Comments on: Add a key-fob opener to your door

By: Chris Mavrakis

Chris Mavrakis — Thu, 16 Sep 2010 11:41:18 +0000

You could use Li-Po rechargable batteries instead of the 9V, if you have a suitable charger.

A 11.1V 1000Mah one should cost less than $10.

By: Stan

Stan — Wed, 13 Jan 2010 02:36:37 +0000

Found your blog on Ask and was so glad i did. That was a great read. I have a quick question.Is it alright if i send you an email???…

By: vernon

vernon — Sat, 31 Oct 2009 04:25:06 +0000

I remember playing with 555s in EE lab many moons ago. Nice use of the IC and nice set-up.

By: 0x808080

0x808080 — Fri, 16 Oct 2009 13:27:25 +0000

Clean install, can’t be cleaner

By: dan

dan — Thu, 15 Oct 2009 16:30:18 +0000

@Paul: Good point about power consumption. I think Adam’s setup uses a DC wall-wart to power the keyfob receiver anyway, as you can see a wire on the bottom left. So I guess battery drain is not really an issue for the receiver. It struck me as odd that he uses four 9V batteries as well, maybe the motor needs more than 12V to operate or the motor would draw too much power?
I use cars with fobs, but my current car didn’t come with one and I didn’t care to install such a system. Frankly, I find these very convenient when I’m looking for the car in a parking garage, but that’s just about it.

@Adam: Thanks for the clarifications! Overall, it’s a great hack!

@all: Car remotes are also not 100% safe, just google “Keeloq”.

By: Tom

Tom — Thu, 15 Oct 2009 15:59:34 +0000

@Garthok: This is where I shine. Glue a small spring in some inconspicuous place around the door jam.

By: Garthok

Garthok — Thu, 15 Oct 2009 14:50:47 +0000

You could add something to push the door open for you as well.

By: jonjon

jonjon — Thu, 15 Oct 2009 13:55:55 +0000

This is a very nice piece of work. Firstly, the execution is clean. Note the microcontroller, the breadboard and the power supply compartments neatly abstracted from each other. Note the adherence to requirements — no physical mods to the door. Note the attention paid to portability (he’s actually planning to be able to take the setup with him when he moves). Note the attention paid to security.
We should appreciate and applaud this guy’s talent.
How hard would it be to fab this up? Trivial. Not trivial to fab because of trivial implementation, trivial to fab because of clever and elegant design. This dude is going to show up on your radar screens again after he gets done with school, that’s for sure.

By: PlastBox

PlastBox — Thu, 15 Oct 2009 09:53:10 +0000

Nice setup! Always fun to see talented geeks to projects like these for fun. Things that need utility to have the right-of-life belong at work. =P

@rkor123:
You mean you have to twist the lock while pushing down the handle? Or just twist the lock? If it’s the latter just make a wooden lever with a slot cut into it to fit the “knob”, with a couple of metal rings that slide into place behind the “knob” to keep it in place.

If you need to turn both the lock and the handle, make a lever for each and attach string so that the lock-lever is pulled first.

By: @AMK

@AMK — Thu, 15 Oct 2009 03:08:13 +0000

@amk, the security on that door opener is an illusion, as the easiest way to get in is probably a nearby window, or to push in the door.

Anyways, I thought up something similar with a cheap eBay car alarm, the whole setup would have cost about $20, and included a rolling code key fob.

By: amk

amk — Wed, 14 Oct 2009 22:23:16 +0000

@Adam, I think the interesting part is not the opener itself, but the fact that is uses a key-fob with a rolling code, which is going to be at least 40bits, making it much more secure than other methods, like RFID, or the christmas light remote you mentioned.

By: Adam

Adam — Wed, 14 Oct 2009 21:35:32 +0000

why does everyone go so big with these setups? I did one with a 2″ throw cylinder, a slinky airline and the CO2 tank we used to pump up the keg.

The remote I used was formally one of those ones lazy people use to turn off their christmas lights.

By: A_Blind_Man

A_Blind_Man — Wed, 14 Oct 2009 21:00:05 +0000

Are you allowed to put screws into your door at the dorm? or if not how the heck did you hold that thing up?

By: Adam

Adam — Wed, 14 Oct 2009 20:29:24 +0000

Hey guys,

just to respond to some of your comments.

@Concino.
-You aren’t allowed to alter the door/lock in any way. Also, I am making a new set-up that puts everything in the main unit anyway, so it should be even “cleaner.”

@dan.
-The lock is actually one of the most expensive you can buy. The key itself is laser cut with two different sets of ridges. The door jam is made of steel and overlaps where a would-be intruder would try to shim.
-At first, I was skeptical that the system would really be useful (I was making it just for fun) However, much like another commenter said, it is similar to using the remote on a car. I actually don’t need to remove it from my pocket to use it and I can let other people into my room when I am busy or somewhere else (When roommate loses his key/remote). I am surprised by the many uses it has.

@All – The reason I used 555′s and the RF remote is that they are really easy to find/buy/use. I wanted a system that others could see and easily recreate. Other than the wireless circuit which I ordered online, the whole project can be made after a single trip to Lowe’s and RadioShack.

Thanks to everyone for your comments.

Peace

Adam

By: IceBrain

IceBrain — Wed, 14 Oct 2009 19:58:02 +0000

A passive RFID tag could not implement a rolling key system, rendering it extremely insecure.

The best way, imho, would be to add bluetooth, along with a phone app, implementing a simple challenge-response authentication protocol.

Even if a BT-enabled board is too expensive, many young “tech” guys have routers/seedboxes, which could easily be setup to drive a cheap BT dongle and control the engine via RS232.