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I want to make my sonic screwdriver unlock doors. Yes I am serious. Answered

I want to take my sonic screwdriver (http://www.thinkgeek.com/geektoys/cubegoodies/8cff/?srp=11) and use it to unlock my bedroom door. I am thinking that if I make an electronic lock that uses a photocell I can just use the light that is in the screwdriver already.  I am having trouble finding a lock that will be easy to modify that is cheap. If it is a keypad lock I can probably just replace the buttons with photocells, but I am not sure. Any advice and ideas would be very helpful. 

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bwrussell (author)2012-05-14

You could add a small RFID chip into the screwdriver and and make an RFID controlled lock. Just search here, there are several good guides posted already. You should build some sort of physical override in or if the power ever goes out, your screwdriver breaks or is lost, etc. you will be forced to take more drastic measures to get through the door.

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countryboysc (author)bwrussell2012-05-14

It should be battery powered so power outages shouldn't be an issue, I worked on a diagram earlier but I can't scan it right now. I want the photocell to be a switch for a servo that move the bolt. The bolt mill most likely be wood so that if anything goes wrong I can force entry. The main issue that I'm having is finding a cheap photocell that will work for 9v and I also need a way to reverse the servo to lock the door.

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bwrussell (author)countryboysc2012-05-14

Right, but the electronics for the lock need to be in the room or it will be easy to disable. If you use batteries instead of mains then you avoid power outages but you run into the problem of batteries running out juice. That will happen much more than power outages.
Forcing entry isn't as simple as it seems if you make or use an actual dead bolt that is built into the door. I've had to kick in a few dead bolted doors and what usually happens is the deadbolt doesn't break, the door does. Your parents will not be happy if you break your door.

https://www.instructables.com/id/Photocell-tutorial/
The photocell he uses is $1.50 and has a max 150V. You can also salvage photocells from those garden lights that turn on at night.

Maybe instead of using a bolt use a servo, like you said you wanted to, with essentially a stick attached to one of the servo's arms. See the attached picture. That should keep anything from being damaged in the case of a loss of power.

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countryboysc (author)bwrussell2012-05-16

The door opens in, so to do that I would need to put a catch of some sort, which should be relatively easy. I am also worried about it simply just ripping the entire servo assembly off of the door. I was planning on the servo and locking assymbly being on the back and the photocell on the front of the door, which would be relatively simple if the wiring is right. Also if I built a catch for the stick, I would have to have a way to reverse the motor from the outside.

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bwrussell (author)countryboysc2012-05-16

That's always a possibility. You could make a weak point in the stick that shears when forced. You could also mount the servo to the wall instead of the door.

You are going to need to be able to run the servo in both directions from outside no matter what, to lock and unlock. You could have a timer that automatically locks the door after a certain amount of time.

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countryboysc (author)bwrussell2012-05-17

If there was a timer, it could lock while the door was open, and the door would crush the stick. Any ideas on a way to reverse the servo from outside other than using a timer?

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steveastrouk (author)2012-05-14

Shining a light on it is hardly a secure method. And what happens when you forget your sonic screwdriver ? Really, what you want to do is drive the light with a circuit for an IR remote control, and pick it up on the door with an IR receiver.

Steve

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I'm not too concerned with security. I mainly just want it so I can show my friends who would understand the references. If I forget my sonic screwdriver I can use a flashlight or something. I was originally going to use a garage door opener, but it would have been difficult to find a transmitter that would fit inside the body. That's why I decided on a photocell because the screwdriver already has a light built in.

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Burf (author)countryboysc2012-05-14

So, with your plan, on a bright, sunny day or when you turn on the room light, what's to keep the door from unlocking?

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