Alternative input devices. Information output device - what is it? User information output devices

Laser printer - printing is formed due to the effects of xerography

Inkjet printer – printing is formed by micro drops of special ink.

Dot matrix printer – forms characters using several needles located in the printer head. The paper is pulled in by a shaft, and an ink ribbon is placed between the paper and the printer head.

Matrix (needle) printers

Dot-matrix-Printer , also known as matrix) has long been a standard output device for PCs. In the recent past, when inkjet printers still performed unsatisfactorily and the price of laser printers was quite high, needle printers were widely used. They are still often used today. The advantages of these printers are determined primarily by the printing speed and their versatility, which consists in the ability to work with any paper, as well as the low cost of printing.

When choosing a printer, you should always proceed from the tasks that will be assigned to it. If you need a printer that needs to print various forms all day without interruption, or printing speed is more important than quality, then it is cheaper to use a needle printer. If you want to get a high-quality image on paper, then use an inkjet or laser printer, but in this case, naturally, the cost of each sheet will increase significantly. Pin printers have a significant advantage - the ability to print several carbon copies of a document at once. The disadvantage of such printers is the noise they produce during operation.

The principle by which a needle printer prints characters on paper is very simple. A pin printer produces characters using multiple pins located in the printer head. The mechanics of paper feeding are simple: the paper is pulled in using a shaft, and an ink ribbon is placed between the paper and the printer head. When a needle hits this tape, a painted mark remains on the paper. The needles located inside the head are usually activated electromagnetically. The head moves along a horizontal guide and is controlled by a stepper motor.

There are heads: 9*9 needles, 9*18, 18*18, 24*37. The needles are arranged in one or two rows. Using a multi-color ink ribbon, color printing is possible.

Inkjet printers

The first company to produce an inkjet printer is Hewlett Packard. The basic operating principle of inkjet printers is somewhat reminiscent of the operation of needle printers, but instead of needles, they use nozzles (very small holes) that are located in the printer head. This head contains a reservoir of liquid ink, which is transferred through nozzles, like microparticles, onto the media material. The number of nozzles depends on the printer model and manufacturer.

Ink supply methods:

The printer head is integrated with the ink tank; Replacing the ink tank simultaneously involves replacing the head

- a separate reservoir is used, which supplies the printer head with ink through a capillary system; replacing the head is associated only with its wear

Color printing using inkjet printers is quite high quality, which has led to the widespread use of inkjet printers.

Typically, a color image is formed when printing by superimposing three primary colors on each other: cyan (Cyan) , purple (Magenta) and yellow (Yellow) . Although in theory the superposition of these three colors should result in black, in practice most cases result in gray or brown, and so black is added as a fourth primary color. Based on this, this color model is called CMYK ( C yan- M agenta - Y ellow-Blac k ).

Laser printers

Despite strong competition from inkjet printers, laser printers can achieve significantly higher print quality. The quality of the image obtained with their help is close to photographic. Thus, to obtain high-quality black and white or color printouts, you should prefer a laser printer over an inkjet printer.

Most laser printer manufacturers use the same printing mechanism as copiers. The most important structural element of a laser printer is the rotating drum, which is used to transfer the image onto paper. The drum is a metal cylinder coated with a thin film of photoconductive semiconductor. The static charge is evenly distributed over the surface of the drum. For this purpose, a thin wire or mesh is used, called a corona wire. A high voltage is applied to this wire, causing a glowing ionized area called a corona to appear around it. The laser, controlled by a microcontroller, generates a thin beam of light that is reflected from a rotating mirror. This beam, arriving at the drum, changes its electrical charge at the point of contact. Thus, a hidden copy of the image appears on the reel. In the next working step, toner is applied to the phototypesetting drum - tiny ink dust. Under the influence of a static charge, these small particles are easily attracted to the surface of the drum at the exposed points and form an image. The paper is pulled from the input tray and moved to the drum by a roller system. Just before the drum, a static charge is imparted to the paper. The paper then comes into contact with the drum and, due to its charge, attracts toner particles from the drum. To fix the toner, the paper is recharged and passed between two rollers at a temperature of about 180 ° C. After the printing process itself, the drum is completely discharged, cleaned of adhering excess particles and is ready for a new printing process.

Laser printers of this class are equipped with a large amount of memory, a processor and, as a rule, their own hard drive. The hard drive contains a variety of fonts and special programs that control operation, monitor the status, and optimize the printer’s performance.

Thermal printers

Color laser printers are not yet perfect. To obtain photographic quality color images, thermal printers or, as they are also called, high-end color printers are used.

There are three technologies for color thermal printing:

Jet transfer of molten dye (thermoplastic printing)

Contact transfer of molten dye (thermal wax printing)

Thermal dye transfer (sublimation printing)

What the last two technologies have in common is heating the dye and transferring it to paper (film) in the liquid or gaseous phase. Multicolor dye is usually applied to a thin lavsan film (5 microns thick). The film is moved using a tape mechanism, which is structurally similar to a similar unit in a needle printer. The matrix of heating elements forms a color image in 3-4 passes.

Printers that use molten ink jet transfer are also called solid ink wax printers. When printing, blocks of colored wax are melted and splattered onto the media, creating vibrant, rich colors on any surface.

Let us list the main qualities of printers that determine their comparative merits from the user’s point of view.

Print quality and speed - does the printer provide the required print quality, and if so, at what speed.

Reliability - How reliable is the printer when printing typical documents and when working with the user's existing paper?

Changing ink elements - how long does the printer operate with a given ink element?

Compatible with existing programs.

Printers are almost always connected to a parallel port on an LPT (Line Printer, 25-pin Sub-D connector). Wireless infrared printers are rare and are used mainly by notebook PC users.

Plotter (graph plotter) - nThe lotter is an output device that is used only in special areas. Plotters are usually used in conjunction with CAD programs. The result of almost any such program is a set of design or technological documentation, a significant part of which consists of graphic materials. Thus, the plotter's domain is drawings, diagrams, graphs, diagrams, etc. For this, the plotter is equipped with special auxiliary tools. The plotter's drawing field corresponds to A4 - A0 formats.

All modern plotters can be classified into two large classes;

Flatbed for AZ-A2 (less often A1-A0) formats with sheet fixation electrically, less often magnetically or mechanically

Drum (roll) plotters for printing on A1 or A0 paper, with roller sheet feed, mechanical or vacuum clamp.

Frequency synthesis is based on the fact that to obtain any sound, mathematical formulas (models) are used that describe the frequency spectrum of a particular musical instrument. The sounds produced by this technology are characterized by a metallic tint.

Wave synthesis is based on the use of digital recording of real instruments, the so-called samples (samples). Samples - these are sound samplesvarious realinstruments stored in the sound card memory.

When playing sounds using wave synthesis technology, the user hears the sounds of real instruments, so the created sound picture is closer to the natural sound of the instruments.

Samples can be stored in two ways: either permanently in ROM, or loaded into the RAM of the sound card before they are used. There is a large variety of samples , which allows you to create an almost endless variety of sounds.

Output devices

Monitor. Monitor is a universal information output device and connects to the video card installed in the computer.

The image in computer format (in the form of sequences of zeros and ones) is stored in video memory located on the video card. The image on the monitor screen is formed by reading the contents of video memory and displaying it on the screen.

The frequency of image reading affects the stability of the image on the screen. In modern monitors, image updating usually occurs at a frequency of 75 or more times per second, which ensures comfortable perception of the image by the computer user (a person does not notice the flickering of the image). For comparison, we can recall that the frame rate in cinema is 24 frames per second.

Desktop computers typically use cathode ray tube (CRT) monitors - Fig. 4.14.

The image on the monitor screen is created by a beam of electrons emitted by an electron gun. This beam of electrons is accelerated by high electrical voltage (tens of kilovolts) and falls on the inner surface of the screen, coated with a phosphor (a substance that glows under the influence of an electron beam).

Rice. 4.14. CRT monitor

The beam control system forces it to run across the entire screen line by line (creates a raster), and also regulates its intensity (accordingly, the brightness of the phosphor dot). The user sees the image on the monitor screen, since the phosphor emits light rays in the visible part of the spectrum. The smaller the image dot size (phosphor dot), the higher the image quality; in high-quality monitors, the dot size is 0.22 mm.

However, the monitor also emits high static electrical potential, electromagnetic radiation and x-ray radiation, which may have adverse effects on human health. Modern monitors are practically safe, as they meet strict sanitary and hygienic requirements set out in the international safety standard TCO"99.

Laptop and pocket computers use flat-panel liquid crystal (LCD) monitors. Recently, such monitors have begun to be used in desktop computers.

LCD (Liquid Crystal Display, LCD monitors- rice. 4.15) are made of a substance that is in a liquid state, but at the same time has some properties inherent in crystalline bodies. In fact, these are liquids that have anisotropy of properties (in particular, optical ones) associated with order in the orientation of molecules. Molecules of liquid crystals under the influence of electrical voltage can change their orientation and, as a result, change the properties of the light beam passing through them.

Rice. 4.15. LCD monitor

The advantage of LCD monitors over CRT monitors is the absence of electromagnetic radiation harmful to humans and their compactness.

Monitors may have different screen sizes. Screen diagonal size is measured in inches (1 inch = 2.54 cm) and is usually 15, 17 or more inches.

Printers. Printers are intended for printing on paper (creating a “hard copy”) of numerical, text and graphic information. According to their operating principle, printers are divided into matrix, inkjet and laser.

Dot matrix printers(Fig. 4.16) are impact printers. The print head of a dot matrix printer consists of a vertical column of small rods (usually 9 or 24) that are "popped" out of the head by a magnetic field and strike the paper (through the ink ribbon). As the print head moves, it leaves a string of characters on the paper.

Rice. 4.16. Dot Matrix Printer

The disadvantages of dot matrix printers are that they print slowly, produce a lot of noise, and print quality is poor (about the quality of a typewriter).

In recent years, black-and-white and color inkjet printers have become widespread (Fig. 4.17). They use an ink print head that, under pressure, releases ink from a series of tiny holes onto the paper. As the print head moves along the paper, it leaves a line of characters or a strip of image.

Rice. 4.17. Inkjet printer

Inkjet printers can print quite quickly (up to several pages per minute) and produce little noise. The quality of printing (including color) is determined by the resolution of inkjet printers, which can reach photographic quality of 2400 dpi. This means that a 1-inch horizontal stripe of image is formed from 2400 dots (ink drops).

Laser printers(Fig. 4.18) provide virtually silent printing. Laser printers achieve high printing speeds (up to 30 pages per minute) through page-by-page printing, in which the entire page is printed at once.

Acoustic speakers and headphones. To listen to sound, use speakers or headphones that are connected to the output of the sound card.

Questions to Consider

1. What physical parameters affect the quality of the image on the monitor screen?

Practical tasks

4.6. Get acquainted with the structure of the computer and the history of computing by visiting virtual computer museums on the Internet.

After the user enters the initial data, the computer must process it in accordance with the existing program and output the results for perception by the operator or for use by automatic devices. The output information can be displayed on a monitor screen, printed on paper (using a printer or plotter), reproduced in the form of sounds (using speakers or headphones), recorded in the form of tactile sensations (virtual reality technology), distributed in the form of control signals ( automation devices), transmitted in the form of electrical signals over the network.

The most common output devices are monitors (displays). The vast majority of monitors use cathode ray tubes (CRTs) or liquid crystal matrices to form images. Moreover, currently there is a gradual displacement of monitors with CRT monitors using liquid crystals.

There are monitors based on other physical principles: plasma, fluorescent, etc.

For example, monitors made using FED (Field Emission Display) technology are based on the effect of creating emission across the entire surface of the screen. Unlike a CRT, the source of electrons is not a separate point (electron gun), but an entire emitting surface. Irradiation is carried out through a mask in which the number of holes is equal to the number of pixels. Due to this design, it is possible to obtain the same image brightness as that of CRT monitors, and the dimensions (thickness) are the same as those of liquid crystal monitors.

A new monitor manufacturing technology, OLED (Organic Light Emitting Diodes), is considered promising. Their design is based on the use of organic light-emitting diodes.

Printers, depending on the order of image formation, are divided into sequential, line and page. Whether a printer belongs to one group or another depends on whether it produces on paper character by character or an entire line at once, or even a whole page.

According to the physical principle of operation, printers are divided into the following types: thermographic, petal (chamomile), matrix (needle), inkjet and laser.

The design of the first two types of printers is obsolete, and they are practically no longer used.

IN dot matrix printers The image is formed from dots by hitting needles on an ink ribbon. Under the influence of control signals sent to electromagnets, the needles “knock out” the paint from the tape, leaving marks on the paper. Depending on the design, the print head of a dot matrix printer can have 9, 18 or 24 pins. All symbols are formed from individual dots.

Printheads inkjet printers Instead of needles, they contain thin tubes - nozzles, through which droplets of ink are thrown onto the paper. The print head of an inkjet printer contains from 12 to 64 nozzles, the diameters of which are thinner than a human hair.

Several principles of operation of inkjet print heads are known.

One design houses a small ink reservoir at the inlet end of each nozzle. Behind the tank is a heater (thin film resistor). When a resistor is heated by current passing through it to a temperature of 500°C, the ink surrounding it boils, forming a bubble of steam. This expanding bubble pushes ink droplets with a diameter of 50...85 microns out of the nozzle at a speed of about 700 km/h.

In another print head design, the pressure source is a membrane driven by a piezoelectric element. Applying electrical voltage to the piezo element causes it to deform, which is used to spray ink.

In all printer designs, electromechanical devices move the print heads and paper so that printing occurs in the desired location.

IN laser printers The electrographic principle of image creation is used. The printing process involves the formation of an invisible relief of electrostatic potential in a semiconductor layer and its subsequent visualization. Visualization (development) is carried out using particles of dry powder - toner, applied to paper. Toner is pieces of iron coated with plastic. The most important parts of a laser printer are the semiconductor drum, the laser, and the precision optical-mechanical system that moves the beam (Figure 10.5).

The laser generates a thin beam of light that, when reflected from a rotating mirror, forms an electronic image on a light-sensitive semiconductor drum.

The surface of the drum is preliminarily given a certain static charge. A mesh or thin wire is used to create an electrostatic charge. When high voltage is applied to a wire, a corona discharge occurs, as a result of which a glowing ionized region of space appears around the wire. Due to the corona discharge, the surface of the drum is evenly charged. To obtain an image on the drum, the laser must be turned on and off in accordance with the image being formed, which is ensured by the control circuit. Control signals come from the computer in accordance with the image stored in memory. The rotating mirror serves to rotate the laser beam into a line formed on the surface of the drum.

When the laser beam hits a pre-charged drum, the charge “drains” from the illuminated surface. Thus, the areas of the drum illuminated and not illuminated by the laser have different charges. As a result of scanning the entire surface of the semiconductor drum, a latent (electronic, invisible to humans) image is created on it.

The drum is rotated to a new line by a precision stepper motor. This offset determines the printer's resolution and can be, for example, 1/300, 1/600, or 1/1200 inch. The process of scanning an image on a drum is in many ways similar to constructing an image on a monitor screen (creating a raster).

Rice. 10.5. Laser printer printing process

At the next stage of the printer’s operation, the image is developed, i.e., the hidden electronic image is converted into a visible one. When developing an image, the following physical phenomenon is used: charged toner particles are attracted only to those places in the drum that have the opposite charge to the toner charge.

When the visible image on the drum is built and it is covered with toner according to the original, the fed sheet of paper is charged so that the toner from the drum is attracted to the paper. The adhered powder is fixed to the paper by heating the toner particles to the melting point. As a result, a waterproof imprint is formed. Color laser printers create an image by sequentially depositing cyan, magenta, yellow and black toners onto a photosensitive drum.

A four-pass color printer prints at significantly lower speeds than a black-and-white printer. In a single-pass color printer, four toner cartridges are installed in one plane behind each other, each next to its ram. All colors are applied in one pass instead of four, so image formation speed is increased.

In addition to laser printers, there are so-called LED printers (Light Emitting Diode), which got their name due to the fact that the semiconductor laser in them is replaced by a “comb” (line) of LEDs. In this case, a complex mechanical system for rotating the mirror is not needed. The image of one line on the semiconductor drum is formed simultaneously.

In table 10.1. The characteristics of printers of various designs are given.

Table 10.1. Printer Specifications

Plotters (or plotters) are graphic information output devices that are used in the design of large posters, drawings, geographic maps, printed circuit board sketches, diagrams, and histograms.

The plotter's operation is based on mechanical and non-mechanical methods for displaying graphic information. The mechanical method uses pencils, pens and ink. Similar to printers, non-mechanical plotters use thermal, matrix, inkjet and laser printing methods.

Devices capable of performing information input and output functions can be used communication adapters. With their help, communication between computers is carried out via a telephone line. Since telephone networks still often work not with digital, but with analog electrical signals in the audio range, it is necessary to convert digital signals coming from the computer into analog signals and transmit them to the telephone network. At the other end of the telephone line, the reverse conversion must be performed. These transformations are performed by a special device - a modem (from the words MOdulator - DEModulator).

The modem is implemented either in the form of an external device, which is connected with one output to the telephone line and the other to a standard computer port, or in the form of an ordinary board (card) that is installed on the computer system bus (internal modem).

Sound information is output using speakers and headphones (Fig. 10.6), which are connected via a special adapter (controller, sound card).

Rice. 10.6. Headphones

There are several ways to reproduce sounds (particularly music). The frequency method (FM synthesis) of sound reproduction is based on simulating the sound of real instruments, and the tabular method (wave-table synthesis) operates with the sounds of real instruments recorded in memory.

Frequency synthesis is based on the fact that to obtain any sound, mathematical formulas (models) are used that describe the frequency spectrum of a particular musical instrument. The sounds produced by this technology are characterized by a metallic tint.

Wave synthesis is based on the use of digital recordings of real instruments, so-called samples. Samples are samples of the sound of various real instruments stored in the memory of the sound card. When playing sounds using wave synthesis technology, the user hears the sounds of real instruments, so the created sound picture is closer to the natural sound of the instruments.

Samples can be stored in two ways: either permanently in ROM, or loaded into the RAM of the sound card before using them. There is a large set of different samples, which allows you to create an almost endless variety of sounds.

Display (monitor) is the most popular information output device. There are monochrome (black and white) and color displays. First, let's look at the operating principle of black-and-white monitors.

Rice. 10.7. Cathode ray tube

The main display unit is cathode ray tube (CRT). Sometimes the abbreviation CRT (Cathode Ray Tube) is used to refer to CRT. One of the possible CRT designs is shown in Fig. 10.7.

Let us list the main parts that make up a CRT: cathode, anode, modulator, horizontal deflection plates, vertical deflection plates, screen, bulb.

The cathode, anode and modulator form an electron projector, which is sometimes called an electron gun. Horizontal and vertical deflection plates form a deflection system. Such a deflection system is called electrostatic. There are magnetic deflection systems in which coils are used instead of plates to change the trajectory of the electron flow.

A CRT uses a stream of electrons focused into a narrow beam, controlled in intensity and position in space, and interacting with a tube screen. The electron beam is emitted by an electron spotlight (more precisely, the cathode), and the beam position on the screen is changed by a deflection system.

The movement of an electron beam across the CRT screen in accordance with a certain law is called scanning, and the pattern drawn by the trace of the electron beam on the screen is called a raster. Scanning is carried out by applying periodically varying voltages to the CRT deflection system. During scanning, the electron beam sequentially runs along the surface of the CRT screen line by line.

During the formation of the raster, the flow of electrons moves along a zigzag path from the upper left corner of the screen to the lower right corner. In Fig. 10.8 the solid lines show the raster, the dashed lines show the trajectory of the electron beam, along which it is “quenched” (made invisible).

Rice. 10.8. Raster and trajectory of the electron beam

The screen is covered with a phosphor, so a glow appears in the places where the electron beam falls, the brightness of which is proportional to the intensity of the beam. The intensity of the electron flow changes in accordance with the signals supplied to the control electrode - the modulator. It is these signals that form the necessary image on the display screen.

Rice. 10.9. Image of the letter "I"

In Fig. Figure 10.9 shows a large-scale image of the letter “I”. In this case, eight raster lines were required to image it. In Fig. 10.10. timing diagrams for control signals supplied to the modulator are shown. High potential corresponds to white areas of the screen, low potential corresponds to black areas. Using a deflection system, the modulated beam of electrons is deployed into a raster, displaying line by line on the screen, thus reproducing the image frame by frame. Thanks to the inertia of vision, a person sees a continuous, often dynamic, image on the screen.

Rice. 10.10. Timing diagrams for control signals

Any image on a monitor screen consists of many discrete points called pixels (pixel - picture element).

The display communicates with its adapter, which may also be called a graphics card, video adapter, or controller. The display and adapter are very closely related to each other and jointly determine the image quality - resolution, number of reproduced colors, regeneration speed (number of frames per unit of time).

Resolution depends on the screen size and the minimum image element (the so-called “grain”, equal to 0.24...0.28 mm for the best monitors). For 14-inch monitors, the resolution is usually no more than 800x600 elementary dots (pixels), for 15-inch monitors - 1024x768, for 21-inch monitors - 1280x1024 pixels.

The ability of the adapter to display an image on the monitor screen with a given resolution and color depth (i.e., the number of color shades) is determined by the amount of RAM installed on the adapter board. To display 16.7 million shades of colors (24 bits per pixel), you need to install in the adapter at least 1.37 MB of memory at a resolution of 800×600 elementary pixels, 3.75 MB at a resolution of 1280×1024 and 5.49 MB at a resolution of 1600 ×1200.

For comfortable image perception, without tiring flicker, you need fairly high frame rates (at least 85 Hz is recommended).

The operating principle of a color monitor is similar to that of a monochrome monitor, but the design of a color monitor is much more complex. The color display contains three electron guns with separate control circuits. The screen is made in the form of a mosaic structure (rectangular matrix), consisting of phosphor grains of three glow colors: red (Red), green (Green) and blue (Blue). The grains are arranged in threes (triads) so that the electrons from each of the three guns hit only the grains of their “own” color. To ensure this, masks are placed in the path of electron movement.

The operating principle of a color display is based on the physiological characteristics of human vision. So, with the same glow intensity of three multi-colored small neighboring grains, this section of the screen is perceived as a white dot. The glow of neighboring red and green grains is perceived as a yellow dot, and the glow of blue and green grains produces a blue dot, etc. By changing the glow intensity of the three primary colors (RGB), you can get any color or shade. This method of obtaining any colors is one of the color rendering systems and is called the RGB system (after the first letters of the corresponding English words).

Liquid crystal monitors (LCM) have the following advantages: low power consumption (2-3 times less than that of a CRT), absence of X-ray radiation, static electrification, and geometric distortions. LCDs are light in weight and dimensions: the thickness of the monitor does not exceed 5...6 cm. The disadvantages of LCDs are a limited viewing angle, lower contrast and color depth than CRTs, and significant unevenness of brightness in different places on the screen. LCMs have a high percentage of defects during their production (the presence of “dead” pixels). This is currently considered the main reason for the higher cost of LCD monitors compared to CRT monitors.

In cathode ray tubes, the phosphor is placed at certain points on the screen, forming a matrix. The flow of electrons is directed to these points using continuous (analog) control signals applied to the deflection system. The electron beam sequentially line by line “runs around” all the points (pixels) of the screen and alternately changes the intensity of their glow.

The complete image on a CRT screen, resulting from all pixels, is called a frame. To get the illusion of a moving image, successive frames must quickly replace each other (at least 25...30 times per 1 s). In a CRT, during the movement of the electron beam from the beginning of the frame to its end, the glow of the first excited elements of the matrix (phosphor) manages to weaken somewhat. To reduce screen flickering, you have to increase the frequency of changing (updating) successive frames (they say: increase the frame rate). The vertical scanning frequency of the CRT must be at least 85 Hz.

The operating principle of an LCD monitor is significantly different from the operating principle of a CRT monitor. LCM uses the physical effect of changing the spatial position of crystal molecules under the influence of an electric field. Just like in a CRT, in LCD an image is formed from a large number of dots (pixels) that form a rectangular matrix. However, in a liquid crystal matrix, the image formation process is controlled digitally. In the LCD, the glow of all elements of the entire row of the matrix (screen) changes simultaneously. The flicker of LCDs is fundamentally less than that of CRT displays, since only the changing pixels are updated when the image is formed. The image of static pictures does not require updating, so in these cases there is no flickering of the LCD screen at all. The LCD matrix (Liquid Crystal Display, LCD) is made of a substance that is in a liquid aggregate state, but has the properties of crystals. Under the influence of an electric field, liquid crystals change their spatial orientation (rotate) and thereby vary the intensity of the transmitted light.

Rice. 10.11. Multi-layer monitor design

The monitor is a multilayer structure (Fig. 10.11), which contains polarizers, a matrix of control transistors, color filters, glass plates, between which liquid crystals are placed.

The operating principle of LCM (Fig. 10.12) is based on the polarization effect. First, the light passes through the first polarizing filter (Polarizer 1), which is characterized by a certain polarization angle. Another polarizer (Polarizer 2) is installed in the LCM. Depending on the polarization angle of the second filter, the light will either be completely absorbed by it (if the polarization angle of the second filter is perpendicular to the polarization angle of the first filter), or pass through unhindered (if the angles are the same). A smooth change in the polarization angle of transmitted light allows you to adjust the intensity of visible (transmitted) light. The polarization angle of transmitted light is changed using liquid crystals. Their orientation in space depends on the magnitude of the control voltage supplied to the transistor matrix.

Rice. 10.12. Operating principle of ZhKM

Thus, by changing the control voltage on each transistor of the matrix, it is possible to vary the spatial position of the liquid crystals at a given point. A change in the spatial position of the crystals leads to a change in the polarization angle of light at a given point on the screen (and, therefore, to a change in the intensity of the glow of a given point on the screen).

The discrete design of the LCD allows, in principle, to do without analog-to-digital conversion, i.e., to work directly with digital signals. Obviously, this design is more promising compared to devices that work with analog signals. Recall that a CRT is an analog device. The signals on the deflector plates and the modulator are continuous. To control the operation of a CRT, it is necessary to transform the digital signal generated by the computer into an analog signal. However, any digital-to-analog conversion is associated with the occurrence of distortion and interference, complicating the design of the controllers.

Introduction

A computer is a universal device for processing information. To allow the computer to process information, it must be entered there somehow. To enter information, special devices were created - primarily a keyboard, CD-ROM. Once in the computer, the information is processed and then the ability to output this information is realized, i.e. the user has the ability to visually perceive the data. To display information, the main devices are used - a monitor, a video adapter and a printer. After entering and processing information, it can be saved, for which a hard drive, magnetic disks and optical data storage devices were created. This course work presents the topic “Input/Output Devices”.

Output devices- These are devices that translate information from machine language into forms accessible to human perception. Information output devices include: monitor, video card, printer, plotter, projector, speakers.

Input devices are those devices through which information can be entered into a computer. Their main purpose is to implement an impact on the machine. The variety of input devices produced has given rise to entire technologies from touch to voice. Although they work on different principles, they are intended to implement one task - to allow a person to communicate with a computer. Graphic information input devices are widely used due to the compactness and clarity of the way they present information to humans. Based on the degree of automation of the search and selection of image elements, graphic information input devices are divided into two large classes: automatic and semi-automatic. In semi-automatic graphic information input devices, the functions of searching and selecting image elements are assigned to a person, and the transformation of the coordinates of the read points is performed automatically. In semi-automatic devices, the process of searching and selecting image elements is carried out without human intervention. These devices are built either on the principle of scanning the entire image, followed by its processing and conversion from a raster representation to a vector one, or on the principle of line tracking, which ensures reading of graphic information presented in the form of graphs, diagrams, and contour images. The main areas of application of graphic information input devices are computer-aided design systems, image processing, training, process control, animation and many others. These devices include scanners, encoding tablets (digitizers), light pens, touch screens, digital cameras, video cameras, computer keyboards, mice, and others.

Input devices- devices for entering (entering) data into a computer during its operation. Input devices are those devices through which information can be entered into a computer. Their main purpose is to implement an impact on the machine. The variety of input devices produced has given rise to entire technologies from touch to voice. Although they work on different principles, they are intended to implement one task - to allow a person to communicate with a computer. Graphic information input devices are widely used due to the compactness and clarity of the way they present information to humans. Based on the degree of automation of the search and selection of image elements, graphic information input devices are divided into two large classes: automatic and semi-automatic. In semi-automatic graphic information input devices, the functions of searching and selecting image elements are assigned to a person, and the conversion of the coordinates of the read points is performed automatically. In semi-automatic devices, the process of searching and selecting image elements is carried out without human intervention. These devices are built either on the principle of scanning the entire image, followed by its processing and conversion from a raster representation to a vector one, or on the principle of line tracking, which ensures reading of graphic information presented in the form of graphs, diagrams, and contour images. The main areas of application of graphic information input devices are computer-aided design systems, image processing, training, process control, animation and many others. These devices include scanners, encoding tablets (digitizers), light pens, touch screens, digital cameras, video cameras, computer keyboards, mice, and others.

Chapter 1. Information output devices.

1.1.Monitor

The monitor provides information communication between the user and the computer. The first microcomputers were small units with virtually no display devices. All that the user had at his disposal was a set of flashing LEDs or the ability to print the results on a printer. Compared to modern standards, the first computer monitors were extremely primitive: text was displayed only in green, but in those years this was almost the most important technological breakthrough, since users were able to input and output data in real time. With the advent of color monitors, screen sizes increased and they moved from laptop computers to desktop users. There are two types of monitor: cathode ray and liquid crystal monitor.

Cathode ray monitor. In such a monitor, the image is transmitted using a cathode ray tube (CRT). A CRT is an electronic vacuum device in a glass bulb, in the neck of which there is an electron gun, and at the bottom there is a screen covered with a phosphor. As the electron gun heats up, it emits a stream of electrons that move toward the screen at high speed. The electron flow passes through the focusing and deflection coils, which direct it to a specific point on the phosphor-coated screen. When struck by electrons, the phosphor emits light that is visible to the user. EL monitors use three phosphor layers: red, green and blue. To equalize the flow of electrons, a shadow mask is used - a metal plate with slits or holes that separate the red, green and blue phosphors into groups of three dots of each color. The quality of the image is determined by the type of shadow mask used; The sharpness of the image is affected by the distance between the groups of phosphors.

The chemical used as a phosphor is characterized by a persistence time, which represents how long the phosphor glows after exposure to an electron beam. The persistence time and image refresh rate must match each other so that there is no noticeable flickering of the image and there is no blurring or doubling of contours as a result of superimposing successive frames.

The electron beam moves very quickly, sweeping lines across the screen from left to right and top to bottom in a path called a raster. The horizontal scanning period is determined by the speed of the beam moving across the screen. During the scanning process (moving across the screen), the beam affects those elementary areas of the phosphor coating of the screen where the image should appear. The intensity of the beam is constantly changing, as a result of which the brightness of the corresponding areas of the screen changes. Since the glow disappears very quickly, the electron beam must run across the screen again and again, renewing it. This process is called image renewal (or regeneration).

LCD monitor. Borrowing technology from laptop display manufacturers, some companies have developed liquid crystal displays, also called LCDs (Liquid-Crystal Displays). They are characterized by a glare-free screen and low power consumption (some models of such displays consume 5 W, while monitors with a cathode ray tube consume about 100 W). In terms of color rendering quality, active matrix LCD monitors are currently superior to most EL monitor models. LCD monitors use analog or digital active matrix. LCD monitors with screen sizes larger than 15 inches provide both analog (VGA) and digital (DVI) connectors, which are equipped with many mid- and high-cost video adapters. A polarizing filter creates two separate light waves and transmits only the one whose plane of polarization is parallel to its axis. By placing a second filter in the LCD monitor so that its axis is perpendicular to the axis of the first, you can completely prevent the passage of light. By rotating the polarization axis of the second filter, i.e. changing the angle between the axes of the filters, you can change the amount of transmitted light energy, and therefore the brightness of the screen. The color LCD monitor has another additional filter; which has three cells for each pixel in the image - one each to display the red, green and blue dots. The red, green, and blue cells that make up a pixel are sometimes called subpixels.

A dead pixel is a pixel whose red, green or blue cell is constantly on or off. Always-on cells are very clearly visible against a dark background as a bright red, green or blue dot. LCD monitors come in active and passive matrix.

Most LCD monitors use thin film transistors (TFT). Each pixel contains one monochrome or three color RGB transistors, packaged in a flexible material that is exactly the same size and shape as the display itself. Therefore, the transistors of each pixel are located directly behind the LCD cells that they control. Currently, two materials are used to produce active matrix displays: hydrogenated amorphous silicon (a-Si) and low-temperature polycrystalline silicon (p-Si). The main difference between the two is the production price. To increase the apparent horizontal viewing angle of LCD monitors, some manufacturers have modified the classic TFT technology. In-plane switching (IPS) technology, also known as STFT, involves aligning LCD cells in parallel with the glass of the screen, applying electrical voltage to the in-plane sides of the cells, and rotating the pixels to output images clearly and evenly across the entire LCD panel. Super-IPS technology - rearranges LCD molecules in a zig-zag pattern rather than in rows and columns, reducing unwanted color mixing and improving the uniform distribution of color gamut on the screen. In a similar technology, multi-domain vertical alignment (MVA), the monitor screen is divided into separate areas, for each of which the orientation angle is changed.

In passive matrix LCD monitors, the brightness of each cell is controlled by the voltage flowing through transistors whose numbers are equal to the row and column numbers of a given cell in the screen matrix. The number of transistors (in rows and columns) determines the screen resolution. For example, a screen with a resolution of 1024x768 contains 1024 transistors horizontally and 768 vertically. The cell reacts to an incoming voltage pulse in such a way that the plane of polarization of the passing light wave rotates, and the higher the voltage, the greater the rotation angle.

A pulsating voltage is supplied to the cells of an LCD monitor with a passive matrix, so they are inferior in image brightness to LCD monitors with an active matrix, in which each cell is supplied with a constant voltage. To increase image brightness, some designs use a control method called double scanning and corresponding devices - double-scan LCD monitors. The screen is divided into two halves (upper and lower), which operate independently, which leads to a reduction in the interval between pulses arriving at the cell. Dual scanning not only improves image brightness, but also reduces screen response time because it reduces the time it takes to create a new image. Therefore, dual-scan LCD monitors are more suitable for creating fast-paced images.

1.2Printer

One of the purposes of a computer is to create a printed version of a document, or a so-called hard copy. This is why a printer is an essential computer accessory. Printers (printing devices) - These are devices for outputting data from a computer, converting ASCII information codes into corresponding graphic symbols and recording these symbols on paper. The printer expands the computer's relationship with the material world by filling paper with the results of its work. In terms of speed capabilities, printers range from sluggish to light. They compete with plotters in their ability to draw graphic images. Today there are three types of printers:

Laser. A laser printer works as follows: an electrostatic image of a page is created on a photosensitive drum using a laser beam. When placed on the drum, a specially colored powder called toner “sticks” only to the area that represents the letters or image on the page. The drum rotates and presses against a sheet of paper, transferring toner to it. After fixing the toner to the paper, the finished image is obtained.

Once the data is loaded into the printer, the computer begins the process of interpreting the code. First, the interpreter extracts control commands and document contents from the incoming data. The printer processor reads the code and executes the commands that are part of the formatting process, and then carries out other printer configuration instructions (such as selecting a paper tray, single-sided or double-sided printing, etc.).

The data interpretation process includes a formatting phase, during which commands are executed to indicate how the document's content should be laid out on the page. The formatting process also involves converting font outlines and vector graphics to rasters. These character bitmaps are placed in a temporary font cache, from where they are retrieved as needed for immediate use elsewhere in the document.

The formatting process uses a detailed set of commands to determine the exact location of every character and graphic on every page of the document. At the end of the data interpretation process, the controller executes commands to create an array of points that will then be transferred to paper. This procedure is called rasterization. The created array of points is placed in the page buffer and remains there until it is transferred to paper. Printers that use stripe buffers divide the page into multiple horizontal stripes. The controller rasterizes the data of one strip, sends it for printing, clears the buffer and begins processing the next strip (the page falls on a photosensitive drum or other printing device in parts).

After rasterization, the page image is stored in memory and then transferred to the printing device, which physically performs the printing process. Printing unit is a general term for devices that directly transfer an image to paper in a printer and includes the following elements: laser scanning unit, photosensitive element, toner container, toner distribution unit, corotrons, discharge lamp, fixing unit, and paper transport mechanism. Most often, these elements are structurally made in the form of one module (a similar printing device is used in copying machines).

Jet. In inkjet printers, ionized ink droplets are sprayed onto the paper through nozzles. Spraying occurs in those places where it is necessary to form letters or images.

The data interpretation processes for inkjet and laser printing are essentially similar. The only difference is that inkjet printers have less memory and a less powerful computing system. Liquid ink is sprayed directly onto the paper - in those places where an array of dots is formed in a laser printer. There are currently two main types of inkjet printing: thermal and piezoelectric. The cartridge consists of a reservoir of liquid ink and small (about one micron) holes through which the ink is pushed onto the paper. The number of holes depends on the printer resolution and can range from 21 to 256 per color. Color printers use four (or more) reservoirs of different color inks (cyan, magenta, yellow, and black). By mixing these four colors, almost any color can be produced.

1.3Plotter

The task of displaying information presented in graphical form arose simultaneously with the advent of computing, and its solution is one of the main goals of computing tools used for design automation. Devices that perform the functions of displaying graphic information on paper and some other media are called plotters or plotters (from the English plotter).

Pen plotters

Pen plotters are vector-type electromechanical devices. Graphic images and various vector software systems such as AutoCAD are traditionally output to them. Pen plotters create images using writing elements, collectively called pens, although there are several types of such elements, differing from each other in the type of liquid dye used. Writing elements can be disposable or reusable (rechargeable). The pen is mounted in a writing unit holder, which has one or two degrees of freedom of movement.

There are two types of pen plotters: tablet, in which the paper is stationary and the pen moves across the entire image plane, and drums, in which the pen moves along one coordinate axis, and the paper along the other due to capture by the transport shaft. Movements are performed using stepper or linear electric motors, which create quite a lot of noise. Although the accuracy of information output with drum plotters is slightly lower than with flatbed plotters, it meets the requirements of most tasks. These plotters are more compact and can automatically cut a sheet of the required size from a roll (A3 pen plotters are usually flatbed).

A distinctive feature of pen plotters is the high quality of the resulting image and good color rendition when using colored writing elements. Unfortunately, the speed of information output in them is low, despite faster mechanics and attempts to optimize the drawing procedure.

Inkjet plotters

Inkjet imaging technology has been known since the 70s, but its true breakthrough became possible only with the development by Canon of the technology for creating a reactive bubble (Bubblejet) - directed spraying of ink onto paper using hundreds of tiny nozzles of a disposable print head. Each nozzle has its own microscopic heating element (thermistor), which instantly (in 7-10 μs) heats up under the influence of an electrical pulse. The ink boils and the vapor creates a bubble that pushes a drop of ink out of the nozzle. When the pulse ends, the thermistor quickly cools down and the bubble disappears.

Print heads can be “color” and have a corresponding number of nozzle groups. To create a full-fledged image, the standard CMYK color scheme for printing is used, using four colors: Cyan - cyan, Magenta - magenta, Yellow - yellow and Black - black. Complex colors are formed by mixing basic colors, and shades of different colors are obtained by thickening or thinning out the dots of the corresponding color in a fragment of the image.

Inkjet technology has a number of advantages. These include ease of implementation, high resolution, low power consumption and relatively high printing speed. Reasonable price, high quality and great capabilities make inkjet plotters a serious competitor to pen devices, however, the low speed of displaying graphic information and fading of the resulting color image over time without taking special measures limits their use.

Electrostatic plotters

Electrostatic technology is based on the creation of a latent electrical image on the surface of the carrier - special electrostatic paper, the working surface of which is covered with a thin layer of dielectric, and the base is impregnated with hydrophilic salts to provide the required humidity and electrical conductivity. The potential relief is formed when free charges are deposited on the surface of the dielectric, formed when the thinnest electrodes of the recording head are excited by high-voltage voltage pulses. When paper passes through a developing unit containing liquid magnetized toner, toner particles are deposited on charged areas of the paper. The full color gamut is obtained by four cycles of creating a latent image and passing the media through four developing nodes with the corresponding toners.

Electrostatic plotters could be considered ideal devices, if not for the need to maintain stable temperature and humidity in the room, the need for careful maintenance and their high cost, due to which they are purchased by users who have justifiably high demands on performance and quality. To achieve maximum efficiency, electrostatic plotters usually operate as network devices, for which they are equipped with network interface adapters. Also important are the high resistance of the image to ultraviolet rays and the low cost of electrostatic paper.

Direct image plotters

The image in such plotters is created on special thermal paper (paper impregnated with a heat-sensitive substance). Thermal paper, which is usually fed from a roll, moves along the “comb” and changes color where it is heated. The image is high quality (resolution up to 800 dpi (dots per inch)), but only monochrome. Given their high reliability, productivity and low operating costs, direct image output plotters are used in large design organizations to output test copies.

Thermal transfer plotters

The difference between these plotters and plotters for direct image output is that in them, between the thermal heaters and the paper, a “donor color carrier” is placed - a thin, 5-10 micron thick, tape facing the paper with an ink layer made on a wax base with a low (less than 100 ° C) melting point.

On the donor tape, areas of each of the primary colors are sequentially applied in a size corresponding to the sheet of the format used. In the process of outputting information, a sheet of paper with a donor tape applied to it passes under the print head, which consists of thousands of tiny heating elements. The wax melts in places of heating, and the pigment remains on the sheet. One color is applied in one pass. Her image is obtained in four passes. Thus, each sheet of color image uses four times more ink ribbon than each sheet of monochrome image.

Due to the high cost of each print, these plotters are used as part of computer-aided design tools for high-quality output of 3D modeling objects, in cartography systems, and by advertising agencies for outputting color proofs of posters and banners for colorful presentations.

Laser (LED) plotters

These plotters are based on electrographic technology, which is based on the physical processes of the internal photoelectric effect in photosensitive semiconductor layers of selenium-containing materials and the force of an electrostatic field. The intermediate image carrier (a rotating selenium drum) can be charged to a potential of hundreds of volts in the dark. A beam of light removes this charge, creating a latent electrostatic image that attracts magnetized fine toner, which is then mechanically transferred to the paper. The toner-coated paper is then passed through a heater, causing the toner particles to bake to create an image.

Due to their high speed (an A1 sheet is printed in less than half a minute), laser plotters are convenient to use as network devices, and they have a network interface adapter as standard. Equally important, these plotters can operate on plain paper, which reduces operating costs.

1.4 Projector

A projector is a lighting device that redistributes lamp light with a concentration of luminous flux on a small surface or in a small volume. The main element of any projector is a lamp, the light of which, passing through certain elements, hits the screen and thus forms a picture. Depending on which elements the light from the lamp passes through, projectors are divided into LCD And DLP(micromirror). The advantages of liquid crystal projectors include a less negative impact on vision, as well as compactness. Their disadvantage is the insufficiently saturated black color (owners of LCD monitors will understand what we are talking about). The advantage of micromirror projectors is a higher quality picture, but their main disadvantage is considered to be visual fatigue when viewed for a very long time.

Like any technical device, projectors have characteristics that you should pay attention to first. Firstly, this is the so-called “base graphics resolution”. It is indicated by two numbers reflecting the number of points horizontally and vertically. Like monitors, the resolution can be 800x600, 1024x768, etc. up to 1600x1200. Of course, the higher the resolution, the better the picture quality will be. For a home projector whose main task is watching movies, a resolution of 800x600 will be quite sufficient. This is due to the fact that films intended for viewing on a TV screen have an even lower resolution, so 800x600 is already quite enough. Secondly– projector brightness. The brighter the projector, the better. If the brightness is too low, the room may need to be completely darkened for comfortable viewing. And a brightness of 1000 lumens (lumen is a unit of measurement of brightness) will be quite enough for home conditions; lower values ​​are practically not found today. In this case, it is necessary to take into account the operating conditions of the projector. If it is installed in a separate room with the possibility of complete darkness, then such a parameter as brightness is not too important. If you plan to use the projector in a living room, where complete darkness is difficult to achieve, then you should pay attention to such a parameter as brightness. Thirdly– projector contrast. With a low contrast ratio, dark scenes in films may simply not be visible. The contrast ratio of a home video projector should be between 1000:1 and 2000:1.

1. 5 Columns

Speakers, or acoustic system, are another information output device that connects to the computer (there is an input socket on the back of the motherboard) and is used to play sound effects, music, movies, etc. Currently, there are two operating principles for acoustic systems: active And passive.

There is an opinion that active acoustics It is used mostly by professionals, although it can also be connected to computers. The sound is sent from the DVD player through the amplifier (receiver) directly to the speakers of the speaker system. Sound signal amplification plays a key role in this process. How can sound be amplified? There are two ways. First this is when, before being sent to the speakers, the sound signal enters the amplifier, and second– using the speaker system itself, the speakers of which have a built-in amplifier.

In addition to all this, the design of active acoustics allows for feedback between the amplifier and the speaker. This allows the amplifier to change the load on the speaker during maximum load and prevent damage to the speaker. Due to the fact that the amplifiers and speakers in active speakers are directly connected, maximum performance of the speaker system is achieved. This provides a very good sound output with small speaker sizes. Active speaker systems for home use usually consist of a subwoofer and a set of 5 satellites. The subwoofer has a built-in amplifier, which is distributed over six speakers.

But active speakers have a minus - the impossibility of modernization. Such a speaker system will always sound the same. The significance of this fact is very significant. Having become interested in acoustic systems, the buyer turns into a lover of audio equipment and tries from time to time to improve the sound quality of his home acoustics. Therefore, the owner of active acoustics will have to come to terms with the quality of the sound produced by it once and for all. They try to make active speakers initially of a high level.

When working passive speaker system The built-in crossover gets hot, because it takes on a fairly large output power. Manufacturers are trying to avoid this in various ways, but the main thing is to understand the essence of this process. The amplifier sufficiently loads the electronics of the speaker system, as a result of which the quality of the sound produced, just like the characteristics of passive speakers, changes. If the speakers are used in a home theater, then an amateur is unlikely to hear the difference. But for a professional, this difference will be quite critical. Passive speakers need to be slightly more powerful than the amplifier in order to cope with the power entering them at critical moments. Otherwise, when the amplifier is more powerful than the acoustics, the speakers may simply fail. Passive loudspeaker systems cannot provide feedback to the amplifier so that it delivers less power, and the amplifier itself cannot monitor the load. Despite its shortcomings, a passive loudspeaker system is not so bad. Most buyers of speaker systems buy it for a home theater, computer, and at home, as you know, comfort and coziness are very much valued. Active acoustics require a separate power cord for each speaker. So connecting all active speakers to the network can become a very confusing task. The next point is much more important. Since all speaker systems are divided into classes, when using passive acoustics, you can upgrade the system over time by purchasing a new amplifier and receiver. The sound quality of good passive speakers can improve significantly. Therefore, when choosing passive acoustics, you can take speakers, as they say, “for growth.”

Chapter 2.Input Devices

2.1Keyboard

Now the main widely used input device

The computer has a keyboard (keyboard device). She implements

interactive communication between the user and the PC:

Entering user commands to provide access to PC resources;

Recording, adjusting and debugging programs;

Entering data and commands into the problem solving process.

The MFII keyboard standard has now been adopted. Conditionally in it

We can distinguish five groups of keys that carry their own functional meaning.

Among other types of keyboards, we can mention special keys for

blind people with touchable dots on the keys; keyboards for shops and

warehouses equipped with devices for reading barcodes or

reading magnetic cards; industrial keyboards - touch, with

as protection against harmful influences (shavings, ash, etc.)

additional covering of keys with special touch foil; keyboard

for medical institutions with devices for reading information from

insurance cards. Currently, keyboards have appeared with additional

keys for ease of working with a particular operating system (OS),

for example, a keyboard for Windows 95.

Thus, the choice of keyboard depends on the OS with which

supposed to work.

2.2Mouse

It is used to enter data or single commands selected from a menu

or textograms of graphical shells displayed on the monitor screen.

The mouse is a small box with two or three

keys and a recessed ball that rotates freely in any direction

on the bottom surface. It connects to the computer using

special cord and requires special software support.

To operate the mouse you need a flat surface, for this purpose

use rubber mats.

Since the mouse cannot be used to enter a series of commands into the computer,

Therefore, the mouse and keyboard are not interchangeable devices. Purpose

graphical shells - in ensuring the initialization of many commands without

long time typing them from the keyboard. This reduces the likelihood of typos and

saves time. On an object in the form of a tectorgram, select a menu item or

symbol and a mouse click is initialized. Of course, when typing or

When performing some functions, using a mouse may be irrational,

if, for example, these functions are performed by pressing function keys.

Nowadays there is also an optical mouse where the signal

transmitted using a mouse beam to a special pad and analyzed

electronics. While less common is the tailless (cableless)

infrared mouse (the principle of its operation is similar to that of remote controls

remote control) and radio mouse.

In portable PCs (Lapton, Notebook), the mouse is usually replaced with a special built-in

into the keyboard with a ball on a stand with two keys on the sides, called

The principle of its operation is the same as the principle of the mouse. Despite

presence of a trackball, a laptop PC user can use a regular

2.3.Scanners

For direct reading of graphic information from paper or

Optical scanners are used for other media in PCs.

The scanned image is read and converted into digital form

elements of a special device: CCD chips.

There are many types and models of scanners. Which one to choose?

depends on the tasks for which the scanner is intended.

The simplest scanners recognize only two colors: black and white.

These scanners are used to read bar codes.

Hand-held scanners are the simplest and cheapest. The main disadvantage is

that the person himself moves the scanner around the object, and the quality of the result

images depend on the skill and steadiness of the hand. Another important drawback is

small scanning strip width, which makes it difficult to read wide

originals.

Drum scanners are used in professional printing

activities. The principle is that the original is on the drum

is illuminated by a light source, and photosensors convert the reflected radiation into

digital value.

Sheet scanners. Their main difference from the previous two is that

When scanning, the ruler with CCD elements is fixedly fixed, and the sheet

with the scanned image moves relative to it using special

Flatbed scanners. This is the most common type now

professional works. The object to be scanned is placed on a glass sheet,

the image is read line by line at a uniform speed by the reading head with

CCD - sensors located at the bottom. A flatbed scanner can be

equipped with a special slide attachment for scanning

slides and negatives.

Slide scanners are used to scan micro-images.

Projection scanners. A relatively new direction. Color projection

the scanner is a powerful multifunctional tool for entering into a computer

any color images, including three-dimensional ones. He may well replace

camera.

Nowadays, scanners have another application - reading

handwritten texts, which are then used by special recognition programs

characters are converted to ASC II codes and can be further processed

text editors.

Conclusion

This course work provided fairly detailed information about information output/input devices and the principles of their operation. It is impossible to imagine the operation of a modern computer without equipping it with the above devices, since they provide indispensable assistance when the user works with a computer, and knowledge of the principles of operation of these devices ensures their more efficient use.

Conclusions from the laboratory work performed. During...