Touchpad

The term touchpad [ˈtʌtʃˌpæd] or touch field refers to a touch-sensitive surface that can be used, for example, as a mouse and key replacement in notebooks, usually mounted below the keyboard.

Touchpads are also used as control elements for electronic musical instruments and effect devices. In addition to the almost square design for control in 2 dimensions, there are often also one-dimensional ribbon controllers that work according to the same principle.

There are different modes of operation.

Operating principle

Modern touchpads use electrical capacitance to determine the position of an object (e.g. a finger) on the surface of the pad. To do this, they have a rectangular grid of electrodes between which the capacitance is constantly measured. The capacitance depends on the permittivity of the matter in the immediate vicinity of the electrodes. If you now come close to this arrangement with your finger, which has a much stronger permittivity than the surrounding air due to its water content, the capacitance between the electrodes is changed. This allows the two-dimensional position to be determined. If a finger is dragged across the grid, the change in capacitance between the electrodes also moves.

Measuring the approach of a finger to the touchpad and thus also the contact pressure would in principle be possible by measuring the strength of the change in capacity. However, a two-dimensional arrangement cannot distinguish whether a small finger is applied forcefully or a large finger only lightly, which is why this measurement is usually ignored. Capacitive touchpads can also be operated with other objects that have a permittivity similar to the human finger, such as special input pens. Depending on the design, the pressure measurement function can also be used with these pens.

The measurement of position and movement on the touchpad is passed on to the operating system. The touchpad driver receives these signals and displays them, for example, like the movement of a computer mouse. Most touchpad drivers recognize a light tap of the finger and simulate a click. A double click is created by tapping twice. If you hold your finger on the touchpad after the second tap, you can select or move objects (symbols).

Some manufacturers reserve one or more areas of the touchpad for frequently used functions such as scrolling or mouse buttons. Modern touchpad devices with multi-touch can register touches with multiple fingers and transform them into their own commands via the touchpad's driver. Thus, a light tap with two fingers can call up a context menu or "swiping" with three fingers can switch to the next image.

Synaptics touchpad: grid side glued to the back of the plastic part of the keyboard

Advantages

The use of the touchpad makes it possible to dispense with other input devices such as a mouse. Due to their compact design, touchpad devices can be integrated directly into the housing of laptops or keyboards. Their proximity to the keyboard allows faster access to the cursor than, for example, reaching for the mouse, where the hand first has to be placed and the cursor repositioned after a long journey. Another important advantage, which is important for use in public facilities such as libraries or lecture halls, is the much lower noise level during operation compared to the use of a mouse, even if the option of finger pressure on the touchpad is used for simple clicks. There is also no need for additional flat surfaces or cabling (mouse, external trackball), radio connections or power sources (wireless mouse), which reduces the overall weight and facilitates the mobile use of these devices.

CHERRY keyboard G80-11900 with touchpad.