Punched card technology

A medium for feeding data into a computer, essentially a card punched with holes or notches to represent letters and numbers or with a pattern of holes to represent related data. Also called Hollerith card.This definition is old now the definition is another one with code lock implementation.punched cards can be used as door-open cards provided there is a ckt designed to decode the code using any logic the coding can be done in a number of ways as in the case of program encryption.
A simple punched card-reader mechanism can be emulated with the help of an array of LED -LDR pairs connected so as to make the card an intermediate b/w the pairs .ie card can be inserted in b/w these two to open the door.presence or absence of a hole can be detected by the ldr very easily.
But the reader will be a bulky one to make this compact we may use some approximations with the ldr array we can process the signals from ldrs and find some real number corresponding to the punches and their positions.

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