The electrical engineering handbook CH089

The electrical engineering handbook

Sherr, S., Durbeck, R.C., Suryn, W., Veillette, M. “Input and Output” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000 © 2000 by CRC Press LLC 89 Input and Output 89.1 Input Devices Keyboards • Light Pen • Data Tablet (Graphics, Digitizer) • Mouse • Trackball • Joystick • Touch Input • Scanners • Voice • Summary • Advantages and Disadvantages 89.2 Computer Output Printer Technologies Classification of Printer Technologies • Page Printer Technologies • Serial Nonimpact Printer Technologies • Impact Printer Technologies 89.3 Smart Cards Hardware Architecture • Contact ICC, Contactless ICC • Operating Systems • Standards • Applications • Readers • Card-to-System Solutions•Trends 89.1 Input Devices 1 Solomon Sherr Input devices are those portions of computer, data processing, and information systems that perform the essential function of providing some means for entering commands and data into the system. Therefore, input devices are found in all such systems, but are treated here as a separate equipment group, independent of the total system configuration. However, the place of input devices in a representative computer system may be clarified by reference to Fig. 89.1(a), which shows the interface of the main input device categories in relation to the portions of the generalized system that accept the inputs. The categories and the devices listed in Table 89.1 are the subject of this section. Keyboards Keyboards are essentially electromechanical devices, and are still ubiquitous, in spite of the inroads of other input devices. The primary type of keyboard in use as an input device is the alphanumeric (A/N) form, well known in its typewriter application, but with various additions and expansions consisting of numeric and special function keys. This type of keyboard is shown in Fig. 89.1(b) with a standard QWERTY format, so named because of the layout of the top left alpha keys, for the A/N portion, a separate numeric set to the right, and a group of function keys at the top. Other layouts for the A/N portion have been proposed and at least one (Dvorak) accepted by the American National Standards Institute (ANSI), but it has not received much use in spite of its advantages in increased efficiency. At present, the overwhelming majority of system keyboards still use the QWERTY layout, and it is the only one considered here. As illustrated in Fig. 89.1, a keyboard consists of a number of keyswitches whose exact structure is of prime importance in keyboard design. The relevant characteristics of keyswitch operation are life, actuation force, travel distance, and feedback. Accepted values are shown in Table 89.2 for different keyswitch designs. The elastomer type is preferred to a limited extent over the other two when the electronic audio feedback is included. This indicates that some type of audio feedback is desirable. One form of keyswitch design using an elastomer 1 The material contained in this section is a shortened version of that which appears in Electronic Displays, 2nd ed., by Sol Sherr, Chapter 6, Section 6.1, 1993, published by John Wiley & Sons, Inc., and is reprinted here by permission. Solomon Sherr Westland Electronics Robert C. Durbeck IBM Corporation Witold Suryn Gemplus Michel Veillette Gemplus © 2000 by CRC Press LLC A RT OF C OMPILING S TATISTICS Herman Hollerith Patented January 8, 1889 #395,781 n excerpt from Herman Hollerith’s patent application: Having thus described my invention, what I claim as new is (1) The improvement in the art of compiling statistics, which consists in first preparing a series of separate record-cards, each card representing an indi- vidual or subject; second, applying to each card at predetermined intervals circuit-controlling index points arranged according to a fixed plan of distribution, to represent each item or characteristic of the individual or subject, and third, applying said separate record-cards successively to circuit-controlling devices acted upon by the index-points to designate each statistical item represented by one or more of said index-points, substantially as described. This patent, along with two others, describes a system for tabulating statistical items represented by holes punched in cards. The 1890 U.S. census was completed $5 million under budget and two years ahead of schedule because of Hollerith’s system. The punch card system with encoded holes (the code for representing alphanumeric characters with holes was named after Hollerith) was widely used for sorting, counting, and tabulating even into the 1980s. Hollerith’s original Tabulating Machine Company was the forerunner to the computer giant, IBM. (Copyright © 1995, DewRay Products, Inc. Used with permission.) A © 2000 by CRC Press LLC TABLE 89.1 List of Input Devices Category Designation Operation Mode Keyboard Alphanumeric Electromechanical Keyboard Function Electromechanical Pointing Light pen Screen pointing Pointing Touchscreen Screen pointing Pointing Pen tablet Tablet pointing Coordinates Digitizer X-Y conversion Coordinates Data tablet X-Y location Cursor Mouse Movement Cursor Trackball Movement Cursor Joystick Movement Image Scanner Conversion Verbal Voice Conversion FIGURE 89.1 (a) Generalized display-system block diagram. (Source: After S. Sherr, Electronic Displays, New York: John Wiley & Sons, 1979.With permission.) (b) Alphanumeric keyboard. (Courtesy of Key tronic.) TABLE 89.2 Keyboard Parameter Values Parameter Snap Switch Elastomer Foam Pad Key travel 3.8 mm 3.2 mm 3.8 mm Force >60 gm >50 gm >30 gm Life 10 million cycles 10 million cycles 10 million cycles Feedback Audio mechanical Audio electric Tactile © 2000 by CRC Press LLC or “molded boot” is shown in Fig. 89.2(a), in which the boot consists of two collapsible domes. In this design, the internal movement of the keyswitch is completely silent so that some source of sound must be added to achieve the desired audible feedback. The snap switch design shown in Fig. 89.2(b) has built-in sound and achieves a small reduction in insertion errors over the elastomer design with audio feedback. The life requirement is estimated on the basis of workstation users operating at approximately half the accepted rate of 20 million actuations per key used for electronic typewriters. The actual layout and content of the keyboard may vary greatly, ranging from the standard typewriter arrangement, through different com- binations of alphanumerics and symbols, to the special-function keyboards that contain legends and symbols specific to the particular application. However, the outputs of each type are the same in that they must contain coded signals that relate the action to be performed by the information system to that defined by the key being operated, in terms of the input code of the system. Thus, many of the keyboards output the ASCII code, and the system is usually designed so that it can accept this type of standard code. Incidentally, ASCII, the acronym for American Standard Code for Information Interchange, is the standard means for encoding alphanumerics and a group of selected symbols for transmission to a display system, among others. It is the standard code used in the United States and most other English-speaking countries and corresponds to the ISO seven-bit code. The seven-bit ASCII is usually used, and it should be noted that for serial data transmission an eighth bit is added for parity. Various keyboard arrangements are possible, and many variants are found in particular applications. The means for coding the key operation may be through magnetic reed relays, solid-state circuits, or more exotic devices such as Hall effect sensors. These device characteristics are only incidental to the operation and beyond the scope of this chapter. Similarly, we do not discuss the human-factors aspects of keyboard design, not because they are not important, but because, apart from the visual considerations, the other factors have to do with tactile and physical features best left to others. Light Pen The light pen initially was a very popular means for accomplishing manual input to the random deflection information display systems, but fell out of favor when raster systems became more popular due to its being FIGURE 89.2 (a) Elastomer-type keyswitch. (b) Snap switch. ( Source: After H. Brunner et al., “Effects of key action design on keyboard preference and throughput performance,” Micro Switch. With permission.) © 2000 by CRC Press LLC somewhat difficult to use with raster systems. This device goes by a misleading name, as it does not emit light and is not a pen other than being somewhat similar to one in its physical appearance, as shown in Fig. 89.3(a). However, when we consider its functional characteristics, the validity of the term becomes apparent, as it is used to cause the electron beam to “write” patterns on the cathode ray tube (CRT) that are defined by the motion of the light pen on the CRT faceplate. The light pen operates by sensing the existence or nonexistence of a pulse of light at the point on the screen of the CRT or surface of any other light-emitting device where the point of the pen is placed. This is accomplished by means of the circuit shown in Fig. 89.3(b), where the light pulse is collected and transmitted through the fiber optics to a light-sensitive device that converts the light pulse into an electrical pulse which is shaped by some form of electronics (of which a Schmitt trigger is one example). We need not concern ourselves with the exact form of the electronics except to note that this pulse is then sent to the computer, as shown in Fig. 89.4, and provides a complete, closed-loop system. As the electronic pulse occurs at the time when the light pulse passes under the light pen, the computer is informed of the location at which the designated operation is to be performed and may proceed accordingly. Thus, the light pen is a pointing device that designates a point on the display screen and can be used as an input device. Various light pen programs have been written to expand the capabilities of the original one, and it should be noted that the light pen is coming back into favor as improvements in accuracy, ease of operation, and reliability occur. There are two characteristics of light pen operation that affect the capabilities of this input device. The first is the sensitivity, given by FIGURE 89.3 (a) Light pen. (Courtesy of FTG Data Systems.) (b) Light pen schematic. ( Source: After S. Sherr, Electronic Displays , New York: John Wiley & Sons, 1979, p. 388. With permission.) © 2000 by CRC Press LLC S = E L m p A p A m m s m f t L (89.1) where E L = illuminance at photodetector, m p = photodetector sensitivity, A p = preamplifier gain, A m = main amplifier gain, m s = Schmitt trigger sensitivity, m f = flip-flop sensitivity, and t L = optical loss. Equation (89.1) may be used to calculate the light output required from the display surface, which may be a CRT or other light-emitting device, but with the limitation that most of the flat panel units are matrix driven and must track the drive sequence in order to know the location of the light pen from the drive pulse timing. When phosphors are involved as for the CRT, vacuum fluorescent displays (VFDs), thin-film electroluminescent (TFEL) units, and color liquid crystal displays (LCDs), the phosphor delays must be entered into the timing, and the total delay is given by E o = E i (1 – e – t / t ) (89.2) where E o = voltage at triggering element, E i = voltage equivalent of phosphor light output, t = time, and t = sum of all delays. These delays set limits to the positional accuracy, as the computer tracking the signal will be in error by this amount. Other inaccuracies are due to the dimensions of the optical pickup surface, all of which somewhat negate the simplicity of operation. The result is the parameter values shown in Table 89.3. Data Tablet (Graphics, Digitizer) A very convenient means for data entry, retaining some of the ease of operation of the light pen but with much better accuracy, are the various forms of data tablets available. These tablets differ from the light pen in another significant way in that they do not require a moving spot of light to detect the location of the beam or direct it to a new location. This need for a moving light spot made the light pen difficult to use with the data tablets initially designed to overcome this limitation while still using a device with a pen-like input. The first successful example was the Rand tablet, a digital device that used an X–Y assembly from which a wand placed above some point on the X–Y wire matrix could pick up pulse generator output that fed X and Y electrical pulses into the matrix. By determining the number of pulses in a time period, the location of the wand is established. Another similar device used magnetostrictive rather than electrical signals to accomplish the same result, and this location is converted into display coordinates used to position a cursor on the CRT screen. The cursor may then be FIGURE 89.4 Block diagram of light pen computer system. ( Source: S. Sherr, Electronic Displays , New York: John Wiley & Sons, 1979, p. 389. With permission.) TABLE 89.3Light Pen Data Field of View Response Time Sensitivity 0.02–0.08 in. 120–150 ns 0.02–0.04 ft.L © 2000 by CRC Press LLC used as a visual feedback element so that the operator can correct the position of the wand until the cursor is properly placed. At this time the information from the tablet may also be transferred to either the host computer or the resident desktop or portable computer, as desired. Since the cursor is not used to signal its position to a pickup device, as is the case with the light pen, it may be used with any type of display system, including the non-light-emitting flat panel displays. Another advantage of the tablet is that it may be used to position cursors in the blank areas of the display, where no light pulses are available unless they are specially generated by the light pen. There have been numerous improvements and new developments using a variety of technologies that include magnetostrictive, electromagnetic, electrostatic or capacitive, scanned X–Y grid, resistive, and sonic. Of these, electromagnetic tablets dominate the digitizer market, and sonic is of interest because it does not require a tablet, but most of the other technologies are essentially restricted to touch input devices covered later. As noted previously, electromagnetic is the most popular technology for high-performance digitizer tablets. Operation is based on transformer principles, whereby a conductor carrying ac creates a magnetic field around it that induces a current in a second conductor. The digitizer tablet uses the amplitude and phase of the induced current to determine digitizing data. The tablet contains an X–Y pattern of conductors beneath its surface, in a manner similar to the Rand Tablet, but instead of counting pulses in a time period a circular conductor is used as the pick-up element for the induced current. This coil is placed on the tablet surface, and its position is determined by measuring the phase and amplitude of the current in the coil. Its center is interpolated by sweeping through the X–Y grid lines and demodulating the signal in the coil to determine the phase reversal point, or by calculating this point using digitized data fed into a microprocessor. The X–Y coordinates may be resolved to better than 0.025 mm using either of these two techniques. Figure 89.5(a) is a photograph of a representative digitizer tablet. Another digitizer technology is the one that uses the measurement of the time required for sound waves to travel from a source to movable microphone pickups.This sonic technology has the advantage that no special digitizing board is required, and either a stylus or a cursor can be used as the digitizer. Two sonic sources are contained in an L frame so that both X and Y coordinates can be determined by calculating the time it takes for the sound wave to reach the microphones contained in the pickup device. This calculation is made on the basis of sound traveling at 345 m/s at 20 ° C, and the accuracy is dependent on stable ambient conditions. This tends to limit the resolution to about 300 lpi, and the accuracy to ± 0.1%. The device may also be implemented with a single sonic source as the digitizing means and a pair of microphones located outside the digitizing area. In this case the location of the transducer is calculated by triangulation and converted into Cartesian coordinates. Digitizers are used primarily for inputting accurate coordinate data from maps and engineering drawings. Their high accuracy requirements have led to relatively high prices. Alternative means for inputting data are the data and graphics tablets that meet most input requirements at a lower cost and accuracy. The main technology is still electromagnetic, and the units are essentially the same as the digitizers, but with lower accuracies. However, several of the other technologies have also been used to achieve lower costs. Most successful among them are the capacitive and resistive versions, which may also be used as digitizers. The capacitive units, also termed electrostatic, use capacitive coupling where the coupling between the tablet and the cursor or stylus is determined by the capacitance made up of the tablet surface as one plate and the pickup element as the other. In this case, the capacitance is given by C = f ( ௣ A / d ) (89.3) where C = capacitance, ௣ = permittivity of dielectric, A = relative area of two plates, d = distance between plates, and f = proportionality factor. A scanned grid approach is used to determine the location of the cursor. As in the electromagnetic tablet, an X–Y grid of conductors is embedded in the tablet, with semiconductor switches on each line providing contact on a scanned basis. The charge flowing from each capacitance is summed through a summing amplifier as shown in Fig. 89.5(b). The resultant voltage peaks twice, once for the X and once for the Y lines, as they are scanned. The peak positions are digitized by means of a counter that starts at the beginning of the scan, and runs at some multiple of the scan rate. The digital values represent the coordinates of the cursor location. © 2000 by CRC Press LLC Mouse The mouse has gone a long way from its original invention by Engelbart in 1965, through its redesign at Xerox and introduction by Apple as a main input device, and its general acceptance by computer users as an important addition to the group of input devices. It should be noted, in passing, that the mouse is essentially an upside- down trackball, although the latter is now being referred to as an upside-down mouse. However, the trackball came first and is described further in the next section. FIGURE 89.5 (a) Digitizer tablet. (Courtesy of Numonics.) (b) Capacitive technology. ( Source: After T. E. Davies et al., “Digitizers and input tablets,” in Input Devices , S. Sherr, Ed., New York: Academic Press, 1988, p. 186. With permission.) © 2000 by CRC Press LLC Mice contain motion-sensing elements and are operated by moving mechanical or optical elements. One form uses wheels and shafts to drive the sensing elements, as shown schematically in Fig. 89.6. The angular velocity ( w ) of the wheel and shaft is given by w = V r / R rad/s (89.4) where V r = velocity of wheel and R = wheel radius. The rotation angle ( q ) is given by ( q ) = X / R rad (89.5) where X = distance moved. This type of mouse has two sets of wheels and shafts, one for horizontal and the other for vertical motion. A more popular type of mechanical mouse is the one that uses a ball for the motion sensing device, as shown in Fig. 89.7. Again, the velocity of the ball circumference equals the velocity of the mouse, and the angular velocity is given by w = V/R 1 rad/s (89.6) where R 1 = shaft radius. The smaller the shaft the more rapid its rotation for a given mouse velocity. Another form of the ball-and-shaft mouse is the one that uses an optical interrupter, as shown in Fig. 89.8. In this form, the light from the light-emitting diodes (LEDs) is interrupted by the coded disks that are rotated by the shafts, and is then picked up by the phototransistors and converted into the digital signal that represents the disk rotation. An optical interrupter is also used for the optomechanical mouse, and here the interrupter contains a set of slots; as the inter- rupter rotates quadrature signals are created that correspond to the shaft rotation. In addition to the shaft and optomechanical mice, an early form of mouse used multiturn potentiometers connected to the wheels, and the output voltage that represented the motion varied in direct proportion to the mouse motion. The voltage was then converted by means of an analog-to-digital converter into digital form for input to the computer. Finally, there are the true optical mice that use a special surface that is printed with a set of geometric shapes, usually a grid of lines or dots, that are illuminated and focused on a light detector. The most common form uses a grid made up of orthogonal lines, with the vertical and horizontal lines printed in different colors. These colors absorb light at different frequencies so that the optical detectors can differentiate between horizontal FIGURE 89.6Wheel showing velocities and slip angle. (Source: After C. Goy, “Mice,” in Input Devices, S. Sherr, Ed., New York: Academic Press, 1988, p. 225. With permission.) FIGURE 89.7Ball and shaft. (Source: C. Goy, “Mice,” in Input Devices, S. Sherr, Ed., New York: Academic Press, 1988. With permission.)