A Remotely Tuned Magnetic Loop Antenna

If you are a radio amateur, you may be familiar with the magnetic loop antenna. It’s different from most conventional wire antennas, taking the form of a tuned circuit with a very large single-turn coil and a tuning capacitor. Magnetic loops have the advantage of extreme selectivity and good directionality, but the danger of a high voltage induced across that tuning capacitor and the annoyance of needing to retune every time there is a frequency change.

[Oleg Borisov, RL5D] has a magnetic loop, and soon tired of the constant retuning. His solution is an elegant one, he’s made a remote retuning setup using a stepper motor, an Arduino, and a Bluetooth module (translated here). The stepper is connected to the capacitor via a short flexible coupling, and tuning is performed with the help of a custom Android app. We’d be interested to know what the effect of a high RF field is on these components, but he doesn’t report any problems so it must be working.

He’s posted a video of the unit in operation which we’ve posted below the break, if you’ve ever had to constantly retune a magnetic loop you will appreciate the convenience.

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Conflict Escalates Between Brilliant Rat and 555 Timer

After [Casey Connor] captured and relocated a number of unwanted rodents in his home using commercially available live traps, he was presented with a problem: a rat had learned to avoid them.

In an epic, and adorable, conflict caught on video (and embedded below),  he documents the  designs used and how the rat escaped them by either recognizing the trap, or sheer agility. We can only tip our hat to the determination of both parties.

All the trap mechanisms are based on a 555 monostable solenoid triggering circuit that ensures that a pulse of sufficient duration is sent to the solenoid to trigger the trap correctly. This way even intermittent contacts will trigger the trap rather than just causing the solenoid to twitch without fully actuating. This is the same technique used to debounce a switch using a 555 timer.

A Raspberry Pi Zero detects motion using an IR camera to film the interesting parts. This is also a good indicator for when you’ve trapped your quarry – if you’re trying be humane then leaving it in a trap for days is counterproductive.

With the time and effort we spend building better and more complex rodent traps, we sometimes wonder who has cleverly trapped whom.

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Cooking With The Awesome Power Of Plasma!

There is something special about food that has been cooked in a grill, barbecue, or broiler. The charred surface brings both flavour and texture to the food, that other cooking methods fail to emulate. Of course, should you come from a part of the world in which the locals steam their hamburgers those are fighting words, but for [Robots Everywhere] the prospect of a flaccid patty cooked in a microwave oven was too much.

His solution? Broil the microwaved meat in double-quick time, using a plasma arc generated with a high voltage supply. The patty is placed in a grounded metal frying pan, and the high voltage probe is run over each side with accompanying plasma and sparks to lend that essential grilled exterior.

The power supply is a fairly simple affair, if a little hair-raising. A simple push-pull MOSFET oscillator drives a pair of flyback transformers whose secondaries are connected in series. It’s not the most efficient way to generate high voltages with a flyback transformer – the key is in the word “flyback” – but it generates enough juice for the job in hand.

It’s hardly the safest cooking method, and we’d be worried about contamination from whatever metal the electrode is made from. But it’s entertaining to watch, as you’ll be able to see from the video below the break.

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Hackaday Prize Entry: Secure Storage on SD Cards

Here’s a puzzler for you: how do you securely send data from one airgapped computer to another? Sending it over a network is right out, because that’s the entire point of an airgap. A sneakernet is inherently insecure, and you shouldn’t overestimate the security of a station wagon filled with tapes. For his Hackaday Prize entry, [Nick Sayer] has a possible solution. It’s the Sankara Stones from Indiana Jones and the Temple of Doom, or a USB card reader that requires two cards. Either way, it’s an interesting experiment in physical security for data.

The idea behind the Orthrus, a secure RAID USB storage device for two SD cards, is to pair two SD cards. With both cards, you can read and write to this RAID drive without restriction. With only one, the data is irretrievable so they are safe during transit if shipped separately.

The design for this device is based around the ATXMega32A4U. It’s pretty much what you would expect from an ATMega, but this has a built-in full speed USB interface and hardware AES support. The USB is great for presenting two SD cards as a single drive, and the AES port is used to encrypt the data with a key that is stored in a key storage block on each card.

For the intended use case, it’s a good design. You can only get the data off of these SD cards if you have both of them. However, [Nick] is well aware of Schneier’s Law — anyone can design a cryptosystem that they themselves can’t break. That’s why he’s looking for volunteers to crack the Orthrus. It’s an interesting challenge, and one we’d love to see broken.

The SHA2017 Badge Revealed

It’s that excellent time of year in which one slowly comes to the realisation that the summer’s eagerly anticipated events are now no longer at some impossibly distant point in the future, but in fact only a matter of a few months or even weeks away. For our European readers, this means that August’s SHA2017 hacker camp is appearing on the horizon, four days of outdoor technological indulgence for our community in a scout camp on the Dutch polders.

As it is a tradition of such events to have an electronic badge incorporating ever more impressive levels of computing power, it follows that the pre-production announcement of an event badge has become an important milestone in the countdown to the day. SHA2017 is no exception, and thus today we see the announcement of their take on the essentials for a hacker camp badge in 2017.

The most immediately obvious thing about the badge is its 296×128 pixel e-ink display, which should provide an immediate benefit in terms of battery life. There are the usual plethora of interfaces, GPIOs, USB, and Neopixels, and the user input is via a set of capacitive buttons. Powering the device is an ESP32, and a key design goal was to have a network for the badges that does not put pressure on the 2.4GHz infrastructure. We’re guessing they’re doing this using raw WiFi packets in the same way as the MAGfest swadge. On the software front it will provide a straightforward development route via MicroPython, and there will be an app library for those without the inclination to code their own. You can get an early look at the schematic from the project repo (PDF).

Their target is to have the badge ready and with stable software on day 1 of the event, a laudable aim if they can manage it.

Members of the Hackaday team will be making the trip to the Netherlands for SHA2017, we look forward to seeing you if you attend too, and please show us anything interesting you do with your badges! Keep your eyes peeled for the Jolly Wrench, and come say hello. You’ll find me with the OxHack contingent and giving a talk on the kit biz which I have also published in the Project to Kit series of articles.

We’ve covered so many badges here at Hackaday that we could almost serve of a retrospective exhibition of the art form. Of particular interest to us though is our own [Voja Antonic]’s badge for last year’s Hackaday SuperConference.

Thanks [Sebastius] for the tip.

Make Munich was Awesome

It was a good weekend to be geeky in Bavaria. In addition to our own Hackaday Prize Bring-a-Hack party, there was the reason that we scheduled it in the first place, Munich’s independent DIY expo, Make Munich.

If you’re a loyal Hackaday reader, many of the projects would seem uncannily familiar. I walked in and was greeted by some beautiful word clocks in both German and English, for instance. Still, seeing the Open Theremin being sold with an “as seen on Hackaday” sticker made us smile. And then we had a great conversation about [Urs Gaudenz]’s other project: DIY biological apparatus, also seen on Hackaday.

There were robots galore. Someone (from Gmünd?) was driving around a graffiti-bot and spraying the floor with water instead of paint or chalk to very nice effect. The full evolution of the Zoobotics robot family was on display. Even the Calliope (a German version of the micro:bit) booth had this cute Bluetooth vibrobot. Join me after the break as I dive into all of the great stuff on display over the weekend.

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The Dangers of Engineering While Unlicensed

Citizen engineers, beware the Beaver State. If you want to discuss engineering in a public setting, you’d better have a license. If you don’t, you could end up like Oregon resident Mats Järlström — paying a $500 fine and being threatened with even larger civil penalties and jail time.

The story of how Järlström became ensnared in this unfortunate series of events begins innocently enough, and it’s a story that any Hackaday reader can probably relate to. After his wife received a traffic ticket in the mail from a red-light camera in the town of Beaverton, Järlström began pondering the math of traffic signal timing. After a little digging, he found the formula used for calculating the time traffic signals stay in the yellow stage. Moreover, he found a flaw in the formula, which dates back to 1959, that could lead to incorrect violations issued by automated traffic cameras.

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