The new Nintendo Wii and Sony Playstation 3 gaming systems, just released for the holidays, both include motion-sensing controllers.
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But how are the controllers able to precisely and accurately measure physical movement? At the heart of the controller technology are tiny accelerometers. Inside these chips, silicon springs anchor a silicon wafer to the rigid controller. As you wave the controller through the air at an attacking enemy, the wafer presses onto the springs, just as you are pressed against the seat of a car when you stomp on the gas pedal. The faster the controller accelerates, the more the wafer moves relative to the rest of the chip.
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But accelerometers alone cannot provide complete control, because small positional errors add up over time, like when you need to re-center your mouse on a mousepad. Nintendo addressed this problem by including a sensor bar that can be placed above or below the television. Each end of the bar emits a beam of infrared light like a television remote, which is monitored by a sensor on the controller that works like a digital camera: by seeing where the two spots of light fall on its grid of more than 750,000 pixels, the sensor can determine where the controller is pointing and translate it to a position on the television screen.