A Joystick Is A Personal Computer Peripheral Or General Control

Joystick A joystick is a personal computer peripheral or general control device consisting of a handheld stick that pivots about one end and transmits its angle in two or three dimensions to a computer. Joysticks are often used to control video games, and usually have one or more pushbuttons whose state can also be read by the computer. The term joystick has become a synonym for game controllers that can be connected to the computer since the computer defines the input as a "joystick input". Apart from controlling games, joysticks are also used for controlling machines such as aircraft, cranes, trucks, powered wheelchairs and some zero turning radius lawn mowers. More recently miniature joysticks have been adopted as navigational devices for smaller electronic equipment such as mobile phones. Joysticks are significantly less accurate than a mouse-keyboard. This is one of the fundamental reasons why multiplayer console games are not compatible with PC versions of the same game

How Joysticks work ???????

Hydraulic joysticks The advent of hydraulics allowed controlling much higher levels of power via valves. A hydraulic joystick connects directly to low-pressure ( pilot) hydraulic valves, allowing an operator to control the high-pressure "working side" of the hydraulic system. The benefits of hydraulic joysticks over mechanical linkage or cable systems include simpler installation for complex control applications, the ability to substantially increase power, and minimize maintenance. As with mechanical controls, another significant advantage is the ability of the operator to feel any force feedback through the joystick. The disadvantages of pilot valve joysticks are the close proximity of pressurized hydraulic fluid to the operator, the temperature effect on hydraulic fluid performance, and the considerable cost of routing multiple hydraulic lines throughout the system. Hydraulic pilot valve joysticks gained widespread use on construction equipment, aerial work platforms, and forklifts. When this was the state-of-the-art technology, hydraulic joysticks were used in most applications of this type, because the advantages over mechanical linkages were many.

Hydraulic joysticks offer the simplicity of controlling pilotoperated valves directly, and without electronic controls that can add cost to systems. This makes them most attractive for smaller machines where the close proximity of pressurized hydraulic fluid is not objectionable. ELECTRIC JOYSTICK TECHNOLOGY.

Most electric joysticks operate on low-voltage DC circuits and can be located a long distance from the electrohydraulic valve they control. Wiring from the joystick to the valve is much easier and costs only a fraction of what would be required to route hoses and tubes from the joystick to the hydraulic valve. This allows the freedom to design a more ergonomic operator station without compromising the cost of the equipment. The primary disadvantage as compared to a manual or pilot-operated valve is the higher cost of the electrohydraulic valves.

Electric joystick types Electric joysticks are manufactured in a wide variety of types, ranging from large handoperated displacement and force controls to very small finger-operated devices. Each has its own niche application. Joysticks can be further classified into discrete control, which use switch contacts, or proportional control, which use potentiometers (pots), digital encoders, rotary variable differential transformers Displacement and force controls to very small finger-operated devices. Each has its own niche application. Joysticks can be further classified into discrete control, which use switch contacts, or proportional control, which use potentiometers (pots), digital encoders, rotary variable differential transformers (RVDTs), induction coils, or Halleffect devices. Force (nondisplacement) controls primarily use induction coils or strain gauges as output devices. Small finger-operated joysticks are also made in displacement and force types. Displacement joysticks in this category generally use potentiometers and Hall-effect devices for proportional output and microswitches for discrete output. Switching-type joysticks use high current and voltage mainly on equipment that requires stepped, discrete control of a motor drive. At the other end of the spectrum are fingeroperated joysticks that control microswitches. These are often used as simple discrete (bang-bang) controls — one switch closure in each direction — for single-speed directional control. The most-common use of a joystick is for proportional control of machinery through an electric motor control, electrohydraulic valve, hydraulic pump or computer.

Encoders and RVDTs are highly reliable, non-contacting output devices. Because of their large size and high cost, they are normally used in large controllers that are integrated into equipment that requires highly reliable components, where failure and downtime come at an extraordinarily high cost. Cranes used in metal-producing mills and containerhandling terminals are examples of applications using these devices. Strain gauge-type joysticks are generally relegated to use as small force-type joysticks. This leaves joysticks using pots, induction coil or Hall effect as the most-commonly preferred controllers. Of these three types, the joystick using a potentiometer as a primary output device is predominant. Pot joysticks using conductive plastic pots have published life spans in excess of 10 million cycles. In applications that don't have severe vibration, this duty cycle results in a very respectable lifetime for the joystick, if it is operated and maintained properly. Because pots are small devices, they can be included as components on both large and small joysticks. This allows flexibility in the design of machine control because the joysticks can be placed almost anywhere. Electronically, the pot output can be used directly, producing a variable DC voltage, or that signal can be processed further through circuitry to produce a pulse width modulated (PWM) signal, a digital serial stream (RS232, etc.) or other variants of analog and digital signals. Potentiometers also are relatively immune to electrical emissions from outside sources. This makes their operation predictable around high voltage power transmission lines or in any application where the joystick may come in close proximity to a strong electric field. As the most-widely used type of joystick, pots are found controlling the movements of excavators, agricultural equipment, aerial work platforms, scissor lifts, skid steer loaders, pavers, compactors and a wide variety of other construction equipment. The disadvantage of using a potentiometer in a joystick is realized only if the application involves very high duty cycle or vibration. A potentiometer is a variable resistive device using a delicate wiper contacting a resistive element. Although the joystick may be in neutral (center) position for much of the time a machine is active, vibration from the machine can continuously dither the pot wiper on the element and produce heavy wear in the center region. Devices using contacts are always subject to wear and potential failure, but the use of non-contacting technology is a way to avoid this. Non-contacting types The two most popular types of non-contacting joystick technologies are induction and Hall effect. Both offer highly reliable output at reasonable costs. In addition, the gear train used to drive potentiometers is eliminated, enhancing the reliability of the joystick even more. Inductive joysticks work on the principle of varying an induced field in a set of secondary coils by changing the relative position of a primary coil or ferrous shaft to the secondary coils. Protection from outside electrical fields is provided by an internal

detection system. The size and number of coils limit how small these joysticks can be practically manufactured. Hall-effect joysticks operate on the principle of varying voltage output by disturbing a current flow through interjection of a magnetic field. An advantage of Hall-effect technology over inductive technology is miniaturization of the output device and redundancy at a very modest cost. When properly designed and packaged, Hall-effect devices offer very high resistance to electromagnetic and radio frequency interference. Because the increase in reliability comes at little-to-no increase in cost, these joysticks can be used in all of the applications where the more-traditional potentiometertype joysticks fit.

JOYSTICKS HOW DIFFERENT TECHNOLOGY WORKS The various joystick technologies differ mainly in how much information they pass on. The simplest joystick design, used in many early game consoles, is just a specialized electrical switch. This basic design consists of a stick that is attached to a plastic base with a flexible rubber sheath. The base houses a circuit board that sits directly underneath the stick. The circuit board is made up of several "printed wires," which connect to several contact terminals. Ordinary wires extend from these contact points to the computer. The printed wires form a simple electrical circuit made up of several smaller circuits. The circuits just carry electricity from one contact point to another. When the joystick is in the neutral position -- when you're not pushing one way or another -- all but one of the individual circuits are broken. The conductive material in each wire doesn't quite connect, so the circuit can't conduct electricity.

Each broken section is covered with a simple plastic button containing a tiny metal disc. When you move the stick in any direction, it pushes down on one of these buttons, pressing the conductive metal disc against the circuit board. This closes the circuit -- it completes the connection between the two wire sections. When the circuit is closed, electricity can flow down a wire from the computer (or game console), through the printed wire, and to another wire leading back to the computer.

The Simplest System: Communication When the computer picks up a charge on a particular wire, it knows that the joystick is in the right position to complete that particular circuit. Pushing the stick forward closes the "forward switch," pushing it left closes the "left switch," and so on. In some designs, the computer recognizes a diagonal position when the stick closes two switches (for example, closing the forward switch and the left switch simultaneously would mean a forward/leftward diagonal position). The firing buttons work exactly the same way -when you press down, it completes a circuit and the computer recognizes a fire command.

Two variations on the "switch" design: In both, the stick's motion closes movable metal contacts.

This design communicates joystick motion in a sort of shorthand -- it processes movement as absolute values instead of subtle gradations. In other words, it can't distinguish between pressing forward on the stick a little bit and pushing it as far as it will go -- there is only one value for forward. This is fine -- even ideal -- for some games. It's the perfect design form something like Pac Man or Tetris, for example. But it can be fairly limiting for other games, such as flight simulators. In the next section, we'll look at the conventional analog joystick design that can pick up on subtle shifts in position.

Conventional Analog: Design In order to communicate a full range of motion to the computer, a joystick needs to measure the stick's position on two axes -- the X-axis (left to right) and the Y-axis (up and down). Just as in basic geometry, the X-Y coordinates pinpoint the stick's position exactly.

In the standard joystick design, the handle moves a narrow rod that sits in two rotatable, slotted shafts. Tilting the stick forward and backward pivots the Y-axis shaft from side to side. Tilting it left to right pivots the X-axis shaft. When you move the stick diagonally, it pivots both shafts. Several springs center the stick when you let go of it.

To determine the location of the stick, the joystick control system simply monitors the position of each shaft. The conventional analog joystick design does this with two potentiometers, or variable resistors. The diagram below shows a typical arrangement.

Conventional Analog: Potentiometers Each potentiometer consists of a resistor, in the form of a curved track, and a movable contact arm. The computer power supply conducts electricity to the input terminal, through the curved resistor, through the contact arm and back to the joystick port on the computer. By moving the contact arm along the track, you can increase or decrease the resistance acting on the current flowing through this circuit. If the contact arm is on the opposite end of the path from the input connection terminal, electricity will have to flow through a long length of resistor, so it will face maximum resistance. If the contact arm is near the input terminal, the potentiometer will have minimal resistance. Each potentiometer is connected to one of the joystick shafts so that pivoting the shaft rotates the contact arm. In other words, if you push the stick all the way forward, it will turn the potentiometer contact arm to one end of the track, and if you pull it back toward you, it will turn the contact arm the other way. Varying the resistance of the potentiometer alters the electrical current in the connected circuit. In this way, the potentiometer translates the stick's physical position into an electrical signal, which it passes on to the joystick port on the computer.

This electrical signal is totally analog -- it's a varying wave of information, like a radio signal. In order to make the information usable, the computer needs to translate it into a digital signal -- a strict numerical value.

The Problem with Analog There are a couple of big problems with the conventional analog joystick system. First of all, the crude analog-to-digital conversion process isn't very accurate, since the system doesn't have a true analog-to-digital converter. This compromises the joystick's sensitivity somewhat. Second, the host computer has to dedicate a lot of processing power to regularly "poll" the joystick system to determine the position of the stick. This takes a lot of power away from other operations. Next, let's take a look at how designers have addressed these problems to date. Joystick manufacturers have addressed these problems in a couple of different ways. One solution is to add a sensitive analog-to-digital converter chip in a specialized game adapter card or in the joystick itself. In this system, the converter spits out digital information directly to the computer, which improves the accuracy of the stick and reduces the work load on the host processor. These new joystick models can usually connect to USB ports, which also improves speed and reliability (see How USB Ports Work for details). Another solution is to skip the analog potentiometer technology all together. Many newer controllers use optical sensors to read stick movement digitally. The diagram below shows one common system.

In this system, the two shafts are connected to two slotted wheels. Each wheel is positioned between two light-emitting diodes (LEDs) and two photocells (the graphic only shows one photocell, LED pair for simplicity's sake). When light from each LED shines through one of the slots, it causes the photocell on the other side of the wheel to generate a small amount of current. When the wheel rotates slightly, it blocks the light and the photocell doesn't generate current (or it generates less, anyway). When the shaft pivots, it spins the wheel, and the moving slots repeatedly break the light beam shining on the photocell. This causes the photocell to generate rapid pulses of

current. Based on the number of pulses that the photocells have generated, the processor knows how far the stick has moved. By comparing the patterns coming from both photocells monitoring one wheel, the processor can figure out which way the stick is moving. This is the same basic system used in many computer mice. (Check out Electronics Circuits Reference Archive for more information.) One of the biggest additions to the world of joysticks is force feedback technology. In the next section, we'll find out how these joysticks let you experience the game on a new level.

Force Feedback The basic idea of a force feedback joystick (also called a haptic feedback joystick) is to move the stick in conjunction with onscreen action. For example, if you're shooting a machine gun in an action game, the stick would vibrate in your hands. Or if you crashed your plane in a flight simulator, the stick would push back suddenly. Force feedback joysticks have most of the same components as ordinary joysticks, with a few important additions -- an onboard microprocessor, a couple of electrical motors and either a gear train or belt system. The diagram below shows one simple design.

The X-axis and Y-axis shafts connected to the stick both engage a belt pulley. The other end of the belt for each axis engages a motor's axle. In this setup, rotating the motor axle will move the belt to pivot the shaft, and pivoting the shaft will move the belt to rotate the motor axle. The belt's function is to transmit and amplify the force from the motor to the shaft. Both an electrical signal from the onboard processor and the physical movement of the joystick will rotate the motor axle. In this way, you can still move the joystick even when the motor is moving it. On the opposite end of the motor, the axle is connected to the joystick's position sensors (its potentiometers or optical sensors, for example). Whenever the stick moves, whether due to the motor or the player, the sensors detect its position. The joystick has a built-in ROM chip that stores various sequences of motor movement. For example, it might have a machine gun sequence that instructs the motors to rapidly

change direction, or a bazooka sequence that instructs the motor to shift the joystick backward suddenly and then forward again. The game software requests a particular sequence, and the computer transmits the request to the joystick's onboard processor, which brings up the appropriate data from its own memory. This reduces the work load on the computer and makes for faster reaction times. As joysticks continue to evolve, manufacturers will take force feedback technology to whole new levels. This is great for avid gamers, of course, but it could also have a big effect on the rest of the population. Force feedback controller technology could lead to significant changes in industrial machinery, wheelchairs and other equipment for handicapped people, and even medical care. Researchers are also developing force feedback controllers to let people "feel" the Internet as they surf. The possible applications are endless! In the future, joysticks could be as ubiquitous as computer keyboards are today.

Industrial Applications In recent times, the employment of joysticks has become common place in many industrial and manufacturing applications, such as; cranes, assembly lines, forestry equipment, mining trucks, and excavators. In fact, the use of such joysticks is in such high demand, that it has virtually replaced the traditional mechanical control lever in nearly all modern hydraulic control systems. Due to the abusive nature of such applications, the industrial joystick tends to be more robust than the typical video-game controller, and able to function over a high cycle life. This led to the development and employment of Hall Effect sensing to such applications in the 1980s as a means of contactless sensing.

Assistive Technology Specialist joysticks, classed as an assistive technology pointing device, are used to replace the computer mouse for people with fairly severe physical disabilities. Rather than controlling games these joysticks plug into the USB port and control the mouse pointer. They are often useful to people with athetoid conditions, such as cerebral palsy, who find them easier to grasp than a standard mouse. Miniature joysticks are also available for people with conditions involving muscular weakness such as muscular dystrophy or motor neurone disease. They are also used on electric powered wheelchairs for control since they are simple and effective to use as a control method.

TRACKBALL

A trackball is a pointing device consisting of a ball housed in a socket containing sensors to detect rotation of the ball about two axes—like an upside-down mouse with an exposed protruding ball. The user rolls the ball with the thumb, fingers, or the palm of the hand to move a cursor. Large tracker balls are common on CAD workstations for easy precision. Before the advent of the touchpad, small trackballs were common on portable computers, where there may be no desk space on which to run a mouse. Some small thumbballs clip onto the side of the keyboard and have integral buttons with the same function as mouse buttons. An early example of the trackball, perhaps the earliest, was employed in the Canadian military's DATAR system.[1] When mice and trackballs still had chopper wheels, trackballs had the advantage of being in contact with the user's hand, which is generally cleaner than the desk or mousepad and doesn't drag lint into the chopper wheels. The late 1990s advent of scroll wheels, and the replacement of mouseballs by direct optical tracking, put trackballs at a disadvantage and forced them to retreat into niches where their distinctive merits remained important. Most trackballs now have direct optical tracking which follows dots on the ball. Some mice, in place of a scroll wheel, acquired a small trackball between the buttons, useful in maps and other circumstances calling for scrolling in two dimensions. Early Beginnings The trackball was actually invented circa 1949 by Tom Cranston and Fred Longstaff, two Canadian engineers who were working to develop a better way to coordinate target data displayed on a then state of the art radar system CRT display they were developing. Called "DATAR", the original trackball used a 4" Canadian duck pin bowling ball and weighed several pounds. The DATAR project was eventually cancelled but the idea of using the trackball to position a cursor and select items on a computer display screen using X-Y axis orthogonal outputs survived and trackballs ultimately ended up being incorporated into radar tracking and fire control systems by a number of defense contractors worldwide.

Special applications Large tracker balls are sometimes seen on computerised special-purpose workstations, such as the radar consoles in an air-traffic control room or sonar equipment on a ship or submarine. Modern installations of such equipment may use mice instead, since most people now already know how to use one. However, military mobile anti-aircraft radars and submarine sonars tend to continue using trackballs, since they can be made more durable and more fit for fast emergency use. Large and well made ones allow easier high precision work, for which reason they are still used in these applications (where they are often called "tracker balls") and in computer-aided design.

Ergonomics People with a mobility impairment use trackballs as an assistive technology input device. Access to an alternative pointing device has become even more important for them with the dominance of graphically-oriented operating systems. There are many alternative systems to be considered. The control surface of a trackball is easier to manipulate and the buttons can be activated without affecting the pointer position Some disabled users find trackballs easier since they only have to move their thumb relative to their hand, instead of moving the whole hand, while others incur unacceptable fatigue of the thumb. Elderly people sometimes have difficulty holding a mouse still while double-clicking; the trackball allows them to let go of the cursor while using the button.

Trackballs offer a number of advantages: •

Small Footprint - even large trackballs take less work surface area than what is routinely required to use a mouse. For comparison here's the footprint of a popular trackball model superimposed on the outline of a standard mouse pad. And remember, the trackball stays put.

•

Stationary Use - not having to move means a trackball: o Never runs out of work surface o Never requires re-positioning o Allows fast, continuous scrolling o Doesn't make you pick it up and put it back on the mouse pad. o Doesn't bump into your coffee cup. o Doesn't jam your thumb into the side of your keyboard o Is always where you left it. o Eliminates "mouse rowing" from the shoulder for long movements.

•

Precise Control - most modern trackballs allow you to control cursor movement with your finger tips or thumb. Much more precise than the hand and wrist movement required to move a mouse.

•

Self Cleaning - while some are better than others, most trackballs require little or no cleaning in normal use. Mice, on the other hand, either slide across or roll rubber coated or plastic balls across your desk or mousepad which generates static electricity and makes them magnets for dirt.

KEYBOARD A keyboard is a peripheral partially modeled after the typewriter keyboard.

Keyboard Basics A keyboard's primary function is to act as an input device. Using a keyboard, a person can type a document, use keystroke shortcuts, access menus, play games and perform a variety of other tasks. Keyboards can have different keys depending on the manufacturer, the operating system they're designed for, and whether they are attached to a desktop computer or part of a laptop. But for the most part, these keys, also called keycaps, are the same size and shape from keyboard to keyboard. They're also placed at a similar distance from one another in a similar pattern, no matter what language or alphabet the keys represent. Most keyboards have between 80 and 110 keys, including: • • • •

Typing keys A numeric keypad Function keys Control keys

The numeric keypad is a more recent addition to the computer keyboard. As the use of computers in business environments increased, so did the need for speedy data entry. Since a large part of the data was numbers, a set of 17 keys, arranged in the same configuration found on adding machines and calculators, was added to the keyboard. n 1986, IBM further extended the basic keyboard with the addition of function and control keys. Applications and operating systems can assign specific commands to the function keys. Control keys provide cursor and screen control. Four arrow keys arranged in an inverted T formation between the typing keys and numeric keypad move the cursor on the screen in small increments. Other common control keys include: •

Home, End ,Insert ,Delete ,Page Up,Page Down ,Control (Ctrl) ,Alternate (Alt) ,Escape (Esc)

Inside the Keyboard A keyboard is a lot like a miniature computer. It has its own processor and circuitry that carries information to and from that processor. A large part of this circuitry makes up the key matrix.

The microprocessor and controller circuitry of a keyboard

The key matrix is a grid of circuits underneath the keys. In all keyboards (except for capacitive models, which we'll discuss in the next section), each circuit is broken at a point below each key. When you press a key, it presses a switch, completing the circuit and allowing a tiny amount of current to flow through. The mechanical action of the switch causes some vibration, called bounce, which the processor filters out. If you press and hold a key, the processor recognizes it as the equivalent of pressing a key repeatedly. When the processor finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map in its read-only memory (ROM). A character map is basically a comparison chart or lookup table. It tells the processor the position of each key in the matrix and what each keystroke or combination of keystrokes represents. For example, the character map lets the processor know that pressing the a key by itself corresponds to a small letter "a," but the Shift and a keys pressed together correspond to a capital "A."

The key matrix

A computer can also use separate character maps, overriding the one found in the keyboard. This can be useful if a person is typing in a language that uses letters that don't have English equivalents on a keyboard with English letters. People can also set their computers to interpret their keystrokes as though they were typing on a Dvorak keyboard even though their actual keys are arranged in a QWERTY layout. In addition, operating systems and applications have keyboard accessibility settings that let people change their keyboard's behavior to adapt to disabilities.

Keyboard Switches Keyboards use a variety of switch technologies. Capacitive switches are considered to be non-mechanical because they do not physically complete a circuit like most other keyboard technologies. Instead, current constantly flows through all parts of the key matrix. Each key is spring-loaded and has a tiny plate attached to the bottom of it. When you press a key, it moves this plate closer to the plate below it. As the two plates move closer together, the amount of current flowing through the matrix changes. The processor detects the change and interprets it as a key press for that location. Capacitive switch keyboards are expensive, but they have a longer life than any other keyboard. Also, they do not have problems with bounce since the two surfaces never come into actual contact. All of the other types of switches used in keyboards are mechanical in nature. Each provides a different level of audible and tactile response -- the sounds and sensations that typing creates. Mechanical key switches include: • • • •

Rubber dome Membrane Metal contact Foam element

This keyboard uses rubber dome switches.

Rubber dome switches are very common. They use small, flexible rubber domes, each with a hard carbon center. When you press a key, a plunger on the bottom of the key pushes down against the dome, and the carbon center presses against a hard, flat surface beneath the key matrix. As long as the key is held, the carbon center completes the circuit. When the key is released, the rubber dome springs back to its original shape, forcing the key back up to its at-rest position. Rubber dome switch keyboards are inexpensive, have pretty good tactile response and are fairly resistant to spills and corrosion because of the rubber layer covering the key matrix. Rather than having a switch for each key, membrane keyboards use a continuous membrane that stretches from one end to another. A pattern printed in the membrane completes the circuit when you press a key. Some membrane keyboards use a flat surface printed with representations of each key rather than keycaps. Membrane keyboards don't have good tactile response, and without additional mechanical components they don't make the clicking sound that some people like to hear when they're typing. However, they're generally inexpensive to make. Metal contact and foam element keyboards are increasingly less common. Metal contact switches simply have a spring-loaded key with a strip of metal on the bottom of the plunger. When the key is pressed, the metal strip connects the two parts of the circuit. The foam element switch is basically the same design but with a small piece of spongy foam between the bottom of the plunger and the metal strip, providing a better tactile response. Both technologies have good tactile response, make satisfyingly audible "clicks," and are inexpensive to produce. The problem is that the contacts tend to wear out or corrode faster than on keyboards that use other technologies. Also, there is no barrier that prevents dust or liquids from coming in direct contact with the circuitry of the key matrix. SOME MODERN VERSIONS OF KEYBOARD Das Keyboard is a completely black keyboard with weighted keys that require more pressure from a person's strongest fingers and less pressure from the weaker ones. The Virtual Laser Keyboard projects a representation of a keyboard onto a flat surface. When used successfully, a person's fingers pass through the beam of infrared light above the projected surface, and a sensor interprets it as a keystroke. The True-touch Roll-up keyboard is flexible and can be rolled up to fit in a backpack or bag. Illuminated keyboards, like the Ion Illuminated Keyboard, use light-emitting diodes or electroluminescent film to send light through the keys or the spaces between keys. The Optimus keyboard has organic light-emitting diodes (OLEDs) in the keys. Users can change what letter, command or action each key represents, and the OLED can change to display the new information.

How a Keyboard works with a computer As you type, the processor in the keyboard analyzes the key matrix and determines what characters to send to the computer. It maintains these characters in its memory buffer and then sends the data. The following briefly describes a "dome-switch" keyboard (sometimes incorrectly referred to as a membrane keyboard), the most common type in use today: 1. When a key is pressed, it pushes down on a rubber dome sitting beneath the key. A conductive contact on the underside of the dome touches (and hence connects) a pair of conductive lines on the circuit below. 2. This bridges the gap between them and allows electric current to flow (the open circuit is closed). 3. A scanning signal is emitted by the chip along the pairs of lines to all the keys. When the signal in one pair becomes different, the chip generates a "make code" corresponding to the key connected to that pair of lines. 4. The code generated is sent to the computer either via a keyboard cable (using onoff electrical pulses to represent bits) or over a wireless connection. It may be repeated. 5. A chip inside the computer receives the signal bits and decodes them into the appropriate keypress. The computer then decides what to do on the basis of the key pressed (e.g. display a character on the screen, or perform some action). 6. When the key is released, a break code (different than the make code) is sent to indicate the key is no longer pressed. If the break code is missed (e.g. due to a keyboard switch) it is possible for the keyboard controller to believe the key is pressed down when it is not, which is why pressing then releasing the key again will release the key (since another break code is sent). Other types of keyboards function in a similar manner, the main differences being how the individual key-switches work. For more on this subject refer to the article on keyboard technology.

Connection TYPES Keyboard can be classified Here as Parallel and serial keyboards A parallel Keyboard send data as a byte in parallel form and all the bits are sent simultaneously on different lines . A serial keyboard send the data a bit by bit in serial fashion so we can reduce the number of wires between the keyboard and computer

Nowadays mostly serial keyboards are used …. Many keyboards connect to the computer through a cable with a PS/2 or USB (Universal Serial Bus) connector. Laptops use internal connectors. Regardless of which type of connector is used, the cable must carry power to the keyboard, and it must carry signals from the keyboard back to the computer. Wireless keyboards, on the other hand, connect to the computer through infrared (IR), radio frequency (RF) or Bluetooth connections. IR and RF connections are similar to what you'd find in a remote control. Regardless of which sort of signal they use, wireless keyboards require a receiver, either built in or plugged in to the USB port, to communicate with the computer. Since they don't have a physical connection to the computer, wireless keyboards have an AC power connection or use batteries for power.