diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index 82b5694bb..93d8d2632 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -293,14 +293,14 @@ Books on general-purpose programming that don't focus on a specific language are
 ### Arduino
 
 * [Arduino-docs : A beginner's guide](https://arduino-doc.readthedocs.io/en/latest/) - Paramesh Chandra (HTML)
-* [Arduino Programming Notebook](https://unglue.it/work/152452) - Brian Evans (PDF) ( :card_file_box: *archived at unglue.it*)
+* [Arduino Programming Notebook](https://unglue.it/work/152452) - Brian Evans (PDF) ( :card_file_box: *archived at unglue.it*) (CC BY-NC-SA)
 * [Arduino Projects Book](https://www.eitkw.com/wp-content/uploads/2020/03/Arduino_Projects_Book.pdf) - Scott Fitzgerald and Michael Shiloh (PDF)
 * [Arduino Tips, Tricks, and Techniques](https://cdn-learn.adafruit.com/downloads/pdf/arduino-tips-tricks-and-techniques.pdf) - lady ada (PDF)
 * [Getting started with Arduino – A Beginner’s Guide](http://manuals.makeuseof.com.s3.amazonaws.com/for-mobile/Arduino_-_MakeUseOf.com.pdf) - Brad Kendall (PDF)
 * [Getting Started with Arduino products](https://www.arduino.cc/en/Guide) - Official Arduino Documentation *( :construction: in process)*
 * [Introduction to Arduino](http://playground.arduino.cc/Main/ManualsAndCurriculum)
 * [Introduction to Arduino : A piece of cake!](http://www.introtoarduino.com) - Alan G. Smith
-* [Learn Arduino](https://riptutorial.com/Download/arduino.pdf) - Compiled from StackOverflow documentation (PDF)
+* [Learn Arduino](https://riptutorial.com/Download/arduino.pdf) - Compiled from StackOverflow documentation (PDF) (CC BY-SA)
 * [Open softwear - Fashionable prototyping and wearable computing using the Arduino](https://softwear.cc/book/files/Open_Softwear-beta090712.pdf) - Tony Olsson, David Gaetano, Jonas Odhner, Samson Wiklund (PDF) (CC BY-NC-ND)
 * [Science, Programming, Art and Radioelectronics Club (SPARC)](https://github.com/artyom-poptsov/SPARC) - Artyom V. Poptsov (PDF) (CC BY-SA)