Plasma globe

Plasma globes, or plasma lamps (also called plasma balls, domes, spheres, tubes or orbs, depending on shape), are novelty items that were most popular in the 1980s.^[1] The plasma lamp was invented by Nikola Tesla^[2] after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena, but the modern versions were first designed by Bill Parker.^[1] Tesla called this invention an inert gas discharge tube.^[3] 

Working principle

Most commonly, plasma globes are available in spheres or cylinders. Although many variations exist, a plasma lamp is usually a clear glass orb filled with a mixture of various gases (most commonly neon, sometimes with other noble gases such as argon, xenon and krypton) at nearly atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 2–5 kV, generated by a high-voltage transformer. A much smaller orb in its center serves as an electrode. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge).

Placing a hand near the glass offers an attractive place for the energy to flow. The capacity of the body to accept radio-frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. The energy is flowing through the filaments, so the filaments move too. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.^[1] The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object the size of a human. The filament is thinner because the magnetic fields around it, augmented by the now-higher current flowing through it, causes a magnetohydrodynamic effect called self-focusing: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself.

An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in a capacitor formed between the ionized gas and the hand.

The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments.

The neon available for purchase for a neon-sign shop often comes in glass flasks at the pressure of a partial vacuum. These can not be used to fill a globe. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gasses involved.

Of the noble gasses, radon is radioactive, helium escapes through the glass too quickly, and krypton is quite expensive. Other gasses can be used. The plasma will take apart any molecular gas.

Caution

Caution should be taken when placing electronic devices near or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge on the device, even through a protective plastic casing. The radio frequency field produced by plasma lamps can interfere with the operation of touchpads used on laptop computers, digital audio players, cell phones, and other similar devices.^[1] Some types can radiate sufficient RFI to interfere with cordless telephones and Wi-Fi devices several feet away. If a medium-sized lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens of milliamperes to ground through the foil, enough to light a small lamp or give a small arc burn. This is possible because the glass acts as a capacitor dielectric: the inside of the lamp acts as one plate, and any conductive object on the outside acts as the other capacitor plate.^[3] Ozone, which is harmful to humans, may also accumulate outside of the surface of the glass orb after a few minutes of constant operation.^[1]

Plasma globe

Plasma globes, or plasma lamps (also called plasma balls, domes, spheres, tubes or orbs, depending on shape), are novelty items that were most popular in the 1980s.^[1] The plasma lamp was invented by Nikola Tesla^[2] after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena, but the modern versions were first designed by Bill Parker.^[1] Tesla called this invention an inert gas discharge tube.^[3] 

Working principle

Most commonly, plasma globes are available in spheres or cylinders. Although many variations exist, a plasma lamp is usually a clear glass orb filled with a mixture of various gases (most commonly neon, sometimes with other noble gases such as argon, xenon and krypton) at nearly atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 2–5 kV, generated by a high-voltage transformer. A much smaller orb in its center serves as an electrode. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge).

Placing a hand near the glass offers an attractive place for the energy to flow. The capacity of the body to accept radio-frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. The energy is flowing through the filaments, so the filaments move too. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.^[1] The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object the size of a human. The filament is thinner because the magnetic fields around it, augmented by the now-higher current flowing through it, causes a magnetohydrodynamic effect called self-focusing: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself.

An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in a capacitor formed between the ionized gas and the hand.

The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments.

The neon available for purchase for a neon-sign shop often comes in glass flasks at the pressure of a partial vacuum. These can not be used to fill a globe. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gasses involved.

Of the noble gasses, radon is radioactive, helium escapes through the glass too quickly, and krypton is quite expensive. Other gasses can be used. The plasma will take apart any molecular gas.

Caution

Caution should be taken when placing electronic devices near or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge on the device, even through a protective plastic casing. The radio frequency field produced by plasma lamps can interfere with the operation of touchpads used on laptop computers, digital audio players, cell phones, and other similar devices.^[1] Some types can radiate sufficient RFI to interfere with cordless telephones and Wi-Fi devices several feet away. If a medium-sized lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens of milliamperes to ground through the foil, enough to light a small lamp or give a small arc burn. This is possible because the glass acts as a capacitor dielectric: the inside of the lamp acts as one plate, and any conductive object on the outside acts as the other capacitor plate.^[3] Ozone, which is harmful to humans, may also accumulate outside of the surface of the glass orb after a few minutes of constant operation.^[1]

Working of DVD Player

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.

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

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.

Working of Flexplay DVD

What is Flexplay DVD?

In most foreign countries, people rent a lot of DVD’s from the shop. All you have to do is watch the movie and return the DVD back within the agreed time. But, if we are pretty much unorganized, we tend to forget about the DVD. This is where the DVD rental shop makes money. They take late fees and this money sums up to a large amount equal enough to buying a DVD. This disadvantage can be overcome by using a Flexplay DVD.

The Flexplay DVD, introduced by a company called Flexplay Technologies is a special type of DVD that can be rented and need not be returned back. The rental prices will be the same as that of a normal DVD. But this does not mean that you can keep watching the movie all your life. The Flexplay DVD has a fixed life, after which the DVD destroys itself. That is, there is an in-built stopwatch which starts automatically when you start playing the disc. The stopwatch is chemical in nature and is designed to destroy the DVD after a fixed time.

Advantages of Flexplay DVD

1. You are actually buying the Flexplay DVD for the same price as the rental DVD.
2. You need not return the DVD. So there is no tension on extra charges.
3. As there is no risk involved in selling it like a rental DVD, Flexplay DVD’s can be sold in any store.

How Flexplay DVD Works?

The working of a Flexplay DVD is very much the same as that of a Digital Versatile Disc [DVD], except for an additional component. Just like a DVD, the sound and video are digitally encoded into the Flexplay DVD. This information will be stored in the disc in the bumps and trenches in the DVD and thus form a long track of information. Like the normal DVD, Flexplay DVD will also have the tracks spiral in nature. These tracks will then be covered with the help of protective layers like poly-carbonate plastic and then a gold layer n top of it.

Like a normal DVD, this DVD also has two tracks with the same information holding capacity. They will also have two reflective layers out of which one is inside and the other is outside. The outside reflective layer will be semi-transparent. These two layers are stuck together with the help of resin adhesive, thus making a two-layer single disc.

DVD vs Flexplay DVD

The only difference between them is in an additional layer inside the disc. This layer is situated on the front side of the inside reflective layer. This layer is made up of a special transparent chemical compound that reacts with the external atmospheric oxygen to form another chemical compound.

The resultant chemical compound obtained is opaque in nature. When the laser beam of a DVD player passes through the different layers, the layers that are reflective causes it to read the DVD. But after the reaction, the opaque nature stops the DVD player from reading the disc. Thus the DVD shows the sign “No Disc”. The special layer cannot be easily setup inside the disc. For this, the manufacturers made a special adhesive that bonds the two separate layers with this layer.

In the beginning, when you purchase the Flexplay DVD, it is sold as an air-tight package. Thus, the DVD will not have any contact with the atmospheric oxygen. As soon as you open the package, the oxygen starts a slow reaction with the chemical. Though the reaction starts slowly, it later reacts quickly when it nears the expiry period. When the expiry period is near the special layer becomes opaque. This change can be understood easily by just looking at the disc. When the disc is take n out of the package it will have a red colour. After the complete reaction, the colour changes to black.

The expiry period of the disc is decided by the manufacturer and the chemical compound can be balanced accordingly.

Usually, there will be small chemical reactions even if the disc is kept in an air-tight package. But still the disc will be working properly for as long as one year, before it is opened. The special adhesive used in the bonding process helps in keeping the disc usable for a maximum of 48 hours without being damaged.

Though this technology has not yet been marketed, it will surely be a replacement for the rental DVD stores in future.

Disadvantages

Though the Flexplay discs can be economical to us, it  will not be so economical to the manufacturers. When each DVD is disposed off after watching, you will have to make many more copies for others as well. Though this may sound like profit, the selling of these DVD’s for cheap rental cash makes it a loss.

Recycling Options

The use and dispose of a large number of Flexplay DVD’s can cause serious environmental pollution. But the company has made tie-ups with many environmental organizations like Greendisk and Geo-tech polymers so that they can fully recycle the waste and thus maintain the environmental standards. All the wasted discs will be collected and the poly-carbonate plastic present in it will be recycled and later used for high-end applications. The company also claims that the pollution caused by the discs are not so harmful compared to the energy emitted due to the use of a vehicle to return the DVD back to the rental store.

Remote control tester

Description.

This is a simple remote controller tester circuit  based on infrared sensor IC TSOP 1738. When the IR waves fall on the sensor it output changes to low state.This makes the transistor Q1 ON and LED will blink according to the code contained in the signal. So for press of each button the LED blinks in different ways. This is a good indication of the working of remote.The diode D1drops 0.7 V to give the IC ~ 5V supply from the available 6V . R2 is a current limiting resistance.

Preamplifier for dynamic microphones

Description.
Here is a low noise preamplifier design for dynamic microphones. The circuit is based on the uA739 IC from Fairchild Semiconductors. uA739 is a dual audio operational amplifier with high gain and excellent stability. Out of the two opamps available in the IC, only one is used here. The audio signals from the microphone are coupled to the non inverting input of IC1 through the capacitor C1 and resistor R1. C1 performs input DC decoupling. The R1, C2 network bypasses the unwanted high frequency signals from the microphone. A fraction of the output is fed back to the inverting input in order to prevent oscillations and ensure better stability. The input impedance of this circuit is around 50K.This amplifier can handle signal from 20Hz to 20 KHz, which makes it excellent for audio applications.
Circuit diagram.

Working of Digital Cameras

I have already described about the working of a camera. Almost all the basics of this post have been explained there. Now let us know more about a digital camera, its working, and also advantages.

The digital camera can be considered as an alteration of the conventional analog camera. Most of the associated components are also the same, except that instead of light falling on a photosensitive film like an analog camera, image sensors are used in digital cameras. Though analog cameras are mostly dependent on mechanical and chemical processes, digital cameras are dependent on digital processes. This is a major shift from its predecessor as the concept of saving and sharing audio as well as video contents have been simplified to earth.

Digital Camera Basics

As told earlier, the basic components are all the same for both analog and digital cameras. But, the only difference is that the images received in an analog camera will be printed on a photographic paper. If you need to send these photos by mail, you will have to digitally convert them. So, the photo has to be digitally scanned.

This difficulty is not seen in digital photos. The photos from a digital camera are already in the digital format which the computer can easily recognize (0 and 1). The 0’s and 1’s in a digital camera are kept as strings of tiny dots called pixels.

The image sensors used in an digital can be either a Charge Coupled Device (CCD) or a Complimentary Metal Oxide Semi-conductor (CMOS). Both these image sensors have been deeply explained earlier.

The image sensor is basically a micro-chip with a width of about 10mm. The chip consists arrays of sensors, which can convert the light into electrical charges. Though both CMOS and CCD are very common, CMOS chips are known to be more cheaper. But for higher pixel range and costly cameras mostly CCD technology is used.

A digital camera has lens/lenses which are used to focus the light that is to be projected and created. This light is made to focus on an image sensor which converts the light signals into electric signals. The light hits the image sensor as soon as the photographer hits the shutter button. As soon as the shutter opens the pixels are illuminated by the light in different intensities. Thus an electric signal is generated. This electric signal is then further broke down to digital data and stored in a computer.

Pixel Resolution of a Digital Camera

The clarity of the photos taken from a digital camera depends on the resolution of the camera. This resolution is always measured in the pixels. If the numbers of pixels are more, the resolution increases, thereby increasing the picture quality. There are many type of resolutions available for cameras. They differ mainly in the price.

• 256×256 – This is the basic resolution a camera has. The images taken in such a resolution will look blurred and grainy. They are the cheapest and also unacceptable.
• 640×480 – This is a little more high resolution camera than 256×256 type. Though a clearer image than the former can be obtained, they are frequently considered to be low end. These type of cameras are suitable for posting pics and images in websites.
• 1216×912 – This resolution is normally used in studios for printing pictures. A total of 1,109,000 pixels are available.
• 1600×1200 – This is the high resolution type. The pictures are in their high end and can be used to make a 4×5 with the same quality as that you would get from a photo lab.
• 2240×1680 – This is commonly referred to as a 4 megapixel cameras. With this resolution you can easily take a photo print up to 16×20 inches.
• 4064×2704 – This is commonly referred to as a 11.1 megapixel camera. 11.1 megapixels takes pictures at this resolution. With this resolution you can easily take a photo print up to 13.5×9 inch prints with no loss of picture quality.
• There are even higher resolution cameras up to 20 million pixels or so.

Color Filtering using Demosaicing Algorithms

The sensors used in digital cameras are actually coloured blind. All it knows is to keep a track of the intensity of light hitting on it. To get the colour image, the photosites use filters so as to obtain the three primary colours. Once these colours are combined the required spectrum is obtained.

For this, a mechanism called interpolation is carried out. A colour filter array is placed over each individual photosite. Thus, the sensor is divided into red, green and blue pixels providing accurate result of the true colour at a particular location. The filter most commonly used for this process is called Bayer filter pattern. In this pattern an alternative row of red and green filters with a row of blue and green filters. The number of green pixels available will be equal to the number of blue and red combined. It is designed in a different proportion as the human eye is not equally sensitive to all three colours. Our eyes will percept a true vision only if the green pixels are more.

The main advantage of this method is that only one sensor is required for the recording of all the colour information. Thus the size of the camera as well as its price can be lessened to a great extent. Thus by using a Bayer Filter a mosaic of all the main colours are obtained in various intensities. These various intensities can be further simplified into equal sized mosaics through a method called demosaicing algorithms. For this the three composite colours from a single pixel are mixed to form a single true colour by finding out the average values of the closest surrounding pixels.

Take a look at the digital camera schematic shown below.

Parameters of a Digital Camera

Like a film camera, a digital camera also has certain parameters. These parameters decide the clarity of the image. First of all the amount of light that enters through the lens and hits the sensor has to be controlled. For this, the parameters are

1. Aperture – Aperture refers to the diameter of the opening in the camera. This can be set in automatic as well as the manual mode. Professionals prefer manual mode, as they can bring their own touch to the image.

2. Shutter Speed – Shutter speed refers to the rate and amount of light that passes through the aperture. This can be automatic only. Both the aperture and the shutter speed play important roles in making a good image.

3. Focal Length – The focal length is a factor that is designed by the manufacturer. It is the distance between the lens and the sensor. It also depends on the size of the sensor. If the size of the sensor is small, the focal length will also be reduced by a proportional amount.

4. Lens – There are mainly four types of lenses used for a digital camera. They differ according to the cost of the camera, and also focal length adjustment. They are

• Fixed-focus, fixed-zoom lens – They are very common and are used in inexpensive cameras.
• Optical-zoom lenses with automatic focus – These are lenses with focal length adjustments. They also have the “wide” and “telephoto” options.
• Digital zoom – Full-sized images are produced by taking pixels from the centre of the image sensor. This method also depends on the resolution as well as the sensor used in the camera.
• Replaceable lens systems – Some digital cameras replace their lenses with 35mm camera lenses so as to obtain better images.

Digital Cameras v/s Analog Camera

• The picture quality obtained in a film camera is much better than that in a digital camera.
• The rise of technology has made filming the help of digital techniques easier as well as popular.
• Since the digtal copy can be posted in websites, photos can be sent to anyone in this world.