Passcode-Security-System

The main objective of this project is to provide a passcode based security system having the provision to change the passcode by the authority only, using XOR Gates as bit comparators and NOR Gates as controlled inverters. This proposed system will provide a user friendly security system for organizations and homes. If the passcode entered is right, it is indicated by a LED. Any wrong attempt to open the door (by entering the wrong password), an alert will be actuated, indicated by another LED. This circuits the uses XOR gates as bit comparators. Four of these XOR gates compare the respective bits of two 4-bit binary numbers, each number “entered” into the circuit via a set of DIP switches. If the two numbers match, bit for bit, the green “Go” LED will light up when the “Enter” pushbutton switch is pressed. If the two numbers do not exactly match, the red “No go” LED will light up when the “Enter” pushbutton is pressed. Because four bits provides a mere sixteen possible combinations, this lock circuit is not very sophisticated. The “key” code that must be matched at the data entry switch array should be hidden from view. If this were part of a real security system, the data entry switch assembly would be located outside the door and the key code switch assembly behind the door with the rest of the circuitry. It is the nature of an XOR gate to output a “high” (1) signal if the input signals are not the same logic state. The four XOR gates’ output terminals are connected through a diode network which functions as a four-input OR gate: if any of the four XOR gates outputs a “high” signal—indicating that the entered code and the key code are not identical—then a “high” signal will be passed on to the NOR gate logic. If the two 4-bit codes are identical, then none of the XOR gate outputs will be “high,” and the pull-down resistor connected to the common sides of the diodes will provide a “low” signal state to the NOR logic. The NOR gate logic performs a simple task: prevent either of the LEDs from turning on if the “Enter” pushbutton is not pressed. Only when this pushbutton is pressed can either of the LEDs energize. If the Enter switch is pressed and the XOR outputs are all “low,” the “Go” LED will light up, indicating that the correct code has been entered. If the Enter switch is pressed and any of the XOR outputs are “high,” the “No go” LED will light up, indicating that an incorrect code has been entered