I'm brand new to the Arduino world and want to tackle an interesting real life project. I want to create a wireless door unlock mechanism for my front door, just like unlocking your car as you walk up to it.
How feasible is this? So far I have completed just a few basic Arduino projects that mostly just control leds using a button and a breadboard. What hardware do I need to make this new project work? What would be the most cost effective way to do both wireless and a way to control a motor that could unlock a deadbolt?
My background is in software, but not electronics, and I'd like to pick this up as a hobby.
PS I just realized this should probably go in the "Project Guidance" section, mods, please move it there if that's a better place for this type of question.
jgehrs:
I'm brand new to the Arduino world and want to tackle an interesting real life project. I want to create a wireless door unlock mechanism for my front door, just like unlocking your car as you walk up to it.
Unlocking doors electrically happens all the time; typically there is a solenoid that pulls the locking bolt. You can even buy electric door locks/jambs that have this built in.
However, the "sensing you approaching" part is much harder -- you will need a RFID system that can read from a distance, which will cost you a fair bit of money (a few hundred, most likely.)
Some alternatives include NFC, where I have no idea of the cost of the range, sender, and transmitter, and Bluetooth 4, where the "key" could be recharged pretty seldom, and the reader would use a rotating secret system to make it reasonably secure -- but latency of syncing up might be slow.
If you're going to do this, you might want to look into using a commercial electric door strike (this is what they are called); something that is proven to function over the long haul, and is designed for remote lock/unlock of a door. If you build something like this on your own, there's a chance that you could run into problems down the road causing you to be locked out of your house due to a premature mechanical failure. That isn't to say that a commercial door strike can't fail, just that they have been designed and tested for the purpose.
With that said, if you wanted to avoid the cost (and installation) of a commercial door strike, the next best thing would be to use and/or modify one of the home electric keypad deadbolts that you can find at many home building centers (Lowes, Home Depot, etc). If that doesn't work for you, then you'll have to go homebrew with either some form of high-power solenoid, or a gear motor (and all the mechanical and electrical "complexity" that will entail).
Ultimately, whatever you build you want to be as robust as possible, otherwise you might be looking at a visit from a locksmith (or a rock thru the window) just to get back into your house due to a failure.
Forgive an obvious question, but is this a house you own? If not, forget the whole idea.
Getting back to the idea, as crOsh said, using hardware desined for the purpose is really important here. There's a reason that lock hardware, both mechanical and electro-mechanical, is UL listed, and the consequences of failure more serious than having to break a window or call out a locksmith. It could cause you to be delayed or trapped and unable to exit quickly in an emergency, like a fire.
Brewgyver:
Forgive an obvious question, but is this a house you own? If not, forget the whole idea.
I rent, but I don't see why this wouldn't be feasible. All I'm talking about is something that would mount above my deadbolt, and turn my deadbolt when I pressed some kind of key-fob when I was within site, or maybe even over the internet with a wireless router signal. Thanks for all your guys ideas so far, but I'm still not sure what I would need to start at all.
What kind of motors can you attach to an Arduino? Would a 9v battery suffice? What's the cheapest/easiest way to get an Arduino hooked up to either the internet over Wifi or some kind of near field communicator?
And I would obviously always have the key with me at all times in case of failure.
I rent, but I don't see why this wouldn't be feasible.
Feasability is one issue, legalities and liabilities are another. You would have to get your landlord's permission to make any changes to the lock. You won't be able to install something like this without drilling holes into the door, which could open you up to the cost of replacing the door when you vacate.
And I would obviously always have the key with me at all times in case of failure.
The safety issue is about EXITING, not entering. Having a key in your hand will not help if the mechanism jams up, leaving you unable to quickly EXIT in the event of an emergency.
What kind of motors can you attach to an Arduino? Would a 9v battery suffice?
The Arduino cannot DIRECTLY drive ANY motor. You would need to either use a Motor Shield (made to piggyback on Arduino) or other Motor Controller to operate ANY motor via the Arduino. And no, a 9 volt battery would not work - it doesn't have the current capacity.
So at the least you would need the Arduino, the Motor Shield, a Wireless Shield, and XBee (or similar) wireless module, a hefty battery pack, and a gearmotor. Probably at least $200, and more later when you don't get your security deposit back from the landlord.
If all you do is have the Arduino turn the key in a deadbolt, then I would wire that into a hobby servo of some sort. It's easy to make hobby servos turn 180 degrees from an Arduino, and they need no shield (as long as you power them separately correctly.)
A HiTec HS-311 or 322 might do fine, depending on how hard your deadbolt key is to turn. This is also probably safe enough, because the key remains there and can be turned by hand if needed.
