What Is the Purpose of an Accelerometer on a Tablet PC?

By Fred Decker

The tablet PC that lives in your purse or backpack is a deceptively simple device, providing you with easy and intuitive ways to be productive or entertained while you're on the road. Behind that simplicity lies a great deal of sophisticated engineering, both in hardware and software. A key component is the accelerometer, a tiny electromechanical device that detects the movements of your tablet. It's responsible for providing mobile devices with much of their magic.

The Basic Technology

Although it's usually incorporated into a small circuit board, the accelerometer itself is not a computer chip. It's an example of a microelectromechanical system, or MEMS, a collective term for very small-scale machines. The accelerometer detects movement through very delicate springs or -- more commonly -- through a sophisticated bubble-based system, a microscopic equivalent of the ordinary carpenter's level. By relating the position of the bubbles to the earth's gravitational field, the accelerometer can detect the movement and orientation of your tablet computer. That's where the fun begins.

Baby Steps

High-end computer manufacturers were early adopters of accelerometers, using them to detect a dropped computer and rapidly "park" the hard drive's heads to limit the risk of data loss. Nintendo incorporated accelerometer technology into the Wii gaming console's handheld controllers, adding a new dimension to gameplay, but the accelerometer didn't really come into its own until it was incorporated into the original iPhone. The phone's screen automatically re-oriented itself from portrait to landscape mode when it was rotated, an advantage so overwhelmingly obvious it became universal in mobile devices.

The Interface Advantage

Enabling a quick change from "tall" to "wide" is useful, but it only scratches the surface of what an accelerometer can do in a well-designed tablet. The device can detect tilting and rolling as well as simple rotation, providing many ways to incorporate motion into the user interface. In a 2007 article, MIT's "Technology Review" interviewed researchers at British Telecom who saw the technology's tremendous potential for users who struggled with conventional mouse-and-keyboard arrangements. Game developers were similarly quick to adopt the technology, cutting out the need for a controller and using the tablet's own motions to manage gameplay.

Innovative Examples

App developers continue to find innovative ways to incorporate the accelerometer into their designs. For example, reading app Instapaper allows you to scroll through articles by simply tilting your tablet, and turn pages by flipping it. An iOS app called Sleep Cycle is even more imaginative. With the app activated and your iPad under a sheet at the corner of your bed, it detects your movements and gauges how deeply asleep you are. It will wake you up within a 30-minute window of a light segment of your sleep cycle.