const int ledPin = 23;  // Pin connected to the LED
unsigned long previousMillis = 0;  // To store the last time we toggled the LED
const long interval = 500;  // Interval for the square wave (500 ms, 1 Hz frequency)

void setup() {
  pinMode(ledPin, OUTPUT);  // Set the LED pin as an output
}

void loop() {
  unsigned long currentMillis = millis();  // Get the current time in milliseconds
  
  // Check if it's time to toggle the LED
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;  // Save the last time we toggled the LED
    digitalWrite(ledPin, !digitalRead(ledPin));  // Toggle the LED state
  }
}