int latchPin = 5; 
int clockPin = 6; 
int dataPin = 4; 
int outputEnablePin = 3;
byte leds = 0; 
void setup()
{
 // Set all the pins of 74HC595 as OUTPUT
 pinMode(latchPin, OUTPUT);
 pinMode(dataPin, OUTPUT);
 pinMode(clockPin, OUTPUT);
 pinMode(outputEnablePin, OUTPUT);
}
void loop()
{
 setBrightness(255);
 leds = 0; // Initially turns all the LEDs off, by giving the variable 'leds' the value 0
 updateShiftRegister();
 delay(500);
 for (int i = 0; i < 8; 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(500);
 }
 for (byte b = 255; b > 0; b--) // Gradually fade all the LEDs back to off
 {
setBrightness(b);
 delay(50);
 }
}
/*
 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, LSBFIRST, leds);
 digitalWrite(latchPin, HIGH);
}
/*
 setBrightness() - Generates PWM signal and writes it to OE pin.
 */
void setBrightness(byte brightness) // 0 to 255
{
 analogWrite(outputEnablePin, 255-brightness);
}