|
Arabic
Bengali
Chinese
English
French
German
Hebrew
Hindi
Italian
Japanese
Korean
Malay
Polish
Portuguese
Spanish
Turkish
Ukrainian
Vietnamese|
ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING How TV works. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur [an error occurred while processing this directive] Do you love TV as much as I don't? TV is generally a disgusting thing. Than sitting for hours in front of the "blue screen", it is much more useful to lead a healthy lifestyle: slowly, with a cup of coffee - at the computer ... Nevertheless, the things that I will tell in this series of articles may be quite useful in our practical activities. So, now we will figure out how the video signal is transmitted. We will consider the painfully native SECAM system, because in our country (namely, the Russian Federation) this television system has been officially adopted. However - first things first. How does a TV work? The TV is on 24 hours a day, 7 days a week. It's clear. It has a screen - 1 piece and a speaker - from 1 to infinity, depending on the "tricks" of the unit. He also has an antenna and a remote control. But we are now only interested in the screen. And translating from the language of housewives into the language of wise cats - kinescope (cathode ray tube - CRT). I understand perfectly well that in our age of plasma and liquid crystal, the cathode-beam kinescope seems to someone a relic of antiquity. However, to understand the principle of operation of the TV, the easiest way is to deal with the CRT. Cathode-ray tube What is it. And what about the electrons? And what about rays? The fact is that the picture on the screen is drawn using an electron beam. An electron beam is very similar to a light beam. But a light beam consists of photons, and an electron beam consists of electrons, and we cannot see it. A bunch of electrons are rushing at breakneck speed in a straight line from point A to point B. This is how a "beam" is formed. Point B is the anode. It's right on the back of the screen. Also, the screen (on the reverse side) is smeared with a special substance - a phosphor. When an electron collides at breakneck speed with a phosphor, the latter emits visible light. The faster the electron flew before the collision, the brighter the light will be. That is, a phosphor is a converter of the "light" of the electron beam into light visible to the human eye. Point B is dealt with. What is point "A"? A is "electron gun"The name is terrible. But there is nothing terrible in it. It is not intended to brutally shoot aliens from Mars. But it still knows how to" shoot "- with an electron beam at the screen. How is it all arranged? In general, a CRT is such a large electronic lamp. How? Do you know what a lamp is? OK… Electronic lamps - these are the same amplifying elements as the transistors we all love. But lamps appeared much earlier than their silicon "colleagues", back in the first half of the last century.
Lamp - This is a glass container from which air is pumped out. In the simplest lamp, there are 4 terminals: a cathode, an anode, and two filament terminals. The filament is needed to heat the cathode. And you need to heat up the cathode in order for electrons to fly from it. And the electrons must fly then, so that an electric current arises through the lamp. To do this, a voltage is usually applied to the filament - 6,3 or 12,6 V (depending on the type of lamp) In addition, in order for electrons to fly, a high voltage is needed between the cathode and the anode. It depends on the distance between the electrodes and on the power of the lamp. In conventional radio tubes, this voltage is several hundred volts; the distance from the cathode to the anode in such lamps does not exceed a few millimeters. In a kinescope, the distance from the cathode located in the electron gun to the screen can exceed several tens of centimeters. Accordingly, much more tension is needed there - 15…30 kV. Such brutal voltages are created by a special step-up transformer. It is also called a horizontal transformer because it operates at horizontal frequency. But more on that later. When an electron hits a screen, besides visible light, other radiations are also "knocked out". Particularly radioactive. That is why it is not recommended to watch TV closer than 1 ... 2 meters from the screen.
So, we got the beam. And it shines so beautifully exactly in the center of the screen. But we need it to "draw" lines on the screen. That is, you need to make it deviate from the center. And in this moms will help ... electromagnets. The fact is that an electron beam, unlike a light beam, is very sensitive to a magnetic field. Therefore, it is used in CRT.
It is necessary to put two bunk deflecting coils. One pair will deflect horizontally, the other vertically. Skillfully managing them, you can drive the beam around the screen anywhere. And anywhere? This is where we begin our story about lines of dots and hooks ... A Tale of Lines, Dots and Hooks The picture on the TV screen is formed as a result of the fact that the beam draws from left to right from top to bottom across the screen at breakneck speed. This method of sequential drawing of the image is called "scan".
Since the scan is very fast - for the eye all the points merge into lines and the lines into a single frame. In PAL and SECAM systems, the beam has time to run through the entire screen 50 times in one second. In the American NTSC system - even more - as many as 60 times! Generally speaking, PAL and SECAM systems differ only in color reproduction. Everything else they have is the same. The picture is formed due to the fact that during the "running", the beam changes its brightness in accordance with the received video signal. How is brightness controlled? And very simple! The fact is that in addition to the considered electrodes - anode и cathode, in lamps there is also a third electrode - net. Сетка is the control electrode. By applying a relatively low voltage to the grid, the current flowing through the lamp can be controlled. In other words, it is possible to control the intensity of the flow of electrons "flying" from the cathode to the anode. In a CRT, a grid is used to change the brightness of the beam.
By applying a negative voltage to the grid (relative to the cathode), it is possible to weaken the intensity of the electron flow in the beam, or even close the "road" for electrons. This may be necessary, for example, when moving a beam from the end of one line to the beginning of another. Now let's talk in more detail about the principles of sweep. To begin with, it is worth remembering a few simple numbers and terms: Raster - this is one "line" that the ray draws on the screen. Field - these are all the lines that the ray drew in one vertical pass. Frame - This is the elementary unit of the video sequence. Each frame consists of two fields - even and odd. This is worth explaining: the image on the TV screen unrolls at a rate of 50 fields per second. However, the television standard is 25 frames per second. Therefore, one frame during transmission is divided into two fields - even and odd. The even field contains only the even lines of the frame (2,4,6,8…), the odd field contains only the odd ones. The image on the screen is also "drawn" through the line. Such a sweep is called "interlacing".
It still happens"progressive scan"- when the entire frame is deployed in one vertical beam stroke. It is used in computer monitors. So, now dry numbers. All numbers given are valid for PAL and SECAM systems. Number of fields per second - 50 Number of lines per frame - 625 Number of effective lines per frame - 576 Number of effective points per line - 720 And these numbers are derived from the above: Number of lines in the field - 312,5 Horizontal frequency - 15625 Hz Duration of one line - 64 μs (together with the reverse beam path)
Next, we will talk about the parameters of the video signal and draw up a circuit that synthesizes synchronization pulses. Publication: radiokot.ru
Traffic noise delays the growth of chicks
06.05.2024 Wireless speaker Samsung Music Frame HW-LS60D
06.05.2024 A New Way to Control and Manipulate Optical Signals
05.05.2024
▪ Efficient triboelectric generator ▪ Optical Neural Network Accelerator ▪ Smart material based on shark skin ▪ APD-CMOS image sensor shoots at 0,01 lux illumination
▪ site section Tone and volume controls. Article selection ▪ article Anesthesiology and resuscitation. Crib ▪ article How did imperfect knowledge of English help discover a sugar substitute? Detailed answer ▪ article Physician for the hygiene of children and adolescents. Job description ▪ article Turpentine varnishes. Simple recipes and tips ▪ article Pencils as rays. physical experiment
Home page | Library | Articles | Website map | Site Reviews
www.diagram.com.ua |
See other articles Section 
Latest news of science and technology, new electronics:
All languages of this page