Arduino UNO Tutorial for Beginners

Chapter 1: Start Learning with the Arduino UNO Board

Welcome to our Arduino journey! This is where we’ll start from scratch, exploring the basics of Arduino to kickstart your programming adventure. I’ll guide you through setting up your computer and crafting your very first program on the Arduino Uno board. Let’s dive in!

What better place to start learning about the Arduino platform than with the Arduino Uno board. For PLC programmers it can often be an advantage to know microcontrollers. They are very similar in many aspects, and knowing about microcontrollers can help your understanding of how the PLC works.

If you’re in Europe Arduino recently changed its name to Genuino.

The Arduino Uno, also known as Genuino Uno, is more than just a board; it’s an open-source gateway to the world of electronics and coding. Its heart, the Atmel ATmega328P microcontroller, is your perfect companion for diving into the essentials of embedded programming.

There are several reasons the Arduino Uno is perfect for beginners:

  • Simple connection to a computer
    The Arduino Uno board has a USB port and can therefore easily be connected to a computer. All the drivers are even included in the Arduino IDE so that’s the only thing you’ll have to install.
  • Easy wiring
    All the pins on the ATmega328P microcontroller are connected to headers on the side. In that way, you can wire it to a breadboard without any hassle.
  • Simplified programming language
    When you are programming the Arduino Uno you will be using a simplified programming language. Actually, it is a simplified C programming language.
  • Lots of support
    The whole Arduino platform is very popular and has millions of users. This means that there’s a lot of help to get when you are having problems. You will be able to Google many of your problems and find many solutions.

Since it is so good for beginners why don’t we just go ahead and start the Arduino Uno tutorial by setting up your computer? If you don’t have an Arduino Uno, you can pick up one here (affiliate link) or grab a good beginner’s Arduino starter kit.

Arduino Uno Software

First of all, you want to install some software for the Arduino Uno.

There are several IDE’s (integrated development editors) available to program the Arduino boards. In this tutorial, we will be using the Arduino IDE which is a free open source IDE by Arduino.

Arduino IDE is a very simple piece of software to program Arduino boards. The download and installation process is very simple.

Download the Arduino IDE here.

When you have downloaded the IDE you have to install it. Installing it is simple and you don’t have to do much else than accepting terms of conditions and select the components you want to install.

Here are some instructions to install Arduino IDE on the different platforms:




After the installation, you can start the Arduino IDE.

The bulk of the IDE is a white canvas, waiting for your code. You’ll find handy menus at the top and a useful terminal at the bottom, making your coding experience smooth and efficient.

The next step is to connect your Arduino Uno to your computer.

Connecting the Arduino Uno

Before you connect the Arduino Uno for the first time you should close the Arduino IDE.

To connect the board to your computer you will need a USB 2.0 A/B cable.

On the side of the Arduino Uno, there is a USB type B plug. Plug the cable into that and the other end to one of the USB ports on your computer. The board will automatically be powered up via the USB and you will see the ON LED light up green.

If you’re using Windows you will have to find the drivers the first time you connect your Arduino. In the pop-up window, you should choose to look up the drivers on your computer. When you click browse go to the folder where you’ve installed Arduino and choose the folder called Drivers.

After that, you can start the Arduino IDE.

Let’s check if the connection to your Arduino Uno works.

Go to the menu Sketch -> Upload or press Ctrl+U.

This should start uploading the code written in the white box to your Arduino. The code doesn’t do anything or have any functions. It is just to check if you have a connection to the board.

If the upload is successful you should see the message “Done uploading.” in a blue bar just above the black terminal window at the bottom of the IDE.

You might see the bar is orange instead of blue with the message: “An error occurred when uploading the sketch.”

This is most likely because you haven’t chosen the right port.

Go to the menu Tools -> Port and then choose the COM port where (Arduino/Genuino Uno) is included in the name.

Choosing the right COM port in Arduino IDE

Choosing the right COM port in Arduino IDE

Now try again to upload the code (Sketch -> Upload or Ctrl+U) and it should work.

Congratulations! You are now ready to start programming with the Arduino Uno!

Your First Arduino Uno Program

Before we go ahead there’s one new word you have to learn. In the Arduino IDE the code is not called a program but a sketch.

Since we are using the Arduino IDE I will be using the word sketch for our code because it makes it easier to navigate in the IDE.

Let’s start with our first sketch!

The only things you need for this are the Arduino Uno board and the USB cable. The Arduino Uno board has a built-in LED (light emitting diode) connected to one of the digital inputs/outputs.

Arduino Uno Digital Pins

If you look at a pinout for the Arduino Uno board you will find that all the header connectors in the sides are connected to the microcontroller.

There are both pins for powering and communicating with the Arduino but what we need to look at now is the digital inputs/outputs.

At the top of the Arduino Uno board, there are headers counting from 0 to 13 followed by one called GND. These are all digital inputs or outputs and the last one is the ground. You can see on the Arduino board that they are all marked as “DIGITAL”.

So what are all these digital pins? And what do I mean when I say they are both inputs and outputs?

Digital Inputs or Outputs

All the digital pins from 0 to 13 can be set to be either inputs or outputs. You will do that in the code.

These pins are termed ‘digital’ because they toggle between two states, offering a simple yet powerful way to control electronics.


These two states are the voltage level. For example, if you set one of the digital pins to be an output (as we’re going to do soon) you can set the output to be either HIGH or LOW in the code.

If the output is LOW the pin will be at 0 volts. But if it’s set to HIGH the voltage level is 5 volts.

This is very useful for us. If you know a little bit about electronics, you will quickly realize that we can use this change between 0 and 5 volts to control things.

Let’s go back to the code and see how we can set up the digital pins.

Arduino Minimum Code

When you open the Arduino IDE you will typically see a piece of code that looks like this:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:


This streamlined snippet represents the bare essentials that your Arduino Uno needs to spring to life.

Setup and loop are both functions in C. C is the programming language used for Arduinos. In fact, it’s a simplified version of C, but the syntax is the same. Programming microcontrollers with C can quickly become complicated because you have to deal with memory and so on. The fact that you don’t have to is one of the biggest advantages of the Arduino platform.

If you have never seen the C programming language before or want to improve your C programming skills, I highly recommend The C Programming Language (affiliate link) by K&R. The first chapter of this C tutorial is also very helpful.

First, take a look at the setup function. Inside you will see one line of code. This is not really code but rather a comment. Everything on a line after two slashes is a comment and will be ignored by the Arduino.

Arduino Setup Function

As the comment says, this function will only run once. It happens when you power up the Arduino or when you press the reset button.

This can come in very handy. You can use it as a function to set variables and so on in your program. That’s why the function is called setup. The Arduino will simply run this code one time and then go to the main function.

Remember that the digital pins on an Arduino can be set to either inputs or outputs. The setup function is the perfect place to define that since you only need to do that one time.

Defining Output with pinMode()

In order to define whether a digital pin on your Arduino Uno board should be an input or an output, you have to use another function. This is also a standard Arduino function. We will be using the function pinMode().

Arduino uses simplified C with a lot of built-in functions. As described before, this will make it a lot easier to configure and program the board. The standard function for defining the digital pins is the pinMode() function.

If you look in the reference for the pinMode() function you will see this:

pinMode(pin, mode)

This is the syntax of the function. You can see that the function takes 2 parameters: pin and mode.

pin: The number of the pin you want to set

mode: To what you will define the pin (e.g. INPUT or OUTPUT)

With that in mind, let’s go back to our first program.

On the Arduino Uno board, there’s a built-in LED. This LED is connected to pin # 13. Remember that this is an LED, so we want to set that pin to an output. This is how we will do it:

void setup() {
  // put your setup code here, to run once:

  pinMode(13, OUTPUT);

void loop() {
  // put your main code here, to run repeatedly:


You can see that the pinMode() function is placed in the setup() function. This is because we only need to set the pin one time.

Be aware that the default state of the Arduino digital pins is input. So if you want to use them as inputs you don’t even need the pinMode() function.

Built in LED and Constants

There’s another way to set the pin number 13. The pin is special because it has the built in LED connected to it. So instead of just using the number 13 in our function, we can use something called a constant.

Like the functions, Arduino also has some predefined constants.

A constant is a predefined expression. Just take a look at the reference site for constants provided by Arduino. You will see some constants like the pin levels (HIGH and LOW), and pin modes (INPUT, OUTPUT and INPUT_PULLUP). But if you scroll down a little further you will find a constant called LED_BUILTIN.

This constant always refers to the pin where the built-in LED is connected. On most Arduino boards it is connected to pin # 13. So instead of just using 13 in the pinMode() function we could use LED_BUILTIN:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:


In this way our code becomes a little more generic. You can now use this code on any Arduino board and not just the Arduino Uno.

Arduino Loop Function

Next step is to look at the loop() function. Because now that we’ve setup the pin we need it’s time to do something with that pin.

After running the setup() function the Arduino will go on to the loop() function and run that. But this function is a little different than the setup() function. The loop() function as the name says will run over and over. Like an infinite loop.

The loop is where the real fun happens. It’s here you will write the behavior of the program.

Since we already defined pin # 13 (LED_BUILTIN) to an output, let’s start by turning on the output. This will turn on the built-in LED on the Arduino board. Because what we will be doing is setting the state of the output to HIGH. As said before the state of HIGH will set the voltage level of the pin to 5V.

Setting Output with digitalWrite()

To change the state of an output guess how?

Again, Arduino has a predefined function for doing so. Just like the pinMode() function, this function also takes parameters. Here is how the syntax looks in the official reference from Arduino:

digitalWrite(pin, value)

The function also takes two parameters: pin and value.

pin: The number of the pin you want to write to

value: The value you want to give this pin

The values we’re going to use are HIGH and LOW. These are the predefined constants that will set the voltage level of the pin.

Since we want to turn on the LED we have to use HIGH. Because when we apply 5 volts the LED will turn on. The function we have to write in the loop will look like this:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:

  digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)

Take note that I use the constant LED_BUILTIN instead of just the number 13. You can use this constant every time you want to work with this pin. It makes your code much easier to read and understand. You will always see that this is the pin where the built-in LED is connected.

You can also see that I’ve added a comment after the line of code. This is also to make the code easier to read and understand. Especially when you are learning it’s very important to comment on your code.

It is now time to put this code into the Arduino and run it!

Compiling and Uploading the Sketch

I already showed you how to upload the sketch (program) to the Arduino board. But there is one thing you always should do before uploading. That is to verify your code. We have written some lines of code, and we want to make sure that they work. Because things can go wrong if you upload a piece of code with errors to the Arduino board.

Verify the Arduino Code

With all the above code in the editor go to Sketch -> Verify/Compile or press Ctrl+R.

This will not upload the code to your Arduino. It will verify your code. Check the code for any errors and make sure it will work on your board.

If your code has no errors the verification will look like this:

Verify Arduino Code with Sucess

Verify Arduino Code with Sucess

Good job! You’ve written Arduino code that works!

But what will happen if there is some errors in the Arduino code?

For the sake of learning, let’s make a syntax error on purpose. After every expression, there is a semicolon to end the expression. In this way, the compiler will know when an expression ends and a new one begins. Forgetting to put the semicolon is one of the most common programming mistakes. Even for experienced programmers. Let’s make that mistake and see what happens.

Change line 4 from this:


to this:


Now, go to Sketch -> Verify/Compile or press Crtl+R

The verification will now look a bit different:

Verify Arduino Code with Syntax Error

Verify Arduino Code with Syntax Error

What you will see is that the status bar turns orange. At the same time, an error message is shown in the status bar and one line turns red. This is extremely helpful because you will both see what the error is and where it is.

The error message is:

expected ‘;’ before ‘}’ token

What this message means is that the compiler needs to see a semicolon before the bracket.

Line 4 is an expression. But without the semicolon, the expression never ends. The compiler will just continue to read the code expecting the expression to continue or end. When the compiler meets a bracket sign it gets confused. Because the bracket will end the setup function before the expression ends.

To fix this, simply put the semicolon back on line 4.

Uploading Sketch to Arduino

Now that you have a code without errors it’s time to upload it to the Arduino board.

As described before this is done in the menu Sketch -> Upload or just by pressing Ctrl+U.

Upload Arduino Code to Board

Upload Arduino Code to Board

If you get the message: “Done uploading.” you have successfully compiled and uploaded your sketch to the Arduino board.

To those of you who have good eye you might have noticed something before the upload. Before uploading the Arduino IDE will compile your sketch. Compiling means that your code will be translated into code that the Arduino (AVR microcontroller) can understand. A microcontroller is not as intelligent as we are. In fact, the only thing it can understand are 0’s and 1’s. All your code will be translated into 0’s and 1’s when compiling.

With the code now in the Arduino, take a look at the board.

You should see that the LED on the board (close to pin 13) called L1 is now on. This is because we’ve changed the state of the pin to HIGH. Pin 13 now has a voltage level of 5 volts.

As a little experiment, we will change the code. Instead of setting the pin state to HIGH, we will set it to LOW. This should set the voltage level to 0 volts (ground) and turn off the LED.

The code should look like this:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:

  digitalWrite(LED_BUILTIN, LOW); // turn the LED off (LOW is the voltage level)

Look closely at the Arduino board while uploading this code.

You will see that two other LEDs start to blink. They are called “TX” and “RX”. These two LEDs are the indicators of communication. Every time they blink communication to the Arduino Uno board is going on. Communication happens when you upload a sketch to the board.

As soon as the uploading process is done the LEDs will turn off. The built-in LED will also turn off due to our new code.

Working with the Loop()

Let’s dig a little deeper into this loop() function. Again, this loop runs over and over again. We can use this to make our program a little more fun.

Right now we only have one line of code in the loop() function. This line of code will be executed over and over. Pin # 13 will be set to the same state again and again. The result will be that the LED will always be either on or off.

What if we write two lines of code in the loop? One that turns the LED on and one that turns it off. This should in theory make the LED blink.

Here is how our code will look now:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:

  digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
  digitalWrite(LED_BUILTIN, LOW); // turn the LED off (LOW is the voltage level)

The loop will now run these two lines of code over and over. First, turning the LED on and then off, then on, then off…

Try to upload the code and see what happens on the Arduino board. What happens now is something that you might not have expected. The LED does not turn on and off but rather shines vaguely.

Arduino UNO LED lights with half brightness

Arduino UNO LED lights with half-brightness

This is because the Arduino is fast. Very fast. Faster than the human eye. As a matter of fact, the LED actually blinks. It blinks so fast that you will neither see the LED on or off. You will see the average of this. Since the LED is on 50% of the time and off 50% of the time you will see the LED shining with 50% intensity.

Slow Down the Code with Delay()

What we want to do now is to slow down the code a bit. Slow it down so we can see the LED blink.

This is done by putting in delays. So that after the LED is turned on we want to wait a bit. The same after we have turned it off. In that way, we will have time enough to see the LED blink.

Here again, we are lucky to use the Arduino platform. Because the Arduino has a predefined function for putting in delays in our program. This function is simply called delay() and takes one parameter. This is how the syntax looks like in the Arduino reference:


The parameter in this function is ms. Here goes the amount of time you want the delay to be. The delay is set in milliseconds. In one second there are 1000 milliseconds (ms).

Let’s put these delays into our code. Half a second should be enough to see the LED blink. We will therefore put 500ms as a parameter in the delay functions:

void setup() {
  // put your setup code here, to run once:


void loop() {
  // put your main code here, to run repeatedly:

  digitalWrite(LED_BUILTIN, HIGH); // turn the LED on (HIGH is the voltage level)
  delay(500); // Wait 500 milliseconds
  digitalWrite(LED_BUILTIN, LOW); // turn the LED off (LOW is the voltage level)

Take note that I put the delay() function both after turning the LED on and off. By doing so the LED will be on for 500ms and then off for 500ms.

Try to upload this code and see how the LED now behaves.

Arduino UNO blinking builtin LED

Arduino UNO blinking built-in LED

You now have a blinking LED!

And the LED keeps blinking since the loop runs over and over again.

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