/*
   Arduino code for Individual control over each pin
   Support for 40+ 74HC595 8 bit shift registers
   http://bildr.org/2011/02/74hc595/
*/

#define dataPin  8  // Pin connected to DS of 74HC595
#define latchPin 9  // Pin connected to STCP of 74HC595
#define clockPin 10 // Pin connected to SHCP of 74HC595

word leds = 0;         // Variable to hold the pattern of which LEDs are currently turned on or off

/*
   setup() - this function runs once when you turn your Arduino on
   We initialize the serial connection with the computer
*/
void setup()
{
  // Set all the pins of 74HC595 as OUTPUT
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
}

/*
   loop() - this function runs over and over again
*/
void loop()
{
  leds = 0;        // Initially turns all the LEDs off, by giving the variable 'leds' the value 0
  updateShiftRegister();
  delay(200);
  for (int i = 0; i < 16; i++)        // Turn all the LEDs ON one by one.
  {
    bitSet(leds, i);                // Set the bit that controls that LED in the variable 'leds'
    updateShiftRegister();
    delay(300);
  }
}


/*
   updateShiftRegister() - This function sets the latchPin to low, then calls the Arduino function 'shiftOut' to shift out contents of variable 'leds' in the shift register before putting the 'latchPin' high again.
*/
void updateShiftRegister()
{
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, leds >> 8);
  shiftOut(dataPin, clockPin, MSBFIRST, leds >> 0);

  digitalWrite(latchPin, HIGH);
}