I have worked on this for a while, and made an OR-NOR-AND Combination lock in minecraft.
It has two rows of 4 levers, one on top of the other, with a space of gap in between each lever in a row, and two spaces of a gap between rows, for a total input board size of 7X4 Blocks Code is set by placing redstone torches behiind levers in some areas, and not in others.
When the code is set for a row, the output is off. Both rows output to a NOR gate, which is an anti glitch measure. The NOR gate goes to an AND gate, where i can lock using safety lever placed at one of the AND gate inputs, with the output of the NOR gate on the other input, that way, if someone knows the code, they can't get in anyway while I am there, unless i am letting them. It is still a work in progress. My next one will be an order compliant lock, possibly using RS Latches.
If anyone wants the save file, just PM me your Email and I will send you the zip File