arduino: photocell controlled led strobe

strobe-led.ino

// CONST's
int DS_pin = 8;
int STCP_pin = 9;
int SHCP_pin = 10;
int NUM_LED = 8;

// 8 LED Registers
boolean registers[8];
// Direction of LED travel
boolean goingUp = true;
// Currently lit LED
int currentLED = 0;


int photocellReading;
int photocellPin = 0;
int photoDelay = 50;

void setup()
{  
  // Configure output pins
  pinMode(DS_pin,OUTPUT);
  pinMode(STCP_pin,OUTPUT);
  pinMode(SHCP_pin,OUTPUT);

  writereg();
}

// Writes the LED registers to the Shift-register
void writereg()
{
  // Prepare to write new data
  digitalWrite(STCP_pin, LOW);
  for (int i = 7; i>=0; i--)
  {
    // Prepare for bit
    digitalWrite(SHCP_pin, LOW);
    // Write bit
    digitalWrite(DS_pin, registers[i] );
    // Done writing bit
    digitalWrite(SHCP_pin, HIGH);
  }
  // Done writing new data
  digitalWrite(STCP_pin, HIGH);
}

void loop()
{
  for(int i = 0; i < NUM_LED; i++){
    // Turn on an LED
    // Turn off the other LEDs
    registers[i] = i == currentLED;
  }

  writereg();
  
  if(goingUp){
    currentLED++;
    if(currentLED == NUM_LED - 1){
      goingUp = false;
    }
  } else {
    currentLED--;
    if(currentLED == 0){
      goingUp = true;
    }
  }

  photocellReading = analogRead(photocellPin);
  photocellReading = 1023 - photocellReading;
  //now we have to map 0-1023 to 0-255 since thats the range analogWrite uses
  photoDelay = map(photocellReading, 0, 1023, 0, 255);

  delay(photoDelay);
}

https://www.youtube.com/watch?v=bqfPZXEuyuc

http://staticjolt.com/shift-registers-arduino-tutorial/
http://www.dannyg.com/examples/res2/resistor.htm
http://www.instructables.com/id/Identifying-LED-pins/