With my boyfriend's 21st birthday coming up, I knew I had to think of something to commemorate another year of this amazing human being on the earth. While browsing through Adafruit's blog section I stumbled across some really cool projects related to geocaching. They were reverse geocaches where instead of being led to a cache, you start with the cache and it leads you to a specific location to find a hint. I decided to take some inspiration from these projects and put my own spin on things.
To create an amazing birthday surprise I had to start planning early. I had the idea in July and my boyfriend's birthday wasn't until October, so I had almost 4 months to brainstorm and build. I had a lot of ideas but landed on something that I was really excited about.
This project is pretty complicated so I'll run you through a quick explanation of everything that went down. It ended up being a regular geocache hunt within a reverse geocache hunt. The physical object is a mysterious clear acrylic box with an electronically locked lid, an LCD, a keypad, and a GPS. Visible, but not accessible until the challenge is complete, is a wrapped present.
top, front, and back views of the finished box (wrapped present not included)
When you turn the box on using the switch on the back, the LCD on the top displays a hello message for a couple seconds and then, if the GPS can't get a fix, tells you that there is no signal.
welcome message that displays when box is turned on
Taking the box outside and letting the GPS connect prints a new message to the LCD telling you to input a code and providing a distance in meters. After figuring out what direction to head in, you can start looking for the first location. Supporting birthday presents included an atlas of the US, a compass, and a pencil for triangulating locations that were too far away to walk to.
When arriving at a location I provided a verbal hint to aid in finding the cache hidden there. Every cache in this hunt had some sort of puzzle associated with it, some were physical puzzles and others were more like brainteasers. Solving the puzzle would present you with a four digit code to input into the box. After inputting the correct code, the LCD prints "Correct!" and then asks for another code and provides another distance to a new location.
all the different caches containing the codes for the box
This find and solve process repeats until you've input all of the codes and reached all 7 locations spanning the University of Delaware campus, Rocks State Park in Maryland and home in Baltimore, Maryland. The final code prints a happy birthday message and opens a small solenoid, unlocking the box.
the happy birthday message that displays when the box is opened
The wrapped present locked inside was a little smart mirror kit that I'd put together using some 3D printed parts, laser cut acrylic, components, hardware, and a QR code to an Adafruit learn module on the project. Going through the whole challenge took us an entire Saturday and was so much fun for both of us to do together. It was great to watch him solve all of the puzzles I had set up and figure out where we were going based solely on distance. Now that you know the end result, I can explain the process of putting the box together.
smart mirror kit
The design for the acrylic box was created in Fusion 360. Included in my design were cutouts for the top for the LCD, its associated potentiometer, the GPS module, and the cable that attached to the keypad. On the back there was a spot for the on/off switch, and on the front I added a latch for the lock mechanism. I didn't create any of the screw holes in my CAD because I wasn't sure exactly how everything would fit together so instead I decided to come around on the tail end and drill them in the correct spot later. After doing some research on different techniques to turn flat acrylic pieces into a box, I decided to go with box joints. Unfortunately, my box was cut out using the wrong thickness of acrylic so the box joints looked a little silly with each of their little overhangs. The lid was also a bit long so I had to cut a sliver off the front. Looking back, I can't remember why I didn't trim off the overhangs on each piece as well. It may have been due to a time constraint, but I think that the little edges give the box character! Assembling the box was a process. I didn't have access to weld-on for acrylic so I went with the super glue method. It worked just fine, but turned out a little messy. With the box made, all that was left was to install the electronics, add some hinges, and figure out the lock mechanism.
For the electronics, I used an Arduino mega, a flat keypad, a slide switch, an Adafruit GPS module, and an LCD. Prototyping was done using a breadboard so that I could catch any mistakes before making things permanent. Unfortunately, the Arduino came with headers preinstalled so I wasn't able to solder anything to it directly and had to rely on plugging the wires in. After designing and testing my circuit, I soldered everything to two separate perf boards. I used different colored wires to brighten it up and make it easier to tell things apart and made sure to have the nice looking stuff facing up and the uglier attachments hidden below. This was a pretty important step in the overall look of the box. Because of the clear housing, the wiring is on full display and so it's important that it looks nice.
wiring inside of the box
Something else I wanted to mention is the secret back door that I included in the box. I wanted to make sure that I could get into the box easily after it had been locked, whether is was to update code or save a wire from falling out of the Arduino's headers (both of which I had to do at least once). While researching related projects I came across someone who hadn't done this initially and was forced to disassemble their entire box to change some of the code. The back door I included is accessed by pressing the pound key while the initial hello message is displayed. It also prints a happy birthday message and serves as a way for us to open the box later to show family and friends.
This project took me hours of researching, building, coding, and troubleshooting to complete but was absolutely worth it in the end to see how happy my boyfriend was to receive this gift!
my boyfriend and I with the box on his birthday
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