How to Create Functions in Arduino

In this Arduino tutorial, I’ll show you how to create simple functions to wrap code in, so you can clean up your loop() function and eventually make functions that return values and make your program run better.

First, we’ll combine the default Servo knob example and the Blink without Delay example into one sketch. Then, we’ll look at the loop() function and see if there’s anything that we can separate from the loop and replace with a function call.

We have two main parts of the loop() function: the servo if conditional statement that is running the servo in the potentiometer, and the if statement that is blinking the LED from the Blink without Delay LED sketch. We’ll go ahead and remove the servo code and put it in a function, and replace it with a function call in the loop.

First, we’ll leave the currentMillis() function call at the top of the loop, because we want that to always be called. Then, we’ll highlight lines 49 to 55 and press Ctrl+X or Command+X to cut the code.

Next, we’ll type the function name in the loop() function, so we don’t forget to add it back later. We can call it checkServoKnob(). Then, we’ll put two parentheses and a semicolon.

Now, if we try to compile the code, it will give us an error because the checkServoKnob() function doesn’t exist yet. So, we’ll go all the way down to the bottom of the loop() function and create the function.

To create a function, we start with the keyword void. Then, we type the name of the function, which is checkServoKnob(). After the name, we put two parentheses, even though we’re not passing any parameters to the function yet. Finally, we put curly braces to open the function body.

Now, we can paste the code that we cut earlier into the function body. Once we’ve done that, we can compile the code and it should work.

Now, our loop() function is much shorter and easier to read. We can also see exactly what the checkServoKnob() function is doing, because we added a comment.

We can use the same process to create another function called blinkWithoutDelay(). This function will blink the onboard LED every second.

Once we’ve created both functions, our loop() function is very short and easy to read. This is especially helpful when we start making state machines to control our sketches.

I hope this tutorial has shown you how to create simple functions in Arduino. By wrapping code in functions, you can make your programs more organized and easier to read.