A Lesson In RF Design Thanks To This Homebrew LNA

November 4, 2024 by Dan Maloney No comments

If you’re planning on working satellites or doing any sort of RF work where the signal lives down in the dirt, you’re going to need a low-noise amplifier. That’s typically not a problem, as the market is littered with dozens of cheap options that can be delivered in a day or two — you just pay your money and get to work. But is there a case to be made for rolling your own LNA?

[Salil, aka Nuclearrambo] thinks so, and he did a nice job showing us how it’s done. The first step, as always, is to define your specs, which for [Salil] were pretty modest: a low noise figure, moderate gain, and good linearity. He also wanted a bandpass filter for the 2-meter amateur radio band and for weather satellite downlinks, and a bias-tee to power the LNA over the coax feedline. The blog post has a detailed discussion of the electrical design, plus some good tips on PCB design for RF applications. We also found the discussion on bias-tee design helpful, especially for anyone who has ever struggled with the idea that RF and DC can get along together on a single piece of coax. Part 2 concentrates on testing the LNA, mostly using hobbyist-grade test gear like the NanoVNA and tiny SA spectrum analyzer. [Salil]’s tests showed the LNA lived up to the design specs and more, making it more than ready to put to work with an RTL-SDR.

Was this more work than buying an LNA? Absolutely, and probably with the same results. But then again, what’s to learn by just getting a pre-built module in the mail?

A side view of an Asian woman with brown hair. She has a faint smile and is wearing an earring that looks somewhat like a large copper snowflake. Near the ear hole is a small PCB with a blinking LED. To the right of the image is the text "LED Earring, Recieved power 50 µW"

Power-Over-Skin Makes Powering Wearables Easier

November 4, 2024 by Navarre Bartz 13 Comments

The ever-shrinking size of electronics and sensors has allowed wearables to help us quantify more and more about ourselves in smaller and smaller packages, but one major constraint is the size of the battery you can fit inside. What if you could remotely power a wearable device instead?

Researchers at Carnegie Mellon University were able to develop a power transmitter that lets power flow over human skin to remote devices over distances as far a head-to-toe. The human body can efficiently transmit 40 MHz RF energy along the skin and keeps this energy confined around the body and through clothing, as the effect is capacitive.

The researchers were able to develop several proof-of-concept devices including “a Bluetooth
ring with a joystick, a stick-and-forget medical patch which logs data, and a sun-exposure patch with a screen — demonstrating user input, displays, sensing, and wireless communication.” As the researchers state in the paper, this could open up some really interesting new wearable applications that weren’t possible previously because of power constraints.

If you’re ready to dive into the world of wearables, how about this hackable smart ring or a wearable that rides rails?

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Supercon 2024: Badge Add-On Winners

November 4, 2024 by Tom Nardi 2 Comments

This year we challenged the Hackaday community to develop ~~Shitty~~ ~~Simple~~ Supercon Add-Ons (SAO) that did more than just blink a few LEDs. The SAO standard includes I2C data and a pair of GPIO pins, but historically, they’ve very rarely been used. We knew the talented folks in this community would be able to raise the bar, but as they have a tendency to do, they’ve exceeded all of our expectations.

As we announced live during the closing ceremony at the 2024 Hackaday Supercon, the following four SAOs will be put into production and distributed to all the attendees at Hackaday Europe in Spring of 2025.

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[miko_tarik] wearing diy AR goggles in futuristic setting

Pi Zero To AR: Building DIY Augmented Reality Glasses

November 4, 2024 by Heidi Ulrich 10 Comments

If you’re into pushing tech boundaries from home, this one’s for you. Redditor [mi_kotalik] has crafted ‘Zero’, a custom pair of DIY augmented reality (AR) glasses using a Raspberry Pi Zero. Designed as an affordable, self-contained device for displaying simple AR functions, Zero allows him to experiment without breaking the bank. With features like video playback, Bluetooth audio, a teleprompter, and an image viewer, Zero is a testament to what can be done with determination and creativity on a budget. The original Reddit thread includes videos, a build log, and links to documentation on X, giving you an in-depth look into [mi_kotalik]’s journey. Take a sneak peek through the lens here.

Creating Zero wasn’t simple. From designing the frame in Tinkercad to experimenting with transparent PETG to print lenses (ultimately switching to resin-cast lenses), [mi_kotalik] faced plenty of challenges. By customizing SPI displays and optimizing them to 60 FPS, he achieved an impressive level of real-time responsiveness, allowing him to explore AR interactions like never before. While the Raspberry Pi Zero’s power is limited, [mi_kotalik] is already planning a V2 with a Compute Module 4 to enable 3D rendering, GPS, and spatial tracking.

Zero is an inspiring example for tinkerers hoping to make AR tech more accessible, especially after the fresh news of both Meta and Apple cancelling their attempts to venture in the world of AR. If you are into AR and eager to learn from an original project like this one, check out the full Reddit thread and explore Hackaday’s past coverage on augmented reality experiments.

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I Installed Gentoo So You Don’t Havtoo

November 4, 2024 by Bryan Cockfield 40 Comments

A popular expression in the Linux forums nowadays is noting that someone “uses Arch btw”, signifying that they have the technical chops to install and use Arch Linux, a distribution designed to be cutting edge but that also has a reputation of being for advanced users only. Whether this meme was originally posted seriously or was started as a joke at the expense of some of the more socially unaware Linux users is up for debate. Either way, while it is true that Arch can be harder to install and configure than something like Debian or Fedora, thanks to excellent documentation and modern (but optional) install tools it’s no longer that much harder to run than either of these popular distributions.

For my money, the true mark of a Linux power user is the ability to install and configure Gentoo Linux and use it as a daily driver or as a way to breathe life into aging hardware. Gentoo requires much more configuration than any mainline distribution outside of things like Linux From Scratch, and has been my own technical white whale for nearly two decades now. I was finally able to harpoon this beast recently and hope that my story inspires some to try Gentoo while, at the same time, saving others the hassle.

A Long Process, in More Ways Than One

My first experience with Gentoo was in college at Clemson University in the late ’00s. The computing department there offered an official dual-boot image for any university-supported laptop at the time thanks to major effort from the Clemson Linux User Group, although the image contained the much-more-user-friendly Ubuntu alongside Windows. CLUG was largely responsible for helping me realize that I had options outside of Windows, and eventually I moved completely away from it and began using my own Linux-only installation. Being involved in a Linux community for the first time had me excited to learn about Linux beyond the confines of Ubuntu, though, and I quickly became the type of person featured in this relevant XKCD. So I fired up an old Pentium 4 Dell desktop that I had and attempted my first Gentoo installation.

For the uninitiated, the main thing that separates Gentoo from most other distributions is that it is source-based, meaning that users generally must compile the source code for all the software they want to use on their own machines rather than installing pre-compiled binaries from a repository. So, for a Gentoo installation, everything from the bootloader to the kernel to the desktop to the browser needs to be compiled when it is installed. This can take an extraordinary amount of time especially for underpowered machines, although its ability to customize compile options means that the ability to optimize software for specific computers will allow users to claim that time back when the software is actually used. At least, that’s the theory. Continue reading “I Installed Gentoo So You Don’t Havtoo” →

Reusing An Old Android Phone For GPIO With External USB Devices

November 4, 2024 by Maya Posch 27 Comments

Each year millions of old smartphones are either tossed as e-waste or are condemned to lie unloved in dusty drawers, despite the hardware in them usually being still perfectly fine. Reusing these little computers for another purpose once the phone’s manufacturer drops support is made hard by a range of hardware and software (driver) issues. One possible way to do so is suggested by [Doctor Volt] in a video where a Samsung Galaxy S4 is combined with a USB-connected FT232R board to add external GPIO.

The idea is pretty simple: the serial adapter is recognized by the existing Android OS and within the standard Android development environment this module can be used. Within this demonstrator it’s merely used to blink some LEDs and react to inputs, but it shows how to reuse one of these phones in a non-destructive manner. Even better is that the phone’s existing sensors and cameras can still be used as normal in this way, too, which opens a whole range of (cheap) DIY projects that can be programmed either in Java/Kotlin or in C or C++ via the Native Development Kit.

The only wrinkle is that while the phone is connected like this, charging is not possible. For the S4 it’s easy to solve as it has a removable battery, so an external power input was wired in with a dummy battery-sized bit of perfboard. With modern phones without removable batteries simultaneous USB/audio dongle and charging usage via the USB-C connector is claimed to be possible, but this is something to check beforehand.

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Three 3D printed, spring loaded contraptions sit on a wooden shield. There are arrow shafts connected to the end and a piece of monofilament fishing line extending away from them and through a small eyelet at the edge of. the shield.

How To Shoot Actors With Arrows Sans CGI

November 4, 2024 by Navarre Bartz 12 Comments

Today, movie effects are mostly done in CGI, especially if they’re of the death-defying type. [Tyler Bell] shows us how they shot actors with arrows before CGI.

Almost every medieval movie has someone getting shot with an arrow, but how do you do that non-destructively? [Bell] shows us two primary methods that were used, the pop up rig and steel pronged arrows. The pop up rig is a spring loaded device with one end of an arrow attached that pops up when a mechanism is triggered. [Bell] 3D printed his own version of the mechanism and shows us how it can be used to great effect on shots from the side or rear of the victim.

But what about straight on shots where the rig would be blatantly obvious? That’s when you get to actually shoot the actor (or their stunt double anyway). To do this safely, actors would wear wooden body armor under their costumes and arrows with two small prongs would be shot along a wire into the desired impact site. We appreciate [Bell] using a mannequin for testing before letting his brother shoot him with an arrow. That’s definitely the next level above a trust fall.

We even get a look at using air cannons to launch arrow storms at the end which is particularly epic. Looking for more movie magic? How about the effects from King Kong or Flight of the Navigator?

Thanks to [Xerxes3rd] on Discord for the tip!

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