Electrical – Design a sequence detector to detect 1001 or 11

Here's a hint: The states in your state machine are not associated with the binary codes representing the key inputs, they're associated with the number of correct numbers entered so far. You start out in an initial, or "reset" state, in which no valid keys have been entered so far, and then proceed to states representing 1 valid key entered, 2 valid keys entered, etc. until you get to the final state with 5 valid keys entered. In the last state, the output is 1; in all others it's 0.

In each state, if the next valid key is entered, you proceed to the next state; otherwise, you go back to the initial state.

Being kind of old myself, I expect you to study like #### too. :D

One question may help clarify the circuit you need : how does it distinguish between 2 successive states that are the same? Or alternatively : Is there a separate clock signal, not mentioned above? If so, the basic pattern of the circuit may become clear.

Ask yourself :
how many states do you have?
how many bits are required to implement all these states?

You have already given each state a unique number : it will help to write those numbers out in binary as part of each state table.

Then treat each bit of that number separately : first create a Karnaugh map for the next state for bit 0. What are the input variables for that KMap?