Binary Clock(update minute and hour variable with current time before writing to device).

gistfile1.ino

/*
  Layout of pins:
     3     10
     4  7  11
  1  5  8  12
  2  6  9  13
*/
#include <EEPROM.h>

int startupDone = 0;
int i = 0;
int sinceStart = 0;
int second = 0;
int minute = 0;
int hour = 0;
int munit = 0;
int hunit = 0;

void setup() {  
  for (i = 0; i < 13; i++) {    
    pinMode(i+1, OUTPUT);
  }
}

void loop() {
  static unsigned long lastTick = 0;
  
  // Run the start up sequence.
  if (!startupDone) {
    startupDone = 1;
    
    // Read the saved time.
    second = EEPROM.read(1);
    if (second == 255) {
      second = 0;
    }
    minute = EEPROM.read(2);
    if (minute == 255) {
      minute = 0;
    }
    hour = EEPROM.read(3);
    if (hour == 255) {
      hour   = 0;
    }
    
    for (i = 0; i < 13; i++) {
      digitalWrite(i+1, HIGH);
      delay(80);
      digitalWrite(i+1, LOW);
    }
    
    for (i = 13; i >= 0; i--) {
      digitalWrite(i-1, HIGH);
      delay(80);
      digitalWrite(i-1, LOW);
    }
  }
  
  // Update second every 1000 milliseconds.
  sinceStart = millis();
  if (sinceStart - lastTick >= 1000) {
    lastTick = sinceStart;
    second++;
  } else {
    // Return here instead of continuing, this way we save EEPROM writes.
    return;
  }
  
  // Update minute every 60 seconds.
  if (second >= 60) {
    minute++;
    second = 0;
  }
  
  // Update hour every 60 minutes.
  if (minute >= 60) {
    hour++;
    minute = 0;
  }
  
  // Only 24 hours a day.
  if (hour >= 24) {
    hour = 0;
    minute = 0;
  }
  
  // Write times to EEPROM.
  EEPROM.write(1, second);
  EEPROM.write(2, minute);
  EEPROM.write(3, hour);
  munit = minute%10;
  hunit = hour%10;
  
  // Minute units.
  if (munit == 1 || munit == 3 || munit == 5 || munit == 7 || munit == 9) {
    digitalWrite(13, HIGH);
  } else {
    digitalWrite(13, LOW);
  }
  
  if (munit == 2 || munit == 3 || munit == 6 || munit == 7) {
    digitalWrite(12, HIGH);
  } else {
    digitalWrite(12, LOW);
  }
  if (munit == 4 || munit == 5 || munit == 6 || munit == 7) {
    digitalWrite(11, HIGH);
  } else {
    digitalWrite(11, LOW);
  }
  if (munit == 8 || munit == 9) {
    digitalWrite(10, HIGH);
  } else {
    digitalWrite(10, LOW);
  }

  // Minutes.
  if ((minute >= 10 && minute < 20) || (minute >= 30 && minute < 40) || (minute >= 50 && minute < 60))  {
    digitalWrite(9, HIGH);
  } else {
    digitalWrite(9, LOW);
  }
  if (minute >= 20 && minute < 40)  {
    digitalWrite(8, HIGH);
  } else {
    digitalWrite(8, LOW);
  }
  if (minute >= 40 && minute < 60) {
    digitalWrite(7, HIGH);
  } else {
    digitalWrite(7, LOW);
  }

  // Hour units.
  if (hunit == 1 || hunit == 3 || hunit == 5 || hunit == 7 || hunit == 9) {
      digitalWrite(6, HIGH);
  } else {
      digitalWrite(6, LOW);
  }
  if (hunit == 2 || hunit == 3 || hunit == 6 || hunit == 7) {
    digitalWrite(5, HIGH);
  } else {
    digitalWrite(5, LOW);
  }
  if (hunit == 4 || hunit == 5 || hunit == 6 || hunit == 7) {
    digitalWrite(4, HIGH);
  } else {
    digitalWrite(4, LOW);
  }
  if (hunit == 8 || hunit == 9) {
    digitalWrite(3, HIGH);
  } else {
    digitalWrite(3, LOW);
  }

  // Hour.
  if (hour >= 10 && hour < 20)  {
    digitalWrite(2, HIGH);
  } else {
    digitalWrite(2, LOW);
  }
  if (hour >= 20 && hour < 24)  {
    digitalWrite(1, HIGH);
  } else {
    digitalWrite(1, LOW);
  }
}