Keyless entry using touch sensing

posted Oct 20th 2008 8:30am by Caleb Kraft
filed under: arduino hacks, daily, home hacks

[Alex] sent us this slick little keyless entry system. He wanted a discreet way to trigger the door to unlock. Knocking was too loud, and would give away his secret access code. He decided that touch sensors would be the best. Initially he planned on using the doorknob itself, which would have been awesome, but it was just too much surface area for his touch sensor. Ultimately, he settled for a wire he could touch. An Arduino detects whether or not the correct code has been put in and initializes a high torque servo which turns the doorknob from the inside. In the video, after the break, you can see that it works fairly well.

One thing that is pretty cool about this is that it could be removed and reinstalled somewhere else in a matter of minutes. That’s good, since he’s in a dorm and would probably be in some trouble for damaging the door. It would be nice to see this put into an enclosure that hooked over the top of the door so it could be truly portable.

Comments [18]

tagged: arduino, keyless entry, lock, touch sensor

Reader Comments

Very nice project. Well documented. But how practical. A very creative Idea and I don’t know how. but using all this technology, could the touch sensitive sensor be wired to an unobvious piece of metal like the screw in an outlet wall plate. So you just pushed on the screw which was connected to the wire for the sensor and you activate the project that way. I would be worried about thieves catching wind of your smarts and breaking… er.. waltzing right in. Very cleaver hack none–the-less

Posted at 9:36 am on Oct 20th, 2008 by kyle007

Could be useful for car entry as well, especially since many cars already have electric door locks.

Posted at 10:19 am on Oct 20th, 2008 by JDN

Cool hack, but Hackaday, can you guys drop that Ad for fixing red-ring xboxes? It’s CLEARLY a scam, go check it out yourself, it reminds me of those “run your car on water” scams. I’m worried someone might actually spend their money on it! I know you need money, but not at the risk of your readers getting scammed.

Also, for the hack, you could get away with a smaller servo if it retracted the latch directly, rather than turning the handle.
-Taylor

Posted at 10:30 am on Oct 20th, 2008 by Taylor Alexander

“damaging the door.” no damage to the door. everything is duct taped or in the case of the servo held in by the spring like metal

Posted at 10:40 am on Oct 20th, 2008 by Mick

taylor I think you missed the point about not wanting to damage or change the door in any way since he is in a dorm and would be liable for any damages. I like the idea of enclosing the components into something that could be hung from the top of the door with the servo. It is a great hack.

Posted at 10:44 am on Oct 20th, 2008 by Buzzkill

Great project, I’m sure the touch sensor was just a test. It would be really easy to integrate a keypad. I saw something on Sparkfun.com that did something similar. They used a color changing keypad. 8 keys that lite up random colors, you press the right colors in order to unlock the door. Adds a little more security then a numbered keypad even.

Posted at 11:52 am on Oct 20th, 2008 by kurf

“An Arduino detects weather…”

Hehe, cool. So it works in the rain too?

Posted at 12:07 pm on Oct 20th, 2008 by D

Very cool. Stick the servo, arduino, etc in a nice enclosure, add a flat hook so it can be hung on the door, and run the touch wire alongside the hook.

That would make installation as simple as hanging the thing on the door and tightening a strap around the doorknob. You might even be able to market something that simple to people in temporary housing situations.

Six tap lengths might be pushing it, three seems reasonable. With a key length of 12 taps that would provide about half a million combinations, which is reasonable.

Posted at 1:04 pm on Oct 20th, 2008 by amk

Maybe you could build a retina scanner into the peep hole.

Posted at 2:27 pm on Oct 20th, 2008 by Insipid Melon

I don’t know if this door had one but the peep hole on most dorm doors would be ideal since it’s usually brass and goes all the way through the door… that way you wouldn’t have a suspicious wire sticking out.

though this reminds me of a few EE friends I had in college that wired a camera flash capacitor with one end on a wire hanging in front of the peep hole with a sign that said: “DONT TOUCH” and the the other end ont he peep hole itself, you’d see people stop as they’d walk by hit the sign and get scared half to death by the resultant electrical _pop_

Posted at 3:32 pm on Oct 20th, 2008 by twistedsymphony

How about a camera in the peep hole connected to a computer that can recognise sign language?

Posted at 3:58 pm on Oct 20th, 2008 by Haku

or you could hook the touch wire onto the doorknob so there wasnt a wire sticking out. just tap your fingers on the doorknob and it opens for you.

Posted at 5:09 pm on Oct 20th, 2008 by peter

kyle, it is a specific tap order and length – thieves couldn’t just ‘waltz right in’ unless you were really obvious in entering the series!

I’m hoping that someone does make a real portable version of this – like a box with a retractable wire and the shoelace(s) so that, once you remove the two wires/strings, you really can just pick it up and move it.

Posted at 5:41 pm on Oct 20th, 2008 by Metroid48

Excellent hack!
An alternate touch sensor that I used years ago is an FET amplifier. It picks up the ambient 60Hz when you touch the single wire. This could be used for the doorknob.

Using the circuit at this URL you could reduce it t to give a logic level input:
http://www.uoguelph.ca/~antoon/circ/touch1.html

Posted at 5:56 pm on Oct 20th, 2008 by Richard Cook

WTF is up with the crap ad post get that crap off of my hackaday! this goes to smith, not Taylor, his grievance is real. (Love the hack) Spam just pushes my buttons.

Posted at 11:18 pm on Oct 20th, 2008 by nick

@ Metroid48
I totally missed that about the sequence… I was wondering why [Alex] in the video was making contact with the wire several times. I though he was trying to make an initial contact which was eventually connected. Many many moons ago I had a simple touch lamp which eventually found it self taken apart. The touch sensor was a wire just like the one that [Alex] made. And I wired the whole thing up with speaker wire to each of the lights from the lamp. And hung them in my ceiling rafters the touch sensor I connected to a decorative piece of brass, and depending on the moisture of your skin it either made contact or not so you might have to hit the sensor a few times.. this is why I over looked the sequence which you brought to light. Thank you.

@ Smith wth! we should hack your ip and break your computer. jerk!

Posted at 9:02 am on Oct 21st, 2008 by kyle007

You could do it on the doorknob too–I’ve found that doing touch sensing circuits manually (i.e. provide the analog yourself or just use digital I/Os in less extreme cases. Better yet, if you really know what you’re doing, it’s not unreasonable to sense through the wooden door, provided that you compensate for moisture changes and if there’s no nearby metal.

Posted at 1:41 am on Oct 22nd, 2008 by threepointone

hmm… interesting idea, cool implementation, but not very secure… for a variety of obvious reasons… however… nothing really is secure, is it?

Posted at 2:54 am on Oct 23rd, 2008 by Louis II

Keyless entry using touch sensing

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