A strain gauge is a device that is used to measure the strain that occurs in an object. The device was invented in the year 1938 by Edward E. Simmons and Arthur Ruge. The device is still being used in many electronic circuits mainly as the principle sensing element for sensors like torque sensors, pressure sensors, load cells and so on.

Strain Gauge working

Strain Gauge Working Principle

Although strain gauges are available in many shapes and sizes, the fundamental working of this device is the same. They also vary in both shape and size according to their field of application.

A strain gauge consists of a foil of resistive characteristics, which is safely mounted on a backing material. When a known amount of stress in subjected on the resistive foil, the resistance of the foil changes accordingly. Thus, there is a relation between the change in the resistance and the strain applied. This relation is known by a quantity called gauge factor. The change in the resistance can be calculated with the help of a Wheatstone bridge.

TAKE A LOOK : WHEATSTONE BRIDGE

The strain gauge used is connected to the Wheatstone bridge with the help of an adhesive called cyanocrylate.

The property of the strain gauge not only depends on the electrical conductivity of the conductor, but also in the size and shape of the conductor used. As a matter of fact, the electrical conductivity also depends on the electrical conductance of the foil. This, in turn depends on the material of the conductor. The electrical resistance of the foil changes according to the change in the foil when it is stretched or compressed. The stretching or compressing is considered normal as long as there is no permanent change in the original appearance of the foil. Stretching causes an increase in the resistance from one end to other. Compressing causes a decrease in the resistance from one end of the conductor to another. Basically, the conductor will be a long strip with parallel lines with the condition that a little stress in the path of the orientation of the parallel lines will cause a resultant bigger strain multiplicatively over the effective length of the conductor. Thus a larger resistance change will be obtained.

The force applied to change elongate or shorten the strip can also be calculated with the help of the obtained output resistance.

An ideal strain gauge resistance varies from a few 3 ohms to 3 kilo ohms when it is unstressed. This value will change by a small fraction for the full force range of the gauge. It also depends on the elastic limits of the foil material. If there are forces applied to such an extent that they lose their original shape and size, the strain gauge will no longer be fit to use as a measuring device. So measurement of small fractional changes in the resistance must be taken accurately in order to use the strain gauge as a measuring device.

Applications

The voltage output in accordance to the stress is about a few millivolts. This voltage can be amplified to about 10 volts and can be applied to external data collection systems like recorders or PC data acquisition and analysis systems.

Strain gauges can be used to measure the stress developed in particular machinery and thus is used to mechanical engg. R&D.

The device is used aircraft component testing. Here also the measure of stress is the main issue. For this, strain gauges of very small size are connected to structural members, linkages and so on.

Gauge Factor Equation

The gauge factor of a strain gauge is given be the equation

GF = [∆R/R_G]/E

∆R – Resistance produced by the strain

R_G ­­– Resistance of gauge before application of stress

E – Strain produced

Types of Strain Gauges

This classification is based on the type of bridge circuit that is connected to the strain gauge. There are mainly three types of connections. They are

1. Quarter Bridge Strain Gauge Circuit

As shown in the diagram below, the imbalance is detected by the voltmeter in the center of the bridge circuit. The resistance R2 will be a rheostat and hence adjustable. The value of this resistance is made equal to the strain gauge resistance without the application of any force. The resistances R1 and R3 will have equal values. Thus, according to the Wheatstone bridge principle the entire circuit will be balanced and the net force will be zero. Thus the strain will also be zero. Now provide a compression or tension on the conductor and the circuit will be imbalanced. Thus you will get a reading at the voltmeter. Thus, the strain produced in response to the measured variable (mechanical force), is known as a quarter-bridge circuit.

Quarter bridge strain circuit

2. Half Bridge Strain Gauge Circuit

As shown in the circuit there are two strain gauges connected. If one of them does not respond to the strain produced it becomes a quarter bridge circuit. If both of them respond in such a way that both the strain gauges experience opposite forces it becomes a half bridge strain gauge circuit. By opposite forces, we mean that a compression on the upper strain gauge makes a stretch on the lower strain gauge. This causes both the gauges to make a better response to strain, thus increasing the response of the bridge to the applied force. As both the strain gauges act opposite and proportionally the response to the changes in temperature will be cancelled thus reducing the errors due to it.

Half bridge strain gauge circuit

3. Full Bridge Strain Gauge Circuit

In the case of sensitivity, a half bridge strain circuit is more sensitive than a quarter bridge circuit. The sensitivity can be increased if all the elements of the bridge are active. Such a circuit is called full bridge strain gauge circuit. The circuit is also advantageous in the fact that it can be used to bond the complimentary pairs of strain gauges to the testing specimen. Thus, this is considered to be the best bridge circuit for strain measurement. The circuit is also advantageous because of its linearity. That is, the output voltage is exactly directly proportional to the applied force. But in the case of a half bridge and quarter bridge the output voltage is only approximately proportional to the applied force. Take a look at the circuit diagram given below.

Full bridge strain gauge circuit

A Wheatstone bridge is used to calculate an unknown resistance with the help of a bridge circuit. For this, the two legs of the bridge circuit are kept balanced and one leg of it includes the unknown resistance. The Wheatstone bridge principle is similar to the working of potentiometer. Slight modifications in the Wheatstone bridge can help in finding other quantities like capacitance and inductance as well. It also helps in finding the amount of a particular gas that is mixed among a sample. The Wheatstone bridge measurement is very accurate and the value of the unknown resistance is mostly found out in order to measure other physical values like temperature, force, pressure and so on. It can be used in all electronic circuits. The device was first invented by Samuel Hunter Christie in 1833. The concept was later modified and popularized by Sir Charles Wheatstone in the year 1843.

TAKE A LOOK : POTENTIOMETER

Wheatstone Bridge Measurement

Balanced Condition

As shown in the circuit diagram, there are four resistances connected as a bridge circuit. The three resistors R1, R2 and R3 will have known values. The value of the resistance R_X will be unknown and has to be calculated. The value of resistance R2 is adjustable. A galvanometer has to be set between the points B and D.

TAKE A LOOK : GALVANOMETERS

Wheatstone bridge

The condition to be satisfied at the point of balance is given below.

If R2/R1 = R_X/R3, then V_BD = 0 and current through V_G = 0. To reach this condition, the adjustable resistor is varied. The direction of the current can be known from the value of the resistor R2.

As soon as the balance condition is obtained the value of the resistance R_X is obtained.

Thus, R_{X =} [R2/R1] x R3

This method is very accurate as the other values of resistors are of high precision.

Unbalanced condition

If the value of the resistors R1, R2 and R3 are fixed, then the value of the unknown resistor R_X has to be found out with the help of Kirchhoff’s voltage and current laws. For this, the bridge circuit will produce a voltage as well as a current as the circuit will not be balanced. This is the process mostly used in the measurement of strain gauges and resistance thermometers. This method is much easier to use as calculations can be done more easily with a voltage and current value than trying to make the circuit balanced.

To calculate the currents between the junctions B and D use Kirchhoff’s current law.

I3 – I_X + I_G = 0

I1 – I2 – I_G = 0

This can be further simplified as

I3 = I_X and I1 = I2…………………………………..[1]

To calculate the voltage in the loops ABD and BCD use Kirchhoff’s voltage law.

[I3 R3] – [I_G R_G] – [I1 R1] = 0

[I_X R_X] – [I2 R2] + [I_G R_G] = 0

On re-arranging the above equations we get the value of unknown resistance as

R_X = [R2 I2 R3 I3]/ [R1 I1 I_X]…………………..[2]

Substituting value of [1] in [2]

R_X = [R3 R2]/ R1.

There may be cases when the values of all the resistors are known.  If so, the value of the voltage between B and D [V_G] can be found out from the following equation.

V_G = V_S * ([R3 /{R3 + R_X}] – [R2/{R1 + R2}])

In my earlier posts I have already explained the working of Charge-coupled devices and its application as an image sensor. Recently, most of the scanners and cameras have introduced a new image sensor called Contact Image Sensors [CIS]. To know more about CCD and its applications click on the links below.

TAKE A LOOK : CHARGE COUPLED DEVICES (CCD)

TAKE A LOOK : WORKING OF DIGITAL CAMERAS

TAKE A LOOK : WORKING OF SCANNER

Working of Contact Image Sensor

Contact Image Sensor is one compact module consisting of three sub-systems. They are

1. Illumination system

The illumination system consists of two sets of LED’s which is used to illuminate the document that is to be scanned. Each LED pack consists of LED’s of the three composite colours – Red, Green and Blue. These three colours join together to form the white light. The light from the LED is focussed with the help of light guides. The way the LED glow depends on the type of scan that is required. If a colour scan is needed all the LED’s will glow at high intensities. If a black and white scan is enough, the LED’s will shine simultaneously.

The main advantage of LED in CIS when compared to fluorescent bulbs in CCD is that they glow at a constant rate the minute they are turned on. But, fluorescent bulbs need a warm-up time as they begin to glow. They also have the advantage of being turned off whenever the device is not in use. Thus they help in saving a lot of power and are also environment friendly.

2. Optical system

The optical system consists of an array of lenses and a focus that is used to carry the light reflected from the document to be scanned to the light sensing system. Unlike a CCD, the optical system in CIS is shorter and less complex. This helps in saving more space and is also economical. As the apparatus is lighter and compact, it is applicable in making portable scanners.

3. Light sensing system

The light sensing system mainly consists of a sensor with a silicon surface. The light intensity that hits on the silicon surface varies according to the document to be scanned. The silicon surface will be divided into square cells. Though the same mechanism is carried out in a CCD, there is a difference in the ratio of the cell size to the information size. Here, the size of the information hitting on the silicon cell is same as the size of the cell. That is, for a 500 dpi scanner each cell will be 1/500″ across. Thus the ratio is 1:1. Thus, the need for the reduction or enlargement is no required in such a device. For this reason, the sensor will be kept very near to the document to be scanned. Most sensors rest right under the document at a distance of about 13 millimetres. As soon as the light hits the sensor, this will be recorded and will be converted into an electrical signal.

Take a look at the picture below to get a clear understanding.

Contact Image Sensors (CIS)

Advantages of Contact Image Sensor (CCD vs CIS)

• The size of contact image sensors is very small and also lighter than the CCD sensors. They are always available as contact image sensor modules. That is, all its associated optical devices are included in a single compact module. This will also help in producing very flat and light-weight scanners. They also pave the way to applications in cameras and so on.
• These Contact image sensor scanners do not consume as much power as CCD scanners. They are also equipped to run with in battery power and can also be connected through USB port.
• When compared to a CCD, the sharpness of the image that is scanned is more for a contact image sensor. Thus they are applicable for scanning documents which requires even the smallest details to be displayed.

Disadvantages of Contact Image Sensor (CCD vs CIS)

• The image quality of a CIS is much lower when compared to a CCD sensor. The quality of the picture and the picture resolution is poor in comparison.
• As the depth of the field is limited to a certain extent, there will be problems while scanning a material that is nor completely flat in nature.
• In large scanning formats, CCD sensors use white LED’s or white fluorescent tubes for the colorization. In color compact image sensor, this is replaced by the composite color composite LED’s. The CIS LED’s cannot provide a wide range of color as CCD can. Thus CIS is not suitable for large scanning formats of photos or colourful documents with shadow details.

Applications of Contact Image Sensors

• The largest application of the device is in the field of scanning. Contact Image Sensor scanners have taken a large part of the industry. Since the CIS is lighter and smaller in size than CCD arrays, they are used in scanners that can be carried around. The most commonly used Contact Image Sensor scanner is the flat-bed scanner. The most famous brand among these is the Canon contact image sensor.
• Other applications of Contact image scanners include bar-code readers, electrograph and also optical identification technology.

What is a Scanner?

A scanner is a device that is used for producing an exact digital image replica of a photo, text written in paper, or even an object. This digital image can be saved as a file to your computer and can be used to alter/enhance the image or apply it to the web. The most comonly used scanner is the flatbed scanner, in which you keep the object on top of the glass window. The scanned output will be obtained in your computer. The image and text are obtained exactly through the process of optical character recognition [OCR].

Scanner

The historical precedence of scanners originates from the telephotography input devices, which was mainly used by the printing press. It mainly consisted of a rotating drum, which rotated at a maximum speed of 240 rpm. The signal used was analog in nature and were sent through telephone lines to the receptor end. The receptor recognizes the signal synchronously and a proportional output is printed on special paper.

Types of Scanners

1. Drum Scanners

Drum scanner was the first ever image scanner to be developed. It was made in the year 1957 at the US National Bureau of Standards. The first image was black and white with a resolution of 176 pixels.

This scanner is mainly used in the publishing industry. The technology used behind the scanning is called a photomultiplier tube (PMT).

As the name implies, the drum scanner consists of a drum type cylinder on the top of which the image/document to be scanned is mounted. This cylinder rotates at a very high speed and thus the object placed on it will deliver the image copy with the help of precision optics. Though the precision optics sends the reflected light from the image, they will be sensed by a sensor in the PMT. It will be received by the filter in the PMT and the replica is made. Modern drum scanners can also recognize colour images by using three separate colour filters. Each colour filter will be for each composite colour [RGB]. The reflected light will be split into the three colours and will be filtered.

The size of the image produced depends on the design of the drum by the manufacturer.

This scanner finds its application in publishing field because of its ability to capture the smallest details out of film negatives. It also has an advantage in its ability to control sample area and aperture size independently. This feature helps in clearing the grains in negative films as well as colour films while scanning it.  Thus, they also help in producing scans that are high in resolution, colour gradation and value structure. As the resolution may be increased up to 12,000 PPI, they are particularly useful when a scanned image is to be enlarged.

After the invention of flatbed scanners, the production of drum scanners has been limited. A flatbed scanner also has the same features, but at a lower production cost. Still drum scanners are used in places like printing of high quality books and magazines and many other publishing areas.

2. Flatbed scanners

Flatbed scanner is the most commonly used scanning machine nowadays. They are also called desktop scanners. The detailed working of flatbed scanners will be given below. They use Charge-coupled device (CCD) to scan the object. To know more about CCD click on the link below.

TAKE A LOOK : CHARGE-COUPLED DEVICE (CCD)

3. Hand-Held Scanners

This device found popularity during the early 90’s. Hand-held scanners are used to scan documents by dragging the scanner across the surface of the document. They are available as document scanners as well as 3-D scanners. This scanning will be effective only if with a steady hand technique, or else the image may seem distorted.  They have sensors to detect the distortion rate and an indicator will be provided to alert if the motion of the scanner is too fast.

They also have a START button, which has to be on during the scan duration. They are synchronized with the computer and also have an automatic optical resolution. The scanner also has LED’s which light up the image to be scanned. As the image can be distorted most of the time there are special reference markers available in the device which helps in compensating the distortion.

Though poor image quality is obtained, fast scanning of texts can be done with this device.

4. Film Scanners

This device is manufactured to specially scan positive and negative photographic images. The film will be inserted into the carrier. It will be moved with a stepper motor and the scanning process will be done with a CCD sensor. The output can be obtained on a computer.

Working of Flatbed Scanner

The main difference in the old scanners and modern scanners is the type of image sensor used. In old scanners, a photomultiplier tube [PMT] was used. For modern scanners a Charge-coupled device [CCD] is used. A CCD sensor is used to capture the light from the scanner and then convert it into the proportional electrons. The charge developed will be more if the intensity of light that hits on the sensor is more. To know more about CCD click on the link below.

TAKE A LOOK : CHARGE-COUPLED DEVICE (CCD)

Any flatbed scanner will have the following devices.

• Charge-coupled device (CCD) array
• Scan head
• Stepper motor
• Lens
• Power supply
• Control circuitry
• Interface ports
• Mirrors
• Glass plate
• Lamp
• Filters
• Stabilizer bar
• Belt
• Cover

Though the configuration of the above components differs according to the manufacturers design the basic working is almost the same.

A scanner consists of a flat transparent glass bed under which the CCD sensors, lamp, lenses, filters and also mirrors are fixed. The document has to be placed on the glass bed. There will also be a cover to close the scanner. This cover may either be white or black in colour. This colour helps in providing uniformity in the background. This uniformity will help the scanner software to determine the size of the document to be scanned. If a page from a book is to be scanned, you may not be able to use the cover.

The lamp brightens up the text to be scanned. Most scanners use a cold cathode fluorescent lamp (CCFL).

A stepper motor under the scanner moves the scanner head from one end to the other. The movement will be slow and is controlled by a belt. The scanner head consists of the mirrors, lens, CCD sensors and also the filter. The scan head moves parallel to the glass bed and that too in a constant path. As deviation may occur in its motion, a stabilizer bar will be provided to compromise it. The scan head moves from one end of the machine to the other. When it has reached the other end the scanning of the document has been completed. For some scanners, a two way scan is used in which the scan head has to reach its original position to ensure a complete scan.

As the scan head moves under the glass bed, the light from the lamp hits the document and is reflected back with the help of mirrors angled to one another. According to the design of the device there may be either 2-way mirrors or 3-way mirrors. The mirrors will be angled in such a way that the reflected image will be hitting a smaller surface. In the end, the image will reach a lens which passes it through a filter and causes the image to be focussed on CCD sensors. The CCD sensors convert the light to electrical signals according to its intensity. Take a look at the diagram given below.

The electrical signals will be converted into image format inside a computer. This reception may also differ according to the variation in the lens and filter design. A method called three pass scanning is commonly used in which each movement of the scan head from one end to another uses each composite colour to be passed between the lens and the CCD sensors. After the three composite colours are scanned, the scanner software assembles the three filtered images into one single -colour image.

There is also a single pass scanning method in which the image captured by the lens will be split into three pieces. These pieces will pass through any of the colour composite filters. The output will then be given to the CCD sensors. Thus the single-colour image will be combined by the scanner.

In some recent scanners, a contact image sensor [CIS], has replaced the CCD sensor. Though this method is not as expensive as the CCD scanner, the quality of the image produced and the resolution is much lower. To know more about CIS, click on the link below.

TAKE A LOOK : CONTACT IMAGE SENSORS (CIS)

Parameters of a Scanner

• The resolution of the image is one of the main parameters of the scanner. Each scanner varies according to its resolution and hence the cost. The resolution may be expressed in pixels per inch [ppi] and also samples per inch (spi). But, instead of defining the scanner’s correct optical resolution the manufacturers mostly define the interpolated resolution of the scanner. The latest flatbed scanner has an interpolated resolution of 5400 ppi and almost 12,000 ppi for a drum scanner.
• Interpolated resolution actually refers to the increase in the resolution of the image with the help of the scanning software. This is done by adding extra pixels in between the ones actually scanned by the CCD array. These extra pixels can be added only as an average of the adjacent pixels. Suppose a scanner has a true resolution of 300×300 dpi and the interpolated resolution declared by the manufacturer is 600×300 dpi. Thus an additional pixel is added in each row of the CCD sensor by the software. As the resolution increases, the size of the file also increases. This size can be reduced through lossy compression technique like JPEG. Through this method the quality of the picture will only be reduced to a small amount. Usually this method is done to load an image faster on the internet and also to print the image on a full page.
• A scanner has a least original resolution of about 300×300 dots per inch (dpi). This increases with the increase in the CCD sensors row wise and also by the precision of the stepper motor.
• As the scanner’s lamp brightness increases along with the use of high quality optics the sharpness of the image also increases. Density range is another parameter through which the minor shadow and brightness details can also be reproduced through scanning. The higher the density range, the higher the details.
• Another parameter used is the colour depth. In colour scanning, the colour depth refers to the number of colours that can be reproduced by the scanner. Though a 24 bit/pixel scanner is sufficient enough there are scanners with 30 bits and 36 bits available now.

Scanner to Computer Connection

The image that has been successfully scanned has to be transferred to our home computer for useful applications.  For this transfer to occur, two main problems have to be dealt with. They are

1. Physical connection between the scanner and computer.

• Parallel Connection

This is one of the oldest method and the slowest method available. Though this type of connection is much economic it only had a data transfer rate of 70 kbps.

• Small Computer System Interface [SCSI] Connection

This method can be appropriate only with the help of an SCSI interface card. Earlier the scanners used to come with a dedicated SCSI card. Though the data transfer rate is high enough, much more economical and easier connections like the Firewire and USB came in its place.

• Universal Serial Bus [USB] Connection

USB connection is the latest and most economical method of data transfer. It has speeds up to 60 MBPS and can be easily connected to the scanner.

• FireWire Connection

This is the fastest of all the above methods. It has been introduced in the latest high-end scanners and is ideal for scanning high resolution images. It can transfer data at a maximum speed of 800 MBPS.

2. Transfer of information from the scanner to computer

For the transfer of information from the scanner to the computer application programming is the main solution. For this there are also Applications Programming Interfaces [API]. Through API standards a computer can transfer the details with any scanner without even knowing the details of the scanner. The most commonly used software for transferring details from the scanner is the ADOBE PHOTOSHOP. Photoshop supports a standard called TWAIN. If the scanner also supports the same standard, then transfer of information can be done. The TWAIN API is used in most scanners and is also used in most high and low-end equipments. TWAIN is just like a driver which helps in communicating with all other scanners in a common language.

Processed Data

After reaching the computer, the actual output will be a non-compressed composite image. This image will be later edited in Photoshop or other graphics programs to convert it into lossy compresses JPEG format or non-lossy compressed PNG format. If it is a text image, it will be converted to .txt file with the help of Optical character recognition (OCR) software’s. The text will be accurate depending on the clarity of its image.

Automatic cleaning technique of a scanner

The films used in scanning may be prone to dust and scratches. Modern scanners have an in-built cleaning process called infrared cleaning. In this method an infrared beam will be used to scan the film. When the beam hits places with dust and scratches, the beam will be cut-off. Thus the correct position, size and also the shape of the dust will be calculated and will be removed. Most modern companies like Nikon, Microtek and Epson name this technique as Digital ICE while Canon calls this technique as Film Automatic Retouching and Enhancement system [FARE].

Applications of Scanner

1. Applications vary according to the type of scanner used. Flatbed scanners are mostly used for scanning documents. But, for large format documents a mechanical scanner will have to be used.
2. There are hand-held scanners which are used for scanning an object according to the movement of our hand [the scanner does not move by itself]. This scanner helps in 3-D scanning of materials and is applicable in industrial designs, test and measurement of devices, gaming applications and so on. 3-D scanning can also be done with the help of planetary scanners. There are also developments going on in producing a combination of 3-D scanners with digital cameras so that realistic photos with true colour can be obtained in the 3-D mode.
3. A new concept called reprographic cameras has paved their way for digital camera scanners. This type of scanner has many advantages like easy digitalization of large format documents, high processing speed, and portability and so on. They also produce high resolution images with anti-shake features. Studies are still going on to remove the main disadvantages like shadow and reflection interference, image distortion and low contrast.
4. Scanners also find high end application in field like bio-medical research. High resolution scanners with a resolution of almost 1 µm/ pixel are used to detect DNA microarrays. Here also, the charge coupled devices are used for detection.

An article regarding the detailed working of a DVD has been explained earlier. To know more about it, click on the link below.

TAKE A LOOK : WORKING OF DIGITAL VERSATILE DISC (DVD)

Now we are going to look at how a DVD player works and the essential components for its working.

Parts of a DVD Player

The DVD player is not only used for playing the data present in a DVD, but also to write the content onto a DVD. To know this process it is essential to know the basics of a DVD.

As told earlier, DVD’s have pits and bumps in their track which holds the information that is required to be played. This information can be a video, audio or a mixture of both. When a DVD player reads this data, the smooth surface is usually taken as a ‘0′ and pits are usually taken as a ‘1′.

In order to create as well as read these data, a red laser with a wavelength of 600 nanometers. This is about 180 nanometers lesser than the wavelength of CD, which enables it to have a higher density of pits. Thus the size of the DVD increases. Though the first released DVD’s were only a single layer, 2 layered discs have been released nowadays. Single layer can hold only up to 4.7 GB of data while double layered DVD can hold up to 17 GB of data. The DVD design is similar to a CD a reflective silver layer in the centre and a semi-transparent gold layer on the top of it.

A DVD does not have the capacity to hold hi-def movies. So a MPEG-2 compression system is introduced. As this is used, the data will be encoded onto the DVD as elements of the changing frames. This has to be successfully decoded and decompressed by the DVD player.

Thus the parts of a DVD player are

1. Disc drive mechanism

The disc drive mechanism consists of a motor that will drive the disc in a circular motion. The mechanism will also have a disc feed – a loading tray that is used to accept the DVD from the user. Thus the entire disc drive is basically a spindle that holds the disc and a motor that is used to circle the disc. The spindle is held in its position with the help of small gears and belts that are attached internally. Some players have an automatic feed system in which, there will be no tray. Instead the disc will be automatically recognized after inserting a part of it.

2. Optical system

The optical system mainly consists of the laser beam, lenses, prism, photo-detectors and also mirrors. The output of this mechanism will be the input for the disc-drive. The laser beam will be a red laser diode which works at a wavelength of 600 nanometers. The optical system also requires a motor to drive it. The laser system and photo-detector is placed together on a single platform. The laser diode as well as other diodes is made with the help of glass.

3. Printed Circuit Board

The PCB is similar to that of any other electronic circuits. The electronic outline must be drawn on the PCB with the correct placement of all the IC’s resistors as well as capacitors. After the outline has been drawn, the components must be soldered to their respective places. All this must be done in a very clean environment so that the board does not become contaminated by dust. All the primary components of the electronic circuit should be made out of silicon.

Working of DVD Player

Take a look at the basic block diagram of how a DVD player works.

Block Diagram of DVD Player

DVD Player-Block Diagram

The pits and bumps in the DVD are hit by the laser from the optical mechanism of the DVD player. This laser will be reflected differently according to the change of pits and bumps. Though the laser hits a single spot, the DVD moves in a circular motion so that the entire area is covered. Mirrors are also used to change the spot.

These reflected laser beams are then collected by a light sensor (eg. photo-detector) which converts the different signals into a binary code. In short, the optical system helps in converting the data from the DVD into a digital code.

The binary signal is then sent to a Digital to Analog converter which will be setup in the PCB. Thus the corresponding analog signal of the DVD is obtained. The PCB also has amplifiers which amplify the signal and then sends it to the graphic and audio systems of the computer/TV. Thus, the corresponding audio/video signal is obtained. The basic working of a DVD player is shown below.

Assembling a DVD Player

As the different parts of the DVD player are all complicated electronic circuits, they are all manufactured by different people. They are later brought together and assembled at one place. During the assembling, the PCB will be connected to the rest of the machine and all the components are placed in the right positions. The whole package is then placed inside an outer plastic housing with a front panel with the buttons for various operations. This DVD player is then sent to a packaging station where they are placed safely inside boxes along with the respective power cords, operating manual, installing disks and so on. They are then taken by the distributors to various shops and then sold to customers.

Cautions while assembling a DVD Player

A DVD player will only be satisfactory to a customer only if it has a high performance. The degree of quality varies according to the flaws in the assembling process. Thorough inspections in both the visual as well as electrical divisions must be done most of the time. Flaws in the positioning of the different components can also cause the player to become faulty. After manufacturing the DVD also, the working performance is tested. To see the adverse effects of these players in different temperatures, the tests will be carried out in excessive heat as well as humidity. Since most of the parts of a DVD player is made by suppliers, they rely on other companies for good quality. The DVD assemblers will set a minimum standard for the supplies that they buy from outside. This specification must be met by them. The lenses and mirrors should be highly polished and cleaned before placing them.