// Code based on shiftOutCode, Hello World                                
// By  : Carlyn Maw,Tom Igoe, David A. Mellis 
// Updated by Daniel Hirschmann to offer a way to control
// cascading shift registers

//This example is intended to create a night rider effect - speed based on a potentiometer

int latchPin = 8;    //Pin connected to latch pin (ST_CP) of 74HC595
int clockPin = 12;   //Pin connected to clock pin (SH_CP) of 74HC595
int dataPin = 11;    //Pin connected to Data in (DS) of 74HC595

int totalLeds = 8;
int ledPos = 0;
int ledDirection = 1;
int delayPeriod = 10;

int potVal = 50;

void setup() {
  //set pins to output because they are addressed in the main loop
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
  pinMode(clockPin, OUTPUT);
  
  Serial.begin(9600);
  Serial.println("STARTED");
}

void loop() {
//  potVal = analogRead(0)/4;    //get the pot reading for the speed.
  
  //Handle the night rider effect
  ledPos+=ledDirection; 
  // same as: ledPos = ledPos + ledDirection
 
  
  if (ledPos >= totalLeds - 1) {
   ledDirection = - 1;
  } else if (ledPos <= 0) {
    ledDirection = 1;
  }
  Serial.println(ledPos);
  shiftToRegister(ledPos,HIGH);  
  delay(potVal);
}

// Function to send bits to the shift register:
void shiftToRegister(int whichPin, int whichState) {
  digitalWrite(latchPin, LOW);  //Prepares the SR to receive data
  byte shiftRegisterByte = encodeBits(whichPin, whichState);
  shiftOut(dataPin, clockPin, MSBFIRST, shiftRegisterByte);
  digitalWrite(latchPin, HIGH); //Tell the SR's to show us what we've just sent it!

}

//Function to encode a position value into a resulting position on the shift registers
byte encodeBits(int pos, int val)
{
  byte result = 1 << pos;
  return result;
}