How Do Touchpads Work?

How do touchpads work? If you've got a laptop, that's a good question to answer. For years, the primary pointing device for computers has been the mouse. Mice, however, require a significant amount of flat, stable space to be effective.

The development of laptop computers made finding this desktop real estate difficult. As a result, several alternative pointing devices were developed, including trackballs, touchpads and miniature joysticks. Ultimately it was the touchpad that became the industry standard as a portable mouse replacement.

How Do Touchpads Work Their Magic?
Basically, touchpads work by sensing the changes in an electrical field. There are two major technologies to sense these changes:

• Capacitance: In electronics, capacitance is the ability of an item to hold an electrical charge. In a touchpad, two arrays are created-one vertical and one horizontal. Each array is composed of parallel lines of conductors and is separated from the other array by an insulating layer. A signal passes through the conductors and is monitored by sensors. When your finger touches the pad, it creates a change in the signal. The sensors record these changes and the computer converts them to a set of coordinates that are used to position the cursor on the computer screen.
• Conductance: In this less-common method, the touchpad is comprised of two flexible surfaces separated by a series of tiny insulators. When you press your finger against the top surface, it comes in contact with the lower surface and current flows between the points of contact. Sensors measure the location of the current flow and the computer converts that location into screen coordinates, positioning the cursor as needed.

Other Touchpad Features
Since most software is developed with a mouse in mind, a computer touchpad often has buttons beneath it to mimic the features of a mouse. A PC touchpad may also have hot spots that serve a specific function, like controlling the scroll bar of a window or controlling media playback.

A software driver controls the functions of a touchpad. Software-based functionality includes touch zones to launch applications and the ability to use more than one finger for increased functionality.