A Braille display is a device, typically attachable to a computer keyboard, that allows a blind person to read the contents of a display one text line at a time in the form of a line of Braille characters. Each Braille character consists of six or eight movable pins in a rectangular array. The pins can rise and fall depending on the electrical signals they receive. This simulates the effect of the raised dots of Braille impressed on paper. There are usually 40, 65, or 80 arrays (characters) per line of text, depending on the device. Less expensive devices display fewer characters per line, and require the user to read the standard 80 characters of a normal text line in several readings.
A Braille display operates on either electromagnetic or piezoelectric principles. When currents or voltages are applied to points in each six-pin array, various combinations of elevated and retracted pins produce the effect of raised dots or dot-absences in paper Braille.
In the electromagnetic Braille display, each pin is surrounded by a cylindrical casing that contains a coil. The pin is attached to a spring, and also to an iron rod passing through the casing. This forms a miniature solenoid. When a current passes through the coil, the pin is pulled inward. Thus when there is no current, the pin is elevated, corresponding to a raised dot in Braille; when there is current in the coil, the pin retracts, corresponding to the absence of a dot.
In the piezoelectric display, each pin is mounted above a piezoelectric crystal with metal attached to one side. If a sufficient voltage is applied to the crystal, it becomes slightly shorter. This causes the metal to bow upwards, raising the pin. Thus when there is no voltage, the pin is retracted, corresponding to the absence of a dot in Braille; when there is voltage across the crystal, the pin is elevated, corresponding to a dot.
When used in conjunction with a Braille keyboard, the Braille display makes it possible for a person to operate a computer - read the display, send and receive e-mail, and browse the Web. Other approaches instead of or in addition to the Braille display include voice recognition and speech synthesis technologies.