Editing Refreshable braille display (section)

==Mechanical details==
[[File:Baum David System 90 (cropped).jpg|thumb|A Baum David System 90 special-purpose computer for the blind, with a braille "screen" and special keyboard]]
The base of a refreshable braille display often integrates a pure braille keyboard. Similar to the [[Perkins Brailler]], the input is performed by two sets of four keys on each side, while output is via a refreshable braille display consisting of a row of electro-mechanical [[braille cell|character cells]], each of which can raise or lower a combination of eight round-tipped pins. Other variants exist that use a conventional [[QWERTY]] keyboard for input and braille pins for output, as well as input-only and output-only devices.

The mechanism which raises the dots uses the [[piezo effect]] of some crystals, whereby they expand when a voltage is applied to them. Such a crystal is connected to a lever, which in turn raises the dot. There has to be a crystal for each dot of the display (''i.e.'', eight per character).

Because of the complexity of producing a reliable display that will cope with daily wear and tear, these displays are expensive. Usually, only 40 or 80 [[braille cell]]s are displayed. Models with between 18 and 40 cells exist in some notetaker devices. 

On some models the position of the [[cursor (computers)|cursor]] is represented by vibrating the dots, and some models have a switch associated with each cell to move the cursor to that cell directly.