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Reverse Geocache


What the heck it this you might say? A reverse geocache is named upon the very populare hobby «Geocaching». In this hobby you look for small objects around the world with only coordinates and a hint as your clues. When you find it you open the box and sign a logbook in it. The reverse geocache is exactly this, reverse the game. Here you have the box, but the coordinates need to be found and the only hint you get is number of meters you are away When at the correct coordinates the box opens and you can sign the log!

The idea

First I had to create a «mind-map» on how this was supposed to work. This started something like this:

  1. Press button to start the «geocache»
  2. Check what the coordinates are
  3. If correct coordinates, open the box
  4. If not show the meters away from the center.

So i started creating a schematic in Fritzen, and after a while here is what i got: (Dont mind the part numbers, just for connecting this schematic)

Screen Shot 2014-10-28 at 13.21.44

Click to enlarge

I must add a special thanks to lot of the IRC people on #arduino@freenode and #openlrs@freenode for help with this. Now let me explain the idea here. The servo is ofcourse to unlock the box. But the two transistors you see there are for a software switch. Then you press the switch S1 the PNP Q1 goes active and poweres the UBEC which powers the Arduino.

When the Arduino gets powered it also puts D4 high so that enables current from Q2 to the ground which enables Q2 to do what the switch initially does and you can release the switch. This way the power is handled by the Arduino, when the Arduino want to save battery it can put D4 low and the power is cut.

So, i started sourcing the parts. Luckily i had all of the parts at my home. Here is a short partlist:

  • Atmega328P-PU chip
  • Arduino UNO (To program the chip)
  • GPS Unit
  • PNP Transistor
  • NPN Transistor
  • 5V Regulator
  • 25v 330µF Capacitor
  • 1k Resistor
  • Pushbutton
  • Diode


This was the fun part, connecting the dots! So I started prototyping the whole thing with a GPS from Hobbyking.


Testing prototype


Sampling 15 coordinates to average


This part i got very happy with, after the prototype board worked i sourced new parts and soldered everything on a new perfboard (?). This is the result:


New soldering station!


Started with atemega socket


Dremel away the connection


Sockets and headers


Headers on


5V Regulator i used


Stripped the UBEC


Soldering on the ubec


Soldering under


Finished product under


Finished «product»

Finished PRoduct

And then i went into Eagle to create the Schematics & finished product. Here are some pictures of that and the finished idea!

Eagle Schematics

Eagle Schematics

Finished PRoduct

Finished PRoduct

What you think? Comment below! Any input appreciated!




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