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

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
}

void loop() {
  // pu t your main code here, to run repeatedly:
  unsigned long currentMillis = millis();

  if(currentMillis-previousMillis>=interval){
    previousMillis = currentMillis ;
    if(ledState == LOW){
      ledState = HIGH;
    
    }else{
      ledState = LOW;
    }
    Serial.print("Current :");
    Serial.println(currentMillis);
    Serial.print("Previous :");
    Serial.println(previousMillis);
    digitalWrite(ledPin,ledState);
  }
}