Making A One-Of-A-Kind Lime2 SBC

April 22, 2025 by Matt Varian 5 Comments

Upgrading RAM on most computers is often quite a straightforward task: look up the supported modules, purchase them, push a couple of levers, remove the old, and install the new. However, this project submitted by [Mads Chr. Olesen] is anything but a simple.

In this project, he sets out to double the RAM on a Olimex A20-OLinuXino-LIME2 single-board computer. The Lime2 came with 1 GB of RAM soldered to the board, but he knew the A20 processor could support more and wondered if simply swapping RAM chips could double the capacity. He documents the process of selecting the candidate RAM chip for the swap and walks us through how U-Boot determines the amount of memory present in the system.

While your desktop likely has RAM on removable sticks, the RAM here is soldered to the board. Swapping the chip required learning a new skill: BGA soldering, a non-trivial technique to master. Initially, the soldering didn’t go as planned, requiring extra steps to resolve issues. After reworking the soldering, he successfully installed both new chips. The moment of truth arrived—he booted up the LIME2, and it worked! He now owns the only LIME2 with 2 GB of RAM.

Be sure to check out some other BGA soldering projects we’ve featured over the years.

A photo of Aaron Danner with a current mirror schematic in an overlay.

Biasing Transistors With Current Sources

April 21, 2025 by John Elliot V 3 Comments

Over on his YouTube channel [Aaron Danner] explains biasing transistors with current sources in the 29th video of his Transistors Series. In this video, he shows how to replace a bias resistor (and consequently an additional capacitor) with a current source for both common-emitter and common-collector amplifiers.

A current source provides electrical energy with a constant current. The implication is that if the resistance of the load changes the current source will vary the voltage to compensate. In reality, this is exactly what you want. The usual resistor biasing arrangement just simulates this over a narrow voltage range, which is generally good enough, but not as good as a true current source.

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Building A Custom Zynq-7000 SoC Development Board From The Ground Up

April 20, 2025 by John Elliot V 8 Comments

In this series of 23 YouTube videos [Rich] puts the AMD Zynq-7000 SoC through its paces by building a development board from the ground up to host it along with its peripherals. The Zynq is part FPGA and part CPU, and while it has been around for a while, we don’t see nearly as many projects about it as we’d like.

[Rich] covers everything from the power system to HDMI, USB, DDR RAM, and everything in between. By the end, he’s able to boot PetaLinux.

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Supercon 2024: Exploring The Ocean With Open Source Hardware

April 17, 2025 by Tom Nardi 10 Comments

If you had to guess, what do you think it would take to build an ocean-going buoy that could not only survive on its own without human intervention for more than two years, but return useful data the whole time? You’d probably assume such a feat would require beefy hardware, riding inside an expensive and relatively large watertight vessel of some type — and for good reason, the ocean is an unforgiving environment, and has sent far more robust hardware to the briny depths.

But as Wayne Pavalko found back in 2016, a little planning can go a long way. That’s when he launched the first of what he now calls Maker Buoys: a series of solar-powered drifting buoys that combine a collection of off-the-shelf sensor boards with an Arduino microcontroller and an Iridium Short-Burst Data (SBD) modem in a relatively simple watertight box.

He guessed that first buoy might last a few weeks to a month, but when he finally lost contact with it after 771 days, he realized there was real potential for reducing the cost and complexity of ocean research.

Wayne recalled the origin of his project and updated the audience on where it’s gone from there during his 2024 Supercon talk, Adventures in Ocean Tech: The Maker Buoy Journey. Even if you’re not interested in charting ocean currents with homebrew hardware, his story is an inspirational reminder that sometimes a fresh approach can help solve problems that might at first glance seem insurmountable.

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A man is looking at a volumetric display while using one finger to interact with it. Two roughly-spherical blue shapes are visible in the display, and he is moving his index finger toward one of them.

Elastic Bands Enable Touchable Volumetric Display

April 14, 2025 by Aaron Beckendorf 12 Comments

Amazing as volumetric displays are, they have one major drawback: interacting with them is complicated. A 3D mouse is nice, but unless you’ve done a lot of CAD work, it’s a bit unintuitive. Researchers from the Public University of Navarra, however, have developed a touchable volumetric display, bringing touchscreen-like interactions to the third dimension (preprint paper).

At the core, this is a swept-volume volumetric display: a light-diffusing screen oscillates along one axis, while from below a projector displays cross-sections of the scene in synchrony with the position of the screen. These researchers replaced the normal screen with six strips of elastic material. The finger of someone touching the display deforms one or more of the strips, allowing the touch to be detected, while also not damaging the display.

The actual hardware is surprisingly hacker-friendly: for the screen material, the researchers settled on elastic bands intended for clothing, and two modified subwoofers drove the screen’s oscillation. Indeed, some aspects of the design actually cite this Hackaday article. While the citation misattributes the design, we’re glad to see a hacker inspiring professional research.) The most exotic component is a very high-speed projector (on the order of 3,000 fps), but the previously-cited project deals with this by hacking a DLP projector, as does another project (also cited in this paper as source 24) which we’ve covered.

While interacting with the display does introduce some optical distortions, we think the video below speaks for itself. If you’re interested in other volumetric displays, check out this project, which displays images with a levitating styrofoam bead.

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A slide from a talk about Spade language with a diagram about how it fits in with Verilog, VHDL, and HLS.

The Spade Hardware Description Language

April 13, 2025 by John Elliot V 15 Comments

Spade is an open-source hardware description language (HDL) developed at Linköping University, Sweden.

Other HDLs you might have heard of include Verilog and VHDL. Hardware engineers use HDLs to define hardware which can be rendered in silicon. Hardware defined in HDLs might look like software, but actually it’s not software, it’s hardware description. This hardware can be realized myriad ways including in an FPGA or with an ASIC.

You have probably heard that your CPU processes instructions in a pipeline. Spade has first-class support for such pipelines. This means that design activities such as re-timing and re-pipelining are much easier than in other HDLs where the designer has to implement these by hand. (Note: backward justification is NP-hard, we’re not sure how Spade supports this, if it does at all. If you know please enlighten us in the comments!)

Spade implements a type system for strong and static typing inspired by the Rust programming language and can do type inference. It supports pattern matching such as you might see in a typical functional programming language. It boasts having user-friendly and helpful error messages and tooling.

Spade is a work in progress so please expect missing features and breaking changes. The documentation is in The Spade Book. If you’re interested you can follow development on GitLab or Discord.

So now that you know about the Spade language, are you planning to take it for a spin? You will find plenty of Verilog/VHDL designs at Hackaday which you could re-implement using Spade, such as an easy one like Breathing LED Done With Raw Logic Synthesized From A Verilog Design (see benchmarks) or a much more challenging one like Game Boy Recreated In Verilog. If you give Spade a go we’d love to see what you come up with!

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How Shrinking Feature Size Made Modern Wireless Work

April 5, 2025 by Elliot Williams 4 Comments

If you’re living your life right, you probably know what as MOSFET is. But do you know the MESFET? They are like the faster, uninsulated, Schottky version of a MOSFET, and they used to rule the roost in radio-frequency (RF) silicon. But if you’re like us, and you have never heard of a MESFET, then give this phenomenal video by [Asianometry] a watch. In it, among other things, he explains how the shrinking feature size in CMOS made RF chips cheap, which brought you the modern cellphone as we know it.

MESFET

MOSFET

The basic overview is that in the 1960s, most high-frequency stuff had to be done with discrete parts because the bipolar-junction semiconductors of the time were just too slow. At this time, MOSFETs were just becoming manufacturable, but were even slower still. The MESFET, without its insulating oxide layer between the metal and the silicon, had less capacitance, and switched faster. When silicon feature sizes got small enough that you could do gigahertz work with them, the MESFET was the tech of choice.

As late as the 1980s, you’d find MESFETs in radio devices. At this time, the feature size of the gates and the thickness of the oxide layer in MOSFETs kept them out of the game. But as CPU manufacturers pushed CMOS features smaller, not only did we get chips like the 8086 and 80386, two of Intel’s earliest CMOS designs, but the tech started getting fast enough for RF. And the world never looked back.

If you’re interested in the history of the modern monolithic RF ICs, definitely give the 18-minute video a watch. (You can skip the first three or so if you’re already a radio head.) If you just want to build some radio circuits, this fantastic talk from [Michael Ossmann] at the first-ever Supercon will make you an RF design hero. His secrets? Among them, making the most of exactly these modern everything-in-one-chip RF ICs so that you don’t have to think about that side of things too hard.

Thanks [Stephen] for the tip!

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