This invention was made as a result of work under Grant 1R43/44EY11059 between the National Institutes of Health, National Eye Institute and Orbital Research Inc., Grant RA 94129004 between the U.S. Department of Education and Orbital Research Inc., and Grant DMI-9760377 between the National Science Foundation and Orbital Research Inc. and the U.S. Government has rights in this invention pursuant thereto. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates, generally, to refresbable Braille display systems for use as monitors in computer systems and, more particularly, to refreshable Braille display systems using microelectromechanical (MEMS) actuators. 
     2. Description of the Related Art 
     The flourishing computer and information revolution has left behind visually impaired and particularly visually and hearing impaired individuals. This is due to the fact that visual display units, typically cathode ray tubes (CRTs), are the heart of all modern communication and information systems including the Internet. This especially affects those impaired individuals in the technical fields. To remedy this situation and promote the mandates of the Americans with Disabilities Act that mandates equal access and opportunities be presented to all capable individuals, Congress has proposed a State Model Bill. The bill would provide materials in a computer-accessible format capable of Braille reproduction. It states, “the Legislature finds that: 
     (1) the advent of the information age throughout the United States and around the world has resulted in lasting changes in information technology; 
     (2) use of interactive visual display terminals by state and state-assisted organizations is becoming a widespread means of access for employees and the public to obtain information available electronically, but nonvisual access, whether by speech, Braille, or other appropriate means has been overlooked in purchasing and deploying the latest information technology; 
     (3) presentation of electronic data solely in a visual format is a barrier to access by individuals who are blind or visually impaired, preventing them from participating on equal terms in crucial areas of life, such as education and employment; 
     (4) alternatives, including both software and hardware adaptations, have been created so that interactive control of computers and use of the information presented is possible by both visual and nonvisual means; and 
     (5) the goals of the state in obtaining and deploying the most advanced forms of information technology properly include universal access so that segments of society with particular needs (including individuals unable to use visual displays) will not be left out of the information age.” 
     Prior art computer interfaced Braille devices use various mechanisms to actuate the Braille dots and “refresh” the text. The dots are controlled via macroscopic actuators comprised of piezoelectric materials, shape memory alloys, and solenoids to raise individual pins in the Braille characters. Most of these devices display one or two lines and up to 80 Braille characters per row. Ideally, more rows of Braille text are desired, however, the complexity of the actuators and the close spacing of the Braille dots limit the number of Braille characters. Such actuators also require a very large “volume overhead” to accommodate this complex network of actuators and wires needed to operate the Braille dots. The result is that the foot print of the unit is much larger than the display surface and it is difficult to skin information based on the limited number of Braille characters. 
     Recently, a company in Cambridge Mass. called Braille Displays overcame the limitation of two rows of Braille cells. This company with the support of the National Science Foundation was able to produce a prototype 4 line by 40 column prototype refreshable Braille display. This 160 cell display is not commercially available. Telesensory produces an 80 character unit, PowerBraille 80 (PB80). This device has many user friendly features integrated into its device such as a cursor locator, a touch sensitive strip and scrolling toggle. 
     U.S. Pat. No. 5,685,721, to Decker, discloses a macro-sized shape-memory alloy based actuator enclosed in a series of tubes and housed in modules which are mounted into a multi-row display under ledges. U.S. Pat. No. 5,766,013, to Vuyk, discloses another macro-sized actuation technique utilizing an intrinsically conducting polymer sheet that expands when a charge is applied. Another macro-sized actuation technique, utilizing a rotary actuator with cams is disclosed by U.S. Pat. No. 5,453,012, to Hudecek. Also, Garner, U.S. Pat. No. 5,496,174 utilizes an electrorheological fluid that expands when a high voltage is applied. All of these devices suffer from the same fundamental problems: a large number of individual components needed for each Braille dot increasing assembly problems; high power requirements eliminating the potential for portability and creating problems dissipating the excess heat; responding fast enough to allow refresh rates appropriate for computer based communications; and, the difficulties in assembling the large number of Braille dots needed for true replication of computer display terminals. 
     Another approach to providing access to the visually impaired has been the development of optical recognition systems attached to voice synthesizers. Although these devices represent an enormous leap forward in access to both computerized and printed material, they are not appropriate for all tasks. Specifically, they cannot be used with detailed technical material which has a very specialized vocabulary. Medicine, law, accounting, engineering, and science careers are restricted by this limitation. Voice Synthesizing devices are not effective at dealing with tabular material. The voice synthesizing devices do not provide blind accountants and bookkeepers the access they require to spreadsheets and databases. Furthermore, voice synthesizers are not capable of limited document skimming, or provide a means to address accessing links otherwise known as sub-directories or complementary subject indicators. Perhaps most important, these reading devices provide limited ability to edit text or tables. 
     The devices currently available for the sight impaired are limited and have drawbacks in that they do not have fast enough refresh rate or sufficient Braille character ability to replicate a computer display, including memory capacity, readable area, and scanning and highlighting functions; are bulky and heavy; can not be adapted for different applications, i.e., a lap top vs. a desk top computer; and cannot “display” technical, accounting, spreadsheets, or other specialized forms of display which are not a basic textual document. 
     Accordingly, a need exists for a refreshable Braille display that overcomes the above mentioned limitations and drawbacks. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a device to satisfy the aforementioned need. 
     One object of the present invention is to provide a Braille display system which has a rapid refresh rate of the Braille dots. 
     Another object of the present invention is to provide a refreshable Braille display system that has the ability to conveniently present text, spreadsheet and database information, technical material and information in tabular or columnar format to visually impaired persons. 
     Still another object of the present invention is to provide a refreshable Braille display that allows a user to access links or subdirectories without removing their hands from the display surface. 
     Still another object of the present invention is to provide a modular Braille display system that is flexible so that it can be sized and arranged to fit a user&#39;s needs. 
     Still another object of the present invention is to provide a Braille display system which is modular and therefore, quickly and easily assembled or repaired. 
     Still another object of the present invention is to provide a Braille display system which can present text and limited graphics, normally displayed on a computer display terminal or CRT, to a visually impaired person. 
     Still another object of the present invention is to provide a Braille display system that has a tactile surface with no holes, gaps or voids, and provides a continuous uninterrupted tactile reading surface for the user eliminating any interference with reading of Braille characters and preventing environmental damage to the underlying Braille display hardware. 
     Accordingly, the present invention relates to a refreshable Braille display; comprising a plurality of Braille dots that extend and retract, arranged in Braille characters such that the Braille dots are operable as a personal computer monitor to allow a blind person to discern the information displayed thereon by reading the Braille characters. At least one microelectromechanical device operably connects to the Braille dots such that the Braille dots retract and extend based upon the operation of the microelectromechanical device. The Braille character comprises six or eight Braille dots. Multiple Braille characters are arranged in functionally independent modules of rows and columns. The microelectromechanical device operates electrostatically or comprises shape memory alloy material. The microelectromechanical device will either directly move a pin or directly form the individual Braille dots, or it will pneumatically move a pin or directly form a Braille dot. 
     In another aspect, the present invention relates to a refreshable Braille display; comprising a housing; a plurality of Braille dots arranged in Braille characters mounted in the housing; at least one microelectromechanical device operably attached to each Braille dot; a compressor which provides air pressure to the microelectromechanical devices; a microcontroller mounted in the housing and programmed to directly control the operation of the microelectromechanical devices to extend and retract the Braille dots; a personal computer programmed with Braille translation software and connected to the microcontroller. The information and data from the personal computer is translated and transferred to the microcontroller. The microcontroller operates the microelectromechanical device in response thereto which extends and retracts the Braille dots allowing a blind person to discern the information displayed thereon by reading the Braille characters formed by the extended Braille dots. 
     In yet another aspect, the present invention relates to a refreshable Braille display system, comprising a housing; at least one module mounted in the housing, and a top surface sealed to the housing and the modules. The top surface is an elastomeric material and is selectively deformable. At least one microelectromechanical device is mounted in the module such that the microelectromechanical device selectively deforms the top surface by forming dimples therein. The dimples function as Braille dots and form Braille characters. The microelectromechanical device selectively flattens the dimple thereby removing the Braille dot and thereby changing or removing the Braille character. The Braille dots and the Braille characters form a Braille display. A module microcontroller controls the microelectromechanical device. A microcontroller coordinates each individual module microcontroller and communicates with the computer. A personal computer programmed with Braille translation software connects to the microcontroller such that information and data from the personal computer is translated and transferred to the microcontroller. The microcontroller or the module microcontrollers operate the microelectromechanical devices in response thereto which forms the Braille dots allowing a blind person to discern the information displayed thereon by reading the Braille characters formed by the Braille dots. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Further features of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following specification with reference to the accompanying drawings in which: 
     FIG. 1 is a view of the present invention. 
     FIG. 2 is a layout of the module showing Braille characters. 
     FIG. 3 is a view of the section cut along lines  2 — 2  on FIG.  2 . 
     FIG. 4 is a block diagram of the control function of a single module of the present invention. 
     FIGS. 5A and 5B are detail views of a MEMS device and Braille dot extended and retracted, respectively 
     FIG. 6 a schematic representation of the Braille dots actuation scheme. 
     FIG.7 is another design for the MEMS device utilizing an actuator based upon a sliding element. 
     FIGS. 8A, and  8 B are details of a MEMS devices that directly actuates a Braille dot using a thin film SMA element. 
     FIGS. 9A, and  9 B are details of a MEMS device that directly forms the Braille dot using a thin film SMA element. 
     FIGS. 10A, and  10 B are details of a MEMS device that directly forms the Braille dot using a thin film SMA element. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and, more particularly, to FIG. 1 there is shown a view of the present invention. A Braille display  2  comprises Braille dots  20  arranged into Braille characters  14 . Although, each Braille character  14  requires only six Braille dots  20 , the Braille character  14  of the present invention is preferably comprised of eight Braille dots  20 . The two extra Braille dots  20 , (by convention referred to as Braille dots  7  and  8 ) are used to highlight text within a document such as hyperlinks, boldface or italicized text. The Braille characters  14  are arranged in modules  18 . In this embodiment of the present invention, the Braille characters in each module are arranged in two rows and twelve columns (FIG.  2 ), although other configurations could be used. For pneumatic actuation, a compressor  6  provides pneumatic pressure to the Braille display  2  through tubing  12 . The Braille display  2  receives electrical power through power cable  8  which can plug into a standard 120 or 220 volt receptacle or batteries that may be mounted separately or within the Braille display  2 . A data cable  10  connects a personal computer  4  to the Braille display  10 . 
     Referring now to FIG. 2 there is shown a layout of a module  18  with the Braille characters  14  arranged in two rows and twelve columns. The present invention is not limited by any particular layout of the modules  18 . Since in this particular embodiment of the present invention, each Braille character comprises eight Braille dots  20 , each module  18  will have 2×12×8=192 Braille dots  20 . Also, in this particular embodiment (10 rows, 84 characters wide) there are 35 modules  18  on the Braille display  10  arranged in 5 rows and seven columns for a total number of 6720 Braille dots  20  on the Braille display  22 . This modular design allows the production of various sized Braille displays  2  based upon the number of modules  18  used. The modular design allows for longer row (e.g. 10 rows, 84 characters wide) Braille displays to display spreadsheets and other tabular data, or longer and narrower (e.g. 20 rows, 44 characters wide) for reading text, or single module (2 rows, 12 characters wide) Braille displays for use with a portable computer, ATM machines, or other embedded or portable devices. 
     Referring now to FIG. 3 there is shown a view of the section cut along lines  2 — 2  on FIG.  2 . The Braille display  2  is enclosed in a housing  22 . FIG. 3 shows four Braille dots  20   a, b, c, d , one-half of a Braille character  14  inside of the module  18 . The Braille dots  20  are shown alternately extended and retracted,  20   a  and  20   c  extended,  20   b  and  20   d  retracted. Each Braille dot  20  is operably attached to a microelectromechanical (MEMS) device  16   a, b, c, d , respectively, this actuation can be either direct or indirect utilizing a pneumatic or hydraulic force. In this embodiment, the Braille dot  20  is attached and operates using pneumatic force. Additionally, the Braille dot  20  does not have to be a distinct, separate element but can also be a portion of the top surface  46  (see FIGS.  5 A and  5 B). The MEMS device  16  is comprised of a base  26  and frame  24 . The base  26  has a base aperture  34  which provides a passage from the plenum  32  to the chamber  30 . The frame  24  has a port  36  opening from the chamber  30 . Actuator  28  (for illustrations purposes shown as a sliding element or boss in FIG. 3) operates to open and close the MEMS device  16 . The Braille dot  20  is made from a flexible, resilient polymer and is secured to the inside of the housing  22  juxtaposed between the port  36  and an opening  38  in the housing  22 . When the actuator  28  operates to open the MEMS device  16  air in the plenum  32  flows into and pressurizes the chamber  30 . The pressure is exerted on the Braille dot  20  through port  36 . The pressure on the Braille dot  20  forces the Braille dot  20  to expand through the opening  38  ( 20   a  and  20   c ). When the actuator  28  operates to close the MEMS device  16 , it closes the base aperture  34  and pressure is removed from the chamber  30  and vents therefrom. With the pressure venting, the Braille dot  20  contracts, retracting back through the opening  38  ( 20   b  and  20   d ) Venting can be accomplished by leak holes in the Braille dots  20 , or by vents from the chambers  30 . The second valve position in a three way valve is a vent that will allow faster refresh rates. The actuator  28  can be operated electrostatically, piezoelectrically or using shape-memory alloys. 
     Referring now to FIG. 4 there is shown a block diagram of the control function of the present invention. Data cable  10  connects between a personal computer  4  and the microcontroller  40  mounted in the housing  22 . Braille translation software is programmed into the personal computer  4  to translate display information into commands for the Braille display system. Both commercially available Braille Translation software, such as Duxbury or MicroDots, or custom programmed software may be used with the Braille device. The data cable  10  transfers data and information, translated and otherwise conditioned by the software, from the computer to the microcontroller  40 . The microcontroller  40  contains firmware and memory capacity, including nonvolatile memory, which is programmed to actuate the appropriate Braille dots  20  in response to the data and information from the personal computer  4 . The Braille display system can take two different configurations, one configuration utilizes a single microcontroller  40  which control the Braille dots by sending appropriate signals through leads  44  (also shown in FIG.  4 ), and a second configuration that utilizes a microcontroller  40  to coordinate the operation of individual module microcontrollers  45  which then control the Braille dots in the respective module by sending appropriate signals through leads  44 . Each individual module  18  has individual connectors and wiring to connect each module  18  with either the neighboring modules  18  or the microcontroller  40  for signal, power, and, depending on actuation technique, a pneumatic supply line  12 . The modules  18  are mechanically attached to a housing  22  that will hold each individual module  18  and the supporting hardware: power conditioning  9 ; potentially a compressor  6 ; and, a coordinating microcontroller  40  which will control the individual modules  18  and communicate with the computer  4 . The use of module microcontrollers simplifies the overall control system, reduces the total computational power needed in a single processor, and allows the Braille dots to be operated at a rapid refresh rate. The refresh rate is the amount of time it takes for a Braille dot  20  to extend and retract. A high refresh rate is important for many computer based applications where rapid scrolling and moving through information is needed, such as a spreadsheet or other tabular data. 
     For the pneumatically actuated Braille display systems, compressor  6  provides pneumatic pressure to each Braille dot  20  through tubing  12  and which provides pneumatic pressure to the plenums  32 . The compressor  6  can be any appropriate air pump but in the present invention a Medo linear compressor, AC0102, is used. In designs where the MEMS device  16  directly actuates the Braille dot  20 , no pneumatic force is needed and therefore, neither is a compressor  6 . Power is provided from a power source  42 , to the compressor  6  and the microcontroller  40  by power cables  7  and  8 , respectively. The power can be conditioned by power conditioning means  9  before connection to the microcontroller  40 . In another embodiment, the compressor  6  can be located inside of the housing  22  and one power cable can be used for both the compressor  6  and the microcontroller  40  with power provided from either the power conditioning means  9  or directly from 120 VAC  42 . The power conditioning means  9  can convert and condition either AC or DC power coming from batteries, standard wall receptacles, or other electrical power source. 
     Referring now to FIG. 5A and 5B there are shown a detail views of a Braille dot  20  with a MEMS device  16  extended and retracted, respectively. The actuator  28  is a sliding element operating between two electrodes,  281   a  and  281   b  depending on to which electrode voltage is applied. In FIG. 5A voltage is being applied to electrode  281   b  and the slide element  28  is attracted to it, opening a passage to plenum  32  and closing the passage to the vent  33 . In this position air flows into the chamber  30  and the chamber  30  is allowed to pressurize and expand the Braille dot  20 . In this the Braille dot  20  is formed by distorting the top surface  46  attached to the frame  24  (which may be part of the housing  22  module  18  and is not shown in FIG. 5A or  5 B). The Braille dot  20 , is just a dimple in the top surface  46 . Referring now to FIG. 5B, voltage is applied to electrode  281   a  and the slide element  28  is attracted to it closing the passage to the plenum  32  and opening the passage to the vent  33  and allowing the pressure to vent out of the chamber  30 . Without the pressure, the Braille dot  20  contracts, flattening out the Braille dot in the top surface  46 . The voltage to the electrodes  281   a ,  281   b  is controlled by either the microcontroller  40  through lines  44  or the module microcontroller  45  through lines  44  allowing independent extension and retraction of the Braille dots  20 . 
     Referring now to FIG. 6 there is shown a schematic representation of the Braille dots  20  electronic addressing scheme. The Braille dots  20  are actuated based upon a row and column scanning mechanism. Although, only 4 rows and 5 columns are shown on FIG. 6, the scanning mechanism can be applied to any number of rows and columns. If at any time “t” both the row and column are at open electrode voltage (signified by “0”) the MEMS device is open and the Braille dot  20  is extended. If either the row or the column is at close electrode voltage (signified by “1”), the MEMS device  16  is closed and the Braille dot  20  is retracted. In this manner, at any time “t” a specific Braille dot  20  based upon its row and column location can be operated. For example, at t 1  row  1  has open electrode voltage and column  1  has open electrode voltage. The Braille dot  20  is extended as shown by the X on the actuation scheme. 
     Referring now to FIG. 7, there is shown an internal elevation of the housing  22 . In this FIG. 7, the modules  18  are mounted to the inside of the housing  22  near its top. The top surface  46  attaches to the top of the housing  22 . The top surface  46  is constructed of a single sheet of polymer material stretched over the top of the housing  22 . The top surface  46  presents a continuous surface which provides both environmental protection to the MEMS devices  16  (not shown in FIG. 7) and other electronic hardware as well as providing a tactile surface with no discrete holes, seams, gaps or voids. In the present invention a low modulus elastomer with a thickness of approximately 0.004″ is used for the top surface  46 . Two commercially available elastomer films can be used; a medium modulus latex polymer mix, or a blend of Natural Rubber, Neoprene and Nitrile. The top surface  46  is sealed to the modules  18  and/or housing  22  using either a suitable epoxy or adhesive or a vacuum seal. This provides a continuous uninterrupted tactile reading surface for the user eliminating any interference with reading of Braille characters  14 . This modular design allows different size Braille displays  2  to be assembled from a different number of individual modules  18 . 
     Referring now to FIGS. 8A and 8B there are shown detail views of a Braille dot  20  with a MEMS device  16  extended and retracted, respectively. The actuators are a pair of MEMS microvalves  284   a ,  284   b  which open or close. The MEMS microvalves  284   a ,  284   b  can be actuated electrostatically, piezoelectrically or using thin film shape-memory alloys. In FIG. 8A, the MEMS microvalve  284   a  is open allowing pressurized air from the plenum  32  into the chamber  30 , while the MEMS microvalve  284   b  is closed blocking the pressurized air from leaving the chamber  30 . The pressurized air in the chamber  30  expands the Braille dot  20 . In this the Braille dot  20  is formed by distorting the surface covering  45  attached to the frame  24  (which may be part of the housing  22  module  18  and is not shown in FIG. 8A or  8 B). The Braille dot  20 , is just a dimple in the top surface  46 . Referring now to FIG. 8B, the MEMS microvalve  284   a  is now closed blocking the flow of pressurized air from the plenum  32  and the MEMS microvalve  284   b  is now opened allowing the air to evacuate from the chamber  30  to the vent  33 . With the pressure vented, the Braille dot  20  contracts, flattening out the dimple on the top surface  46 . The voltage to the two the MEMS microvalves  284   a ,  284   b  are controlled either directly by the microcontroller  40  or by the module microcontroller  45  to extend and retract Braille dots  20  independent of other Braille dots  20 . 
     Referring now to FIGS. 9A and 9B there is shown a detail view of a Braille dot  20  and MEMS device  16  which uses a thin film shape memory alloy (“SMA”) element  282  as the actuator. A thin film SMA based microelectromechanical actuator is significantly different then traditional bulk shape memory alloy actuators in size, fabrication techniques, and operation. The mechanical properties of a thin film SMA can be precisely tailored by changing the alloy ratios during fabrication while a macro sized bulk SMA actuator may have regions where the alloy ratio changes within the bulk material of the actuator, these regions will increase power consumption, reduce fatigue resistance and limit life. Thin film SMA actuators have greater fatigue life and improved phase transition characteristics then traditional bulk SMA actuators. The thin film SMA also has faster response and lower power consumption then traditional bulk SMA actuators due to their reduced volume and large surface area which allows the actuator to change from one phase state to another faster then the larger bulk SMA actuators. The rapid response of the thin-film SMA actuators allows a user to quickly scroll through a document without having the refreshable Braille display lag behind. The lower power consumption of a thin film SMA actuator reduces the amount of heat that needs to be dissipated from the actuators during operation and can permit battery operation for use with portable electronic devices. 
     FIGS. 9A and 9B also show the application of a direct actuation of the Braille dot  20  without the need of a pneumatic force. Shape Memory Alloys (SMA&#39;s) are a unique class of alloys which have the ability to form two different crystalline phases, defined as martensite and austenite, in response to temperature and strain. SMA&#39;s are produced by equiatomically combining at least two component metals into a desired shape which is then annealed. When produced, the SMA is in the austenite phase, having a certain shape and characterized by low ductility, high Young&#39;s modulus and high yield stress. Upon cooling the SMA changes to the martensite phase characterized by high ductility, a low Young&#39;s modulus and low yield stress. In the martensite phase, the SMA is easily deformed and can take on a different shape from its austenite or original shape by applying an external strain. The SMA will retain this different shape until it is heated to its austenitic transformation temperature. When the SMA is heated to its austenitic transformation temperature the SMA transitions to its austenite phase and transforms back to its original shape. 
     In FIG. 9A the thin film SMA element  282  is in its martensite phase with the Braille dot  20  retracted. Since the martensite phase is characterized by high ductility, low Young&#39;s modulus and low yield stress, the thin film SMA element  282  is easily deformed by external stresses like biasing means  283 , shown as a spring in FIG.  9 . When heated to its austenitic transfer temperature, the thin film SMA element  282  transitions from its martensite phase to its austenite phase transforming to its austenitic or original shape. The force produced by the biasing means  283  is less than the force produced by the thin film SMA element  282  during this transformation. The thin film SMA element  282 , thereby, overcomes that force during this transformation, and, in so doing, extends the Braille dot  20  as shown in FIG.  9 B. The thin film SMA element  282  is heated by joule heating using electric current from an electric power source controlled by the microcontroller  40  (not shown in FIGS. 9A or  9 B). Because the austenite phase is characterized by low ductility, high Young&#39;s modulus and high yield stress, the thin film SMA element  282  remains in its austenitic or original shape and the Braille dot  20  remains extended. When the electric current is removed, the thin film SMA element  282  cools to its martensitic transfer temperature at which point it transitions to the martensite phase and the external stress from the biasing means  283  deforms the thin film SMA element  282 , retracting the Braille dot  20 . Alternately, the thin film SMA element  282  can be operably connected to the Braille dot  20  to retract it when transitioning from its martensite phase to its austenite phase. The Braille dot  20 , then, will be extended by the biasing means  283 , when the thin film SMA element  282  transitions from the austenite phase to the martensite phase. The Braille dot  20  is extended and retracted based upon the crystalline phase of the thin film SMA element  282 . Instead of a spring as shown, the biasing means  283  can be any mechanism including a second thin film SMA element, a diaphragm or manipulated boss. 
     In FIG.  10 A and FIG. 10B, the thin film SMA element is shown directly forming the Braille dot itself  282 . The Braille dot may be covered with a polymer cover  20  which can provide a biasing force to flatten the Braille dot. The biasing force may be provided by either a pressure or a vacuum applied through the orifice located directly under the SMA film  282 . 
     Similarly direct actuation of the Braille dot  20  can be accomplished with a MEMS device  16  utilizing other mechanisms not based on shape memory alloy like springs, diaphragms and bosses. It is only necessary to have opposite biasing forces operably attached to the Braille dot  20  in a manner such that the Braille dot  20  can be extended and retracted in response to signals from the microcontroller  40  or module microcontrollers  45 . 
     While the preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in this art that various modifications may be made in these embodiments without departing from the teachings of the present invention.
A refreshable Braille display comprising a plurality of Braille dots that extend and retract arranged in Braille characters such that the Braille dots are operable as a personal computer monitor allowing a blind person to discern the information displayed thereon by reading the Braille characters formed by the extended Braille dots. At least one microelectromechanical device operably connects to the Braille dots such that the Braille dots retract and extend based upon the operation of the microelectromechanical device.