I was intrigued by Mikal’s article on his Reverse Geocache Puzzle Box from Make issue 25. This is a box which will open only in a very specific place (as determined by its internal GPS system). The LCD display shows how far the place the box will open is from the current location. You can find Mikal’s story about his puzzle box in the article and on the web. In Mikal’s example, there was one very precise place the box would open. I planned to have several places my box would open and it would only display the distance to the closest one. I could have substituted other components but I particularly liked the blue lit button (which Adafruit just began offering recently). I ordered the various parts and bought one of Mikal’s unpopulated boards. I got the box from a local World Market. The longest wait was for the precise button and LCD that were used since these shipped out of China. But eventually everything arrived and I set out to build it. I wanted to get the cutout for the LCD in the top of the case done neatly so I unscrewed the top of the box and used my CNC machine to make the precise rectangular cut needed.
The trickiest part of the build involved positioning the elements in the top of the box in a suitable configuration and designing the locking mechanism. I worked to make sure the Arduino’s USB jack was positioned so that one of the longer USB plugs could actually reach it through a hole from the outside of the box — this provided a way to open the box electronically should the power fail or GPS reception be lost. I found that a brown ceramic magnet virtually perfectly plugged the hole making it look somewhat less obvious. The components were fastened down with small screws (from a craft store), wires by thumbtacks, and the locking blocks with wood glue. The hardest part to hold down was the servo but eventually it held with hot glue after roughing up the surface a bit.
The first video shows the mechanism in action.
The second video shows what the box looks like from the outside when attempting to open it. The time to get the reading isn’t bad considering the box is getting the reading indoors.
Finally my daughter takes the box outside culminating in the final clip where the box opens.