Electronic Cardlock System
by Vijay D. Sathe
The circuit presented here can be used as a lock for important electronic/electrical appliances. When card is inserted inside the mechanism, depending upon the position of punched hole on the card, a particular appliance would be switched on.
The card is inserted just like a floppy disk inside the disk drive. This card should be rectangular in shape with only one punched hole on it.
The Circuit uses eight photo-transistors (T1 through T8). When there is no card in the lock, light from incandescent lamp L1(40watt), 230V)falls on all the photo-transistor detectors. Transistor T8 is used as enable detector for IC1 (74LS244). When light is incident on it, it conducts and its collector voltage goes low. This makes transistor T16 to cut-off, and its collector voltage goes high. This logic high on its collector terminal will inhibit IC1 as long as light is present on photo-transistor T8.
IC1 will get enabled only when the card is completely inserted inside the lock mechanism. This arrangement ensures that only the selected appliance is switched on and prevents false operation of the system.
You can make these cards using a black, opaque plastic sheet. A small rectangular notch is made on this card to indicate proper direction for insertion of the card. If an attempt is made to insert the card wrongly, it will not go completely inside the mechanism and the system will not be enabled.
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