Touchpads

A touchpad is a fixed place pointing device that has become very common in notebook computers. A touchpad, is a small, flat square or rectangular surface on which you slide (touch) your finger to move the cursor on the display, select objects, and run programs. A touchpad. provides the same actions as a mouse.

A touchpad works on the principle of coupling capacitance that uses a two layer grid of electrodes to hold an electrical charge. The upper layer of the grid has small vertical electrodes, and the lower layer has small horizontally placed electrodes. An IC is attached to the grid that detects any changes in the capacitance of the pad. The chip is constantly monitoring the capacitance between each of the horizontal electrodes and a corresponding vertical electrode. The user's finger when placed over a pair of the electrodes serves as a conductor and alters the capacitance of the electrode pair, since a human finger has a very different dielectric property than air. The chip detects the change and data is sent to the PC using the same techniques that are used by a mouse. As the finger moves over the grid, each of the electrode pairs affected are converted into x y placements for the PC.

Like an optical mouse, the touchpad has no moving parts and does not require preventive maintenance. Touchpads are being integrated into desktop PC keyboards as well as notebook computers. An external touchpad can be added to a PC via its PS/2 port.