In the past, the use of tangible programming languages has shown several advantages compared to screen-based graphical programming languages. Especially when presented to novices, such interfaces may represent a more intuitive and straightforward alternative to teach basic computer science and programming concepts. Previous studies have reported increased interest and improved collaboration when tangible programming languages were used. However, additional financial expenses have often hindered the use of such interfaces in formal education settings. This work therefore presents a low-cost and customizable solution of a tangible programming language for Thymio, an educational robot widely used in primary and secondary schools. Using a computer vision algorithm, graphical icons printed on paper are captured by a camera, and subsequently interpreted and sent to the robot for execution. Two user studies with in total 77 university students showed promising results, indicating that the devised interface can elicit more interest and a higher level of collaboration within groups.