# Electromagnetic Door Lock

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#### noobtech+

##### New Member
I need help building one for use in my shop so I can filter customers coming in and out. Possibly one which looks like a Car door actuator will do.

#### Electric Rain

##### New Member
You could use a reed switch. Can you give me details about how you want it to alert you?

#### tdb

##### New Member
What you are looking for is a solenoid driven linear actuator. These are typically driven by 12 or 24 VDC, and force magnet through a coil when activated. A metal rod is attached to the magent that can be used to bolt the door shut. I don't know of a specific manufacturer off-hand, but do a search on the web for them.

#### noobtech+

##### New Member
What I need is a diagram to build it myself! Anyone?

#### noobtech+

##### New Member
It's main function is to lock the door at all times. When I hit the switch the mechanism must release the lock so the customers can open the door!

#### pebe

##### Member
noobtech+ said:
It's main function is to lock the door at all times. When I hit the switch the mechanism must release the lock so the customers can open the door!
Further to what tbd has said, locks are available for 12vAC operation also. They can be supplied as 'normally locked' or 'normally unlocked'

You need a normally locked one, then by applying 12v via a push button you can unlock it for as long as you hold in the button.

#### Qema

##### New Member
tdb said:
What you are looking for is a solenoid driven linear actuator. These are typically driven by 12 or 24 VDC, and force magnet through a coil when activated. A metal rod is attached to the magent that can be used to bolt the door shut. I don't know of a specific manufacturer off-hand, but do a search on the web for them.

That is an exelent way to begin. yes this will be the heart of your project but there are a few things you should look at first.

1. should the system Fail close or fail open. ie. when power is cut to your locking mechanisim should the door lock or should it unlock. Personly Id say have a main lock (deadbolt or such) and set up your system to Fail open(unlocks when power is lost). This is a safety percotion. incase you are in your shop and the pwoer cuts out (say do to a fire) you want a clear escape route. also if it fails closed (locks when power goes out) will make sure that if the power goes our (or the unit melfunctions) that it will not prevent you form entering your own shop.

2. Now you got to look at it mechanicly: The rod of the acutatior SHOULD NOT be used as the bolt for the lock. People will yank on your door and bend the rod which will eventualy stop it form moving in and out.

I sugest you cut two 1inch long pieces of hollow square metalic tubing mount one on the door and one just off the wall so that a wedge of some sort can travel through both of them. Then create some sort of wedge that can fit into thouse braces (square tubing) a smaller piece of squaretubing should work. Make sure the wedge is metalic and not wood or plastic you dont want it wearing out its edges on the small gap between the braces. you might want to create some travels in one of the braces so that the wedge has limits to its movements. Now make sure the the wedge sticks out so that you could attack the solinoid to it. attach it so that the solinoid can pivit a bit this way if someone is yanking on your door it wount sent the movement to your solinoid rod (againt he whole dont wanna bend the rod thing)

I suggest using something that resebles a simple 3 wire control for a motor for your project.

Code:
(+xV)                                                 (-xV)

|  Open PB    Close PB                         Relay   |
|-----|/|----+---| |----+----------------------(  )----|
|            |          |                              |
|            |   Relay  |                              |
|            +---| |----+                              |
|                                                      |
|     Relay                                  Solinoid  |
|-----| |--------------------------------------(  )----|
|                                                      |

So you will need:
2 push buttons (1 normaly open and one normaly closed)
1 Relay with 1 Normaly Open contacts
1 Solonoid (liniar action retracts when power is cut)

If you have any questions ask away. but i hope that points you in the right direction.

#### tdb

##### New Member
Here's a diagram to what pebe said. It's really just this simple (and sometimes the simplest answer is often the best). Just determine whether you want the door to be locked or unlocked when power is applied to the solenoid, and keep that in mind when buying the solenoid. For linear actuators, it's sometimes called push or pull, meaning the rod is either pushed out when power is applied or it is pulled in when power is applied. For safety reasons and to follow fire code, I would highly recommend that the door be unlocked when power is NOT applied (so probably a push-type). Also, whatever SPST switch you get, make sure it can handle the current that the solenoid will draw. The diode is optional, but I would recommend it to protect your DC power source. Here's a manufacturer for solenoid driven linear actuators:

http://www.ledex.com/

#### Attachments

• simple_solenoid_switch.jpg
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#### Qema

##### New Member
tdb said:
sometimes the simplest answer is often the best

No offence tdb but i think mine is the simpler solution, its alot easyer to get a relay then it is to get a diode.

I find that if you go to an industrial surplus store such as www.princessauto.com you could pick up a relay for pocket change. As far as diodes are conserned i find that its becoming harder to get off the shelfs. My local Radio Shack doesnt even carry them anymore and electrosonic is now charging money for there catalogs

On a related note today while i cheacked out princess auto i found a small liniar actuator for $5 and a 2 contact relay for$3, an a 9 volt AC adapter for $10 (the actuator i found was a 9volt), some cheapo push butons for$3 a piece (new) so the project i sugested would run you about 20 bucks of electrical components and 10 bucks for the wire and the metal.[/url]

#### Manihigh

##### New Member
Solenoid Door Lock

I am currently building just such a lock. I am using a combination of quad NOR gate and XOR gate to make a digitally 'coded' entry mechanism. If you are using a manually activated 'switch' then all you need is the solenoid. I have about five 'linear actuators' --> strip down a few quality Cassette decks or VCR's and you'll have a host to choose from-- that's where I got mine. Salvage is the go!!

#### Roff

##### Well-Known Member
Are we reinventing the wheel here? This is not the first requirement for this type of device. Witness remote access door entry locks in apartment buildings. I found **broken link removed** and **broken link removed** by doing a Google search for "electric door latch". I'm pretty sure they're the same part, but there are probably others that would work if this doesn't fill the need. I just wonder how this one handles power outages. If it had a key for outside access and a knob for inside access (which seem to be required in any case), that would solve the problem.
The problem with a simple solenoid is that it doesn't allow the door to fully close and latch once it has been opened unless you actuate it again. Otherwise, the door will close against the extended solenoid bolt. QEMA's latching circuit solves that problem, but it requires a conscious effort to relock the door, which doesn't seem reasonable.
Basically, what is required is a bolt which retracts automatically when it hits the strike upon closing (like an ordinary latch), but can only be opened by a key from the outside and a knob from the inside.

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