Direction Finding And Passive Radar With RTL-SDR

September 10, 2018 by 19 Comments

To say that the RTL-SDR project revolutionized hacker’s capabilities in the RF spectrum would be something of an understatement. It used to be that the bar, in terms of both knowledge and hardware, was so high that only those truly dedicated were able to explore the radio spectrum. But today anyone with $20 can pick up an RTL-SDR device, combine it with a wide array of open source software, and gain access to a previously invisible world.

That being said, RTL-SDR is usually considered an “Economy Ticket” to the world of RF. It gets your foot in the door, but experienced RF hackers are quick to point out you’ll need higher-end hardware if you want to start doing more complex experiments. But the KerberosSDR may soon change the perception of RTL-SDR derived hardware. Combining four R820T2 SDRs on a custom designed board, it allows for low-cost access to high concept technologies such as radio direction finding, passive radar, and beam forming. If you get bored with that, you can always just use it as you would four separate RTL-SDR dongles, perfect for applications that require monitoring multiple frequencies such as receiving trunked radio.

KerberosSDR (which was previously known as HydraSDR) is a collaborative effort between the Othernet engineering team and the folks over at RTL-SDR.com, who earlier in the year put out a call for an experienced developer to come onboard specifically for this project. Tamás Peto, a PhD student at Budapest University of Technology and Economics, answered the call and has put together a system which the team plans on releasing as open source so the whole community can benefit from it. In the videos after the break, you can see demonstrations of the direction finding and passive radar capabilities using an in-development version of KerberosSDR.

As for the hardware, it’s a combination of the RTL-SDR radios with an onboard GPIO-controlled wide band noise source for calibration, as well as an integrated USB hub so it only takes up one port. Everything is wrapped up in a shielded metal enclosure, and the team is currently experimenting with a header on the KerberosSDR PCB that would let you plug it directly into a Raspberry Pi or Tinkerboard.

The team hopes to start final hardware production within the next few months, and in the meantime has set up a mailing list so interested parties can stay in the loop and be informed when preorders start.

If you can’t wait until then, we’ve got a detailed write-up on DIY experiments with passive radar using RTL-SDR hardware, and you can always use your browser if you want to get your radio direction finding fix.

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Doing One Thing, Well: The UNIX Philosophy

September 10, 2018 by 102 Comments

The Unix operating system has been around for decades, and it and its lookalikes (mainly Linux) are a critical part of the computing world. Apple’s operating system, macOS, is Unix-based, as are Solaris and BSD. Even if you’ve never directly used one of these operating systems, at least two-thirds of all websites are served by Unix or Unix-like software. And, if you’ve ever picked up a smart phone, chances are it was running either a Unix variant or the Linux-driven Android. The core reason that Unix has been so ubiquitous isn’t its accessibility, or cost, or user interface design, although these things helped. The root cause of its success is its design philosophy.

Good design is crucial for success. Whether that’s good design of a piece of software, infrastructure like a railroad or power grid, or even something relatively simple like a flag, without good design your project is essentially doomed. Although you might be able to build a workable one-off electronics project that’s a rat’s nest of wires, or a prototype of something that gets the job done but isn’t user-friendly or scalable, for a large-scale project a set of good design principles from the start is key.

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Trebucheting Tennis Balls At 124 MPH

September 10, 2018 by 21 Comments

A trebuchet is one of the older machines of war. It’s basically a sling on a frame, with a weight that you can lift up high and which pulls the sling arm over on release. Making one opens up the doors to backyard mayhem, but optimizing one opens up the wonders of physics.

[Tom Stanton] covers just about everything you need to know about trebuchet building in his four-part video series. Indeed, he sums it up in video two: you’ve got some potential energy in the weight, and you want to transfer as much of that as possible to the ball. This implies that the optimal path for the weight would be straight down, but then there’s the axle in the way.  The rest, as they say, is mechanical engineering.

Video three was the most interesting for us. [Tom] already had some strange arm design that intends to get the weight partially around the axle, but he’s still getting low efficiencies, so he builds a trebuchet on wheels — the classic solution. Along the way, he takes a ton of measurements with Physlets Tracker, which does video analysis to extract physical measurements. That tip alone is worth the price of admission, but when the ball tops out at 124 mph, you gotta cheer.

In video four, [Tom] plays around with the weight of the projectile and discovers that he’s putting spin on his tennis ball, making it curve in flight. Who knew?

Anyway, all four videos are embedded below. You can probably skip video one if you already know what a trebuchet is, or aren’t interested in [Tom] learning that paying extra money for a good CNC mill bit is worth it. Video two and three are must-watch trebucheting.

We’re a sad to report that we couldn’t find any good trebuchet links on Hackaday to dish up. You’re going to have to settle for a decade-old catapult post or this sweet beer-pong-playing robotic arm. You can help. Submit your trebuchet tips.

Thanks [DC] for this one!

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120 Second Shower Cap

September 10, 2018 by 24 Comments

Do you have a couple of minutes? Literally and precisely, two minutes. That’s how long these ten songs play. So what? A short song is not new, but these ten songs are part of a campaign to encourage residents of Cape Town, South Africa to cap their showers at one-hundred-twenty seconds. Some of us do not have to worry about droughts or water bills, but most of us are concerned about one or both of those, and this ingenious campaign alerted people to the problem, gave them the means to time themselves, and made it pleasant, not oppressive. The songs are freely available, and one might even pique your listening tastes from the biggest stars in South Africa.

So, where is the hack? Some of us have experimented with egg timers on the towel rack, timers on the showerhead, servos on the faucet knobs, or occupancy sensors, but those are strong-arm techniques or only for measuring, not regulating water use. These songs attack the most viable vector, the showerer. Or is it showeree? Telling people there is a drought is one thing, but giving them the ability to regulate themselves in such a way that they comply is a hacker’s approach. The songs on the site do not autoplay so there will be no hanging out under the water spray to find the best song. Which is your favorite?

3D Printed Radius Gauge, Just Add Calipers (And A Wee Bit Of Math)

September 9, 2018 by 16 Comments
With 3D printed arms of fixed measurements, the depth reading from a set of digital calipers can be used to calculate the radius of a curve.

Specialized tools that focus on one particular job tend to get distilled right down to their essentials and turned in an economical consumer product. One example of this is radius (or fillet) gauges: a set of curves in different sizes that one uses to measure the radius of a curved surface by trial and error. To some, such products represent solved problems. Others see opportunities for a fresh perspective, like this caliper-enabled 3D printed radius gauge by [Arne Bergkvist].

[Arne]’s 3D printed radius gauge is a simple object; a rigid attachment for a nearly ubiquitous model of digital caliper. By placing the curve to be measured between the two arms of the device and using the depth measurement of the caliper to measure distance to the curve’s surface, a simple calculation (helpfully printed on the unit itself) of radius = distance * 2.414 reveals the radius of the curve. However, this shortened calculation makes a number of assumptions and only works for [Arne]’s specific design.

Another version by [Fredrik Welander] represents a more flexible take on the same concept. His RadGauge design (pictured up top) has a few different sizes to accommodate a variety of objects, and his Git repository provides a calculator tool as well as some tips on fine tuning to allow for variations in the dimensions of the printed attachment.

3D printing has opened a lot of doors, and items like this show that the plastic doodads created aren’t always the end result in and of themselves; sometimes they are the glue that enables a tool or part to work in a different way. To help get the most out of 3D printing, check out the in-depth coverage of how to best tap 3D printed parts for fasteners, and [Roger Cheng]’s guide to using 3D printed brackets and aluminum extrusion to make just about anything.

Electromagnetic Field: A Cyberpunk Headdress To Be Noticed In

September 9, 2018 by 3 Comments

At the recent Electromagnetic Field hacker camp in the UK, one of the highlights was the Null Sector, a cyberpunk-themed zone best described as something close to the set of Blade Runner made from shipping containers, clever props, and lighting. Our community rose to the occasion with some truly impressive costumes and wearable electronics, lending the venue a real authenticity.

Among the many creations on show there was one that stood quite literally head and shoulders above the rest. [Chebe]’s colour stealing sound reactive LED headdress is a confection of Neopixels, organza, and transparent floor protectors on a wire frame, driven by a Lillypad wearable microcontroller board with a microphone and colour sensor attached. The resulting sound-and-colour-reactive display stood out across a crowded venue full of hackers who’d all made their own efforts to produce similar outfits, which is really saying something!

The Lillypad and LEDs are standard fare, but the wire part of this project isn’t, and that’s what makes it rather interesting from our perspective. Anyone can make something that goes over their head, but to make something that’s comfortable takes a bit of effort and thought. Have you ever tried a set of ill-fitting sunglasses? If you have then you might understand. In this case stiff garden wire is used, bent to shape and joined with rolled-up tape, before being covered with wound-on ribbon for extra comfort. A Hackaday scribe travels the field at a hacker camp, and though [Chebe]’s cranium is a little more petite than the Hackaday bonce it was certainly an enveloping fit when we tried it.

Anyone can attach an LED to an item of clothing and call it a wearable. But to be noticed like this one it has to be done with style. If you’ve not had your fill of this topic, we suggest you continue with the Hackaday Belgrade talk from our friend [Rachel “Konichiwakitty” Wong].

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Hackaday Links: September 9, 2018

September 9, 2018 by 64 Comments

Octoprint is one of those must-have apps for 3D printers. All you need is a Raspberry Pi, an SD card, and a USB cable, and you can control your 3D printer from anywhere in the house. Of course, some people take it too far and open up their Octoprint to the greater Internet. Gizmodo reports thousands of people are doing so, with possible dire consequences. Choice quotes: “Imagine waking up in the morning to find that your 3D printer was used to produce a gun” and “Once again, 3D guns come to mind”. Yes, they referenced 3D printed guns twice in a story. Call me when you can 3D print bullets. Or when bioprinters can print airborne HIV, which was also suggested in the story.

ARS Electronica is going on in Linz this weekend, and it’s the largest new media art festival where cyber artists are recognized for their innovations. One of the more interesting exhibits is [Sarah Petkus]’ Noodlefeet. Its [Sarah]’s kid, that’s a robot, that’s made out of pool noodles. She’s talked about it at the Hackaday Superconference, and now there’s an entire exhibit behind it. You can check out her ‘making of’ post right here.

A mirror is a useful survival tool, if only for signalling people. Here’s a video showing long-distance mirror signalling, over a distance of 27.5 miles. The mirror used was 330 x 254mm, but the real challenge here is pointing the mirror in the right direction. For that, [Andy] used a bamboo pole a few meters in front of the mirror. By reflecting sunlight onto the pole, he knew it was going in about the right direction. Accuracy versus precision, or something like that.

Last week, a slow leak was detected aboard the International Space Station. The leak was quickly traced to a 2mm hole in the upper orbital module of a visiting Soyuz spacecraft. prompting call of micrometeoroid damage and plenty of speculation on what would have happened if this hole appeared anywhere else on the station. Now, it looks like this hole was put there by a drill, probably during assembly or testing, and was somehow plugged until the Soyuz was in space for a few weeks. Why this hole just magically appeared one night is anyone’s guess, but there you go.