#define CD_TIME 1000
#define ON_TIME 100

unsigned long long lastUpdate = 0;
int led = 13;
boolean isCooldown = false;

void setup()
{
  pinMode(led, OUTPUT);
}

void loop()
{
  if (isCooldown)
  {
    if (millis() - lastUpdate > CD_TIME)
    {
      digitalWrite(led, HIGH);
      lastUpdate = millis();
      isCooldown = false;
    }
  }
  else
  {
    if (millis() - lastUpdate > ON_TIME)
    {
      digitalWrite(led, LOW);
      lastUpdate = millis();
      isCooldown = true;
    }
  }
}