Computer keyboard

A keyboard is an input device that includes as a control element with a plurality of the fingers to press keys. Today, most keyboards are electronic keyboards. There are also other functional principles, such as mechanical or pneumatic keyboards. Keyboards are available for a variety of technical devices, including computers, remote controls, telephones and cell phones. Other possible input devices and versions are listed below.

A computer keyboard has compared to a typewriter keyboard more keys that are used to operate the computer and its peripherals if necessary. The computer keyboard has some other key assignment and labeling. A fixed arrangement, there is not any system architecture offers certain Eigenständigkeiten, especially in notebooks arising from the space problem further differences. Significant differences from the typewriter keyboard are the lower stroke ( distance from the touch of the finger to the stop) and the reduced energy expenditure when pressing the buttons. Wherein the haptic is also different. Some computer keyboards are backlit so that the keys are visible even in the dark.

2.1 Keyboard types
2.2 Applications option

3.1 Ergonomic Keyboards
3.2 metal keyboards
3.3 Compact designs
3.4 island keyboard
3.5 LCD keypads
3.6 Projected virtual keyboard
3.7 Black Font Keyboard

4.1 beginnings
4.2 Standardization: IBM PC keyboard and Apple keyboard 4.2.1 PC keyboard
4.2.2 Apple keyboard

5.1 Input Devices according to the same principle of operation
5.2 Input devices using different operating principles

6.1 Mechanical keys
6.2 Capacitive Contact
6.3 Electro-mechanical short-stroke keys
6.4 Carbon contact with plastic plunger and silicone cover
6.5 Flexible membrane keypad with silicone superstructure
6.6 silicone keyboard (direct switching principle)
6.7 flat input principle ( metal snap dome on PCB )
6.8 Piezo switch
6.9 Hall sensor

Operation of the computer keyboard

Basically, it does not make sense to connect each button directly on the keyboard controller, which would require a large number of ports on the controller and appropriate wiring. The individual keys are instead disposed in an electrical matrix of row and column lines. If a key is pressed, a specific row with a specific column is electrically connected. This compound evaluates a microcontroller ( for example, in earlier XT keyboards, a microprocessor 8042 ) and sends this information to the computer - with the currently prevailing IBM PC architecture (even the Apple Macintosh) a so-called key code (english scan code ). Thus, for example in a 16 x 8 matrix of 24 lines up to 128 keys realized.

This operating principle is almost universally applicable to all modern input devices with multiple buttons. Some older architectures, the main processor itself took over the keyboard query, for example, when Commodore PET 2001, Commodore 64, Atari 800 and Sharp MZ- 700th

From the touch of a button to scan code

The keyboard matrix consisting for example of 13 columns and 8 rows (104 buttons). First, the output of the first column is activated ( due to the negative logic pulled to a low voltage ), and then checks whether or not in one or more of the eight inputs of the lines, this again is low voltage. Then the output of the first column is again ( high impedance ) is disabled and the activated for the second column, and so on. After the last column, possibly after a pause, starts again at the first column. This process is repeated continuously for at least a few dozen times per second, and is called "Scan". When a key is pressed, the compound identified in a certain column to the active line. From the coordinate within the column and row matrix of the keyboard processor detects a key number, which is then converted into a code for the key position, the scan code. This is transmitted to the computer. It does not matter which (national) keyboard layout (English " keyboard layout" ) is used; the scan code only indicates the position of the button pressed for a standard keyboard, regardless of the external arrangement, the language of the operating system or the type parameters.

More detailed information on the various scan codes, which are specifically used by today's Windows PC keyboards, and keyboard control codes can be found at scancode and keyboard layout.

Key rollover

Generally, it is a keyboard of an electronic musical instrument or a computer keyboard, it is possible that more than one key is pressed at the same time. Depending on the design of the keyboard, this, in the worst case, recognize a maximum of two simultaneous key presses correctly ( 2 -key roll over ) or in the best case, all ( n -key rollover ).

Depending on the arrangement of the keys in the matrix may lead to false positives in the simultaneous activation of three or more keys. This may be detected as active keys that are not actually operated, this effect is referred to as phantom key.

To explain a 6- key keyboard with two rows ( A, B) and three columns (1, 2, 3) is taken as an example. U = A1, y = B2 = A2 and v are pressed simultaneously, it is not possible to distinguish for the keyboard controller, if only x v or compressed or both. If line A is activated during scanning, the controller detects correct column 1 and 2 corresponding to u and v. However, if line B is active, the controller detects correct column 2 for y and falsely column 1 for x, because over y, v and u ( from line B to column 2, to row A to column 1) has a connection with column 1. In contrast, simultaneous actuation of w = z = A3 or B3 with u and y are not a problem and would reliably detected. Generally, this effect occurs when three corners of a rectangle to be pressed within the matrix.

A common countermeasure is the key matrix to be so arranged that such patterns do not occur at the usual key combinations. Here is exploited, for example, that only very rarely more than one character keys must be pressed simultaneously while about the combination of " signs and caps lock " is frequent. In addition, some keyboards have a limit on the number of keys that they recognize the same as pressed, for example, only two keys (2 -key roll over ).

Intelligent is a recognition of (possible) Phantom Keys. Since it is very unlikely that a person more keys as quick succession served that the keyboard controller can not detect a sequence of operating more, it is possible so long to realize more simultaneously active buttons until a combination occurs, a phantom -Key could contain. In the above example, this would mean that, for example, only u, then y are recognized as operating, it can not phantom -Key occur, so both keys are accepted. If now v added, the phantom - key effect and the keyboard controller creates ignores the keys v and x.

For cost reasons, can only be found in special applications is the option to put each key with a diode, so that the current can flow only from row to column and not vice versa (true n -key rollover ). However, this is dependent on the technology of the keypad does not always possible and in any case associated with higher production costs. A compromise solution is to seek a more favorable mix of key arrangement and diodes on some keys.

Transfer to PC

DIN 41524 connector and PS/2-interface

Both the pressing and releasing a key on the keyboard controller sends a code to the PC, which triggers an interrupt in this. The interrupt handler evaluates the scan code for each key that determines which ( key, Caps Lock, Num Lock, roles and introduction Shift, Ctrl, Alt, Alt Gr ) is the modifier keys in addition active, and stores the result in the keyboard buffer. The operating system or active application program works with software interrupts from this buffer and the associated scan code now with a character ( keycode ) as number, letter or punctuation, etc., or an action ( for example, program exit ). That is, the keyboard provides only key numbers and non-ASCII characters, this link will only take place in the software of the PC operating system or application program.

The communication between the keyboard and computer via a serial interface, so that only a few wires in the cable and only a compact connectors are required.

The predecessor of PS/2-interface was the PC / XT keyboard interface, which is cognate to the operation, but only allows the transfer of data from the keyboard to the computer. With the AT keyboard interface is bi-directional, in order to represent certain states such as Num Lock, Caps Lock and Scroll Lock LEDs can.

When PC/XT- and the AT interface is a five pin DIN connector used with the introduction of the IBM PS/2-Computerfamilie by a six- pin mini - DIN connector ( " PS/2-plug " ) was replaced was. Electrically AT interface and PS / 2 are identical, the protocol was amended for the PS/2-Tastaturen.

USB interface

The keyboard is handled by the host controller as a Class Human Interface Device. The necessary device drivers are already integrated into any USB - compatible operating system. The data transfer is done in interrupt transfer. Many wireless keyboards have a USB receiver, this log on to the system is equal to as wired keypads.

In contrast to PS/2- and ADB port the USB keyboard so-called make- or break codes, but a block of data with status information (flags ) for the shift keys and bytes for the other does not send at every depressing and releasing a key keys, in which the entire current status of the keyboard is provided.

The USB interface has certain advantages over the PS2 format:

Devices can be connected or removed while operation (so-called hotplug mechanism ).
The device port can be used universally, not only for keyboards.
Any number of keyboards are connected simultaneously, for example, additional keypad for left-handers
The integration of other devices with a USB port in the keyboard housing for space and cost savings are possible, for example, trackball, smart card reader, USB hub.
More different key codes are possible and thus more specialized function keys.

However, there are also disadvantages keyboards PS2 format:

The HID protocol supports a maximum of 6 keys pressed simultaneously common, while there is no restriction on PS / 2.
Behind the one used in standard USB label " interrupt transfer " actually hides a polling mode. The CPU polls the keyboard in a fixed time frame - typically every 8 ms - according to their condition, while PS / 2 offers real interrupt mode. This not only leads to higher latency, but also energy saving functions disabled because the CPU simply " sleep " until the next keystroke can not, but must actively check for input.

Large Font Keyboard

A large print keyboard for the visually impaired is equivalent to a conventional standard PC keyboard. The label, however, is significantly larger. The letters are here about 10 mm high, and fill the face of the individual keys. This makes them much easier to read than the default label. You can choose between different housing and font colors. In addition, the keyboard can be provided with tactile markings.

Keyboard types

Mostly large print keyboards for desktop computers are available. This is mainly to standard keyboards which are converted accordingly. However, some companies also offer keyboards with large font for laptops. Convert an existing laptop is not always possible. If required, you should contact the provider.

Possible use

When a large print keyboard can be used sensibly depends on the personal needs of the user. Large labeled keys are a useful facilities for computer users who are far from visually impaired and not feel safe on the keyboard. The large print is also good if you want to find rarely used keys relaxed. If you professionally or privately writes a lot, but you should be using the touch typing ( formerly known as touch-typing ) familiarize yourself. If you do not have to constantly look at the keyboard can be changed in an upright sitting posture and work with relaxed. Who sits bent forward to read the keyboard can, can pull tension in the neck, shoulder and back muscles.

Designs and materials

Ergonomic Keyboards

Since the 1990s, there are approaches certain problems that can arise when working with "normal" keyboards (eg RSI ) to counter with new ergonomic keyboards.

Therefore keyboards were put on the market (notably by the German company Marquardt in collaboration with the Fraunhofer Institute ) to allow a more natural position of the hands by a fatigue-free and healthy work. These keyboards are divided in two and A- shaped bent. Moreover, the two parts are increased as a swallow wing in itself and the keyboard can - optional - backwards fall, whereas " normal" increase keyboards backwards. The palm rest on a cushion. The ergonomic keyboard allows for a more natural writing posture than the normal keyboard, because the hands do not have to be bent outward and upward while writing, but stay with the forearm in a line. Disadvantage are those keyboards with the " two-finger search system " of Little writers and at the same time using mouse and keyboard.

Ergonomic keyboards should be used in conjunction with ergonomic computer programs that permit use even without a mouse. The earlier name Marquardt keyboard has not prevailed.

Metal keyboards

There are keyboards made of stainless steel, aluminum or other metals that are specifically designed for use in harsh, dirty environments or in public spaces. Application areas are:

Public telephone facilities
Web terminals (for example, in Internet cafes )
Information terminal for visitors (for example, in companies or museums)
Plants of the food industry
Medical

Metal keyboards are more resistant, easier to clean to mechanical stress, UV light and temperature insensitive. Disadvantages are the higher weight and higher manufacturing costs. Also for writing longer texts, they are not suitable, because the buttons are usually very hard to press.

Moreover, there is contamination resistant rubber keyboards. These are often used in garages or companies that work with liquids, such as oil.

Compact designs

Compact keyboards occupy a smaller footprint than conventional keyboards and are therefore particularly suitable for applications where little space is available, for example on the knees of wheelchair users. Another use case are so-called low-profile keyboards, which usually have a normal keyboard layout but much flatter (slim = " slim " ) are.

For applications where mobility is important, there are folding keyboards and keypads flexible plastic that can be rolled up. Rubber-made models are also waterproof and also against other liquids resistant. Folding and rubber keypads are offered as a supplement to the mounting position due to very small screen keyboards of PDAs, and other portable tablet computers like the iPad.

Island keyboard

As an island keyboard, island style, island - style or English Iceland style keyboard is called, in which there is a gap between the keys; the housing of the keyboard has accordingly individual holes for each key. Therefore, such a keyboard has a certain similarity to Radiergummitastaturen, which have also ( by design ) for each key a single hole. Accordingly, the English term can chiclet keyboard for both types are available.

LCD keypads

As early as 1985 a keyboard was presented, whose keys were provided with small LCDs, so their labeling by the user could be reprogrammed at any time. Due to the significantly higher price, such devices must be regarded as niche products. Even keyboards based on a touch screen could so far as a standalone peripheral device does not prevail.

Projected virtual keyboard

In this form of keyboard a projected keyboard is generated on any flat surface and captures the user action on it with a camera. The device detects by means of image processing, which fields are involved, and forwards the information to the computer on ( not to be confused with the virtual keyboard).

Black Font Keyboard

This term refers to in connection with keyboards for the blind every computer keyboard with printed characters on the keys as opposed to the specially developed for blind braille machine. With knowledge of the Tastschreibens and in conjunction with a Braille display, such a conventional keyboard can also be used by the blind.

Formation

Already the Z3 by Konrad Zuse had keys. First telegraph were used with mechanical typewriter keyboards. Later purely electronic keys were used. The layout and arrangement of keys was taken over by the typewriter. There were also various modifier keys. For decades, that almost every computer model had its specific keyboard. The result, especially in the period around 1980, the heyday of 8- bit home computer, to a huge variety. In addition to the occupancy of letters, numbers and special characters possessed some computer graphics characters, some even about programming commands ( for example, in BASIC) on the keyboard. Examples are the keyboards of the Commodore 64 or the Sinclair ZX81. Often a button with the logo of the manufacturer was present.

The more the IBM PC and its successors penetrated the market, initially supplanted the so-called XT keyboard, then AT keyboard and later the MF2 keyboard any other keyboard types. In addition to the PC keyboard has only still can claim the Apple keyboard today, but now has a very similar key assignment.

Standardization: IBM PC keyboard and Apple keyboard

PC keyboard

Due to the spread of the IBM PC was also the keyboard to the most commonly used type. Although the keyboards for IBM PCs follow a uniform standard, PC history have in 25 years due to expansions and local adaptations ( umlauts etc. ) developing many different types of keyboards:

83-Tasten-PC/XT-Tastatur: Function keys F1 to F10 leftmost vertical, common cursor control on numeric keypad, numeric keypad directly adjoins other keys, with some keys are not clearly assigned.
84-key AT keyboard Escape key: now the numeric pad, clearly separated from the rest of the keyboard numeric keypad, additional SysRq or SysRq key new protocol; This and the following are interconnected, but are not interchangeable with the PC / XT keyboard.
101-key - MF2 Keyboard: U.S. version 1985, so-called " Enhanced" layout with the model M, additional medium keypad with separate cursor keys separated from the numeric keypad and Esc and function keys now arranged horizontally across the top, new: F11 and F12, second Ctrl and second Alt key, divide key on the numpad, independent pause button for the independent SysRq key is omitted.
102 keys: Appropriate non- American version of the keyboard with 101 keys, additional key to the right of the left Shift key; first Alt - function (replaces second Alt key ); modified layout of the Enter key. Also used mostly for German keyboards.
104 keys: two Windows keys and a context menu button be introduced by Microsoft with the release of Microsoft Windows 95. These are placed to the left or right of the space bar (on the left between Ctrl / Ctrl key and Alt key, right between Alt Gr / key and Ctrl / Shift key).
105 keys: How difference of 101 to 102 keys.

Image of a U.S. keyboard with 104 keys
View of a British keyboard with 105 keys: How the U.S., only with an additional button to the right of the left Shift key and abgewandeltem layout of the Enter key
Image of a German keyboard with 105 keys: As the British, with only a few changes such as getauschtem Z and Y

Apple keyboard

The Apple keyboards differ only minimally from the PC keyboards. The extended Apple keyboard has 19 function keys. These are some with functions for controlling the volume ( quiet, loud, and dumb ) occupied. In addition, a button for ejecting optical media exists. Furthermore, the numeric keypad is arranged differently and has a special key that can be used program-specific. In addition to the space bar can be found on both sides of each one Ctrl or Control-click ( ^ ), a selection button ( ⌥ ) and a command key (⌘ ), with the help as well as with the shift keys not only the keyboard but also the mouse buttons in a variety of way multiple functions (up to 16-fold ) was used. The Druck-/Print-Screen-Taste, the roles / Scroll Lock key, the Pause button, the Insert / Insert key, the Alt Gr key as the Windows key does not exist on an Apple keyboard. The assignment of the @ sign is in Apple keyboards which do not have the U.S. occupation, different. The character is inserted at the German keyboard layout by pressing ⌥ ( Option key) L and with Swiss layout by ⌥ G.

For switching from a PC keyboard to the Mac affects most confusing probably the displacement of the square brackets and the amount of: the latter are in German and Swiss layout generated by ⌥ 8 or 9, ie on the keys corresponding to the round brackets, but with which the PC the square brackets are generated. These lie in the Apple keyboard on ⌥ 5 or 6 Also the pipe, the vertical bar is achieved not by ⌥ <, but via ⌥ 7. About ⌥ Shift 7 to get to the backslash.

In general, let Apple keyboards newer design (USB) also operate relatively smoothly on PC systems, the Command ( cmd) then acts as a Windows key. Thus, the right Alt key has the function of Alt Gr. The key assignment is otherwise used as a PC. The @ character is thus not on L and G, but on Q on German or Swiss 2 on keyboards.

Other Input Devices

Input devices according to the same principle of operation

Computer Keyboards: Big box keyboard, Kleinfeld keyboard, wireless keyboard, a Braille keyboard with six buttons
Keyboards on musical instruments: keyboard, pedal
A mobile phone keypad: The keypad represents characters using a multiple occupancy dar. on the digit keys
Industrial and specialty keyboards
Typewriter keyboard

Optimized keyboards for a particular purpose, so they are suitable worse circumstances for other purposes. Thus, at keypads transfer and ATMs that use a lot of different people, or are exposed to the elements, made of metal and have a low key game room up. This allows for durability and virtually indestructible properties, but no smooth writing.

Input devices for other operating principles

Even though the keyboard until today is the dominant input device, but a number of alternatives have been established over the decades.

An alternative is the so-called touchscreen. Here is a screen lying on the touch-sensitive fields that can be used for input. Through the combination of keyboard and screen in a device they can save space especially. The lack of tactile feedback, such as a pressure point as sensible entry confirmation is only important for inexperienced writers and data entry without visual feedback, and plays no role for entering text.

Other alternatives form so-called pointing devices. These are devices with which a pointer icon can be moved around the screen. Examples of pointing devices are: mouse, touchpad, joystick, trackball, trackpoint, light pen

Other alternatives are:

Laser keyboard. A key pad with a laser beam is projected on the table, or a surface light. The sampling is visually evaluated (see above for Projected virtual keyboard).
Screen keyboard. The keyboard is displayed on the screen and, for example, with a mouse or with a pen is operated ( when a touch panel or touch screen).

Key technology

Mechanical keys

Some of the traditional keyboards have a coil spring for resetting and a guide that will prevent jamming the key. Keys, which occupy more than one grid square, also have ironing that support a position balancing against tilting. Previously, springs usually stainless or corrosion -protected steel wire, today the buttons are easily at a lower height and suspension, pressure point latching, self-leveling ( also the longer keys) as well as assembly and disassembly is often achieved by a spread double scissors from self-lubricating plastic.

A variant of mechanical coil spring buttons from the 1980s, so-called buckling spring keys ( engl. " buckling spring" ), in which the spring is not compressed purely axial, but also vertically experiences forces and then suddenly under massive decreasing drag, fold over and turns on. The umknickenden springs produce a clear sound, which acts as acoustic feedback, the sudden decline in resistance acts as a tactile feedback. Known example of this technique is the IBM Model M- series, which was built between 1985 and 1999 and widely used.
Some notebook keyboards, such as HP / Compaq, Acer have, for each key scissor- like guides, fold the on depression as sun loungers. This mechanism consists of two closed sides, which are joined together at the ends by means of joints. These brackets are connected on the one hand at the lower ends to the printed circuit board and on the other hand at the opposite ends by means of snap connections to the underside of the printed key. In this way it is ensured that the keys - always be moved approximately perpendicular to the PCB - comparatively as scissor lifts.
Robust keypads may have a round, convex metallic leaf spring with a pressure point ( before jumping into the concave shape ), which requires a certain minimum force to overcome the signal or contactless rest position. Thus, the user is given a tactile feedback.

Capacitive Contact

( IBM Model F or Cherry - G3000 keyboard)

Mechanical support plate with guide movable plunger - these bear on the side of the board, a foam rubber pad with a metal foil which is covered with an insulating plastic film.
On the circuit board there are two adjacent surfaces, which are decoupled by an intervening, connected to ground conductor.
Upon depression of the plunger, the metal foil covers both surfaces, so that they are capacitively coupled with each other.

Electromechanical short-stroke keys

Discreet button in combination with a mechanical superstructure, carried out individually depending on the manufacturer.
Mounted directly on a printed circuit board, terminal lugs for electrical contacting.
Major manufacturers are Cherry GmbH with the MX-Key series, which is being built in many variants since about 1985, and ALPS with the same keys that were installed including in the first Apple keyboards.

Carbon contact with plastic plunger and silicone cover

Plastic housing for guiding a movable plunger - this carries a conductive contact pill on the board side.
Implementation of key - restoring force and sealing with a silicone cover.
Plunger with fitting operator side for receiving a key cap - mechanical recording of the entire unit in a metal support plate.

Flexible membrane keypad with silicone superstructure

(Separated at rest by a spacer) realization of the switch contact by two facing, conductive printed polyester films.
Actuation of the film, and the realization of the restoring force by a silicone mat.
Key cap is placed on the silicone pad.
Embedding of the whole in an array of front and backing plate.

Silicone keypad (direct switching principle)

Switching contact resulting from contact of the meander-shaped printed circuit board or a single layer conductive film, and the printed conductive pill at the bottom of an overlying silicone switching mat.
Embedding of the whole in an array of front and backing plate.

Flat input principle ( metal snap dome on PCB )

Switch contact is formed from PCB Contact and located thereabove metal snap disk (usually gold-plated ).
Embedding of the whole in an array of front and backing plate.

Piezo switch

Embedding a discrete piezo switching element in a metal front panel, alternatively use with piezoelectric paint printed films.
Key operation without tactile key stroke, evaluation of the impact load.

Hall sensor

A permanent magnet under each key drives past a Hall sensor on the bottom plate in the attack. The sensor registers the movement of the buttons magnets and reports them to the controller.
Hall keyboards are virtually indestructible, durable ( many manufacturers > 1,000,000 attacks as life on ) and insensitive to interfering electromagnetic fields and ionizing radiation. With appropriate design, they are also dustproof and waterproof.
Areas of application: on-board computer in airplanes and space ships, machine controls
Very expensive, since one sensor per key is required, therefore, hardly to be found in office applications. One of the few exceptions were some keyboards ( K7604 and K7606 ) of the East German manufacturer Robotron.

Others

As an aid to blind Writing Computer keyboards usually have two tactile markings on the keys of the letters F and J, as well as a marker for the center of the number field on the key for the digit 5 It is sensible surveys in the form of a point or a stroke ( sensing beams ), or a different shape of the tactile buttons. These facilitate the finding of the keys ( positioning ) and are therefore referred to as orientation keys.

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