LED Sh Segment Hole Segment Hole FIGURE 89.8 Optical interrupter. Source: C. Goy, "Mice, "in Input Devices, S Sherr, Ed, New York: Academic Press, 1988, and vertical movement of the mouse. If such a structure is used as the mouse, then the photodetector will pick p a series of light-dark impulses consisting of the reflections from the mirror surface and the grid lines and convert them into square waves. A second LED and photodetector that is mounted orthogonally to the first is sed to detect motion in the orthogonal direction, and the combination of the two inks avoids confusion between the two directions of motion. The system then counts the number of impulses created by the mouse motion and converts the result into motion information for the cursor. This type of mouse has the advantage that no mechanical elements are required. Trackball As noted previously, the trackball uses technology similar to the mouse, but preceded it as an input device. Thus, the comment that it is an upside-down mouse should be reversed. The movable element is housed in an assembly as is shown in Fig. 89.9, and the assembly remains stationary so that much less desk space is quired than for the mouse. In addition, the trackball may be mounted on a keyboard so that very little additional desk space is needed. The movable element can be the same as used in the mouse, and the output can be a set of bits corresponding to the coordinates to which the cursor should be driven, or where the command should be carried out. The output format is essentially equivalent to that used for the mouse, and the same protocols are used. The typical trackball has an X and Y optical encoder that generates a pulse for each 0.76 mm of incrementa motion of the ball. This means that the pulse train may range from 10 to 2500 pulses per second (pps), depending on how fast the ball is rotated. This is much more rapid than required for satisfactory updates, which need not be greater than about 100 times per second. This can easily be accomodated by the rS-232 protocol using an eight-bit word. Thus, the trackball is an excellent alternative for the mouse, and is rapidly returning to a preferred position as an input device. Joystick The joystick has not achieved much acceptance as an input device for electronic display systems, except for video games, although it has been the preferred control for many types of aircraft. However, it can be used to me extent in display systems other than those used in video games, and therefore warrants inclusion in this section. There are two basic types of joysticks, termed"displacement"and"force-operated"" A typical displace- ment joystick is shown in Fig. 89.10, and may have two or three degrees of freedom. The activating means may ary from as few as four switches mounted 90 degrees apart, to full potentiometers for analog output, and optical encoders for digital output. a third axis may be added by allowing the handle to rotate and drive a third potentiometer. Spring forces of 5 to 10 lbs are usual for the other two axes, and displacements go from 6 to e 2000 by CRC Press LLC
© 2000 by CRC Press LLC and vertical movement of the mouse. If such a structure is used as the mouse, then the photodetector will pick up a series of light-dark impulses consisting of the reflections from the mirror surface and the grid lines and convert them into square waves. A second LED and photodetector that is mounted orthogonally to the first is used to detect motion in the orthogonal direction, and the combination of the two inks avoids confusion between the two directions of motion. The system then counts the number of impulses created by the mouse motion and converts the result into motion information for the cursor. This type of mouse has the advantage that no mechanical elements are required. Trackball As noted previously, the trackball uses technology similar to the mouse, but preceded it as an input device. Thus, the comment that it is an upside-down mouse should be reversed. The movable element is housed in an assembly as is shown in Fig. 89.9, and the assembly remains stationary so that much less desk space is required than for the mouse. In addition, the trackball may be mounted on a keyboard so that very little additional desk space is needed. The movable element can be the same as used in the mouse, and the output can be a set of bits corresponding to the coordinates to which the cursor should be driven, or where the command should be carried out. The output format is essentially equivalent to that used for the mouse, and the same protocols are used. The typical trackball has an X and Y optical encoder that generates a pulse for each 0.76 mm of incremental motion of the ball. This means that the pulse train may range from 10 to 2500 pulses per second (pps), depending on how fast the ball is rotated. This is much more rapid than required for satisfactory updates, which need not be greater than about 100 times per second. This can easily be accomodated by the RS-232 protocol using an eight-bit word. Thus, the trackball is an excellent alternative for the mouse, and is rapidly returning to a preferred position as an input device. Joystick The joystick has not achieved much acceptance as an input device for electronic display systems, except for video games, although it has been the preferred control for many types of aircraft. However, it can be used to some extent in display systems other than those used in video games, and therefore warrants inclusion in this section. There are two basic types of joysticks, termed “displacement” and “force-operated”. A typical displacement joystick is shown in Fig. 89.10, and may have two or three degrees of freedom. The activating means may vary from as few as four switches mounted 90 degrees apart, to full potentiometers for analog output, and optical encoders for digital output. A third axis may be added by allowing the handle to rotate and drive a third potentiometer. Spring forces of 5 to 10 lbs. are usual for the other two axes, and displacements go from 6 to 30 degrees. FIGURE 89.8 Optical interrupter. (Source: C. Goy, “Mice,” in Input Devices, S. Sherr, Ed., New York: Academic Press, 1988, p. 229. With permission.)
GURE 89.9 Trackball.( Courtesy of CH Products, Vista, FIGURE 89.10 Three-axis displacement joystick. Calif.) Courtesy of CH Products, Vista, Calif. X Axis Supply Output Y Axis IGURE 89.11 Schematic connections in a force joystick. ( Source: After D. Doran, " Trackballs and joysticks, "in Input Devices, S Sherr, Ed, New York: Academic Press, 1988, P. 260. With permission. The force joystick operates by responding to pressure on the handle to generate the X-Y coordinates. It may However, it is difficult to use a rotating handle for the third dimension because some force is usually transmitted to the other dimensions causing crosstalk. Therefore, a separate lever is preferred. The force is detected by means of piezoelectric sensors that are bonded to the handle rod, and a voltage source is applied across the network, as shown in Fig. 89.11. The output is taken from the strain gauge and the analog voltage will be proportional to the amount of force. The same type of protocol and output circuitry may be used as for the displacement unit, and both can generate either position or rate data. An exponential curve with a dead zone threshhold is preferred for pulse rates in order to avoid starting pulse rate uncertainties, with the first pulse starting as soon as the threshhold is exceeded Touch Input Touch input devices come in two basic forms, either placed directly on the display surface, or as a separate panel attached to the computer system. In its second form it is essentially a data tablet differing mainly in that it acts as another display unit with some form of a touch-sensitive surface. In this implementation it is the e 2000 by CRC Press LLC
© 2000 by CRC Press LLC The force joystick operates by responding to pressure on the handle to generate the X–Y coordinates. It may be either a two- or three-dimensional version, with the same types of handles as for the displacement joysticks. However, it is difficult to use a rotating handle for the third dimension because some force is usually transmitted to the other dimensions causing crosstalk. Therefore, a separate lever is preferred. The force is detected by means of piezoelectric sensors that are bonded to the handle rod, and a voltage source is applied across the network, as shown in Fig. 89.11. The output is taken from the strain gauge and the analog voltage will be proportional to the amount of force. The same type of protocol and output circuitry may be used as for the displacement unit, and both can generate either position or rate data. An exponential curve with a dead zone threshhold is preferred for pulse rates in order to avoid starting pulse rate uncertainties, with the first pulse starting as soon as the threshhold is exceeded. Touch Input Touch input devices come in two basic forms, either placed directly on the display surface, or as a separate panel attached to the computer system. In its second form it is essentially a data tablet differing mainly in that it acts as another display unit with some form of a touch-sensitive surface. In this implementation it is the FIGURE 89.9 Trackball. (Courtesy of CH Products,Vista, Calif.) FIGURE 89.10 Three-axis displacement joystick. (Courtesy of CH Products, Vista, Calif.) FIGURE 89.11 Schematic connections in a force joystick. (Source: After D. Doran, “Trackballs and joysticks,” in Input Devices, S. Sherr, Ed., New York: Academic Press, 1988, p. 260. With permission.)
ame as the Touchscreen input device, and this discussion concentrates on the technologies used for Touch- screens. There are five different technologies used for touch input devices, which are capacitive or resistive relays, piezoelectric, light beam interruption, and surface acoustic wave. The system may be divided into the sensor unit, which senses the location of the pointing element, and the controller that interfaces with the sensor and communicates the location information to the system computer. Since the controller is an electronic device that does not use technology different from the computer it is not covered here. The main differences among the different touch input devices are due to the choice of sensor technology, and the discussion concentrates on these technologies Capacitive. Capacitive overlay technology is illustrated in Fig 89. 12 where a transparent metallic coating is placed over the display screen and the finger or stylus capacitance is sensed to Glass substrate determine the touch location. The overlay may consist of a group of separate sections etched into the surface with each separate section connected to the controller, or a continuous surface con- nected at the four corners. The first form is termed discrete capac itive, and touch location is determined by having each section sequentially connected to an oscillator circuit where the frequency of oscillations is affected by the pointing device. The oscillation frequency is measured and compared to a stored reference fre- quency. If the frequency difference is large enough then it is rec- d as a touch at that location. It is a simple system, but suffer from low resolution and slow response so that it is only practical for menu selection The analog capacitive system uses the same metallic overlay, but the metallic surface is continuous rather than etched. The conne tions at the four ends are each connected to a separate oscillator, FIGURE8912 Capacitive overlay technology and the frequency of each is measured and stored. Then when the (Source: After A. B. Carrell and J. Carstedt, overlay is touched the change in capacitance will have a different"Touch input technology, SID Sem. Lecture the differences are used to determine the coordinates of the touch Society for Information Displays on. Courtesy effect on the frequency of each oscillator. These are measured and Notes p. 15.30, 1987. With permissi by means of an algorithm. This technique is capable of much higher resolution(250 x 250) than the digital approach and is preferred for graphics or other high-density displays Resistive. Resistive overlay technology requires a more complex assembly consisting of two layers, as illustrated in Fig. 89.13. The layers both contain transparent metallic surfaces and are separated by spacers so that an air gap exists between the layers in the absence of any pressure on the touch panel. The metallic layers face each other and when the outer panel is pressed the metallic layers make contact and form a conductive path at the point of contact. When a voltage is applied between the top of the outer layer and the bottom of the inner layer, the two layers act as a voltage divider, and the voltage at the point of contact may be measured in the X and Y directions by applying the voltage in first one and then the other direction. The measured voltages are then transmitted to the controller where they are converted into coordinates which are then sent to the computer. The panel may be discrete, in which the conductive coating on the top layer is etched in one direction and that on the bottom layer in the other direction, or analog, where the conductive coatings in both layers are continuous In the discrete case, the panel then acts as an X-Y matrix, and the resolution is determined by the number of etched lines. The analog configuration requires the addition of linearization networks on each edge of the panel so that a large-area resistor is created with a voltage drop in one direction. Other linearization techniques are also possible, but only the four-element system is described here as shown in Fig. 89.14. In this arrangement, one of the layers acts as the large-area resistor and the other as a voltage probe where either can function in either role. For the Y coordinate value the top layer is the voltage probe, and the voltage is applied by the controller to the bottom layer. Similarly, the X coordinate is found by connecting the voltage to the top lyer and making the bottom layer into the voltage probe. In either type of system, the resolution can be very high, but the transmissivity is reduced to under 80% due to the multiple layers e 2000 by CRC Press LLC
© 2000 by CRC Press LLC same as the Touchscreen input device, and this discussion concentrates on the technologies used for Touchscreens. There are five different technologies used for touch input devices, which are capacitive or resistive overlays, piezoelectric, light beam interruption, and surface acoustic wave. The system may be divided into the sensor unit, which senses the location of the pointing element, and the controller that interfaces with the sensor and communicates the location information to the system computer. Since the controller is an electronic device that does not use technology different from the computer it is not covered here. The main differences among the different touch input devices are due to the choice of sensor technology, and the discussion concentrates on these technologies. Capacitive. Capacitive overlay technology is illustrated in Fig. 89.12 where a transparent metallic coating is placed over the display screen and the finger or stylus capacitance is sensed to determine the touch location. The overlay may consist of a group of separate sections etched into the surface with each separate section connected to the controller, or a continuous surface connected at the four corners. The first form is termed discrete capacitive, and touch location is determined by having each section sequentially connected to an oscillator circuit where the frequency of oscillations is affected by the pointing device. The oscillation frequency is measured and compared to a stored reference frequency. If the frequency difference is large enough then it is recognized as a touch at that location. It is a simple system, but suffers from low resolution and slow response so that it is only practical for menu selection. The analog capacitive system uses the same metallic overlay, but the metallic surface is continuous rather than etched. The connections at the four ends are each connected to a separate oscillator, and the frequency of each is measured and stored. Then when the overlay is touched the change in capacitance will have a different effect on the frequency of each oscillator. These are measured and the differences are used to determine the coordinates of the touch by means of an algorithm. This technique is capable of much higher resolution (250 ¥ 250) than the digital approach and is preferred for graphics or other high-density displays. Resistive. Resistive overlay technology requires a more complex assembly consisting of two layers, as illustrated in Fig. 89.13. The layers both contain transparent metallic surfaces and are separated by spacers so that an air gap exists between the layers in the absence of any pressure on the touch panel. The metallic layers face each other and when the outer panel is pressed the metallic layers make contact and form a conductive path at the point of contact. When a voltage is applied between the top of the outer layer and the bottom of the inner layer, the two layers act as a voltage divider, and the voltage at the point of contact may be measured in the X and Y directions by applying the voltage in first one and then the other direction. The measured voltages are then transmitted to the controller where they are converted into coordinates which are then sent to the computer. The panel may be discrete, in which the conductive coating on the top layer is etched in one direction and that on the bottom layer in the other direction, or analog, where the conductive coatings in both layers are continuous. In the discrete case, the panel then acts as an X–Y matrix, and the resolution is determined by the number of etched lines. The analog configuration requires the addition of linearization networks on each edge of the panel so that a large-area resistor is created with a voltage drop in one direction. Other linearization techniques are also possible, but only the four-element system is described here as shown in Fig. 89.14. In this arrangement, one of the layers acts as the large-area resistor and the other as a voltage probe where either can function in either role. For the Y coordinate value the top layer is the voltage probe, and the voltage is applied by the controller to the bottom layer. Similarly, the X coordinate is found by connecting the voltage to the top layer and making the bottom layer into the voltage probe. In either type of system, the resolution can be very high, but the transmissivity is reduced to under 80% due to the multiple layers. FIGURE 89.12 Capacitive overlay technology. (Source: After A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.30, 1987.With permission. Courtesy Society for Information Display.)
ansparent Metallic Film FIGURE 89.13 Resistive overlay technology. Source: After A. B. Carrell and J Carstedt, " Touch input technology, "SID Sem. Lecture Notes, p. 15.31, 1987. With permission. Courtesy Society for Information Display. Linearization Network Top Layer Bottom Layer FIGURE 89. 14 Four-wire analog resistive. Source: A B. Carrell and J Carstedt, "Touch input technology, "SID Sem. Lecture Notes, P. 15.32, 1987. with permission. Courtesy Society for Information Display. CRT Face Transducers= P1, P2, P3, P ouch Activation= f(P1, P2, P3, P4) FIGURE 89. 15 Piezoelectric technology. Source: A B. Carrell and J. Carstedt, Touch input technology, " SID Sem. Lecture Notes, p. 15.34, 1987. with permission. Courtesy Society for Information Display. Piezoelectric. The piezoelectric technology uses pressure-sensitive transducers as the means for determining the location of the touch, as shown in Fig. 89.15. The sensor is a glass plate with transducers connected to the four corners. Pressure on the plate causes readings to occur at each of the transducers, which depend on the location of the pressure. Thus, the controller can measure the readings and obtain the coordinates by means of a proper algorithm. This technique allows a high-transmissivity plate to be used that can be curved to follow the CRT face plate curvature, but it allows only a limited number of touch points to be used. Light Beam Interruption. This is a fairly straightforward technology that requires a matrix of light sources nd detectors facing each other in the X and y directions. When the beams from the X and Y light sources are interrupted, this is sensed by the facing light detectors and the signals are sent to the controller. The light beams e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Piezoelectric. The piezoelectric technology uses pressure-sensitive transducers as the means for determining the location of the touch, as shown in Fig. 89.15. The sensor is a glass plate with transducers connected to the four corners. Pressure on the plate causes readings to occur at each of the transducers, which depend on the location of the pressure. Thus, the controller can measure the readings and obtain the coordinates by means of a proper algorithm. This technique allows a high-transmissivity plate to be used that can be curved to follow the CRT face plate curvature, but it allows only a limited number of touch points to be used. Light Beam Interruption. This is a fairly straightforward technology that requires a matrix of light sources and detectors facing each other in the X and Y directions. When the beams from the X and Y light sources are interrupted, this is sensed by the facing light detectors and the signals are sent to the controller. The light beams FIGURE 89.13 Resistive overlay technology. (Source: After A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.31, 1987. With permission. Courtesy Society for Information Display.) FIGURE 89.14 Four-wire analog resistive. (Source: A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.32, 1987. With permission. Courtesy Society for Information Display.) FIGURE 89.15 Piezoelectric technology. (Source: A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.34, 1987. With permission. Courtesy Society for Information Display.)
Retro Reflectors Rotation Sensor Module Typical Probe Point Mirror FIGURE 89. 16 Rotating infrared beam technology.( Source: A. B. Carrell and J. Carstedt, "Touch input technology, "SID Se. Lecture Notes, p. 15.34, 1987. With permission. Courtesy Society for Information Display. are turned on sequentially by pulsing the LEDs and thus create a full matrix of light beams without requiring each of them to be on continuously. This system does not reduce the screen transmissivity as there is no obstruction of the screen output, but it is limited in resolution to the number of led detector pairs that can be placed on the periphery of the screen. Another approach to light interruption is to use a rotating beam of light, which has the advantage that only one light source and detector pair is required. This technology is depicted in Fig. 89.16 and consists of a LED and a light detector placed inside a rotating drum which has a slit that allows light to be transmitted outside the drum. The light is swept across the surface and strikes the retroreflectors that sends it back directly to the detector. The beam scan is sampled 256 times on each scan, and Fig 89.16 shows how two angles of interruption are created, angle B by direct interruption, and angle C by mirror reflection interruption. The result is that the location of the interruption can be calculated by comparing the two angles. Again, there is no obstruction of the screen but a moving element must be added, and parallax errors may occur. Pen-Based Computing. This is an application for touch input devices that is growing at a rapid rate. The nput device comes in several forms, each of which can recognize hand printing with the special operating system and software recognizing this type of input. The pen-based input device comes in several forms, of which the one termed TouchPen" can function both as a digitizer with a touch tablet, and as the touch input device with a touch input pen-based computer system. A second one is that developed by Wacom, Inc, primarily for the GO Systems computer, but used by other pen-based systems as well. Finally, a third unit is that made by Scriptel Corp and used by Wang Laboratories in its system. TouchPen" was developed by Microtouch Systems, Inc, initially for use in GridPad made by the Grid Systems Corp. It is essentially a high-resolution digitizer consisting of an all-glass tablet that can be use of stylus input operating systems to digitize handwriting. It is basically a touch input device using resistive techniques to digitize the handwriting appearing on the display surface of pen-based computer systems. The glass tablet is placed on the display surface and the system pen is used to transmit the digitized data to the computer. As noted previously, the tablet may also be used as a standard touch input devic The second form of pen-based input device is one that uses electromagnetic technology and consists of a grid of wires that transmit radio waves that are picked up by a tuned circuit in the stylus. This circuit resonates at its own frequency and transmits that signal back to the wires at the grid location it is touching. The pen also transmits its signal to the computer, which turns off the grid transmission, and locates the position of the pen y determining which of the grid wires pick up the pen signal. The pen does not need to actually touch the display surface and does not require any power, which is an advantage somewhat counteracted by the higher cost. Finally, the Scriptel unit is similar to that made by Microtouch, but differs in that it technology and is also similar to the capacitive touch panel. e 2000 by CRC Press LLC
© 2000 by CRC Press LLC are turned on sequentially by pulsing the LEDs and thus create a full matrix of light beams without requiring each of them to be on continuously. This system does not reduce the screen transmissivity as there is no obstruction of the screen output, but it is limited in resolution to the number of LED detector pairs that can be placed on the periphery of the screen. Another approach to light interruption is to use a rotating beam of light, which has the advantage that only one light source and detector pair is required. This technology is depicted in Fig. 89.16 and consists of a LED and a light detector placed inside a rotating drum which has a slit that allows light to be transmitted outside the drum. The light is swept across the surface and strikes the retroreflectors that sends it back directly to the detector. The beam scan is sampled 256 times on each scan, and Fig. 89.16 shows how two angles of interruption are created, angle B by direct interruption, and angle C by mirror reflection interruption. The result is that the location of the interruption can be calculated by comparing the two angles. Again, there is no obstruction of the screen but a moving element must be added, and parallax errors may occur. Pen-Based Computing. This is an application for touch input devices that is growing at a rapid rate. The input device comes in several forms, each of which can recognize hand printing with the special operating system and software recognizing this type of input. The pen-based input device comes in several forms, of which the one termed TouchPen™ can function both as a digitizer with a touch tablet, and as the touch input device with a touch input pen-based computer system.A second one is that developed by Wacom, Inc., primarily for the GO Systems computer, but used by other pen-based systems as well. Finally, a third unit is that made by Scriptel Corp. and used by Wang Laboratories in its system. TouchPen™ was developed by Microtouch Systems, Inc., initially for use in GridPad made by the Grid Systems Corp. It is essentially a high-resolution digitizer consisting of an all-glass tablet that can be used with a number of stylus input operating systems to digitize handwriting. It is basically a touch input device using resistive techniques to digitize the handwriting appearing on the display surface of pen-based computer systems. The glass tablet is placed on the display surface and the system pen is used to transmit the digitized data to the computer. As noted previously, the tablet may also be used as a standard touch input device. The second form of pen-based input device is one that uses electromagnetic technology and consists of a grid of wires that transmit radio waves that are picked up by a tuned circuit in the stylus. This circuit resonates at its own frequency and transmits that signal back to the wires at the grid location it is touching. The pen also transmits its signal to the computer, which turns off the grid transmission, and locates the position of the pen by determining which of the grid wires pick up the pen signal. The pen does not need to actually touch the display surface and does not require any power, which is an advantage somewhat counteracted by the higher cost. Finally, the Scriptel unit is similar to that made by Microtouch, but differs in that it uses electrostatic technology and is also similar to the capacitive touch panel. FIGURE 89.16 Rotating infrared beam technology. (Source: A. B. Carrell and J. Carstedt, “Touch input technology,” SID Sem. Lecture Notes, p. 15.34, 1987. With permission. Courtesy Society for Information Display.)