a dot - type printer of the type using printing pins or wires is improved by employing a driving system which includes a variable - volume sealed container enclosing a pressure transmitting medium . electrodes are disposed in the medium and are closely spaced such that the application of a high voltage will cause arc discharge across the same . the discharge energy applied to the medium causes an expansion of the medium , which in turn causes an expansion of the sealed container . the printing pins or wires are abutted against a movable membrane or bellows portion of the container , so that container expansion effects linear movement of the pins or wires .