RTC-Real Time Clock-DS1307

The DS1307 Serial Real-Time Clock is a low-power, full binary-coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially via a 2-wire, bi-directional bus. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307 has a built-in power sense circuit that detects power failures and automatically switches to the battery supply.
This allows the module to retain the time, even when it’s not being powered up by the Arduino. This way, every time you turn on and off your module, the time doesn’t reset. This module uses I2C communication. This means that it communicates with the Arduino using just 2 pins.
PIN DETAILS:

MODULE PIN Arduino Connection
SCL A5
SDA A4
Vcc 5V
GND Ground

If you’re using other Arduino board rather than the Uno, check out what are their SCL and SDA pins.
Nano: SDA (A4); SCL(A5)
MEGA: SDA (20); SCL(21)
Leonardo: SDA (20); SCL(21)
CIRCUIT DIAGRAM:

Code
Working with the RTC requires two important steps:
1. Setting the current time, so that the RTC knows what time is it
2. Retaining the time, so that the RTC always gives the correct time, even when it is turned off
3. Set the current time in the Real Time Clock
For setting the current time you need to change the code provided. Set your current time in the function setDS3231time()
Copy and paste with Arduino IDE.
#include “Wire.h”
#define DS3231_I2C_ADDRESS 0x68
// Convert normal decimal numbers to binary coded decimal
byte decToBcd(byte val)
{
return( (val/10*16) + (val%10) );
}
// Convert binary coded decimal to normal decimal numbers
byte bcdToDec(byte val)
{
return( (val/16*10) + (val%16) );
}
void setup()
{
Wire.begin();
Serial.begin(9600);
// set the initial time here:
// DS3231 seconds, minutes, hours, day, date, month, year
// setDS3231time(30,42,21,4,26,11,14);
}
void setDS3231time(byte second, byte minute, byte hour, byte dayOfWeek, byte
dayOfMonth, byte month, byte year)
{
// sets time and date data to DS3231
Wire.beginTransmission(DS3231_I2C_ADDRESS);
Wire.write(0); // set next input to start at the seconds register
Wire.write(decToBcd(second)); // set seconds
Wire.write(decToBcd(minute)); // set minutes
Wire.write(decToBcd(hour)); // set hours
Wire.write(decToBcd(dayOfWeek)); // set day of week (1=Sunday, 7=Saturday)
Wire.write(decToBcd(dayOfMonth)); // set date (1 to 31)
Wire.write(decToBcd(month)); // set month
Wire.write(decToBcd(year)); // set year (0 to 99)
Wire.endTransmission();
}
void readDS3231time(byte *second,
byte *minute,
byte *hour,
byte *dayOfWeek,
byte *dayOfMonth,
byte *month,
byte *year)
{
Wire.beginTransmission(DS3231_I2C_ADDRESS);
Wire.write(0); // set DS3231 register pointer to 00h
Wire.endTransmission();
Wire.requestFrom(DS3231_I2C_ADDRESS, 7);
// request seven bytes of data from DS3231 starting from register 00h
*second = bcdToDec(Wire.read() & 0x7f);
*minute = bcdToDec(Wire.read());
*hour = bcdToDec(Wire.read() & 0x3f);
*dayOfWeek = bcdToDec(Wire.read());
*dayOfMonth = bcdToDec(Wire.read());
*month = bcdToDec(Wire.read());
*year = bcdToDec(Wire.read());
}
void displayTime()
{
byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
// retrieve data from DS3231
readDS3231time(&second, &minute, &hour, &dayOfWeek, &dayOfMonth, &month,
&year);
// send it to the serial monitor
Serial.print(hour, DEC);
// convert the byte variable to a decimal number when displayed
Serial.print(“:”);
if (minute<10)
{
Serial.print(“0”);
}
Serial.print(minute, DEC);
Serial.print(“:”);
if (second<10)
{
Serial.print(“0″);
}
Serial.print(second, DEC);
Serial.print(” “);
Serial.print(dayOfMonth, DEC);
Serial.print(“/”);
Serial.print(month, DEC);
Serial.print(“/”);
Serial.print(year, DEC);
Serial.print(” Day of week: “);
switch(dayOfWeek){
case 1:
Serial.println(“Sunday”);
break;
case 2:
Serial.println(“Monday”);
break;
case 3:
Serial.println(“Tuesday”);
break;
case 4:
Serial.println(“Wednesday”);
break;
case 5:
Serial.println(“Thursday”);
break;
case 6:
Serial.println(“Friday”);
break;
case 7:
Serial.println(“Saturday”);
break;
}
}
void loop()
{
displayTime(); // display the real-time clock data on the Serial Monitor,
delay(1000); // every second
}
Download Wire Library: Here

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