Objective: Design and implement a special purpose system that allows access to doors 1 and 2 (D1 and

D2 respectively) by persons who have been given a valid four-bit binary code. The code is entered using

four switches: A, B, C, and D. Each valid switch can be set to 0 or 1. The system gives access to doors

according to the following scheme:

a) D1 if 0101 or 1110 is entered.

b) D1 and D2 if 0111 is entered.

c) D2 if 0100 is entered.

Derive your truth table and simplify your circuit.

Implement your circuit only using NAND gates.