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The Dead Man's Switch

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Last night's LOST season finale made mention of a "Dead Man's Trigger," which is another term for a Dead Man's Switch. Although these devices are well known to some geeks, I thought I'd write a little explainer to introduce the notion more broadly. (Warning: very minor LOST spoilers follow.) While the LOST switch was in fact a "fail-deadly" (the opposite of a fail-safe), the concept is similar. In fact, this isn't the first time we've seen a Dead Man's Switch on LOST: Season 2 was all about Desmond's switch.

The Dead Man's Switch is generally a fail-safe device intended to take action if a human fails to routinely activate it -- in other words, if the human dies, the switch goes off, and something happens.

Historically, a Dead Man's Switch was installed in potentially dangerous machinery like locomotives, streetcars, and subways. The switch itself could take many forms, though typically it was a handle of some sort that needed to be operated by the user. By forcing the human operator of these machines to occasionally (or even continuously) activate the switch, you could (theoretically) ensure that the machine would shut down if the operator was dead, incapacitated, or missing. Common mechanical Dead Man's Switches exist in New York subways and even lawnmowers and tractors. Here's a snippet from Wikipedia:

In many modern New York Subway trains, for example, the dead man's switch is incorporated into the train's speed control. On the R142A the train operator must continually hold the lever in place. This was depicted in the movie and book The Taking of Pelham 123, in which a group of men hijack a New York City subway train for ransom, but because of the Dead-man's feature, cannot escape while the train is moving.

Every lawn mower sold in the US since 1982 has an "operator-presence" device, which by law must stop the blades within 3 seconds after the user lets go of the controls.

Many modern systems could benefit from a Dead Man's Switch. For example, typical automative Cruise Control systems don't have such a switch, which could allow a vehicle to effectively drive itself after the user falls asleep. Of course, this doesn't last long, as the vehicle hits something sooner or later -- but wouldn't a better failure mode be to slow down rather than keep going?

In high tech, ubergeeks have been using Dead Man's Switches to protect their data or implement disaster-containment protocols in case something goes terribly wrong. If you're a political dissident or involved in something else potentially dicey, a Dead Man's Switch can be implemented as software, a sort of "nuclear option" that will zap your data -- or contact trusted compatriots -- if you fail to activate it. Slashdot held a discussion entitled What Does Your Dead Man's Switch Do? in 2007, leading to several interesting stories (and tons of off-topic discussion). Here's a good example:

I often take part in political protests, and have on occasion been arrested and held for days.

So, I put together a quick routine using perl and chron that dispatches email to my workplace, the local legal rep contact, and some friends. The later includes directions to a hidden key and asks them to feed my cat until they hear from me. I only enable the system when I'm expecting a significant risk of arrest. Once it's started, if I don't either log into the machine or send myself an email containing a specific string once every 24 hours, the alarm goes off.

The Dead Man's Switch has also appeared in literature; one popular example I can recall is the nuclear trigger on Raven's motorcycle in Neal Stephenson's Snow Crash. But I'm sure there are more examples out there. Have you come across a Dead Man's Switch, in life or in fiction? Share in the comments!

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Name the Author Based on the Character
May 23, 2017
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