PUNCHED_TAPE_READER

Published:2009/7/6 6:06:00 Author:May | From:SeekIC

Connection of 555 timer as Schmitt trigger produces output pulses with sharp rise and fall times that are independent of tape speed. Output is compatible with TTL or CMOS circuits. When scanning light beam hits hole in punched card or tape, resistance of light-sensitive resistor drops sharply and voltage at pins 2 and 6 rises above 0.67 VCC. Voltage at output pin 3 then drops sharply from VCC to 0 V. When PC1 goes dark, circuit switches rapidly back to original state. Reverse PC1 and R1-R2 for positive edge-triggered logic.-S. Sarpangal, 555 Timer Implements Tape Reader, EDN Magazine, Jan. 5, 1978, p 86 and 90.



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