Abstract: Apparatus is disclosed for use with typewriters of the type having trip hammers and is adapted to receive combinations of electrical signals which uniquely define the respective characteristics and to decode the electrical signals to selectively activate the trip hammers of the typewriter. The apparatus has a number of coded plates located adjacent one another in general alignment, with each of the plates having a number of transverse slots at one edge thereof at predetermined positions. Lateral or longitudinal movement of the elongated plates between first and second positions in response to receiving appropriate electrical signals causes the slots to be either into or out of alignment with an activating member which effects triggering of the trip hammer of the typewriter. Any one of the coded plates having a slot in a nonaligned orientation will prevent activation of the particular hammer.