This letter describes our source-level debugger for Arduino which can be used to debug the code in Arduino using GNU debugger. The presented solution uses Eclipse as the visual front-end. It does not require any modification of the Arduino board or additional hardware; debug functionality is achieved by adding a program library to the user application. Standard functionality expected from a debugger is available, such as setting breakpoints while debugging, stepping through the code and viewing variables. This allows developing projects with Arduino more efficiently and also using the Arduino for teaching embedded programming at a more advanced level, including debugging the program.