Even with electronic musical instruments and effects devices touch pads are used as controls are used. In addition to the almost square design for control in 2 dimensions, there are also often one-dimensional ribbon controllers that work on the same principle.
There are different ways of working.
Modern touchpads determine the position of an object (e.g. a finger) on the surface of the pad based on the electrical capacitance . For this purpose they have a rectangular grid of electrodes , between which the capacitance is constantly measured. The capacity depends on the permittivity of the matter in the immediate vicinity of the electrodes. If you come near this arrangement with your finger, which due to its water content has a much higher permittivity than the ambient air, the capacitance between the electrodes is changed. This allows the two-dimensional position to be determined. If a finger is dragged over the grid, the change in capacitance also migrates between the electrodes.
A measurement of 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 capacitance. However, a two-dimensional arrangement cannot distinguish whether a little finger is put on 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 that of a human finger, such as special input pens . Depending on the design, the pressure measurement function can also be used with these pins.
The measurement of position and movement on the touchpad is passed on to the operating system . The driver of the touchpad receives these signals and provides them e.g. For example, it looks 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 consequently generated by tapping twice. If you keep your finger on the touchpad after the second tap, you can mark or move (drag) objects (symbols).
Some manufacturers reserve one or more areas of the touchpad for frequently used functions such as B. Scroll or mouse buttons. Modern touchpad devices with multi-touch can register touches with multiple fingers and transform them into their own commands via the driver of the touchpad. A light tap with two fingers can call up a context menu or "swiping" with three fingers can switch to the next image.
The use of the touchpad makes it possible to do without additional input devices such as a mouse . Due to the compact design, touchpad devices can be integrated directly into the housing of laptops or keyboards. Their proximity to the keyboard allows quicker access to the cursor than e.g. B. the grip on the mouse, in which the hand has to be placed after a long way and the cursor has to be repositioned. Another important advantage, which is important for the usability in public facilities such as libraries or lecture halls, is the considerably lower noise development when using a mouse, even if the possibility of finger pressure on the touchpad is exhausted for simple clicks becomes. There are also no further requirements such as additional, flat surfaces or cabling (mouse, external trackball), radio connections or power sources (wireless mouse), which reduces the overall weight and makes the mobile use of these devices easier.
Many manufacturers forego the addition of additional touchpad buttons that can serve as replacements for mouse buttons. However, these are necessary for some applications. An updated or specialized driver that allows recognition of the second or third finger can help. Otherwise the only option is to use an external mouse.
It is often found annoying when the touchpad is below the keyboard - especially if you are used to typing with one hand. The ball of the hand then generates completely arbitrary movements and clicks on the touchpad. Some manufacturers therefore position the touchpad in a small recess and exactly in the middle of the keyboard (see picture above) so that it is not touched when typing with two hands. The disadvantage is increased in models that have a particularly large or poorly positioned touchpad. As a remedy, you can also deactivate the touchpad and connect an external mouse to the notebook instead. Many newer notebooks have a predefined key combination or an extra key to (de) activate the touchpad easily. There are now touchpad drivers that, due to the very different movement and thus signal patterns of the palm of the hand and fingers, are able to distinguish them from one another and thus ignore a hand that may be on the touchpad.
Touchpads cannot be operated with conventional gloves because the distance to the finger is too great, but there are special touchscreen gloves and the option of retrofitting your own gloves.
Another disadvantage is that sweat or moisture on the finger impair the function of the touchpad, so that input can be difficult at high temperatures, for example. In addition, touchpads are poorly suited for quick, precise inputs, such as those used in games.
Operating concepts / gestures
The vocabulary with regard to operation is expanded in particular through the possibilities of the multi-touchpad:
Horizontal or vertical movements with more than one finger can be interpreted as additional functions instead of moving the mouse (e.g. scrolling backwards / forwards).
Tap and hold
Double-clicking without lifting your finger after the second click and subsequent movement can, depending on the touchpad, be interpreted as a single click with subsequent drag-n-drop. Without this function, a drag-n-drop function that can only be operated via the touchpad would not be possible.
Pulling two fingers up or down over the touchpad at the same time is interpreted as scrolling by many manufacturers. Pressing the "mouse wheel button" can also be simulated by double-clicking with two fingers.
- CNET: How to hack your own touch screen gloves
- Andreas Sebayang: Clickpad - clickable touchpad without buttons from Synaptics. In: Golem.de . June 3, 2009, accessed June 27, 2015 .
- Clickpad software button behavior in the libinput documentation.