Computer keyboards can be classified by the switch technology they use. Computer alphanumeric keyboards typically have 80 to 110 durable switches, generally one for each key. The choice of switch technology affects the key response (positive feedback that the key has been pressed) and the pre trip (the distance required to push the key to enter the character reliably). Newer keyboard models use hybrids of various technologies to achieve greater cost savings.
Video Keyboard technology
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Membran keyboard
There are two types of membrane-based keyboards, flat-panel membrane keyboard, and full travel membrane keyboard:
Flat panel membrane keyboards are most commonly found in appliances such as microwave ovens or copiers. The general design consists of three layers. The top layer has a label printed on the front and a conductive line printed on the back. Below has a spacer layer, which holds the front and back layers separately so they usually do not make electrical contact. The rear layer has a conductive line that is printed perpendicular to the front layer. When placed together, the lines form a box. When the user presses at a certain position, their finger pushes the front layer down through the spacer layer to close the circuit at one of the grid intersections. This indicates to the computer or keyboard the processor controls that certain keys have been pressed.
Generally, flat panel membrane keyboards do not produce real physical feedback. Therefore, devices that use this issue beep or flash light when the button is pressed. They are often used in harsh environments where water or anti-leaking is required. Although used in the early days of personal computers (the Sinclair ZX80, ZX81 and Atari 400), they have been replaced by more tactile domes and mechanical switchboards.
The full membrane-based keyboard is the most common computer keyboard today. They have a one-piece plastic keytop/switch plunger that presses the membrane to drive the contacts in the matrix of the electrical switch.
Keyboard dome key
The dome-switch keyboard is a hybrid of a flat-panel membrane and a mechanical switch keyboard. They carry two traces of circuit boards together under a rubber or silicon keypad using a metal "dome" or dome-shaped switch that forms polyurethane. Metal dome switches are formed pieces of stainless steel which, when compressed, gives the user fresh and positive tactile feedback. These types of metal dome switches are very common, usually reliable for more than 5 million cycles, and can be plated in either nickel, silver or gold. Dome rubber switches, most commonly referred to as polydoms, form a polyurethane dome where the inner bubbles are coated with graphite. While polydomis are usually cheaper than metal dome, they do not have a sharp dome snap, and usually have lower life specifications. Polydoms are considered very quiet, but purists tend to find them "soft" because the collapsed dome does not give as many positive responses as metal dome. For metal or polydom, when the button is pressed, it disables the dome, which connects two traces of the circuit and completes the connection to enter the characters. Patterns on PC boards are often gold-plated.
Both are common switch technologies used in bulk market keyboards today. This type of switch technology is most commonly used in handheld controllers, cell phones, autos, consumer electronics, and medical devices. The switch-dome keyboard is also called the keyboard of the direct switch.
Slide-shift Keyboard
The special case of a dome-switch computer keyboard is the scissors. The buttons are attached to the keyboard through two plastic pieces that adhere to the "scissor-like" style, and snap to the keyboard and key. It still uses a rubber dome, but a special plastic 'scissor' mechanism connects keycap to a pusher which compresses the rubber dome with a much shorter ride than the regular rubber dome keyboard. Usually the keyboard-switch-scissor also uses a 3-layer membrane as an electrical component of the switch. They also typically have shorter key travel distances (2 mm instead of 3.5-4 mm for standard dome button switches). These keyswitch types are often found on the built-in keyboard and laptops that are marketed as 'low-profile'. The keyboard is generally quiet and the buttons require a bit of power to press.
Keyboard switches-scissors are usually slightly more expensive. They are harder to clean (due to the limited movement of locks and some of their attachment points) but are also less likely to get the debris inside because the gap between the buttons is often smaller (since there is no need for extra space to allow 'shake' in key, as is usually found on the membrane keyboard).
Capacitive keyboard
On this keyboard type, pressing the button will change the capacitance of the capacitor bearing pattern. This pattern consists of two D-shaped capacitor pads for each switch, printed on a printed circuit board (PCB) and covered by thin and thin insulation films of soldermask acting as dielectric.
Despite the sophistication of the concept, the capacitive switching mechanism is physically simple. The movable part ends with a flat foam element the size of an aspirin tablet, which ends with aluminum foil. Opposite switch is PCB with capacitor pads. When the lock is pressed, the foil tightly attaches to the PCB surface, forming a daisy chain of two capacitors between the contact pads and itself separated by a thin soldermask, and thus "shorting" the contact pads with a decrease in easily detectable capacitive reactance. among them. Usually this allows pulses or pulse trains to be felt. Since the switch has no actual electrical contact, no debouncing is required. The keys do not need to be fully pressed to move, allowing multiple people to type faster.
The best known companies for their capacitive (electrostatic) switching technology are Topre Corporation of Japan. Unfortunately, their products are not available in most parts of the world.
Keyboard mechanical button
Each button on the keyboard of the mechanical switch contains a complete switch underneath. Each switch consists of housing, springs, and rods. Switches come in three variants: linear with consistent resistance, and tactile with unheard bulges, or touch with audible clicks. Depending on the resistance of the spring, the key requires a different amount of pressure to move. The shape of the bar varies the distance of actuation and the travel distance of the switch. The number of votes generated by actuation can also be changed. The mechanical keyboard allows to remove and replace the lock button.
The mechanical keyboard also has a longer lifespan than the membrane keyboard or dome, with an expected period of 50 million clicks per switch for the Cherry MX switch, while the switch from Razer has an identifier life of 60 million clicks per key.
The mainstream mechanical switch manufacturer is Cherry. Alps Electric, the former major producer, ended production in the early 2000s. The Alps style buttons continue to be made in smaller quantities by Matthias. Companies such as Cooler Master, Corsair, Razer, Thermaltake, Logitech and SteelSeries offer a variety of mechanical keyboard models targeted to gamers.
Keyboard springs
Many typists prefer spring buckling keyboard. The buckling spring mechanism (expiration U.S. Patent 4.118.611 ) above the switch is responsible for the tactile and aural keyboard responses. This mechanism controls the small hammer that attacks the capacitive switch or the membrane.
In 1993, two years after spawning Lexmark, IBM shifted its keyboard operation to the princess company. The new M Model Keyboard continued to be produced for IBM by Lexmark until 1999, when Unicomp purchased keyboard technology.
Today, the new spring-buckling keyboard is produced by Unicomp. Unicomp also fixes old IBM and Lexmark keyboards.
Keyboard Hall-effect
Hall effect boards use magnets and Hall effect sensors instead of switches with mechanical contacts. When the key is pressed, it moves the magnet detected by the solid state sensor. Since they do not require physical contact for actuation, the Hall-effect keyboard is very reliable and can accept millions of keystrokes before it fails. They are used for ultra-high reliability applications such as nuclear power plants, aircraft cockpits, and critical industrial environments. They can be easily made completely waterproof, and can withstand dust and contaminants in large quantities. Because magnets and sensors are required for each key, as well as custom electronic controls, they are expensive to produce.
Laser projection keyboard
Laser projection devices roughly the size of a computer mouse project the outline of a keyboard button to a flat surface, such as a desk or table. Keyboards of this type are portable enough to be used easily with PDAs and mobile phones, and many models have retractable cables and wireless capabilities. However, a sudden or accidental disruption of the laser will register unwanted keystrokes. Also, if the laser malfunctions, the whole unit becomes useless, unlike conventional keyboards that can be used even if various parts (such as keycaps) are removed. Keyboard of this type can be frustrating because it is prone to error, even in normal typing, and the lack of tactile feedback makes it even more user-friendly than the lowest quality membrane keyboard.
Keyboard scroll
Keyboards made of flexible silicone or polyurethane materials can be rolled in tight enough bundles. Folding the keyboard tightly can damage the internal membrane circuitry. When they are completely sealed in rubber they are waterproof. Like membrane keyboards, they are reportedly very difficult to use, because there is little feedback, and silicon will tend to attract dirt, dust, and hair.
Optical keyboard technology
Also known as photo-optical keyboards, light responsive keyboards, photo-electric keyboards, and optical key actuation detection technology.
Optical keyboard technology was introduced in 1962 by Harley E. Kelchner for use in typewriters with the aim of reducing the resulting noise by moving the typewriter.
Optical keyboard technology uses light-emitting devices and photo sensors to detect optically driven keys. Most common emitters and sensors are located on the perimeter, mounted on a small PCB. The light is directed from side to side of the interior of the keyboard, and can only be blocked by the actuated keypad. Most optical keyboards require at least 2 beams (most often vertical beams and horizontal beams) to determine which keys are moved. Some optical keyboards use special key structures that block light in certain patterns, allowing only one beam per row of keys (most often horizontal beams).
The optical keyboard mechanism is very simple - light beam is sent from the emitter to the receiver sensor, and the key block is driven, reflecting, refracting or interacting with the light, generating the identified keys.
Some of the earlier optical keyboards are limited in structure and require special casing to block external light, no multi-key functionality is supported and the design is very limited to thick rectangular boxes.
The advantage of optical keyboard technology is that it offers a real waterproof keyboard, resistant to dust and liquids; and uses about 20% of the PCB volume, compared to a membrane or dome switch keyboard, significantly reducing electronic waste. The added advantage of optical keyboard technology versus other keyboard technologies such as Hall effects, lasers, roll-ups and transparent keyboards lies in cost (Hall effect keyboard) and nuances - the optical keyboard technology does not require different lock mechanisms, and the nuances of touch typing remain the same over more than 60 years.
Keyboard DataHand specialists use optical technology to sense key presses with single light rays and sensors per key. Keys are held in their resting positions with magnets; when the magnetic force is overcome to press the button, the optical path is opened and the button is pressed.
Maps Keyboard technology
Debouncing
When pressing the keyboard button, the button oscillates (or bounces) against its contact several times before it settles. When it is released, it oscillates again until it returns to its resting state. Although it happens on a small scale as it is invisible to the naked eye, it is enough for the computer to register some key blows by mistake.
To overcome this problem, the processor on the keyboard "debounces" keystrokes, by combining it all the time to produce a "confirmation" keystroke (usually) in accordance with what is usually a solid contact. Early membrane keyboards have limited typing speeds as they have to do significant debouncing. This is a real issue on ZX81.
Keycaps
Keycaps are used on full travel keyboards. While modern buttons are usually printed on the surface, they can also be printed twice, laser-printed, sublimation prints, engraved, or they can be made of transparent material with printed paper inserts.
There is also a button that is a thin shell placed on top of the main base. This is used on the IBM PC keyboard.
Other parts of the PC keyboard
The modern PC keyboard also includes a control processor and indicator lights to provide user feedback on keyboard status. Depending on the sophistication of the controller program, the keyboard can also offer other special features. Processor is usually one chip 8048 variant microcontroller. The keyboard switch matrix is ​​connected to its input and processes incoming keystrokes and sends the result down the serial cable (keyboard cable) to the receiver in the main computer box. It also controls the "caps lock", "num lock" and "scroll lock" lighting.
Common test whether the computer is stuck pressing the "caps lock" key. The keyboard sends the lock code to the keyboard driver running on the main computer; if the main computer is operating, it commands the lights on. All other indicator lights work in the same way. The keyboard driver also tracks the status of shift, alt, and keyboard controls.
Keyboard switch matrix
Keyboard keyboard matrices are often drawn with horizontal cables and vertical cables in a grid called a matrix circuit. It has switches at some or all intersections, very similar to multiplexed displays. Almost all keyboards only have buttons at each intersection, which causes "ghost keys" and "key interruptions" when multiple keys are pressed (rollover). Certain keyboards, often more expensive, have diodes between each intersection, allowing the microcontroller keyboard to accurately sense a number of simultaneous keys being pressed, without producing the wrong ghost keys.
References
External links
- Schofield, Jack (May 9, 2014). "Which ThinkPad laptop has the best keyboard?". The Guardian . Retrieved January 4 2018 . < span>
Source of the article : Wikipedia
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