Tag Archives: STEM

LESSON 32: Understanding Arduino Functions

So far we have written programs as a long string of code, pretty much all in the void loop. As we begin to need to develop more complicated code, putting all the programming in the void loop can become unmanageable. It is easy to lose track of what we are doing. For more complicated programs, we want to break the problem up into manageable chunks of code. This is called modular program. We develop small modules that do specific tasks, and then our void loop simply calls these modules. The modules are called “Functions” in arduino.

Lets consider an example. Lets say we want to write an arduino program that prompts the user for the number of grades he has. Then it averages the grades, prints the grades and then prints the average. The following program would do this job, with all the code in the void loop:

You can see that the void loop is getting pretty complicated, and it would be easy to begin to lose track of what is going on. If we think about what we are trying to do, lets try to break it down more logically. These are the logical tasks we need to do:

Input Grades

Average Grades

Print Grades and Average

I think that is the logical way to break the program down. Hence, we need three modules or functions, which we could define as follows:




We could call these three functions in the void loop. then down below the void loop we would need to define, or teach arduino what each of these functions do. In effect, the code in the example above is put down in three logical blocks, which we call functions. Notice that when we do that, the functions must be defined AFTER the void loop. That means it is done after the closing curly bracket for the void loop. Using functions, we can rewrite the program above as follows:

Notice now that the void loop is very simple to understand, since each function is logically named. Also, if we look down at the function definition, it is clear what each chunk of code does. In this example, we are using global variables, so each function, and the void loop are all working with the same set of variables. In future lessons we will look at the use of local variables, and then how that would affect the structure of our functions.

LESSON 31: Understanding Arduino Arrays

So fare we have used variable declarations like float, int, char and string. We have a variable declaration for any type of data we want to work with, but each of these allows storing a single piece of information.  Often times we want to store more than just one variable, we want to store lists. We can store lists of variables in an array. We can make arrays of all the variable types we already know how to use. For example, if we wanted to store a single grade, we could use the following variable declaration:

float grade;

But, if we wanted to store a list of grades, we could define grades to be an array with the following command:

float grades[15];

This command creates an array called grades, which has 15 slots, so up to 15 grades can be stored. To specify which slot you are working with in your program, you simply reference the slot you are working with inside the brackets. For example:


would set slot 3 in the grades array to the value 97.

Realize when you create an array in arduino, the first slot is slot zero, hence if you wanted to put a grade in the first slot you would use the command:


You can create arrays for all the arduino variable types you are familiar with. You can create int, float, char and string arrays. The video above gives simple to understand examples of how to use arduino arrays.

LESSON 29: The Dos and Don’ts of Arduino Software Interrupts

This is a follow on to lesson 28, to address some of the questions that come up. It is important to understand that all functions are not well suited for use with software interrupts. You must be mindful of timing. Key to being successful with Arduino Software Interrupts is the function called needs to be small and very fast. When the interrupt calls the function, you need to get in and out of that function as quick as you can. Hence, you should avoid doing printing in the function called by the interrupt. You should try and avoid working with serial data, because things can get lost if you are not careful. Also, you should know that you can not use a delay in the function.

For most beginner programmers, interrupts should just be used to call short functions, with minimal lines of code, that can be run quickly.

ARDUINO LESSON 28: Tutorial For Programming Software Interrupts

In this lesson we will show you how to take your arduino programs to the next level by learning to program software interrupts. The challenge with the Arduino platform is that you can only have one program or “thread” running at a time. Hence, something simple like blinking two LED’s at the same time at different rates can not be done because only one line of code is executed at a time. Much more powerful projects can be achieved if we learn how to get around this by programming interrupts. An interrupt can be thought of like an alarm clock. You set the alarm clock, and then when the alarm goes off, no matter where your program is in the execution code, it stops what it is doing, and then runs and executes the interrupt code. In order to use software interrupts, you must load a new library. The TimerOne interrupt library can be downloaded here:


Click on the TimerOne-r11.zip link, and it will download a zip folder to your computer. Find your Arduino Library folder (Video above explains how if you do not know how). In your Arduino Library folder create a new folder called TimerOne. Take the CONTENTS of the zip folder you just downloaded and put it in your TimerOne library folder. Remember that when you install a new library, you have to close and reopen the Arduino IDE for it to find the new library.

Now you will want to build a simple circuit to allow control of a yellow and red LED. The current limiting resistors in the circuit should be between 200 and 500 ohms. So, lets build the following circuit:

Make sure to connect the long legs of the LED to the control pins.

Now we are ready to create our first interrupts.  First matter of business is your program should load the interrupt library:

This should be at the top of your code, and will load the library.

To create an interrupt, you need to first now initialize the interrupt, specifying what time frame you want it to “interrupt” on,  and then what you want it to do when the interrupt alarm goes off. You would typically set these two things up in the Void Setup. Consider this sample code:

If you place this code in the void setup, it will do two things. The first is it will initialize an interrupt that will go off every .1 seconds. Understand the units for the Timer1.initialize command are in microseconds, so 100,000 microseconds would create an interrupt every .1 seconds. Now you have to tell arduino what to do when the interrupt goes off. This is done with the Timer1.attachInerrupt command. In the code above, you can see that the command is telling the arduino that every time the interrupt goes off, it should pause what it is doing, go and run the BlinkYellow function, and then afterwords return to whatever it was doing.

So, lets pull all this together to crate a program that will blink a Red LED slowly, 1 second on, followed by one second off, and then at the same time blink a yellow LED quickly using the Timer1 interrupt. The following code would do just that.