unsigned long tiempo;
unsigned long comparador=3000;
void setup() 
{
  pinMode(17, OUTPUT);
  pinMode(16, OUTPUT);
  pinMode(4, INPUT_PULLDOWN);
  pinMode(14, INPUT_PULLDOWN);
  digitalWrite(17, HIGH);
  digitalWrite(16, LOW);
  tiempo=millis();
}
void loop() 
{
  if (millis()-tiempo>comparador)
  {
    digitalWrite(17,!digitalRead(17));
    digitalWrite(16,!digitalRead(16));
    tiempo=millis();
  }
  if (digitalRead(4)==HIGH)
  {
    comparador=comparador+500;
    delay(100);
  }
  if (digitalRead(14)==HIGH)
  {
    comparador=comparador-500;
    delay(100);
  }
  delay(10);
}