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parpadeo sin retardo (delay)

En ocasiones puede ser necesario hacer parpadear un LED (o alguna otra cuestión visible) al mismo tiempo que se hacen otras cosas (como controlar la pulsación de un botón). Esto implica no poder utilizar delay(), o todo se pararía mientras el LED parpadea. Aquí tienes un código que muestra cómo hacer parpadear el LED sin usar delay(). Controla la última vez que se encendió o apagó el LED. Entonces, cada vez que pasa por el bucle() compara si ha transcurrido un intervalo suficiente de tiempo y si es así, apaga el LED si estaba encendido o viceversa.



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/* Blink without Delay
 Turns on and off a light emitting diode(LED) connected to a digital  
 pin, without using the delay() function.  This means that other code
 can run at the same time without being interrupted by the LED code.
 The circuit:
 * LED attached from pin 13 to ground.
 * Note: on most Arduinos, there is already an LED on the board
 that's attached to pin 13, so no hardware is needed for this example.
 created 2005
 by David A. Mellis
 modified 8 Feb 2010
 by Paul Stoffregen
 modified 11 Nov 2013
 by Scott Fitzgerald
 This example code is in the public domain.

// constants won't change. Used here to set a pin number :
const int ledPin =  13;      // the number of the LED pin

// Variables will change :
int ledState = LOW;             // ledState used to set the LED

// Generally, you shuould use "unsigned long" for variables that hold time
// The value will quickly become too large for an int to store
unsigned long previousMillis = 0;        // will store last time LED was updated

// constants won't change :
const long interval = 1000;           // interval at which to blink (milliseconds)

void setup() {
  // set the digital pin as output:
  pinMode(ledPin, OUTPUT);      

void loop()
  // here is where you'd put code that needs to be running all the time.

  // check to see if it's time to blink the LED; that is, if the
  // difference between the current time and last time you blinked
  // the LED is bigger than the interval at which you want to
  // blink the LED.
  unsigned long currentMillis = millis();
  if(currentMillis - previousMillis >= interval) {
    // save the last time you blinked the LED
    previousMillis = currentMillis;  

    // if the LED is off turn it on and vice-versa:
    if (ledState == LOW)
      ledState = HIGH;
      ledState = LOW;

    // set the LED with the ledState of the variable:
    digitalWrite(ledPin, ledState);