A research center in Spain has been working on ways to solve recent supply chain issues. One of these issues is a shortage of materials to make magnets. Their answer? Recycle ferrite residue by treating it and mixing it with ABS for 3D printing.
The mixing of ferrite with a polymer isn’t the key though, instead the trick is in the processing. The team collected strontium ferrite waste and ground it to a powder. Heating to the point of calcination (about 1000C) creates a superior material with a 350% increase in coercitivity and a 25% increase in remanence over the original waste material.
Continue reading “Printing Magnets”
Looking to get into fault injection for your reverse engineering projects, but don’t have the cash to lay out for the necessary hardware? Fear not, for the tools to glitch a chip may be as close as the nearest barbecue grill.
If you don’t know what chip glitching is, perhaps a primer is in order. Glitching, more formally known as electromagnetic fault injection (EMFI), or simply fault injection, is a technique that uses a pulse of electromagnetic energy to induce a fault in a running microcontroller or microprocessor. If the pulse occurs at just the right time, it may force the processor to skip an instruction, leaving the system in a potentially exploitable state.
EMFI tools are commercially available — we even recently featured a kit to build your own — but [rqu]’s homebrew version is decidedly simpler and cheaper than just about anything else. It consists of a piezoelectric gas grill igniter, a little bit of enameled magnet wire, and half of a small toroidal ferrite core. The core fragment gets a few turns of wire, which then gets soldered to the terminals on the igniter. Pressing the button generates a high-voltage pulse, which gets turned into an electromagnetic pulse by the coil. There’s a video of the tool in use in the Twitter thread, showing it easily glitching a PIC running a simple loop program.
To be sure, a tool as simple as this won’t do the trick in every situation, but it’s a cheap way to start exploring the potential of fault injection.
Thanks to [Jonas] for the tip.
Amateur Radio as a hobby has a long history of encouraging experimentation using whatever one might have on hand. When [Tom Essenpreis] wanted to use his 14 MHz antenna outside of its designed frequency range, he knew he’d need an impedance matching circuit. The most common type is an L-Match circuit which uses a variable capacitor and a variable inductor to adjust the usable frequency range (resonance) of an antenna. While inefficient in some specific configurations, they excel at bridging the gap between the 50 ohm impedance of the radio and the unknown impedance of an antenna.
No doubt raiding his junk box for parts, [Tom] hacked together a variable capacitor and inductor using ferrite rods from AM radios, hot glue, magnet wire, copper tape, and some surplus 60ml syringes. You can see that he ground out the center of the plunger to make room for ferrite rods. Winding the outside of the syringe with magnet wire, the alignment of the ferrite can be adjusted via the plunger, changing the characteristics of the element to tune the circuit. [Tom] reports that he was able to make an on-air contact using his newly made tuner, and we’re sure he enjoyed putting his improvised equipment to use.
If Amateur Radio isn’t your thing, then maybe we can entice you with this syringe based rocket, syringe actuated 3D printed drill press, or vacuum syringe powered dragster. Have your own hack to share? By all means, submit it to the Tip Line!
So far in the $50 Ham series, I’ve concentrated mainly on the VHF and UHF bands. The reason for this has to do mainly with FCC rules, which largely restrict Technician-level licensees to those bands. But there’s a financial component to it, too; high-frequency (HF) band privileges come both at the price of learning enough about radio to pass the General license test, as well as the need for gear that can be orders of magnitude more expensive than a $30 handy-talkie radio.
But while HF gear can be expensive, not everything needed to get on the air has to be so. And since it’s often the antenna that makes or breaks an amateur radio operator’s ability to make contacts, we’ll look at a simple but versatile antenna design that can be adapted to support everything from a big, powerful base station to portable QRP (low-power) activations in the field: the end-fed half-wave antenna.
Continue reading “The $50 Ham: A Cheap Antenna For The HF Bands”
Amateur radio operators and shortwave listeners have a common enemy: QRM, which is ham-speak for radio frequency interference caused by man-made sources. Indiscriminate, often broadband in nature, and annoying as hell, QRM spews forth from all kinds of sources, and can be difficult to locate and fix.
But [Emilio Ruiz], an operator from Mexico, got a little help from Mother Nature recently in his quest to lower his noise floor. Having suffered from a really annoying blast of RFI across wide swaths of the radio spectrum for months, a summer thunderstorm delivered a blessing in disguise: a power outage. Hooking his rig up to a battery — all good operators are ready to switch to battery power at a moment’s notice — he was greeted by blessed relief from all that noise. Whatever had caused the problem was obviously now offline.
Rather than waste the quiet time on searching down the culprit, [Emilio] worked the bands until the power returned, and with it the noise. He killed the main breaker in the house and found that the noise abated, leading him on a search of the premises with a portable shortwave receiver. The culprit? Unsurprisingly, it was a cheap laptop power supply. [Emilio] found that the switch-mode brick was spewing RFI over a 200-meter radius; a dissection revealed that the “ferrite beads” intended to suppress RFI emissions were in fact just molded plastic fakes, and that the cord they supposedly protected was completely unshielded.
We applaud [Emilio]’s sleuthing for the inspiration it gives to hunt down our own noise-floor raising sources. It kind of reminds us of a similar effort by [Josh (KI6NAZ)] a while back.
Let’s say you’re stranded on a desert island and want to get the news from the outside world. You’ll have to build your own crystal radio, of course, but your parts bin is nowhere to be found and Digi-Key isn’t delivering. So you’ll need to MacGuyver some components. Capacitors are easy with a couple of pieces of tinfoil, and a rectifier can be made from a pencil and a razor blade. But what about an inductor? Sure, air-core inductors will work, but just because you’re marooned doesn’t mean you’ve abandoned your engineering principles. Luckily, you’ve read [AC7ZL]’s treatise of making inductors from dirt, and with sand in abundance, you’re able to harvest enough material to put together some passable ferrite-core inductors.
Obviously, making your own inductive elements isn’t practical even in fanciful and contrived situations, but that doesn’t make the doing of it any less cool. The story begins with a walk in the Arizona desert many years ago, where [AC7ZL], aka [H.P. Friedrichs], spied bands of dark sand shooting through the underlying lighter sediments. These bands turned out to be magnetite, one of many iron-bearing minerals found in the area. Using a powerful magnet from an old hard drive and a plastic food container, he was able to harvest magnetite sand in abundance and refine it with multiple washing steps.
After experimentally determining the material’s permeability — about 2.3 H/m — [AC7ZL] proceeded with some practical applications. He was able to make a bar antenna for an AM radio by packing the sand into a PVC pipe and rewinding the coils around it. More permanent cores were made by mixing the sand with polyester resin and casting it into bars. Toroids were machined from fat bars of the composite on a lathe, much to the detriment of the cutting tools used.
The full-length PDF account of [AC7ZL]’s experiments makes for fascinating reading — the inductive elements he was able to create all performed great in everything from a Joule Thief to a Hartley oscillator up to 27 MHz. We love these kinds of stories, which remind us of some of the work being done by [Simplifier] and others.
Anyone who has ever wound a toroidal coil by hand can tell you that it’s not exactly a fun job. Even with the kinds of coils used in chokes and transformers for ham radio, which generally have relatively few windings, passing all that wire through the toroid time after time is a pain. And woe unto anyone who guesses wrong on how much wire the job will take.
To solve those problems, [Sandeep] came up with this clever and effective toroid winder. The idea is to pass a small spool of magnet wire through the toroid’s core while simultaneously rotating the toroid to spread the windings out as evenly as possible. That obviously requires a winding ring that can be opened up to allow the toroid form to be inserted; [Sandeep] chose to make his winding ring out of plywood with a slit in it. Carrying the wire spool, the winding ring rotates on a C-shaped fixture that brackets the toroid, which itself rotates under stepper motor control on a trio of rollers. An Arduino controls the rotation of both motors, controlling the number of windings and their spread on the form. lacking a ferrite core for testing, [Sandeep] used a plywood ring as a stand-in, but the results are satisfying enough to make any manual coil-winder envious.
We love tools like this that make a boring job a snap. Whether it’s cutting wires for wiring harnesses or winding guitar pickups, tools like these are well worth the time spent to build them. But we suppose when it comes to toroid winding, one could always cheat.
Continue reading “Homebrew Coil Winder Makes Toroids A Snap To Wind”