Lock Decombinator

From NerdLab Projects

May 9, 2022

Step screenshot

 Updated at: May 10, 2022

A fun exercise to brute for a master lock combination if you forgot it.

This has been an idea of mine that I have wanted to build ever since forgetting a combo for one of my locks. Yes I know there are ways to limit the amount of combinations down to a manageable amount, but what fun is that?

Tools Used:

Materials Used:


First prototype

Very first prototype from years ago that was more or less a fail do to lack of programming/design/building skills

Current iteration

New successful end product 

Opening a lock




How to use

After wiring it all up and starting the Arduino, use the right button switch to move the combo until it is on 0. Once there, you will click the other switch to start the decombination. The LCD screen should show which combo it is trying and display the last combo tried if it opens the lock.




Browse to your Arduino sketch directory, and clone this repo into a subdirectory called decombo, e.g.,

cd ~/Arduino
git clone https://github.com/BluGeni/decombinator.git decombo

Then, launch Arduino, load up the decombo sketch from your sketchbook, and click “Verify”.

Note: VSCode can be configured to have way more passive dev-friendly features for Arduino.

Things learned/Struggles:

  • Pins 2 and 3 are the only pins you can use for interrupts.
  • There are 2038 steps per rev in the stepper motor I used – not 2048 like some tutorials said.
  • If your stepper motor is not super strong, attempting to open the lock will sometimes move the number a half number.
  • Ran into a lot of memory issues with all the combinations as a String array. Fordi helped me solve that.



View Github