Mechanical and Opto Mechanical Devices

Most mechanical and opto-mechanical mice and all trackballs of these types use a small ball that rotates against two rollers in the body of the mouse or trackball, as shown in Figure 15.10. There's usually also a third roller that's used solely to stabilize the ball; no sensors are attached to this roller.

The mechanical and opto-mechanical designs deviate at this point. In a purely mechanical device, the rollers activate some form of mechanical sensor, whereas in opto-mechanical devices, an optical sensor is used. Most mice and trackballs sold today use an opto-mechanical design. In this configuration, the roller rotates a wheel that contains spokes through which light can pass. A small light source sends light through those spokes, and an optical sensor on the other side detects these light changes. This arrangement is depicted in Figure 15.11. Circuitry in the mouse can then combine the input from both rollers to determine in which direction the mouse or trackball is moving.

Chapter 15

Figure 15.10

The rollers inside a mouse sense the movements of the ball that are associated with movements of the mouse against a

Figure 15.10

The rollers inside a mouse sense the movements of the ball that are associated with movements of the mouse against a

Figure 15.11

When the roller rotates in response to a mouse movement, the light beam's passage through the spoked wheel is interrupted, allowing the mouse to sense movement.

Figure 15.11

When the roller rotates in response to a mouse movement, the light beam's passage through the spoked wheel is interrupted, allowing the mouse to sense movement.

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