Who didn’t dream of a hidden door or secret passage in the house when they were kids? Some of us still do! [SPECTREcat] had already built a secret door in a fully functioning bookcase with a unique opening mechanism. The intriguing mechanism allows the doors to start by sliding slightly away form one another before hinging into the hidden space. Their operation was, however, was manual. The next step was to automate the secret door opening mechanism with electronics.

The project brain is an off-the-shelf Arduino Uno paired with a MultiMoto Arduino shield to drive 4 Progressive Automations PA-14 linear actuators. These linear actuators have 50lb force, allowing the doors to fully open or close within 10 seconds and maintain a speed that wouldn’t throw the books off the bookcases.

Not wanting to drill a hole through the bookshelf for a switch or other opening mechanisms, [SPECTREcat] added a reed switch that is activated on the other side by a DVD cover with a magnet inside. In addition to that, there is a PIR sensor on the inside room to automatically close the doors if no motion is detected for 2 hours. Dont worry, there’s also a manual switch inside just in case.

Using one of the items on the shelf to trigger the secret passage is a classic move. He could also have used a secret knock code, like the Secret Attic Library Door we covered in the past. Check out the video below to see the hinge and slide movement in action.

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.