Mechanical safe-cracking using Android audio and orientation sensors

Question

I’m writing an app that helps lock-smiths with safe manipulation, mainly by creating the charts they need on the fly. When trying to gain entry to a safe via manipulation, a detailed analysis of the "wheel-pack" is required and accomplished by charting the relative depth of a “fence” over a “gate”. If all gates are lined up on the pack, the fences lever will drop into the cam gate and the lock will open. If anyone’s interested in a much more detailed explanation, you can find an awesome treatment by Matt Blaze here (starting around 3.3): www.crypto.com/papers/safelocks.pdf

Making the charts is important, and all it really requires is accurately measuring two places on the dial over and over and over, and recording the dial distance between two sounds. So, say the “drop-in” point is between 10 and 15, a sound event might occur at 11.5 and 14.5, or the next time around it might occur at 12 and 15. The lock-smith makes a chart of distance between these numbers and looks for say, a narrowing of numbers, on a chart, or maybe just the lowest place on the chart.

I’m using an old-school radio-shack Telephone Pickup (suction-cup mic) via my Androids headphone jack, to listen for the sound events. And to precisely measure on the dial where the events occur, I’ve simple mounted the phone to the dial with velcro and use SensorManager to figure the distance between the sounds based on how far the phone has been rotated from audio spike-event to spike-event. Which is fine, but I’d like to do it without mounting the phone to the dial. A couple companies used to accomplish it by having a webcam look at the dial itself, but that seems much less accurate than just mounting the phone as I can get more precision using fractional degrees of rotation.

Once you enter the drop-in location, you always will hit one sound, then backup the dial to the next sound, so I was thinking I could simply, listen for the sound event, and then once the dial reverses direction measure to the next sound event, but this would require that the dial move at constant, which won’t happen in real-life. And I guess I could do it by using a dynamixel or servo to move the dial for the locksmith, but again, not a good solution. So my question is if any of you smart folks can think of way that these related rates (distance between sound events and change of dial position) can be quantified without mounting the phone to the dial?

Answer 1

Not a full answer but a few of ideas I can throw at you:

from a control systems engineer point of view I can tell you that the way to accurately measure a rotation without direct access to the shaft is with an encoder.

So maybe you can use Android accessory mode to read an encoder (through an Arduino) that you'll mount on the dial (probably placing a rubber disc on the encoder shaft and touching it against the safe-dial).

This whole effort would be just to avoid sticking the whole phone to the dial and gain some extra precision.

A different approach could be to attach something else on the dial that would generate click noise that you could filter on the sound to differentiate from the safe sound. But that would definitely lower your precision.