This machine is basically a shift register that has been modified to become a combination lock. When you enter a number it saves it to the ones place in 4 bit binary. When you enter the next number it saves the first number you entered to the tens place and the number and the second number to the ones place and so on. This machine goes to the hundreds place. It displays whatever you entered on a redstone lamp 7-segment display. When the correct combination is inputted and you press the enter button, the lock will be toggled. There is also a clear button that clears your input. I was thinking about adding a circuit that locks you out if you press enter to many times without getting a correct combination, but the wiring is a little clustered already and I don't want to make it more so. It can also have multiple combinations that do different things (This machine has 2 but only 1 is fully integrated). There are technically 1331 possible combinations if you count a blank as a possible number in the combination, but if you don't there are only 1000. I also built with the intention of making it plausible to build in survival, which if you made a smaller version, it could definitely be done.
If you want to enter 351 first you press 3 then 5 then 1. If you want to enter 789 you would press 7 then 8 then 9. Pretty much common sense. You then press enter and if the number you enter was the correct combination, the lock (represented by a lamp) will toggle on or off. when you want to leave or enter something else you press clear.
Comments
Mistake
On the name and current rank I forgot to say that my rank is Learner