Carter Minear's "Lock Decombinator" Pops Master Locks with a Couple of Motors and an Arduino

DevOps engineer and hobbyist Carter Minear's latest project is designed to put the screws on rotary combination padlocks — by "decombinating" them via a 3D-printed jig and an Arduino-compatible microcontroller board.

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

Designed with Master-brand rotary combination padlocks in mind, and using knowledge of combinations that can't physically be set, the Lock Decombinator holds its target in a 3D-printed jig. A digital servo motor connects to the rotary dial on the lock and begins entering combinations, while a stepper motor tests to see if the shackle has been released for each. If not, the system moves onto the next combination.

Building on an earlier wooden prototype, the 3D-printed version is surprisingly slick — though shaped exclusively for Master locks. The system is driven from an Arduino Uno-compatible microcontroller development board, while the electronics are soldered onto prototyping board — and an on-board display is included to read off a successful combination.

"After wiring it all up and starting the Arduino, use the right button switch to move the combo [dial] until it is on 0," Minear explains. "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."

More information on the project is available on Minear's website, while the full source code and 3D print files have been published to GitHub under the reciprocal GNU General Public License 3.