MagnID – Sneaky New Way of Interacting With Tablets

New magnetic tech dubbed “MagnID” is being presented this weekend at Stanford’s annual TEI conference. It is a clever hack aimed to hijack a tablet’s compass sensor and force it to recognize multiple objects. Here is a sneak peek at the possibilities of magnetic input for tablets.

Many tablets come with some sort of triaxial magnetic sensor but as [Andrea] and [Ian]’s demo shows, they are only capable of passing along the aggregate vector of all magnetic forces. If one had multiple magnetic objects, the sensor is not able to provide much useful information.

Their solution is a mix of software and hardware. Each object is given a magnet that rotates at a different known speed. This creates complex sinusoidal magnetic fields that can be mathematically isolated with bandpass filters. This also gives them distance to each object. The team added an Arduino with a magnetometer for reasons unexplained, perhaps the ones built into tablets are not sufficient?

The demo video below shows off what is under the hood and some new input mechanics for simple games, sketching, and a logo turtle. Their hope is that this opens the door to all manner of tangible devices.

Check out their demo at Standford’s 9th annual “Tangible, Embedded, Embodied Interaction” this January 15-19, 2015.

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DIY Magnetic Stirrer Looks Professional

Stirrers are used in chemistry and biology labs to mix containers full of liquids. Magnetic stirrers are often preferred over the mechanical types because they are more sterile, easier to clean and have no external moving parts. Magnetic stirrers quickly rotate a magnet below the glass beaker containing the liquids that need mixing. The magnetic field travels effortlessly through the glass and reacts against a small magnetic cylinder called the stir bar. The spinning stir bar mixes the contents and is the only part of the mixer that touches the liquids.

[Malcolm] built his own magnetic stirrer. Unlike some DIY stirrers out on the ‘web, this one gets an “A” for aesthetics. It’s clean white lines allow it to look right at home in the professional laboratory. The graduated knob looks good and is functional too as the the potentiometer it is attached to allows multiple mixing speeds. Surprisingly, a D-size battery is all that is needed to power the stirrer. Most of the parts required for this project can be found in your spare parts bin. [Malcolm] has written some excellent instructions on how he made the stirrer including a parts list and schematics.

Want to make a magnetic stirrer but aren’t into chemistry or biology? No worries… I pity the fool who don’t build one of these….

How a quarter shrinker works

This machine is capable of shrinking coins. What you’re looking at is actually a 3D model of the Geek Groups impulse generator, which is called Project Stomper. The model is used to explain how induction shrinks a quarter to the size of a dime.

The grey chamber to the left is a reinforced containment device. It’s a safety feature to keep people in the same room as the Stomper safe from flying particles which may result from the forces this thing can put out. You see, it uses a mountain of magnetic energy to compress the edges of a coin in on itself.

As the video after the break illustrates, the main part of the machine on the right starts off by boosting mains voltage using a microwave oven transformer. This gets the AC to 2000V, which is then rectified and boosted further to get to 6000V DC. This charges three huge parallel capacitors which are then able to source 100,000A at 6 kV. When it comes time to fire, the charge is dumped into a coil which has the coin at its center. The result is the crushing magnetic field we mentioned earlier.

This isn’t a new concept, we featured a different coin crusher build in the early years of Hackaday’s existence.

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Reading credit cards with a tape head

A company called Square is giving out free credit card readers that turn any iPhone or iPad into a Point of Sale terminal. [Steve] got a hold of one of these tiny peripherals and did what any sane person would do: tear it apart and learn how it works. This bit of hardware is a little unimpressive; unsurprising because Square is giving them away. With simplicity comes an ease in understanding, and [Steve] was able to successfully read his own credit card with this tiny and free credit card reader.

[Steve]’s work in decoding credit card data builds off [Count Zero]’s article from the bbs days. Basically, each credit card has two or three tracks. Track three is mostly unused, whereas track one contains the card holder name, account number, cvc code and other ancillary data. Track two only contains the credit card number and expiration date.

The only components in the Square card reader are a head from a tape player and a 1/8″ microphone jack. The magnetic head in the Square card reader is positioned to only read track two. With a small shim, it’s possible to re-align the head to get the data from track one. After recording an audio file of him sliding his card though the Square reader, [Steve] looked at the number of times the waveform flipped from positive to negative. From this, he was able to get the 1s and 0s on the card and converted them to alphanumeric using the 6-bit ANSI/ISO alpha format.

[Steve] isn’t going to share the code he wrote for Android just yet, but it should be relatively easy to replicate his work with the Android tutorial he used. Also, yes, we did just pose the question of how these Square credit card readers work just hours ago. Good job being on the ball, [Steve]. Tips ‘o the hat go out to [Bobby], [Leif], [Derek] and anyone else we might have missed.

EDIT: [Stephen] sent in his teardown minutes after this post went live. Hackaday readers are too fast at this stuff.

Building a magnetic rotary encoder

[Long Haired Hacker] has undertaken a high-resolution 3D printer build. He got his hands on some motors to drive the build platform but it doesn’t have a built-in encoder. He knows that optical encoder wheels can have problems due to dirt and grim as well as ambient light so he set out to find a better way of providing feedback to the controller. He ended up building his own magnetic rotary encoder which is shown above.

At the heart of the system is an AS5043 magnetic rotary sensor. The chip, which runs from $6.50-$11, can detect and report the rotation of a magnetic field with great precision. The rotation data can be read out in degrees using SPI, but it sounds like there’s also grey code output on a few pins if that suits your needs a bit better. The magnet which the chip measures is mounted in a sleeve milled to seat inside of a bearing ring.

The 3D printing method [Long Haired Hacker] has chosen uses a projector and light-cured resin to achieve the kind of results seen in this other hi-res printer.

Controlling muscles with high intensity magnetic pulses


We’re not quite sure what’s going on with our fellow hackers lately, but they all seem quite interested in finding inventive ways to scramble their brains. [Ben Krasnow] has put together a pair of videos detailing his experiments in transcranial magnetic stimulation, a process that looks like it would go quite nicely with the Brainwave Disruptor we showed you just yesterday.

Instead of building a coil gun with a set of supercapacitors he had on hand, [Ben] decided to build a magnetic coil that can be used to stimulate his brain through his skull. Once his capacitor bank is charged, a high current pulse is sent through the coil held against his head. This pulse generates a strong magnetic field in the coil, which in turn produces neuron stimulation in his primary motor cortex.

Be sure to watch both videos embedded below, as the first one mostly covers the theory behind his experiments, while the second video gives us the goods.

[Ben’s] day job involves working with professional grade TMS devices, so he has some experience with this technology. Before you try this on your own, be sure that you are doing this safely, because a misdirected pulse of 1700 volts to the head does not sound like a fun time at all.

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Enhance your magnetic silly putty with personal lubricants


Instructables user [killbox] seems to have come across a process that actually makes magnetic silly putty “better”, depending on your specific needs. He had tons of fun making a batch of magnetic putty, but thought that the addition of iron oxide made it stiff and a bit slow moving for his tastes.

He tried to find a household item that could act as silly putty thinner, but after trying various oils, gylcerin, and rubbing alcohol, he came up empty handed. Undeterred, he researched how silly putty itself is made, and based on its list of ingredients, decided to seek out some sort of silcone-based lubricant.

He headed out to the local sex shop, and spent some time browsing through the “personal lubricant” section, in hopes of finding what he needed. He settled on ”Gun Oil”, a silicone lubricant that also contained Dimethicone, an item on the ingredient list of the lubricant he initially used to make the batch of magnetic putty.

After adding the lubricant, he found that the putty retained its texture, but flowed far more easily. The thinner putty also consumes rare earth magnets more quickly than its unaltered brethren, as you can see in the picture above.

We’re not sure how far you could push the ferro-putty before it would become a mess, but it’s certainly warrants further experiments.

[Thanks, Mike]