Tablet interacts with magnets, how does that work?

Making computers interact with physical objects is a favorite of the HCI gurus out there, but these builds usually take the form of image recognition of barcodes or colors. Of course there are new near field communication builds coming down the pipe, but [Andrea Bianchi] has figured out an easier way to provide a physical bridge between computer and user. He’s using magnets to interact with a tablet, and his idea opens up a lot of ideas for future tangible interfaces.

Many tablets currently on the market have a very high-resolution, low latency magnetometer meant for geomagnetic field detection. Yes, it’s basically a compass but Android allows for the detection of magnets, and conveniently provides the orientation and magnitude of magnets around a tablet.

[Andrea] came up with a few different interfaces using magnets. The first is just a magnets of varying strengths embedded into some polymer clay. When these colorful magnetic cubes are placed on the tablet, [Andrea]’s app is able to differentiate between small, medium, and large magnets.

There are a few more things [Andrea]’s app can do; by placing two magnets on an ‘arrow’ token, the app can detect the direction in which the arrow is pointing. It’s a very cool project that borders on genius with its simplicity.

You can check out [Andrea]’s demo video after the break.

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Revolight clone

[Fabian.E] wanted to light up the rims on his bike, but didn’t want to shell out a bunch of clams to get it done. He came up with this system which uses magnets and reed switches to light up one arc or each bicycle wheel.

He calls it the lightrider and it’s based on the revolights concept. That design uses a microcontroller which is capable of animating patterns when the wheels aren’t spinning. [Fabian’s] version can’t do that, but the effect while moving is basically the same. The ring of LEDs around the rim is connected to a battery via a set of reed switches. When these switches move past a magnet on the fork it completes the circuit and switches on that segment of LEDs. The clip after the break gives a demonstration of the finished product, and includes a fast-motion video of the fabrication process.

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Your theme song greets you at the front door

One thing you can look forward to when arriving at home after a long, arduous day at the office is some peppy theme music when you walk in the door. [Sebastian Sommer] built the system, and shows it off in the video after the break by dancing to James Brown’s I feel good.

The setup uses an Arduino as a microcontroller. It monitors a hall effect sensor on the jamb which detects a passing magnet on the door. We guess this means the system doesn’t know if you’re coming or going but perhaps a future upgrade would add an infrared beam to detect your legs as head out the door. The music itself is played by an SparkFun MP3 shield which has a decoder chip, microSD slot, and audio jack for the powered speakers. [Sebastian] grabbed a copy of [Bill Porter’s] mp3 shield library to get the project up and running quickly.

This is a pretty cool addition if you’re already using an Arduino for a door lock or vice versa. Or maybe you’re not home enough to make this hack worth it, in which case you simply must take this music playing Tesla coil hat along on your commute.

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Give yourself a sixth sense on the cheap

sixth-sense-magnetic-ring

Hackaday regular [Mikey Sklar] is no stranger to body modifications. He enjoys tweaking his body in ways that help him with day to day tasks, including a ruler tattoo on his arm and an RFID chip embedded in the web of his hand. Lately, he has been toying around with a less invasive means of getting a better feel for magnetic fields in his surroundings.

Turned on to magnetic rings by a friend, he now wears an epoxy-coated rare earth ring every day, changing the way he interacts with the world. He says that besides the obvious ability to tell when he’s near iron-heavy material, he can also feel cell phone calls, as the speaker draws the ring closer while producing sound.

He says that holding the electric cord of his tea kettle gave him the biggest start, making him feel as if he had been electrocuted, minus the actual shock.

While it’s not the most high-tech hack, [Mikey] is quite happy with the “sixth sense” this reasonably price ring has been able to provide – we just might have to try it out ourselves.

Frustrating fun with magnetic levitation

[Andrey Mikhalchuk] built his own magnetic levitation device and you can too… if you have the patience. He’s not using electromagnets, like the Arduino levitator or the floating globe. Instead, a pair of ceramic ring magnets and a few hours are all it takes.

The base of his device is a couple of very large ring magnets that would most often be used in speakers. It’s hard to see them in the image above because there’s an inverted plastic container obscuring them. A second (or third depending on how you’re counting) ring magnet is selected because it is smaller than the circular void in the magnetic base. It’s impossible to simply balance the magnet in the air, but spinning it is a different story. By creating a perfectly balance magnetic top, then spinning it inside the magnetic field of the base, you can leave it floating in mid-air.

Check out the video after the break. It’s a neat effect, but you really do have to have a perfect setup for it to work. [Andrey] mentions that it takes a couple of hours to fine-tune. And if the ambient conditions change slightly, it throws the whole thing off.

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Salvaged coil magnetizes tools on demand

magnetizing_wand

When working in hard to reach areas, magnetized tools can mean the difference between wrapping things up quickly and spending way too much time blindly grasping for dropped screws. [Damir] wrote in to share a handy little contraption he built which allows him to magnetize and demagnetize his tools as needed.

While rubbing a magnet against the tip of a screwdriver will impart a weak and temporary magnetic field, he felt that a stronger more permanently magnetized tool was far more useful. It is pretty well known that subjecting metal to a direct current magnetic field will magnetize the item, and an alternating magnetic field will demagnetize the same object. [Damir’s] wand will perform either task with the simple flip of a switch.

He salvaged the motor coil from a broken washing machine and mounted it in a project box, along with a single-pole changeover switch. A small diode is used to perform rectification on the AC input, providing the DC current required for magnetizing his tools.

Every once in awhile we find the need for magnetized tools, so we think this would be great to have around the workshop.

Check out a quick video demo of the magnetizing wand after the jump.

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Automated chess set does it from below

You can get class credit for the coolest things these days. Take for instance, this Automatic Chessboard that [Brian] and [James] built for the final project in one of their classes this spring. We just looked at a robotic chess setup on Monday that used a gripper mounted on a gantry to move the pieces. This one’s a lot more user-friendly and borders on magical. That’s because the moving parts are all located below the board and could be hidden from view if a proper case were built around the edges.

There are two main components to this build. The first is a grid of reed switches that detect the moves made by a human. This works because each piece the human player uses has a weak magnet glued to the bottom which is just strong enough to actuate the reed switch and let the computer sense what move was just made. On the robotic side of things this works like a plotter. Each of the computer’s pieces has a metallic disc glued to the base. What basically amounts to a plotter under the board uses rare-earth magnets to grab the computer’s piece and drag it to the next playing position.

The use of two separate magnetic systems provides some interesting design challenges. You can see the device in action in the video after the break, and a full writeup and source code package is available at the blog linked at the top of this feature. But for your convenience we’ve also mirrored the PDF whitepaper after the break which lays bare all of the juicy details.

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