const int ledPin = 13;                
bool ledState = LOW;                   

unsigned long previousMillis = 0;     
const unsigned long interval = 1000;  

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);                 
}

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

  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;       

    ledState = !ledState;
    digitalWrite(ledPin, ledState);

    unsigned long seconds = currentMillis / 1000;
    Serial.print("Czas dzialania: ");
    Serial.print(seconds);
    Serial.println(" s");
  }

}