Keyboard technology
Encyclopedia
There are many types of keyboard
s, usually differentiated by the switch
technology employed in their operation. Keyboards are defined by the number (usually about 80–110) of highly durable switches that are incorporated into the system. The choice of switch technology affects key response (the positive feedback that a key has been pressed) and travel (the distance needed to push the key to enter a character reliably). Newer models use hybrids of various technologies to achieve greater cost savings.
Flat-panel membrane keyboards are most often found on appliances like microwave oven
s or photocopier
s. 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 as people 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.
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.
See also: Chiclet keyboard
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).
(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 pad
s and itself separated with thin soldermask, and thus "shorting" the contact pad
s 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 . 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 , and they resist wear, water, foreign objects and dirt.
(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.
The buckling spring
mechanism (expired ) 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.
In 1993, two years after spawning Lexmark
, IBM
transferred its keyboard operations to the daughter company. New Model M keyboard
s 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.
keyboards use magnet
s and Hall effect sensor
s 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 extremely reliable, 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.
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 to be very hard to get used to, as there is little tactile feedback.
See Roll-away computer
.
Optical keyboard technology was 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 at 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 a vertical beam and a 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 one beam per row of keys (most commonly a horizontal beam).
The mechanism of the optical keyboard is very simple – a light beam is sent from the emitter to the receiving sensor, and 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 keyboard and can be used for laptop and desktop keyboards, ATM keypads, etc.
The advantages of optical keyboard technology are that it offers a real waterproof keyboard, resilient to dust and liquids; it is electromagnetic emissions free (thus cannot be eavesdropped wirelessly); and it uses about 20% PCB volume, compared with membrane or dome switch keyboards, significantly reducing electronic waste
.
Additional advantages of optical keyboard technology over other keyboard technologies such as Hall effect, laser, roll-up, and transparent keyboards lie in cost (Hall effect keyboard) and feel – optical keyboard technology does not require different key mechanisms, and the tactile feel of typing has remained the same 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 magnet
s; when the magnetic force is overcome to press a key, the optical path is unblocked and the keypress is registered.
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.
There are also Keycap
s, which are thin shells that are placed over keytop bases. These were especially used on IBM PC keyboards.
microcontroller
variant. The keyboard switch matrix is wired to its inputs and it processes the incoming keystrokes and sends the results down a serial cable (the keyboard cord) to a receiver in the main computer box. It also controls the illumination of the "caps lock
", "num lock
" and "scroll lock
" lights.
A common test for whether the computer has crashed is pressing the "caps lock" key. The keyboard sends the key code to the keyboard driver
running in the main computer; if the main computer is operating, it commands the light to turn on. All the other indicator lights work in a similar way. The keyboard driver also tracks the shift
, alt
and control
state of the keyboard.
. It has a switch at some or all intersections, much like a multiplexed display
. Almost all keyboards have only the switch at each intersection, which causes "ghost keys" and "key jamming" when multiple keys are pressed (see rollover
). Certain, often more expensive keyboards have a diode between each intersection, allowing the keyboard microcontroller to accurately sense any number of simultaneous keys being pressed, without generating erroneous ghost keys..
Computer keyboard
In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches...
s, usually differentiated by the switch
Switch
In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....
technology employed in their operation. Keyboards are defined by the number (usually about 80–110) of highly durable switches that are incorporated into the system. The choice of switch technology affects key response (the positive feedback that a key has been pressed) and travel (the distance needed to push the key to enter a character reliably). Newer models use hybrids of various technologies to achieve greater cost savings.
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 oven
Microwave oven
A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...
s or photocopier
Photocopier
A photocopier is a machine that makes paper copies of documents and other visual images quickly and cheaply. Most current photocopiers use a technology called xerography, a dry process using heat...
s. 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
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
(on the Sinclair ZX80
Sinclair ZX80
The Sinclair ZX80 is a home computer brought to market in 1980 by Science of Cambridge Ltd. . It is notable for being the first computer available in the United Kingdom for less than a hundred pounds...
, ZX81
Sinclair ZX81
The ZX81 was a home computer produced by Sinclair Research and manufactured in Scotland by Timex Corporation. It was launched in the United Kingdom in March 1981 as the successor to Sinclair's ZX80 and was designed to be a low-cost introduction to home computing for the general public...
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
Physical disability
A physical disability is any impairment which limits the physical function of one or more limbs or fine or gross motor ability. Other physical disabilities include impairments which limit other facets of daily living, such as respiratory disorders and epilepsy....
, visual
Visual impairment
Visual impairment is vision loss to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive...
, or cognitive disabilities as well as people who require assistive technology
Assistive technology
Assistive technology or adaptive technology is an umbrella term that includes assistive, adaptive, and rehabilitative devices for people with disabilities and also includes the process used in selecting, locating, and using them...
to access a computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
.
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.
Dome-switch keyboard
Dome switch keyboards are a hybrid of flat-panel membraneMembrane keyboard
A membrane keyboard is a computer keyboard whose "keys" are not separate, moving parts, as with the majority of other keyboards, but rather are pressure pads that have only outlines and symbols printed on a flat, flexible surface...
and mechanical keyboards. They bring two circuit board traces together under a rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
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.
See also: Chiclet keyboard
Chiclet keyboard
A chiclet keyboard or island-style keyboard is a computer keyboard built with an array of small, flat rectangular or lozenge-shaped rubber or plastic keys that look like erasers or "Chiclets", a brand of chewing gum manufactured in the shape of small squares with rounded corners...
Scissor-switch keyboard
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. 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'. These keyboards 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).
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 boardPrinted circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
(PC board) and covered by a thin, insulating film of soldermask which plays the role of a dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing 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
Tablet
A tablet is a pharmaceutical dosage form. It comprises a mixture of active substances and excipients, usually in powder form, pressed or compacted from a powder into a solid dose...
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 pad
Contact pad
Contact pads are designated surface areas of a printed circuit board or die of an integrated circuit. Possibilities to contact to pads include soldering, wirebonding, Flip chip mounting, or probe needles....
s and itself separated with thin soldermask, and thus "shorting" the contact pad
Contact pad
Contact pads are designated surface areas of a printed circuit board or die of an integrated circuit. Possibilities to contact to pads include soldering, wirebonding, Flip chip mounting, or probe needles....
s 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
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
keyboards . Vintage
Retrocomputing
Retrocomputing is the use of early computer hardware and software today. Retrocomputing is usually classed as a hobby and recreation rather than a practical application of technology; enthusiasts often collect rare and valuable hardware and software for sentimental reasons...
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
Model M Keyboard
The Model M keyboard is a class of computer keyboards manufactured by IBM, Lexmark and Unicomp, starting in 1984. The many different variations of the keyboard have their own distinct characteristics, with the vast majority having a buckling spring key design and many having fully swappable keycaps...
, 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
Fujitsu
is a Japanese multinational information technology equipment and services company headquartered in Tokyo, Japan. It is the world's third-largest IT services provider measured by revenues....
, which sells a keyboard custom-manufactured for it to its specifications as the Happy Hacking Keyboard
Happy Hacking Keyboard
The Happy Hacking Keyboard is a small computer keyboard produced by PFU Limited of Japan, co-developed with Japanese computer pioneer Eiiti Wada...
. 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 , and they resist wear, water, foreign objects and dirt.
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 KeyboardApple Extended Keyboard
The Apple Extended Keyboard is a keyboard that was first sold separately alongside the Macintosh II and SE.Later the Apple Extended Keyboard II prepackaged with Apple Professional Desktops during the early 1990s...
(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
Northgate Computers
Northgate Computer Systems, Inc., based in Eden Prairie, Minnesota, USA, was a mail-order personal computer company, founded in 1987 by Arthur Lazere....
was popular, and the line is now carried by Creative Vision Technologies under the Avant brand.
Buckling-spring keyboard
Many typists prefer buckling-spring keyboards.The buckling spring
Buckling spring
A buckling spring is a type of keyswitch mechanism, popularized by IBM's keyboards for the PC, PC/AT, 5250/3270 terminals, PS/2, and other systems. It was used by IBM's Model F keyboard, and the more common Model M. It is described in ....
mechanism (expired ) 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.
In 1993, two years after spawning Lexmark
Lexmark
Lexmark International, Inc. is an American corporation which develops and manufactures printing and imaging products, including laser and inkjet printers, multifunction products, printing supplies, and services for business and individual consumers...
, IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
transferred its keyboard operations to the daughter company. New Model M keyboard
Model M Keyboard
The Model M keyboard is a class of computer keyboards manufactured by IBM, Lexmark and Unicomp, starting in 1984. The many different variations of the keyboard have their own distinct characteristics, with the vast majority having a buckling spring key design and many having fully swappable keycaps...
s continued to be manufactured for IBM by Lexmark until 1996, when Unicomp
Unicomp
Unicomp is a manufacturer of computer keyboards and keyboard accessories based in Lexington, Kentucky. The company was founded in April 1996 when they purchased the license to the buckling-spring keyboard technology from Lexmark International, Inc.Unicomp's product line consists mostly of...
purchased the keyboard technology.
Today, new buckling-spring keyboards are manufactured by Unicomp. Unicomp also repairs old IBM and Lexmark keyboards.
Hall-effect keyboard
Hall effectHall effect
The Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...
keyboards use magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s and Hall effect sensor
Hall effect sensor
A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications....
s 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 extremely reliable, 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.
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 is susceptible 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.Roll-up keyboard
Like membrane keyboards, they are reported to be very hard to get used to, as there is little tactile feedback.
See Roll-away computer
Roll-away computer
A Roll-away computer is an idea introduced as part of a series by Toshiba in 2000, which aimed to predict the trends in personal computing five years into the future...
.
Optical keyboard technology
Also known as photo-optical keyboard, light responsive keyboard, photo-electric keyboard, and optical key actuation detection technology.Optical keyboard technology was 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
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
and photo sensors
Photoelectric sensor
A photoelectric sensor, or photoeye, is a device used to detect the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are used extensively in industrial manufacturing. There are three different functional types: opposed ,...
to optically detect actuated keys. Most commonly the emitters and sensors are located at the perimeter, mounted on a small PCB
Printed circuit board
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board or etched wiring...
. The light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
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 a vertical beam and a 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 one beam per row of keys (most commonly a horizontal beam).
The mechanism of the optical keyboard is very simple – a light beam is sent from the emitter to the receiving sensor, and the actuated key blocks, reflects
Reflection
Reflection or reflection may refer to:-Science:* Mirror image, a reflection in a mirror or in water* Reflection nebula, a nebula that is extended and has no boundaries* Reflection , a common wave phenomenon...
, refracts
Refraction
Refraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
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 keyboard and can be used for laptop and desktop keyboards, ATM keypads, etc.
The advantages of optical keyboard technology are that it offers a real waterproof keyboard, resilient to dust and liquids; it is electromagnetic emissions free (thus cannot be eavesdropped wirelessly); and it uses about 20% PCB volume, compared with membrane or dome switch keyboards, significantly reducing electronic waste
Electronic waste
Electronic waste, e-waste, e-scrap, or Waste Electrical and Electronic Equipment describes discarded electrical or electronic devices. There is a lack of consensus as to whether the term should apply to resale, reuse, and refurbishing industries, or only to product that cannot be used for its...
.
Additional advantages of optical keyboard technology over other keyboard technologies such as Hall effect, laser, roll-up, and transparent keyboards lie in cost (Hall effect keyboard) and feel – optical keyboard technology does not require different key mechanisms, and the tactile feel of typing has remained the same for over 60 years.
The specialist Datahand
Datahand
The DataHand keyboard was introduced in 1995 by DataHand Systems, Inc. Before that it was produced by Industrial Innovations as early as 1992. The keyboard consists of two completely separate "keyboards", one for the left hand and one for the right, that are molded to rest your hands in. This...
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 magnet
Magnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s; when the magnetic force is overcome to press a key, the optical path is unblocked and the keypress is registered.
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 to be 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.
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 Keycap
Keycap
A keycap is a small plastic cover placed over the keyswitch of a computer keyboard. Keycaps are illustrated to indicate the key function or alphanumeric character they correspond to...
s, which are thin shells that are placed over keytop bases. These were especially used on IBM PC keyboards.
Other parts of the PC keyboard
The modern PC keyboard also includes a control processor and indicator lights to provide feedback to the user about what state the keyboard is in. Depending on the sophistication of the controller's programming, the keyboard may also offer other special features. The processor is usually a single chip 8048Intel 8048
The MCS-48 microcontroller series, Intel's first microcontroller, was originally released in 1976. Its first members were 8048, 8035 and 8748....
microcontroller
Microcontroller
A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...
variant. The keyboard switch matrix is wired to its inputs and it processes the incoming keystrokes and sends the results down a serial cable (the keyboard cord) to a receiver in the main computer box. It also controls the illumination of the "caps lock
Caps lock
Caps lock is a key on many computer keyboards. Pressing it sets an input mode in which typed letters are uppercase by default. The keyboard remains in caps lock mode until the key is pressed again...
", "num lock
Num lock
Num Lock is a key on the numeric keypad of most computer keyboards. It is a toggle key, like Caps Lock and Scroll Lock. Its state is commonly represented by an LED light built into the keyboard....
" and "scroll lock
Scroll lock
Scroll lock is a keyboard button on some computer keyboards. The key is not frequently used and therefore some keyboards lack Scroll Lock altogether....
" lights.
A common test for whether the computer has crashed is pressing the "caps lock" key. The keyboard sends the key code to the keyboard driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
running in the main computer; if the main computer is operating, it commands the light to turn on. All the other indicator lights work in a similar way. The keyboard driver also tracks the shift
Shift key
The shift key is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters. There are typically two shift keys, on the left and right sides of the row below the home row...
, alt
Alt key
The Alt key on a computer keyboard is used to change the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key. For example, simply pressing "A" will type the letter a, but if you hold down either Alt key while pressing A, the computer...
and control
Control key
In computing, a Control key is a modifier key which, when pressed in conjunction with another key, will perform a special operation ; similar to the Shift key, the Control key rarely performs any function when pressed by itself...
state of the keyboard.
Keyboard switch matrix
The keyboard switch matrix is often drawn with horizontal wires and vertical wires in a grid which is called a matrix circuitKeyboard matrix (music)
Most electronic keyboards used in synthesizers, electronic organs, and digital pianos use a keyboard matrix circuit to connect the switches for each key. In this matrix circuit, the rows and columns are made up of wiring...
. It has a switch at some or all intersections, much like a multiplexed display
Multiplexed display
Multiplexed displays are electronic displays where the entire display is not driven at one time. Instead, sub-units of the display are multiplexed, that is, driven one at a time, but the electronics and the persistence of vision...
. Almost all keyboards have only the switch at each intersection, which causes "ghost keys" and "key jamming" when multiple keys are pressed (see rollover
Rollover (key)
Rollover is the ability of a computer keyboard to correctly handle several simultaneous keystrokes.-Normal typing:During normal typing on a conventional computer keyboard, only one key is typically being pressed by the user at any given time; each key is released before the next key is struck. ...
). Certain, often more expensive keyboards have a diode between each intersection, allowing the keyboard microcontroller to accurately sense any number of simultaneous keys being pressed, without generating erroneous ghost keys..