How to unlock my front door via bluetooth proximity
September 21, 2012 8:18 PM   Subscribe

Can you suggest a USB motor / solenoid / actuator that can by activated via the command line on my Windows 8 PC? I would like my front door to automatically unlock every time I approach it. Details are as follows:

I downloaded BTProx for windows, which is an application that senses when a bluetooth device comes within range (about 30 feet) of the computer. I installed BTProx and paired it wit my smartphone. Now everytime my computer senses my smartphone, the BTProx application will launch a program on my computer.

My front door is within range of my computer's bluetooth sensor, and I successfully have BTProx running a basic command line program that prints the current time, and I would like to find a way to unlock my front door with this setup.

My question to the hive mind is: can you suggest a USB motor / solenoid / actuator that can by activated via the command line on my Windows 8 PC? I'm going to attach the motor / solenoid / actuator to the doorjam to automatically turn the doorknob. My vision for a finalized version of this setup will be: 1. I approach front door. 2. BTProx senses my phone's bluetooth and runs a .bat file that turns on the USB device. 3. The USB device turns the doorknob, then resets itself back to resting position after 10 seconds.

Any suggestions for USB powered devices or other ideas altogether? I'd like to find a device that's simple and cheap.
posted by thankyoumuchly to Computers & Internet (11 answers total)
This plus a stepper motor is probably the easiest to work with without having to understand too much of the hardware. (But not cheap)
posted by wongcorgi at 9:15 PM on September 21, 2012

Im guessing you are looking for a PLC . I have worked with industrial (Allen Bradley) ones that aren't going to be of much use here or would be overkill. Try searching for home use PLCs or somesuch for reviews.
posted by asra at 9:17 PM on September 21, 2012

@asra - thanks for the suggestion. It looks like a PLC is in essence the whole system i described above. I believe functionally already have 90% of what a PLC would do for me set up with the Windows box, BTProx software and my BT enabled smart phone.

All I need at this point is the software to hardware motor (preferably with a USB interface that can take commands from a batch file/via the windows command line). This could be as simple as a USB toy i strip down to the gears that has enough strength in the motor to apply a few pounds of torque, or it could be a more job specific piece of hardware, such as a raw actuator with USb interface.
posted by thankyoumuchly at 9:32 PM on September 21, 2012

What about an Arduino board, in combination with a stepper, servo, or solenoid controller in the form of a "shield" board?

There are numerous variants on the arduino, and scads of information on how to program them and wire them up.
posted by sebastienbailard at 9:33 PM on September 21, 2012

@wongcorgi - Phidgest look interesting. Do you think I could achieve a similar outcome with an Arduino, breadboard and a raw DC motor for a little bit cheaper than the Phidget? Do you have experience with these boards? I'm assuming I'd need to get it to talk to windows so it knows when the BTProx spftware senses my phone. Another alternatie (that would be a lot more work) is to install the Linux equivalent of BTProx on my RaspberryPI and hook that up to a breadboard, and the bread to a raw DC motor (with a transistor of course).

posted by thankyoumuchly at 9:38 PM on September 21, 2012

I've seen electronic door locks with a keypad; some might also have remotes or even BT functionality. Is it an option to change the lock out? Even one that just has a keypad (or a proximity card) might be easily hacked a bit to receive a signal, wired or wireless.
posted by attercoppe at 9:46 PM on September 21, 2012 [1 favorite]

In my experience, "simple and cheap" are mutually exclusive goals in this domain. Unless you have the smoothest, best-adjusted, most perfectly lubricated door lock of all time, you will need to provide a fair amount of kick to move the laych
posted by range at 10:28 PM on September 21, 2012

(ugh, posting on phone, sorry...)

... to move the LATCH. For that you will need either a gear motor or a solenoid, and neither of those will provide the oomph you need from solely USB power. So at best you'll be using USB to drive relays/transistors that gate a beefy power supply.

You also need a strong, rigid coupling and/or transmission between the actuator and the latch, and whatever you build needs to not bind up, deform, wiggle around, or otherwise add required effort.

In my opinion the winning solution is to buy an electronic strike plate (example; not an endorsement, just the first Google result) and figure out how to connect that to the DIY computer interface of your choice.

(source: watching this exact project fail for at least 3 consecutive semesters in my college electronics course)
posted by range at 10:40 PM on September 21, 2012 [1 favorite]

Unless you're deliberately going for the Rube Goldberg look, you probably don't want to put the mechanicals in the door. Putting them in the striker plate instead means you can keep all the wiring nicely concealed and don't need to make any of it flex at the door hinge, which is exactly why electric striker plates are readily available but electric door knobs are not.
posted by flabdablet at 3:21 AM on September 22, 2012 [1 favorite]

You don't want to attach something to your lock that could bind in the event of a fire and make it more difficult for you to leave the house. Even if you don't care, your landlord and the fire marshal will.

On the other hand, if your computer has serial or parallel ports - even as headers on the motherboard- it's entirely possible to drive a solenoid via those with exponentially less parts and effort than using USB.
posted by Orb2069 at 11:00 AM on September 22, 2012

One thing to note about the electronic strike's (I too did this project back in the day) is that there are 2 types (at least that I know of).

There is the "regular" ones, which are cheap. These only work with the non-deadbolt type doors.

Then there is the ones that allow you to work with a deadbolt, they're more expensive.

I bought the cheap kind, and before I had a chance to install it the building I was living in upgraded all their locks to deadbolts.
posted by Sonic_Molson at 7:49 PM on September 22, 2012

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