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Topic: Door lock using RFID (Read 8617 times) previous topic - next topic


I'm building a RFID reader, one arduino and one electric lock. The system is working well, so far.. but i would like to make it bulletproof! after all it's a front door!

The project is here: http://www.balua.org/Balua/RFID_lock.html you can find the code and the electric connections...

Does some one has ideas do get the code safer?
I'm afraid that one day i find the door opening on it's own!



You should also worry about being locked in the house in case of a power outage or god forbid a fire.


At the moment i'm using the mechanical lock as the "master", the electric part is something like this:


So going out shouldn't be a problem.. but having it open when it shouldn't really worries me...

Implementing a watchdog will improve the system?


The sort of system you are using... an electro-mechanical strikeplate seems by far the best alternative for your application... it is "fail safe".... if it doesn't get electricity, the door can't be opened.

The other sort of electrical lock, the magnet type, is "fail weak"... the door is only "locked" when the device IS receiving electricity.

More on electromechanical strikeplates at...


Try to think through all the possible scenarios... I haven't looked in detail at your circuits, but ask yourself...

What does it take (in terms of "steps", not volts/amps) to "turn on" (i.e. unlock) the strikeplate? How could that happen, other than the ways I mean for it to happen.

Ask yourself what happens if your power goes off, and then on again. Is there a relay in your system? What happens if it fails? What happens if the Arduino program starts, but then freezes up before getting to the "loop" part?

The good news is, that with the lock you are using, it shouldn't be too hard to make the system failsafe.

You might want to put a switch, inside the house, on the line to the strikeplate. If you were going away for a few days, open the switch, thus ABSOLUETLY disabling the electronic lock. Can't open when there's a "break" in the wire just before the lock, can it?

Is this on your home? What home is hard for a burglar to get into? If someone is willing to steal your TV, they won't be shy about breaking a window. I'd almost make it easy for someone to break in, so that repairing the break-in isn't expensive. I put my energies into alarm systems, which make it unpleasant for burglars to STAY in.

And I set them up so that I can have them on when I am at home, in bed, asleep, monitoring the parts of the house I don't use in the middle of the night. You do not want to be the person who has seen the face of some burglars. And while I already have bells wired up, I connect them to smoke detectors, too.


Further fail-safeing option....

In addition to the RFID "open the door" provisions, you could add a little panel with four switches, outside the house. All would me momentary (like a doorbell). Two would be normally open, two would be normally closed. You could make one of them your doorbell, too... even if it took using a DPST switch there.

They would be wired into the circuit to the electromechanical strikeplate... entirely "dumbly"... they wouldn't be "seen" by the Arduino at all. But you would wire them up so that the strikeplate would only work if one (or maybe you'd do it so that all were required) of the right buttons ARE pressed, and none of the wrong buttons are NOT pressed.


Also, consider how you will get out of the house if these is a fire. Especially a fire that has cut the electricity off. Would you have a battery backup and hard switch, if you are using a fail-to-locked lock?

I think I would prefer a lock that could be mechanically overridden.

Also, whatever you do, I would test thoroughly in isolation, turning power off etc and then run it in parallel with an ordinary lock for a few weeks until you are confident about it.

Its now safety critical software. When I worked in defence, the main rule for that in your programming was 'allocate everything statically' and yes, a watchdog reset is a good idea - as long as it doesn't open the door ;)
I write books about Arduino and Electronics: http://simonmonk.org


I used to have something like this http://buyaccess.com/samsung-ezon-shs-3120-digital-keypad-deadbolt?gdftrk=gdfV22700_a_7c1040_a_7c3889_a_7cSHS_d_3120 at my place in Korea...
I think it works with a motor, requiring the installation of the door to be perfectly aligned with the frame. One interesting feature it had was two contacts on the outside where I could connect a 9V battery to open the door in case the batteries died or the power was off in the whole house.

Mind you, it wasn't a dangerous area where I lived and I had it inside a building... but it's quite a nice possibility too. And some also tell you when the door is open or close with a girly voice.
This... is a hobby.


Hi everyone!

First of all, thanks for the replies and ideas!

I'm using the system for 2month now, and no problem so far =)
I found a bug that caused an unintended "open door" when a tag read fail had place! The important is that now that is solved the system is working like fine!
And yes i'm now pre-allocating all space

In the meanwhile I found a cheaper way to do the same thing! how?
Using iButtons devices instead of RFIDtags and a RFID reader..

Using Ibutton the system becomes simpler and cheaper! the project is here:

Again thank you all!


Be sure to check what your system does during and after a power failure.

I finally finished putting all the elements of an RFID door lock together in the same place, at the same time...


One of the last "little gotchas" I had to deal with was that the lock was briefly UNLOCKED when the Arduino was powering up... as it will do, each time the public supply fails and then comes back... not uncommon where I live in England. I HAVE dealt with it... it just took a capacitor... but it is a fail scenario which is easy to overlook.

(And yes, the Dallas fob is another good solution, if you don't mind putting a "key" in a "slot".)


I took my degree in Porto, and I still remember two police detectives (PJ, dcoimbra knows what it means) walking in the laboratory I used to work in with an iButton asking for some help to figure out what it was and how could this bug be used and if we could track who was listening to the judge calls in his office. LOL

It was my first time seeing one of these things... of course, the Maxim-ic mark on them took us to their website and we found out what they were. We asked about where he had found such a "bug" and it was in a recently bought very expensive piece of furniture for his office. The iButton was used as some sort of serial number for the piece. Probably it was forgotten when he bought the piece.

Never used one though... :(
This... is a hobby.


At the moment i'm using the mechanical lock as the "master", the electric part is something like this:


So going out shouldn't be a problem.. but having it open when it shouldn't really worries me...

Implementing a watchdog will improve the system?

If that's the hardware you are using, I'd think that the biggest security threat is physical - a latch-and-strike plate combination is not very strong - a good kick can usually break the door open.  We have a similar electric strikeplate in the office (controlled by the phone/intercom system), and it's very flimsy - a solid kick to the door will break it wide open.

You should never have just a latch securing a door - you need a deadbolt, as well!  Unfortunately, deadbolts are much more difficult to implement with automation.

Another good option is a magnetic lock, something like this: http://www.sdcsecurity.com/category.aspx?id=6 

You can find a cheaper one for around $90 on-line.

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