Touchscreen

A touch screen (rare name: " Touch Screen " ) is a combined input and output device, in which, by contact with parts of an image, the program flow of a technical device, usually a computer, can be directly controlled. The technical implementation of the command prompt is as it invisible to the user, thus creating the impression of a direct control of a computer by touching the screen. The image which is made touch-sensitive through it or underneath touchpad can be generated in several ways: by dynamically monitors via projection or physically (such as printing).

Instead of controlling a cursor with the mouse or the like, the finger or a stylus can be used. The display of a mouse pointer is unnecessary.

The analogy to the mouse click is a quick tap. By pulling the finger or stylus on the touch screen a " drag and drop " operation can be performed. Some systems can have multiple simultaneous touches to process commands (Multi- Touch), for example, to rotate the displayed items or to scale. The term " multi-touch " is used mostly in connection with the system's ability to recognize gestures ( eg " Wipe " to turn over a page ).

• 3.1 Application Examples of optical touch screens

Applications

Touchscreens find info monitors as, for example at trade shows, for guidance in major department stores, the operation of smartphones or for timetable information at stations use. Every now and then can also be found in the windows of pharmacies or tour operators touchscreens, can be accessed through the detailed information. In addition, touch screens are used in slot machines and arcade games. Often they are also used for the control of machines in industry ( Industrial PCs ), especially because they are less susceptible to dirt than other input devices such as keyboards. In some banks, there are ATMs with touchscreen display. In banks, they are becoming more frequently used for transfer terminals, wherein the SAW (Surface Acoustic Wave) is used because it is relatively vandal-proof. Scratched through its glass surface and it will not damage as quickly as example systems with resistive ITO film as a surface.

Touch screen terminals that are used for public information dissemination, are in the IT industry (abbreviated to POI) as a Point of Interest system or kiosk called. Terminals that are for sale are the point of sale, or abbreviated as POS. The latter have prevailed only partially meet the high expectations of the business and the IT industry. Reasons for this are in addition to the maintenance requirements for the equipment often the lack of adaptation of the software to the specific operating conditions of touchscreen devices, or often simply the unergonomic and unattractive software and lack of benefits for the operator.

In newer, modern cars multifunction displays often are always interpreted as a touch screen. New technologies offer here even an electronically generated, tactile perceptibility.

In home systems, touch screens have become widespread, especially in the field of PDAs, tablet PCs, smart phones and game consoles Nintendo DS, PlayStation Vita and Wii U, they are in greater use. The input pins used earlier due to the small screens and the unadjusted because user interfaces ( also: Stylus ) are quite unergonomic and have prevented the breakthrough of Touchsceens in this area a long time. Only with the projected - capacitive systems ( first in LG Prada ) has it changed significantly.

A touch screen is not mandatory mounted in front of a display, also use as a replacement of a membrane keyboard is possible. This is applied to a printed (polyester ) sheet ( at the point on the computer screen of the normally seated ) behind the touch screen. There are different approaches to solve the touch screen completely from physical monitors to make projections of user interfaces can be used interactively. Example of this is the now re- set "Virtual touch " by Siemens or different systems at the Fraunhofer Institute.

Operation

There are several operating principles for the implementation of contact sensitivity:

• Resistive systems
• Surface capacitive systems
• Projected capacitive systems
• Inductive systems
• SAW (Surface Acoustic Wave ) - " (sound ) wave- driven systems "
• Optical systems (usually infrared light grid in front of the monitor)
• Dispersive signal technology systems

The optical system

The first touch screens were curved tube Bildschrime facing a flat surface of the light matrix was stretched. The beams - each between a pair of LED and Sensor - ran in rows and columns between columns or rows of holes in the parapet of the screen enclosure framework and were disrupted by a fingertip. In order for a resolution of the order of 5 mm was realized, which was sufficient to choose a sufficiently gross buttons on-screen menus ( see picture). Today, the robustness because even at long planning screens of ATMs or ticket machines.

Resistive touchscreens

Resistive touchscreens respond to pressure, which connects two electrically conductive layers in places. The layers thus form a voltage divider, at which the electrical resistance is measured in order to determine the position of the pressure point. The name of the touchscreens on the English word resistivity due for ( electrical ) resistance.

They consist of an outer polyester layer and an inner glass or plastic pane, which are separated by spacers. The facing surfaces are coated with indium tin oxide, a light-transmitting semiconductor. The spacers are so small that they can be seen only by very close examination. They are called spacer dots, literally translated distance points.

To determine the position of the pressure point, a DC voltage is applied to the conductive layers., The voltage drops from an edge of the layer to the opposite edge through evenly. At the pressure point, the voltage of both layers is the same, because they are connected there. The second conductive layer is the compound of this point to the outside. Two voltages can be measured between the edge of the second layer, and the two opposite edges of the first layer. When both voltages are equal, the pressure point exactly in the middle between the two edges of the first layer. The higher a voltage relative to the other, the more the pressure point is removed from the respective edge.

An example:

• The touch screen is x = 75 mm wide.

• The voltage U is = 5 volts is applied between left and right edge of the lower layer.

• The upper layer is not connected to the external voltage.

• It is pressed at a point on the bottom. The resistors within the upper layer up to their edges play in the following consideration for the time being not important because high impedance is measured.

• On the edge ( an edge ) of the upper layer are measured the following voltages:

• The distances between the printing position and the edges of the touch screen are as follows:

It must always be carried out a second measurement of this kind, so that the distances to the other edges are calculated with exchanged roles of the two layers. Only then is the position in the area is found. To detect the two dimensions, the DC voltage is thus applied alternately across.

Four -Wire

Four -wire (four- wire ) is the simplest and oldest design to accomplish this intersection. The voltage is applied alternately to both conductive layers, each in a different orientation. Therefore, there are four wires for connection required, which gives its name to the whole.

Four -Wire has the disadvantage of quickly decreasing precision in detecting the pressure point. The outer polyester layer of the touch screen is mechanically loaded by its use. Thus, the conductive coating its inner side loses uniformity. This coating is of Four -wire but a measure of the position of the pressure point.

Five -Wire

Five -wire avoids the deterioration of precision by the outer conductive layer is not used as a measure for the position of the pressure point. It only serves to forward the tension of the lower layer and is connected with an additional fifth wire. The other four ports are located at the corners of the lower layer. Before each of the two measurements in each case two adjacent vertices are directly connected and then the voltage is applied to the two corner pairs. Between the first and second measurement is switched to the second possible set of corner pairs.

Six -Wire, Wire - Seven and Eight -Wire

Six - and Seven - Wire Wire are variations of Five -Wire, while Eight -Wire is a variation of Four -Wire. In these designs, the additional lines are used to not tap the measured voltages on the lead, but on separate test leads ( principle of the four-wire measurement).

Advantages and disadvantages of resistive touchscreens

Advantages:

• Operation with every possible Stylus
• Operated even when wearing gloves

Cons:

• Only limited multitouch ( Two - touch)
• Gesture operation only very limited
• Usually less accurate than capacitive touch screens
• Wear due to the mechanical loading when pressing
• Nuisance tripping during transport through contact with other objects possible

Application examples for resistive touch screens

• Tablet PCs
• Electronic organizers, PDAs
• Cell phones / smart phones with touch screen
• Industrial PCs, Panel PCs ( control of machines )
• Kiosk systems (for example, trade information systems)
• Automotive sector ( such as navigation systems, multimedia systems )
• Screens of in-flight entertainment in commercial aircraft
• Home entertainment
• Office equipment (such as copiers )
• All- in-one computer
• Coffee machines for home use
• Handheld consoles

Surface capacitive touch screens

A surface capacitive touchscreen is a coated with a transparent metal oxide film (usually laminated to glass). A voltage applied to the corners of the coating produces a constant AC voltage, uniform electric field. The touch results in a low charge transport that is measured in the discharge cycle in the form of a current at the corners. The resulting currents from the corners are in direct proportion to the touch position. The controller processes the information.

Projected Capacitive Touch

Another type (usually " PCT" = " Projected Capacitive Touch" or " PCAP " ) uses the two levels with a conductive pattern (usually stripes or diamonds). The planes are mounted isolated from each other. Up one level serves as a sensor, the other takes over the task of the driver. A finger is at the intersection of two strips, so changes the capacitance of the capacitor and there is a larger signal at the receiver strips on. The main advantage of this system is that the sensor can be mounted on the back of the cover glass ( the detection is " projected through ", hence the name). Thus, the operation is done on the virtually wear-free glass surface. Further, the detection of gestures and a plurality of contacts ( multi-touch so ) is possible. This touch version is now used by virtually all smartphones and tablet computers.

Capacitive touchscreens can only with the bare fingers ( if the touch screen is now touched with a hot or cold fingers, does not matter ), conductive styluses or specially-made tools, but are not covered by a conventional stylus or thick gloves. This restriction especially people with prosthetic hands are affected because they have only with special gloves or styluses the ability to activate the control panels. In this regard, capacitive systems are sometimes a hurdle in terms of accessibility.

Applications for Capacitive Touchscreens

• Tablet computer
• Electronic Organizers and PDAs
• Smart phones or cell phones with touch screen
• Portable Media Player
• Game consoles
• Restaurant systems

Inductive touch screen

Inductive touch screens have the advantage over the other two methods have the disadvantage that they can be used only on special input pins ( with an integrated coil), a technique that has been adopted by graphics tablets.

Nevertheless, they offer several advantages, not provided by other techniques and are, for example, often used in more expensive tablets and screens with integrated graphics tablet such as the Wacom Cintiq:

• In the writing position, no reaction is caused by the lying palm. For the other versions here, the software must detect and ignore, if the screen is touched with a pencil resting hand.
• The screen surface can - as with the projected - capacitive touch screens - are made of glass or a similarly sturdy material because there is no mechanical action, as in the resistive models is necessary.
• The pin position can also be determined if the pin does not touch the surface, but is in a ( small ) distance above it.
• Of the induced current can be used to operate additional pin elements, such as buttons or gauge in order to determine how tightly the pin is pressed onto the surface.
• Some models can also also determine the angle of inclination of the stylus.

Graphics programs can provide a more realistic behavior of the simulated pens and brushes by this additional information. Inductive touch screens are less suitable for portable devices due to the significantly higher energy demand.

Application examples for inductive touch-screens

• Tablet PCs, such as Surface Pro, FSC Stylistic 500, etc. (in conjunction with capacitive technology ), HP TC1100, HP Slate (in conjunction with capacitive technology ), IBM X61T. ( Wacom Technology )
• Wacom Cintiq ( screen with integrated graphics tablet )
• PocketBook Pro 603 & 903 (?)
• Various graphics tablets the low price range

Application examples for hybrid systems

These systems use several techniques to compensate for mutual disadvantages.

• Samsung Galaxy Note successor It is used, the capacitive technique of manual input and the inductive for the S -Pen, wherein the inductive technology increased priority.

• Pin to hand priority so that an undisturbed writing is possible

Examples of applications for optical touch screens

• Meters
• Bank terminals
• HP -150
• Sony PRS -650 eReader
• Kindle Touch
• Tolino Shine
• Evoluce ONE (Full - HD LCD, optical sensors track an unlimited number of inputs on or above the surface )