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LIBRARY OF THE 
 
 UNIVERSITY OF ILLINOIS 
 
 AT URBANA-CHAMPAIGN 
 
 5/0. S4 
 IJKor 
 
 no. 590-5% 
 
 Cop A 
 
Digitized by the Internet Archive 
 in 2013 
 
 http://archive.org/details/beaconlightemitt591jerm 
 
y) pf/ UIUCDCS-R-73-591 
 
 r/iA^u 
 
 C00-1U69-0233 
 
 *f 
 
 BEACON : 
 
 A Light Emitting Diode Television Display 
 
 by 
 
 Martin Ming Tak Jer 
 
 September, 1973 
 
 DEPARTMENT OF COMPUTER SCIENCE 
 UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 
 
 URBANA, ILLINOIS 
 
UIUCDCS-R-73-591 C00-1U69-0233 
 
 BEACON : 
 A Light Emitting Diode Television Display 
 
 by 
 
 MARTIN MING TAK JER 
 
 September, 1973 
 
 Department of Computer Science 
 University of Illinois 
 Urbana, Illinois 6l80] 
 
 This work was supported in part by Contract No. US AEC AT ( 11-1 ) IU69 
 and was submitted in partial fulfillment of the requirements for the 
 degree of Master of Science in Electrical Engineering, at the 
 University of Illinois, Urbana, Illinois. 
 
Ill 
 
 ACKNOWLEDGMENT 
 
 The author wishes to express his gratitude to Professor W. J. Poppel- 
 baum for suggesting this thesis topic. He is also grateful to Dr. W. J. 
 Kubitz for his advice and guidance. 
 
 Furthermore, he would like to thank Frank Serio for his help in 
 building the project. 
 
 Thanks are also due to Ms. Evelyn Huxhold for typing the thesis, and 
 to Mark Goebel for the drawings, and to my wife, Ellen for typing the 
 first draft. 
 
IV 
 
 TABLE OF CONTENTS 
 
 Page 
 
 I. INTRODUCTION 1 
 
 1.1 System Description _-----_______ 2 
 
 II. REFRESH MEMORY 5 
 
 2.1 The Light Emitting Diodes (LED) 8 
 
 2.2 The Driving Circuit 11 
 
 2.3 Freeze Circuit -----_---______ li| 
 
 2.U Gray-Scale Freeze --------______ 14 
 
 III. GENERAL COMMENTS 17 
 
 REFERENCES . l8 
 
 APPENDIX 19 
 
LIST OF FIGURES 
 
 Figure Page 
 
 1. System Block Diagram -__--_______ 3 
 
 2a. Cross Talk 6 
 
 2b. Fiber Optic Cathode Ray Tube 6 
 
 3. Alternate Method for Fiber Optic CRT 7 
 
 k. Method Used in BEACON 9 
 
 5. Comparison Graph for GaP and GaAsP LED 10 
 
 6. LED Characteristics -------------12 
 
 7. Amplifying Cell 12 
 
 8. Input vs. Output of Amplifying Cell ----- 13 
 
 9. Sequential Freeze Circuit ---------- 15 
 
 10. Gray Scale Freeze -------------- 16 
 
 11. Fiber Optic Bundle Arrangement ------- 20 
 
 12. Fiber Optic Faceplate 20 
 
I. INTRODUCTION 
 
 Seventy-five years ago Ferdinand Braun invented the CRT. Since 
 
 then the tube has developed into the sophisticated, reliable, mass- 
 produced device known today. It has become a unique kind of display 
 device which is capable of presenting gray-scale, color or monochrome 
 images, graphics, and alphanumeric characters. But there are handicaps 
 that limit the performance of the tube. 
 
 A regular CRT has a limited light output. If a regular television 
 set is used outdoors, a sun visor or a special louvered film must be 
 placed on or over the faceplate of the CRT to reduce the ambient light. 
 Another limitation is the life of the electron gun. The electron gun 
 in a CRT has about 10,000 hours of operation time. When that time is 
 up, a new tube must be installed. In addition, the largest glass-walled 
 CRT manufactured today is 25 inches. Larger tubes are being built, but 
 they must use metal walls to withstand the atmospheric pressure exerted 
 on the walls. A 36-inch circular faceplate CRT, built for the Air Force 
 and used to train pilots, weighs 226 pounds. 
 
 Other methods of implementing a display panel have been sought 
 which would replace and out-perform the CRT. Display devices such as 
 the plasma panel, arrays of incandescent lamps and neon bulb matrices 
 have been studied. However, the incandescent lamp has a long buildup 
 and decay time. It takes some time for them to build up to the required 
 intensity and about twice as long for them to decay to zero. Incandes- 
 cent lamps do not respond fast enough for the 15 milli-second refresh 
 required by a standard television display. 
 
2 
 Neon bulbs required a high voltage drive. Zenith Corporation has 
 used a plasma panel to display a TV picture and proven it to be practical 
 for large screen display. 
 
 Light Emitting Diodes (LED) seem to possess the greatest potential 
 in taking over the display field. Their characteristics are like those 
 of ordinary diodes, except that there is light output which is propor- 
 tional to the forward current that passes through the diode. It is 
 rugged, light weight, and can be easily integrated and mass produced. 
 Alphanumeric LED displays are currently very popular. The price of 
 these devices has become relatively low recently. In addition, green 
 and yellow LEDs are now being manufactured. It is possible that someday 
 a full color, high intensity display panel will be constructed. At that 
 time a color television set can be hung on the wall like a picture. 
 
 1.1 System Description 
 
 The purpose of this project is to display a TV picture on a 32 x 32 
 LED display panel. Figure 1 is a block diagram of the system. 
 
 The input to the system is a TV picture obtained from a conventional 
 monochrome television set. A square area on the CRT of the television 
 set is picked out and is divided into 102*1, i.e. 32 x 32 small areas. 
 Each area is monitored by one photo transistor. The electrical signal 
 from the photo transistor is amplified and used to drive an LED. In 
 other words, the light output of the LED is an amplified version of the 
 light sensed by the photo transistor. The purpose of the television set 
 is to utilize the phosphor decay time on the CRT as a gray-scale memory 
 to keep the picture information for a full 15 milli-seconds. The system 
 is also equipped with a switch that activates a feed back loop in each 
 amplifier which enables each cell to store permanently information on an 
 on/off fashion. 
 

 
 
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The project employs only a 32 x 32 LED display array. However, it 
 is possible to extent it to a 512 x 512 cell array for a full size tele- 
 vision display. In this case four CRTs are required for control pur- 
 poses with each CRT divided into a 128 x 128 array. The 512 x 512 array 
 will be a large screen measuring ik x lU feet and having an intensity of 
 about 1500 lambert, 50 times that of a CRT. 
 
II. REFRESH MEMORY 
 
 It was originally proposed that a Fiber Optic Cathode Ray Tube 
 (FOCRT) be used for this project. The justification for using it was 
 as follows: a regular CRT faceplate is about 1/2 inch in thickness. 
 When an electron hits the phosphor layer, the light is emitted in a 
 random direction. If light sensors such as CdS are lined up side by 
 side, considerable cross-talk will occur. See Figure 2a. The reason 
 for using a Fiber Optic CRT was to have a faceplate constructed like 
 that shown in Figure 2b, such that all the light in one area is "cap- 
 tured" by the light pipe and thus cross-talk is reduced to a minimum. 
 
 A specification for a FOCRT was sent to several manufacturers and 
 is included in the Appendix. Price quotes from manufacturers were all 
 above 5,000 dollars. 
 
 Mr. Ken Cooper at Westinghouse Electric Corporation came up with an 
 interesting idea. He suggested that a regular 5" CRT be used with the 
 regular faceplate cut off, and replaced with a fiber optic faceplate. 
 Then a piece of plexiglas would be used having holes drilled in a 32 x 32 
 array. The diameter of each hole would be the same as that of the fiber 
 optic pipe. Each hole would be filled with a fiber optic light pipe as 
 shown in Figure 3- The air gap between the fiber optic faceplate and the 
 plexiglas would be filled with immersion oil, which has the closest re- 
 fractive index match to that of the optic fibers. This would allow light 
 to be transmitted with minimum loss through the faceplate to the light 
 pipe. The price of the fiber optic CRTs will certainly go down, and 
 this approach will become an economical solution for the memory required 
 by BEACON. 
 
PHOSPHOR 
 
 GLASS FIBER OPTIC 
 S* V 2 INCH CLEARENCE 
 
 V 
 
 PLASTIC FIBER OPTIC 
 
 Figure 2a. Cross Talk 
 
 32 BUNDLES EACH SIDE 
 
 Figure 2b. Fiber Optic Cathode Ray Tube 
 
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8 
 Since the price of the fiber optic CRT was high, other methods 
 of solving the problem were investigated. The most economical methods 
 was determined to be that of using a TV monitor. In a regular TV tube 
 the phosphor layer is about 1/2 inch to 1 inch away from the outside 
 world. If a regular photo sensor is used, a great deal of light from 
 adjacent areas will impinge on the sensor thus producing substantial 
 cross-talk. A method for controlling and confining the sensing effect 
 of each photo transistor to one certain area was required. The photo 
 transistor used has a plastic case molded into a semi-spherical top 
 which acts as a lens. The manufacture's specification indicates that 
 it has a capture angle of 30°. However, if a tubing is attached to 
 the top of the lens, the angle is controlled by the length of the tubing. 
 In this way, the problem of cross-talk was eliminated. See Figure k. 
 
 The television set used in BEACON has a IT inch diagonal CRT. The 
 thickness of the faceplate is measured to be 0.U7 inches. Each photo- 
 transistor monitors a circular area of 0.3 inches diameter. The total 
 monitored area of the faceplate is measured of 9.6 inches square. The 
 tube, which is used to control the apacture angle, is calculated to be 
 0.25 inches long. 
 
 2.1 The Light Emitting Diodes (LED) 
 
 Two kinds of visible LEDs are now available on the market , GaAsP 
 and GaP. Their respective emission wave lengths are plotted in Figure 5. 
 0PC0A makes the visible red GaP which is said to be more efficient than 
 the GaAsP LED. That is, at the same current level GaP gives more light 
 output than GaAsP. However, the price for GaAsP is lower than that of 
 GaAsP, so the LED used in BEACON is the GaAsP type which has a current 
 
VIEWING ANGLE 
 
 CRT 
 
 CARD EDGE MOUNT^ 
 
 Figure k. Method Used in BEACON 
 
10 
 
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 Figure 5. Comparison Graph for GaP and GaAsP LED 
 
11 
 
 vs. light output as in Figure 6. It is noted that the efficiency in- 
 creases when current increases. 
 
 2.2 The Driving Circuit 
 
 The driving circuit used here must perform several functions. It 
 must linearly amplify the signal from a photo sensor and drive an LED. 
 It must be able to compensate for the nonlinearity of the LED and the 
 photo transistor. It must have a threshold detector and be able to 
 store information permanently in an on/off fashion. And last, but not 
 the least, it must be economical. 
 
 Figure 7 shows the diver circuit used in the project. A logic 
 circuit is the control element. When the output is in the "0" state, 
 the circuit acts as an amplifier. The output versus input light inten- 
 sity is plotted in Figure 8. 
 
 Transistor T acts as a level detector. When the output of 7^05 is 
 in the "l" state it will freeze the information of the LED in an on/off 
 fashion. If the light output of the LED is above, the threshold, the 
 circuit will "freeze" it to full on; and if the light output of the LED 
 is below the threshold, the freeze mechanism will turn it off. In the 
 freeze mode each cell will be latched to on or off. However, the cell 
 is so constructed that light on the CRT screen above the threshold can 
 cause a change from the "0" state to the "l" state and cannot be re- 
 versed. To prevent this, the electron beam is turned off at the end of 
 a freeze cycle. 
 
 The voltage reference to the base of T controls the voltage thres- 
 hold. It also controls the brightness and contrast of the picture. If 
 the brightness is high, the contrast is low, and vice versa. 
 
12 
 
 Brightness Venus Forward Current (lp) 
 
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 Figure 6. LED Characteristics 
 
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 Figure T» Amplifying Cell 
 
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 2.3 Freeze Circuit 
 
 The freeze circuit is a control mechanism which changes the display 
 from gray-scale to bi-level or from bi-level to gray-scale operation. 
 The freeze operation is completed in IT milli-second, the time needed to 
 scan either the even or the odd lines of the TV picture. The freeze 
 starts on the first row, then proceeds to the second row, etc. It is 
 done synchronously with the raster lines of the TV set. The first row 
 is frozen after 8 raster lines have been completed. At the end of 32nd 
 row, it turns the electron beam of the CRT off, so that the face of the 
 CRT is completely dark. 
 
 The horizontal and vertical synchronization pulses are taken out 
 from the TV monitor and are shaped for digital application. A serial- 
 in, parallel-out shift register is used for the sequential freeze. It 
 shifts a "0" for a linear display and a "l" for a bi-level display. See 
 Figure 9- 
 
 2.U Gray-Scale Freeze 
 
 Another circuit which has the same function as the circuit above 
 in the display mode but is different in the freeze mode is shown in 
 the diagram in Figure 10. It can freeze the information in a gray- 
 scale. The circuit employs a sample and holds concept with an extra 
 long hold time. The capacitor is able to hold the information within 
 5 percent for 3 minutes and decreases to 25 percent in about 7 minutes, 
 
15 
 
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 III. GENERAL COMMENTS 
 
 The LED display panel of Beacon is a square 7»25 inches on a side. 
 Each element is 0.192 inches in diameter. The average current which 
 saturates the cell in the gray scale display mode is about 16-18 milli- 
 amperes. The ultimate maximum of 20 milliampere is not attained be- 
 cause of the non-uniformity of the transistors, phototransistors and 
 LEDs. An adjustable feedback resistor is used to compensate for these 
 non-uniformities as much as possible. However, in the bi-level display, 
 all of the active LEDs have 20 milliampere of current flowing through 
 them. Converting the above measurements to light quantities, the fol- 
 lowing numbers are obtained. In the gray-scale mode, the highest inten- 
 sity is 9 ft-lambert /element . The contrast ratio is 1+0:1. 
 
 A 32 line display is only a small fraction of a 525 line display. 
 It is the equivalent of looking at a one-inch square on a lU-inch diag- 
 onal TV picture tube. The resolution is poor. An object is distin- 
 guishable only with high contrast and/or with a simple geometrical out- 
 line. Any complicated configuration is not easily recognizable. 
 
 The linear display mode of BEACON produces a fine picture. The 
 freeze mechanism adds another dimension to the display. The red color 
 is quite acceptable to the viewer. If a larger matrix array is built, 
 it will certainly be an excellent display device. 
 
18 
 
 REFERENCES 
 
 1. Ahrons , R. W. , "Gallium Phosphide Diodes Offer Brighter Lamps and 
 
 Displays," Computer Design, January, 19T1« 
 
 2. Ahrons, R. W. , "In Strobed LED Displays, How Bright is Bright?" 
 
 Electronics, November 22, 1971, p. 78. 
 
 3. Fletcher, D. , "The Photometry of LED's, A Primer in Photometry," 
 
 Application Note, Monsanto Company. 
 
 h. Forman, J., "Gas Discharge Display as an Alternate to CRTs," 
 Computer Design, April 1973, p. 77 • 
 
 5. Jer, M. , "Quarterly Technical Progress Reports," Department of 
 
 Computer Science, University of Illinois, starting January 
 1972 to March 1973. 
 
 6. Luxenberg, H. R. and Kuehn, R. L. , Display System Engineering , 
 
 McGraw-Hill, 1968. 
 
 7. Nettle, V., Jr., and Gregory, R. , "A Scanned Light Emitting Diode 
 
 Display," Proceedings of the Society of Information Display, 
 Vol. 13 A, Fourth Quarter, 1973, p. 183. 
 
19 
 
 APPENDIX 
 
 Specifications for a Special Fiber Optic Faceplate CRT 
 
 June 12, 1972 
 
 1.0 General Description 
 
 A special fiber optic faceplate CRT is needed for a current research 
 project. The CRT is used to display television pictures, with its electri- 
 cal properties no different from those of standard TV cathode ray tubes. 
 A fiber optic faceplate is used in place of the regular glass faceplate. 
 The faceplate consists of fiber bundles arranged in a square matrix of 
 32 x 32 bundles. Each fiber should extend far enough from the faceplate 
 so that a plastic fiber optic light pipe can be coupled to it optically 
 and mechanically. 
 
 2.0 Faceplate 
 
 2.1 Fiber Optic Arrangement 
 
 The bundles are to be arranged in a square matrix with thirty-two 
 bundles on each side. Each bundle should have 1/2" clearance from the 
 faceplate so that a plastic fiber optic lightpipe can be coupled to it. 
 See Figure 11. 
 
 2.2 Size of the Faceplate 
 
 The useful area of the fiber optics faceplate should be no more than 
 3-5 inches on each side of the square array. See Figure 12. 
 
 3.0 Phosphor 
 
 3.1 P3 which decay to 10$ in 30m sec. 
 
20 
 
 SENSOR 
 
 SENSOR 2 
 
 LIGHT EMITTING PHOSPHOR 
 
 ELECTRON BEAM 
 
 Figure 11. Fiber Optic Bundle Arrangement 
 
 G Us s 
 
 LIGHT EMITTING PHOSPHOR 
 
 GLASS FIBER 2 
 
 FIBER 
 
 FACEPLATE 
 
 CRT 
 
 Figure 12. Fiber Optic Faceplate 
 
21 
 
 3.2 Brightness 
 
 approximately 100 foot-lambert . 
 
 3.3 Resolution 525 lines per 3-5 inches. 
 
 U.O Electronics 
 
 k.l Deflection 
 
 Either electrostatic or magnetic. 
 
 k.2 Scan 
 
 Each row of bundles is scanned by approximately l6 television raster 
 lines. 
 
 5.0 Quotation 
 
 All quotations should include the specifications of the CRT being 
 bid. 
 
 Please contact the person below for further information concerning 
 
 specifications : 
 
 Martin Jer 
 
 203 Digital Computer Lab 
 
 University of Illinois 
 
 Urbana, Illinois 6l801 
 
 217-333-0658 
 
FormAEC-427 U.S. ATOMIC ENERGY COMMISSION 
 
 ]2® UNIVERSITY-TYPE CONTRACTOR'S RECOMMENDATION FOR 
 
 DISPOSITION OF SCIENTIF.C AND TECHNICAL DOCUMENT 
 
 ( See Instructions on Reverse Side ) 
 
 1. AEC REPORT NO. 
 
 COO-li+69-0233 
 
 2. TITLE 
 
 BEACON: A Light Emitting Diode Television Display 
 
 3. TYPE OF DOCUMENT (Check one): 
 
 PE| a. Scientific and technical report 
 
 [~| b. Conference paper not to be published in a journal: 
 
 Title of conference 
 
 Date of conference 
 
 Exact location of conference _ 
 
 Sponsoring organization 
 
 [] c. Other (Specify) 
 
 4. RECOMMENDED ANNOUNCEMENT AND DISTRIBUTION (Check one): 
 
 Ha a. AEC's normal announcement and distribution procedures may be followed. 
 ~\ b. Make available only within AEC and to AEC contractors and other U.S. Government agencies and their contractors. 
 ] c. Make no announcement or distribution. 
 
 5. REASON FOR RECOMMENDED RESTRICTIONS: 
 
 6. SUBMITTED BY: NAME AND POSITION (Please print or type) 
 
 W. J. Poppelbaum 
 
 Professor and Principal Investigator 
 
 Organization 
 
 Department of Computer Science 
 University of Illinois 
 Urbana, Illinois 6l801 
 
 Signature 
 
 Date 
 
 September, 1973 
 
 FOR AEC USE ONLY 
 
 7. AEC CONTRACT ADMINISTRATOR'S COMMENTS, IF ANY, ON ABOVE ANNOUNCEMENT AND DISTRIBUTION 
 RECOMMENDATION: 
 
 8. PATENT CLEARANCE: 
 
 LJ a. AEC patent clearance has been granted by responsible AEC patent group. 
 I I b. Report has been sent to responsible AEC patent group for clearance. 
 I I c. Patent clearance not required. 
 

 
 
 
 
 
 JIBLIOGRAPHIC DATA 
 iHEET 
 
 1. Report No. 
 
 UIUCDCS-R-73-591 
 
 2. 
 
 3. Recipient's Accession No. 
 
 . Tide and Subtitle 
 
 BEACON: A Light Emitting Diode Television Display 
 
 5. Report Date- 
 September, 1973 
 
 6. 
 
 . Author(s) 
 
 Martin Ming Tak Jer 
 
 8. Performing Organization Rept. 
 No. 
 
 . Performing Organization Name and Address 
 
 Department of Computer Science 
 
 University of Illinois at Urbana-Champaign 
 
 Urbana, Illinois 6l801 
 
 10. Pro)ect/Task/Wotk Unit No. 
 
 11. Contract /Grant No. 
 
 2. Sponsoring Organization Name and Address 
 
 US AEC Chicago Operations Office 
 9800 South Cass Avenue 
 Argonne , Illinois 60^39 
 
 13. Type of Report & Period 
 Covered 
 
 14. 
 
 5. Supplementary Notes 
 
 6. Abstracts 
 
 The CRT tube was invented seventy-five years ago. Since then the tube has 
 developed into the sophisticated, reliable, mass-produced device known today. 
 It has become a unique kind of display device which is capable of presenting 
 gray-scale, color or monochrome images, graphics, and alphanumeric characters. 
 But there are handicaps that limit the performance of the tube. 
 
 7. Key Words and Document Analysis. 17a. Descriptors 
 
 Beam Control 
 
 i 
 
 i 
 
 1 
 
 i 
 
 7b. Identifiers/Open-Ended Terms 
 7c. COSATI Field/Group 
 
 8. Availability Statement 
 
 19. Security Class (This 
 Report) 
 
 UNCLASSIFIED 
 
 21- No. .-if Pages 
 
 1 
 
 
 
 
 20. Security Class (This 
 Page 
 
 UNCLASSIFIED 
 
 22. Price 
 
 i 
 
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