int dataPin = 2;
int clockPin = 4;
int latchPin = 6;
int ledExp[] = {7,6,5,4,3,2,1,0};
byte leds;
int chaserRightToLeftTurnOnPattern[] = {1, 3, 7, 15, 31, 63, 127, 255}; 
int chaserLeftToRightTurnOffPattern[] = {255, 127, 63, 31, 15, 7, 3, 1, 0};
uint32_t oldOptionSwitch = 0;
const int pulseWidth = 10;

void setup() {
  Serial.begin(115200);
  pinMode(dataPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(latchPin, HIGH);
}

void loop() {
  // Give a pulse to the parallel load latch of all 74HC165
  digitalWrite( latchPin, LOW);    
  delayMicroseconds( pulseWidth);
  digitalWrite( latchPin, HIGH);

  // Reading one 74HC165 at a time and combining them into a 32 bit variable
  // The last 74HC165 is at the bottom, but the switches start numbering
  // at the top. So the first byte has to be shifted into the highest place.
  uint32_t optionSwitch = 0;
  for( int i=24; i>=0; i-=8) {
    optionSwitch |= ((uint32_t) ReadOne165()) << i;
  }

  for( int i = 0; i<32; i++)
  {
    if( bitRead(optionSwitch, i) != bitRead( oldOptionSwitch,i))
    {
      Serial.print("Switch ");
      if(i < 10)
        Serial.print(" ");
      Serial.print(i);
      Serial.print(" is now ");
      Serial.println(bitRead(optionSwitch, i) == 0 ? "down ↓" : "up ↑");
    }
  }
  
  oldOptionSwitch = optionSwitch;
  delay(25);
}

void updateShift(byte leds, int ms){
  digitalWrite(latchPin, HIGH);
  shiftOut(dataPin, clockPin, LSBFIRST, leds);
  digitalWrite(latchPin, LOW);
  delay(ms);
}

void chaserRightToLeftTurnOn(){
  for(int i=0; i<8; i++){
    int val = chaserRightToLeftTurnOnPattern[i];
    updateShift(val, 500);
    Serial.println(val);
  };
}

void chaserLeftToRightTurnOff(){
  for(int i=0; i<9; i++){
    int val = chaserLeftToRightTurnOffPattern[i];
    updateShift(val, 500);
    Serial.println(val);
  };
};

byte ReadOne165()
{
  byte ret = 0x00;

  // The first one that is read is the highest bit (input D7 of the 74HC165).
  for( int i=7; i>=0; i--)
  {
    if(digitalRead(dataPin) == HIGH)
      bitSet(ret, i);

    digitalWrite(clockPin, HIGH);
    delayMicroseconds(pulseWidth);
    digitalWrite(clockPin, LOW);
  }

  return(ret);
}