A Braille terminal, also known as a refreshable Braille display is a mechanical device used to display Braille characters. This is usually done by raising dots through holes located in a flat surface. The device enables blind computer users, who are unable to use a normal monitor to read textual output. Braille displays are often used alongside speech synthesizers and many blind users switch between the two systems or may use both at the same time. Due to the complexity of manufacturing a reliable refreshable display that's able to cope with constant useage, the displays can be expensive. Most types of refreshable braille terminals use display between 40 to 80 braille cells. However it is possible to get a braille display with a differing number of cells in some notetaker devices. Some models come with the ability to relay the position of the cursor by vibrating the cells, some models also allow the user to move the cursor directly to the desired cell.
How Braille Displays work
For most models the mechanism used to raise the effect uses something known as the piezo effect of certain crystals. This means the crystals will expand when a voltage is applied to them. These crystals are in turn connected to a leaver which then raises the dot. Each dot on the display requires a crystal. The software used to control the display is known as a screen reader. The screen reader is used to gather the content from the screen by communicating with the computer's operating system. It then converts the content into braille characters and transmits the information to the display. As many computers now use graphical operating systems, screen readers have become increasingly complex in order to display graphical elements such as slidebars or windows in a textual format. Many operating systems now come with an interface which can help screen readers obtain this information, like MSAA for Microsoft Windows.
In 2000 a new development, known as the rotating-wheel Braille display was created. In this system Braille dots are placed on the edge of a spinning wheel. This allows the user to read text continuously using a stationary finger as the wheel spins round at a selected speed. As the Braille dots are set in a fairly simple scanning-style and the Braille characters are set by an actuator, the cost and complexity of manufacturing a unit is reduced greatly. Although the units are currently still under development, when they eventually reach production they should be much less expensive than traditional Braille displays.