The Reverse Geocache™ Puzzle

The "Reverse Geo-cache" Puzzle

Fig. 1 - The Box

[Author's note: This post is the first in a real-life story that ultimately took a full year and four chapters (1, 2, 3, 4) to tell. Read them all, then browse through the other surprising puzzle box stories that have popped up along the way.]

Early this summer, the friend who first introduced me to Arduino amazed us with the news that he was moving to France to get married. Once I recovered from the surprise, it occurred to me that putting together some sort of Arduino-based wedding present might be a uniquely fitting thanks for his years of friendship and for helping get me started in this delightful enterprise. And so after weighing several ideas — I didn’t fancy adding some ugly techno-junk to the pretty collection of tea cozies and china sets — I finally settled on building the device I describe here: a puzzle box that won’t open until it is taken to a certain location.

To better understand my conception, let’s fast forward and imagine the gift opening. The new couple, freshly back from their honeymoon, remove the wrapping to reveal a book-sized wooden box elaborately carved with elephant images. (I didn’t carve it; I bought it that way at World Market.) Mounted into the lid, perhaps incongruously, are an illuminated button, a small display, and a mysterious module that sharp-eyed readers might recognize as a GPS. There’s also some kind of connector tucked away on the box’s left side. More about that later.

What do they make of all this? It’s hard to guess, but naturally I imagine they might try to open it up and take a look inside. When they do, however, they find the lid stuck tight — it seems to be latched from the inside. Will they push the button? Pretty buttons are awfully hard to resist, so let’s assume so. The blue display fires up and displays a friendly, personal greeting:

Bonsoir, famille Immel!
This is attempt 1 of 50.


Now they don’t know this yet, but the box’s embedded electronics require a good GPS fix – something that’s probably hard to come by inside a Parisian apartment. And so the display flashes “SEEKING SIGNAL” for a couple of minutes and gives up.

No signal acquired...
Powering off...

Now my hope is that they’ll realize they need to take the box outdoors or near a window. Is that a stretch? I don’t think so. My friend is a patient fellow with an engineering background, so I expect he will at least try moving it before throwing it against the wall or chiseling off the hinges. Let’s assume, then, that they go outside and push the button again. This time the series of messages is different:

This is attempt 2 of 50.
Distance 391km
*Access Denied*
Powering off...


Fig. 2 - Distance 391km

Fig. 2 - Distance 391km

Hmm. What does “Distance 391km” mean? “Access Denied” suggests that getting inside the box is indeed the objective of all this button pushing. Just for fun, let’s try again.

This is attempt 3 of 50.
Distance 391km
*Access Denied*
Powering off...

Uh oh. We seem to be consuming our limited supply of “attempts”. The “No signal” problem seems to be solved, but the message “Distance 391km” remains puzzling. Does the box know its own location? Is there something 391 kilometers away? London? The Hague? A circle of that radius drawn around Paris intersects quite a few interesting places in France, England, Holland, Switzerland, and Germany.

Knowing my friend, he will eventually think to move the box to a new location to see how the message changes. Let’s imagine, then, that he hops in his car and motors down the A11 to the famous city of Le Mans, about two hours to the southwest. After a brief tour of the cathedral and a snack at a sidewalk café, he pulls the elephant box from his backpack and pushes the button again.

This time the display is once again slightly different:

This is attempt 4 of 50.
Distance 226km
*Access Denied*
Powering off...

Aha. We seem to be getting somewhere. If we are in fact looking for a specific place, it would appear that it is 391 kilometers from Paris but only 226 from Le Mans. As you can see by the map in Figure 3, there are only two places on earth that meet these criteria – a spot just off the northern Brittany coast, and a rural area in the southwest near Bordeaux. And, as my friend is aware, one of these can be quickly eliminated simply by taking a third “reading” in a new spot.

Fig. 4 - and a circle around Le Mans

Fig. 3 - Circles around Paris and Le Mans

I suspect that from here things will proceed relatively quickly. My friend will triangulate that the “magic spot” is Île-de-Bréhat, a tiny island just a short ferry ride off the northern coast of Bretagne. If and when the couple do bring the box here, they’ll be greeted with a congratulatory “Access Granted!” and the whir of a motor announcing that the treasure inside is about to be finally revealed!

Fig. 5 - The box is unlocked!

Fig. 4 - The box is unlocked!



The electronics for this project are fairly simple. At the core, of course, is the Arduino, surrounded by a handful of devices that talk harmoniously through various native and third-party libraries. The peripherals are wired to a custom “shield” that I soldered together. The shield design makes the system modular and easy to disassemble for moving. Power is provided by 4 AA lithium batteries mounted in the box’s interior.

Major components

Fig. 6 - Arduino and the custom shield

Fig. 5 - Arduino and the custom shield

1 Arduino Duemilanove
1 USGlobalSat EM-406A GPS module
1 8×2 blue backlight HD44780 LCD
1 Hitec HS-311 servo motor
1 illuminated pushbutton
1 low voltage Pololu power switch
1 2.5mm female DC power connector
1 Adafruit Arduino prototype shield
1 ornamental box

Minor components

1 severed chopstick used as latching dowel
3 #14 eyelet screws
1 Battery pack with 4xAA lithium batteries
Various mounting screws and glue
Wire, headers, solder, and other circuit connecting items

I designed this project to last a long time. The batteries are locked inside the box and can’t be replaced if they run down — not while the puzzle remains unsolved, anyway — so it’s important to conserve power. That’s why a given “session” lasts at most 2-3 minutes before the system powers off. Furthermore, the owner is allowed only 50 attempts to discover the box’s secret, so the active lifespan of the batteries need be no more than about 150 minutes. Between sessions, the electronics draw virtually no power and should last idle for years.

Fig. 7 - The tiny Pololu switch

Fig. 6 - The tiny Pololu switch

The secret to this power conservation is the clever little Pololu switch, which gives a circuit the ability to completely turn itself off through software. When you push the button, it latches and distributes power to the system. When the sketch decides it’s time to shut down — either because it can’t find a GPS signal or it’s not close enough to the target — it simply brings the Pololu’s power control pin high, cutting power. In this “off” state the switch draws just 0.01 microamps.

Fig. 8 - The EM-406A GPS module

Fig. 7 - The EM-406A GPS module

Like most GPS units, the EM-406A generates a stream of NMEA position data. This stream enters the Arduino via a “soft” serial port managed by my NewSoftSerial library. The NMEA data is parsed into latitude/longitude using TinyGPS, a popular library I built especially for this project. If the GPS is getting a good fix, the box can determine its location within 10 meters and, through a simple calculation, how close it is to the target.

Fig. 9 - The 8x2 Liquid Crystal Display

Fig. 8 - The 8x2 Liquid Crystal Display

The display is an HD44780-compatible device controlled by the Arduino LiquidCrystal library. I wanted to incorporate some visual effects like flashing and scrolling, so my sketch contains several custom display routines. These were carefully written so as not to block the all-important serial input stream coming from the GPS.

Fig. 10 - The interior showing chopstick latch

Fig. 9 - The interior showing chopstick latch

The internal latch is built around a Hitec servo, three eyelet screws, and, as a sentimental salute to the little Chinese restaurant my friend and I used to eat at, a dowel made from one of its chopsticks. One chopstick end is attached to the servo arm, and the other threaded through the two eyelet screws mounted into the box bottom. The servo operates in one of two positions – “open” and “closed”. When instructed to close, it drives the chopstick laterally through a third eyelet screw hanging from the box lid. At this point, the box is latched. Once the puzzle is finally solved, the servo pulls the chopstick back, and the box can again be opened.


The box is running the Arduino version 0016 framework. The sketch I wrote uses native libraries Serial, Servo, and LiquidCrystal, as well as several of my own: TinyGPS, NewSoftSerial, PString, Streaming, and Flash. My libraries are freely available for download at

Conceptually, the software is fairly straightforward. At power up, the system hunts for a GPS signal. If it detects that the box is within 2 kilometers of the target spot — in this case the center of the little island — it unlocks the latch. Otherwise, it displays the somewhat cryptic “Distance: nnn km” and keeps the latch firmly locked.

How the software works

How the software works

Fig. 11 - A fake voltage overload

Fig. 10 - A fake voltage overload

The Back Door

It may seem risky to create a device that can only be activated a limited number of times before it locks permanently. What happens if the bride’s four-year-old gets hold of it? What if the batteries unexpectedly run out? What if, despite all my care and attention, there are still bugs in the implementation? Will the treasure inside be forever sealed? To address these concerns, I built a “back door” into the design. This is where the mysterious 2.5mm coaxial connector to the left in Figure 1 comes in.

If you apply some current here at a reasonable voltage, the system will power up just as if you pressed the button. But since this circuit bypasses the Pololu switch, when the box claims to be “Powering down”, it is actually lying. Instead, after a two-minute delay, the latch opens, regardless of where the box is actually located. This gives the sheepish designer (me) emergency access and one more chance to replace the batteries or repair the latest design flaw.

You might question whether it’s a good idea to leave such a gaping back door. After all, it’s a lot easier for my friend to open the box by simply plugging it in than driving it the 391 kilometers to Bréhat. Quite true. So to dissuade him from snooping too far down this path, I built in a few frightening messages. Remember, he has no idea how to use this “back door” or what voltage and current to apply. If he does figure out how to power the box this way, I feel fairly confident that whatever satisfaction he gains will rapidly disappear when the LCD starts flashing the completely fake warnings

Excess Voltage!
Remove Power!

And if these aren’t discouraging enough, they are followed by a blast of random “garbage”, suggesting that a critical failure is underway. (See Figure 10.) Whoever opens the box this way will have to stare at these ominous characters for a full two minutes.

Last minute disasters

Just a couple of days before I left for France I made a pretty serious mistake. At the time I had completed the physical construction and was just beginning the first full-scale closed-lid tests. Everything was going swimmingly – so smoothly, in fact, that I became a bit cavalier about my methodology. To address an intermittent problem, I made the last-minute decision to upgrade my system software. Reflecting back, I should have done plenty of preliminary “open box” tests before sealing it up; instead, riding the wave of my enthusiasm into disaster, I uploaded the new version, confidently closed the lid, and pressed the button. The latch engaged normally, but then the whole system went haywire. The motor began jerking crazily and the LCD limped along, displaying dimly only the top halves of each message. Soon I discovered that I had locked myself out of my own box and that disassembling it was the only way to recover. Because I had designed it to be somewhat tamper proof, this was far from easy. Ultimately, I had to break a bracket to get a screwdriver far enough into the interior to pry open the latch.

In France I had left myself just one short day to reassemble the box (which had been taken apart to increase my chances with airport security), run some last-second tests, and perform the final reset. When it came time to rearm it, something you do by connecting power to the “back door” for four minutes, I found that I had brought the wrong power supply with me. I fruitlessly combed the house I was staying in for a telephone or router with a 2.5mm connector, and then tried desperately to locate the French equivalent of a Radio Shack. After my panic subsided I realized I could just jimmy up what I needed with a couple of paper clips. It wasn’t pleasant or easy to hold those clips in place for four minutes, but I finally did manage to rearm the box with mere hours to go.

Frequently Asked Questions

What happened when they unwrapped the box?

The day after the wedding, the bride’s family hosted a brunch in the back lawn of their beautiful country house. I hadn’t expected to be present at the opening, but at one point I noticed some furtive activity in the corner of the lawn and saw that the box was being passed around, accompanied by much head scratching and gesturing in my direction. My friend, who had apparently already consumed three “attempts”, was darting back and forth exhorting everyone in halting French “Ne poussez pas le bouton!” (“Don’t push the button!”). To his dismay, his new father-in-law didn’t understand and pushed it anyway. Several people approached me to ask questions about the box, which I apologetically declined to answer. At one point a friend of the family, a charming gentleman from up the street, said to me with a thick accent, “You are — how you say in English? — a BASTARD!” That one comment made this whole project worthwhile. As of this writing I do not think they have yet managed to open the box.

What did you put inside?

With all the electronics, there wasn’t much room inside the box for anything too substantial. I put in a few local (US) gift cards to entice them to visit soon, a set of Kazuo Ishiguro audio books (on a USB key), and an overly sentimental card. And of course, as I pointed out in the card, if either of them fancies doing a little Arduino development, there’s a perfectly good Duemilanove to play with, not to mention an LCD, a servo, and a GPS.

How did you choose the target location?

Île-de-Bréhat, a charming island where motorized vehicles are prohibited, is a special place for this couple. It was while my friend was filming a movie here that he first began to realize his feelings for the young lady starring in it. And she for him, if I understand correctly. To help matters, the bride’s family owns a house here, making it a doubly attractive destination. (I may be a bastard, but I’m not going to make them travel 400 kilometers to some random, isolated location just to open a few gift cards.)

How did you get it through airport security?

I worried a lot about this. At first, when I was not certain whether I would be able get to France to attend the wedding, I had thought to present them the fully “armed” box while they were visiting the US. Fortunately, someone pointed out the foolishness of this idea. Can you imagine the interview at airport security when the hand soldered electronics show up in the X-ray?

Sir, did you pack this yourself?– No.

What’s inside?– I have no idea.

Can you open it please?– Nope.

Eventually, I decided that the best strategy was to disassemble it as much as practically possible and hope that none of the individual pieces were sufficiently suspicious to warrant being detonated on the tarmac. This seemed to work. I brought the disassembled box on two major trips without a hint of trouble.

Why limit the number of attempts to 50?

Two reasons. First, a puzzle is just more exciting if it is bounded. If it’s fun to solve a Sudoku, how much more fun is it to try and do it in under ten minutes?

The second reason is a practical one. I needed some way to make sure that power consumption would not end up being a problem. How disappointing would it be if, after all the work I put into it, the batteries ran out and the puzzle was ruined? Constraining the number of attempts helps ensure that this won’t be an issue.

The number 50 has no special significance. 25 or 20 would probably have worked just as well.

Why the 2000-meter tolerance?

There is always a little bit of error in a GPS reading, so some tolerance is necessary. The island is about 4 kilometers across, so setting the tolerance at 2000 meters forces them to actually ferry across to it without constraining them to any particular part.


The box is unwrapped

The box is unwrapped

Building this project was a joy. It was rewarding to conceive of a relatively unique GPS application and to work through the various problems as they arose. Designing the latch, for example, was a challenge I spent a good deal of time on. My experience solving mechanical problems is fairly limited, but I’d like to think that the next time I build something with a mechanical component I’ll be able to approach it with a little more savvy. Meanwhile, when you think about all the cheap sensors, displays, lights, motors, modules, radios, and buttons you can attach to an Arduino, you realize that imagination is the only constraint on the kinds of projects that can be built. This little box is a novel way of combining a GPS, a servo, a button and a display. How many more marvelous combinations lurk out there, if only someone has the imagination to put them together the right way?

[Make sure you read the sequel to this story when you're finished here.]

Page last updated on January 10, 2011 at 8:54 am
268 Responses → “The Reverse Geocache™ Puzzle”

  1. Michael

    6 years ago

    This idea is so incredible brilliant. Thank you for all that inspiration!
    Since a few weeks I developing my own (very affordable) version from scr.

    But currently it’s about… mhm, lets say 50% finished.

    Till then: have a nice time and keep creating things!


  2. Mikal

    6 years ago

    Can’t wait to read about your work, Michael!

  3. Brian Carrigan

    6 years ago

    I made a clone of this project where the entire electronics system was replaced by a single circuit board with a PIC instead of the Arduino. The full writeup can be found at:

    Thanks for the inspiration!

  4. Mikal

    6 years ago

    Great work, Brian! Nice write up too. May I link to it on my new website as a “community story”?

    I like the custom circuit board. We are going down that path too, and hope to have some sample boards to share in the next few weeks.

    Read Brian’s blog everyone!

  5. rené

    6 years ago

    Hello Mikal,

    I have started building a box like this one (with more instructions though) for my sister and her fiancé. I have question about the power though.
    In your pictures you are showing the box with 4 standard alkaline batteries, which should give ~6v, which I guess is fine to feed the system via the 5v shield port on the arduino, but.. in the description you mention AA Lithium cells in the final version. 4 lithium cells would give ~14-15v to the arduino, which is way too much to feed directly through the shield port. Are you feeding it through a linear power converter first, or maybe just using 2 cells instead of 4?
    I was thinking of powering my box with 4xAA NiMH-cells (Eneloop, or something similar that keeps charge for a long time) – also using the power switch to keep idle usage at a minimum.

    Thanks for the imspiration!

  6. Mikal

    6 years ago

    Hi rené,

    I’m sorry that’s not clear. Let me explain.

    The very first box I built — the one mentioned in this article — used 4 1.5V AA Lithium (NOT 3.7V Lithium Polymer) batteries. This generated a nominal voltage of 6V, which is (just) within range of what Arduino’s built-in regulator can handle when it generates the 5V power bus.

    When I was making later boxes I decided that I wanted the electronics to be smaller, so I opted for the design that uses 2 AA alkaline batteries (nominal 3.0V). This of course is not enough to power a normal 5V Arduino, so I use the Pololu boost regulator to boost that to 5V, which is injected directly into the Arduino 5V power bus, bypassing the onboard regulator entirely.

    I have a new design coming out soon that uses the 3.7V LiPoly battery boosted to 5V. This will be cool because it’s rechargeable.

    Does that make sense?

  7. rené

    6 years ago

    Hello Mikal,

    Thank you for your swift response and specific answer.
    It makes sense, and yet it doesn’t. It sounds like all power, regardless of coming from the battery pack or the external connector is fed through the built in regulator, but from the picture of the first box, it seems like only the external power is fed through the barrel connector on the arduino (and thus also the regulator) whereas the battery is fed to the shield (through the polulu power switch, and being enough to run everything without a regulator or boost).
    Is this not correct? and if not, how do you bypass the polulu switch with the external power?
    I am probably still going ahead with the 4 AA cells (Lithium or NiMH) to feed 6v to the shield (through the power switch) and use the external port to provide 7-12v dirctly to the arduino (my backdoor is going to be a combination of external power and a reset between two specific metal features on the outside of the box (two nails out of many) – so that it can run normally on external power in case the batteries die and just ask for the power to be removed when a task is complete.


  8. Mikal

    6 years ago


    On the initial box the “normal” power route is

    6V battery pack (4 AA) —> Pololu switch —> Vin (Arduino onboard regulator) —> 5V Arduino power bus.

    The handmade shield I used on the initial box has the Pololu switch upstream from the onboard regulator.

    On the initial box the “backdoor” power route involved a 9V power supply with the 2.5mm connector. I could just “plug in” if I needed backup power. Its route was

    9V supply —> Arduino onboard regulator —> 5V Arduino power bus.

    If you have bought my latest shield you may be confused, because it bypasses the onboard regulator:

    3V battery packet (2 AA) —> Pololu switch —> Pololu boost (to 5V) regulator —> 5V Arduino power bus

    If you are using my new shield and board layout, don’t use the 4 AA cells, because the Pololu boost regulator isn’t rated to work at 6V.

    Make sense?

    Hey, let us know when your project is complete! Lots of good stories out there…

  9. rené

    6 years ago

    Ah. I forgot about Vin. Now it makes sense. I was planning on supplying voltage directly to the 5v pin, but maybe a boost adapter and Vin will come into play after all.
    I will let you know when my project is done :)

  10. Brian Carrigan

    6 years ago

    Thanks Mikal, by all means please do link! Hope that my writeup helps you to make the perfect custom board :)
    Shoot me an email if you have any questions.

  11. rené

    6 years ago

    Hello Mikael,

    Just to let you know that my project is still ongoing. It won’t be delivered to my sister until May, so there won’t be anything public on the net until after august (where the wedding is).

    Meanwhile, I’ve cracked how to use SoftwareSerial and the new PWM-library without any problems. I’m sure others had the same problems as you as well and I am also guessing that other solved it, but during the time I was struggling with I couldn’t find any shared code.

    What I basically do is that I have a flag that is set to wether we talk to the GPS or the Servo – and when we need to talk to the servo, I issue a nss.end() (my software serial object is called ‘nss’), wait for a few ms and then attach() the servo – do what it needs to do (after the backdoor is over and the servo is repositioned) i detach() the servo and begin() the nss-object again.

    Works like a charm. Full source will be disclosed when the mission of the box is over.



  12. Mikal

    6 years ago


    Thanks for the good feedback. Yes, you’re quite right that with the Reverse Geocache you never need to talk to the GPS and the servo at the same time. That’s a good solution. I had forgotten that you could *detach* a servo. Thanks!

  13. rené

    5 years ago

    The mission is over, and since I promised to get back with info when it was over, I will post the link to my project page (which I could finally publish a few days ago).

    The couple loved the adventure, even though they actually had guess from day one that I was the one who’d done it.. but they were great sports and played along and even sent pictures to the anonymous email account I had set up.

    I don’t think I’ve mentioned in the description (yet) that I ran into problems fitting all the text in the flash memory – the night before delivery – and so a quick fix was introduced with the pgmStrToRAM.h library (quick wrapper around all lcd.print-commands) to put text into progmem instead of flash.

    There will be more pictures to come, but my build log should be complete.
    The resulting (messy) code is on github (link should be on the wiki-page above).

    Thank you for the great inspiration (.. now.. which project should I throw my time at now.. hmm…)



  14. Dean Walsh

    5 years ago

    That’s a really lovely gift, and the story made me smile; thanks or sharing!

  15. Jaime Ortega

    1 year ago

    Lo he leído una y otra vez y siempre me emociona, soy maestro y está historia es de las primeras que suelo contar en clases para motivar e
    inspirar a mis alumnos algún día quisiera hacer algo así. Puedo contar con su ayuda?

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    [...] esto es lo que se le ocurrió al buen Mikal Hart — The Reverse Geocache Puzzle — para la boda de un buen amigo suyo y a quien en verdad [...]

  26. Nouvelles technologies: Geocaching inversé

    [...] Ce puzzle de geocaching inversé est réellement ingénieux : Mikal l’a créé en utilisant Arduino, et il consiste basiquement en boîte j’offre (des mariages) qui pouvait seulement être ouvert quand il était physiquement situé dans un lieu concret du monde. Dans son intérieur il y avait un GPS qui contrôlait un mécanisme qui bloquait la serrure, qui serait seulement ouverte après être arrivé aux coordonnées correctes, nourri par une batterie. À travers d’un écran, et après une pulsation, il indiquait pendant trois minutes la distance à l’objectif. Tout un cadeau geek avec un style, terriblement ingénieux et amusé pour les amants des puzzles. § Hack-a-day. # Un lien Permanent Posted by lisa conley at 10:41 AM [...]

  27. Technology society: Umgekehrter Geocaching

    [...] Dieses Puzzle von umgekehrtem Geocaching ist wirklich sinnreich: Es hat Mikal geschaffen, Arduino benutzend, und hauptsächlich besteht es in einer Kiste ich schenke (von Heiraten), der nur geöffnet sein konnte, wenn er in einem konkreten Ort der Welt physisch gelegen war. In seinem Innenraum gab es einen GPS, der einen Mechanismus kontrollierte, der das Schloss blockierte, das nur ernährt von einer Batterie geöffnet werden würde, nachdem er zu den fehlerfreien Koordinaten kommen würde. Über einen Schirm zeigte er die Entfernung und nach einem Pulsschlag, während drei Minuten im Ziel an. Das ganze Geschenk geek mit Stil, fürchterlich sinnreichem und unterhaltenem für die Liebhaber der Puzzles. § Hack-A-Day. # Bleibende Verbindung Posted by Lupe Mura at 9:50 AM [...]

  28. Learning technology: Обратный Geocaching

    [...] Эта головоломка обратного geocaching действительно изобретательная: это создал Mikal используя Arduino, и главным образом он состоит из ящика я дарю (свадеб), что только мог быть открытым, когда он был физически расположенным в конкретном месте мира. В его внутреннем помещении был GPS, который контролировал механизм, который блокировал замок, который только открылся бы, прибыв в правильные координаты, питаемый батареей. Через экран, и вслед за пульсацией, он показывал в течение трех минут дистанцию в цель. Целый подарок geek со стилем, ужасно изобретательным и развлеченным для любовников головоломок. § Hack-a-day. # Постоянное соединение Posted by Lupe Mura at 4:10 PM [...]

  29. EPISODE 126 – Midwest Meet Up Cacher Coffee « Goecaching Podcast

    [...] LogTools for making Garmin custom raster mapsReverse Geocaching PuzzleState Parks permit sales up [...]

  30. Homemade Geocache Puzzle Box — The Gadgeteer

    [...] good friend David Simpson sent me an email tonight with a link to a really cool story. I love a good story and I love a good gadget. Make it a 3 part story about [...]

  31. DIY Reverse Geocache Puzzle | Must Have Gadgets

    [...] you don’t see everyday, a DIY reverse geocache puzzle box, given as a wedding gift. Using the Arduino prototyping platform and a GPS device, it will lead you to a specific location on the globe, before [...]

  32. The Reverse Geocache Puzzle «

    [...] [...]

  33. Buzzle – Morse Code based Puzzle

    [...] was checking out the new posts on when I bumped into The Reverse Geocache Puzzle™ made by Mikal [...]

  34. The Frustromantic Box, Part 1: Intro « New Bright Idea

    [...] Frustromantic Box, Part 1 A few months ago, Hack A Day featured an ingenious hack called the Reverse Geocache Puzzle by a gentleman named Mikal Hart (please note that “Reverse Geocache Puzzle” is [...]

  35. The Frustromantic Box, Part 2: Assembly « New Bright Idea

    [...] Box, Part 2: Assembly The Frustromantic Box is my implementation of Mikal Hart’s Reverse Geocache Puzzle.  In Part 1 of this series I gave an overview of the project and its parts list.  This post [...]

  36. The Frustromantic Box, Part 3: Electronics « New Bright Idea

    [...] I had a real problem processing the output of the PNA4612 module when the batteries are even slightly discharged.  This might be something I could correct in software, but if I were doing it again, I’d probably just run a barrel jack through the side of the box, similar to what Mikal did on the original puzzle box. [...]

  37. Morse code puzzle box | Products & Tech News

    [...] box that can only be opened if a specific morse code sequence is entered. His starting point was a Reverse Geocache Puzzle he’d read about on Hack a Day, where a person has to bring a box to specific coordinates to release [...]

  38. Morse code puzzle box | SquareCows

    [...] box that can only be opened if a specific morse code sequence is entered. His starting point was a Reverse Geocache Puzzle he’d read about on Hack a Day, where a person has to bring a box to specific coordinates to [...]

  39. adoption curve dot net » Blog Archive » links for 2010-02-18

    [...] The Reverse Geocache Puzzle ™ | Arduiniana "The new couple, freshly back from their honeymoon, remove the wrapping to reveal a book-sized wooden box elaborately carved with elephant images. (I didn’t carve it; I bought it that way at World Market.) Mounted into the lid, perhaps incongruously, are an illuminated button, a small display, and a mysterious module that sharp-eyed readers might recognize as a GPS. There’s also some kind of connector tucked away on the box’s left side." (tags: arduino geocaching geodata location projects ideas) [...]

  40. Dorkbot 23 – SXSW Interactive 2010 « dorkbot-austin

    [...] Mikal Hart – Reverse Geocache box [...]

  41. My first (completed) project! « Stromberg Labs

    [...] couple months ago I saw this awesome project and realized that I had a couple of the parts already, so it got into my head that I could build [...]

  42. Reveling in dorkery – tales from SXSW #1 | Rubber Republic

    [...] up was a guy called Mikal Hart who’s invented the “Reverse Geocache box“.  I expect you know what one of these is – but if you don’t the shortened [...]

  43. صندوق الأحجية المتصل بالقمر الصناعي: كان يُقدم في البداية كهدية زفاف… « Endoacustica Arabic Blog

    [...] الصندوق المتصل بالقمر الصناعي عبارة عن قطعة خشبية من النوع الذي من الممكن أن تجده [...]

  44. Introduction | Jordan LeGrand's Arduino Journey

    [...] inspiration from Mikal Hart’s Reverse Geocache Puzzle, I wil be constructing a gps scavenger hunt. Upon completion, the box will be locked from the [...]

  45. Little Reverse GeoCache - Markus’ Blog

    [...] Markus on Jun.19, 2010, under Electronics A few months ago I stumbled across the very first Reverse GeoCache project by Mikal Hart. I was fascinated by the idea and decided to build one of my [...]

  46. Smallest reverse geocache puzzle yet | Komprol

    [...] latest version of Mikal Hart’s original reverse geocache puzzle–a box that only opens in one location on the Earth’s surface–is by Markus. At [...]

  47. GPS Box Project - Opens at secret location - Hacked Gadgets - DIY Tech Blog

    [...] featured before. Markus has made a project he calls the Little Reverse GeoCache, it is based on a similar project that was made by Mikal Hart. The box can only be opened when it is in the correct location, the trick is that the location is [...]

  48. Caja Fuerte con GPS

    [...] El proyecto es un DIY por lo que podemos, si tenemos las ganas y los conocimientos llevarlo a cabo y no se ustedes, pero lo primero que me viene a la mente es por ejemplo: Una propuesta de matrimonio muy original con un estilo diferente. [...]

  49. GPS Box Project – Opens at secret location |

    [...] featured before. Markus has made a project he calls the Little Reverse GeoCache, it is based on a similar project that was made by Mikal Hart. The box can only be opened when it is in the correct location, the trick is that the location is [...]

  50. Blog ETBnetco » Caja Fuerte con GPS

    [...] proyecto es un DIY por lo que podemos -si tenemos las ganas y los conocimientos llevarlo a cabo- animarnos a hacer [...]

  51. “Special” Caches « GeoCass UK GeoCaching

    [...] doesn’t support so I will just ignore them), Cache In Trash Out, and the locationless “Reverse Caches” which sound mega exciting, but I don’t believe we have any in the UK. Reverse caches [...]

  52. Kristians lille hjørne på verdensveven » Reverse Geocache del1

    [...] A Day en artikkel om en fyr som hadde laget en reverse geocache. Dere kan lese om hele prosjektet her. I bunn og grunn så er prinsippet at man får en boks som er programmert med en fast geo-lokasjon. [...]

  53. Reverse geocache puzzle « at0mic blog

    [...] gift for his friend who was moving to France. After experimenting with a few things, he settled on creating a puzzle box that would only open in a certain location. Since his friend introduced him to the Arduino, he fittingly used one in the design, along with a [...]

  54. Un regalo ingenioso y original a la vez

    [...] Mikal Hart usando el sistema Arduino. Puedes encontrar toda la información sobre este proyecto en: The Reverse Geocache Puzzle. También puedes encontrar más información en microsiervos. Arduino, batería, caja de [...]

  55. GPS Puzzle Box Popularity |

    [...] featured a cool GPS Puzzle Box earlier this year that Markus built. It was based on a version that Mikal Hart created. Turns out there is quite a bit of interest in these GPS Puzzle Boxes, Mikal has since written a [...]

  56. GPS Puzzle Box Popularity | new technology, latest technology, robonaut, pc technology, latest business technology, technology in business, technology innovation, information technology, emerging technology

    [...] featured a cool GPS Puzzle Box earlier this year that Markus built. It was based on a version that Mikal Hart created. Turns out there is quite a bit of interest in these GPS Puzzle Boxes, Mikal has since written a [...]

  57. The Reverse Geocache Puzzle « Yeah Totally

    [...] Leave a Comment via [...]

  58. The Reverse Geocache Puzzle | myninjaplease

    [...]> Share this: [...]

  59. London to host Internet Week « V E X E D

    [...] last night New EC2 Features: Tagging, Idempotency, Filtering, Bring Your Own Keys JDK 7 Features The Reverse Geocache Puzzle Box Everyday at Vexed we round up the industry stories that we find interesting and insightful. These [...]

  60. Tuesday various « occasional fish

    [...] The Reverse Geocache Puzzle Box [via] [...]

  61. Self-Aware Building Blocks « Reputation Research Blog – Ben Turner

    [...] unlock a secret temple.  After all, one inventor using Arduino and GPS geolocation already made a wedding gift puzzle box that only opens when it’s taken to a small island near [...]

  62. Stubborn Treasure Chest | Rolang's Creeping Doom

    [...] was inspired by a real product, that uses a GPS-based lock that will only open in one location on earth. Be sure to read the [...]

  63. Il puzzle… fisico! Genio & follia «

    [...] questo The Reverse Geocache™ Puzzle Box e poi il seguito: cinque settimane dopo, le riflessioni su questo mondo di guardoni e finalmente [...]

  64. CacheDuino – Part 1 « Steve's Projects

    [...] my Mikal Harts “Reverse Geocache Puzzle” and Russ Weeks “Frustromantic Box” I thought I’d try build my own and use [...]

  65. Thomas Kalil, White House Office of Science and Technology Policy, talks Maker Movement | Live Sock

    [...] engineer who had the inspired idea to use reverse geocaching to design a wedding present — a puzzle box that only opens on one spot on the [...]

  66. New Arduino boards make electronics prototyping even easier « HackColorado Blog

    [...] and programming. Tons of cool projects have been created with the Arduino, including the Reverse Geocache Puzzle, high altitude balloons, and even lift status displays for Copper Mountain Resort. The new Arduino [...]

  67. Hidden Distance » Reverse Geocaching

    [...] Idee! Zur Bastelanleitung… Permalink — Kategorie: Randnotiz · Worthwhile — Hirschi @ 6:55 — [...]

  68. Reversing all the way to France « Lavonardo

    [...] wedding gifts go, this reverse geocache ranks amongst the finest. Filed under geocaching Comment (RSS) [...]

  69. World’s Strangest | Reverse Geocache Puzzle Box

    [...] Link | Part 2 of the story – via Gizmodo [...]

  70. The Reverse Geocache™ Puzzle Box « Verbasterd

    [...] A puzzle box that won’t open until it is taken to a certain location. Bron: Arduiniana [...]

  71. Yesterday

    [...] [...]

  72. Geolinkdump GPS, geocaching week 46

    [...] over de Reverse Geocache Puzzle Box. Erg mooi uitgevoerde ‘omgekeerde’ geocache die alleen open gaat op een vooraf [...]

  73. Connect Phi-1 shield with an EM 406A GPS « Liudr's Blog

    [...] you thought of making a fun Geocache box for outdoor adventure or a wonderful reverse-Geocache box for friends or loved ones? Maybe you want a GPS tracker for field trips or position-sensitive [...]

  74. Fully functional Arduino GPS logger « Liudr's Blog

    [...] exist endless ways that you can use a GPS sensor in your projects. Geocaching and reverse geocaching are just two typical applications. Last time I made an attempt to use GPS with Arduino and my Phi-1 [...]

  75. Reverse Geocache | Alternet

    [...] project was inspired by the “Reverse Geocache Puzzle Box“, an idea that has been duplicated a few times.  For Christmas this year, I drew my [...]

  76. Mikal Built a Magical Box :: CultureBy – Grant McCracken

    [...] Mikal. n.d. “The Reverse Geocache™ Puzzle Box.” Arduiniana. (Accessed October 4, 2010). Categories : [...]

  77. LlamaByte | Ramblings of a man named Bill

    [...] had read The Reverse Geocache Puzzle story awhile back and thought it was a fantastic idea. As I was thinking about a creative way to [...]

  78. Finding this wedding gift was quite a trip | It's In The Stars

    [...] what’s in the box with the GPS screen? Gift cards. Mikal has been getting inundated with orders to make more of these one-off boxes which took him nine months to [...]

  79. Arduino – Maximum and Minimum Temperature

    [...] PS: I know these last few posts aren’t about Geocaching, but bear with me. I am learning this stuff so I can create my own version of the Reverse Geocache… [...]

  80. Puzzle Box – The Paleotechnologist

    [...] since reading about the (original) Reverse Geocache a few months ago, I had wanted to build one. Except for the box itself, I already had all of the [...]

  81. Physical Computing | maplemuse

    [...] interesting examples of physical computing change the way we interact with technology. Take the GPS locked treasure box, which will only unlock at particular coordinates, telling the user how far away the correct [...]

  82. Reverse Geocaching | worms wiggle

    [...] not know about, and I stumbled upon something called reverse geocaching. You can read about it in Mikal Hart’s post (recommended). Basically, The idea is that you give someone a locked gift box, that they cannot [...]

  83. Interessante Arduino-Setups | wer bastelt mit

    [...] the-reverse-geo-cache-puzzle und [...]

  84. OSCON 2011 « Ted Leung on the Air

    [...] makes it possible for these people to make smart craft items. Some examples of such items are this “reverse geocache” wedding gift box, and a bicycling jacket with turn signal lights embedded in [...]

  85. Self-Aware Building Blocks « Ben Turner's Blog

    [...] unlock a secret temple.  After all, one inventor using Arduino and GPS geolocation already made a wedding gift puzzle box that only opens when it's taken to a small island near [...]

  86. Moments « Ben Turner's Blog

    [...] even the story about the wedding gift a man made for his newlywed friends which consisted of a locked box that had a butt….  The box said the newlywed couple would have 50 presses of the button to figure out how to open [...]

  87. Link Dumpage for 2010-05-25 | b2c8b8

    [...] The Reverse Geocache Puzzle ? | Arduiniana Delicious tags: puzzles "I finally settled on building the device I describe here: a puzzle box that won?t open until it is taken to a certain location … Mounted into the lid, perhaps incongruously, are an illuminated button, a small display, and a mysterious module that sharp-eyed readers might recognize as a GPS." [...]

  88. Dosenfischen: Geocaching-Podcast 195 › Geocaching-Podcast Dosenfischer

    [...] * Reverse Geocaching – Noch so ein talentierter Bastler, der hier Boxen für Reverse Geocaching vorstellt. Weitere Infos zum Thema gibts auch auf dieser Seite. [...]

  89. My Proposal Box, Part 1: Intro

    [...] seeing a project from Mikal Hart called The Reverse GeoCache™ Puzzle Box, I knew that I had to build one. My girlfriend and I really enjoy geocaching together, so I [...]

  90.’s top ten arduino projects - DIYourfaceoff | DIYourfaceoff

    [...] Check out the full write-up and build here [...]

  91. Puzzle Box |

    [...] stumbled across a link some time ago that showed how Mikal Hart built a Reverse Geocache(TM) as a wedding gift using an Arduino, a GPS, a small LCD display and a servo to drive the lock. For [...]

  92. Puzzle Box Part 2 |

    [...] Hart’s original Reverse Geocache Puzzle (TM) and More Puzzle Box Tales on his [...]

  93. Valentine’s day puzzle box « Matt's Hacks

    [...] I didn’t really have a specific project in mind for a while.  Then, one day I remembered a reverse geocache box that was also featured on hackaday, and realized that I could do something similar.  The F3 [...]

  94. Phul's Phantasmagorium

    [...] the other day I read about the “Reverse Geocache” project  ( and it gelled a rather important concept for me.  It was an example of something that has been [...]

  95. The Traveling Geocache using Arduino - Arduino for ProjectsArduino for Projects

    [...] The original reverse geocache: [...]

  96. Finding my creative spark - Geocaching Librarian

    [...] for the Arduino which let you create some amazing projects. A couple of examples that I found are a reverse geocache, and The Inebriator. Both of these are well outside my skill level at the moment, but hopefully [...]

  97. Reverse Geocaching Wedding Gift Box |

    [...] A while ago, friends of mine got married. Like so often, we tried to come up with some extraordinary cool wedding present. They both enjoy hiking and geo-caching, which inspired us to make the following present. We found an awesome idea online, the reverse geo-caching puzzle. The original description can be found here: [...]

  98. bildr » Finding Location With The EM-406A GPS + Arduino

    [...] this that will return the value in miles, nautical miles, or kilometers. You can use this to create reverse geo-caching gifts or have it trigger something every X [...]

  99. MindTribe | Geeky Romantic Suggestions

    [...] can also combine gifts. The perfect customized or handmade item could fit inside a reverse geocache box which leads your beloved to the location where you’ll be serving your awesome home-cooked [...]

  100. » Der umgekehrte Geocache

    [...] Tüftler Mikal Hart hat das Spiel nun einmal etwas anders aufgezogen bzw. [...]

  101. Reverse GeoCaching | Huinink-Jongen

    [...] link – Arduiniana – de uitvinder van….  YouTube [...]

  102. CS 436 Lecture ? – O Marks The Spot | teaching machines

    [...] app we’ll write today is inspired by the Reverse Geocache Puzzle. Intel software engineer Mikal Hart had a friend who was getting married. This friend had [...]

  103. Reverse geocaching: bouw zelf zo'n box met Arduino - Mancave

    [...] je kan ook middels coördinaten de box laten openen. Zoals Mikal Hart laat doen. Hij heeft er een coördinaat ingestopt en pas als je daar in de buurt bent, kan je de [...]

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