/*
Materials:

    Arduino board
    Two 74HC595 Shift Registers
    16 LEDs
    16 220-Ohm resistors
    Breadboard
    Jumper wires

Connection:

Connect the data pin (DS), latch pin (STCP), and clock pin (SHCP) of both shift registers in parallel to the Arduino (pins 8, 12, and 11 respectively).
Connect the serial output (Q7S) of the first shift register to the data input (DS) of the second shift register.
Connect each output pin of both shift registers to a different LED via a 220-Ohm resistor.

Purpose:

We're looping through each bit of two bytes. The first shiftOut() function call sends a byte with a single '1' bit to the first register. The second shiftOut() call sends a byte of all '0's to the second register (only on the first loop, when j == 0). This allows us to light up each LED in sequence from 1 to 16. Remember, this is a very simple example and there are many more ways to use daisy-chained shift registers!
*/

//Pin connected to ST_CP (12) of 74HC595
int latchPin = 8;
//Pin connected to SH_CP (11) of 74HC595
int clockPin = 12;
////Pin connected to DS (14) of 74HC595
int dataPin = 11;

void setup() {
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() {
  for (int j = 0; j < 2; j++) { // two bytes for two shift registers
    for (int i = 0; i < 8; i++) { // loop through 8 bits
      digitalWrite(latchPin, LOW);
      shiftOut(dataPin, clockPin, LSBFIRST, 1 << i); // shift out bit
      if (j == 0) shiftOut(dataPin, clockPin, LSBFIRST, 0); // fill second register with zeros
      digitalWrite(latchPin, HIGH); // update output
      delay(250);
    }
  }
}