Friday, November 23, 2012

30 Second Science: The Wiimote

One of the most innovative gaming systems in the last few years is the Nintendo Wii. The Wii is designed for interactive gameplay that hasn't been seen since the Power Pad.

I can proudly say I own one of these.
But how does it work? In today's 30 second science I'm going to give you a quick tour of the gaming system and explain how a few things work.

The Wiimote
It may be one of the most childish names for a controller, but the Wiimote is actually a pretty advanced piece of technology. Inside it has a speaker, an infrared sensor (we'll get to that later), a microphone, bluetooth, a 16 kB memory chip (which isn't by itself impressive at all), an expansion slot for accessories, and most importantly an accelerometer. 

Now an accelerometer is cool enough technology to warrant it's own article, but we'll just state the obvious: it measures acceleration. It can also measure the angle of the remote relative to the ground as well as roll (movement around the Y-axis), pitch (movement around the X-axis), and yaw (movement around the Z-axis).1

The Sensor Bar
The Wii Sensor Bar may be one of the biggest misnomers in all of gaming. The Sensor Bar actually doesn't do any sensing at all. Sure, when you're playing the game you'd like to imagine that you're pointing the Wiimote to the Sensor Bar which then sends information to the Wii, but that's not what actually happens.

The Wiimote can know everything about its position (from the accelerometer) except where the TV is - and that's an important piece of inormation. The Sensor Bar is actually just a source of infrared light.2  The Wiimote has a filter on the front that blocks all light except the frequency that the Sensor Bar emits.  When it "sees" the light it knows that it's pointing at the TV.3 The following examples shows what the Wiimote "sees".


When you point the Wiimote down

When you point the Wiimote up

When you point the Wiimote left

When you point the Wiimote right


Because the Sensor Bar isn't actually sensing anything at all, you actually don't even need it. You just need two IR sources (Using one won't work, the Wiimote needs two to triangulates its position). Candles work fine as an IR source, and I do suggest you try it at home, but I think it would be cool to try and play the Wii while being fired at by a pair of high power Nd:YAG lasers...

Now THIS is how you play the Wii...
Trying to dodge lasers makes playing Mario much more fun.


















Notes
[1] Of course I should mention here that X, Y, and Z are completely arbitrary. I'm using the labels on the picture. I really wanted the blue pictured axis to be the Z-axis to fit with the convention I'm used to, but whatever...
[2] Pronounced "INFRAred" not "INFAred". Start mocking people that say it wrong; it's the new "Nuclear". 
[3] In the direction examples, notice that the directions are inverted from normal vision. When you point the Wiimote all the way to the left, it sees the IR light move to the right of it's vision. 

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