874 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



lar C\SP, the cards representing destinations. The capacity of a single 

 machine is about 1000 cards. The cards are lined up in a box as in a liUng 

 drawer, with tabs along the bottom of the cartl resting on select bars 

 which run the length of the box. One-hinidred and eighteen holes are 

 punched out in all cards in fixed positions so that in the normal condition 

 118 tunnels are formed from one end to the other. A light source at one 

 end of the box shines through the tuiniels upon phototransistors (Fig. 5) 

 at the other end but the phototransistors are disabled until, concurrently 

 with the dropping of a card, voltage is applied to them. 



All tabs along the bottom of the card are cut off except those which 

 serve to identify the particular card. When a code is presented to the 

 machine a combination of select bars corresponding to the code is 



Fig. 5 — Transistor. 



