How Store Anti-Theft Alarms Work: Magnetostriction

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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Scanning Electron Microscope Images And Animations Pulled By Impressive Teensy LC Setup

When you’ve got a scanning electron microscope sitting around, you’re going to find ways to push the awesome envelope. [Ben Krasnow] is upping his SEM game with a new rig to improve image capture (video link) and more easily create animated GIFs and videos.

The color scheme of the SEM housing gives away its 80s vintage, and the height of image capture technology back then was a Polaroid camera mounted over the instrument’s CRT. No other video output was provided, so [Ben] dug into the blueprints and probed around till he found the high-resolution slow scan signal.

To make his Teensy-LC happy, he used a few op-amps to condition the analog signal for the greatest resolution and split out the digital sync signals, which he fed into the analog and digital ports respectively. [Ben] then goes into a great deal of useful detail on how he got the video data encoded and sent over USB for frame capture and GIF generation. Reading the ADC quickly without jitter and balancing data collection with transmission were tricky, but he has established a rock-solid system for it.

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Phonographs Through The Eye Of An Electron Microscope

Hackaday Prize judge [Ben Krasnow] has been busy lately. He’s put his scanning electron microscope (SEM) to work creating an animation of a phonograph needle playing a record. (YouTube link) This is the same 80’s SEM [Ben] hacked back in November. Unfortunately, [Ben’s]  JSM-T200 isn’t quite large enough to hold an entire 12″ LP, so he had to cut a small section of a record out. The vinyl mods weren’t done there though. SEMs need a conductive surface for imagingphono_anim_1. Vinyl is an insulator. [Ben] dealt with this by using his vacuum chamber to evaporate a thin layer of silver on the vinyl.

Just imaging the record wouldn’t be enough; [Ben] wanted an animation of a needle traveling through the record grove. He tore apart an old phonograph needle and installed it in on a copper wire in the SEM. Thanks to the dual stage setup of the JSM-T200, [Ben] was able to move the record-chip and needle independently. He could then move the record underneath the needle as if it were actually playing. [Ben] used his oscilloscope to record 60 frames, each spaced 50 microns apart. He used octave to process the data, and wound up with the awesome GIF animation you see on the left. 

pits[Ben] wasn’t done though. He checked out a few other recording formats, including CD and DVD optical media, and capacitance electronic disc, an obscure format from RCA which failed miserably in the market. The toughest challenge [Ben] faced was imaging the CD media. The familiar pits of a CD are stored on a thin aluminum layer sandwiched between the lacquer label and the plastic disc. He tried dissolving the plastic with chemicals, but enough plastic was left behind to distort the image. The solution turned out to be double-sided tape. Sticking some tape down on the CD and peeling it off cleanly removed the aluminum, and provided a sturdy substrate with which to mount the sample in the SEM.

We’re curious if stereo audio data can be extracted from the SEM images.  [Oona] managed to do this with a mono recording from a toy robot.  Who’s going to be the first one to break out the image analysis software and capture some audio from [Ben’s] images?

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How To Zip, Stick, And Screw Stuff Together

One of the first problems every new hacker/maker must solve is this: What’s the best way to attach part “A” to part “B”. We all have our go-to solutions. Hot glue, duck tape ( “duct tape” if you prefer) or maybe even zip ties. Super glue, epoxy, and if we’re feeling extra MacGyver-ish then it’s time for some bubble gum. For some Hackaday readers, this stuff will seem like old hat, but for a beginner it can be a source of much frustration. Even well versed hackers might pick up a few handy tips and tricks presented in this video after the break.

In part one of this series, [Ben Krasnow] shows us the proper use of just a few of the tools and techniques he uses in his shop. [Ben] starts out with a zip-tie tool which he loves in part because of a tension setting that ensures it’s tight but not overly. He moves on to advice for adhesive-vs-material and some tips on using threaded fasteners in several different circumstances. He also included a list of the parts and tools he uses so you don’t have to go hunting them down.

[Ben] is no stranger to us here at Hackaday. He does some epic science video. You can subscribe to his channel or follow his blog if you enjoy what you see.

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Celebrating The Omnibus Launch

On Thursday night Hackaday hosted an event in San Francisco to commemorate the launch of the 2014 Hackaday Omnibus. Our first print edition, compiled to commemorate some of the finest original content which we published last year should begin shipping as early as today. To celebrate the occasion, we were graced by a full house of amazing guests. Is it lame to say some of the people I respect most in the world were there?

Lightning Talks

Whenever you get a lot of people together, a good rule of thumb is to seize the opportunity to have them speak about what they’re doing. It’s not a big “ask” either; 8-minutes on what you’re passionate about is pretty simple.

[Jonathan Foote] gave a talk on generating RGBY colors from Hue. The project is ongoing but explores the concept of mixing colors of light with one additional source added to traditional red, green, and blue. [Priya Kuber] recently moved to San Francisco. She recently concluded more than a year of standing up the Arduino office in India (relevant but unrelated video). Her talk covered the emerging maker/hacker hardware scene in India which is showing amazing growth. [Chris McCoy] demonstrated his Raver Rings which began a Kickstarter on the same day. [Elecia White] of embedded.fm spoke about the educational opportunities that podcasts and other delivery medium provide and the responsibility we all have to guide our continued learning. [Emile Petrone] talked about an upcoming feature for his site Tindie which will add manufacturer information and ratings to the mix. And rounding things out [Dave Grossman] gave a talk on his Virtual Carl project which used video footage of his grandfather, combined with a Raspberry Pi and peripherals to create a remembrance of the man in virtual form.

Demos

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[Ben Krasnow] shows off the chamber containing supercritical carbon dioxide.
During the rest of the evening there were a few spectacular demos going on. First, [Ben Krasnow] who is well known for his Applied Science series (among a million other accolades), brought at least two demos with him. The first was a pressure chamber made out of two massively thick discs of acrylic separated by a metal ring. Inside the void he had pumped and pressurized CO2. When the chamber is heated it, the contents become Supercritical Carbon Dioxide and the visual transition between liquid and gas disappears.

He also showed off a lens that can be focused electronically. This is not mechanical, there are zero moving parts. Instead a droplet of oil floating in water is the lens. A 75V, AC power supply pulls on the droplet, altering the meniscus to focus the lens. He didn’t fabricate the device from scratch, but the concept is completely new to us and quite interesting.

[Brian Benchoff] poses with Othermill hardware
[Brian Benchoff] poses with Othermill hardware
Othermill is located in the SF area. They produce a desktop milling machine which is spectacular at routing PCBs. The little wonder isn’t limited to that though. Above you can see [Brian] holding up a milled wooden plaque which has milled mother-of-pearl inlays. The table is also strewn with other examples in wax, metal, wood, and more.

Cocktail Hour

The rest of the evening was devoted to conversation on all topics. Get enough hardware geeks in one room and they’ll solve the world’s problems, right? That’s a conversation for another post.

Couldn’t make it to this one but still in the San Francisco area at least occasionally? We held this at the Supplyframe office. They host a ton of great events like the Hardware Developers Didactic Galactic.

[Thanks to Richard Hogben for the photos!]

[Ben Krasnow] Hacks A Scanning Electron Microscope

[Ben Krasnow] is quite possibly the only hacker with a Scanning Electron Microscope (SEM) collection. He’s acquired a JEOL JSM-T200, which was hot stuff back in the early 1980’s. [Ben] got a great deal, too.  He only had to pay shipping from Sweden to his garage. The SEM was actually dropped during shipment, but thankfully the only damage was a loose CRT neck plug. The JSM-T200 joins [Ben’s] homemade SEM, his DIY CT scanner, the perfect cookie machine, and a host of other projects in his lab.

The JSM-T200 is old tech; the primary way to store an image from this machine is through a screen-mounted Polaroid camera, much like an old oscilloscope. However, it still has a lot in common with current SEMs. In live video modes, an SEM can only collect one or two reflected electrons off a given section of a target. This creates a low contrast ghostly image we’ve come to associate with SEMs.

Attempting to fire more electrons at the target will de-focus the beam due to the electrons repelling each other. Trying to fire the electrons from higher voltages will just embed them into the target. Even SEMs with newer technology have to contend with these issues. Luckily, there is a way around them.

When “writing to photo”, the microscope switches to a slow scan mode, where the image is scanned over a period of a minute. This slower scan gives the microscope extra time to fire and collect more electrons – leading to a much better image. Using this mode, [Ben] discovered his microscope was capable of producing high-resolution digital images. It just needed a digital acquisition subsystem grafted on.

Click past the break to see how [Ben] modernized his microscope!

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