Shift register using 74HC595

I used two 74HC595 chips hooked to the Serial Peripheral Interface Bus of an Arduino.   This bus will runs at 4MHz so the updates to the LEDs were very snappy.

A single chip can only control 8 LED's.  In order to control another 8 chips you have to connect a second chip to the first chip in series.   

/*
 Shift Register Example
 for 74HC595 shift register

 This sketch turns turns your arduino into a cylon.

 Hardware:
 * 74HC595 shift register attached to hardware SPI
 Arduino               74HC959
  pin# name            pin#  name
  10 SS        --->    12 RCK
  11 MOSI      --->    14 SI
  13 SCK       --->    11 SCK
 
 * LEDs attached to each of the outputs of the shift register

 Created 02 Oct 2014
 by James M. Rogers

 Based on work of others found in following locations:
 http://forum.arduino.cc/index.php/topic,149470.0.html
 http://arduino.cc/en/tutorial/ShiftOut
 http://arduino.cc/en/Tutorial/SPIDigitalPot

 */

#include <SPI.h>

int pinSS=10; //latch

int d=40;

void setup() {
  SPI.begin(); 
}

//#define d 40
void loop() {

    int i;
    for (i=0 ; i<16 ; i++) {
      registerWrite(i, HIGH);
       delay (d);
    }
    for (i=15 ; i>=0 ; i--) {
      registerWrite(i, HIGH);
       delay (d);
    }

  if (d>10)
    d-=5;
  else 
    d--;
    
    if (d==0)
      d=40;
}

// This method sends bits to the shift register:
void registerWrite(int whichPin, int whichState) {
// the bits you want to send
  byte lowbitsToSend = 0;
  byte highbitsToSend = 0;

  if (whichPin <8) {
    // turn on the next highest bit in bitsToSend:
    bitWrite(lowbitsToSend, whichPin, whichState);
  } else {
    bitWrite(highbitsToSend, whichPin-8, whichState);
  }
  
  SPI.transfer(highbitsToSend);
  SPI.transfer(lowbitsToSend);

  digitalWrite(pinSS,LOW);
  delayMicroseconds(1);
  digitalWrite(pinSS,HIGH);
}