A Simplified Linear Refreshable Braille Displayby Christopher W. Tullar

A Thesis Submitted to the Graduate Faculty of APPALACHIAN STATE UNIVERSITY in Partial Fulfillment of the Requirements for the degree of MASTER OF SCIENCE in Applied Physics December, 2001

A Simplified Linear Refreshable Braille DisplayA Thesis by Christopher W. Tullar December, 2001

Approved By: __________________________________________ Thomas L. Rokoske, Ph.D. Chairperson, Thesis Committee __________________________________________ J. Sid Clements, Ph.D. Member, Thesis Committee __________________________________________ Brian W. Raichle, Ph.D. Member, Thesis Committee __________________________________________ Anthony G. Calamai, Ph.D. Chairperson, Department of Physics and Astronomy __________________________________________ Judith E. Domer, Ph.D. Dean of Graduate Studies and Research

Copyright by Christopher W. Tullar, 2001 All Rights Reserved

A Simplified Linear Refreshable Braille Display Christopher W. Tullar Abstract A linear braille display has been developed which is simple in design so that it may be of low cost. The display is activated by movement of the hand and automated by the use of an 8051 microcontroller. The braille display uses a 40-cell line composed of standard-sized braille cells on a magnetic display actuated by three solenoids, a unique design developed at ASU. These cells are the same size as used in braille books, so they are easy to read. Text to be read is first converted to an ASCII document, and then downloaded to the braille display for reading. The instrument uses sound to guide the user through the process of reading and is designed to be simple to use.

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Acknowledgments I would like to thank my thesis advisor, Dr. Tom Rokoske, for starting the refreshable braille display projects at ASU, giving me something neat to do for a year, and for his willingness to help on every occasion I asked for it. Mr. Robert Miller deserves a great deal of thanks for his constant help in the mechanical design process, his excellent machining skills, and his dedication to make room for my schedule. I would also like to thank Dr. Sid Clements, who helped at troubleshooting software, gave ideas for electronic hardware, and let me all but live in his computer lab. I wish to thank Graduate Studies and Research at ASU for the grant that partially funded my project. Thanks to Guardian Electric, who donated the solenoids used in this project. Thanks also to Mr. Josh Hastings who seems to always save the day. Thanks to Mr. Mike Abaray who did some footwork and sent me a huge history on braille displays. And I would finally like to thank my wife Raeleen, who helped me with the thought process, helped build the testing apparatus, and who is my personal presentation wizard.

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Table of Contents Page List of Figures....viii Chapter 1: Introduction. 1 1.1 Braille... 1 1.2 Grades of Braille... 1 1.3 Ways to Reproduce Braille... 3 1.4 Refreshable Braille Displays.3 1.5 Previous ASU Braille Displays.5 1.6 The Proposed Machine. 7 Chapter 2: Mechanical Hardware. 12 2.1 Pinboard 12 2.2 Solenoids...13 2.3 Solenoid Carriage..14 2.4 Solenoid Carriage Mounting.16 2.5 Mounting Plate and Rails..17 2.6 Optcouplers and Encoder Strips18 2.7 Shuttle... 19 2.8 Eraser 20 Chapter 3: Electronic Hardware21 3.1 SBC-51..21

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3.2 Optocouplers. 22 3.3 Solenoid Signals... 22 3.4 Shuttle Switches....23 3.5 Speaker..23 3.6 Handshaking. 23 Chapter 4: Software.. 24 4.1 Getting Started...24 4.2 Overall System Objective. 24 4.3 External Buffer.. 25 4.4 Internal Buffer...25 4.5 External Interrupts 28 4.6 Polling Interrupts.. 30 4.7 Sound 30 4.8 Monitor Display 31 4.9 Testing...32 Chapter 5: Discussion... 34 5.1 Review of Accomplishments 34 5.2 Problems... 36 5.3 Possible Future Endeavors36 References..38

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Appendix A: Mechanical and Electronic Schematics...39 Appendix B: System Software..50 Vita..66 List of Figures 1-1 Refreshable Braille Displays.. 4 1-2 Xiong Lus Rotating-disk Display..5 1-3 Bruce Stansells Rotating-disk Display .6 2-1 Pinboard Cross-section...13 2-2 Conceptual Drawing of the Solenoid Carriage...15 2-3 Close-up of the Solenoid Carriage..16 2-4 View From Below the Mounting Plate...17 2-5 Conceptual Drawing of the Solenoid Carriage, Mounting Plate, and the Teflon Sliders.. 18 2-6 Optocouplers and Encoder Strips... 18 2-7 Shuttle and Eraser Mechanism... 20 3-1 System Electronics..21 4-1 Braille Cell Encoding Byte Translation..27 4-2 Filling the Internal Buffer28 4-3 Cell Direction/Counting Method 29 4-4 Apparatus for Testing Software..33

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5-1 The Finished Refreshable Braille Display. 34 A-1 SBC-51 Circuit Diagram... 40 A-2 Circuit Diagram for Optocouplers. 43 A-3 Output Control Circuitry... 44 A-4 Circuit/wiring Diagram for Shuttle Switches 45 A-5 Placement of Interior Components 46 A-6 Specifications for Solenoid Carriage Parts 47 A-7 Specifications for the Adjustable Mounting.. 48 A-8 Specifications for the Mounting Plate... 49

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Chapter 1: Introduction 1.1 Braille Perhaps the most significant invention bestowed upon the blind has been braille. This international system of reading for the blind has endured for over 175 years without significant rivalry from any other form of written communication. Braille is found at automatic teller machines, elevators, hospitals, on public signs and menus, and many other, often unnoticed, places. Before the advent of braille, the blind read ordinary letters in relief. This method was cumbersome and difficult to read quickly. However, around 1824 in Paris, France, a fifteen-year-old boy by the name of Louis Braille completed a full sixty-three-character code that used cells made of six easily producible dots. He was directly influenced by a new code shown to him by a French artillery captain Charles Barbier. The captain had developed what he called night writing for messages delivered in the dark within the army. He almost immediately tried to make it accessible to the blind under the name of sonography and in doing so met Louis Braille, who developed the idea into what is todays most common reading method for the blind.1 1.2 Grades of Braille Despite the ease of creating braille cells with the proper tools, it soon became apparent that transliterating every letter (English or otherwise) into braille was going to be a problematic practice. The characters could not be the same size as written text because of the resolutional capability of the average human fingers. So they were made

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larger and their size became standardized for the most part (the Japanese have slightly smaller characters).2 This meant that a page of braille was immensely larger than a page of standard written text. Also, braille could only be written on one side of a page because the dots were punched from the reverse side. So, to contain the same information, a braille page would have to be four times as long and three times as wide as a printed page. Naturally, a page that size would be hard to handle, very tedious to transcribe, slow to read, and would make impractical book sizes. As a result, many braille contractions were created. Groups of two or more letters, as well as many words, were assigned their own characters, or groups of characters. Every contraction had to be methodically chosen to ensure it would be efficient to read. This new contracted braille was dubbed Grade II braille and is the type most widely used today. Thus, the uncontracted form of braille became Grade I.3 Some criticize Grade II of being arcane and difficult to use. There are many nested rules regarding when contractions should be used and several common symbols are not represented. Early on, many of the contractions were created in direct relation to Christianity, because a main focus was enabling the blind to read the bible, and many today feel that too many contractions were used for this practice. There are many other codes in existence and people are constantly working on new ones. Most of the current projects involve eight-dot cells and include characters to enable the blind to read mathematical and other non-Latin symbols. It should be noted that even with contracted braille, a book that could fit in a pocket in printed text form would be several large volumes in Grade II braille. Nevertheless, Grade II documents are considerably smaller than uncontracted braille documents.

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1.3 Ways to produce/reproduce Braille Braille can be produced in several ways. The simplest form is with a slate and stylus. In this method, the braille is manually embossed into paper with a stylus. Using guide depressions, the stylus presses the paper into depressions on the slate. Unfortunately, this method requires writing backwards because the braille is embossed from the under-side. Similarly, a braille typewriter embosses a page mechanically. A more modern and rapid way to produce braille is with a braille printer. In this case a computer sends the printer information and the printer embosses the braille on a page. This is usually done with a lot of pressure, sometimes up to ten tons per braille cell!4 Many braille printers, called interpoint printers, can emboss braille on both sides of a page by adjusting spacing on each side. The main disadvantage to braille printers is that they are very noisy. They routinely produce noise at levels of 70dba or more.4 Many models on the market today have sound-attenuating hoods to reduce noise. Finally, there is the refreshable braille display, which is a device that produces braille electronically by raising and lowering pins which correspond to cell dots. Since this is the main concern of this thesis, it will be discussed in detail. 1.4 Refreshable Braille Displays Refreshable Braille displays were first introduced in the mid-1970s and were electromechanical displays that used tiny solenoids to move the pins. By the late 1970s, piezoelectric displays, first introduced by Oleg Tretiakoff, were on the market. The piezoelectric cell consists of a small ceramic substrate which, when around 200 volts is applied, bends and activates a pin. These actuators are small, which is preferred, but they are expensive. The first mass produced display, the VersaBraille, was based on his

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design and manufactured by TeleSensory in the early 1980s, and by the end of the 1980s everything on the market was piezoelectric.5

Figure 1-1: Refreshable Braille Displays 20, 40, and 80 Cell Models6 Manufacturers of refreshable braille displays have been motivated all along to find a cheaper alternative to piezoelectric technology. One idea was a moving braille cell, tried by IBM, which slid along a track and merely punched braille into the finger. This was deemed unacceptable because the movement of the finger over the braille is important. In another prototype, dots were pressed into a moving belt of Mylar and then pressed flat again after being read. This was tried more than once by separate companies, but was rejected because the Mylar wore out too quickly, was noisy, and felt unnatural. The pneumatic display was also a promising technology which was abandoned. One attempt at cost efficiency called the BrailleMate (TeleSensory) eliminated all but one cell.5 In the early 1990s, more experimental methods were being tried, mainly fluids technology and with materials which change their integrity when a voltage is applied. And then there are the rotating display ideas. In this technique, the fingers remain stationary and the braille, constantly being refreshed, moves underneath. Only three prototypes were accounted for in the research for this paper. Two rotating disk displays

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were created at Appalachian State University which will be discussed in detail. A prototype built at NIST (National Institute of Standards and Technology) in Gaithersburg, Maryland, uses a rotating drum with the braille cells on the perimeter of the drum. This machine uses stationary solenoids to punch specially designed pins into one of two states, up or down.7 Of the braille displays that exist on the market, the most important and competitive features are those that involve navigation through a screen of text. Some of the newer models use two-dimensional navigational control, where horizontal and vertical screen positions can be changed. Other competitive features include compatibility with Windows environments and speech synthesis. Speech software, though not replacing the reading of braille, is becoming a standard in technology for the blind. In the refreshable braille display, however, speech synthesis is usually confined to simple messages giving information about text attributes or graphics located at the cursor position. 8 1.5 Previous ASU Braille displays

Figure 1-2: Xiong Lus Rotating-Disk Braille Display (1993)

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Xiong Lus prototype was built at Appalachian State University and completed in 1993. This showed that a display was feasible in which the actuators remain stationary and the pins move above them by means of a rotating disk. This display has only two refreshable cells which are larger than standard braille cell size, and its operation is relatively slow. The cells are held in place by means of a spring mechanism. One optocoupler sensor informs the computer that the six solenoids are in line with the pins and a character was formed on the display. This machine is an external apparatus driven by an IBM PC.9

Figure 1-3: Bruce Stansells Rotating-Disk Display (1997) Bruce Stansells prototype was completed in 1997. The machines display consists of 36 braille cells lining the perimeter of a rotating disk. The pins, which correspond to the individual dots, are held by magnetic attraction in a rotating disk. Holes were drilled through a piece of flexible magnetic material sandwiched between two pieces of plastic. The pins were inserted into the holes and were kept from falling by means of being attracted to the wall of the hole. This is by no means a bistable mechanism, which would be ideal, but greatly simplified the machining of the pin and

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proved to be effective. This method had two drawbacks however, both related to the instability of the material. First, the flexible material is difficult to machine, making the holes very tedious to drill and leaving the end result less than accurate. Second, it absorbs moisture and swells. When the machine was examined three years after its completion, nearly all of the pins had to be worked into moving condition again. In Bruce Stansells prototype, six optocoupler sensors determine when one of the six solenoids is in line with a pin. Text is translated on the PC by ASCII-to-Grade II software available through the American Federation of the Blind. The encoded dot file is then transmitted to the braille display. The user can scroll 50 or 150 cells at a time, and there are also the options of scrolling by word or sentence. The display can insert bookmarks to save the readers place in the file. This prototype includes a keypad interface, LCD display, both serial and parallel ports for PC interface, and adjustable disk speed control. Software is contained both on-board the display and on the IBM PC. Maximum reading rate is one hundred fifty cells per minute, or, using an average word length of five characters, around 30 words per minute.10 1.6 The Proposed Machine As sophisticated technology makes braille easier to produce, the blind are faced with the unavoidable problem of high cost. Currently braille printers cost from $1,700 to $80,000 and refreshable braille displays cost from $3,500 to $15,000 (usually around $5,000 per 40 cells).11 Unfortunately, most visually impaired people cant afford these prices and the available machines are limited mainly to business and educational uses. The current project and many others are dedicated to making affordable braille displays using innovative technology.

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The goal for this thesis was to create a greatly simplified in-line refreshable braille display which is reliable and easy to use, using the fewest, most cost-efficient parts. The following are the desired features for the proposed display: Standard Cell Size Due to the size limitations of the actuators used in most braille displays, the cells are larger than standard size. Since the blind prefer to read standard cell size and spacing, this machine should ideally have these characteristics. This has been shown possible by Stansells prototype. Dependable Pinboard An innovative concept in Stansells display was to use a magnetic material to hold the braille pins in place. Holes were drilled through a flat vinyl magnet and the pins were inserted through the holes.10 Unfortunately, the material which was chosen was rather unstable and subsequently became brittle and left residue on the pins. When the machine was examined after several years of not being used, it was found that many braille pins were locked fast and required considerable pressure to free them. It should also be noted that machining the holes was difficult and at the end of the project no suitable lubrication had been found to improve the stability of the pinboard. So without question this method of holding the pins must be improved to ensure reliability of the display. Shuttle An innovative technique to be implemented during the present research is the use of a shuttle which will move the solenoid carriage underneath the braille pins with the movement of the hand. The shuttle is to be similar in size and function to a computer

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mouse, and its linear position will be slightly offset from the solenoid carriage so that each cell will be formed in advance of the hand's position. There are several benefits to the use of a shuttle. Besides reducing cost, noise (mechanical and electrical), and software, it would also ease navigation and spacial orientation within a document. This could be done by adding several buttons to the shuttle, similar to those on a mouse. Two buttons will be used for scrolling back and forth through the document, and in a more advanced version, a third button could be added to act as a left mouse click, for example. This feature would eliminate the need for touch dots which are sensors situated above each braille cell in many commercially available models to position the cursor. If the proposed braille display system is to be thought of in analogy with a dot matrix printer, with solenoids making up the print head, several disadvantages come into view. In order to provide a maximum reading rate of 100 - 200 words per minute, a fast motor would be needed to ensure that the user would not have to wait to read a line. This would require more software, more hardware, and therefore more complexity and cost. It would be desirable for the reader to control the reading speed. Three actuators There will be a carriage on which the solenoids travel beneath the pins. The solenoids will strike the pins at designated times determined by the exact position of the solenoid carriage. However, horizontal travel only requires three actuators, as there are three rows of dots. So the solenoid carriage need only house three solenoids. Compared to commercial displays, this saves 237 parts! Compared to Stansells prototype, this eliminates the need for three solenoids at a total saving of $60.00.

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Speed Average braille reading rates are under 100 words per minute in Grade II braille, and most common rates are from 50 - 70 words per minute. However, some can read over 300 words per minute, which if read aloud would be very fast speech.12 Since an ASCII to Grade I translator will be used, producing one hundred words (around 500 characters) per minute would be a conservative upper limit. Grade I is approximately 20% longer than Grade II, so it would take 20% longer to read.13 The maximum speed of this machine in Grade I is expected to be at least one hundred fifty words per minute. A software governor will be added to protect the hardware in the event that the maximum speed is exceeded. On-board translator The device will have an on-board translator which will translate ASCII into Grade I braille. This feature will maintain the machines independence and make the system easier to operate. In text-editing modes, many braille displays switch from Grade II to the Nemeth Code, which is a character-to-character translation of ASCII to braille. This is used so the user can read each character on the screen when editing text. However, this is not comfortable to read. Translating ASCII to Grade I avoids the contractions and exceptions of Grade II, but comes with its own set of exceptions, which will have to be taken into consideration. These will be discussed in further detail in the software implementation. Admittedly, Grade I is also not completely comfortable to read, but will be used for this prototype due to the massive amount of software required for a Grade II translation and small amount of available code memory.

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Ease of use Finally, the machine should be as easy to use as possible. It should connect to a

PC and start up without need for a technical tutorial. Whenever possible, messages such as too fast, buffer full, etc. will be conveyed by a sound. It should require as little setup on the PC as possible. There should be one simple connection to the serial port of the computer and when the power is turned on the braille display will await information from the PC.

Chapter 2: Mechanical Hardware The mechanical hardware was built from the pinboard outward so each part could be built referencing the previous part, the most important reference being the fixed location of the pins. When possible, lightweight materials such as aluminum and PVC were used. This is especially important for the moving carriage assembly which should be as lightweight as possible to reduce friction, and therefore minimize fatigue to the reader. 2.1 Pinboard Improving the stability of the pinboard was a major goal of this project. The pinboard is the mechanism which holds the braille pins in place. Several non-magnetic methods were attempted, but the final solution involved ceramic magnets. Holes of .0625 inch diameter were drilled through two thin plates of low carbon steel, chosen for its ferromagnetic properties, and the pins were fitted through the two layers. The pins were turned from steel welding wire, which also has optimal ferromagnetic properties. Ceramic magnets were placed between the two layers, on either side of the pins. Since the ceramic magnets have higher magnetic strength than the flexible magnetic material, their close proximity to the pins is enough to pull the pins to the sides of their holes and hold them in place. The magnets are kept from touching the pins by means of recessed shoulders which were milled into the top steel layer (shown in Figure 2-1). Before the final pinboard was assembled, the steel plates were treated chemically to prevent potential rust damage. The final pinboard of 40 braille cells contains 240 pins and is highly stable.

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Figure 2-1: Pinboard Cross-section. The ceramic magnets (dark areas) are sandwiched between the two layers of low-carbon steel, and the pins fit through the center. 2.2 Solenoids Solenoids were chosen for the highest impulse and speed. It was calculated that a maximum reading rate of 200 words per minute, which is in excess of the original goal, would allow a maximum total stroke time of around 24 ms. The solenoids were therefore tested using a 10 ms pulse, assuming that the downward stroke of the plunger would take longer than the upward stroke. In addition, a translational mechanism would be needed to raise the pins, which are separated by only 0.10 inch, while the centers of the solenoids are 0.50 inch apart. The energy absorbed from the solenoid stroke by the translational mechanism had to be taken into consideration when choosing the proper solenoid. The Guardian T-3.5X9 DC 24V solenoid was chosen for high speed, strength, and small dimensions. Modifications were made to prevent the plunger from sticking to the solenoid cavity at the top of its stroke and to keep it from dropping from the solenoid at the bottom of its stroke. Small aluminum collars were machined and fitted to the bottoms of the plungers to prevent the plunger cone from striking the interior of the solenoid. A small plastic plate was used to position the bottom of the solenoid stroke (see Figure 2-4).

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The strength of the solenoid depends partially on the distance of its stroke, so the plate was positioned to maximize strength. 2.3 Solenoid Carriage The solenoid carriage is responsible for holding the solenoids in place and translating the centers of the solenoid strokes to the centers of the pins. The mechanical drawings for the solenoid carriage parts are shown in the Appendix as Figures A-5 (page 46) and A-6 (page 47). The problem with translating this force is overcoming the lateral torque that will be created about the centers of the solenoids. Merely bending a plunger tip will not solve the problem because the plungers are free to rotate about their longitudinal axis. Thus, hitting the pins would be very unlikely. Stabilizing the bent plunger tip would create unwanted friction. The translational mechanism is shown in Figure 2-2. It uses two paddles that are free to rotate about an axis that is 1.5 inches from the centers of the plunger tips. The tips of the outer solenoid plungers are hinged to the outer edges of the paddles with small pins, so that the plunger and the paddle will function as a unit. A plunger pushes the outer edge of a paddle and forces it to rotate upward until the inner edge of the paddle, equipped with a small striking pin, contacts the cell pin. In this way the torque is absorbed by the rigid aluminum paddles axis, and the energy of the stroke is minimally affected. The horizontal component of the rotation of the paddle, which is a few thousands of an inch, is negligible.

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Figure 2-2: Conceptual Drawing of the Solenoid Carriage. The threaded bushings, which hold the solenoids into the carriage base plate, are not shown. The solenoid plunger tips are hinged at the outer edges of the paddles, while the middle plunger tip is extended. The middle plunger, being lined up with the center pin already, was merely lengthened to reach the pin. All striking pins are chamfered to allow the striking pins to be forced back down in the event of a collision with a cell pin. Without the chamfer, the entire carriage would lock in position due to one collision. The plungers are also fitted with small springs (see Figure 2-3) which apply a constant downward pressure. These springs greatly increase the speed of the downward stroke as well as reduce bouncing of the plungers off the plastic stop plate. The solenoids are threaded into brass bushings that fit into 0.5 inch diameter holes in the base plate of the solenoid carriage. The bushings are held in place with setscrews so the solenoid position may be adjusted. The height of the pins is ultimately controlled by vertically adjusting the solenoids.

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Figure 2-3: Close-up of the Solenoid Carriage. The restraining springs lie just below the paddles. 2.4 Solenoid Carriage Mounting The solenoid carriage is fixed by means of an adjustable mounting to a plate which slides on a pair of parallel rails as the user slides the shuttle. To allow for vertical adjustment of the carriage, the mounting was made in two pieces that are dovetailed together to minimize movement in other directions (shown in Figures A-7 and A-8). The mounting is adjusted vertically by turning two screws whose ends rotate freely in the bottom surface of the upper part of the mounting. The screws are threaded through the mounting plate and are thus able to pull or push the upper portion of the mounting. When the desired vertical position is achieved, a set screw, which is threaded through the back of the lower piece, pushes the dovetailed pieces in opposite directions, thereby locking them in place. These adjustment screws are shown in Figure 2-4. The carriage mounting is also laterally adjustable. A key on the lower part of the mounting fits into a slot in the mounting plate. The whole fixture may be moved in the slot by means of another adjusting screw. Two screws fasten the mounting to the

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mounting plate in the desired lateral position from underneath. The carriage adjustments serve to more precisely place it in alignment with the pins.

Figure 2-4: View from Below the Mounting Plate. Shown above is the plastic stop plate. In the middle are the adjusting screws for the adjustable mounting. To the right is one of the Teflon sliders and at the left are the aluminum encoder strips and optocoupler circuit. 2.5 Mounting Plate and Rails The aluminum mounting plate supports the solenoid carriage rigidly in place with respect to the rails. It is attached directly to Teflon sliders which move along the rails. The plate was designed so the shuttle would push it approximately from the center of mass of the solenoid carriage assembly, thereby reducing torque and friction on the sliders.

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Figure 2-5: Conceptual Drawing of the Solenoid Carriage, the Mounting Plate, and the Teflon Sliders 2.6 Optocouplers and Encoder Strips Optical sensors are used to locate the position of the shuttle. Two are used, one for each of the two vertical columns of dots in a braille cell. The U-shaped optocouplers straddle aluminum encoder strips which run the length of the encasing and have slits corresponding to cell locations. This arrangement is shown in Figure 2-6.

Figure 2-6: Optocouplers and Encoder Strips. Seen above the mounting plate is the horizontal adjustment screw for the adjustable mounting. At left are the wires that power the shuttle switches. The sensors are mounted to the underside of the mounting plate and the strips are attached at the ends to the case, so the optocouplers move and the strips remain

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stationary. The strips may be adjusted to align properly with the cell placement. The offset distance between slits is also adjustable using screws that set the strips in place. 2.7 Shuttle The shuttle consists of a shell made from Sculpey, a modeling material that sets when baked, and an aluminum frame which is equipped with the two shuttle switches. The shell was made by making a sculpture of the desired shuttle shape with modeling clay that was 0.25 inch smaller on every surface than the predetermined shuttle dimensions. Then a 0.25 inch sheet of Sculpey was laid over the clay model and worked into shape. Next, the model was baked, hardening the outer layer so the clay could be removed from the inside. Once fully hardened, the inside of the shell was reinforced with epoxy. The shell encloses a small aluminum frame which holds the switches and mounts the shuttle to the shuttle plate. The switch buttons are elongated with aluminum extension rods to reach the outer surface of the shuttle. On the inner surface of the shuttle there is a plate to which the erasing mechanism is fastened. The entire shuttle assembly,

complete with erasing mechanism, is screwed through a spacer to the carriage mounting plate below. The finished shuttle and eraser assembly is shown in Figure 2-7.

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Figure 2-7: Shuttle and Eraser Mechanism 2.8 Eraser The erasing mechanism must move the raised pins back to their recessed position. There are two options to do this: push or pull. Pulling requires a strong electromagnet, which requires an inefficient consumption of current and would create unwanted electrical noise. To push the pins down, an arm which is fixed to a plate on the shuttle reaches to the top of the pinboard and applies downward pressure. To reduce the bulk of the materials required to achieve this operation, a two-inch-long cylindrical Alnico magnet was chosen to provide the necessary downward force to erase the cells. The magnet is held in place by a cradle made from PVC. This cradle is attached to the shuttle and moves along with the readers hand.

Chapter 3: Electronic Hardware The electronics include the single-board computer, output-control circuitry, and the shuttle switches and optocouplers. An 8032 microcontoller controls the entire machine. All electronics were made as compact and discrete as possible with removable wiring connections for easy servicing. A modular 5V, 24V DC power supply supplies the voltage for both the electronic circuits and the solenoids. 3.1 SBC-51 The URDA SBC-51 single-board computer was chosen for ease in development of the system. The circuit diagram is shown in Figure A-1. It has a serial port, parallel port, and 16KB of user external memory. It also has three jacks that allow access to the 8155 pins (parallel interface chip) and to the available 8032 port pins. The Timec 12MHz 8032 microcontroller was chosen because it has a third timer, which was used for the polling interrupt.

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Figure 3-1: System Electronics

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3.2 Optocouplers The position of a dot column in a cell is sensed by one of two optocoupler circuits attached to the solenoid carriage. When an optocoupler passes over a slit in the encoder strip, light can pass through the slit, thereby exciting a photo-detector which produces an analog voltage proportional to the amount of light received. The circuitry necessary to power the optocouplers was soldered to a circuit board and attached to the carriage mounting plate. The LED emitter of the circuit, shown in Figure A-2, uses a 470 current-limiting resistor and the detector uses a 1.5 k load resistor. When no light is detected by the optocoupler, the detector voltage goes low. This signal controls a one-shot (74LS123, 74LS122) which produces a 10 ms high pulse on the 8032s corresponding external interrupt line. The one-shot, or monostable multivibrator, is a circuit which uses an RC circuit to produce an output pulse of a desired duration. Here a 33 k resistor and 1 F capacitor are used as shown in Figure A-3. 3.3 Solenoid Signals When the optocoupler-initiated interrupt has been processed, the braille output for that cell column is sent out to the 8155 parallel port. Each of these three lines is sent to a one-shot which outputs a 10 ms pulse (if the input signal was high) to enable a 754410 driver chip, as shown in Figure A-3 (page 44). This chip is triggered by a 5V pulse and outputs a 24V pulse directly to each solenoid. If two highs were sent in succession to this circuit, there would only be one 10 ms output from the monostable multivibrator because it must be first reset with a low. This problem is solved in software by pulsing each output line low before data transfer, thereby resetting the one-shots.

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3.4 Shuttle Switches The shuttle switches require debouncing so they may be accurately monitored by the microcontroller. The simple nand gate latch is shown in Figure A-4 (page 45). As with the rest of the electronic hardware, the circuitry is localized, so the shuttle requires power, ground, and signal wires. 3.5 Speaker System sound is sent directly from port 1 on the 8032 through a 7404 inverter gate (see Figure A-3) because the inverter has more drive-current capability than the 8032 port pin. 3.6 Handshaking The SBC51 is equipped with a MAXIM232 converter chip to achieve proper RS232 signal voltages. The system uses the chip for transmitting and receiving data, so there are three lines for RS232 communication, which are transmit, receive, and ground. However, since a handshaking signal is necessary to control the data flow from the sending device, an extra line is needed. P1.0 on the 8032 controls the CTS line, which was hard-wired through the MAXIMs extra inverter and to pin 5 on jack 1 (RS232 interface).

Chapter 4: Software 4.1 Getting Started The entire program for the display is written in 8051 assembly language. To make the machine more independent and easy to use, all of the software, including the translator, is executed solely by the 8032 microcontroller. The memory of the system has four components: 1) internal 8032 user RAM (128 bytes), 2) external ROM (8K bytes), which contains only I. Scott McKenzies MON51 monitor program, 3) external user ROM (8K bytes), which contains the custom software for the machine, and 4) external user RAM (8K bytes), which is used as the input text buffer. 4.2 Overall System Objective The main objective of the controller software is to input a text file (composed of ASCII characters), translate it into Grade I Braille, and send the braille output to the electronic hardware. This is achieved by first storing the ASCII file in external RAM. The program extracts these stored data one character at a time and translates each byte into Grade I braille. After a byte is translated, it is stored as encoded braille in a buffer inside the 8032s on-board RAM. Finally, the program waits for signals from the cell position sensors on the solenoid carriage and, when activated, transmits the braille characters via the 8155 parallel port to the electronic hardware. The program is mostly interrupt driven. When no interrupts are being executed, the system waits for the reset switch to be pressed or empties the character output buffer, which will be discussed in the section on the internal buffer. The reset switch is responsible for initiating the program and subsequently for resetting the shuttle position as a method of cell position correction. The switch, which is active low, is directly

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connected to a port pin on the 8032 and is depressed when the shuttle is moved to the extreme left, or the home position, where the cell count is -1. 4.3 External Buffer There are two buffers designated to handle the information in the input file. The largest buffer, the external buffer, stores raw data from a text file. Its task is to store as much information as possible, because its size limits how far back the reader can scroll when scanning backwards by line or by page. This buffer is isolated in an 8K byte external RAM chip and is defined in code space. The external buffer fill executes using the 8032s serial port interrupt. In this way a character is stored when it arrives but the system does not exclusively wait for it. This prevents the system from hanging up when the external buffer is not completely full and allows the braille display to operate while the external buffer is being filled. If not hindered, the serial port interrupt subroutine will refill the external buffer, writing over the stored data, as long as there are incoming data on the receive line. A handshaking signal must be used to start and stop the data transmission. When the external buffer is full, the clear-to-send line (CTS) is disabled, forcing the computer to cease transmission. If an incoming word is incomplete at the end of the buffer, the buffer will take in more characters until the word is finished or until the end of memory. This is done to prevent word cutoff at the end of a line. If the file ends before the external buffer is full, the CTS signal remains high and the system is capable of receiving more data. 4.4 Internal Buffer The method of filling the internal buffer is shown in Figure 4-2. Characters are extracted from the external buffer by the fill subroutine. Since there is only one

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external data pointer in the 8032, and all variables are global in 8051 assembly language, special care must be taken not to destroy the data pointer. For this reason, both the external buffer and internal buffer store the current value of the 16-bit data pointer in separate 8-bit memory locations. The fill routine first points to the current external character to be read and sends it to the ASCII to Grade I braille translator subroutine. This translator is mostly a character-to-character translation. However, there are several exceptions, such as when to add one or more number signs, letter signs, or capital signs. For example, if the number 74LS123 is to be translated, the translation would be: number sign-G-D-cap sign-cap sign-L-S-number sign-A-B-C. In this case two capital signs indicate that there is more than one capital letter following, and the numbers are represented with the number sign followed by corresponding letters. There are several characters which must be spelled out in grade I such as plus, greater than, etc. In this case, the data pointer is incremented to the next character as normal and the spelled out translation takes up more characters in the internal buffer. In fact, one of the reasons two buffers are used in this program is because Grade I braille takes up more characters than ASCII, and having a small translated buffer saves more space for the text file in the external buffer. There is a more concise computer braille code than Grade I or Grade II called the Nemeth code. This code is often used by braille displays in text-editing modes, but is not preferable for reading purposes. Most braille displays use Grade II braille, but since a Grade II translator was not a practical task for this prototype, Grade I was chosen as a middle ground to show that on-board translation is a viable option.

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The translated character is stored in the internal buffer as an encoded byte where the most significant hexadecimal digit represents the information for the left side of the braille cell and the least significant digit represents information for the right side. For example, the letter f, which is represented in braille by dots 1, 2, and 4, would be encoded as 31h, or 00110001b. Each nibble has a maximum of binary 7, or 0111b, which would correspond to all three solenoids being fired. This system of encoding leaves two bits unused, which could be utilized for an eight-dot braille code. A half-cell is output by stripping off one of the encoded nibbles and sending the remaining byte to port A on the 8155.

Figure 4-1: Braille Cell Encoding Byte Translation. A) The dot numbers in a braille cell. B) The letter f represented by dots 1, 2, and 4. C) Left and right cell-halves encode into binary 3 and binary 1 respectively. The internal buffer holds 40 characters of data. However, at the end of a line the fill routine checks to see if a word has been cut off. If so, it erases the incomplete word and decrements the data pointer so the word will be printed in its entirety on the next line. If in the middle of an internal fill, the end of the external buffer is encountered, the remainder of the internal buffer is cleared and the CTS is enabled so the external buffer may refill. This is done because the fill routine can take in characters much faster than external fill routine can input characters (2400 baud). Word cutoff is eliminated in this

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case by the external fill subroutine, because as mentioned before, the external buffer always ends with a completed word.

Figure 4-2: Filling the Internal Buffer (current forty cells of braille). 4.5 External Interrupts There are only two external interrupts on the 8032, denoted here as left and right. In this program, they are used to tell the system when to output a character and to keep track of the shuttle position. The left interrupt corresponds to the left column of three dots (1,2,3) in a braille cell and the right interrupt corresponds to the right column (4,5,6). As the shuttle moves, it causes two sets of optical sensors to pass between two sets of slits that each correspond to a cell column. When a columns slit is encountered as the shuttle moves, its corresponding interrupt is generated. Both interrupts are used for cell position sensing so the direction of shuttle movement may be known. A boolean flag, f0 is designated for this purpose. Each interrupt complements the value of the flag (1 or 0) and the left interrupt decides in which direction the shuttle is moving. Lets say the left interrupt is executed and the shuttle is moving forward (to the right). First, the interrupt routine complements f0. If f0 = 0 after

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complementing its value, the shuttle is perceived to be moving forward. Now if the same interrupt is executed before the right interrupt has complemented f0 to 1, then the left interrupt will complement f0 back to 1 and perceive this as a change in direction. This process is illustrated in Figure 4-3. This only works if the shuttle starts from a known position. So the shuttle must be moved to the home position to begin reading.

Figure 4-3: Cell Direction/Counting Method A) Left interrupt executes and the display is moving forward. B) The right interrupt executes, neither count nor direction changes. C) Left interrupt; count changes direction does not. D) The left interrupt executes. Since no right interrupt was detected, direction must have changed. When the shuttle is moving forward, the machine is outputting the information of the current line of braille being read. When it is moving backward, there is no output, because the information is still on the pinboard. A timing system ensures the shuttle does not move too fast for the solenoid stroke while moving forward (the maximum reading rate of the machine is dependent on the response time of the full solenoid stroke). If the machine were to read faster than the maximum speed, hardware damage could occur. When each external interrupt is executed, a timer loaded with a predetermined value is set. The value is easily changed at the beginning of the program. If the next interrupt is

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executed before the timer has finished counting, the interrupt has been requested too early. Though cell count and direction will continue to be updated, there will be no output to the solenoids. The external interrupts are also responsible for keeping count of which cell is being read. Each time a new cell is encountered the count is changed. When the reader comes to the end of a line (cell 40), the last external interrupt refreshes the internal buffer so the next line of text is ready. Then, as the shuttle is moved back toward the start position, the cell count is decremented. If the shuttle were to move forward at a point in the middle of the line, the middle of the newly refreshed line would be the output. 4.6 Polling Interrupt The shuttle is equipped with two document navigation buttons, which may be used to scroll through the document by line or by page. Since there are no remaining external interrupts and high-speed response is not required, a polling timer interrupt is used (Timer 2 on the 8032). This timer interrupts the program and checks the two switches every 50 ms, so no delay can be detected by the user when a switch is pressed. If a switch has been activated, the subroutine for that switch is called and executed. Using one of the timers, the depression of the switch is timed. If the switch is depressed and released quickly (within a half-second), the machine will scroll by line. If the switch is held down for longer, the machine will scroll by page. Using a polling sequence also leaves room for more user switches to be added in the future, such as right and left mouse-click buttons on a PC mouse.

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4.7 Sound The program is equipped to make several differentiable sounds. Sound was primarily used for testing the software (no debugging software was used), but some sounds remain in the final product. All sounds were made using two timers, Timer 0 and Timer 1. Since there are only three timers, Timer 0 had to be borrowed from the serial port. Because there are never any sounds activated during an external fill, borrowing the timer will never pose a problem. One timer determines frequency and the other determines note length, and all tunes are composed in their playing order in a lookup table. There are several important sounds to listen for. A click means that the shuttle has returned to its home position. A short wip! means that the internal buffer has filled and a long bwwwiiiip! means the external buffer has filled. When scrolling forward by page, Shave and a Haircut tells you that the buffer limit has been exceeded. 4.8 Monitor Display For testing purposes and demonstration to sighted people, the machine simultaneously outputs braille to the display through the parallel port and text to a monitor through the serial port. In fact, the braille output is translated back to text directly using a separate lookup table. Examples of characters sent to the screen are shown in Table 4-1. It must be translated from the braille output because the braille is different from incoming text, and in this way each cell may be viewed in text form (number sign, capital sign, etc.). Each time the internal buffer is filled, the data pointer location is loaded into the character output buffer and each time there is a braille output during an external interrupt, its translated ASCII character is loaded into the buffer.

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When the interrupt has finished execution, the main program empties the character output buffer. Character Capital Sign Number Sign Lower Case Sign + >< = Monitor Output ^ # @ plus minus greater/less than equals

Table 4-1: Some Characters As Viewed on the Monitor Because the serial port interrupt is executed when either the transmit or receive flag is set, the transmission of data to the monitor is not entirely straightforward. Another boolean flag was created, called key, which is set when the transmit flag executes the serial port interrupt. Using this flag in the character-send subroutine, the character may be sent to the monitor. Another problem encountered was that only one character was transmitted during an interrupt, but more characters could be transmitted after the interrupt was finished executing. Since all characters transmitted occur during the external interrupts, a method to work around this problem was needed. The solution is to fill a small character output buffer during the interrupt and empty the buffer to the monitor after every interrupt. If no characters are sent to the buffer, then none will be sent to the monitor. This is achieved by incrementing the pointer called obuff when a character is added to the buffer and decrementing it when a character is emptied. This way, if the number is zero upon emptying, no character will be sent.

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4.9 Testing During most of the software development, the braille display had not yet been constructed. Since no debugging software was used, several methods of testing the software were implemented. Sounds and transmission of data to the external monitor were useful methods of debugging, but in order to study the interrupts and the outputs in real-time use, a testing apparatus was needed. The apparatus consisted of two encoder strips, two optocouplers, and the reset switch (see Figure 4-3). The encoder strips were attached to the outside of three strips of plywood of the same width but different heights in such a way that the middle strip of plywood would act as a runner and the plastic strips were spaced apart from the middle piece of plywood enough to slide between the optocouplers (Figure 4-3, right). Finally, a wooden base was fitted with two strips of wood to create a slot for the runner and encoder strips to slide through. The reset switch was attached to the wooden base. When in use, the encoder strips moved and the optocouplers remained stationary. Three LEDs on the output control circuit board allowed the braille output to be monitored, and thus the final machine could be simulated.

Figure 4-4: Apparatus for Testing Software

Chapter 5: Discussion The refreshable braille display created for this thesis has successfully met the requirements of the machine as specified in the introduction. It operates as a single unit without cumbersome external hardware or fragile wiring. The machine has one simple serial connection to the host computer and when it is powered, it awaits a text file. After a text file has been sent, the user merely moves the shuttle to the home position and begins reading the file.

Figure 5-1: The Finished Refreshable Braille Display 5.1 Review of Accomplishments Standard cell size was achieved with the idea of a translational mechanism using paddles that are free to rotate on a fixed axis to reduce torque and friction. The end effect was that all of the striking pins are 0.10 inches apart. The cells on the pinboard are spaced to meet standard cell size and spacing. This is the first machine at Appalachian State University to truly achieve this goal.

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The pinboard is a highly stable device and was relatively simple to machine. It was also made from inexpensive materials. The solenoids chosen were the fastest available and have no trouble moving the pins to the desired height of 0.02 inch. Once the pins are up, they may be read many times without being pushed back down. The Alnico magnet easily erases the cells with downward force provided by the magnetic attraction to the steel pinboard. Only three solenoids were used which further simplified the design and made the solenoid carriage much less expensive to construct. Using three solenoids instead of six should only slightly slow down the device because the critical governor of speed is the time of the return stroke of the solenoids. At just over the maximum speed of the braille display, the striking pins collide with the cell pins, thereby altering the performance of the machine. This is prevented by software timing. The solenoids perform very quickly, even equipped with springs and fastened to the aluminum paddles. The reading speed of the machine was calculated using an oscilloscope to measure the time between cells when the solenoids were being activated at every opportunity and the shuttle was moving at a maximum speed. The desired speed of the machine was at least 150 words per minute. Using an average word length of five characters, it was calculated that the machine performed at rates up to 200 words per minute. The speed governor in the software is set according to this maximum mechanical speed to prevent hardware damage. The shuttle is a very efficient way to reduce cost and to simplify the machine. It prevents the need for a motor and drive system that would be associated with it, and it makes navigation through the document convenient. At the time of this writing, a blind

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user has not tested the machine. The two possible drawbacks are that the shuttle may cause fatigue to the reader and it is not a simple way to read. The shuttle was designed to be relatively ergonomic, but due to time constraints and distance, no visually impaired people were consulted with an actual model of the system. If the system is deemed difficult to use in its present state, then it may be redesigned for use with an idle hand or it may be replaced with an automatic drive system. The onboard translator stands as a very efficient way of dealing with the text. It prevents the need for any external software which makes the machine easier to use and faster to set up. Even though it is only a Grade I translation, the translation subroutine is the largest section of the program. An ASCII to Grade II translator would be a large program, but the only requirement to implement it would be more system memory. Ease of use was a main concern for this project. Its simple connections and portability will allow the machine to be demonstrated easily in the future. 5.2 Problems The friction noticed as the shuttle moves back and forth is higher than was expected. During the construction of the machine, special bearing collars were considered for their very low friction. However, with expense in mind, Teflon sliders were made instead. A less frictional method would be preferred. The optocoupler/encoder strip combination works fairly well, but because of the resolutional limitations of the optocouplers, the cell direction often becomes confused, causing the machine to write backwards. More precise optocouplers should solve the

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problem. If not, it may be necessary to have a direction sensor that would constantly send a direction signal to the microcontroller. Finally, because the striking pins are positioned ahead of the readers hand, the shuttle must move past the beginning of the braille line to align the solenoids with the first cell and activate the reset switch. There is no solution to this but it remains to be seen if it will pose a problem. 5.3 Possible Future Endeavors The next step for this refreshable braille display would be to use it in a textediting situation. In this case, the shuttle would become a much more useful device, because it could be used like a mouse to select the cursor position or other options. When editing text, the braille output would change to the Nemeth Code. A Grade II translator for reading mode would be essential for a more natural reading environment. The ultimate goal would be to use Windows and the Internet.

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References1.

Roblin, Jean, The Reading Fingers, Life of Louis Braille, 1809-1852, (New York: American Foundation for the Blind, 1955). pp. 32-35.

2. Private communication, John A. Gardner, Department of Physics, Oregon State University.3.

English Braille, American Ed., (Louisville, KY: American Printing House for the Blind, 1994).

4. Enabling Technologies Company, Tools for Braille Power 1996, 3102 Jay Street, Stuart, FL 34997.5.

Blazie, Dean, Refreshable Braille Now and in the Years Ahead, Braille Monitor, 43(1) (National Federation for the Blind, 2000) pp. 1-6. Examples of current braille displays located at a private website. www.deafblind.com/Newpba.jpg The NIST Rotating-Wheel Based Refreshable Braille Display, www.nist.gov/itl/div895/isis/projects/Braille pp. 1-6. ALVA Satellite Series, http://www.humanware.com/E/E1/E1K.html, pp. 1-2. Lu, Xiong, Development of a Computer-Aided Single Display-Cell Braille Reading Device, (Appalachian State University, 1993) p. 60.

6.

7.

8. 9.

10. Stansell, Bruce, Design and Development of a Cost Efficient Braille Display, (Appalachian State University, 1997) p. 69.11.

AFB National Technology Program, Braille Technology, (American Foundation for the Blind, 2000) pp. 1-2. White, Jerry, Building Braille Reading Speed: Some Helpful Suggestions, http://nfbn.inetnebr.com/student/NABSinfo/Braille.htm. Private communication, Elinor Pester, American Printing House for the Blind.

12.

13.

14. MacKenzie, I. Scott, The 8051 Microcontroller, (Prentice-Hall, 1999) pp. 210-212.

APPENDIX A Mechanical and Electronic Schematics

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Figure A-1: SBC-51 Circuit Diagram 14

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Figure A-1 (continued): SBC-51 Circuit Diagram

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Figure A-1 (continued): SBC-51 Circuit Diagram

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Figure A-2: Circuit Diagram for the Optocouplers

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Figure A-3: Output Control Circuitry

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Figure A-4: Circuit/wiring Diagram for the Shuttle Switches

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Figure A-5: Placement of Interior Components

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Figure A-6: Specifications for the Solenoid Carriage Parts

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Figure A-7: Specifications for the Adjustable Mounting

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Figure A-8: Specifications for the Mounting Plate

APPENDIX B System Software

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54;---------------------------------------------------------------------------;Cmain.asm ;Chris Tullar ;July 5, 2001 ;The following segments work: ; Xbuffer modified to do its job without hanging up by using the ; 8051s evil serial port interrupt. Waits for character input and is ; open to take interrupts at any time. Characters may be sent to the screen ; for display purposes by using the obuffer during an interrupt. The outchr ; routine may only be accessed by the serial port interrupt. Essential to ; OUTCHR being used by OEMPTY is the 'key' bit. This is set by the SPISR ; upon a high TI flag. ; The internal buffer is used exclusively by the FILL routine. This ; routine translates information from the dptr into grade1 braille using the ; GRADE1 routine (ASCII to braille translator) and stores it in the internal ; cell buffer. Also included in the routine is the ability to wrap words to ; the next line (discarding words that will not fit on the current line). ; The external interrupts (EX0ISR and EX1ISR) have four functions. They ; determine the shuttle direction, output three bits of braille information ; per half-cell, keep count of which cell is being activated, and decide when ; to fill the internal buffer. These interrupts are activated when the begin ; switch is activated. This is initially for reference and subsequently for ; error checking and reinitializing. ; The TUNE routine controls the system sounds. It uses TR0 and TR1 for ; frequency and note length, respectively. The notes to be played are ; selected, as well as speed. Included in reportoire: Shave and a Haircut. ; REHASH is a simple routine to translate braille to ASCII. This is for ; monitor display purposes and allows to see just what is in the internal ; buffer without reading braille. Symbols have been designated for number ; sign, capital sign, etc. ; T2ISR is the polling interrupt initiated by timer2. Its tasks are to ; monitor the fast forward and rewind switches about every 20ms. FF and RW ; subtract or add 40 to the current dptr position. FFPAGE and RWPAGE add ; or subtract a page (about 25 lines of braille). NOTE!: the numbers viewed ; on the screen for the dptr will differ from expected values because the FILL ; routine ignores words it cannot complete, making each line fewer than 40 ; characters total. ; Note: interrupts may be interfered with by electrical noise in the ; system. Easy on the software. ;---------------------------------------------------------------------------$MOD52 ;file including 8032 commands decdptr macro ;decdptr macro dec dpl ;decrement low dptr byte mov r7, dpl ;move to r7 cjne r7, #0ffh,$+4 ;if underflow to ff dec dph ;dec high byte also endm ;end of macro showdptr macro mov a, dhigh ;look at dph/dhigh call show mov a, dlow call show endm showcell macro mov a, @cell call show endm pushdptr macro ;push dptr macro push dPH push dPL endm popdptr macro ;reverse order of push pop DPL

55pop dPH endm cts macro clr p1.2 ;p1.2 activates the cts signal endm ; it is connected to the MAXIM ncts macro setb p1.2 ;opposite of clear to send endm pushcell macro ;push the value of cell mov a, cell push acc endm popcell macro ;pop the value of cell pop acc mov cell, a endm return macro mov a, #0dh call ofill mov a, #0ah call ofill endm inchar macro mov a, sbuf ;read character into a mov c, p ;set p for odd parity in a cpl c ;complementing indicates if error clr acc.7 ;strip off parity endm ;------------------------INTERNAL BUFFER------------------------------------dseg at 40h ;put in data segment (absolute, internal) length equ 40 buffer: ds length ;40 bytes reserved ;------------------------EXTERNAL BUFFER------------------------------------xstart equ 9500h ;external buffer starting at 9000h xlength equ 300h ;109h ; extending to the end of memory xseg at xstart ;set up an external data segment xbuffer: ds xlength ;'buffer' represents 9000h ;-------------------------OUTCHR BUFFER-------------------------------------;this buffer is to eliminate the problem of not being able to output ;a character during an interrupt. This way the serial port interrupt may ;be used to output up to ten characters to the screen after an interrupt dseg at 73h ;internal buffer starting at end of 'buffer' olength equ 10 ; CANNOT start at 69!! messes with memory obuffer: ds olength ;end is at 6Bh + 10d = 75h ;---------------------------------------------------------------------------cseg at 8000h ;without this, code isn't recognized ljmp main ; only after a data seg has been set ljmp ex0isr ;jump over interrupt vectors ljmp t0isr ljmp ex1isr ljmp t1isr ljmp spisr ljmp t2isr org 8050h ;--------------------------DIRECTIVES---------------------------------------;bank zero registers r0-r7 cell equ r0 ;braille cell pointer obuff equ r1 ;obuffer pointer ; r3 ;obuffer place-keeper bdata equ r4 ;data in external buffer dlow equ r5 ;dpl gets saved in this dhigh equ r6 ;dph gets saved in this ; r7 ;open for frequent destruction

56fnote equ 30h ;final note for tune note equ 31h ;initial note for tune speed equ 32h ;note length for tune speed2 equ 33h endlow equ 34h ;registers to mark where xbuffer endhigh equ 35h ; ceased filling page equ 3e8h ;how many characters/page ready equ 7EH key equ 7Fh ;bit-addressable flag begin equ p1.1 ;'hardware home' position switch ; p1.2 ;cts pin ffpin equ p1.6 ;user switch for forward rwpin equ p1.7 ;user switch for reverse speedlim equ -18000 ;how much allowed time beteween sensors count equ -2500 ;note time for tune hold equ 6 ;button hold timer poll equ -65500 ;for polling interrupt ;-----------------------SETUP OF 8155 COMMAND-----------------------------main: mov dptr, #0100h ;point to the 8155 command register mov a, #00000001b ;set up A(8155)(1=output) as an output port movx @dptr, a ;send it over ;Ports B and C are by default imput ports ;---------------------------INTERRUPT SETUP-------------------------------setb it0 ;edge triggered for ex0 setb it1 ;edge triggered for ex1 setb es setb et2 ;timer 2 interrupt setb px0 ;high priority for the external interrupts setb px1 ; because they must keep their count ;ex0, ex1 must be set later to avoid interrupting xfill and ; fill at the start. Nasty old things could happen. ;NOTE: it0, it1 must be set before enabling ex0 and ex1 ;-------------------INITIALIZE SERIAL PORT AND TIMERS---------------------mov scon, #52h ;serial port, mode 1, force TI int. mov tmod, #21h ;timer 1, mode 2 (8bit auto), 16bit timer 0 mov th1, #-13 ;reload count for 2400 baud setb tr1 ;start timer 1 mov t2con, #00h ;16-bit auto reload mov rcap2h, #high poll ;loading the timer2 recapture registers mov rcap2l, #low poll ;-----------------------CLEARING THE BUFFERS-------------------------------mov cell, #buffer ;point at start of ibuffer iclear: mov @cell, #00h ;clear location inc cell ;next cell location cjne cell, #(buffer + length + 20), iclear ;+20 for easy buffer examination mov dptr, #xbuffer ;clear external buffer mov obuff, #obuffer ;output buffer must be cleared here because oclear: mov @obuff, #00h ;it retains a character from xfill inc obuff ;step through buffer cjne obuff, #obuffer+olength, oclear ;end of oclear xclear: clr a movx @dptr, a inc dptr mov a, dpl ;compare dptr and acc. cjne a, #00h, xclear ;#low(xbuffer + xlength), xclear mov a, dph cjne a, #0A0h, xclear ;#high(xbuffer + xlength), xclear ;****************************************************************************; ; MAIN PROGRAM BEGINS ; ;****************************************************************************; clr ready call charge ;a little theme to get you charged up

57setb tr2 clr key mov dptr, #xbuffer mov endlow, dpl mov endhigh, dph cts jnb ri, $ setb ea ;if started earlier, there are problems ;the magic little bean for character output ;start xfill at the start of xbuffer ;dptr must always be saved in variables ;so xfill starts at the start of the buffer ;so the PC can send characters ;a character starts the program ; and the interrupts are activated ;XTERNAL BUFFER FILLS ;'fill' gets the dptr position from the two ; variables dhigh, and dlow ;INTERNAL BUFFER FILLS ;initialize character-out buffer ; with these two lines ; the intro message to be displayed ; display string

jb begin, $ mov dlow, #low(xbuffer) mov dhigh, #high(xbuffer) call fill mov obuff, #obuffer mov r3, #0 mov dptr, #intro call strung

execute: jnb begin, lo ;THE ENTIRE PROGRAM WILL INTERRUPT THIS LOOP call oempty ; waiting on begin switch(active low) and sjmp execute ; and outputting characters with oempty lo: clr f0 ;clear direction flag for braille cells setb tf0 ;tells interrupt not too fast at first mov cell, #(buffer-1) ;so the first interrupt increments to start setb ex0 ;now we are ready for external interrupts setb ex1 ; Play ball! sjmp execute ;wait to be interrupted by exs, tr2, sp ;**************************************************************************** ; SUBROUTINES AND INTERRUPT SERVICE ROUTINES ; ;**************************************************************************** ;-------------------RECEIVE OR TRANSMIT A CHARACTER-------------------------outchr: mov c, p ;put parity bit in c flag cpl c ;change to odd parity mov acc.7, c ;add character code jnb key, $ ;key is set by the sp interrupt clr key ; ti alone will NOT do the trick! mov sbuf, a ;send character clr acc.7 ;strip off parity bit ret ofill: mov @obuff, a ;send character to obuffer spot inc obuff ;go to next spot inc r3 ;r3 keeps track of where we are ret ; and leaves it at that value oempty: cjne r3, #0, oyes ;if r3 is zero then leave subroutine ret oyes: mov obuff, #obuffer ;start at beginning of obuffer o2: mov a, @obuff ;move contents of obuff to a call outchr ; and output to the screen inc obuff ;go to next obuffer location djnz r3, o2 ;decrement until start of buffer mov obuff, #obuffer ;initialize character-out buffer mov r3, #0 ; with these two lines ret ;----------------------------DISPLAY BYTE-----------------------------------;displays a byte held in the accumulator in ASCII form show: push acc ;save byte swap a ;swap nibbles in the accumulator anl a, #0fh ;erase upper nibble orl a, #30h cjne a, #':', $+3 ;see if number or letter jc show1 ;if less than 10, use 3xh add a, #7 ;make it a letter show1: call ofill ;output high nibble

58pop acc ;get low nibble of dlow anl a, #0fh ;mask high nibble orl a, #30h ;ASCII-correct cjne a, #':', $+3 jc show2 ;if less than 10, use 3xh add a, #7 ;make it a letter show2: call ofill ;output low nibble ret ;------------------------OUTCELL SUBROUTINES--------------------------------; Outputs a three bits to the braille cell through the 8155's port A. ; The forty-cell buffer is ready for export by this point. ;---------------------------------------------------------------------------Loutcell: pushdptr ;don't get caught with proverbial pants down mov a, @cell ;for screen representation call rehash ;translate back to text call ofill ;display contents of cell on monitor mov dptr, #0101h ;point to 8155 output port lout: mov a, #00h ;to make sure the one-shot is triggered movx @dptr, a ; it must be initially cleared call slight ;reset one-shots mov a, @cell ;which letter we are on swap a ;exchanges nibbles in a anl a, #07h ;keep low 3 bits for left side mov dptr, #0101h ;point to 8155 port a movx @dptr, a ;export left side of cell popdptr ret Routcell: pushdptr mov dptr, #0101h ;point to 8155 output port rout: mov a, #00h ;to make sure the one-shot is triggered movx @dptr, a ; it must be initially cleared call slight ;reset one-shots mov a, @cell ;opposite of ex0 anl a, #07h ;keep low 3 bits for right side mov dptr, #0101h ;point to 8155 port A movx @dptr, a ;schlep the byte out popdptr ret ;-----------------------------SLIGHT DELAY--------------------------------slight: mov r7, #0ffh ;load multi-purpose, destroyable register djnz r7, $ ;countdown ret ;-----------------------OUTGOING STRING OF CHARACTERS---------------------strung: clr a ;string procedure movc a, @a+dptr ;get string jz strout ;end of string call outchr ;schlep character out inc dptr ;for the string increment sjmp strung ;do it until end of string strout: ret intro: db 'Your file is ready to read.', 0dh, 0ah db 'Move the shuttle to the start position', 0dh, 0ah db 'to begin plugging away.', 0dh, 0ah db '-----------------------------------------',0dh,0ah,0dh,0ah, 00h ;------------------------FILL THE EXTERNAL BUFFER---------------------------spisr: PUSHDPTR jb ti, tiout ;spisr not for transmitting xfill: clr ri ;must be cleared by software mov dpl, endlow ;so interrupt knows where it left mov dph, endhigh ; off in the xfill cycle inchar ;get a character

59movx @dptr, a ;move character out mov a, dpl ;look at low nibble cjne a, #low(xbuffer + xlength - 13), $+3 jc xout ;not at the end, still ready to fill mov a, dph ;look at high nibble cjne a, #high(xbuffer + xlength - 13), $+3 jc xout ; movx a, @dptr ;continue to fill until the end cjne a, #20h, xout ; of a word- important for communication ncts ;buffer full, not clear to send call full ;boooowip! sound SJMP XOUT2 ;IF FULL DON'T SAVE INCREMENT xout: inc dptr ;increment, is it at the top? mov endhigh, dph ;save dptr for current end of mov endlow, dpl ; xbuffer XOUT2: popdptr ;BYPASSING KEY FOR RECEIVE INTERRUPT reti tiout: clr ti setb key ;for sending out a character popdptr reti ;----------------------FILL THE FORTY-CELL BUFFER---------------------------; Internal memory segment defined at the beginning of the program fill: PUSHCELL showdptr ;show dptr before buffer is filled return ;these two things for display purposes mov cell, #buffer ;point to the 1rst buffer location next: mov dph, dhigh ;get value for xbuffer pointer mov dpl, dlow ;16 bits call grade1 ;translate @dptr and transport to @cell inc cell ;next location in buffer inc dptr ;next position in xbuffer mov a, dpl ;look at low nibble cjne a, #low(xbuffer + xlength-13), $+3 jc filla ;if not at xlength fill normally mov a, dph ;look at high nibble cjne a, #high(xbuffer + xlength-13), $+3 ;the -13 is a buffer to prevent jc filla ; words from being cut off in xbuffer ;----------------------------------movx a, @dptr ;look at contents of dptr position cjne a, #20h, filla ;if not at a space, keep reading FILLC: mov @cell, #0 ;whatever is left in the internal buffer, fill it with inc cell ; empty spaces. This is done to prevent reading the cjne cell, #buffer + length, $+3 ; xbuffer on the fly. jc fillc ; continue erasing end of line mov endlow, #low(xbuffer) ;move xfill to start of xbuffer mov endhigh, #high(xbuffer) ; so it doesn't overfill here mov dhigh, endhigh ;make sure dptr is not destroyed mov dlow, endlow ; by an interrupt popcell cts ret ;-----------------------------------filla: mov dhigh, dph ;make sure dptr is not destroyed mov dlow, dpl ; by an interrupt cjne cell, #(buffer+length), $+3 ;fill until end of buffer jc next ;if less than full continue filling bypass: call xfull ;wip! wrap: decdptr ;This section wraps a word to the next line

60movx a, @dptr ;bring in char. at the end of the line cjne a, #20h, wrap ;is it a space? inc dptr ;yes, move to the next character mov cell, #buffer + length ;Why? because we LIKE you. backup: dec cell ;backup through the line and mov a, @cell ; look for the last space cjne a, #00h, backup ;When the last space written is found, fillb: inc cell ; go through and erase the rest of the mov @cell, #00h ; line with braille spaces. cjne cell, #buffer + length, $+3 JC FILLB mov dhigh, dph ;make sure dptr is not destroyed mov dlow, dpl ; by an interrupt popcell ;saving the previous cell position ret ;-----------------------SHUTTLE SUBROUTINES---------------------------------; Shuttle.asm October 21, 2000 ; FF = dptr+40, until the xbuffer limit is exceeded, in which case ; it will be refilled and dptr will be at the start ; RW = dptr-40, until the the start of the xbuffer is reached. ; FFPAGE = dptr+page of characters (ex: 1 braille page = 1000char) ; RWPAGE = dptr-page of characters, until buffer limit exceeded ;-----------------------FAST FORWARD----------------------------------------ff: call fill ;refresh internal buffer ret ;-----------------------------REWIND----------------------------------rw: pushcell ;store current cell status mov dph, dhigh ;get value for buffer pointer mov dpl, dlow ; mov r7, #2 rwb: clr c ;not to mess up first subb command mov a, dpl subb a, #27h ;#4Fh ;subtract line from dptr (40d = 28h) mov dpl, a ; mov a, dph ; by using high and low separately subb a, #00h ; and subtracting high byte with carry mov dph, a ;replace original value cjne a, #high(xbuffer), rwa ;compare dph and xbuffer base mov a, dpl ;if equal, compare low bytes cjne a, #low(xbuffer), rwa jmp rwout ;if dpl =, exit subroutine rwa: jc rwc ;out ;if dptr >, exit subroutine DJNZ R7, RWB ;two steps back one step forward(fill) sjmp rwout rwc: call toofast ;error: that's too far 'blip blip' mov dptr, #xbuffer ;set dptr at the start rwout: mov dhigh, dph ;save the value in dptr mov dlow, dpl call fill ;refresh internal buffer popcell ret ;-------------------------FFPAGE-------------------------------------------ffpage: pushcell mov r7, #(page-1h-27h) ;how many lines to proceed again: inc dptr mov a, dpl ;compare to the top cjne a, #endlow-length, $+3 ;so there will be room to fill once jc ffa mov a, dph ;if equal, compare low bytes cjne a, #endhigh, $+3 jc ffa call shave ;and a haircut, two bits sjmp fpout ;don't increment any more, run out of space

61ffa: fpout: djnz r7, again mov dhigh, dph ;save the value in dptr mov dlow, dpl call doo call fill ;refresh internal buffer popcell ret ;-----------------------------RWPAGE-----------------------------------;the page-1 command is due to the fact that subb subtracts one more ;than needed rwpage: pushcell mov dph, dhigh ;get value for buffer pointer mov dpl, dlow clr c mov a, dpl ;look at low nibble of dptr subb a, #low(page) ;subtract a page of lines mov dpl, a ;restore dpl with new value mov a, dph ;this is similar to the rw routine subb a, #high(page) mov dph, a ;replace original value cjne a, #high(xbuffer), rpa ;compare dph and xbuffer mov a, dpl ;if equal, compare low bytes cjne a, #low(xbuffer), rpa jmp rpout ;if dpl =, exit subroutine rpa: jnc rpout ;if dptr >, exit subroutine call toofast ;error: that's too far 'blip blip' mov dptr, #xbuffer ;set dptr at the start rpout: mov dhigh, dph ;save the value in dptr for 'fill' mov dlow, dpl call doo call fill ;refresh internal buffer mov dhigh, dph mov dlow, dpl popcell ret ;-------------------------EXTERNAL INTERRUPTS------------------------------; ; One interrupt for each optocoupler. Each optocoupler waits for ; the other to pulse before the cell is incremented. If one pulses ; twice without the other pulsing in between, then shuttle direction ; has changed. Direction will be sensed by using the f0 flag. ; A timer is used to make sure the user doesn't exceed hardware speed ; * - * ; * and - * ; * - * ;--------------------------------------------------------------------------; ex0isr: ;for left 3 dots (1,2,3) cpl f0 ;flag=1>forward ... flag=0>backward jnb f0, back ;if backwards up: inc cell ;if not back, forward jb tf0, go ;if tf1 is 1 then we are ok ;call too ; otherwise we got here too quickly jmp out ; and the solenoid won't be activated go: call loutcell ;flag=1 dot jmp out ;jump over decrement back: dec cell ;then backup cjne cell, #buffer, $+3 ;don't go too low jnc out ; if >, then we're OK call click ;a friendly reminder out: clr tr0 ;stop timer clr tf0 ;clear overflow flag mov th0, #high speedlim ;enforce the speed limit mov tl0, #low speedlim ; by using timer0 setb tr0 ;start timer0

62reti ;f0=1>backwards for ex1, f0=0>forwards! ex1isr: ;for right three dots (4,5,6) cpl f0 ;toggle direction flag jb f0, nok ;if going backwards no output jb tf0, ok ;if the timer flag is not set ;call too ; then we got here too quickly jmp nok ; and the solenoids will not fire ok: call routcell ;send out character half cjne cell, #(buffer+length-1), $+3 ;forward until 67h=the top jc nok ;if

;if there were none of these ;exceptions, flat translation

67mov @cell, a mov dhigh, dph ;save the value in dptr mov dlow, dpl popdptr ret ;shew! ;---------------------------------------------------------------; ; trans: ASCII to Braille lookup table ; ;format: LRh where L is the left half-cell and R is the right ; ; xLLLxRRR in binary ;---------------------------------------------------------------; trans: inc a movc a, @a+pc ret ; 0 1 2 3 4 5 6 7 8 9 A B C D E F db 00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h ;0 db 00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h,00h ;1 db 00h,62h,00h,00h,26h,00h,00h,00h,66h,66h,00h,00h,20h,44h,26h,41h ;2 db 23h,10h,30h,11h,13h,12h,31h,33h,32h,21h,22h,60h,00h,00h,00h,64h ;3 db 00h,10h,30h,11h,13h,12h,31h,33h,32h,21h,23h,50h,70h,51h,53h,52h ;4 db 71h,73h,72h,61h,63h,54h,74h,27h,55h,57h,56h,00h,41h,00h,00h,77h ;5 db 00h,10h,30h,11h,13h,12h,31h,33h,32h,21h,23h,50h,70h,51h,53h,52h ;6 db 71h,73h,72h,61h,63h,54h,74h,27h,55h,57h,56h,66h,43h,66h,44h,00h ;7 aust: string: clr a movc a, @a+dptr ;get string jz stout ;end of string call trans ;loosely translate it into braille mov @cell, a ;put letter in cell location inc cell ;get next one ready inc dptr ;for the string increment sjmp string ;do it until end of string stout: ret plus: db 'plus', 00h lthan: db 'less than', 00h gthan: db 'greater than', 00h equals: db 'equals', 00h atsymb: db 01h, 'at', 00h ;--------------------------REHASH-------------------------------------; ;this look up table is used to translate the braille information ; inside the internal buffer to ASCII text which can be output ; to the computer monitor. For demonstration only. rehash: inc a movc a, @a+pc ret ; 0 1 2 3 4 5 6 7 8 9 A B C D E F db 20h,20h,20h,20h,5Eh,20h,40h,20h,00h,00h,00h,00h,00h,00h,00h,00h ;0 db 'a','c','e','d',20h,20h,20h,20h,00h,00h,00h,00h,00h,00h,00h,00h ;1 db 2Ch,'i',3Ah,'j',20h,20h,2Eh,'w',00h,00h,00h,00h,00h,00h,00h,00h ;2 db 'b','f','h','g',20h,20h,20h,20h,00h,00h,00h,00h,00h,00h,00h,00h ;3 db 27h,2Fh,2Ah,7Ch,2Dh,20h,22h,23h,00h,00h,00h,00h,00h,00h,00h,00h ;4 db 'k','m','o','n','u','x','z','y',00h,00h,00h,00h,00h,00h,00h,00h ;5 db ';','s','!','t',22h,20h,28h,20h,00h,00h,00h,00h,00h,00h,00h,00h ;6 db 'l','p','r','q','v',20h,20h,20h,00h,00h,00h,00h,00h,00h,00h,00h ;7 ;-----------------------POLLING EXTERNAL SWITCHES---------------------; October 23, 2000. Debugged December1, 2000 ; Uses timer 2 to poll port pins on the 8032. ; A click less than 'hold' means 40 cells forward or backward ; A click longer than 'hold' yields a whole page forward or back ; This routine depends on ff, ffpage, rw, and rwpage ; which fill buffers as necessary. With no signal on polling pins ; only three lines are executed, minimizing time. ;---------------------------------------------------------------------t2isr: clr tf2 ;clear timer2 flag REQUIRED

68jnb ffpin, rpin mov r7, #hold setb tf0 t2d: jnb tf0, $ clr tf0 clr tr0 mov th0, #high -50000 mov tl0, #low -50000 setb tr0 djnz r7, t2d jb ffpin, $ jb tf0, t2a call ff sjmp t2out t2a: call ffpage sjmp t2c rpin: jnb rwpin, t2out mov r7, #hold setb tf0 t2e: jnb tf0, $ clr tf0 clr tr0 mov th0, #high -50000 mov tl0, #low -50000 setb tr0 djnz r7, t2e jb rwpin, $ jb tf0, t2b call rw sjmp t2c t2b: call rwpage t2c: clr tr0 t2out: reti t1isr: t0isr: ; THE END ;ffpin low, check rwpin ;multiplier for holding button down ;so next inst. doesn't hang up ;clear timer 0 ;wait for low for a set time ; for ffpage ;start timer ;for a longer delay ;wait for the return to low ;timer flag means time's up=ffpage ;go forward forty cells ;skip the remainder ;go forward a page ;if rpin is high, ;so next inst. doesn't hang up ;a nested loop with timer0 ; must be used for a long ; enough hold ;wait for low for a set time ; for ffpage ;start timer ;count down ; wait for the return to low ;timer flag means time's up=rwpage ;go back forty cells ;skip the remainder ;go forward a page ;stop timer 0 ;unused interrupts taken care of ; this is required

VITA Chris Tullar was born in Greensboro, North Carolina in 1974, and lived there until he went to Lenoir-Rhyne College in 1992. He started in a pre-engineering course of study, but decided physics was too interesting to pass up, so he went on to receive a Bachelor of Science degree in physics. He applied for graduate school at Appalachian State University in 1996, but deferred his acceptance for three years. In 1997, he married Raeleen Wilson who, shortly thereafter, went to graduate school at Wake Forest University. During that time Chris worked as a faux painter/muralist and an instructor at Sylvan Learning Center. In August 1999, he started the ASU program in Applied Physics.

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