Build Wii For Fun

Intially, I thought the sensor bar is a sophisticated piece of hardware that acts as the receiver of signals emitted from the Wii-mote and transmitts these signals into the Wii-console for processing. In that case, one would need to hack the Wii-console in order to pull motion tracking information from the device. Later, I realized that this is far from the truth. In fact, it’s the exact opposite - the sensor bar is actually the emitter of infra-red signals, and it is the wii-mote that is doing all the magic!

The Wii-mote itself is a high-resolution IR camera that is capable of tracking 4 infra-red blobs simultaneously. If you know something about blob-tracking from Computer Vision, this is exactly the same concept. Except one crucial difference - no other distractors in the environment! Unlike vision techniques for doing blob tracking, finding the blob from a naturally cluttered environment is extremely challenging. No matter what feature you use, almost always there will be something in the background that is going to cause confusion to the tracking algorithm. To make matters worse, different lighting conditions will royalty screw up tracking as well.

The infra-red technology the Wii uses is different - for most home-environments, there are no other IR light sources other than the ones on the sensor bar.  With such clean signal, tracking is almost trivial. That is why the Wii works regardless of how cluttered you home is, or which time of day you are playing - it makes no difference whether it is broad day-light or at night in the dark.

Other piece of useful information is that IR lights are not visible to the human eye.  However, a camera (such as a web-cam) can pick it up. Similarly, so will the IR camera on the wii-mote. Try placing your web-cam toward the sensor bar and you will see. It’s quite fun.

Intially, I thought the sensor bar is a sophisticated piece of hardware that acts as the receiver of signals emitted from the Wii-mote and transmitts these signals into the Wii-console for processing. In that case, one would need to hack the Wii-console in order to pull motion tracking information from the device. Later, I realized that this is far from the truth. In fact, it’s the exact opposite - the sensor bar is actually the emitter of signals, and it is the wii-mote that is doing all the magic! For more information about the inner workings of Wii, check out the “Wii: Demythified” section.

To recreate the sensor bar, all you need is the following: two IR-LEDs, some wires, and a battery (can be any battery from 1.5V to 9V, although for larger batteries, you will need some resistors). Follow the following schematic diagram to build your sensor bar.

To save soldering, I used a piece of bread-board for connecting the components together. For durability, stability and asthetics, you should do the soldering and preferably mount it on a nice looking case, but that’s all optional. Here is what my final product look like:

I plan to make a video to show you how this is done. Stay tuned.

Update: I actually found a pretty good video on YouTube that teaches you how to do what I explained above to create a sensor bar (without wires) for the Wii itself.

embedded by Embedded Video

YouTube link to: Sensor bar explanation

Testing  Sensor Bar

Despite our sensor bar is extremely simple as a piece of hardware, we still need to test it to make sure we have connected or soldered everything correctly. If the IR LEDS are actually visible, this test would have been very simple - connect the battery and see if the lights would actually turn on. Unfortunately, IR lights are not visible to the human eyes. However, they are visible through a webcam. Connect a webcam to your PC and record a video of the sensor as we plug in and then the battery. If everything’s working, we should see the lights come up and then off through the view of the webcam.