Input Devices
Keyboard
The main device for entering information into a computer is keyboard , which is a set of mechanical sensors that sense pressure on the keys and close a certain electrical circuit in one way or another. There are currently two common types keyboards: with mechanical or membrane switches. In the first case, the sensor is a traditional mechanism with contacts made of a special alloy. In the second case, the switch consists of two membranes: the upper one is active, the lower one is passive, separated by a third membrane gasket.
As a rule, inside the case any keyboards In addition to the key sensors, there are electronic decoding circuits and a microcontroller. Exchange of information between keyboard And system board carried out according to special serial interface 11-bit blocks. Basic operating principle keyboards consists of scanning the key switches. The closing and opening of any of these switches corresponds to a unique digital code - a scan code. When the key is released, keyboard IBM PC AT precedes the scan code with the code F016. When the controller keyboards detects a key being pressed or released, it triggers the hardware interrupt IRQ1. If in keyboards computers such as IBM PC XT, data transfer can only be carried out in one direction, then in keyboards such as the IBM PC AT, such a connection is already possible in two directions, i.e. keyboard can accept special teams(setting the auto-repeat delay and auto-repeat frequency parameters). Connection keyboards To system board performed via electrically identical 5 DIN 5 or 6 mini- connectors DIN, the latter was first introduced in the IBM PS/2, from where it inherited its “slang” name. To provide bidirectional communication, a single data line is used, however, requiring open collector pins.
Mouse
The first computer mouse created by Douglas Engelbart in 1963 at the Stanford Research Center. Spreading mice received due to increased popularity software systems With graphical interface user. Mouse makes it convenient to manipulate such widely used objects in graphics packages as windows, menus, buttons, icons, etc.
First mouse when moving, it rotated two wheels, which were connected to the axes of variable resistors. Moving the cursor like this mice caused by changing the resistance of variable resistors. Most modern mice have an optical-mechanical design (Fig. 16.1). With a surface on which to move mouse, a heavy rubber-coated ball of relatively large diameter comes into contact. When moving mice this ball can rotate two perpendicular rollers pressed against it. The axis of rotation of one of the rollers is vertical, and the other is horizontal. On the axis of the rollers there are sensors installed, which are disks with slots, on opposite sides of which there are LED optocouplers. photodiode". The order in which the photosensitive elements of one axis are illuminated determines the direction of movement mice, and the frequency of impulses coming from them is speed.
Rice. 16.1. Optical-mechanical mouse device
Another popular design mice is an all-optical design. Using an LED and a lens system that focuses its light, mouse a section of the surface is highlighted. The light reflected from this surface is in turn collected by another lens and hits the receiving sensor of the image processor chip. This chip takes pictures of the surface underneath mouse With high frequency and processes them. Based on the analysis of a series of consecutive images, which are a square matrix of pixels of different brightness, the integrated DSP processor calculates the resulting indicators indicating the direction of movement mice along the X and Y axes, and transmits the results of its work to the peripheral interface. Main characteristics that ensure reliable operation of optical mice, are determined technical parameters sensors used (Table 16.1).
Trackball is an “inverted” optical-mechanical mouse- it is not the body of the device itself that is set in motion, but only its ball. This can significantly improve the accuracy of cursor control and, in addition, save space, which is why trackballs are often used in laptops.
Touchpad(touchpad or trackpad) is an input device used in laptops that moves the cursor depending on the movements of the user's finger. Used as a replacement for computer mice. The advantages of touch panels are:
there is no need for a flat surface, as for mice;
The location of the touchpad is usually fixed relative to keyboards;
To move the cursor to the entire screen, just move your finger a little;
working with them does not require much getting used to, as, for example, in the case of a trackball.
The disadvantage of touch panels is their low resolution, which makes it difficult to work in graphic editors and 3D games.
Joystick is an analog coordinate information input device, usually made in the form of two rheostatic sensors with a +5 V power supply. The joystick handle is connected to two variable resistors that change their resistance as it moves. One resistor determines movement along the X coordinate, the other - along the Y coordinate. The joystick is usually connected to a game port adapter located on a Multi I/O Card or sound card (in the latter case, the game port connector is combined with the MIDI interface) .
Light pen works using a small optical detector located at its tip. As the electron beam scans the screen, a pulse is initiated in the optical detector when the beam reaches a point on the screen over which the pen is located. The timing of this pulse relative to the horizontal and vertical sync signals allows the position of the light pen to be determined. At its core, the light pen is an extension of the video system. The connector for connecting a light pen was mandatory for CGA video adapters, was found from time to time on EGA video adapters, but practically disappeared with the spread of VGA.
2.4. Scanner
Scanner is a device that allows you to enter into a computer images of images presented in the form of text, drawings, slides, photographs or other graphic information. Scanners can be classified according to the following criteria:
According to the degree of transparency of the input original image:
opaque originals (photos, drawings, pages of books and magazines), with the image taken in reflected light;
transparent originals (slides, negatives, films), and the light passing through the original is processed.
By kinematic mechanism scanner:
manual scanners- the problem of smooth and uniform movement of the scanning head over the corresponding image (on which the quality of the scanned image depends) rests with the user;
tablet scanners- the scanning head moves relative to the paper using a stepper motor;
roll scanners- individual sheets of documents are pulled through the device so that the scanning head remains in place (not applicable for scanning books and magazines);
projection scanners- the entered document is placed on the scanning surface with the image up, while the scanning unit is also on top, and only the scanning device moves (scanning projections of three-dimensional objects is possible).
By type of input image:
black and white (line or halftone);
To communicate with a computer scanners, as a rule, use one of the universal peripheral interfaces: SCSI, IEEE 1284 or USB.
To unify the driver application programming interface scanner(and digital cameras) in 1992, the TWAIN specification was developed by Aldus, Caere, Eastman Kodak, Hewlett Packard and Logitech 6) .
1. Keyboard. The keyboard keys are connected to a matrix of contacts. Each key or key combination is assigned its own number (code). There is a separate microprocessor inside the keyboard. Each press of a key closes a contact. In this case, in accordance with the contact matrix, the microprocessor generates a code for the pressed key. This code is stored in a special area (microprocessor buffer) and becomes available for processing software. The keyboard driver is usually supplied with operating system. This program allows the user to select the alphabet and implement the key layout.
All keys can be divided into the following groups:
Alphanumeric keys;
Cursor keys;
Special control keys;
Function keys;
Additional keyboard.
| Home | Move the cursor to the first position of the line |
| End | Move the cursor to the last position of a line |
| PgUp | Move through text towards the beginning of one page (usually 25 lines) |
| PgDn | Move text forward one page towards the end of the text |
| Ins | Switching the keyboard from replace mode to insert mode and back |
| Delete | Deleting the character indicated by the cursor on the screen |
| Esc | Cancel any actions or exit the program |
| Ctrl | |
| Alt | Used with other keys, changing their actions |
| Enter | Key for entering information and carriage return, used to complete the entry of the next line |
| Backspace | Move back one screen position to the left, deleting the previous character |
| Tab | Moving the cursor to the right by the number of positions specified on request or, predetermined by the program, moving |
| Shift | Case change key |
| Print Screen | Printing information displayed on the screen |
| Caps Lock | Fixing uppercase/lowercase letters |
| Num Lock | Fixing the operating modes of the small numeric keypad |
| Scroll Lock | Switching the display mode |
| Pause/Break | Interrupting (pausing) the execution of programs and procedures, such as displaying information on the screen |
Function keys F1-F12 are located at the top of the keyboard. These keys are designed for various special actions; they are programmable for everyone software product have their purpose.
2. Manipulators. Mouse manipulator– a command input device, which is a small device with several keys. Moving the mouse pointer across the screen is done by moving the mouse across the table. There are mechanical, optical and wireless devices. The mechanical device consists of a rubber ball that rotates when the mouse moves, and two mutually perpendicular rollers. The roller rotation sensors transmit signals to the computer. The “tail” of wires through which signals travel gives the device the name “mouse.” Electronic motion devices use the principle of processing reflected light pulses from the surface on which the mouse moves. Such devices are much more reliable than mechanical ones. Mice are produced that transmit information to the computer via an infrared channel (wireless). The characteristic of a mouse is resolution. It is measured in dpi (dot per inch - dots per inch). If a mouse has a resolution of 900 dpi and is moved 1 inch (2.53 cm) to the right, then the mouse drive receives information through the microcontroller about a shift of 900 units to the right. The ballistic effect is the dependence of the accuracy of mouse positioning on the speed of its movement. The mouse driver is supplied with the device. Modern operating systems contain drivers for most manipulators of this type and automatically select the most suitable one when you turn on the computer.
Joystick– control device in computer games. It is a lever on a stand that can be tilted in two planes. The lever may contain various types of triggers and switches. The word “joystick” is also commonly used to refer to a control lever, for example, in a mobile phone.
Light pen– one of the tools for entering graphic data into a computer. Externally, it looks like a ballpoint pen or pencil connected by a wire to one of the computer’s I/O ports. Typically, a light pen has one or more buttons that can be pressed by the hand holding the pen. Inputting data using a light pen involves touching or drawing lines with the pen on the surface of the monitor screen. A photocell is installed in the tip of the pen, which registers changes in the brightness of the screen at the point with which the pen comes into contact, due to which the corresponding software calculates the position "pointed" by the stylus on the screen and can, depending on need, interpret it in one way or another, usually as an indication of an object displayed on the screen or as a drawing command. The buttons are used similarly to the buttons of a mouse manipulator - to perform additional operations and enable additional modes.
3. Scanner– translation device graphic information to digital. The function of a scanner is to obtain an electronic copy of a document created on paper. The lamp illuminates the scanned text, the reflected rays fall on a photocell consisting of many photosensitive cells. Each of them, under the influence of light, acquires electric charge. The analog-to-digital converter assigns a numerical value to each cell, and this data is transmitted to the computer. Scanners are hand-held and desktop (portable page or sheet-fed, flatbed, slide scanners, drum scanners); they can be black and white (up to 64 shades of gray) and color (256 - 16 million colors).
Handheld scanners in appearance they resemble a large “mouse” that the user moves over the scanned image. However, manually moving the device across paper small size of the covered scanning area do not provide sufficient speed and require careful joining of individual sections of the image.
Main distinguishing feature flatbed scanner– the scanning head moves relative to the stationary paper. They are simple and easy to use, allowing you to scan images from individual sheets, as well as from books and magazines.
With handheld page scanners, the paper moves relative to the scanning head. They are quite compact, but it is unlikely that you can scan a drawing from a book with them. This type of scanner is used to input document pages in formats from business cards to A4; the automatic paper feeding system ensures uniform scanning across the entire width of the sheet.
Slide scanners are highly specialized devices designed to capture images from transparent material (photographic film) with high resolution and image quality. They have a pronounced professional focus and high cost.
Drum scanners are professional stationary devices, intended for use in printing and scanning of large-format images. The main advantages are high speed and scanning accuracy due to a permanently fixed scanning element and high uniformity of rotation of the drum with the scanned image placed on it.
The main characteristics are:
Resolution ( optical resolution), that is, the number of recognized dots (pixels) per inch;
Scanning speed is a performance indicator that is equal to the time spent processing one line of an image;
Dimensions of the scanned sheet (scanning area);
The width of the bit representation - determines maximum number colors or shades of gray that the scanner can perceive.
The scanner driver is designed to control the scanning process and configure basic scanner parameters. Sometimes drivers are supplemented with means for manipulating scanned images (change brightness, contrast, etc.). Scanners can be used to easily transfer images (photos, drawings, etc.) into computer memory or onto a display screen, or for quickly entering text documents. In the second case from graphic image it is necessary to select (recognize) letters, numbers, spaces, tabs, columns, that is, convert the image into text format. Optical character recognition programs are designed to convert scanned texts into text codes.
4. Touch devices. Digitizer(graphics tablet) is a device for entering handwritten drawings directly into a computer. Consists of a pen and a flat tablet that is sensitive to pressure or proximity of the pen.
Main user characteristics:
The working area is usually equal to one of the standard paper formats (A7-A0);
Resolution – step of reading information;
The number of degrees of freedom describes the number of characteristics of the relative position of the tablet and the pen. The minimum number of degrees of freedom is 2 (X and Y positions of the projection of the sensitive center of the pen), additional degrees of freedom may include pressure, tilt of the pen relative to the plane of the tablet.
Touchpad (Touchpad) is a pointing input device, most often used in laptops. Touchpads work by measuring the capacitance of your finger or measuring the capacitance between the sensors. Capacitive sensors are located along the vertical and horizontal axes of the touchpad, which allows you to determine the position of your finger with the required accuracy. Since the device operates by measuring capacitance, the touchpad will not work if you move a non-conductive object, such as the base of a pencil, over it.
Mouse
Keyboard
Input devices
Timer
Power supply
Controllers
For a computer to work, information must be exchanged between RAM and external devices. This exchange is called “input-output”.
For each external device the computer has electronic circuit which controls it. This circuit is called a controller, or adapter (from the English “controller” - “controller”, “manager”). There is a disk drive controller, a monitor controller, a printer controller, etc. Some controllers can control several devices at once.
One of the controllers that is present in almost every computer is the I/O port controller. These ports are of the following types:
· parallel (designated LPT1-LPT4), printers are usually connected to them;
· serial (COM1-COM3), through which a mouse, modem, etc. are usually connected;
USB – port (digital devices, electronic device- flash memory, etc.)
These are in-machine Digital Watch. The timer is connected to an autonomous power source - a battery and continues to work when the machine is disconnected from the network.
2.3 Data input/output devices, their types and main characteristics
The keyboard is the main device for entering information into Personal Computer. Currently, there are a large number of types of keyboards, differing mainly in ergonomic qualities. Additional devices such as a microphone, acoustic system, touchpad, etc. The keyboard can be equipped with additional keys, for example Start, for use on computers with an operating system Windows system. Despite these innovations, the main purpose of the keyboard is to enter character information. The keyboard contains 101 or more keys (for mobile computers the number of keys is significantly less).
A mouse is a manipulator designed for the convenience of entering information into a computer. The mouse does not replace the keyboard. The mouse has become widespread on computers that use graphics software shells. The mouse has two or three buttons. A two-button wash may have a special wheel (scrolling) between the keys for quick view multi-page information. The rocking middle button has the same purpose. Mechanical mice use a ball that transmits mouse movement to special sensors. More accurate positioning allows you to achieve optical mouse. The mouse can be connected to a computer via a serial COM port, PS/2 port, USB port. The last option is preferable. Are used and wireless mice, operating in the infrared range or radio frequencies.
Joystick - a lever manipulator for entering coordinate information.
Trackball is an inverted mouse with an enlarged ball that must be rotated with your finger.
Trackpoint is a small joystick that is usually located in the center of the keyboard. Controlled by pressing your finger.
A touchpad is a pad that is sensitive to finger pressure.
Keyboard.Keyboard called a device for manually entering information into a computer. Modern types of keyboards differ mainly in the principle of generating a signal about a key press. The most common keyboards have a dome under each key made of special rubber, which bends when a key is pressed and closes the contacts with a conductive layer located on the dome. Some keyboards have a magnet under each key, which, when pressed, moves and passes through the coil, inducing a self-induction current in it.
Among modern types of keyboards we can note wireless keyboard, in which information is transferred to the computer using an infrared radiation sensor, similar to control panels for various household appliances. This keyboard allows you to work in any user-friendly place in the room, without being tied to the location of the system unit. It can also be noted flexible rubber keyboard, which operates silently, is protected from mechanical and chemical destructive influences, is very thin and can be rolled into a cylinder.
Keyboard processor, which processes signals from the keyboard, determines the number of the key that was pressed, the so-called scan code, and the operating system service programs already determine which character or command was entered. This approach allows you to map more than one character to each key. For example, the alphabetic keys of the keyboard are associated with four different characters: lowercase and uppercase characters of the Latin and national alphabet. The same thing happens with control keys. When a key is pressed, the keyboard processor sends to a special keyboard buffer located in RAM a scan code of the key, consisting of two bytes: the byte of the scan code itself and a byte that determines which additional control keys were held down. Control keys include the Ctrl, Alt, Shift keys, which also differ in location: left and right, as well as their combinations. The service program reads these two bytes from the keyboard buffer and passes them to the program, which decides which character or control signal needs to be displayed. This approach to processing keystrokes significantly expands the capabilities of the keyboard when specifying control key combinations or when changing the national alphabet. A special program in the Windows operating system, for example, allows you to change the entire key layout or the national alphabet or the meanings of individual keys.
The keyboard processor provides the user with another interesting opportunity: entering a character that is not displayed on the keyboard. To do this, at low numeric keypad(it is located on the left) the decimal code of the required character is typed while holding down the Alt key. This way you can enter a pseudographic character or control character that is not available on the keyboard.
Mouse type manipulator. The most widely used additional devices for manual input of information are graphic input devices such as "mouse" And devices for entering information into game programs - joysticks.
The mouse is an invaluable tool for working with a computer, especially for novice users. Modern graphical operating systems provide the user with graphical objects placed on the display screen, and they are accessed using a special icon moving across the screen - a cursor, usually in the form of an arrow, which allows you to activate the object without thinking about the commands that are executed. Professional users activate objects using keyboard commands, as this speeds up work and does not require moving their hands away from the keyboard. But professionals also use the mouse, for example, when working in graphic editors or creating applications in visual programming environments. The mouse is also used in some gaming programs.
The mouse is an electronic-mechanical device, appearance which and the principle of operation are very diverse. For example, in laptop computers, the mouse is built into the computer case and is a pad with sensors that track the movement of the finger on the pad and the force of its pressure and move the cursor across the screen or, if pressed harder, execute a command. Such devices are called trackpoints or trackpads. But the most popular types of mice used in desktop computers, look like a small box, on top of which there are two buttons for controlling mouse commands and a scroll wheel, used to scroll information in some applications. On the bottom there is a mechanical or electronic device that tracks the movement of the mouse over the surface.
The mechanical device consists of a rubber ball that rotates when you move the mouse, and two rollers located at right angles to each other. The rollers, in turn, rotate the slotted wheels. Light from the LED passes through the slot onto a photodiode, which counts the number of slots and the direction of their passage, converting them into vertical and horizontal components of movement. These signals enter the computer, and a service program that controls the mouse cursor moves it on the screen in the required direction. The same program monitors left and right clicks. right button and the number of their clicks over a certain period of time. The program is capable of tracking any number of clicks from one to thirty-two thousand, however, in practice, only a single or double click of a button is used.
Electronic motion devices use the principle of processing reflected light pulses from the surface on which the mouse moves. Such devices are much more reliable than mechanical ones. Mice are produced that transmit information to the computer via infrared. Such mice do not have a “tail” that connects it to the computer, which is why it got its name.
Joystick. Manipulator type joystick is the main device for controlling numerous computer games. Although most gaming programs allow keyboard control, joysticks provide greater control over the game and much more fully convey the real game situation associated with the operation of aviation, automobile and other motion simulators. For true fans of games, they produce joysticks that are similar to real object controls: steering wheels, pedals, steering wheels and even entire cockpits.
The simplest joystick is a base with a movable handle attached to it, on which there are four buttons and a two-position trigger. The handle can be tilted in all directions and imitates an airplane steering wheel or a tank control lever. The functions of all buttons and handle positions are programmable and may have different actions for different games. Some expensive models have a game feedback mechanism with the joystick handle, and the handle provides some resistance to movement, simulating the resistance of the environment in which the object is moving. To connect the joystick to a computer, use a standard input, usually located on the connector sound card or other standard computer input.
Printing devices.
There are several types of devices that provide a hard copy of an electronic document on paper or other material. The most common types of such devices are printers and plotters.
Printing devices (printers)– these are devices for outputting data from a computer that form a point-by-point image of a copy of documents on paper or other similar material, for example, transparent film used for printing documents. Printers are very diverse in the principle of operation and quality of image reproduction, in the size of paper on which they can reproduce it, as well as the ability to print color or only black and white images and printing speed.
The main characteristic of a printer that determines the quality of the resulting paper document is resolution, which is measured number of elementary points(dots), which fit on one inch - dots per inch(dpi). The higher the resolution, the more accurately the image details are reproduced. Modern printers provide resolutions from 200 to 2880dpi.
Another important characteristic is printer performance, which is measured by the number of pages produced by the printer per minute - page per minute(ppm). Usually performance is indicated for A4 size pages.
Dot matrix printers. Image in dot matrix printers is formed from dots that are obtained by hitting a thin needle on an ink ribbon, which is pressed against the paper at the moment of impact. The needles, the number of which ranges from 9 to 24, are combined in the head and placed vertically in one row. Each needle is controlled by a separate magnet, and the head moves horizontally along the sheet. Thus, in one pass of the head, a strip is obtained, the height of which in points is equal to the number of needles in the head. The speed of dot matrix printers is not high and is about 2ppm. Resolution is 200 – 360dpi. The advantage of dot matrix printers is the low cost of consumables (ink ribbon) and the ability to print several copies of a document simultaneously. Disadvantages include low printing speed and printing noise.
Inkjet printers. In our country, this is currently the most common type of printer. Printhead inkjet printer Instead of needles, it contains thin tubes - nozzles, through which tiny dosed drops of dye are thrown onto the paper. The number of nozzles in the head ranges from 12 to 64. Inkjet printers also perform color printing. In color printing, a color dot is obtained by mixing in given proportions dyes of three primary colors: cyan, magenta and yellow, fired from three nozzles. The quality of color printing is very high and almost indistinguishable from printing.
To the advantages inkjet printers can be attributed: a high resolution, which depends on the number of nozzles in the head, and ranges from 300 to 1200 dpi; high printing speed, up to 10ppm; quiet operation.
The main disadvantages are the high cost Supplies and the possibility of the dye drying out in the nozzle, forcing the entire print unit to be replaced prematurely. Sometimes, when applying a large amount of dye, the paper warps.
Laser printers.Laser printers provide the highest quality printing with the highest resolution and speed. The image in them is formed in several stages. At the first stage, the drum is illuminated with a narrow intermittent light beam from a laser diode, onto which a thin layer of material is applied that is electrolyzed under the influence of light. At the second stage, the drum is sprinkled with finely dispersed coloring powder, which sticks to the drum at the points of exposure, and the excess powder is removed. The third stage consists of rolling the drum with the powder adhering to it over the paper, as a result of which the dye transfers to the paper. The last stage consists of heat treatment of the paper. It heats up to 200, as a result the powder melts and penetrates the structure of the paper and is fixed on it. Laser printers can print color images. It is obtained by applying powders of different colors to the drum.
To the advantages laser printers This includes high print quality, high print speed (up to 40 ppm), as well as low copy cost and quiet operation.
Plotters.Plotters or plotters are used mainly for displaying graphic information - drawings, diagrams, diagrams, etc. The main advantage of plotters is that they are designed to produce images on large format paper, for example, A1.
Plotters are divided into two large classes: vector And raster. In vector plotters, the writing unit moves relative to the paper simultaneously vertically and horizontally, drawing continuous curves on the paper in any direction. In raster plotters, the writing unit moves relative to the paper in only one direction, and the image is formed line by line from a sequence of dots.
Vector plotters use a node for drawing, which is generally called pen. Pens with ink, fiber and plastic rods (felt pens), pencil leads and crayons, or single- and reusable ballpoint units are used as pens. Pen plotters provide high quality both monochrome and color images, but have low operating speed. Gradually, pen and ball plotter units are being replaced by inkjet units, which are similar to the units of inkjet printers. To get very High Quality seals are used electrostatic plotters, which use special electrostatic paper on which a potential relief is created and a layer of dye is deposited on it in those places where the paper has an electric static charge.
Raster plotters can have an inkjet or laser writing unit. Their main difference from printers with a similar operating principle is the width of the processed image.
The variety of existing types of plotters and their high cost require careful analysis when choosing a plotter. It is necessary to take into account such parameters as image quality, the possibility of using a color palette, productivity, operating costs, expressed in the cost of one copy of the resulting image.
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