Wii Controller’s Optical Sensor

Why have two sensors, a sensor bar and an optical sensor in the remote?

I’ve been mulling over the Wii game console’s innovative controller. One question I haven’t heard the answer to so far is what does the optical sensor do? Does anyone know? I suppose it tells the console that someone is standing in front of the TV and pointing something at the screen. But can’t the rest of the sensors do that?

To back up a little, the Wii’s remote control has some neat built-in motion sensors. That’s what enables the interesting new kinds of game play where the controller extends your body. In a tennis game, you hold the Wii controller and take a whack at the ball coming at you on the screen. As you do so, the ball goes flying back wherever you’re pointing.

The controller senses motion. It’s got a MEMS device. That’s short for micro electro-mechanical system. This is a little silicon chip built with semiconductor manufacturing technology. But in contrast to chips, MEMS devices are like tiny little machines, like gears. In this case, the chip suppliers Analog Devices and ST Microelectronics have built MEMS accelerometers. These are the same devices that they use in laptop hard disk drives. If they start falling, the accelerometer senses the motion and the drive will immediately lock down its head so that it doesn’t damage the disk upon impact. The accelerometers are also used to detect impacts that trigger air bag deployments.

The chip senses direction and acceleration by measuring changes in the electrons within it. The electrons move around depending upon the position and motion of the controller. Picture a couple of charged plates inside the sensor. One stays put, but the other moves. The electrons that surround the plates move with that motion. By measuring the capacitance, the sensor captures movement data. The devices can sense up down, left right, and forward backward motion. They can also sense acceleration. Then the signal processing parts of the chip take that data and ship it over to the Broadcom chip.

Broadcom makes the wireless Bluetooth radio chip that transmits the positional data to the console in real time. All of the components are inexpensive and they are a lot faster than they used to be. That’s how a big backhand stroke by the player gets translated into a virtual stroke in a tennis game. But if all that is in there, what do they need the optical sensor for. Can’t they just calculate where the controller is pointing based on the XYZ data and motion data alone?

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