TOUCH SCREEN TECHNOLOGIES BASIC INFORMATION AND TUTORIALS

What are the different touch screen technologies?

The first touch-screen was created by adding a transparent surface to a touch-sensitive graphic digitizer, and sizing the digitizer to fit a computer monitor. The initial purpose was to increase the speed at which data could be entered into a computer. Subsequently, several types of touch-screen technologies have emerged, each with its own advantages and disadvantages that may, or may not, make it suitable for any given application.

Resistive Touch-screens

Resistive touch-screens respond to the pressure of a finger, a fingernail, or a stylus. They typically comprise a glass or acrylic base that is coated with electrically conductive and resistive layers. The thin layers are separated by invisible separator dots.

When operating, an electrical current is constantly flowing through the conductive material. In the absence of a touch, the separator dots prevent the conductive layer from making contact with the resistive layer. When pressure is applied to the screen the layers are pressed together, causing a change in the electrical current.

This is detected by the touch-screen controller, which interprets it as a vertical/horizontal coordinate on the screen (x- and y-axes) and registers the appropriate touch event. Resistive type touch-screens are generally the most affordable.

Although clarity is less than with other touch-screen types, they’re durable and able to withstand a variety of harsh environments. This makes them particularly suited for use in POS environments, restaurants, control/automation systems and medical applications.

Infrared Touch-screens

Infrared touch-screens are based on light-beam interruption technology. Instead of placing a layer on the display surface, a frame surrounds it. The frame assembly is comprised of printed wiring boards on which optoelectronics are mounted and concealed behind an IR-transparent bezel.

The bezel shields the optoelectronics from the operating environment while allowing IR beams to pass through. The frame contains light sources (or light-emitting diodes) on one side, and light detectors (or photosensors) on the opposite side.

The effect of this is to create an optical grid across the screen. When any object touches the screen, the invisible light beam is interrupted, causing a drop in the signal received by the photosensors. Based on which photosensors stop receiving the light signals, it is easy to isolate a screen coordinate. Infrared touch systems are solid state technology and have no moving mechanical parts.

As such, they have no physical sensor that can be abraded or worn out with heavy use over time. Furthermore, since they do not require an overlay—which can be broken—they are less vulnerable to vandalism, and are also extremely tolerant of shock and vibration.

Surface Acoustic Wave Technology Touch-screens

Surface Acoustic Wave (SAW) technology is one of the most advanced touch-screen types. The SAW touch-screens work much like their infrared brethren except that sound waves, not light beams, are cast across the screen by transducers. Two sound waves, one emanating from the left of the screen and another from the top, move across the screen’s surface. The waves continually bounce off reflectors located on all sides of the screen until they reach sensors located on the opposite side from where they

originated.

When a finger touches the screen, the waves are absorbed and their rate of travel thus slowed. Since the receivers know how quickly the waves should arrive relative to when they were sent, the resulting delay allows them to determine the x- and y-coordinates of the point of contact and the appropriate touch event to be registered.

Unlike other touch-screen technologies, the z-axis (depth) of the touch event can also be calculated; if the screen is touched with more than usual force, the water in the finger absorbs more of the wave’s energy, thereby delaying it even more.

Because the panel is all glass and there are no layers that can be worn, Surface Acoustic Wave touch screens are highly durable and exhibit excellent clarity characteristics. The technology is recommended for public information kiosks, computer based training, or other high-traffic indoor environments.

Capacitive Touch-screens

Capacitive touch-screens consist of a glass panel with a capacitive (charge storing) material coating on its surface. Unlike resistive touch-screens, where any object can create a touch, they require contact with a bare finger or conductive stylus.

When the screen is touched by an appropriate conductive object, current from each corner of the touch screen is drawn to the point of contact. This causes oscillator circuits located at corners of the screen to vary in frequency depending on where the screen was touched.

The resultant frequency changes are measured to determine the x- and y- coordinates of the touch event. Capacitive type touch-screens are very durable, and have a high clarity. They are used in a wide range of applications, from restaurant and POS use, to industrial controls and information kiosks.

SMART CARD READERS BASIC INFORMATION AND TUTORIALS

What are smart cards?

Instead of fumbling for coins, imagine buying the morning paper using a card charged with small denominations of money. The same card could be used to pay for a ride on public transportation. And after arriving at work, you could use that card to unlock the security door, enter the office, and boot up your PC with your personal configuration.

In fact, everything you purchase, whether direct or through the Internet, would be made possible by the technology in this card. It may seem far-fetched but the rapid advancements of semiconductor technologies make this type of card a reality.

In some parts of the world, the “smart card” has already started to obsolete cash, coins, and multiple cards. An essential part of the smart card system is the card reader, which is used to exchange or transfer information.

Why is the smart card replacing the magnetic strip card?

Because the smart card can hold up to a 100 times more information and data than a traditional magnetic strip card. The smart card is classified as an integrated circuit (IC) card. There are actually two types of IC card—memory cards and smart cards.

Memory cards contain a device that allows the card to store various types of data. However, they do not have the ability to manipulate this data. A typical application for memory type cards is a pre-paid telephone card.

These cards hold typically between 1 KB and 4 KB of data. A memory card becomes a smart card with the addition of a microprocessor. The key advantage of smart cards is that they are easy to use, convenient, and can be used in several applications. They provide benefits to both consumers and merchants in many different industries by making data portable, secure, and convenient to access.

History of Smart Cards

Bull CP8 and Motorola developed the first “smart card” in 1977. It was a two-chip solution consisting of a microcontroller and a memory device. Motorola produced a single chip card called the SPOM 01.

Smart cards have taken off at a phenomenal rate in Europe by replacing traditional credit cards. The key to smart card success has been its ability to authorize transactions off-line. A smart card stores the “charge” of cash, enabling a purchase up to the amount of money stored in the card.

Motorola’s single chip solution was quickly accepted into the French banking system. It served as a means of storing the cardholder’s account number and personal identification numbers (PIN) as well as transaction details. By 1993 the French banking industry completely replaced all bankcards with smart cards.

In 1989 Bull CP8 licensed its smart card technology for use outside the French banking system. The technology was then incorporated into a variety of applications such as Subscriber Identification

Modules (SIM cards) in GSM digital mobile phones. In 1996 the first combined modem/smart card reader was introduced. We will probably soon see the first generation of computers that read smart cards as a standard function.

In May 1996 five major computer companies (IBM, Apple, Oracle, Netscape, and Sun) proposed a standard for a “network computer” designed to interface directly with the Internet, and it has the ability to use smart cards. Also in 1996 the alliance between Hewlett Packard, Informix, and Gemplus was launched to develop and promote the use of smart cards for payment and security on all open networks.

Besides e-commerce, some smart card applications are:

■ Transferring favorite addresses from a PC to a network computer

■ Downloading airline ticket and boarding pass

■ Booking facilities and appointments via Websites

■ Storing log-on information for using any work computer or terminal

THIN FILM TRANSISTOR (TFT) DISPLAYS BASIC INFORMATION AND TUTORIALS

What Are TFT Displays?

Many companies have adopted Thin Film Transistor (TFT) technology to improve color screens. In a TFT screen, also known as active matrix, an extra matrix of transistors is connected to the LCD panel—one transistor for each color (RGB) of each pixel.

These transistors drive the pixels, eliminating the problems of ghosting and slow response speed that afflict non-TFT-LCDs. The result is screen response times of the order of 25 ms, contrast ratios in the region of 200:1 to 400:1, and brightness values between 200 and 250 cd/m2 (candela per square meter).

The liquid crystal elements of each pixel are arranged so that in their normal state (with no voltage applied) the light coming through the passive filter is “incorrectly” polarized and thus blocked. But when a voltage is applied across the liquid crystal elements they twist up to ninety degrees in proportion to the voltage, changing their polarization and letting more light through.

The transistors control the degree of twist and hence the intensity of the red, green, and blue elements of each pixel forming the image on the display. Thin film transistor screens can be made much thinner than LCDs, making them lighter. They also have refresh rates now approaching those of CRTs because current runs about ten times faster in a TFT than in a DSTN screen.

Standard VGA screens need 921,000 transistors (640 x 480 x 3), while a resolution of 1024 x 768 needs 2,359,296, and each transistor must be perfect. The complete matrix of transistors has to be produced on a single, expensive silicon wafer, and the presence of more than a couple of impurities means that the whole wafer must be discarded.

This leads to a high wastage rate and is the main reason for the high price of TFT displays. It’s also the reason why there are liable to be a couple of defective pixels where the transistors have failed in any TFT display.

There are two phenomena that define a defective LCD pixel: a “lit” pixel, which appears as one or several randomly placed red, blue and/or green pixel elements on an all-black background, or a “missing” or “dead” pixel, which appears as a black dot on all-white backgrounds.

The former failure mode is the more common, and is the result of a transistor occasionally shorting in the “on” state and resulting in a permanently “turned-on” (red, green or blue) pixel. Unfortunately, fixing the transistor itself is not possible after assembly. It is possible to disable an offending transistor using a laser.

However, this just creates black dots that would appear on a white background. Permanently turned-on pixels are a fairly common occurrence in LCD manufacturing, and LCD manufacturers set limits, based on user feedback and manufacturing cost data, as to how many defective pixels are acceptable for a given LCD panel.

The goal in setting these limits is to maintain reasonable product pricing while minimizing the degree of user distraction from defective pixels. For example, a 1024 x 768 native resolution panel, containing a total of 2,359,296 (1024 x 768 x 3) pixels, that has 20 defective pixels would have a pixel defect rate of (20/2,359,296)*100 = 0.0008%. The TFT display has undergone significant evolution since the days of the early, twisted Nnematic (TN) technology based panels.

HAND SOLDERING METHOD BASIC INFORMATION AND TUTORIALS

The various soldering methods which are used with electronic assemblies differ in the sequence in which solder, flux, and heat are brought to the joint, and in the way in which the soldering heat is brought to the joint or joints.

With hand soldering, the heat source is the tip of a soldering iron, which is heated to 300–350 °C/570 660 °F. A small amount of flux may have been applied to the joint members before they are placed together.

The assembled joint is heated by placing the tip of the soldering iron on it or close to it. Solder and flux are then applied together, in the form of a hollow solderwire, which carries a core of flux, commonly based on rosin.

The end of the cored wire is placed against the entry into the joint gap. As soon as its temperature has reached about 100 °C/200 °F, the rosin melts and flows out of the solderwire into the joint. Soon afterwards, the joint temperature will have risen above 183 °C/361 °F; the solder begins to melt too, and follows the flux into the joint gap.

As soon as the joint is satisfactorily filled, the soldering iron is lifted clear, and the joint is allowed to solidify. Thus, with hands oldering, the sequence of requirements is as follows:

1. Sometimes, a small amount of flux.

2. Heat, transmitted by conduction.

3. Solder, together with the bulk of the flux.

Clearly, this operation requires skill, a sure hand, and an experienced eye. On the other hand, it carries an in-built quality assurance: until the operator has seen the solder flow into a joint and neatly fill it, he – or more frequently she – will not lift the soldering iron and proceed to the next joint.

Before the advent of the circuit board in the late forties and of mechanized wavesoldering in the mid fifties, this was the only method for putting electronic assemblies together. Uncounted millions of good and reliable joints were made in this way.

Hand soldering is of course still practised daily in the reworking of faulty joints. Mechanized versions of hands oldering in the form of soldering robots have become established to cope with situations, where single joints have to be made in locations other than on a flat circuit board, and which therefore do not fit into a wave soldering or paste-printing routine.

These robots apply a soldering iron together with a metered amount of flux-cored solder wire to joints on three-dimensional assemblies, which because of their geometry do not lend themselves to wave soldering nor to the printing down of solder paste.

Naturally, soldering with a robot demands either a precise spatial reproducibility of the location of the joints, or else complex vision and guidance systems, to target the soldering iron on to the joints.

HISTORY OF FIBER OPTICS IN COMMUNICATION BASIC INFORMATION AND TUTORIALS

How the use of fiber optics in electronic communications developed?

In 1880, only four years after his invention of the telephone, Alexander Graham Bell used light for the transmission of speech. He called his device a Photophone.

It was a tube with a flexible mirror at its end. He spoke down the tube and the sound vibrated the mirror. The modulated light was detected by a photocell placed at a distance of two hundred meters or so. The result was certainly not hi-fi but the speech could at least be understood.

Following the invention of the ruby laser in 1960, the direct use of light for communication was re investigated. However the data links still suffered from the need for an unobstructed path between the sender and the receiver. Nevertheless, it was an interesting idea and in 1983 it was used to send a message, by Morse code, over a distance of 240 km (150 miles) between two mountain tops.

Enormous resources were poured into the search for a material with sufficient clarity to allow the development of an optic fiber to carry the light over long distances.

The early results were disappointing. The losses were such that the light power was halved every three meters along the route. This would reduce the power by a factor of a million over only 60 meters (200 feet).

Obviously this would rule out long distance communications even when using a powerful laser. Within

ten years however, we were using a silica glass with losses comparable with the best copper cables.

The glass used for optic fiber is unbelievably clear. We are used to normal ‘window’ glass looking clear but it is not even on the same planet when compared with the new silica glass. We could construct a pane of glass several kilometers thick and still match the clarity of a normal window.

If water were this clear we would be able to see the bottom of the deepest parts of the ocean. We occasionally use plastic for optic fiber but its losses are still impossibly high for long distance communications but for short links of a few tens of meters it is satisfactory and simple to use.

It is finding increasing applications in hi-fi systems, and in automobile control circuitry. On the other hand, a fiber optic system using a glass fiber is certainly capable of carrying light over long distances.

By converting an input signal into short flashes of light, the optic fiber is able to carry complex information over distances of more than a hundred kilometers without additional amplification. This is at least five times better than the distances attainable using the best copper coaxial cables.

The system is basically very simple: a signal is used to vary, or modulate, the light output of a suitable source — usually a laser or an LED (light emitting diode). The flashes of light travel along the fiber and, at the far end, are converted to an electrical signal by means of a photo-electric cell. Thus the original input signal is recovered.

When telephones were first invented, it took 75 years before we reached a global figure of 50 million subscribers. Television took only 13 years to achieve the same penetration and the Internet passed both in only four years. As all three of these use fiber optics it is therefore not surprising that cables are being laid as fast as possible across all continents and oceans.

Optic fibers carry most of the half million international telephone calls leaving the US everyday and in the UK over 95% of all telephone traffic is carried by fiber. Worldwide, fiber carries 85% of all communications.