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INTRODUCTION
More than 90% of the world’s 161 million blind and visuallyimpaired people live in developing
communities. Despite the importance of literacy to employment, social well beingand health, the
literacy rate of this population is estimated at below 3% . Braille, the primary method of reading
and writing for the blind, is a tactile system in which embossed dots representing letters,
symbols, and numbers can be read with the fingers. A Braille letter is formed by embossing
somesubset of six dots arranged in a 3 2cell. Figure 1 shows schematics of a Braille cell and a
photograph of a page of Braille. For the blind, literacy in Braille is often the key to independence
in home and at work. It is said that the system has “liberated a whole class of people from a
condition of illiteracy and dependency and has given them the means for self-fulfillment and
enrichment”
The idea behind the Universal Braille System started in 1821 by Louis Braille . In 1829, Braille
developed the Braille System. Since then, the Braille system has become the most adopted
system for written communication for blind and visually impaired individuals .The Braille
system is a method which translates letters to a combination of dots in order to help individuals
with sight defect read documents. This system consists of three grades and two methods of
representing the characters. The grades are introduced in the Braille system to make the reading
of documents more dynamic and faster. The two methods are either using a six-dot cell or an
eight-dot cell. In addition to the grades, there are four Braille codes. The codes are the Literary
Braille Code, the Nemeth Braille Code, the Computer Braille Code.
To this date, there are no other practical means that re- places this system. Using Braille, blind
individuals can read a character by touch. The individual can read a Braille character by rolling a
finger over its six-dot or its eight-dot representation. The combinations of these dots are
specifically formed by raising the pins to represent a certain letter or symbol. A Braille reader
can learn how to read Braille characters by first learning the position of the dots on the cell, and
then by memorizing the representation of all the letters, numbers and characters.
LITERATURE REVIEW
In the past two decades, several Braille System Output Devices were developed to help the blind
and visually impaired individuals interact with computers. In the late 1990’s, a device called
Braille Lite was developed by Blazie Engineering (Windermere House, Kendal Avenue, London,
England) . It has the ability to represent up to 18 characters and is refreshable; characteristics that
help visually impaired individuals to skim a text document more easily. However, its price made
it difficult for all visually-impaired and blind individuals to acquire it. In order to give blind
persons the ability to read characters easily, Telesensory (Bukit Batok Crescent, Pres- tige
Centre, Singapore) developed a device called Optacon. Optacon is a device that prints the regular
shape of the letters, and enables the readers to feel the letter and thus read it. This was done by
using vibrating metal rods that are moved over a printed page, converting the image of the letter
into a tactile form. The main drawback of the Optacon is that it was not very practical, and it
would take a visually-impaired person a very long time to skim a text document.
In 2001, the Palm Braille was developed by Scott Stoffel. It is a device which
connects to the parallel port of the computer and has the ability to read the characters from a file
in order to output them. The users of the de- vice can sense the six pins on the device and know
which letter they are reading. The problem of the Palm Braille is that it was only able to read one
character at a time . To make reading easier and the time spent by users more efficient,
Benetech® (California Avenue, CA, USA) translated more than 7000 books into Braille
language and made them available online. This action helps the blind or visually-impaired
individuals to print out a book using Braille printers and read it on papers easily, but it does not
help others who wish to read books that are not available online .
BLOCK DIAGRAM EXPLANATION
The block diagram of braille tutor system consist of mainly two parts, one is the input section
and other is the embedded section. The input section mainly consist of a ps2 keyboard and a
microcontroller to interface the letter generated by the keyboard to zigbee module, the zigbee
module is a wireless technology used to send data over a small distance. The embedded section
mainly consist of zigbee module, micro controller and a braille character generator module or it
is called as braille cell. Here the zigbee module is used for receive the signal that send from the
input section and the microcontroller read the letter that received and process it to generate
braille character to braille module.
Keyboard is connected to Uniboard through PS2 Connector.When a key is pressed
the data is transmitted to UART0 at every falling edge of the clock pulse.
PS2 Connector's data line is given to a port pin of ATMEGA128 and clock pin to the external
INT pin.
Uniboardhas the ATMega 128 MCU. It has two UARTs UART0,1. UART1 is directly
connected to serial port via IC MAX232.
Xbeeis connected to the UART0 interface. MCU transmits data to UART0 and
hence forwarded to Xbee. Detailed description of the data frame format is explained later.
The uNiBoard version 1.1 is an ideal development platform for Embeddedand Real Time
systems programming. Apart from its onboard peripherals,adding some interesting features in
uniboard will make it more usable so that it could be used for various numbers of applications.
Prior aim was to interface keyboard to uniboard, instead making it Wireless will make it
morefascinating. So that it can be used for various remote applications. The objective of project
is to display the characters typed using keyboard fromtransmitter side, on UART or LCD of
receiver side. Zigbee PRO OEM module is chosen for this application as it was best suitable for
the purpose. Data from keyboard is given to microcontroller and transmitted via zigbee. Receiver
will receive data and process it. The data can be displayed on gtkterm/lcd or some modification
could be done to display it on Text editor.Remote applications can be controlled using this
wireless keyboard and adding RTOS features to it will make it more usable.
AT KEYBOARD
Let get through Keyboard theory. The IBM keyboard sends scan codes to computer. The scan
codes tells Keyboard Bios, what keys have been pressed or released.Take for example the 'A'
Key. The 'A' key has a scan code of $1C. When the 'A' key is pressed, keyboard will send $1C
down it's serial line. Holding it down, for longer than it'stypematic delay, another $1C will be
sent. This keeps occurring until another key has been pressed, or if the 'A' key has been
released.However keyboard will also send another code when the key has been released.Take the
example of the 'A' key again, when released, the keyboard will send $F0 to tell you that the key
with the proceeding scan code has been released. It will then send 1C, so you know which key
has been released.
SCAN CODE
The diagram below shows the Scan Code assigned to the individual keys. The Scan code is
shown on the bottom of the key. E.g. The Scan Code for ESC is 76. All the scan codes are shown
in Hex. As you can see, the scan code assignments are quite random. In many cases theeasiest
way to convert the scan code to ASCII would be to use a look up table. Below is the scan codes
for the extended keyboard & Numeric keypad.
Schematic diagram of input section is shown above. Keyboard is connected to MCU using
female PS2 connector. Data pin of the PS2 isconnected to the 0th pin of PORT C. Clock pin is
connected to external interrupt pin INT7 of MCU. Other two connections are ground and VCC(
+5 volt). This data is then transmitted to UART0 on which RF Module Xbee is connected. As
Xbee works on supply volt of 2.83.3V, it is given through a external batter source. The
transmitter pin of UART0 provides +5v so a voltage divider circuit is used to drop the volt to
required range and given to Din pin of xbee. Rx pin of UART0 is directly connected to Dout pin
of Xbee, as any voltage above 2.7 volt is considered as logic 1 byMCU.
The software flow of input section is as shown:
Algorithm is working in that way: Keyboard actions are handled by INT7 interrupt.The
algorithm is quite simple: Clock line is connected to one of interrupt pins INT7. Theinterrupt will
be executed every falling edge of clock cycle.The value of the data line isstored in a buffer at
every falling edge of the clock pulse of the keyboard. The frameconsisting of 33 bits(3 frames of
11 bits). First frame of 11 bits consists of scancode of keypressed and next two frames are the
break code of the key, which is $F0 along with thescan code of key pressed. After all 33 bits are
received the data is given to UART0 andfurther transmitted to Xbee.
The main task of the input section application software can be divided into three parts:
1. Read the PS2 bus
2. Transmit a keycode byte
3. Receive an acknowledgement
This partitioning is important because of the way that it separates PS2 bus access from the
interrupts that accompany the transmit and receive activity. Between transmitting keycode bytes,
the application disables the PS2 bus. Since the keyboard scanner still functions, key presses are
detected and loss of service is avoided. However, during a PS2 bus read, it is important that the
sensor board application is not interrupted. Essentially, the PS2 bus interface is implemented as a
software UART – the clock and data lines are polled, and data bits are interpreted one at a time.
If this process were to stop mid-sequence, as would happen if a ZigBee stack interrupt occurred,
then it is highly likely that a (worst case) 30 μs clock half-cycle would be missed, probably
resulting in a corrupt data read. One possible way to avoid this conflict would be to ‘ring fence’
the PS2 bus read by making it a critical section and disabling interrupts. However, this approach
suffers from the obvious limitation that the ZigBee protocol stack would then be processor
limited, possibly leading to loss of the connection. A better approach is to maintain a ‘loose’
synchronisation between the application’s activities and those of the protocol stack – by
transmitting data only on completion of a PS2 bus read, we can be certain that any subsequent
protocol interrupts will occur while the PS2 bus is inhibited. This separation of application task
interrupts and protocol stack interrupts is central to the design of the wireless keyboard
application.
ZIGBEE PROTOCOL:
Data enters the XBee Module UART through the DI pin (pin 3) as an asynchronous serial signal.
The signal should idle high when no data is being transmitted. Each data byte consists of a start
bit (low), 8 data bits (least significant bit first) and a stop bit (high). The following figure
illustrates the serial bit pattern of data passing through the module. The XBee UART performs
tasks, such as timing and parity checking, that are needed for data communications. Serial
communication consists of two UARTs configured with compatible settings (baud rate, parity,
start bits, stop bits, data bits).