Using a Teensy++ 2.0 development board (Arduino Compaitable) with a few photoresistors and an LED. It is possible to use shadows as a way to interact with a computer. In this example I am controlling a HID (human interface device) by simply moving my hand over the resistors and generating a shadow. The initial flashing in the beginning is a calibration of the current "light vs shadows" currently being generated by the ambient light in the room. From there you can take an average of that number and filter out "non movement". Thanks to [Julien] who was able to generate a simple way to store the values and find ambient light averages.