Why was "tantrum" trending last week?
(Or "refreshable braille display", "refreshable display") An electromechanical device that renders braille with tiny, independently controlled pins used to represent the state of dots in braille cells. Each pin, in its "on" state, raises above the top of its hole in the screen; in its "off" state, it drops below the top of its hole. Older systems used tiny solenoids to control the state of the pins; modern systems are piezoelectric.
Typical dimensions of a braille display are 1 line of 40 cells, each cell of two-by-eight dots.