const int ledPin = 12;
int ledState= LOW;
unsigned long previousMillis = 0;
const long interval = 1000;

void setup() {
  pinMode(ledPin, OUTPUT);
}
void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval )  {
    previousMillis = currentMillis;
    if (ledState == LOW) {
      ledState = HIGH;
    } else {
      ledState = LOW;

    }
    digitalWrite(ledPin, ledState);
  }
}