      lcd.print('0');
      lcd.setCursor(1, 1);
      lcd.print(tmp);
    }
    else {
      Serial.print(now.hour(), DEC);
      lcd.setCursor(0, 1);
      lcd.print(tmp);
    }
    Serial.print(':');
    lcd.setCursor(2, 1);
    lcd.print(':');
    
    tmp = now.minute();
    if (now.minute() < 10) {
      Serial.print('0');
      Serial.print(now.minute(), DEC);
      lcd.setCursor(3, 1);
      lcd.print('0');
      lcd.setCursor(4, 1);
      lcd.print(tmp);
    }
    else {
      Serial.print(now.minute(), DEC);
      lcd.setCursor(3, 1);
      lcd.print(tmp);
    }
    Serial.print(':');
    lcd.setCursor(5, 1);
    lcd.print(':');
    
    tmp = now.second();
    if (now.second() < 10) {
      Serial.print('0');
      Serial.print(now.second(), DEC);
      lcd.setCursor(6, 1);
      lcd.print('0');
      lcd.setCursor(7, 1);
      lcd.print(tmp);
    }
    else {
      Serial.print(now.second(), DEC);
      lcd.setCursor(6, 1);
      lcd.print(tmp);
    }
    Serial.print (' ');
    lcd.setCursor(8, 1);
    lcd.print(' ');
    // Serial.println();
    
    for (int i=0;i<span;i++) {
      aRead = aRead + analogRead(potPin);
      // Serial.print(aRead);
      // Serial.print(' ');
    }
    // aRead = aRead / span;
    temperature = (aRead / span * 500.0 / 1024.0);
    // Serial.print(aRead);
    // Serial.print(' ');
    // Serial.print(temperature);
    // Serial.print(' ');
    printTenths(long (temperature * 10));
    lcd.setCursor(14, 1);
    lcd.print(char(223));
    lcd.setCursor(15, 1);
    lcd.print('C');
        
    delay(200);
    
    // Serial.print(" since 2000 = ");
    // Serial.print(now.get());
    // Serial.print("s = ");
    // Serial.print(now.get() / 86400L);
    // Serial.println("d");
    
    // calculate a date which is 7 days and 30 seconds into the future
    // DateTime future (now.get() + 7 * 86400L + 30);
    
    // Serial.print(" now + 7d + 30s: ");
    // Serial.print(future.year(), DEC);
    // Serial.print('/');
    // Serial.print(future.month(), DEC);
    // Serial.print('/');
    // Serial.print(future.day(), DEC);
    // Serial.print(' ');
    // Serial.print(future.hour(), DEC);
    // Serial.print(':');
    // Serial.print(future.minute(), DEC);
    // Serial.print(':');
    // Serial.print(future.second(), DEC);
    // Serial.println();
    
    // Serial.println();
    // delay(3000);
}

Freeduino/Arduino RTC Sensor Shield To Display Date and Time In Arduino Serial Monitor Using Wire.h + RTClib.h

First, download RTClib.h from the following link.

http://www.ladyada.net/make/logshield/download.html

There is a new version using Time.h library and showing day of week.

Pins Used

Analog pins 4 and 5 are used for I2C protocol implemented  by Maxim DS1307.

Serial Monitor Output

Sketch

// Date and time functions using a DS1307 RTC connected via I2C and Wire lib
// 2010-02-04 <jcw@equi4.com> http://opensource.org/licenses/mit-license.php
// $Id: ds1307.pde 4773 2010-02-04 14:09:18Z jcw $
// Revised by Befun Hung <bfhorng@ms4.hinet.net> 2011-11-13
// RTClib.h download webpage http://www.ladyada.net/make/logshield/download.html
// File Name: DS1307RTClib.pde - Display Date And Time in Arduino Serial Monitor
// The sketch works on Arduino IDE 0022

#include <Wire.h>
#include <RTClib.h>

RTC_DS1307 RTC;

void setup () {
    Serial.begin(9600);
    Wire.begin();
    RTC.begin();
 
    // following line sets the RTC to the date & time this sketch was compiled
    // RTC.adjust(DateTime(__DATE__, __TIME__));
}

void loop () {
    DateTime now = RTC.now();
 
    Serial.print(now.year(), DEC);
    Serial.print('/');
    if (now.month() < 10) {
      Serial.print('0');
    }
    Serial.print(now.month(), DEC);
    Serial.print('/');
    if (now.day() < 10) {
      Serial.print('0');
    }
    Serial.print(now.day(), DEC);
    Serial.print(' ');
    if (now.hour() < 10) {
      Serial.print('0');
    }
    Serial.print(now.hour(), DEC);
    Serial.print(':');
    if (now.minute() < 10) {
      Serial.print('0');
    }
    Serial.print(now.minute(), DEC);
    Serial.print(':');
    if (now.second() < 10) {
      Serial.print('0');
    }
    Serial.print(now.second(), DEC);
    Serial.println();
    delay(995);
 
}