First character detector for paper tape reader

1,022,187. Punched tape readers; magnetic tape stores. SPERRY RAND CORPORATION. Sept. 3, 1963 [Sept. 13, 1962], No. 34751/63. Headings G4C and G4M. In an arrangement for reading a punched tape, which may also be applied to reading magnetic tape, a block of data is selected from the tape by means of a presettable counter and no row of data is read unless it is preceded by a blank space on the tape, this latter being effective to eliminate the effects of tape stretching and inaccurate braking. A sensing element, e.g. a photo-cell, is provided for each data-hole position 104 and for the associated sprocket-hole 102. The presence of a gap is signalled by OR gate 130 and inverter 136 to set bi-stable circuit 188. The " 1 " output of this circuit enables AND gate 170 through OR gate 174, and provided the control inputs to gate 170 are present, a following sprocket-hole pulse is passed by gate 170 to trigger 250 Á-sec. monostable circuit 178. The output of this circuit resets bi-stable circuits 188, 182, the latter then providing one input to gate 184, and also directly inhibits gate 184 for 250 Ásec. A third input to gate 184 is provided by a bi-stable circuit 206 which is reset at the same time that counter 194 is preset to a predetermined count. The remaining inputs to gate 184 are from the central control 172, and in normal operation gate 184 provides an output to open gates 162-167 to pass the delayed outputs from the sensing elements. Each output pulse from gate 184 also enables gate 212 to pass a delayed sprocket-hole pulse to counter 194, and after the predetermined number of rows of data have been read, counter 194 sets bi-stable circuit 206 to close gate 184 and set bistable circuit 182 ready for the next block of data. Owing to the fact that a blank space must be detected before any further data can be passed through gates 162-167, the last row of one data-block is not mis-read as the first line of the next block if the tape is stopped at or creeps back to this row at the end of reading the first block. In addition the first row of a block is not read out until its associated sprocket hole is sensed, so that even if the tape is stopped with the first part of holes 104 in register with the sensing elements, read-out does not take place until after the sprocket hole has been sensed.