Blink Without Blocking Arduino Sketch

The “Blink” sketch is fine if you only ever want your Arduino just to blink a light. But odds are good you want it to do some other things as well, like read a button, or run some other outputs.

The trick is to get rid of any long delay() statement, because during delay() the Arduino generally can’t read inputs or change outputs. (There’s an exception: a special thing called an interrupt can run even during a delay, but it’s a bit tricky to implement and not recommended for a beginner.)

Full Source Code

The full code is all in one file BlinkWithoutBlocking.ino.

/*
 * Blink Without Blocking
 *
 * Demonstrates how to use an event loop timer to avoid unnecessary delays in code.
 * This sort of form allows you to juggle multiple inputs and outputs more easily.
 *
 * Robert Zacharias, 2/2017
 * released to the public domain by the author
 */

// "global" variables in this section can be used by any function in the whole sketch
int wait = 250; // this variable, of type integer, is the number of milliseconds we'll wait between blinks
long timer = 0; // this variable, of type "long," will help keep track of passing time
bool light = LOW; // this varialbe, of type boolean, will keep track of the current LED state

void setup() {
  pinMode(LED_BUILTIN, OUTPUT); // LED_BUILTIN is a handy shortcut for the pin connected to the on-board LED
}

void loop(){
  
  blink(); // just a shortcut to go to the blink() function
  
  digitalWrite(LED_BUILTIN, light); // tells the LED to either go on or off, depending on the value of "light"
  
}

// here's where we define what the blink() function does
void blink(){
  
  // if it has been more than "wait" amount of time since the light changed
  if ( (millis() - timer) > wait ) { // (millis() is the number of milliseconds since the Arduino powered up)
    light = !light; // this will "toggle" the value of "light" to its opposite
    timer = millis(); // reset the timer
  }

  // if it has *not* been long enough, the control will just go past the if statement and exit the blink() function
}