Dan Q

Tag: geocaching

Dan Q posted a note for GC54F7N Oxford Steganography #4 – Tilt

This checkin to GC54F7N Oxford Steganography #4 - Tilt reflects a geocaching.com log entry. See more of Dan's cache logs.

As evidenced by recent logs, this cache has “drifted” a long way from where it belongs (for anybody familiar with the hiding place: it should be out-of-sight, but easily reachable by an arm as short even as a child’s). I’ll get down there and check up on it within the next few days. Thanks for letting me know, justinbjacobs/(S)A&J!

You Can’t Do It Alone!

Hot on the heels of the Oxford Steganography Series, a series of “hidden in plain sight”-themed geocaches I placed earlier this year, I’ve recently placed another geocache – GC591VV – and I think that – conceptually – it might be completely unique.

Spoiler warning: this article contains minor spoilers about Oxford-based geocache GC591VV – “You Can’t Do It Alone”. You won’t find any shortcuts by reading this page, but you might ruin part of the surprise.

Geocache GC591VV, ready to hide
Geocache GC591VV, ready to hide

The cache’s name is the first clue that there’s something unusual about it, and this theme continues in its description, where it insists that this is a cache that is impossible to find by yourself. Experienced ‘cachers may have come across geocaches that benefit from a second pair of hands: usually to help “bunk you up” to a high spot. Some really clever caches use your “buddy” to press a battery-powered radio doorbell while you “listen” for the cache’s hiding place nearby, or use your friend to stop up the holes in a pipe as you pour water into it (in order to raise a floating cache to the surface). But every single one of these has a “workaround” – a way in which you can do it by yourself, if you’re imaginative enough. I wanted to make a cache that genuinely required two people.

Dan reprogrammes Box One in a forest
Creating this geocache took months of planning, scouting, construction, and – on one unfortunate occasion – standing around in the rain, deep in a forest, with a C debugger.

The cache description page repeatedly insists that to solve the cache, you need you and a friend to simultaneously visit two different waypoints. When you and your friend get there, you discover why: at each, I’ve hidden a small electronic device, specially-built for this purpose (and instructions on how to use it). The two devices are a synchronised pair, and each shows on its screen a pair of numbers. To find the location of the cache itself, you need to add the first number on Box One’s screen to the first number on Box Two’s screen… and the second number on Box One’s screen to the second number on Box Two’s screen. But… the numbers change every 15 minutes: and because both boxes are hidden on opposite sides of Oxford, there’s no way to get from one to the other within the narrow window. Truly: you can’t do it alone!

Box One and Box Two stess test
The numbers shown on the screens in this photo, taken during their month-long “stress test”, are fake (they point to N 51° 12.123, W 001° 12.123: that’s not where the cache is).

Once the two cachers have each other’s numbers, they can head on to the final coordinates: the actual location of the cache: they can race there, if they like (it’s close-to equidistant from the two points) – though if they’re feeling that competitive, they’ll probably want to agree on some key exchange mechanism by which they can swap numbers without giving the person to speak first a disadvantage: I’ll leave that mathematical exercise for somebody else to solve, though! In any case, I’ve been sure to put two “first to find” prizes into the cache: one for each of the people who worked together to find it.

Visual schematic for You Can't Do It Alone boxes
Each box is operated by a pile of dirt-cheap Chinese-made components, inexpertly soldered together by me.

How does this magic work? Well, it’s reasonably simple, so long as you’re familiar with the conceptual workings of time-based two-factor tokens and the predictability of computer random number generators. I’m offering the source code and support in construction to anybody who successfully finds the cache, in order to try to inspire a new generation of digital caches in Oxfordshire (and further afield!). But the essence of it is an ATmega328 chip acting like an Arduino Nano, hooked up to a clock chip (powered by a long-life lithium “watch battery”) that keeps it in sync with its partner, and – while a switch is pushed – fully-powered by a stack of AA batteries (which provide enough power to do the maths and light up the screen).

Harmless Electronic Game Piece, written above Box One, in situ
Given how alarmed people sometimes get when they find sealed black boxes with digital screens, slowly counting down, I decided to include a reassuring note with each box.

The whole package is sealed up inside a custom-built acrylic box (courtesy of RazorLAB, whom I discovered after Rory did a craft project using them), and I’m hoping that they’ll live at least a year before I need to get out there and replace the AA batteries.

This cache represents a huge leap in complexity over anything I’ve placed before, and – I think! – might be completely unique in design, worldwide. I’m really looking forward to seeing what the community make of it! Want to go find it yourself? Start here!

Update (2018): This cache has now been retired. If you’re interested, you can read the source code here.

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Dan Q found GLF3K5BF Plaque Buildup (Geolympix FTFrenzy-1)

This checkin to GLF3K5BF Plaque Buildup (Geolympix FTFrenzy-1) reflects a geocaching.com log entry. See more of Dan's cache logs.

Finally got around to spending a lunchtime hunting for this cache, and I’m glad I did: what a wonderful tour of some great backstreets, that I already thought I knew so well. Was slowed down by some scaffolding partially-covering one of the clues, but a helpful man working on the site was able to show me what I’d missed (and to be fair, if I’d been paying more attention I’d have found it myself eventually!).

TFTC; and have a favourite point.

Dan Q performed maintenance for GC54F7B Oxford Steganography #2 – Selected Text

This checkin to GC54F7B Oxford Steganography #2 - Selected Text reflects a geocaching.com log entry. See more of Dan's cache logs.

Came out to investigate missing lid. Found lid a short distance away – possibly muggled. Cleaned cache contents, checked silica gel still doing its job, replaced lid. Game on!

Dan Q posted a note for GC54F7B Oxford Steganography #2 – Selected Text

This checkin to GC54F7B Oxford Steganography #2 - Selected Text reflects a geocaching.com log entry. See more of Dan's cache logs.

Thanks, Go catch; I’ll try to get out there for some maintenance at or before the weekend. If you’re having difficulty with the overlays, it’s worth checking that your printout is the right size (after talking to some ‘cachers, I’ve discovered that some computers are printing it a tiny bit smaller: users of these computers need to ensure that the “resize to fit page” or similar checkbox is NOT checked, when printing). So long as your name appears in the log when I get there, though, you’re welcome to PM me and I’ll send you the number you’re missing. Thanks!

Dan Q posted a note for GC56KEX The Bate Collection of Musical Instruments

This checkin to GC56KEX The Bate Collection of Musical Instruments reflects a geocaching.com log entry. See more of Dan's cache logs.

With a difficulty rating of 2/5 I thought this would be a reasonably easy puzzle, but I guess my poor heat-addled brain isn’t up to the task. I thought that perhaps visiting the Bate Collection early this afternoon might help, but it turns out that they only open at 2pm in the afternoon (by which point I had to get back to work), so I’ve not had any luck yet! Some day, perhaps!

But be warned: if you plan to visit the collection, they don’t open until 2pm on weekdays.