Mission Not So Impossible


The name’s Preen … Richard Preen.

But unlike Ian Fleming’s fabled spy, this Greek geocacher (GC handle: r10n) prefers to slay his rivals with hand-built electronic puzzle caches.

Since August 2008, the IT professional has placed 21 hides around the historic Athens community of Pendeli; 13 traditional caches and eight puzzles.

The latter include elaborate inventions he’s built using open-source Ardiuno components – the same electronics platform that allowed American Mikal Hart to build the first Reverse Geocache.

Today, It’s Not About The Numbers is pleased to show you a sneak preview of his latest work of art. For puzzle cache No 9, Preen says he’s created a standalone telephone, upon which cachers must dial the correct code number to receive the final location.

Watch r10n’s Interactive Telephone Puzzle Geocache:

Yet to be published or named, the puzzle’s blurb will read:

Good evening, Mr Phelps.

Yesterday Mr Frank Jones, the notorious thief, was found dead in Halandri. We had been following him for some time in an attempt to recover the blueprints of the Acropolis he stole last year. From our investigations we know that he was a member of the KGB and had been hiding out in a derelict building (co-ordinates provided) on Pendeli. We believe that this building is likely to contain a telephone with a direct line to the KGB and that for the next 48 hours the line will remain connected. After this period, the KGB will sever the link. Dialing Mr. Jones’ four-digit PIN on this telephone should recall the co-ordinates of the final hiding place of the blueprints. Unfortunately, we have been unable to find the four-digit PIN number. We do know though that Mr. Jones was a deeply religious man and even while hiding on Pendeli he visited the local church daily. We believe he may have hidden the code there.

Your mission Jim, should you chose to accept it, is to recover the blueprints. As always, should you or any of your I.M. Force be caught or killed, the Secretary will disavow any knowledge of your actions.

Good luck Jim.

For pop-culture novices: IM Force refers to the American TV show (and later films) Mission Impossible, based on a team of secret agents lead by Jim Phelps – though the inspiration for his new cache was actually James Bond.

Preen says having recently read Fleming’s bestselling books, he “probably had spies and clandestine meetings” on his mind.

“I wanted to try to produce a geocaching experience that really made you feel that you were on a covert mission … not just on a multi-stage geocache.”

And it was this wish to make geocaching experiences less mundane and more mysterious that began his inventing – and blogging – career.

Back then, Preen was a software engineer with years of experience but a relative notive at building electrical puzzles and games.

“But, with the vast amount of information available on the internet and the current electronic development platforms available, it’s very easy to dive in and build anything.”

Invention No 1 was a GPS Puzzle Box – along the lines of the aforementioned Reverse Geocache – which Preen’s wife, Myrto, managed to activate near the Temple of Apollo.

“Going from simply writing software that ran on a PC to creating something ‘real’ was a revelation for me. It opened up a whole new world of possibilities, and an area I wanted to work in was that of geocaching.

“I’ve always loved field puzzle caches, rushing over the countryside counting the number of windows on a building, the number of steps leading up to a castle, all to get to that final location.

“But one thing I’ve always felt was missing was any ‘real’ interaction. Some can be a little too formulaic. You know what you have to do and just have to spend the time going through the steps.

“Using electronic devices placed out in the field, though, I could change this and give geocachers something more to do, some physical interaction beyond the normal caching experience.”

His first such geocache – GC2DC7Z Pendeli Woodpecker – was placed last August. As its name suggests, this work mimics the sound of a woodpecker drumming on a log at a specific time each week.

“If you went to the puzzle co-ordinates at the right time, you would hear the sounds and be able to follow them to find the woodpecker and the geocache.”

Found logs and more cache creations followed, which brings us neatly back to puzzle No 9.

To build his latest invention, Preen assembled:

  • Rotary Telephone, with a working dial, speaker and cradle switch (€3 at a local flea market)
  • Arduino Uno (US$30)
  • Adafruit Wave Shield (US$22)
  • SDRAM Card
  • 470 Ohm resistor
  • 10k  resistor
  • Wire and solder
  • 9-volt battery and Arduino connector

“Once I’d purchased all of the parts, it took about three hours to build everything. The Arduino is connected to the telephone so that;

  1. It is turned on and off by picking up or replacing the handset.
  2. It can play .wav files, with the use of the Wave Shield, through the telephone’s handset speaker.
  3. It can get the number dialled.”

It then took him another few hours to write the necessary software, find the required telephone sound effects, and generate speech .wav files for his spoken messages.

“When turned on the device plays .wav files through the handset’s speaker; dial_tone.wav to begin with, ringing.wav once the correct number has been dialled followed by language_selection.wav, and so on.”

Looks like Preen may have found his calling, but sadly it’s all Greek to me.

* Check out Richard Preen’s other geo-inventions at his Electric Geocaching blog.


  1. Maniatopoulos Dimitri

    Both of this GC’s have worked excellent and where amazing! But unfortunately owner has to move from Greece and removed those fantastic caches , probably due to high cost of maintenance and building cost. Thanks r10n for the experience !

  2. kjwx

    That’s a real shame for Greece but hopefully Richard Preen will relocate his amazing geo-creations to whichever country he now calls home.

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