How to Write an Arduino Library

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Arduino is one of the most versatile open-source electronic platforms, giving you unique and easy to use software and hardware. It is a popular platform among hobbyists who seek to come up with various projects, especially those leaning on robotics and home automation. 

Among the benefits of this platform is its ease of use, which makes it friendly for beginners. Part of its friendliness comes from understanding how its systems work. The Arduino library is an essential system of this platform, and as a pro hobbyist, you need to know how to write an Arduino library. 

What Is an Arduino Library? 

The Arduino libraries are files written in C language, either C or C++, and add an edge of functionality to Arduino sketches. In Arduino language, a sketch is a program or unit code that you install and run on an Arduino board. 

In short, the libraries make the Arduino platform more adaptable by extending its functions in areas like data manipulation. To access your libraries, you go to the sketch menu and click on the import library. 

You will find several libraries preinstalled in the integrated development environment, though you can also add yours from different sources. The libraries come under various categories, including standard libraries, 101 libraries, due only libraries, WiFi 101 libraries, and many more. All of them have a specific function. 

As a hobbyist, you have to come up with your libraries, to give your projects a personal touch. Let us have an in-depth look at how to write an Arduino library. 

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Writing an Arduino Library 

Step 1: Understand the API Language 

To start you off, you need to familiarize yourself with Arduino’s API language of writing libraries. When you grasp the language, you will understand how Arduino’s systems work and how to develop corresponding libraries to support their functionality. 

When learning this language, the following are points to note. 

  • Focus on the end-user, assuming they have no programming experience. 
  • Come up with a clear mental picture of the capabilities of your model. 
  • Avoid using redundant or complicated words in your character string. 
  • Always document and comment as you proceed. 

Step 2: Creating A Library Folder 

Before getting into coding, you have to locate the libraries folder on your system. If you are using the Windows operating system, you can type out this prompt to get the location. 

C: \Users\\Documents\Arduino\libraries 

You can also go to the sketchbook location menu in the preferences section. In this folder, search for libraries. Once you find the libraries folder, create another folder and give it a preferred name. The new folder will have all the files you need. 

Step 3: Creating A Header 

In the C++ language, the header summarizes the library’s contents, and you import the header any time you want to use the library. It also gives a hint to the compiler of the library’s functionality. 

The header file contains the extension .h and has a line for each function in the library. You may wrap the lines with a class having the variables you need. The class consists of functions and variables, which can either be public or private. If it is public, anyone using your library can access it, while if it is private, you restrict access to within the class. 

The class needs to have a special function – the constructor that creates an instance and has the same name as the class, minus a return type. 

The header should have a #include statement, which gives access to standards and constants of Arduino’s language. Complete creating the header by giving a short description at the top of the library, with details such as name, function, creator, and date. 

Step 4: Highlight the Keywords 

To improve the library’s usability to other users, you can highlight the keywords. While it is an optional step, you may do it considering how Arduino’s editor is poor when it comes to highlighting semantic syntax. In highlighting, you give the different keywords color. 

Step 5: Using And Installing The Library 

You now use the library by importing it to the Arduino sketch to see if it meets its intended functionality. If all is good, you can install it. You may zip the library files’ folder for you to redistribute it to other developers. 

There is the option of importing external libraries, where you can extract the files and place them in the right folder. Finally, restart the Arduino system, and you will see your new library. To get to the library, you go to file, sketchbook, then examples. 

Your library is now good to work in adding some functionality level to your Arduino system. 

Installing A New Library 

There is an easy way of getting a library in your Arduino system, which is by installing it. You can use this method if you are getting it from other sources. Here, you use the library manager. Open the integrated development environment and go to the sketch menu. Click on include library then manage libraries. 

The library manager will launch, and you will see a list of libraries, some installed, and others waiting for installation. Go through the list and pick the one you want to install. Select the version you want and finalize the procedure by clicking on the install key. 

It will start downloading, and the speed will depend on your internet’s stability. When done, you will see a tag indicating the library’s installation. To access this library, you go to the sketch menu then include the library. 


Libraries are vital on the Arduino platform as they extend the functionality of both hardware and software. There are several preinstalled in the platform and come in several categories. If you want your libraries, you can write them or install them from another source. 

We can see the steps to follow in writing your libraries, which is a good move if you want to personalize your projects. In this procedure, you can improve your proficiency if you are good in the C++ language. Learn the basics of Arduino’s API language, and you can comfortably create your libraries. 

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