Fun Projects for your LEGO MINDSTORMS NXT!

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Combination Lock Box
Building: Advanced
Program: Expert

Building Instructions


Start by building the Dial Remote Control (Click the picture for building instructions).

Building Instructions











Close the box, then turn it upside-down to attach the lock motor as shown below.



Connect one wire from the box lid motor to port B on the NXT. 

Connect the other wire from the lock motor to port A on the NXT. 


Insert the balls, and close the box.  Then turn the gear on the lock motor with one hand, and guide the locking pin into the center hole of the cross beam with the other hand.
Unlocked Locked

Combination Lock Box Programming

Use the LockBox program for the Combination Lock Box.  The first time the program is run on your NXT, it will ask you to choose and set your combination.  To enter a combination, turn the dial wheel to choose a number 0-50, then press the Enter (orange) button on the NXT to select that number.  After you enter the three numbers, your combination is set, and the NXT will remember this combination even when the NXT is turned off (by using a data file).  To open the box, enter the combination the same way you set the combination.

If you forget your combination, or if you want to change it, run the LockBoxReset program, which will clear the combination, and then the LockBox program will ask you to set it again the next time it is run.


  • Can you modify the lock box to make it stronger and more resistant to forced entry?  

  • Can you use other LEGOs you have to design a box that keeps the contents totally hidden from view?

  • Try using the LockBox program to control another combination lock device of your own design.

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