For a good friend, I decided to make a GPS puzzle box, also known as a reverse geocache box. We have both shared an interest in electronics, how things work, and challenges. Not only is the box a puzzle to get open, but once it is open, he has a PIC based board with a GPS module, LCD screen, button, and an RGB LED that he can hack and make his own project, in addition to the contents of the box.
The GPS puzzle box is much like a treasure box, except that you are carrying the treasure inside of a locked box. The box only unlocks once a series of waypoints have been visited. The box looks like any other box, except it has an LED display and a single button. When the single button is pushed, a message displays greeting the treasure hunter and then proceeds to give a hint to the next waypoint. In my case, the box gives the distance from the waypoint. If the person is close enough to the waypoint, the waypoint is marked as visited and a clue to the next waypoint is given. Once all of the waypoints have been visited, the box unlocks itself, allowing the person to open the box and receive its contents.
In theory, the box is simple. It consists of a mechanized locking mechanism, a microprocessor, and a GPS module. However, in practice, as usual, the implementation is much more complicated. For this box power conservation is key, once the battery goes dead, it could be locked forever. When the button is pushed, it activates a small circuit which then powers the microprocessor. Then microprocessor then powers each of the other modules, as they are needed, and cuts their power, and eventually power to itself, as appropriate. In the power downed state, the circuit draws an extremely small amount of power.
If you would like more details about my implementation, please let me know in the comments below.
Below are pictures of the nearly completed box.