More Pushbutton Action

Moving right along, Exercise 3 involves a button that stays on after you let go of the button. Sounds simple enough, but the exercise is a three-step trial and error process:

In trial one, if the button is pressed down, you change the state of the light from on to off or vice versa:

void loop(){
    val = digitalRead(BUTTON); //read input value and store it

    if (val == HIGH){ //if there is voltage coming in from the button
        state = 1 - state; //change the state, which later is used to
    }                      //turn the light on or off 

    //...etc...
}

But since instructions are executed so rapidly, if the button is held for more than a split second, the "state" of the light will change as many hundreds of a second as you held it. The next example attempts to fix this by making sure there has actually been a transition:

void loop(){
    val = digitalRead(BUTTON); //read input value and store it
    if ((val == HIGH) && (old_val == LOW){ //check for transition
        state = 1 - state;
    }                     
    
    old_val = val; //now remember whether the button was pressed
    //...etc...
}


This works to some extent, but there is still a problem: when you press a button, the spring within it bounces and contact is made and broken a few (short) times in a fraction of a second. The final revision of Example 3 includes "simple debouncing" by including a delay of between 10 and 50 ms (I used 25) after the state change. The result is a working pushbutton light.

Push button (and release), receive light!

Example 3 complete!