This experiment was created during a one-off tutorial session whilst in my final year.
Consisting of a 4x5 LED matrix, Arduino controller and a Processing sketch - this piece allows for the LED's in the matrix to be controlled by moving the cursor around a screen-based grid in the Processing file. Each sector of the grid acts as a switch for the corresponding LED, scrolling the mouse into a sector turns the LED on, and then off again upon removing the cursor from that sector.
Due to an unfortunate incident involving Bootcamp and Windows XP, I recently lost the files for both the Processing and Arduino elements of this project. I did fortunately uplaod a video of it in action, click the link to check it out.