Lock Box, Mark II

Selfbondage software and other kinky developments

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Lock Box, Mark II

Postby ruru67 » 20 Nov 2017, 08:25

So I built a little key lock box a while ago. I also have a kitchen safe acquired back when they first came out. But geek that I am, I wanted to go one better. In fact, I mentioned this in the lock box thread:
It's a pity the timer doesn't have separately configurable "on" & "off" intervals. If I had a lot more time and money on my hands, I'd be thinking about using some kind of micro-controller or single-board computer to do the timing.

Well, I now have more time, a small stack of (now) obsolete single board computers, and, AliExpress wasn't a thing eight years ago when I made that first box.

The new box is a six-drawer wooden mini cabinet. With some, uh, additions out the back (click pics to enlarge):

Lock Box Mark II, front view

The three drawers on the right are unmodified, and can be used for storage. The ones on the left have aluminium latch bars that project through the back of the cabinet into the locking mechanism.

Lock Box Mark II, back view

The back, if you'll excuse my fairly lousy woodwork, has a locking wooden cabinet added. The locking bar has two padlock holes in it for multiple levels of security (e.g. a combo lock and a numbered disposable padlock so your partner/emergency person will know if you pick the padlock). Power and network connectivity arrive via the RJ45 socket - 100 Mbps on the orange and green pairs, +12V on blue and ground on brown.

Lock Box Mark II, back, open

Inside, the SBC and locking mechanism.

Lock Box Mark II, locking mechanisms

The top cable (with the mini-DIN connector) comes from the relay board to a little distribution board containing diodes to keep volts out of places it oughtn't be, and current limiting resistors. You can see the latch bars projecting through. (The bottom one is unlocked.)

Lock Box Mark II, SBC and relay module

Inside the SBC case, the relay module is mounted in the expansion card space, and draws power from the unregulated input power supply, which also powers the locks. There are four relays; relay 4 is connected to +12V, and switches volts to all of the solenoids' open or close inputs. Each of relays 1 through 3 are connected to the common leads of solenoids 1 through 3 respectively. Thus to open drawer 2, you set relay 4 to put volts on the open side, and momentarily connect relay 2. All three solenoids see volts on their open legs, but only No. 2 has a closed circuit. and actually unlocks. To lock it again, you repeat the process, but set relay 4 to connect the close side.

The Soekris net4801 is a 266 MHz AMD Geode, basically a 586 class machine, with 128MB memory. No speed demon, but will do the job. If I was spending actual money on the SBC, I'd have used a Raspberry Pi or similar. Maybe.

I've worked with Soekris and similar machines for a long time doing network stuff using FreeBSD, so can use the software builds I've done for these. In particular, these builds don't write to their flash cards any more often than they need to, which means I don't need to worry about the flash cards dying from overuse (something of a problem with flash). File systems are read-only except for tiny windows when things need to be saved (and the configuration file system is separate from the OS one), so an "orderly shutdown" is just pulling the plug. These things are solid; I've had them in environments where hardware around them was being killed regularly by bad power and never had one fry or be rendered unbootable.

I haven't finished the software (the bits like talking to the relay board are all there), but I'm thinking of games like choosing random, hidden lock-up periods ... where if you ask it to unlock before the period is up, you get more time added. Or having to be present at a specific time to be unlocked. Since there are three separate drawers, one can do concurrent "challenges". And since it's network connected there is lots of scope for external inputs.

Should be a bit of a step up from boxes that just lock for a set period...
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Re: Lock Box, Mark II

Postby Keyless » 20 Nov 2017, 15:34

A great piece of work. Looks as though it is very versatile with lots of scope for new ideas. I can vouch for the idea of having to ask to be released and getting more time if you ask too early.
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