This problem represents a phone pad and a traffic light. The phone pad consists of the numbers $0-9$ along with the pound and star key. The traffic light has three inputs for the red, yellow, and green lights.

Create a circuit for a combination lock. The keypad is used to open the lock by pressed the correct digits in order. The traffic light is used to indicate the current state of the lock:

Locked or Error $=$ Red

Entering Combination $=$ Yellow

Unlocked $=$ Green

The combination is binary consisting of only $1\text{'}$s and $2\text{'}$s$.$ The combination for this lock is: $222211!$

Pressing the $*$ button on the keypad $($output code $0$b$1010),$ resets the circuit to a locked state and ready for the user to enter the combination. The light is red. When the first combination number is pressed $(1$ or $2),$ the light turns yellow and says yellow as long a the correct combination is being entered. Once the entire correct combination has been entered, the light turns green, indicating the lock is open.

As an example, the user would press $*$ to reset the lock. The light is red. They press $2,$ the correct first digit and the light turns to yellow. They then press $2,$ the correct second digit. The light says yellow. If the next four digits are correctly entered, the light turns green.

At any point, if the user enters an incorrect digit $(1$ or $0),$ the light turns red and further digits are ignored until the next time $*$ is pressed. If the lock is unlocked, pressing any digit or $*$ locks it again. The digits $0,3-9,$ and # are ignored.

You can choose to accept the combination $(1$ or $2)$ either when the button is pressed or when it is released. Either will be acceptable. The only difference is inverting the clock input on your flip$-$flops, but clocking on the trailing edge makes it easier to tell what is going on in your circuit.

There are three main tasks required to solve this problem. The keypad output needs to be converted into a reset signal, clock for the state machine, and a single bit indicating which button has been pressed. A state machine is needed to that will recognize the combination. Finally, some logic is needed to convert the states into the color inputs for the traffic light.

PLEASE DRAW$/$CREATE THE CIRCUIT DIAGRAMS ALONG WITH THE LOGIC GATES FOR EACH TRAFFIC LIGHT COLOR STATE. This will help me understand the circuit better for this lock circuit.