How Store Anti-Theft Alarms Work: Magnetostriction

December 3, 2015 by 44 Comments

Now that’s uncanny. Two days before [Ben Krasnow] of the Applied Science YouTube blog posted this video on anti-theft tags that use magnetostriction, we wrote a blog post about a firm that’s using inverse-magnetostriction to generate electricity. Strange synchronicity!

[Ben] takes apart those rectangular plastic security tags that end up embarrassing everyone when the sales people forget to demagnetize them before you leave the store. Inside are two metal strips. One strip gets magnetized and demagnetized, and the other is magnetostrictive — meaning it changes length ever so slightly in the presence of a magnetic field.

A sender coil hits the magnetostrictive strip with a pulsed signal at the strip’s resonant frequency, around 58kHz. The strip expands and contracts along with the sender’s magnetic field. When the sender’s pulse stops, the strip keeps vibrating for a tiny bit of time, emitting an AC magnetic field that’s picked up by the detector. You’re busted.

The final wrinkle is the magnetizable metal strip inside the tag. When it’s not magnetized at all, or magnetized too strongly, the magnetostrictive strip doesn’t respond as much to the sender’s field. When the bias magnet is magnetized just right, the other strip rings like it’s supposed to. Which is why they “demagnetize” the strips at checkout.

We haven’t even spoiled [Ben]’s explanation. He does an amazing job of investigating all of this. He even measures these small strips changing their length by ten parts per million. It’s a great bit of low-tech measurement that ends up being right on the money and deserves the top spot in your “to watch” list.

And now that magenetostriction is in our collective unconscious, what’s the next place we’ll see it pop up?

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Radio Receiver Build Log And More

December 3, 2015 by 8 Comments

At Hackaday, we like to see build logs, and over on Hackaday.io, you can find plenty of them. Sometimes, though, a builder really outdoes themselves with a lot of great detail on a project, and [N6QW’s] Simple-Ceiver project certainly falls into that category. The project logs document many different stages of completeness, and we linked the first one for you as a starting point, but you’ll definitely want to read up to the present. (There were 16 parts, some spanning multiple posts, last time we checked).

It is definitely worth the effort though. The project started out as a direct conversion receiver, but the design goes through and converts it into a superheterodyne receiver. Along the way, [N6QW] shares construction techniques, design advice, and even simulation plots (backed up with actual scope measurements). The local oscillator, of course, uses an Arduino and an AD9850 synthesizer.

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Deployable By Design With Bunnie Huang, Nadya Peek, And Joi Ito

December 2, 2015 by 10 Comments

We follow [bunnie]’s blog as he posts interesting and usable information quite regularly. [bunnie] posted about a video of a recent talk he did at MIT Media Lab with Nadya Peek and Joi Ito. This was in lieu of his monthly “name that ware” competition, which is worth looking into as well.

The talk is focused on small volume manufacturing and the experiences that the speakers have under their collective belt is large enough that the conversation takes a turn from how to do things in practice, to the theory and technique of manufacturing on a philosophical level.

[bunnie] prefaces the conversation with an explanation of some of the design and manufacturing processes involved when working on the circuit stickers project. He talks about the importance of testing the product and the complex test jig that is required to quality check a simple (in comparison to the test jig) product. [bunnie] shares an overview of the project timeline and where some extended design stages might be found in unexpected places.

The design and manufacturing process is discussed on many levels throughout the talk. Among the points that are insightful, we certainly found ourselves a little jelly of all the time [bunnie] gets to spend in Shenzhen.

If you’re not familiar with [bunnie]’s blog you can check it out at www.bunniestudios.com. Pro Tip: you can spend the better part of your workday browsing topics in the sidebar on the right.

We have covered the MIT Media Lab before, including a trip to Shenzhen that is discussed in the Media Lab talk by [Joi] and [bunnie]. Another interesting interview at SXSW earlier this year by [Sophi Kravitz] who spoke with [Sunanda Sharma] about mediated matter.

DIY Lamps Brighten Winter Blues

December 2, 2015 by 30 Comments

As you know, winter is coming. For a lot of people this means that Seasonal Affective Disorder is beginning to set in. [Luke]’s mom already has a light therapy box. It’s one of those commercially available ones that uses fluorescent bulbs and leaves a lot to be desired in the full-spectrum light simulation department. [Luke] jumped on the opportunity to design a better one.

The standard of quality for light therapy units is a rating of 10,000 lux. While lux definitely matters, the rating is a misleading selling point when given on its own. One of the other important factors in mimicking the sun is the Color Rendering Index (CRI). CRI is basically a rating of the bulb’s ability to imitate the color reproduction of natural daylight. The ratings run from 0 to 100 but in reality, the highest-rated bulbs of any kind top out around 98.

For all the fluorescent bulb-bearing light therapy units out there, those bulbs have pretty low CRI ratings. [Luke]’s project page provides emission spectra graphs for a number of bulb types, and we can see how his choice of ceramic metal halide bulbs stacks up against fluorescent, incandescent, and LED bulbs. One of the few downsides to this type of bulb is that they have long startup times.

He ended up making two light therapy lamps, one of them directional and the other omni-directional. They both use ballast-controlled ceramic metal halide bulbs. The ballasts are necessary to provide the high starting voltage that these bulbs require. The omni-directional light is built into a large hurricane candle holder. A lamp holder is fixed into the base and wired to an external ballast box. The directional lamp is a self-contained unit, and [Luke] is happiest with this one. It’s flat and rugged so it can be placed on top of a bookcase and the light bounced off of the ceiling for pleasant, indirect coverage.

We’ve seen a couple of alarm-clock wakeup light builds here, and we’re thinking this would make an awesome mashup.

Shoving A Raspberry Pi Zero Into An Xbox Controller

December 2, 2015 by 18 Comments

With the release of the Raspberry Pi Zero last month, we’ve been waiting in excitement to see the first creative hacks to come out, making use of its tiny size; which if you didn’t know, is smaller than a business card. [Terence Eden] hopped to it and made what might be the first Raspberry Pi Zero emulator: inside an Xbox controller.

10-Pi-Cardboard-insulatorThanks to its small size it’s actually a fairly straight forward hack with minimal modification to the controller in order to make it fit. In fact, you only need to remove the memory card holder from the controller and snip one bit of plastic in order to make it fit right in the middle — awesome.

Now it does stick out a bit as you can see in the pictures, but we’re sure it won’t take someone long to make a 3D printed part that snaps into the controller giving it a more stock appearance. Unfortunately since HDMI can’t carry a power source to the Pi, [Terence] is using a micro-USB to power it — but there is enough space inside the controller for a battery pack if you wanted to make it truly portable.

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Pi Zero HackChat With Lady Ada

December 2, 2015 by 104 Comments

This Thursday, December 3rd, join us for a Live HackChat about the Raspberry Pi Zero with special guest [Limor Fried]. You may know [Limor] as [Lady Ada], the founder of Adafruit Industries. Adafruit has been on the forefront of the Pi Zero release. The $5 single board computer was announced one week ago by the Raspberry Pi Foundation.

Join in the chat to discuss the Raspberry Pi Zero. Limor has done a lot of work with the board already, including hacking analog audio back into the form factor. This is a great opportunity to ask questions, talk about your own plans for the hardware, and to find collaborators for future projects.

Pi Zero HackChat starts Thursday at 5pm PST (here’s a timezone cheat sheet if you need it). Participating in this live chat is very simple. Those who are already part of the Hacker Channel can simply click on the Team Messaging button. If you’re not part of the channel, just go to the hacker Channel page, scroll to the bottom of the “TEAM” list in the left sidebar and click “Request to join this project”.

HackChat takes place in the Hacker Channel every few weeks and is a friendly place to talk about engineering and the projects you’re working on.

The LED Roundsystem

December 2, 2015 by 2 Comments

Gavin Morris has been working on his awesome sound responsive LED sculptures for a while. Technically the sculpture is an interesting application of WS2812 RGB LEDs, Raspberry Pis and a load of styrofoam cups and flower pots. However the artistic development, and inspiration for this project is equally interesting. Gavin shares his thoughts and a brief technical description of the project below.

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