Question

A simple security system for two doors consists of a card reader and a keypad.  


A person may open a particular door if he or she has a card containing the corresponding code and enters an authorized keypad code for that card. The outputs from the card reader are as follows:

A B No card inserted 1 0 Valid code for door 1 1 1 Valid code for door 2 0 1 Invalid card code 0 0
  

To unlock a door, a person must hold down the proper keys on the keypad and, then, insert the card in the reader. The authorized keypad codes for door 1 are 011, 101 and 111, and the authorized keypad codes for door 2 are 001, 010, 100 and 111. If the card has an invalid code or if the wrong keypad code is entered, the alarm will ring when the card is inserted. If the correct keypad code is entered, the corresponding door will be unlocked when the card is inserted.

Design the logic circuit for this simple security system using 4 x 1 Multiplexers. Your circuit’s inputs will consist of a card code A and B, and a keypad code C, D, and E. The circuit will have three outputs X, Y, and Z. If X or Y is equal 1, door 1 or door 2 will be opened; if Z is equal 1, the alarm sound.

Answer 1

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