Use a laser pointer and LED matrix as an input device
Eiji Hayashi has used a property of LEDs and used this knowledge to create a form of input using a laser pointer and an LED matrix. He explains that by reverse-biasing LEDs you can measure the brightness they're exposed to - and therefore if a laser pointer is aimed at the LED. So Eiji has put this to use and created a form of input that can also be used for gaming purposes.
Well done Eiji. Remember when working with laser pointers to ensure the beam doesn't shine or reflect into someone's eyes. To get started with your own embedded Arduino project, consider our Freetronics LeoStick - one of the smallest Arduino-compatibles with onboard USB, RGB LED and piezo:
For more information on Eiji Hayashi's matrix project, visit his website.