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The Skull CTF

A mind-bending hardware puzzle in three acts

$4,031 raised

of $666 goal

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Can You Hack Into ATtiny Brain?

Centuries ago, she was Queen of the Pirates.
Now, you are holding her skull in your hands.
A tiny piece of her mind remains within,
barely alive, and it holds a dark secret.

Awakened by a gentle touch, her eyes will glimmer,
and cease shortly after. They say the eyes are
windows to the soul, and this lost soul is waiting
for you to uncover her secret and set her free.

Will you take up her quest?

For Anyone Who Love Riddles

The Skull is a Capture the Flag (CTF) riddle that invites you to explore the internals of the AVR architecture. It has multiple stages and will likely keep you busy for days, or even weeks, as you exercise the muscles in your brain and apply them to the riddle in hers. Unless of course your mind slips its grasp on reality and you tumble, unmoored, into the swirling, lunatic void. In which case you might be at it a while longer. In order to keep your sanity intact, you will need three things: the ability to read and understand Arduino code, a willingness to spend some quality time with the ATtiny45 datasheet, and basic programming skills.

You will not need any special hardware, an electrical connection to the Skull, a soldering iron, a trephine, or necromancy. Nor will you need a battery, because we’ll send you one. A tiny CR2032 coin cell has enough juice to keep the blinkenlights on for at least a year. And we mean at least a year. The wildly efficient ATtiny draws as little as 0.33 µA while in sleep mode, so that battery could theoretically last for 50 years.

Kind of makes you think about your own mortality, doesn’t it?

Decorative & Spooky

When it’s not breaking your brain, the Skull doubles as a decorative badge that flashes its eyes when you touch a small contact panel on the back of its head. It’s the perfect way to spice up your Halloween wardrobe or to add a little mystery to your porch decor. And remember, our commitment to open source extends well beyond hardware and software. Looking to knit a hat for your Skull? Think it would look kinda badass with an eye patch? Or a forehead tattoo? Or a face mask? Go for it! We’re certainly not going to stop you. In fact, we’re here to help!

A 3D-printable model for these glasses will be made available in our GitHub repository. They are intended for cosmetic use only and should not be prescribed as an optometric intervention for the undead.

Enrage Your Loved Ones & Torture Those Around You

Write your own riddles! The Skull will keep you busy for a long time as it is, but her story doesn’t have to end there. Using the optional programmer and headers, you can devise your own challenges based on her stock firmware, or modify that firmware to flash your own core riddle. The Skull’s the limit!

More interested in hardware mods? Use the programming pads to hook up a small buzzer and teach the Skull to speak. Or give her an I²C accelerometer and, with it, a sense of direction. Come to that, why not attach a Wi-Fi or a Bluetooth adapter and unleash her upon the Internet? What’s the worst that could happen?

And, if you want to share your mods with others, you could even design them as tiny PCBs with castellated mounting holes so they can be soldered directly onto the Skull’s programming pads. Then you’ll be able to call them Bone Shields or Skull Hats or…Slaughterboards?

The Programming Header

The Skull’s programming pads expose three GPIO pins—PB0, PB1, and PB2—as well as 3V (from the battery) and GND. PB0 and PB1 are currently unused by the firmware, and PB2 is used for the small touch panel on the back.

Features & Specifications

Support & Documentation

If you have any questions, you can reach out to us using the Ask a technical question link on our campaign page. And you should feel free to check out our Getting Started Guide, our firmware, and the following KiCAD circuit schematic (all of which are spoiler-free).

The buyer assumes full liability for all mental, emotional, and spiritual risks associated with exposure to the riddle contained within the Skull. Not to be consumed as food.

Programming header not included in the standard version of The Skull

In the Press


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Produced by Wokwi in Ramat Gan, Israel.

Sold and shipped by Crowd Supply.

The Skull

A single The Skull CTF board (☠)

$25 $8 US Shipping / By Weight Worldwide

SparkFun Programmer

From the Crowd Supply Basics project.

Design your own puzzles and load them into The Skull's brain using this programmer! Mini USB cable not included.

AVR Pocket Programmer by SparkFun

$17 $8 US Shipping / $18 Worldwide

EconoStik Header: DR VT SMT 2x3

From the Crowd Supply Basics project.

Use with the SparkFun Programmer.

One Amphenol FCI EconoStik™ 2.54mm Header. SMD/SMT Mounting style, Straight angled male pins, gold-plating. Voltage rating: 110 V

$2 $8 US Shipping / $18 Worldwide

About the Team


Ramat Gan, Israel  ·   wokwi.com

Wokwi creates tools for the Arduino and maker community, such as AVR8js, the Open source Arduino Simulator, and GoodArduinoCode.

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