The three number combination lock on the safe is a classic safe lock - dial 1st number anti-clockwise, 2nd clockwise, 3rd anti-clockwise and if the lock jams solid on a subsequent clockwise turn then the lock is open. If not then try the next number.

The core of the project was a Phidget 57STH56-2804B stepper motor being controlled from a 1067_0B Phidget stepper bipolar HC controller. Mounted on one end of the stepper was a Phidget HKT22 optical encoder using a Phidget 1057_3B encoder interface. The Python program sent the required dial position to the stepper controller and then calculated the theoretical encoder position for that position. If the actual encoder position did not equal the theoretical position then something had physically jammed the lock and the safe was probably open.

As we new little about the lock and run time was not critical we designed the system to run through all combinations sequentially. The lock opened on the 1,018th combo tested. Lucky indeed!