This project presents the design of a digital pattern lock system built entirely using basic logic gates and flip-flops. The lock system uses a keypad with keys labelled 0 to 9 as inputs, where each pressed key sends a decimal signal. The first stage of the circuit is the Decimal to Binary Converter, which is implemented using OR gates. This circuit converts any pressed key into its corresponding 4-bit binary code, labelled as a, b, c, and d. These binary outputs serve as the main inputs for the pattern recognition logic, making it possible to process decimal key presses using simple binary logic circuits.

The converted binary [Figure 1] signals are fed into the pattern matching logic circuit, which is constructed from a combination of AND, OR, and NOT gates along with D flip-flops. These flip-flops act as sequence detectors, storing the pattern entered by the user and checking it against a preset password pattern saved within the gate logic. The circuit advances through each step of the pattern as the user presses keys, controlled by a clock (Ck) input that synchronizes each key press. If the user enters the correct key sequence, each flip-flop transitions through the right states until the final correct state is reached.

The lock circuit also includes a reset mechanism that clears all states if an incorrect key is pressed or if the reset button is activated. This ensures the system is ready for a new pattern input without any leftover state errors. When the user successfully enters the correct pattern, the final output signal y goes high, which can then be used to trigger a door lock mechanism or an indicator light. By using only fundamental logic gates and flip-flops, this project offers a clear and hardware-based solution for secure pattern-based locking, eliminating the need for microcontrollers or programmable logic devices.