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Sunday, 25 July 2021

Scanning Principles of Television

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SCANNING PRINCIPLES OF TELEVISION


Scanning is a technique for converting the charge images created within a television camera tube into a variable electrical signal. The TV image is scanned in a sequence of horizontal lines that are stacked one on top of the other. It's the same as reading a text page and covering all of the words in one line and all of the lines on the page. All of the picture elements are scanned one line at a time, from left to right and top to bottom.


The scene is scanned in both the horizontal and vertical directions at the same time to generate enough full images or frames per second to maintain continuous motion. Most television systems have a frame repetition rate of 25 frames per second. The following is the order in which all of the picture elements should be scanned. They are,


1. An electron beam passes over a horizontal line, transforming all of the image components in that line. Trace is the name given to this period. Horizontal scanning is used to accomplish this.


2. The beam immediately returns to the left side after each line to begin scanning the following horizontal line. Retrace or fly back are the terms used to describe the return lines. Because both the camera tube and the image tube are blanked out during retrace, no picture information is scanned. As a result, the retraces must be very quick, as they lose time in terms of image information.


3. When the beam returns to the left side, the vertical position of the beam is lowered so that it scans the next line down instead of repeating the same line. The vertical scanning motion of the beam achieves this.


Types of scanning:


a. Horizontal Scanning

b. Vertical Scanning

c. Flicker

d. Interlaced Scanning


(A) HORIZONTAL SCANNING:


The electron beam is deflected across the screen with a continuous, uniform motion for the trace from left to right due to the linear increase of current delivered to the horizontal deflection coils. The sawtooth wave direction swiftly reduces to its starting value at the top of the ascent. The retrace or fly back is the result of these quick reversals. At the left border of the raster, the horizontal trace begins. The finish is on the right edge, where the flyback causes a retrace to the left.

Figure 1:   Waveform of Horizontal Deflection Coils

Figure 1 shows the waveform of the horizontal deflection coil. The horizontal displacement to the right corresponds to ‘up' on the sawtooth wave. The usable scanning time is indicated by the dark line, while the retrace time is indicated by the dashed lines. To contain a higher number of image elements and hence more information, the number of scanning lines for a single full picture should be large. The horizontal scanning frequency is 15,625 Hz in the 625 line system.


(B) VERTICAL SCANNING:


While the electron beam is being deflected horizontally, the sawtooth current provided to the vertical deflection coils moves the electron beam at a consistent pace from top to bottom of the raster. As a result, when traveling from top to bottom, the beam creates one below the other. In Figure 2, we can see the vertical scanning waveforms.

Figure 2 Vertical Deflection Waveform

The vertical scanning beam is deflected to the bottom of the raster by the trace component of the sawtooth wave, as illustrated in Fig. After that, the beam is quickly vertically retraced back to the top. At the bottom of the raster, the vertical sweep current achieves its maximum amplitude, delivering the beam to the raster's bottom.


The horizontal scanning is ongoing during vertical retrace, and numerous lines are scanned during this time. The information is transformed into an electrical signal using the scanning beam. The vertical scanning frequency is 25Hz, that is every second 25 frames are scanned.


The scanning beams at the camera tube and picture tube are blanked and no picture information is picked up or reproduced during the horizontal and vertical retrace intervals.


(C) FLICKER:


The television picture's scanning rate of 25 frames per second is insufficient to allow the brightness of one picture or frame to merge seamlessly into the next. The screen is blanked in between each frame as a result of this effect. As the screen alternates between bright and dark, the effect is a distinct flicker of light. All the lines in the frame are scanned in a progressive sequence from top to bottom when progressive scanning is used. The Flicker effect is created because there are only 25 blank-outs each second. 50 blank-outs per the second result from scanning 50 full frames each second. Human eyes can no longer perceive this rapid fluctuation, therefore the flicker effect is no longer visible. The video frequencies associated with the image elements are multiplied in a line as a result of this effect. Interlaced Scanning is the approach used to tackle this sort of problem.


(D) INTERLACED SCANNING:


Flicker is reduced in these television pictures by using 50 vertical scans per second effective rate. This is accomplished by increasing the scanning electron beam's downward velocity of motion, causing each alternative line to be scanned instead of the next line. When the beam reaches the bottom of the picture frame, it quickly returns to the top to scan the lines missed during the previous scan. As a result, the total number of lines is divided into two groups known as "Fields." Each field can also be scanned separately. This scanning method is referred to as 'Interlaced Scanning.' Interlaced scanning is described in Figure 3 for the 625 line system.

Figure 3 Interlaced Scanning

Each Frame's total lines are split into two fields. They are:


a. Odd field and

b. Even field


Odd lines in the frames are contained in the first and subsequent odd fields. The even scanning lines appear in the second and all even fields. The frame repetition rate is 50 per second, with two fields each frame and 25 full frames scanned per second. In reality, increasing the vertical scanning frequency from 25 to 50 Hz scans every other line in the picture. There are 312.5 lines per field.


The beam originates at A and sweeps across the frame at a constant velocity, covering all of the image elements in a single horizontal line. The beam retraces quickly to the left side of the frame after this trace, ready to scan the following horizontal line. Because the vertical deflection signal creates a vertical scanning motion, which is slower than horizontal scanning, the horizontal line slopes downward in the scanning direction.


The beam is now at the left side, ready to scan line 3, omitting the second line, once line ‘1' has been scanned. The vertical scanning frequency is increased from 25 to 50 Hz to achieve this line skipping. The electron beam now scans all of the odd lines before arriving at a location towards the bottom of the frame, such as point B in the diagram. Because of the flyback on their vertical saw tooth defection signal, the vertical retrace starts at time B. The beam then returns to the frame's top, where the second or even fields begin.


The beam now moves several horizontal lines from B to C. 20 horizontal lines are drawn during this time. Because the scanning beam is turned off at this time, these 20 lines are known as inactive lines. As a result, the raster's second field begins in the center. The beam scans line 2 in the second field after scanning half of a line from point C.


The beam then scans the even lines that were left out of the initial field's scanning. In this field, the vertical scanning action is identical to that of the preceding field. As a consequence, the second field's even lines, down to point D, are scanned. Because the second field begins at a half-line point, points D and B are a half-line distance from each other.


In the second field, the vertical retrace starts at point D. The vertical flyback causes the beam to return to the top from here. The beam completes the second vertical retrace at A because there are so many vertical retrace lines. Because the number of vertical retrace lines in both fields is the same, the beam will always end the second vertical retrace where the first trace began. At point A, all odd fields begin. Point C is the starting point for all even fields. This technique is repeated 50 times each second, which effectively eliminates flicker.

Wednesday, 21 July 2021

PAL Colour TV Receiver Block Diagram with Explanation

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PAL Colour TV Receiver Block Diagram with Explanation:


A colour TV receiver is identical to a black-and-white receiver with the addition of a chroma section and a colour image tube. Figure 5.7 shows a block schematic of a PAL colour TV receiver. This receiver's many parts are detailed below.


1. VHF and UHF Tuner:


The TV receiver has a VHF and UHF tuner on the front. It has a tuned circuit that allows you to choose the channel you want. The antennal signal is amplified and transformed into an IF signal, which is then sent into the video IF amplifier. Tuners also include an automatic frequency tuning feature for accurate colour reproduction.


2. Video IF Amplifier:


Since the tuner's output signal isn't strong enough to drive the video detector, it's amplified to the appropriate level via cascaded IF amplifiers.


3. Video Detector:


From the modulated composite video stream, the video detector recovers the original video signal.


4. Sound Section:


Trap Circuit, Limiter, FM Detector, Audio Amplifier, Power Amplifier, and Loudspeaker are all included in the sound area. The original sound signal is initially recovered from the modified sound carrier signal at this step. The FM detector's output is suitably amplified and applied to the loudspeaker for sound reproduction.


5. Automatic Gain Control Circuit:


Despite the intensity of the input signal, the Automatic Gain Control (AGC) circuit keeps the output signal at a consistent amplitude. The sync separator recovers the H and V sync pulses in the deflection circuit. Proper oscillators and amplifiers are used to process them. Finally, applied to the V and H deflection coils to concurrently deflect electron beams in the V and H directions.


6. Luminance Signal:


From the video detector, the chrominance and luminance signals follow independent routes before rejoining in the matrix portion. From the composite video stream, the luminance signal processing network recovers the luminance (Y) signal. The cathodes of colour picture tubes generally receive a negative-going Y signal (-Y).


7.  Color Signal Processing:


The signal available at the output of the video detector is properly amplified before feeding it to the various sections.


a) Chrominance Band Pass Amplifier: The chrominance bandpass amplifier selects the chrominance signal while rejecting the composite signal's other undesirable components.


b) Burst Banking Circuit: During colour burst periods, this circuit blocks signal flow to the chrominance bandpass amplifier.


c) Burst Amplifier: The burst gate amplifier isolates the colour burst signal from the chrominance signal while also enhancing it to the appropriate level. This transmission has a frequency of 4.43 MHz.


d) Generation and Control of Subcarriers: The major goal of this section is to generate a subcarrier with the right frequency. The phase discriminator and variable reactance components combine to serve as an Automatic Phase Control circuit in the subcarrier oscillator, which is a crystal oscillator used for creating subcarrier signals with a frequency of 4.43 MHz. It picks up subcarrier and burst signals.


If the frequency of the subcarrier oscillator is exactly right, its phase is altered by 90o for the incoming burst signal. The APC circuit's output is fed into a 7.8 kHz tuned amplifier. The 7.8 kHz ac component was overlaid on the output signal in this circuit. The output of this circuit is sent into the colour killer and identification circuits.


Before applying the subcarrier output to the V demodulator, the identification circuit controls an electrical switch that alternately reverses the phase of the subcarrier output. The 7.8 kHz component is available at the APC circuit of the reference subcarrier oscillator when a colour signal is received. The chrominance bandpass amplifier now performs the usual operation.


There is no 7.8 kHz during monochrome signal reception. As a result, the chrominance bandpass amplifier is turned off by the colour killer circuits.


8. Separation of U and V Modulation Products:


Here, the PAL delay line circuit, adder, subtractor, V and U sync demodulators, and difference signal amplifiers with matrix network are considered. The chrominance signal generated by the chroma bandpass amplifier is sent into one of the adder and subtractor circuits' inputs. Using a PAL delay line, the same signal is delayed and applied to the other inputs of adder and subtractor circuits.


The U information is the adder's output. Similarly, the subtractor's output is V data. Two separate double sidebands, suppressed carrier RF signals emerge from the adder and subtractor's output. These signals are sent to synchronous demodulators in the U and V bands, respectively. The concern oscillator's colour subcarrier signal is applied straight to the U sync demodulator.


Similarly, the same signal is delivered to the V sync demodulator through an electrical switch to create a + or -90o line by line phase-shifted signal. The original B-Y signal is recovered by the U demodulator. Similarly, the R-Y signal is recovered by the V demodulator. The G-Y signal is produced by combining the two signals in a matrix network. These colour difference signals are applied to the colour picture tube's matching grids.

Friday, 16 July 2021

Compact Disc Recording System Block Diagram

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COMPACT DISC (CD) SYSTEM:


A compact disc (CD) may hold a wide range of data. Compact disc signals are stored in a high-density digital format. As a result, the signals captured are a replica of the original audio stream. Text, picture images, audio, video, and software are all stored on compact discs. The compact disc was formerly the standard for storing audio recordings. The typical CD measures 12 cm (5 inches) in diameter. It is made up of three layers.


1. Transparent Substrate:


A polycarbonate wafer [plastic disc] makes up this layer.


2. Thin metallic Layer:


A thin metallic coating of aluminium alloy is applied to the wafer base. This metallic layer has a lengthy series of pits with a diameter of around 0.5 micrometres. The CD drive generally reads the reflective aluminium film part of the disc.


3. Outer Layer of Protective Acrylic:


The underlying data is further protected by a plastic coating called a protective lacquer layer, which is applied to the aluminium sheet. The CD's layout is seen in Figure.

Fig: Layout CD-ROM Disc

When a CD is made, a glass disc is covered with a photoresist that is sensitive to laser light. The Laser light exposes a precise helical pattern on the photoresist material during recording. Typically, the track width is 0.5m. As each 1 happens, the Laser beam is switched ON and OFF alternately, recording the 1s in the digital data onto the photoresist surface.


No 0's are written to the disc; instead, they are regenerated by the CD player. The photo-resist surface of the disc is exposed during recording 1, resulting in a sequence of pits and lands. Pits appear on the surface of the CD as a result of recording the digital data ‘1'.


Similarly, there is no change in the surface of the digital data 0 when it is recorded. As a result, the pits have a data of 1 and the other areas have a data of 0. The period or distance between 1's determines the length of the pit or land.


1. CD RECORDING :


Using a sample and hold circuit and an ADC, the signal to be recorded on CD is first amplified and then transformed into a digital signal. The output of the ADC is also used by the Laser Beam Generator. The control circuit and the servo system are both controlled by the signal from the crystal oscillator and Laser beam generator.


The servo system, which is controlled by a motor, regulates the disc rotation as well as the track and focus of the Laser beam generator. The picture depicts a block schematic of a CD recording system.


The unexposed photoresist material is chemically removed after recording, leaving a helical pattern across the glass disc's surface. This becomes the glass master for mass-production CDs.

Figure:  Block Diagram of CD Recording

2. CD REPRODUCTION :


The data retrieval system is made up of the phases listed below. 


1. A servomechanism, which spins the CD.

2. A laser head that moves in a radial pattern. The laser head can both emit and detect a 70nm laser beam.


When the disc spins, the laser beam is focused onto the playing surface, where it is reflected by the ‘lands' and scattered by the ‘pits,' resulting in a change in the quantity of light reflected whenever there is a pit-to-land or land-to-pit change. As a result, the pit borders are detected by a laser beam.


A pit border is a ‘1', whereas its absence is a ‘0.' No pit, i.e. land, is indicated by a strong reflection of the light. A light receptor receiver determines whether light is highly reflected, absent, or dispersed. The recorded holes on the CD produce a non-existent or diffused light reflection. The picture depicts the block diagram of a CD replication mechanism.

Figure: Block Diagram of CD Reproduction System

A crystal oscillator signal is compared to the clock signal acquired from the disc. The servo system is controlled by the control circuit's output. The servo system regulates the motor speed as well as the optical mirror and lens system's track correction and focuses adjustments.


The photodetector receives the reflected beam from the disc. The light fluctuations are converted into a digital signal. The digital output is then amplified and transformed to an analogue signal using DAC. As a result, the original modulating signal may be obtained.


The control circuit receives the clock signal from the disc as well as the signal from the crystal oscillator. The servo system is controlled by the control circuit utilizing the two signals. The servo system is in charge of controlling the motor's speed. The optical mirror and lens system, as well as the ray focusing, are all controlled by the servo system. There are two techniques for encoding data on CDs.


They are:

1. CIRC – Cross -Interleave Reed – Solomon Code

2. EFM – Eight to Fourteen Modulations


Advantages of Compact Disc:


1. Certain codes can be used to detect errors on the disc.

2. Because the CD is protected by transparent plastic, it is not damaged by dust, oil, or scratches.

3. The sound reproduction is of high quality, with minimal background noise.

4. There is a high signal-to-noise ratio.

5. The stereo effect is effectively retained.

6. Excellent Channel separation.

7. Small in size.

8. Broad frequency range.

9. There is very little distortion.

10. Flutter does not exist.

11. A compact disc allows for programme selection.

Monday, 12 July 2021

Working Principle of LED Display

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LED DISPLAY UNIT:


While both types of TVs use LCD technology and feature flat-panel designs, LED TV is a more sophisticated form of LCD TV. LED TVs use LED backlighting to illuminate LCDs, making them smaller, brighter, and more detailed than standard LCD TVs. However, not all LED televisions have the same backlighting.


LED television sets have redefined the watching experience in a whole new and improved way. LED displays are even smaller and lighter than LCDs. The operating mechanism of LED televisions is similar to that of LCD televisions. LED televisions may be thought of as a more advanced version of LCD televisions. LED TVs have reduced the disadvantages of LCD TVs.


The fluorescent bulbs in the LCD television took up a lot of space and were heavy, and they didn't always give good colour quality. These flaws have been overcome by LED televisions, which employ an array of LEDs to produce backlighting, as depicted in the figure. LED televisions take up less space than LCD televisions and are thus smaller and lighter. The LEDs may also display the most accurate black-and-white picture.


There are two types of LED TVs on the market right now. One is backlit, and it gets its backlighting from a slew of LEDs mounted on the back of the television display. The other is edge lighted, which gets its illumination from LEDs positioned around the borders of the television display. Edge-lit LED TVs are significantly slimmer than back-lit LED TVs. As a result, edge-lit LED TVs use less energy and are more efficient.


LED TVs use light-emitting diodes to illuminate their LCD panels. LEDs are made up of tiny semiconductors that light when exposed to electricity. The LED TV may change the alignment of the liquid crystal when an electric current is provided to a tiny specified location of the liquid crystal layer.

General concept of LED

This current travels between LED anodes and LED cathodes, which are positively and negatively charged electrodes, respectively. A conventional LCD TV, on the other hand, is backlit by fluorescent lights. These lamps work by emitting ultraviolet rays from mercury vapour, which light up the lamp's phosphor coating.


Unlike pure LED systems, LED-backlit LCDs are self-illuminating. There are several ways to backlight an LCD panel with LEDs, including using white or RGB (Red, Green, and Blue) LED arrays behind the panel, and edge LED lighting, which uses white LEDs arranged around the inside frame of the TV and a light diffusion panel to spread the light evenly behind the LCD panel.


LED Display Features:


1. Reduced energy usage

2. A more evenly distributed colour saturation

3. Creates a picture with a wider dynamic range.

4. a thinner panel

5. More efficient heat dissipation

6. A more vibrant display

7. Increased contrast

8. There are more options available.

9. Less pollution in the environment

Saturday, 10 July 2021

Working Principle of LCD Display

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LCD DISPLAY UNIT:


Colour and monochrome liquid crystal displays (LCDs) of various sizes have been created for TV receivers. LCDs in video display devices are currently available in a variety of sizes and colours, ranging from a few inches to several inches. LCD TVs are television sets that create pictures using LCD technology.


When voltage is applied to an LCD panel, it shines a backlight through a layer of liquid crystals, twisting the changing amounts of light passing through colour filters to form a picture on the screen. By carefully filtering white light, LCD televisions generate a black and colourful image. A series of cold cathode fluorescent lamps (CCFLs) are generally used to give illumination at the back of the panel. A grid of millions of individual LCD shutters is used. It will open and close to enable a specific amount of white light to pass through.


Each shutter is coupled with a coloured filter that removes everything from the original white source except the red, green, and blue (RGB) components. A single sub-pixel is formed by each shutter filter combination. Because the sub-pixels are so small, the three sub-pixels with red, green, and blue colour filters are combined to create a single colour spot known as Pixel.


The relative strength of the light flowing through the sub-pixels is used to adjust the colour shade. The front and rear of a typical shutter assembly are formed by a sandwich of many layers placed on two thin glass sheets. The polarising film, glass sheet, active matrix components, and addressing electrodes appear first on the back sheet, followed by the director.

Fig: General concept of the LCD unit.

The active matrix components are replaced by patterned colour filters on the front sheet, which is comparable to the back sheet. A patterned plastic sheet is sandwiched between the two sheets, dividing the liquid crystal into separate shutters. The shutter assembly is coupled with control electronics and a backlight to form a full television.


A single bulb or a group of lights can be used to create a backlight. To disperse the light, a diffuser or frosted mirror is utilised. A column of liquid crystal molecules is suspended between two transparent electrodes and two polarising filters in each pixel. The polarizer's axes are perpendicular to one another. Light flowing through one would be blocked by the other if the liquid crystals were not there.


The polarization of light entering one filter is twisted by the liquid crystal, allowing it to pass through the other. The liquid crystal molecule is relaxed before an electrical charge is applied. The helical shape or twisting of these molecules is caused by charges on the molecules.


The light that passes through one polarised filter is rotated as it travels through the liquid crystal, allowing it to pass through the second polarised filter and making the assembly transparent. The molecules of the liquid crystal align themselves parallel to the electric field when an electric charge is given to the electrodes, thus restricting the rotation of incoming light. The light travelling through the liquid crystals will be polarised perpendicular to the second filter if they are entirely untwisted, and therefore completely blocked.


The pixel will appear to be dark. Light may be permitted to flow through in various amounts by regulating the twist of the liquid crystal in each pixel, lighting the pixel accordingly. The LCD panel provides excellent colour reproduction and contrast. CRT displays are limited in size, therefore they may be manufactured in bigger proportions. Despite their size, they are light in weight and maybe readily placed, especially if mounted on a wall.

 

Advantages of LCD are:


1. LCD's have great Compactness.

2. LCD's are thinner and lightweight devices.

3. It is inexpensive.

4. It uses a few microwatts for display, compared to a few milliwatts for LEDs.

5. When compared to CRT and LED, it uses less electricity.


Disadvantages of LCD:


1. Contrast and brightness are lacking.

2. Additional light sources are required.

3. The operating temperature range is restricted.

4. Lack of trustworthiness.

5. The speed is really slow.

6. AC drives are required for LCDs.


Applications of Liquid Crystal Display (LCD)


1. Thermometer with liquid crystals.

2. Optical imaging is a type of imaging that uses light to create images.

3. The liquid crystal display technology may also be used to visualise radiofrequency waves in waveguides.

4. It's used in medical settings.

Monday, 28 June 2021

CCTV Simple Block Diagram with Explanation

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CCTV Block Diagram with Explanation


Closed Circuit Television (CCTV) is a system in which the circuit is closed and all of the elements are directly connected. We know that, in broadcast television, from the airwaves, any receiver that is correctly tuned can pick up the signal. In CCTV this is different. Systems interconnected via microwave, infrared beams, and other means are examples of directly connected networks.

CCTV Simple Block Diagram

The camera tube is used to transform light from an item that the camera is focused on into electrical impulses. The lens mechanism focuses light from the object on the light-sensitive surface (called the mosaic or photoconductive material) in the camera tube. An electron gun is housed in the camera tube, which creates and regulates a stream of electrons. The narrow stream of electrons is directed by the cannon in such a way that it crosses (scans) the mosaic line by line. When the beam hits a point in the mosaic, it creates a little electrical impulse that corresponds to the brightness or darkness of that specific small area of the image. The visual amplifier receives the electrical impulses created in this manner.


Control Unit :


In a CCTV, the control unit is considered as the system's heartbeat. This unit links all of the system's other components. Drive pulses are created, and the camera's sweep and blanking signals are developed. The control unit sends synchronizing and blanking pulses to the receiver/monitor.


The camera's video signals are amplified and sent to the receiver/monitor. Vertical and horizontal blanking, sync, and video signals are among the control unit's output signals. The video amplifier, control amplifier, carrier, amplitude modulator, radio-frequency (RF) amplifier, sync generator, and audio controls make up the control unit.


A wide variety of frequencies can be amplified using video amplifiers. The video amplifier amplifies the camera tube's weak electrical impulses and feeds them to a control amplifier.


The control amplifier combines the video, sync, and blanking signals into a single continuous output to the amplitude modulator, all inappropriate order.


Synchronizing (sync) and blanking pulses are generated by circuits in the sync generator. The control amplifier receives these pulses, which constitute part of the broadcast signal. Horizontal synchronization occurs when horizontal scanning at the receiver and horizontal scanning at the camera occur at the same moment. Vertical synchronization keeps the receiver's vertical scanning in sync with the camera's vertical scanning.


The camera circuits also receive synchronization and blanking signals, which are used to generate the appropriate control signals for the electron gun and sweep voltages for the deflection coils (both horizontal and vertical). The main circuit of the carrier is an oscillator that produces a steady, continuous RF signal. Its frequency is set by the relevant civil authorities for the TV station where it is broadcast.


The video, sync, and blanking pulses modify the carrier signal in the amplitude modulator. The R amplifier amplifies the composite (total) signal before feeding it to the antenna for transmission into space.


A frequency-modulated R carrier transmits the sound part of the television broadcast. A microphone picks up the noises, which are then boosted by the audio amplifier and sent to the frequency modulator unit. The frequency of the sound earner is adjusted to match the frequency of the audio signal picked up by the microphone. An R power amplifier then amplifies the frequency modulated signal. The data is then transmitted into orbit through an antenna or a cable system placed throughout the ship.


Receiver/Monitor :


The receiver/monitor unit is the picture-producing unit. The only difference between the receiver and the monitor is the circuitry in each device. The receiver and monitor devices use different types of transmission medium. This discrepancy necessitates the use of extra circuits by the receiver. (Radio waves are used for the receiver, whereas cables are often used for the monitor). The antenna system, tuner, R. The basic TV receiver comprises the same circuits as the monitor, as well as the antenna system, tuner, and R.


Applications of CCTV :


Security systems and applications such as retail shops, banks, and government organizations are among the most well-known uses of CCTV. The real spectrum of possible applications is nearly limitless.


Examples are:


• Focusing on traffic on a bridge.

• Record the inside of a bake oven to figure out what's wrong.

• A makeshift technique for conducting a traffic study in a city center.

• For the animation of plasticizing puppets, the time-lapse recording was used.

• Used by a show's stage manager to see hidden sections of the set.

• Its widespread use in football stadiums.

• Vandalism was controlled by hiding in buses.

• Observing a gorilla's birth at a zoo.

• Using a big model helicopter to create a wildlife program.

• Replicating a goldfish's infrared eyesight!

• Photographs taken from a hot air balloon.

• Factory production control.

Thursday, 24 June 2021

What is Handycam

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Handycam (Camcorder)


The term camcorder refers to a portable device that records audio and video into a storage medium. The term camcorder refers to a device that combines the functions of a camera and a recorder into one item. It's also known as a handy camera. Digital cameras nowadays save their footage on a small DVD or DVD.


It can record and capture both moving and still images. Handy cameras are capable of producing high-definition films and documents. Charge-coupled devices (CCD) and an image sensor are used in the handy camera. It transforms the captured object light (image) into a video signal.


The picture and sound data are stored on the videotape or memory chip once the video signal is transformed to the format required by the handy cam. Analog and digital handy cams are the two varieties available. Analog handy cams record video signals as a continuous track of magnetic patterns on a videocassette. The digital handy cam transforms analog data into digital form and records video and audio in digital format.


Because it offers the following features, a digital handy cam is costly.


1. Make the recording last longer.

2. Provide higher-resolution 16-bit audio.

3. It is simple to modify and archive.


Digital video handy cams use smaller cassettes and capture images in digital mode. DVD handy cams digitally record video onto 8cm DVDs that can contain an hour of footage. To store still pictures and web-quality video clips, many handy cams employ flash memory cards in addition to the basic recording medium. The handy cam's CCD sensor serves as its brain.


It scans the light emitted by the item and transforms it into electric impulses. The size of the CCD sensor, the number of active pixel components, the technology utilized in CCD circuitry, and the quantity of CCDs all influence its efficacy. The color information is scanned and sent by a single CCD in most compact cameras. The picture captured by the lens system is converted into three images, one for each basic color, using a single sensor handy cam (Red, Green, and Blue).


The CCDs transform the resultant pictures into digital data, which is subsequently recorded on the digital video. As a consequence, the recording quality improves. Three CCD handy cameras record color more precisely and collect more information. For high image quality, the lens is frequently the most costly component. Before processing, the object information, which includes color and brightness information, must pass through the lens. The recorded pictures will not be crisp if the lens is unable to correctly guide light onto the CCD sensor.

 

In moderate situations, a Handycam with a greater signal-to-noise ratio produces superior pictures. Many Handycams have an integrated light source for recording in low-light situations. In low-light situations, the light can be turned on automatically. A liquid crystal display panel and a viewfinder are standard on most handy cams. Instant playback is made possible by the LCD and viewfinder.


A zoom lens package is also included on the Handycam's front side. Optical zoom has a higher image quality than digital zoom at high magnification. Shaky pictures might result from recording a quickly moving target. To stabilize pictures, optical image stabilizers utilize motion detectors and a specific lens configuration.


Most handycam's capture interfaced video in progressive scan mode with odd-even fields. This results in high-resolution still pictures. The sound signal is picked up by a microphone attached to the handycam. It is attached to the Handycam's front or top. It's used to record conversations or presentations.

Saturday, 19 June 2021

Plasma Display - Advantages and Disadvantages

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Plasma Display - Its Advantages and Disadvantages


The term "panel" refers to a form of flat panel display that is now extensively utilised for huge television displays. An inert mixture of noble gases is held in many small cells positioned between two glass panels. The cell's gas is electrically converted to plasma, which then excites phosphors to produce light.


When typical gas atoms are stimulated, they release electrons. The atoms become positively charged when the negatively charged electrons are lost, and the gas is said to be ionised. When this process reaches a particular point, the gas transforms into plasma. When an electrical current is transmitted through a gas, a plasma display will light (Zenon or Neon). Hundreds of thousands of microscopic cells are sandwiched between two glass plates to hold the gas.


On both ends of the cells, long electrodes are sand-witched between the glassware plates. Along with the back glass plate, the address electrodes are hidden behind the cells. The figure is a schematic representation of a plasma display.

Figure: Schematic representation of a plasma display

A dielectric substance and magnesium oxide cover the display electrodes (protective layer). This assembly is attached to the front glass plate above the cell. Both sets of electrodes run the length of the screen. The display electrons are placed in horizontal rows and the address electrodes are positioned in vertical columns along with the screen. A simple grid's horizontal and vertical electrodes. The plasma display's microprocessor charges the electrodes that intersect at that cell to ionise the gas in that cell.


When a tiny voltage is applied to the intersecting electrodes, an electric current runs through the gas in the cell. A fast flow of charged particles is created by the current. They use gas toms to imitate the emission of UV photons. The ultraviolet photons emitted interact with phosphor material on the cell's interior wall. When an ultraviolet photon strikes a phosphor atom in a cell, one of the atom's electrons leaps to a higher energy level, causing the atom to heat up.


When an electron returns to its original state, energy is released in the form of a visible light photon, which lights the screen. When colour phosphors in a plasma display are energised, they emit colour light. Each pixel is made up of three subpixel cells with various coloured phosphors (R, G, and B). Their hues combine to produce the panel's overall hue. The control system may adjust the intensity of each subpixel colour by altering the pulse of current flowing through the cells.


Hundreds of distinct red, green, and blue colour combinations may be made with this effect. This allows the control system to generate colours that span the full visible spectrum. Plasma displays are thin and delicate. They're big and heavy, and they need a lot of energy.


Plasma displays have the following advantages:


1. They can provide a higher contrast ratio.

2. It is possible to make a very big, very thin screen.

3. The image is bright and has a broad field of vision.

4. Motion blurs are less evident.

5. Quick reaction time.


Disadvantages of Plasma displays:


1. They use more electricity.

2. A shorter life expectancy

3. The brightness range of the image is smaller.

4. It is ineffective at high elevations.

5. It is necessary to utilise a more costly plasma suitable sensor.

Tuesday, 15 June 2021

Block Diagram of Cable TV Network

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CABLE TELEVISION (CABLE TV):


Cable television is a type of CCTV in which users get regular channel television signals over coaxial cables in exchange for a monthly fee. Master Antenna TV (MATV) is needed,  when a common antennal system is utilized to transmit a strong signal to every TV set connected to the system through coaxial cable.


The cable television system is used to broadcast high-quality television signals to a large number of people. Subscribers that pay a charge for this service get access to more TV programming through this arrangement. The cable system might have more active  channels (VHF and UHF) than a receiver can directly select. This necessitates the employment of a unique active converter in the head end.


Cable TV's primary signal source is a constellation of satellites. Satellite transmissions are received using high power parabolic dish antennas. Most communication satellite downlink communications are in the C-band (3700-4200 MHz) frequency range.

Figure: The block diagram of a cable television system

The block diagram of cable tv network is shown above. Dish antenna signals are first transformed into a lower frequency using a Low Noise Block Converter (LNBC). Conventional antennas erected on high-rise buildings receive VHF and UHF terrestrial broadcast transmissions. Local sports and cultural programming might be broadcast through the cable TV network. Cable network also distributes programmes such as popular movies and music that have been already recorded.


The combining network applies signals from numerous TV stations. The LNB converter converts the signal received by the dish antenna into low frequency signals. Similarly, a translator converts the signal received by a UHF antenna into low-frequency impulses. The combining network combines all of the signals and allocates each channel to a different carrier frequency.


Through a broadband distribution amplifier, the outputs of the combining network are routed to a number of trunk lines. The purpose of a distribution amplifier is to boost the signal amplitude to a higher level in order to compensate for distribution system losses. Through co-axial trunk lines, the distribution amplifier's output is sent to the splitter. Signals are carried by trunk cables to the utilization sites, which may be several kilometres away. Feeder amplifiers are installed at various places along the line to compensate for signal attenuation caused by cable loss.


The signal attenuation that happens as a result of cable failure. Multicore coaxial cables are used to distribute signals from splitters to tap-off locations. A splitter is a resistive-inductive device that offers impedance matching and trunk line isolation. Transformer-coupled, capacitive-coupled, or resistive-pad subscriber taps are all possibilities.


They avoid mutual interference by providing separation between receivers on the same line. Normally, taps are positioned on the wall. Wall taps are available with 300 Ω, 75 Ω, or dual outputs. Standing waves will form as a result of poorly terminated lines. Each 75 Ω distribution cable is terminated by a 75 Ω resistor called a terminator to prevent standing waves.

Saturday, 12 June 2021

Crystal Oscillators

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Crystal Oscillators


Due to the variations in temperature, humidity, transistor, and circuit constants, etc. The frequency stability is usually poor in conventional radio frequency oscillators (using LC circuits). Stable oscillations are required in most applications. In such conditions,  a crystal oscillator works great. It has a high level of stability and quality. In a crystal oscillator, a resonant tuned (tank) circuit is made of a piezoelectric crystal.


Piezoelectric effect


The piezoelectric effect is a highly essential feature of quartz crystals. When an AC voltage is applied, it vibrates at the applied voltage's frequency. On the other hand, if mechanically force to vibrate, it produces an ac voltage. The piezoelectric effect may also be found in Rochelle salt and tourmaline, in addition to quartz.


The most resistant are tourmaline, even though it has the least piezoelectric activity. It is also the most costly. It is used at very high frequencies on occasion. The most piezoelectric activity is found in Rochelle salt, but it is mechanically the weakest. They are readily broken. Microphones, headsets, and loudspeakers are all made with Rochelle salts.


Quartz is a compromise between the Rochelle salt's piezoelectric activity and the tourmaline's strength. It is both affordable and abundant in nature. It is mostly utilized in RE oscillators as a crystal.


Characteristics of crystal oscillator


The crystal is appropriately cut and then placed between two metal plates for use in electronics oscillators, as illustrated in the figure. Let's observe what happens when an ac source is linked across the crystal. Because two metal plates separated by a dielectric operate as a capacitor, even when the attached crystal is not vibrating, it is comparable to a capacitance Cm.

Fig: Quartz Crystal Circuit

Mechanical vibrations are built up when an ac voltage is supplied to the crystal. The natural resonance frequency of these Equivalent circuit vibrations is determined by a variety of variables. Dimensions of the crystal, how the surface is orientated about the axis, and how the crystal is placed are some of these considerations. Although the crystal possesses an electric-mechanical resonance, an analogous electrical resonant circuit may be used to simulate it in motion, as illustrated in the figure.


L = 137H, C = 0.0235, and R = 15 K are typical values for 90 kHz. This is equal to a Q of 5500. The mounting capacitance Cm is substantially higher than the capacitance (C = 3.5pF).


When compared to a discrete LC circuit, the crystal's extraordinarily high Q-value is a standout characteristic. The use of crystals may produce Q values of almost 106, whereas a discrete LC circuit seldom exceeds 100. The extraordinarily high Q of a crystal ensures a relatively steady oscillation frequency.


There are two resonant frequencies in the crystal. First, a series resonant frequency fs, inductance L resonates with capacitance C. The series branch exhibits a parallel resonance with capacitance Cm above the frequency fs. Parallel resonant frequency (FP) is the name given to this frequency. The crystal oscillator has a capacitive reactance above this frequency. Only between the frequencies Fs and FP do the crystal act as an inductor. If the crystal is utilized as an inductor in the circuit, the oscillation frequency must be between Fs and FP. The crystal's two frequencies are temperature-dependent. It is feasible to have a frequency drift of less than 1 part in 1010 by maintaining the crystal in temperature-controlled ovens.


Transistor crystal oscillator


The circuit of a crystal oscillator is shown in the diagram below. In the collector, a tank circuit L1-C1 is installed, and the crystal is installed in the base circuit. Coil L2, which is inductively connected to coil L1, provides feedback. The feedback winding is linked in series with the crystal. The natural frequency of the LC circuit is roughly equivalent to the crystal's natural frequency.

Fig: Crystal Oscillator Circuit

Capacitor C1 will charge when the power is switched on. Oscillations are created as the capacitor discharges. The crystal oscillator produces oscillations as a result of the positive feedback. The frequency of oscillation in the circuit is controlled by the crystal. Because the crystal is connected to the base circuit, it has a far greater impact on the frequency of the circuit than the LC circuit. As a result, the entire circuit oscillates at the crystal's inherent frequency, causing the circuit to create a resonant frequency.

 

Advantages


1. Because the crystal's frequency is independent of temperature, these oscillators have a high degree of frequency stability.

2. It can create high-frequency oscillations.


Disadvantages


1. They are delicate and should only be used in low-power circuits.

2. Oscillation frequency cannot be adjusted significantly.

Sunday, 6 June 2021

What is Current and Voltage in Electronics

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Current and Voltage in Electronics

In electrical circuits, it is important to keep track of two quantities: voltage and current. Both voltage and current usually change with time. 


What is Voltage (symbol: V, or sometimes E)  


The cost in energy (work done) necessary to shift a unit of positive charge from a more negative position (lower potential) to a more positive location is the voltage between two places (higher potential). It is, in other words, the energy released as a unit charge goes "downhill" from a higher to a lower potential. The potential difference or electromotive force (EMF)  is also referred to as voltage (EMF). The volt is the standard unit of measurement, with voltages given in volts (V), kilovolts (1kV = 103V), millivolts (1mV = 10-3V), and microvolts (1µV = 10-6 V). To transport a coulomb of charge over a potential difference of one volt, a joule of effort is required. (A coulomb is a unit of electric charge that roughly matches the charge of 6 x 1018 electrons).  The uncommonly used other voltage levels are nanovolts (1nV = 10-9 V) and megavolts (1MV = 106 V).


What is Current (symbol: I )


Current is the rate of flow of electric charge past a point. The unit of measure is the ampere, or amp, with currents usually expressed in amperes (A), milliamperes (1mA = 10-3A), microamperes (1µA = 10-6A), nano-amperes (1nA = 10-9A), or occasionally picoamperes (1pA = 10-12A). A current of one ampere equals a flow of one coulomb of charge per second. By convention, current in a circuit is considered to flow from a more positive point to a more negative point, even though the actual electron flow is in the opposite direction.


The rate of flow of electric charge through a location is known as current. Currents are commonly represented in amperes (A),


milliamperes (1mA = 10-3A),

microamperes (1µA= 10-6A)

nano-amperes (1nA = 10-9A), or

picoamperes (1pA = 10-12A) as the unit of measurement.


A current of one ampere corresponds to a charge flow of one coulomb per second. Even though the real electron movement is in the opposite drection, the current in a circuit is assumed to flow from a more positive point to a more negative point.


Note: Usually voltage in a circuit is referred to as voltage between two points or voltage across two points. Always use the term "current" to describe the flow of electricity through a device or circuit connection.


It's incorrect, or worse, to state anything like "the voltage across a resistor..." We do, however, commonly refer to the voltage at a circuit's point. This is always taken to indicate the voltage between that point and "ground," which appears to be a well-known position in the circuit.


Voltages are formed by working with charges in devices like batteries (electrochemical), generators (magnetic forces), solar cells (photovoltaic conversion of photon energy), and so on. We get currents by connecting elements (active and passive) with voltages.


The oscilloscope is the most valuable electronic tool because it allows one to look at voltages (and sometimes currents) in a circuit as a function of time. it is often termed as the "eye" of an electronic engineer.


Wires, metallic conductors, and the identical voltage on each of them are used to link items in actual circuits (concerning ground). But this isn't technically true in the domain of high frequencies or low impedances. Since wires may be rearranged, an actual circuit does not have to appear exactly like its schematic representation.


Rules about Voltage and Current:       


1. In a circuit, the sum of the currents entering a point equals the sum of the currents out (conservation of charge). Kirchhoff's present law is a term used to describe this. A node is a term used by engineers to describe such a place. As a result, this may deduce the following: The current in a series circuit (a group of two-terminal devices linked end-to-end) remains constant.


2. When two components are connected in parallel, the voltage across them is the same. In other words, the sum of the "voltage drops" from A to B by one path via a circuit equals the sum of the "voltage drops" via any other route between A and B. This is sometimes described as follows: The sum of any closed circuit's voltage is always zero. This is termed referred to as   Kirchhoff's Voltage Law.


3. A circuit device's power consumption (work per unit time) is P = VI.


This is simply (work/charge) x (charge/ time). For V in volts and I in amps, P comes out in watts. Watts are joules per second (IW = IJ/s).


Usually, power is converted to heat, but it can also be converted to mechanical work (motors), radiated energy (lamps, transmitters), or stored energy (batteries, capacitors). Managing the heat load of a complex system (for example, a computer, where several kilowatts of electrical energy are converted to heat with the energetically inconsequential by-product of a few pages of computing output) can be a critical aspect of the process.


We'll have to expand the basic equation P = VI to deal with average power when dealing with regularly variable voltages and currents, but it's correct as a description of instantaneous power as is. Don't call current "amperage," by the way; that's bush-league. When we get to resistance, the word "ohmage" will be treated with the same discretion.