// Define the Arduino pins connected to the 74HC595
const int dataPin = 11;   // DS (SER) - Serial Data Input
const int clockPin = 12;  // SHCP (SRCLK) - Shift Register Clock
const int latchPin = 9;   // STCP (RCLK) - Latch Pin

// We have 4 shift registers = 32 bits
const int numRegisters = 4;
byte registerState[numRegisters]; // Array to hold the state of each register

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

  // Initialize all outputs to 0 (LOW)
  clearRegisters();
  writeRegisters();
}

// Sets all register bits to LOW
void clearRegisters() {
  for (int i = 0; i < numRegisters; i++) {
    registerState[i] = 0;
  }
}

// Writes the states from the registerState array to the shift registers
void writeRegisters() {
  // Pull the latch pin LOW to start the update
  digitalWrite(latchPin, LOW);

  // Shift out the data, starting from the LAST register.
  for (int i = numRegisters - 1; i >= 0; i--) {
    shiftOut(dataPin, clockPin, MSBFIRST, registerState[i]);
  }

  // Pull the latch pin HIGH to update the outputs all at once
  digitalWrite(latchPin, HIGH);
}

void loop() {
  // Forward scan: 0 to 31
  for (int i = 0; i < 32; i++) {
    
    clearRegisters();
    // Set only the current LED
    int reg = i / 8;
    int bit = i % 8;
    registerState[reg] = (1 << bit);
    
    writeRegisters();
    delay(200); // Longer delay to see clearly
  }

  // Backward scan: 31 to 0
  for (int i = 31; i >= 0; i--) {
    
    clearRegisters();
    // Set only the current LED
    int reg = i / 8;
    int bit = i % 8;
    registerState[reg] = (1 << bit);
    
    writeRegisters();
    delay(200); // Longer delay to see clearly
  }
}