Knock knock… — Who’s There? (GC3Z1EY) — Geocache of the Week

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Geocache Name:

Who’s there? (GC3Z1EY)

Difficulty/Terrain Rating:


Why this is the Geocache of the Week:

First, check out the video up top—that should clear up most of it. This geocache shows an incredibly creative use of the Arduino computing platform. We’ve seen geocaches with pretty creative locks, but never one where you actually have to knock before it will let you in. Furthermore, this geocache, which seems like a pretty complicated device, was conceived and built by a CO with no technical background. His dedication to learning the proper way to build and program is a great example for geocachers looking to hide the next Geocache of the Week.

What the cache owner, Mr. 0, has to say:

What inspired this cool locking mechanism?

It was coincidence, really.  I happened to see a copy of Make Magazine (vol 25) on the shelf for the first time.  I picked it up because it looked interesting.  There was an article showing how to build a secret knock gumball machine that would dispense a piece of candy when the correct knock was given.  I immediately realized that this could be adapted to lock a geocache.

Do you have a programming or technical background?

None at all.  Before this project the most I had done was poorly solder some speaker wires together in an old Jeep, and I once got about 200 lines into a Zork knock-off in Basic on my C-64 when I was a kid.  I just picked up an Arduino Uno, a soldering iron, some parts, and started reading.  Thankfully Arduino microcontrollers are designed to be easy to program and use, and there’s a very helpful community behind them.  Going from nothing to the completed cache took about 3 months of occasional dabbling.

What has been your reaction to all of the positive logs and favorite points?

I wasn’t really sure how it would be received. I figured some would appreciate the novelty, but they might ultimately be put off by it not being a park and grab.  It can also be a little fiddly, so I was worried it wouldn’t work right and just frustrate finders when they couldn’t get it to open up.  I’ve been very pleasantly surprised by the comments, favorites, and messages I’ve received about it.  I’m happy to give the local community something a little different to find.

What geocachers are saying:

“We decided that we wanted to do a fun one today, and this cache came to mind. Hlemont, Denver, and I had a great time. The containers for both stages were awesome! Definitely looks like a lot of time went into both stages. Thank you for sharing this cool idea, and neat spots in the park. Everything is in great shape. Favorite point added :D” – Limont

“One of a couple very select caches today. This has been on my “to do” list since it was published and it exceeded by expectations.” – captphil

“This was a really unique cache. I liked how it combined deep woods hides with 21st century technology. The two stages were nicely balanced. Be sure to pay attention at stage one or you will have to go back. Our first several tries at stage two didn’t work, but we finally got our timings aligned and OPEN SESAME the cache revealed itself to us. This was a great excuse to hike in a park I had not previously visited. Very enjoyable. It gets a solid favorite vote from me. TFTC” – TimeSeeker




The device in stage 1. Photo courtesy of Mr. 0
The device in stage 1. Photo courtesy of Mr. 0
What you'll find when you open stage 2. Photo courtesy of Mr. 0
What you’ll find when you open stage 2. Photo courtesy of Mr. 0
If you find the rhythm, you'll get the reward. Photo courtesy of Mr. 0
If you find the rhythm, you’ll get the reward. Photo courtesy of Mr. 0

What has been your favorite geocache that involves solving a puzzle? Tell us in the comments.

Continue to explore some of the most engaging geocaches around the globe. Check out all the Geocaches of the Week on the Geocaching blog.

If you would like to nominate a Geocache of the Week, leave a comment below with the name of the geocache, the GC code, and why you think we should feature it.