// Declare ESP32 GPIO pins
const int latchPin = 18; // Pin connected to ST_CP of all 74HC595s
const int clockPin = 19; // Pin connected to SH_CP of all 74HC595s
const int dataPin = 23;  // Pin connected to DS of the first 74HC595

// Inverted seven-segment display codes for digits 0-9 (common anode)
const byte digitCodes[10] = {
  0b11000000, // 0
  0b11111001, // 1
  0b10100100, // 2
  0b10110000, // 3
  0b10011001, // 4
  0b10010010, // 5
  0b10000010, // 6
  0b11111000, // 7
  0b10000000, // 8
  0b10010000  // 9
};

int counter = 0; // Variable to hold the current count
unsigned long lastUpdate = 0; // Variable to track the last time the display was updated
const unsigned long interval = 1000; // Interval in milliseconds for the count update

void setup() {
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);

  // Initialize display with 0
  displayNumber(counter);
}

void loop() {
  unsigned long currentMillis = millis();

  // Check if it's time to update the display
  if (currentMillis - lastUpdate >= interval) {
    lastUpdate = currentMillis; // Save the last update time

    counter++; // Increment the counter
    if (counter > 999) { // Reset the counter after 999
      counter = 0;
    }

    displayNumber(counter); // Update the display with the new count
  }
}

void displayNumber(int number) {
  int hundreds = number / 100; // Get the hundreds digit
  int tens = (number / 10) % 10; // Get the tens digit
  int units = number % 10; // Get the units digit

  digitalWrite(latchPin, LOW);
  
  // Shift out data for the hundreds digit (third display)
  shiftOut(dataPin, clockPin, MSBFIRST, digitCodes[hundreds]);
  
  // Shift out data for the tens digit (second display)
  shiftOut(dataPin, clockPin, MSBFIRST, digitCodes[tens]);
  
  // Shift out data for the units digit (first display)
  shiftOut(dataPin, clockPin, MSBFIRST, digitCodes[units]);

  digitalWrite(latchPin, HIGH); // Latch the data to the displays
}