How the Wii Balance Board Works

It all began in Shigeru Miyamoto's bathroom. Miyamoto, one of Nintendo's most prolific game designers, had been weighing himself -- a lot. You could even say that it had become something of a hobby. Every day, without fail, he would step onto his bathroom scale and meticulously record his weight and body fat on a graph. Many months (and graphs) later, Miyamoto and his colleagues began working on a new project, named "Health Pack," that combined his weight-measuring concept with a number of family-friendly activities [source: Iwata: Wii Fit]. This was in 2004. Three years later, when it was announced at E3, it had been renamed "Wii Fit."

With the idea of a game centered on measuring one's balance now fleshed out, Miyamoto's team set out to accomplish the most challenging aspect of the project: designing an intuitive, user-friendly interface. Luckily, the solution already seemed to be staring them in the face. Drawing inspiration from Miyamoto's bathroom routine, Takao Sawano, the project's lead designer, began experimenting with two scales, setting them side by side and trying to balance on both evenly [source: Romano]. (The idea to use two scales came to him after watching sumo wrestlers weigh themselves, because they are too heavy to use only one.) Pleased with the initial results, Miyamoto asked him to connect the scales to a computer and display the weight data onscreen -- this somewhat crude setup eventually formed the basis for "Wii Fit's" balance test.

After several rounds of troubleshooting during which they ran through a few different-shaped prototypes, the team finally settled on a rectangular, step aerobics-like design equipped with load sensors to allow for greater accuracy [source: Casamassina]. In the interest of keeping costs down, the design team had originally intended for the board to be connected to the Wii Remote, through which it would wirelessly communicate with the console. Worried that users might accidentally step onto the remote or trip over it, the cord was nixed from the final model [source: Iwata: Board]. And thus the Wii Balance Board was born.

Next, we'll take a look under the hood, so to speak, and see just how accurate its measurements really are.

The svelte Wii Balance Board weighs in at about 8 pounds (roughly 3.5 kilograms) and can support up to 330 pounds (about 150 kilograms) for in-game functionality. (It can actually support quite a bit more, up to 620 pounds, but games like "Wii Fit" will not work if you weigh more than 330 pounds [source: Casamassina].) It runs on four AA batteries, which Nintendo says can provide up to 60 hours of play time depending on the settings used, and the board shuts off automatically to conserve power when not in use after a short period of time. It has built-in wireless capabilities and communicates with the Wii using the same Bluetooth technology found in the Wii Remote.

Load sensors sit snugly at the bottom of each of the board's four squat, cylindrical-shaped legs. These work together to determine the position of your center of gravity and to track your movements as you shift your weight from one part of the board to another [source: Okamoto et al.]. Each is a small strip of metal with a sensor, known as a strain gauge, attached to its surface [source: Snider].

Strain gauges measure the level of stress applied to an object. A gauge consists of a single, long electrical wire that is looped back and forth and mounted onto a hard surface -- in this case, the strip of metal. Applying a force on the metal by standing on the board will stretch or compress the wire [source: NASA].

Imagine stretching a rubber band: It gets longer as you pull, and it also gets thinner as it stretches. The same thing happens in the strain gauges -- they get longer while their cross-sectional area gets smaller. Because of the changes to length and diameter in the wire, its electrical resistance increases. The change in electrical resistance is converted into a change in voltage, and the sensors use this information to figure out how much pressure you applied to the board, or how much you weigh.

The sensors' measurements will vary depending on your position and orientation on the board; if you're standing in the front left corner, for instance, the sensor in that leg will record a higher load value than will the others. A microcomputer in the board takes the ratio of the load values to your body weight and the position of the center of gravity to determine your exact motion; it then transmits that information back to the Wii at a rate of 60 signals a second [sources: Okamoto et al., Casamassina]. The sensors must be on a flat surface to work properly, so foot extensions -- which come with the board -- provide stability and ensure proper communication with the Wii and the board when it's used on carpet.

The bending in the metal is practically imperceptible to the naked eye: for instance, someone weighing 220 pounds would distort it by less than a millimeter [source: GameSpy]. The sensors are highly accurate and can detect changes in weight of as little as tens of grams [source: Casamassina].

Up next, we'll look at some of the peripheral's known limitations and risks and explain why you can (but probably shouldn't) wear shoes on it.

During its launch period, the Wii Remote, a close sibling to the Wii Balance Board, was plagued with strap-breaking problems. So far, the board has avoided such massive hitches. Most complaints about the board seem to touch on one of two issues: its safety and the synchronization process.

The former brings us to why you should -- but don't necessarily have to -- be barefooted when you use the balance board (unless you snagged a pair of Nintendo's official "Wii Fit" non-skid socks): It can be slippery. Sure, Nintendo designed it to be close to the ground and even included a few inset grooves on top to help gamers find the approximate location of their feet. But, let's face it: If you're wearing either shoes or a particularly thick pair of socks, you won't have a good grip and may fall off. So while there isn't anything technically wrong with wearing something on your feet when you're using the board, you should just be aware that it can be risky. It also goes without saying that, whether or not you are wearing shoes, you should not use the board at all if you weigh more than 330 pounds, because it won't work properly.

Also, before you start playing a game with the Balance Board, you have to synchronize it to the console -- a process called Standard Mode Synchronization -- by pressing the "Sync" buttons in the Wii's SD card slot and in the board's battery cover slot for several seconds. You'll also need to repeat the process for each new board-compatible game.

For the most part, users seem to hit snags when they don't do one of the following:

Otherwise, users sometimes also forget to place the board with the blue power light facing away from the television. If it is facing the wrong way, the movements onscreen are reversed. Gamers also experience problems synchronizing the board with the Wii when they use incompatible rechargeable battery packs. Nintendo's official line in that regard is that you should use standard AA batteries. If you do want to use rechargeable AA batteries, however, they should be nickel metal hydride (NiMH) batteries.

We've spent a lot of time discussing the board's history and capabilities, but what about the games? Now, we'll talk about the game that singlehandedly kicked off the balance board craze, "Wii Fit," and some of the other games that use its functionality.

The Wii Balance Board would be nothing without software. Nintendo's own offering, "Wii Fit," readily springs to mind, but there are in fact many other games. With a few exceptions, they mostly fall into one of two categories: sports or exergaming (a la "Wii Fit").

In the fitness camp, you'll find games such as Electronic Arts' "EA Sports Active," Ubisoft's "Gold's Gym: Cardio Workout" and Majesco Games' "Jillian Michaels' Fitness Ultimatum 2009." These mostly mimic the "Wii Fit" model or build upon it by throwing in some new exercises and features. Games such as Namco Bandai's "We Ski" and Electronic Arts' "Skate It" let players indulge their sports fantasies by using the board as skiis, a snowboard or a skateboard. Still others, such as Nintendo's "Wii Music" and Hudson Soft's "Tetris Party," innovate a little by letting you use the board as an instrument and to control falling blocks, respectively [sources: Scottberg, Bozon].

More than 20 games have been released in the U.S. that support the peripheral to some extent. Plenty of sequels have been planned for 2010, though there should be a few original games, including Sega's "Super Monkey Ball Step & Roll" (which will let players control a monkey in a ball with the board), to tide over fans craving something new [source: Anderson].

So what's next for the Wii Balance Board? Not much, at least that the public knows of. Nintendo is notoriously tight-lipped when it comes to discussing its future projects, so it's entirely possible that its engineers are, or have been, working on some new features. With rumors circulating that Nintendo may be preparing a follow-up to the Wii console in 2011, it is not yet clear whether it will revamp its existing board or simply ditch it in favor of a similar-looking, but more advanced model [source: Davison].

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