Optical Mice and How They WorkThe Optical Mouse is a complete imaging system in a tiny packageWhite Paper

Abstract

The mechanical computer mouse, Douglas Engelbart’s invention of the 1960’s, is starting to look like an endan-gered species. While users praise its ingenuity, many re-sent its unreliability and its need for frequent cleaning.

Change is on the way. Thanks to advances in optical navi-gation, solid-state optical mice have become the new standard. These new mice never need cleaning, track precisely, and work on nearly all surfaces. They may even reduce repetitive stress injury, and, to most people, they feel better.

Their ease of use belies their complexity. Hidden inside the sleek plastic case is a sophisticated design, combining the best of today’s electronic and optical technology.Inside An Optical MouseIf you took apart an optical mouse and looked inside, you’d find a complete imaging system. The mouse is essentially a tiny, high-speed video camera and image processor.As shown in Figure 1, a light-emitting diode (LED) illumi-nates the surface underneath the mouse. The light from the LED reflects off microscopic textural features in the area. A plastic lens collects the reflected light and forms an image on a sensor. If you were to look at the image, it would be a black-and-white picture of a tiny section of the surface. The sensor continuously takes pictures as the mouse moves. The sensor takes pictures quickly—1500 pictures (frames) per second or more—fast enough so that sequential pictures overlap. The images are then sent to the optical navigation engine for processing.

Figure 1. Optical mice illuminate an area of the work surface with an LED to reveal a microscopic pattern of highlights and shadows. These patterns are reflected

onto the navigation sensor, which takes pictures at a rate of 1500 images per second or more