Loop Antenna is Portable

We don’t know if [OH8STN] has a military background, but we suspect he might since his recent post is about a “DIY Man Portable Magnetic Loop Antenna.” “Man-portable” is usually a military designation, and — we presume — he wouldn’t object to a woman transporting it either.

[OH8STN] started with a Chameleon antenna starter kit. This costs about $100 and is primarily a suitable variable capacitor with a 6:1 reduction drive premounted and soldered. Of course, you could source your own, but finding variable capacitors that can handle transmit duty (admittedly, these can apparently handle about 10 W continuous or 25 W on single sideband) can be tricky, especially these days. Although he started with a kit, he did modify the antenna to switch between two different sets of ham radio bands. You can see the antenna in the video below.

Loop antennas aren’t ideal–but neither is any other small antenna. Because the loop is tightly tuned to a particular frequency, it requires retuning for even relatively small frequency changes, even though it can operate on many different frequencies. If you want more technical details, you might enjoy this recent presentation from [W4RAX]. The links at the end are worth checking out, too.

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Decorate Your 3D Prints with Detailed Hydrographic Printing

It’s like the old quip from [Henry Ford]: You can have your 3D prints in any color you want, as long as it’s one. Some strides have been made to bringing more color to your extruded goodies, but for anything beyond a few colors, you’re going to need to look at post-print processing of some sort. For photorealistic 3D prints, you might want to look into a simple hydrographic printing method that can be performed right on a printer.

If some of the prints in the video below look familiar, it’s because we covered the original method when it was presented at SIGGRAPH 2015. [Amos Dudley] was intrigued enough by the method, which uses computational modeling of complex surfaces to compose a distorted image that will be stretched back into shape when the object is dipped, to contact the original authors for permission to use the software. He got a resounding, “Nope!” – it appears that the authors’ institution isn’t big into sharing information. So, [Amos] hacked the method.

In place of the original software, [Amos] used Blender to simulate the hydrographic film as a piece of cloth interacting with the 3D-printed surface. This allowed him to print an image on PVA film that will “un-distort” as the object is dipped. He built a simple tank with overflow for the printer bed, used the Z-axis to dip the print, and viola! Photo-realistic frogs and globes.

[Amos]’ method has its limitations, but the results are pretty satisfying already. With a little more tweaking, we’re sure he’ll get to the point that the original authors did, and without their help, thank you very much.

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Octosonar is 8X Better than Monosonar

The HC-SR04 sonar modules are available for a mere pittance and, with some coaxing, can do a pretty decent job of helping your robot measure the distance to the nearest wall. But when sellers on eBay are shipping these things in ten-packs, why would you stop at mounting just one or two on your ‘bot? Octosonar is a hardware and Arduino software library that’ll get you up and running with up to eight sonar sensors in short order.

Octosonar uses an I2C multiplexer to send the “start” trigger pulses, and an eight-way OR gate to return the “echo” signal back to the host microcontroller. The software library then sends the I2C command to select and trigger a sonar module, and a couple of interrupt routines watch the “echo” line to figure out the time of flight, and thus the distance.

Having two sonars on each side of a rectangular robot allows it move parallel to a wall in a straightforward fashion: steer toward or away from the wall until they match. Watch the video below for a demo of this very simple setup. (But also note where the robot’s 45-degree blind spot is: bump-bump-bump!)

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Do you trust your hard drive indication light?

Researchers in the past have exfiltrated information through air gaps by blinking all sorts of lights from LEDs in keyboards to the main display itself. However, all of these methods all have one problem in common: they are extremely noticeable. If you worked in a high-security lab and your computer screen started to blink at a rapid pace, you might be a little concerned. But fret not, a group of researchers has found a new light to blink (PDF warning). Conveniently, this light blinks “randomly” even without the help of a virus: it’s the hard drive activity indication light.

All jokes aside, this is a massive improvement over previous methods in more ways than one. Since the hard drive light can be activated without kernel access, this exploit can be enacted without root access. Moreover, the group’s experiments show that “sensitive data can be successfully leaked from air-gapped computers via the HDD LED at a maximum bit rate of 4000 bit/s (bits per second), depending on the type of receiver and its distance from the transmitter.” Notably, this speed is “10 times faster than the existing optical covert channels for air-gapped computers.”

We weren’t born last night, and this is not the first time we’ve seen information transmission over air gaps. From cooling fans to practical uses, we’ve seen air gaps overcome. However, there are also plenty of “air gaps” that contain more copper than air, and require correspondingly less effort.

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Ask Hackaday: Bitten by the Crocodile Clip

I have a love/hate relationship with the crocodile clip. Nothing is so quick to lash together a few half-baked prototype boards on your desk, but nothing ends up in such a tangle so quickly, either. I love the range of pretty colors that crocodiles come in, as well as the easy ability to just clip on to the side of a PCB, or any old loose wire. But they come loose, they can have intermittent contacts, and we’re not even sure if there is such a thing as a current rating for them.

When [WarriorRocker] wrote in asking what we use instead of crocodile clips, he included a photo that sent a chill down my spine, from a review of some clips on Amazon. I’ve seen this one in real life. And what’s worse is the one with the loose wires that sometimes make contact with the spring-clip body and sometimes not.

After an hour-long debugging session about twelve years ago now, such an intermittent croc caused us to make a lifelong vow. All of our croco-clips have been disassembled, manually inspected, and many of them soldered together. When I buy new ones, I check them all before mixing them in with the known-goods. Even thinking about this now makes me want to pull back their little rubber booties just to make sure. Continue reading “Ask Hackaday: Bitten by the Crocodile Clip”

Tindie Chat: All About Certifications

The chat functionality on Hackaday.io is quickly turning into the nexus of all things awesome. This Tuesday, February 28th, everyone’s favorite robotic dog is talking certifications. Everything from FCC to UL to OSH to CE and the other CE is on the table. If you want to build hardware, and especially if you want to build a product, this is the talk for you. Join us for the next Tindie Chat on Hackaday.io.

Every month or so, we round up Tindie sellers, buyers, and the Tindie curious to talk about the issues facing hardware creators. We meet up in the Tindie Dog Park to talk about all things Tindie and hardware creation. If you want to know anything about certifications — whether you’re selling on Tindie or not — this is the virtual meetup for you.

This chat is going down Tuesday, February 28th at 11:00 AM PST (or 19:00 GMT). Want to join in the chat? Head on over to the Tindie Dog Park and request to join the project. Then, just head over to the chat by clicking on the ‘Team Messaging’ button. If you have a question, we have a spreadsheet.

There are a lot of experienced product designers over on Tindie, and this is a prime opportunity to learn some of the hard lessons these Tindie sellers have already experienced. Don’t miss this, it’s going to be great.

Growing Plants on Mars… on Earth

One of the biggest challenges of traveling to Mars is that it’s far away. That might seem obvious, but that comes with its own set of problems when compared to traveling to something relatively close like the Moon. The core issue is weight, and this becomes a big deal when you have to feed several astronauts for months or years. If food could be grown on Mars, however, this would make the trip easier to make. This is exactly the problem that [Clinton] is working on with his Martian terrarium, or “marsarium”.

The first task was to obtain some soil that would be a good analog of Martian soil. Obtaining the real thing was out of the question, as was getting similar dirt from Hawaii. [Clinton] decided to make his own by mixing various compounds from the hardware store in the appropriate amounts. From there he turned to creating the enclosure and filling it with the appropriate atmosphere. Various gas canisters controlled by gas solenoid valves mixed up the analog to Martian atmosphere: 96% dioxide, 2% argon, and 2% nitrogen. The entire experiment was controlled by an Intel Edison with custom circuits for all of the sensors and regulating equipment. Check out the appropriately dramatic video of the process after the break.

While the fern that [Clinton] planted did survive the 30-day experiment in the marsarium, it wasn’t doing too well. There’s an apparent lack of nitrogen in Martian soil which is crucial for plants to survive. Normally this is accomplished when another life form “fixes” nitrogen to the soil, but Mars probably doesn’t have any of that. Future experiments would need something that could do this for the other plants, but [Clinton] notes that he’ll need a larger marsarium for that. And, if you’re not interested in plants or Mars, there are some other interesting ramifications of nitrogen-fixing as well.

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