Here’s a twist on the old practice of geocaching: a Reverse Geocaching Puzzle Box! Alternet presents a puzzle box containing a geocache prize which only opens when it is in the correct geolocation.
This fairly complex, novel project uses a PIC 18F*39 microcontroller (exact part not specified on schematic) interfaced with a 2×16 LCD to show distance to target and a servo to open the box when the attached GPS corresponds to the target location. A button near the display gives you up to 50 tries to check if you’re in the correct location. Source code in C is included. (Of course, since the target lat/long are hardcoded in main.c, you would have to change these to your desired target location.)