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DIY Weekend: The scrap metal Turing machine

It might be useless and kind of harsh looking, but this all-mechanical Turing machine is a great exercise in geekdom.

The only thing that could make this cooler is if it was made out of Legos. Jim MacArthur

A Turing machine is a very simple computer that manipulates symbols on a strip of tape to perform feats of logic. There isn't really much of a purpose to them these days; they exist as a novelty based on early computational theory by the great mathematician and computer scientist Alan Turing. They're made as a type of thought experiment to show the advantages and limits of mechanical computing. To really understand what a Turing machine demonstrates, you probably have to be the type who can speak binary.

Many have been made over the years, but one caught our eye on YouTube this week (video below). We didn't notice it because it's elegant or attractive--indeed, it's rather harsh-looking--but because it's entirely mechanical. It uses magnets and springs, but no electronics or even electricity. It was made by British hobbyist Jim MacArthur as a demonstration for a Maker Faire in the U.K.

Most Turing devices use a type of tape on which symbols are punched, but this one moves along a metal grid. Ball bearings are dropped into grid squares based on the data input via a series of small levers. The positions of the balls on the grid act as symbols. When one knows what they're doing, the pattern of ball bearings on the grid can be translated into a rough program.

For a logic unit, it uses a left-or-right switch mechanism to create binary input. It has up to 5 input symbols that allow for 10 "states." If that doesn't make sense to you, that's OK, it's not really supposed to. It's a technical way of saying that while this DIY machine won't catch up to a pocket calculator anytime soon, it's still an impressive feat of engineering for not having any batteries.

The entire thing is made from scrap metal collected by MacArthur. What's more, it's mechanical to the point that it's powered by turning a wheel by hand. At the end of the video, MacArthur points out that his current version uses a small electrical motor as an option, though it works just fine when powered by steam, too.

Again, the machine doesn't actually do much if you're not really into computer science, but MacArthur is considering a new model that actually does do something useful. If you tried to do something productive with this machine, you'd be in for a bit of a wait. MacArthur says on his blog that while the gizmo looks cool, it would take months to add 2 to 3. Yes, you can actually calculate how long the problem would take to solve in a fraction of the time it would take to solve it.

DIY doesn't have to be useful, it just has to be cool.

To share your DIY project, simply e-mail a description of 350 words or less, including all the geeky ins and outs of your invention, plus relevant links and photos, to crave at cnet dot com. Please put DIY Weekend in the subject line.