const int ledPin = 13;
int ledState = LOW; 
unsigned long previousMillis = 0;  
const long interval = 1000;  
void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  unsigned long currentMillis = millis();
   Serial.println(currentMillis);
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;
    }
    digitalWrite(ledPin, ledState);
  }
}