Arduino LCD Clock

Using the Wire library to read a DS1307 RTC chip (I used this one from Seeed Studio and bits of the example code ) and the LCD3wire library to implement, what is almost the "hello world" of arduino projects, a digital clock. The LCD3wire example uses a 4094 shift register, my parts box only had a 74HC595 so the connections are a little different:

74HC595	LCD	Arduino	power
1	4
2	5
3	6
4	14
5	13
6	12
7	11
8			gnd
9
10			+ve
11		4 (clk)
12		2 (strobe)
13			gnd
14		8 (data)
15
16			+ve
	1		gnd
	2		+ve
	3		2.2K to gnd

//the "sketch"

// Example use of LCD3Wire and Wire library
// to read time from RTC and display on LCD

#include <LCD3Wire.h>
#include "Wire.h"
// Arduino pins
#define LCD_LINES 2  // number of lines in your display
#define DOUT_PIN  8  // Dout pin
#define CLK_PIN   4  // Clock pin
#define STR_PIN   2  // Strobe pin

#define DS1307_I2C_ADDRESS 0x68

long previousMillis = 0;        // will store last time time was updated
byte second, minute, hour, dayOfWeek, dayOfMonth, month, year;
long interval = 200;

//create object to control an LCD.  
LCD3Wire lcd = LCD3Wire(LCD_LINES, DOUT_PIN, STR_PIN, CLK_PIN);
// 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) );
}

// Gets the date and time from the ds1307 and prints result
void getDateDs1307()
{
// Reset the register pointer
Wire.beginTransmission(DS1307_I2C_ADDRESS);
Wire.send(0x00);
Wire.endTransmission();

Wire.requestFrom(DS1307_I2C_ADDRESS, 7);

// A few of these need masks because certain bits are control bits
second     = bcdToDec(Wire.receive() & 0x7f);
minute     = bcdToDec(Wire.receive());
hour       = bcdToDec(Wire.receive() & 0x3f);  // Need to change this if 12 hour am/pm
dayOfWeek  = bcdToDec(Wire.receive());
dayOfMonth = bcdToDec(Wire.receive());
month      = bcdToDec(Wire.receive());
year       = bcdToDec(Wire.receive());

}

void printTime()
{
lcd.cursorTo(1, 4);  //line=1, x=4.
lcd.print( char( hour/10 + 0x30) );
lcd.print( char( hour%10 + 0x30) );
lcd.print(':');
lcd.print( char(minute/10 + 0x30));
lcd.print( char(minute%10 + 0x30));
lcd.print(':');
lcd.print(char (second/10+0x30));
lcd.print(char (second%10+0x30));

lcd.cursorTo(2, 3);  //line=2, x=3.
lcd.print(char(dayOfMonth/10+0x30));
lcd.print(char(dayOfMonth%10+0x30));
lcd.print('/');
lcd.print(char(month/10+0x30));
lcd.print(char(month%10+0x30));
lcd.printIn("/20");
lcd.print(char(year/10+0x30));
lcd.print(char(year%10+0x30));
}

void setup() {
Wire.begin();
getDateDs1307() ;
lcd.init();
lcd.clear();

}

void loop() {

unsigned long currentMillis = millis();

if(currentMillis - previousMillis > interval) {
 // save the last time you printed and updated
 previousMillis = currentMillis;
 printTime();
 //read RTC
 getDateDs1307() ;
}
}
//end sketch

The result as expected (just a clock :-) ):