The Trouble with Delay

The problem with using delay() in your pinball machine is that the microcontroller will go to sleep, and will miss everything that happens in the pinball machine until it wakes up again. This is bad, because a well-programmed Robot needs to stay awake and alert at all times.

The way we fix the problem is to stop using delay(), and instead use a stopwatch. Upload the stopwatch program.

Now, you should be able to control the LED on pin 12 using the button, as well as cause the LED on pin 11 to blink without any conflicts.

How did we do that? Well, lets take a look at the program.

The first thing to notice is that the function delay() is not being used anywhere in the program. Instead, we are using a stopwatch.

At the top (before setup()), there is a new line:

Pb_stopwatch mywatch;

This is creating a stopwatch called mywatch (you can name it something else if you like). Inside setup(), there is this line:

mywatch.start();

This tells the stopwatch named mywatch to start counting from zero. Later in the program, you will see:

mywatch.time()

which asks the stopwatch mywatch to tell you how long it has been (in milliseconds) since the last time it started counting.

Inside loop(), there is a new structure you haven’t seen before. There’s a new kind of variable called ledbstate. This new kind of variable is called a state variable. Unlike the variables we’ve used before, which are set at the beginning of the program and stay the same value while the program runs, a state variable can change throughout the program. State variables are usually either 0 or 1, which in the case of an LED can correspond to off and on.

This line:

ledbstate = !ledbstate;

changes ledbstate to 0 (if it was 1), or to 1 (if it was 0).

The if structure looks like this:

if ( mywatch.time() > ontimeb ) { ledbstate = !ledbstate; digitalWrite(ledb, ledbstate); mywatch.start(); }

The first line, if ( mywatch.time() > ontimeb ), checks to see if sufficient time (an amount given by the variable ontimeb) has passed since the last time the stopwatch (mywatch) was started. If the condition is met, then the line ledbstate =!ledbstate changes the LED’s state to the opposite. Note that you have to start the stopwatch inside the if-structure again, so that mywatch will have the correct time to report the next time around the loop.

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