Different types of Keyboard Switches

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Types

[edit]Membrane keyboard

Main article: Membrane keyboard

There are two types of membrane-based keyboards, flat-panel

membrane keyboards and full-travel membrane keyboards:

Flat-panel membrane keyboards are most often found on appliances

like microwave ovens or photocopiers. A common design consists of

three layers. The top layer (and the one the user touches) has the labels

printed on its front and conductive stripes printed on the back. Under this

it has a spacer layer, which holds the front and back layer apart so that

they do not normally make electrical contact. The back layer has

conductive stripes printed perpendicularly to those of the front layer.

When placed together, the stripes form a grid. When the user pushes

down at a particular position, their finger pushes the front layer down

through the spacer layer to close a circuit at one of the intersections of

the grid. This indicates to the computer or keyboard control processor

that a particular button has been pressed.

Generally, flat-panel membrane keyboards do not have much of a "feel",

so many machines which use them issue a beep or flash a light when

the key is pressed. They are often used in harsh environments where

water or leak proofing is desirable. Although used in the early days of

the personal computer (on the Sinclair ZX80, ZX81 and Atari 400), they

have been supplanted by the more tactile dome and mechanical switch

keyboards. However, membrane keyboards with interchangeable key

layouts, such as the IntelliKeys and Discover:board are still commonly

used by people with physical, visual, or cognitive disabilities as well aspeople who require assistive technology to access a computer .

Full-travel membrane-based keyboards are the most common computer

keyboards today. They have one-piece plastic keytop/switch plungers

which press down on a membrane to actuate a contact in an electrical

switch matrix.



[edit]Dome-switch keyboard

How a dome-switch keyboard works: Finger depresses the dome to complete the circuit

Dome switches mesh with keys (keyboard is upside down in this image)

Dome switch keyboards are a hybrid of flat-panel membrane and

mechanical keyboards. They bring two circuit board traces together

under a rubber or silicone keypad using either metal "dome" switches or

polyester formed domes. The metal dome switches are formed pieces of stainless steel that, when compressed, give the user a crisp, positive

tactile feedback. These metal types of dome switches are very common,

are usually reliable to over 5 million cycles, and can be plated in either

nickel, silver or gold. The rubber dome switches, most commonly

referred to as polydomes, are formed polyester domes where the inside

bubble is coated in graphite. While polydomes are typically cheaper than

metal domes, they lack the crisp snap of the metal domes, and usually

have a lower life specification. Polydomes are considered very quiet, but

purists tend to find them "mushy" because the collapsing dome does not

provide as much positive response as metal domes. For either metal or

polydomes, when a key is pressed, it collapses the dome, which

connects the two circuit traces and completes the connection to enter

the character. The pattern on the PC board is often gold-plated.



Both are common switch technologies used in mass market keyboards

today. This type of switch technology happens to be most commonly

used in handheld controllers, mobile phones, automotive, consumer

electronics and medical devices. Dome switch keyboards are also called

direct-switch keyboards.

S ee also: Chiclet keyboard

[edit]Scissor-switch keyboard

Main article: S cissor-switch

A special case of the computer keyboard dome-switch is the scissor-

switch. The keys are attached to the keyboard via two plastic pieces that

interlock in a "scissor"-like fashion, and snap to the keyboard and the

key. It still uses rubber domes, but a special plastic 'scissors' mechanism

links the keycap to a plunger that depresses the rubber dome with a

much shorter travel than the typical rubber dome keyboard. Typically

scissor-switch keyboards also employ 3-layer membranes as the

electrical component of the switch. These stabilizing scissor-like devices

extend the lifespan of the membrane to as much as 10 million

keystrokes.[citation needed ]

They also usually have a shorter total key travel

distance (2 mm instead of 3.5 ± 4 mm for standard dome-switch

keyswitches). This type of keyswitch is often found on the built-in

keyboards on laptops and keyboards marketed as 'low-profile'. Thesekeyboards are generally quiet and the keys require little force to press.

Scissor-switch keyboards are typically slightly more expensive. They are

harder to clean (due to the limited movement of the keys and their

multiple attachment points) but also less likely to get debris in them as

the gaps between the keys are often less (as there is no need for extra

room to allow for the 'wiggle' in the key as you would find on a

membrane keyboard).[1]

[edit]Capacitive keyboard

In this type of keyboard, pressing the key changes the capacitance of a

pattern of capacitor pads. Unlike "dome switch" keyboards, the pattern

consists of two D-shaped capacitor pads for each switch, printed on

a printed circuit board (PC board) and covered by a thin, insulating film

of soldermask which plays the role of a dielectric. The mechanism of



capacitive switches is very simple, compared to mechanical ones. Its

movable part is ended with a flat foam element (of dimensions near to

a tablet of Aspirin) finished with aluminium foil below. The opposite side

of the switch is a PC board with the capacitor pads.

When a key is pressed, the foil tightly clings to the surface of the PC

board, forming a daisy chain of two capacitors between contact pads

and itself separated with thin soldermask, and thus "shorting" the contact

pads with an easily detectable drop of capacitive reactance between

them. Usually this permits a pulse or pulse train to be sensed. The keys

do not need to be fully pressed to be fired on, which enables some

typists to work faster.

As of 2008 they are a rare find in generic PC keyboards[citation

needed ]. Vintage PCs may in some cases be equipped with this type of keyboard, because the original IBM keyboards for the Personal

Computer, Personal Computer XT, and Personal Computer AT

were Model F keyboards, which used the buckling spring mechanism to

actuate a capacitative switch, unlike the 101-key Enhanced Keyboard,

also known as the Model M, which also had the buckling spring

mechanism, but a membrane contact switch. At the present time, the

best-known keyboard for use with desktop personal computers that uses

a capacitative switch is that made by Topre, either under its own name,or for Fujitsu, which sells a keyboard custom-manufactured for it to its

specifications as the Happy Hacking Keyboard. The Topre mechanism

uses a spring underneath a rubber dome, and the depression of the

spring causes a change in capacitance between the underlying capacitor

pads.

There are also industrial makes of flat-panel capacitive keyboards that

are inexpensive[citation needed ]

, and they resist wear, water, foreign objects

and dirt.[edit]Mechanical-switch keyboard

Mechanical-switch keyboards use real switches underneath every key.

Depending on the construction of the switch, such keyboards have

varying response and travel times. Notable keyboards utilizing this

technology are the Apple Extended Keyboard (the original and/or the



"II"), as well as its modern imitator, the Matias Tactile Pro. These two

keyboards use ALPS switches. On PCs, the OmniKey series

from Northgate Computers was popular, and the line is now carried

by Creative Vision Technologies under the Avant brand.

Cherry Corporation of Germany also makes mechanical switches used

in special-purpose and high-end keyboards. Their popular MX series of

keyswitches are available in five distinct designs, often referred to by the

color of the center stem to which the keycap attaches: Cherry MX Black

switches present a linear feel where the force increases as the key is

pressed, Cherry MX Brown switches provide tactile feedback as the

switch travels over a physical bump as the key hits its actuation point,

Cherry MX Blue switches utilize a tactile feel and also an audible click

sound just before reaching their actuation point, Cherry MX Clear switches contain a similar design as MX Browns but require more force

to depress and do not provide the audible click as found in the MX

Blues, and, lastly, Cherry MX Red switches possess an identical

construction as MX Blacks but require less force to depress. Each of the

switch designs is desirable for specific objectives: With games, having a

tactile bump is useless, so a smooth, linear switch is best, as found in

the MX Blacks and Reds. However, because the MX Reds require less

force to depress, they are less desirable in a gaming environment when

compared against the MX Blacks. MX Browns, Blues and Clears are

designed more with typing tasks in mind, owing to their tactile bump

either before or right at the actuation point. The Browns and Clears do

not contain an audible "click" sound as found in the Blues, and as such

are not quite as desirable in a straightforward typing scenario, instead

being considered as more of a "middle-ground" between typing and

gaming.

In India, the TVS Gold mechanical keyboard is very popular despite

costing about five times as much as a membrane keyboard.

[edit]Buckling-spring keyboard

Many typists prefer buckling-spring keyboards.[2]

The buckling

spring mechanism (expired U.S. Patent 4,118,611) atop the switch is

responsible for the tactile and aural response of the keyboard. This



mechanism controls a small hammer that strikes a capacitive or

membrane switch.[3]

In 1993, two years after spawning Lexmark, IBM transferred its keyboard

operations to the daughter company. New Model M keyboards continued

to be manufactured for IBM by Lexmark until 1996,

when Unicomp purchased the keyboard technology.

Today, new buckling-spring keyboards are manufactured by Unicomp.

Unicomp also repairs old IBM and Lexmark keyboards.

[edit]Hall-effect keyboard

Hall effect keyboards use magnets and Hall effect sensors instead of an

actual switch. When a key is depressed, it moves a magnet, which is

detected by the solid-state sensor. These keyboards are extremelyreliable, and are able to accept millions of keystrokes before failing. They

are used for ultra-high reliability applications, in locations like nuclear

powerplants or aircraft cockpits. They are also sometimes used in

industrial environments. These keyboards can be easily made totally

waterproof. They also resist large amounts of dust and contaminants.

Because a magnet and sensor is required for each key, as well as

custom control electronics, they are very expensive.

[edit]Laser keyboard

A laser projection device approximately the size of a computer mouse

projects the outline of keyboard keys onto a flat surface, such as a table

or desk. This type of keyboard is portable enough to be easily used with

PDAs and cellphones, and many models have retractable cords and

wireless capabilities. However, sudden or accidental disruption of the

laser will register unwanted keystrokes. Also, if the laser malfunctions,

the whole unit becomes useless, unlike conventional keyboards which

can be used even if a variety of parts (such as the keycaps) are

removed. This type of keyboard can be frustrating to use since it issusceptible to errors, even in the course of normal typing, and its

complete lack of tactile feedback makes it even less user-friendly than

the cheapest membrane keyboards.

[edit]Roll-up keyboard



Most keyboards are rigid, but this foldable keyboard demonstrates one of many variations from the usual.

Some keyboards are designed out of flexible materials that can roll up in

a moderately tight bundle. Normally the external materials are either

silicone or polyurethane. It is important to note that although many

manufacturers claim that the keyboards are foldable, they cannot be

folded without damaging the membrane that holds the circuitry. Typically

they are completely sealed in rubber, making them watertight like

membrane keyboards. Like membrane keyboards, they are reported tobe very hard to get used to, as there is little tactile feedback.

As of 2005, roll-up keyboards include:

the CoolMac keyboard [1],

the Eumax keyboard,

the VIK ("virtually indestructible keyboard") [2], [3],

the pocket VIK [4],

the Flexboard keyboard [5], the CoolMIR keyboard [6], and

theWhitelite FX100 Keyboard [7].

S ee Roll-away computer .

[edit]Optical keyboard technology



Also known as photo-optical keyboard, light responsive keyboard, photo-

electric keyboard and optical key actuation detection technology.

The optical keyboard technology has been introduced in 1962 by Harley

E. Kelchner ± for use in a typewriter machine with the purpose of

reducing the noise generating by actuating the typewriter keys.

An optical keyboard technology utilizes light-emitting devices and photo

sensors to optically detect actuated keys. Most commonly the emitters

and sensors are located in the perimeter, mounted on a small PCB.

The light is directed from side to side of the keyboard interior and it can

only be blocked by the actuated keys. Most optical keyboards require at

least 2 beams (most commonly vertical beam and horizontal beam) to

determine the actuated key. Some optical keyboards use a special key

structure that blocks the light in a certain pattern, allowing only onebeam per row of keys (most commonly horizontal beam).

The mechanism of the optical keyboard is very simple ± a light beam is

sent from the emitter to the receiving sensor, the actuated key

blocks, reflects, refracts or otherwise interacts with the beam, resulting in

an identified key.

Some earlier optical keyboards were limited in their structure and

required special casing to block external light, no multi-key functionality

was supported and the design was very limited to a thick rectangular

case. None of the known optical technologies were ever developed to a

mass production stage, with the exception of MOBBAL Keyboard

Technology by Aymer International. MOBBAL Technology allows almost

any shape and design of the keyboard, and can be used for laptop and

desktop keyboards, ATM keypads etc.

The advantage of the optical keyboard technology is that it offers a real

waterproof keyboard, resilient to dust and liquids, it is electromagnetic

emissions free (thus cannot be eavesdropped to wirelessly) and it uses

about 20% PCB volume, compare with the membrane keyboard or dome

switch keyboards, significantly reducing the electronic waste. The

advantage of the optical keyboard technology over other keyboards such

as Hall effect keyboard, laser keyboard, roll-up keyboard and

transparent keyboard lies in cost (Hall effect keyboard) and feel ± the



optical keyboard technology do not require different key mechanism,

typing tactile feeling remains to offer its user the same known feeling of

the keyboard, for over 60 years.

The specialist Datahand keyboard uses optical technology to sense

keypresses, with a single light beam and sensor per key. The keys are

held in their rest position by magnets; when the magnetic force is

overcome to press a key, the optical path is unblocked and the keypress

is registered.

[edit]Debouncing

When striking a keyboard key, the key oscillates against its contacts

several times before settling. When released, it bounces again until it

reverts to its rest state. Although it happens on such a small scale as tobe invisible to the naked eye, it's sufficient for the computer to register

multiple key strokes inadvertently.

To resolve this problem, the processor in a keyboard (or computer)

"debounces" the keystrokes, by aggregating them across time to

produce one "confirmed" keystroke that (usually) corresponds to what is

typically a solid contact. Early membrane keyboards limited typing speed

because they had to do significant debouncing. This was a noticeable

problem on the ZX81.[citation needed ]

[edit]Keytops

Keytops are used on full-travel keyboards. While modern keycaps are

typically surface-printed, they can also be 2-shot molded, laser printed,

sublimation printed, engraved, or they can be made of transparent

material with printed paper inserts.

There are also Keycaps, which are thin shells that are placed over

keytop bases. These were especially used on IBM PC keyboards.

[edit]

Different types of Keyboard Switches

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