How to actuate a hidden door

Hi Everyone!

I have a question about how to actuate a hidden door. I have always wanted to build my own in-wall hidden compartment. This will be a small (or maybe even large), storage area. As of now, this will not be a "safe". This is more of a hidden compartment than anything that needs to be secure. It might eventually lead into plans for a gun safe, but there are plenty of commercially available ones that would be better than building my own (for security, fireproofing, .....). Plus something like that is best left to the pros.

With that out of the way, I am trying to figure out how to control a door without OBVIOUS mechanical controls on the outside. This leads me to believe that this will be a perfect use for the arduino and an electronically controlled "release mechanism". What I am looking for is what type of release mechanism I should be looking at. I know I could use car door locks and such, but I am not sure if that would be best.

Ideally there would be a flat panel cut out of the drywall and a case built into the existing wall cavity. I could use various methods to minimize the obviousness of the area, and I think that is outside the scope of this post. The door ideally could be spring loaded and pushing it shut will "lock" the door. Activating the release mechanism could release the door and since it is spring loaded, pop it out a tad. This would negate the need for a handle or door pull. Pushing it in again would lock it shut.

I am not asking for anyone to design this for me, but I am not sure what type of hardware I should be looking at. Linear Actuators, Solenoid, door locks? I do not have experience with any of these.

What somes to mind is the cabinet doors I always used to have on entertainment centers where you push to lock shut, and push again to pop out. The difference of course would be that pushing it only closes the door and there would need to be some kind of electronic trigger to pop it back open. For now, I am ok with it being triggered by a push button. A keypad can be added later.

Long winded I know (sorry). My main question is whether or not there is a premade (reliable) device that already does something like this. I could probably create one, but I am not a mechanical engineer, and I would want it to be reliable, and I do not have extensive fabricating equipment.

Sorry to respond to my own post, but I was jsut thinking again (I know twice in the same day?).

What about something similar to how car trunks can have an electronic release?

If it were a full size door, I would suggest what is called an “electric door strike”; you can probably find small versions of such devices for cabinet doors or such. Then again, such things might be custom for each manufacturer. At any rate, they aren’t likely to be cheap (full sized door strikes can get really pricey).

Your best bet might be to look into a regular cabinet door latch, then see how you could actuate it with a servo or a solenoid, and finally, how to modify it (sorry, but you’ll have to do a little engineering here) so that whatever knob or such used to actuate it in its original form can be removed while still allowing the new mechanism to operate.

I will probably take a trip to home depot or lowes soon then to see if they have door latches there. I am not sure where to look.

Thanks for the help guys!

This guy used a piezo sensor for a 'secret knock pattern' to open a door (no wires outside the door). http://grathio.com/2009/11/secret-knock-detecting-door-lock.html

I made an auto-locking little treasure chest just using a 180 servo and a cheap latch from a hardware store. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1277776942 You could use the sliding kind of latch for your door.

Good information.

Seeing your box has helped me visualize a few things. I would like to have it close passively. I guess that I could have a switch that gets closed when I push the door in, locking it again.

I just dont want to have something that I have to do something to it to get it to close, other than pushing it in.

How did your box latch shut? It looks like it opened when it got cold, did it just close again when it got warm?

Yeah, the 'else' part of the if statement would close it when it warmed up. Since your door would be opening differently though, you could have one of those cheap sliding latches that will slide behind the drywall. You could also use a light sensor (since it will be dark in there) and a delay. Once it's completely dark, wait 5 seconds, then lock it. Unlocking it would have to be something else though.

I am going to look into the solenoid angle first. Does anyone know of a good source of them?

It looks like they are not going to be very cheap.

it looks like something like this would work well.

https://www.allelectronics.com/index.php?&page=item&id=SOL-58&index=1

I dont see how far the solenoid will retract.

What I am thinking with this would be to have the door spring loaded (somehow). When activated, this solenoid will retract and the door will pop out slightly. I am assuming that this solenoid will be spring loaded and return to the out position when power is cut.

At this point, will the solenoid be springy? If so I could put an angled edge on the door, like the strike plate on a regular door. Pushing the door closed will push the solenoid in a little and you will have to push against whatever spring load you have on the back of the door. You push hard enough and you should be able to push the door in to the point that the solenoid will line up with the hole in the door again, and snap in.

I might be overexplaining it, but I am just trying to go through it all to see if I have missed anything. It would work almost exactly like a simple doorknob, except that the part that sticks out will be on the frame, and not on the door.

The parts list would be pretty simple. At first, I would not even need an arduino, but I will probably put one in just for the sake of upgrading to a keypad later, or doing some funky programming.

What do you think? Do you think that would work with only a solenoid?

At this point, will the solenoid be springy? If so I could put an angled edge on the door, like the strike plate on a regular door. Pushing the door closed will push the solenoid in a little and you will have to push against whatever spring load you have on the back of the door.

doesn't the strike plate on screen doors have a spring loaded bar? It would minimize the amount the solenoid would have to retract (if any) when closing it.

http://hardware.hardwarestore.com/73-450-screen-door-strikes-and-catches/screen-door-strike-plate-603778.aspx

Don't forget a manual overide, you don't want to have to knock the wall down because of a programming bug :)


Rob

If I was making a secret compartment I think I would take a very simplistic approach for the door part. I would just mount a small servo into the door or jam and just have a hidden 3 terminal connector wired to the internal servo. The servo output horn would engage or disengage from a slot. Then just plug in my miniature handheld battery powered standalone arduino, possibly press some password keys and hit open or close buttons on the Arduino to activate the servo. However my need for secret compartments ended when I reached adulthood. ;D

I've seen $5 servos on E-bay.

Lefty

However my need for secret compartments ended when I reached adulthood.

I guess I am still a little young at heart =)

doesn't the strike plate on screen doors have a spring loaded bar? It would minimize the amount the solenoid would have to retract (if any) when closing it.

That might not be a bad idea. I like it.

I will have to figure out a backup for sure. A pull ring under the baseboard is exactly what I had been thinking of.

http://www.leevalley.com/us/hardware/page.aspx?c=&p=40353&cat=3,41399,41403

Simples.......

Wow, that is really cool too.

a RDIF reader built in the door will allow you to have a door without a lock.

I have a door like that, but i do have a backup battery hooked for just in case.