const int pinLed=12;
void setup() {
  pinMode(pinLed,OUTPUT);
}

int timeDelay=1000;
void loop() {
  if(timeDelay<=100) {
    delay(3000);
    timeDelay=1000;
  } else 
    timeDelay = timeDelay -100;
  digitalWrite(pinLed, HIGH);
  delay(timeDelay);
  digitalWrite(pinLed, LOW);
  delay(timeDelay);
}