How motion-sensing controllers work

Scienceline reports: [edited]

Seasoned video game players used to laugh when beginners waved the controller up in the air, urging Mario to jump a little further, but now these frantic motions have become part of the game.

The new Nintendo Wii and Sony Playstation 3 gaming systems both include motion-sensing controllers. Nintendo, in particular, has used its motion-sensing controller as the primary selling point of the Wii. 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.

The accelerometer monitors the position of the wafer by measuring capacitance, or the ability to store electric charge, in different directions. When you move the controller forward in a punch, the capacitance increases at the back of the wafer and decreases at the front. Using capacitance to measure how far and in what direction the wafer moves, the system translates your real-life movements into the perfect jab to your opponent’s face.

The accelerometers used in the Nintendo controller are thinner than a penny, small enough to fit twelve on a postage stamp, and sell for under £3 a piece. They can accurately measure forces more than three times stronger than the pull of gravity in three directions – up and down, side to side, and forward and back. The chips also use gravity to determine the orientation of the controller, whether you’re holding it vertically like a golf club or horizontally like a gun.

But accelerometers alone cannot provide complete control, because small positional errors add up over time, think of how you regularly need to re-center your mouse on its mat.

Nintendo addressed this problem by including a sensor bar 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.

If you want to see inside a Wii controller, sparkfun.com has dismembered one for you. For those of you wondering why you can't see any of the little men that we all KNOW do most of the work, that's because they are REALLY, REALLY, REALLY little.

Thanks Conrad for sending me the URL.
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