4dig7seg.c

// 4 digit 7 segment clock
// 2010 kennethfinnegan.blogspot.com
// http://kennethfinnegan.blogspot.com/2010/01/arduino-four-digit-clock.html

#include <Wire.h>

#define DS1307 B1101000
// LED Driver pins
#define LEDDATA  12
#define LEDCLOCK  11
#define LEDLATCH  10
// Anode pins for the 4 digits
int digits[] = {2,3,4,5};

// bitfield for the digits 0-9
// This was built based on how I happened to plug
// in the wires between the driver and display.
// You'll want to rebuild this for your pinout
byte segments[] = {
  B00111111,
  B00100100,
  B10001111,
  B10100111,
  B10110100,
  B10110011,
  B10111011,
  B00100110,
  B10111111,
  B10110110};

byte second=0, minute=0, hour=0;

void updatedisplay();
byte DECTOBCD(byte val);
byte BCDTODEC(byte val);

void setup() {
  Wire.begin();
  pinMode(digits[0], OUTPUT);
  pinMode(digits[1], OUTPUT);
  pinMode(digits[2], OUTPUT);
  pinMode(digits[3], OUTPUT);
  pinMode(LEDDATA, OUTPUT);
  pinMode(LEDCLOCK, OUTPUT);
  pinMode(LEDLATCH, OUTPUT);
  // I didn't bother using the latch
  // But you could to get better brightness
  digitalWrite(LEDLATCH, HIGH);
}

byte curdig = 0, prevdig = 0;

void loop() {
  // Display the next digit
  updatedisplay();
  
}

void updatedisplay() {

  // Update time from DS1307
  Wire.beginTransmission(DS1307);
  Wire.send(0x00);
  Wire.endTransmission();
  Wire.requestFrom(DS1307, 3);
  second = BCDTODEC(Wire.receive() & 0x7f);
  minute = BCDTODEC(Wire.receive());
  hour   = BCDTODEC(Wire.receive() & 0x3f);
  
  byte temphour = hour % 12;
  if (temphour == 0) {
    // Not zero based, not one based, but 12. What the F, world?
    temphour = 12;
  }
  
  byte digitvalue, bitfield;
  switch (curdig) {
    case 0: // low minute digit
      digitvalue = minute % 10;
      bitfield = segments[digitvalue];
      break;
    case 1: // high minute digit
      digitvalue = minute / 10;
      bitfield = segments[digitvalue];
      break;
    case 2: // low hour digit
      digitvalue = temphour % 10;
      bitfield = segments[digitvalue];
      // Blink the decimal to show the clock is running
      bitfield |= (second & 1) << 6;
      break;
    case 3: // high hour digit
      digitvalue = temphour / 10;
      // Blank on 0
      bitfield = digitvalue ? segments[digitvalue] : 0;
      break;
  }
  // Turn off the previous digit
  digitalWrite(digits[prevdig], LOW);
  // Setup the new digit
  shiftOut(LEDDATA, LEDCLOCK, MSBFIRST, bitfield);
  // Turn on the new digit
  digitalWrite(digits[curdig], HIGH);
  // Leave it on for the next cycle of time updates, etc
  prevdig = curdig;
  // Move on to the next digit for the next call
  curdig = (curdig+1) % 4;
}

byte DECTOBCD(byte val) {
  return ((val/10)<<4) + (val%10);
}
byte BCDTODEC(byte val) {
  return (val>>4) * 10 + (val & 0xf);
}