// Pin definitions for 74HC595
const int dataPin = 11;   // DS
const int latchPin = 8;   // ST_CP
const int clockPin = 12;  // SH_CP

void setup() {
  // Set pins as output
  pinMode(dataPin, OUTPUT);
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
}

void loop() {
  // Loop through each LED from left to right
  for (int i = 0; i < 8; i++) {
    byte ledState = 1 << i; // Shift 1 bit to the left
    updateShiftRegister(ledState);
    delay(200);
  }

  // Loop through each LED from right to left
  for (int i = 6; i >= 0; i--) {
    byte ledState = 1 << i;
    updateShiftRegister(ledState);
    delay(200);
  }
}

void updateShiftRegister(byte data) {
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, data); // Send the byte
  digitalWrite(latchPin, HIGH);                // Latch it to output
}