I created a combination lock in witch you need to open and close a door to activate. I also added in a feature to select the combination you would like.
If you guys would like to see me making these devices right from start to end, then just tell me and I'll start doing that.
How it works:
Placing the redstone torch will activate/ dis-activate the block update detector and/ or reset the combination lock.
This feature will allow you to choose specifically when you would like actual have access to the secret room, stop noisy pistons, and keep the fact that you have a hidden room a little bit more secret. When the BUD switch is not activated, the door will function as a simple wooden door.
Now because I have a door under the BUD switch, the door is what will be toggling thing BUD switch every time I open and close it.
Each pulse of the BUD switch will go into a ringcounter and like I just said, every time I open and close the door, it will activate the BUD switch because opening and closing a door is a form of a block update.
A ringcounter is a device that will allow you to choose up to about 5 outputs.
Knowing that, I simply put a redstone torch under the output I want the piece of stone to end on and set the place I want the stone to start. Now, all I have to do is open and close the door to change the output of the ringcounter.
Because the changing of the ringcounter is not random, I am able to set how many times I need to open and close the door to actually get the stone to be on top of the redstone torch to complete the combination lock.
To set what combination I would like, I simply place torches under all the possible outputs the ringcounter has (except for the output the stone resets too).
I can then use some levers to turn on/ off each redstone torch changing the position the piece of stone will need to be on to actually complete the combination lock.
Now all that is left is the resetting system.
I just add a delay to the pistons in the ringcounter and set it up so the piston that I want the stone to start at will grab the stone.