Add A Key-fob Opener To Your Door


It seems like creating an automatic dorm room door opener is a rite-of-geek-passage each fall. [Adam], a student at Vassar, passed with flying colors by creating this clean setup. We’ve got video, more pictures, and a description after the break.


Above we see the device mounted on the inside of the door. The larger box houses a printer head carriage that does the physical turning of the handle. When the carriage moves from right to left it pulls a string attached to a long lever on the door handle (seen in the picture at the top of the post), providing the turning motion. Below this box is the control circuitry that we’ll look at next.


Here we have the brains of the operation. In the project box on the left is a board that takes care of the wireless fob communications. [Adam] tells us this works from about 250′, uses a roll algorithm over RF for security, and has a dedicated 12v DC power supply. In the middle is the timer circuit that controls the motor operation, with four 9v batteries providing the motor with power.


Motor control is provided by a timing circuit using three 555 timer ICs. [Adam] based his design off of a two chip delay circuit but scaled it up to three to give him more options. The circuit is responsible for driving the motor until the latch is open, holding for a set amount of time, then returning the motor to its original position.


Because he’ll be moving out at the end of the year, [Adam] wanted to make the system easily transportable. He’s used a jack system so that the controller can be mounted either above or below the motor unit at his next residence.

This works well and with the covers on the project boxes it’s not the duct-tape mess of the last door opener we saw. Nice work!

27 thoughts on “Add A Key-fob Opener To Your Door

  1. This is by no means a “clean setup” it is “cleaner than others we’ve seen” setup.

    Clean setup would be a selonoid actuated lock hidden in the door itself controlled by the electronics. Kind of like those commercial locks that we see at the HW store with keypads.

  2. @Concino
    Seeing as they cannot modify a dorm room door in any way (no drilling holes, no hollowing out recesses for solenoids, etc…).

    Could it be cleaner? Sure, but it’s all “neatly” installed in project boxes and contained well. It also lacks the duct tape approach seen all too often in these installations.

    Thumbs up!

  3. While the RF comms of the keyfob might be very secure, the door lock itself looks like it could be defeated with minimal effort (a credit card, maybe?).
    I can’t see how using a RF remote instead of the key would be much more convenient-it’s just as easy to forget or lose, it’s bulkier and it also needs to be taken out of the pocket. I’d prefer an RFID-based system with a couple of tags that can go into whatever thing seems to be convenient (like a watch, a shoe, a pocket, a ring, …)

  4. @dan – I actually had my own working RFID setup before switching TO the fob mechanism. The main problem with RFID was how much power it consumed. It chewed through batteries to fast and the wall-wart power setup wasn’t very pretty.

    I take it you don’t have a fob for your car either? My previous car had to be unlocked with the key but I now find fobs much more convenient.

  5. Can’t you just take one of those supper cheap RC cars at Walgreens that only go 2 ways, add a limit switch, an electrolytic cap., string, a diode, exc. Then change the 27 MHz crystal with some other value that isn’t that as popular. And cram it all into a project box then stick it to the door?

  6. 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.

  7. Hey guys,

    just to respond to some of your comments.

    -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.”

    -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.



  8. 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.

  9. @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.

  10. @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.

  11. 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

    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.

  12. 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.

  13. @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”.

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