Secret Attic Library Door

We have a pretty good guess where [Krizbleen] hides away any seasonal presents for his family: behind his shiny new secret library door. An experienced woodworker, [Krizbleen] was in the process of finishing the attic in his home when he decided to take advantage of the chimney’s otherwise annoying placement in front of his soon-to-be office. He built a false wall in front of the central chimney obstacle and placed a TV in the middle of the wall (directly in front of the chimney) flanked on either side by a bookcase.

If you touch the secret book or knock out the secret sequence, however, the right-side bookcase slides gently out of the way to reveal [Krizbleen’s] home office. Behind the scenes, a heavy duty linear actuator pushes or pulls the door as necessary, onto which [Krizbleen] expertly mounted the bookcase with some 2″ caster wheels. The actuator expects +24V or -24V to send it moving in one of its two directions, so the Arduino Uno needed a couple of relays to handle the voltage difference.

The effort spent here was immense, but the result is seamless. After borrowing a knock-detection script and hooking up a secondary access button concealed in a book, [Krizbleen] had the secret door he’d always wanted: albeit maybe a bit slow to open and close. You can see a video of its operation below.

Continue reading “Secret Attic Library Door”

Halloween Knock Box


[Kyle] has been an avid reader of HaD for a long time. In fact, he was inspired by a Halloween knock box from 4 years ago! He saved the link and finally this year, he went ahead and made his own.

So what is it anyway? Well, as the name implies, when you knock on it, it knocks back. And if you knock on it a special number of times, it’ll play a secret tune… It is a great little item to have at any Halloween event — and kids love it!

Design and function of the box is basically the same as the original, with a few modifications — most notably, swapping out the original PICAXE for an ATtiny85 microcontroller. [Kyle] even managed to find the lego skeleton and chains available on eBay. He’s put together a very thorough blog post on it and shared all the code and schematics — so if you’re looking for a last minute Halloween project, this might be it!

Stick around after the break to see the knocking in action!

Continue reading “Halloween Knock Box”