Simple Labs' Quick Start Kit for Arduino - DS1307 Real Time Clock IC Interfacing- How To?

DS1307 - Real Time Clock IC

The DS1307 lets you explore I2C communication on the arduino.

I2C Communication

I2C is short form for 'Inter Integrated Circuit' I2C Communication is Communication Bus standard developed by Phillips for standardising Communication between Integrated Circuits. For Eg. In a circuit, there could be a number of ICs each offering specific functionality[RTC, Temperature Sensor, EEPROM, etc] and they can all communicate on a single I2C Bus and provide combined functionalities. Each device on the I2C Bus would have a unique address by which it can be addressed.

Here's an Interesting Introduction from NXP

I2C on Arduino

The I2C Bus uses 2 lines for Communication - SDA(Serial Data) & SCL (Serial Clock). On the InduinoX / Arduino, these are available on  SDA (Analog Input 4) & SCL (Analog Input 5). The I2C bus can be accessed using the 'Wire' Library of Arduino. First, lets try out a Library

Wiring up the DS1307

DS1307 Pin Mappings. SDA [Serial Data] / SCL [Serial Clock] correspond to lines for I2C Communication. We can ignore Vbat & SQW / OUT Pins.

Components - DS1307, Crystal for DS1307, 2 x 10K Resistors

Place the DS1307 IC as shown

Connect a Wire from the 4th pin of DS1307 (GND) to the '-'ve terminal

Connect a Wire from the 8th pin of DS1307 (+5V) to the '+'ve terminal

Place the Cyrstal as shown between the 1st and 2nd pin of the DS1307 IC- There is no polarity ('+' / '-' ve) for the crystal. So you can place it anyway

Place one resistor between the SDA Pin and the '+'ve terminal and one resistor between the SCL Pin and the '+'ve terminal

Connect a Wire between the SDA pin (pin5 of DS1307) and the SDA pin of the Arduino (Analog IN 4)

Connect a Wire between the SCL pin (pin6 of DS1307) and the SCL pin of the Arduino (Analog IN 5)

Final Setup with output from the following program

Try following Sample Program [LCD_RTC.ino]

/*
This program uses the Wire Library (for i2c communication)
This program sets the initial time for the RTC and keeps updating the time on an LCD everysecond.
*/


#include <Wire.h>
#define rtc 0x68 // The pre-defined address for DS1307

int ss,mm,hh,d,DD,MM,YY,mode;
boolean time_format,meridiem;

int prev;
#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(2,4,8,9,10,11);

void setup()
{
  Wire.begin();
  lcd.begin(16, 2);
  set_time();
}

void loop()
{
  get_time();
  if(ss!=prev)                // lcd Print when the seconds change
  {
    lcd.setCursor(0,0);
    lcd.print("Date:");
    lcd.print(DD);
    lcd.print("/");
    lcd.print(MM);
    lcd.print("/");
    lcd.print(YY);
    lcd.setCursor(0,1);
    lcd.print("Time:");
    lcd.print(hh);
    lcd.print(":");
    lcd.print(mm);
    lcd.print(":");
    lcd.print(ss);
    prev=ss;
  }
}

void get_time()
{
  Wire.beginTransmission(rtc); // start communication over i2c with DS1307
  Wire.write((byte)0); // Write the value of the register to point to
  Wire.endTransmission(); // End communication over i2c with DS1307

  Wire.requestFrom(rtc,7); // This will request 7 bytes of data 

                           //starting from the '0' the register
  ss=bcd_to_dec(Wire.read());
  mm=bcd_to_dec(Wire.read());
  hh=Wire.read();
  time_format=hh&(1<<6);   
  meridiem=hh&(1<<5);          // calculate am or pm
  hh=bcd_to_dec(hh&0x1F);
  d=bcd_to_dec(Wire.read());
  DD=bcd_to_dec(Wire.read());
  MM=bcd_to_dec(Wire.read());
  YY=bcd_to_dec(Wire.read());
  Wire.endTransmission();
}

void set_time()
{
  time_format=0;      // 0=24 hour mode, 1=12 hour mode 
  meridiem=1;         // 0=am, 1=pm    will not be taken into consideration if time format is 24 hour mode
  mode=(time_format<<6)+((time_format&&meridiem)<<5);  //calculate the bits to be added for 12 hour mode 

  Wire.beginTransmission(rtc);
  Wire.write((byte)0);
  Wire.write(dec_to_bcd(50));     // seconds
  Wire.write(dec_to_bcd(59));     // minutes
  Wire.write(mode+dec_to_bcd(11));// hours
  Wire.write(dec_to_bcd(3));     // day of the week, startin monday
  Wire.write(dec_to_bcd(21));    // date
  Wire.write(dec_to_bcd(12));    // month
  Wire.write(dec_to_bcd(11));    // year
  Wire.endTransmission();
}

int dec_to_bcd(int dec)
{
  return dec/10*16 + (dec%10);
}

int bcd_to_dec(int bcd)
{
  return bcd/16*10 + (bcd%16);
}