39C3: Hardware, And The Hard Bit

December 29, 2025 by 9 Comments

The 39th annual Chaos Communication Congress (39C3) is underway, and it kicked off with a talk that will resonate deeply with folks in the Hackaday universe. [Kliment] gave an impassioned invitation for everyone to start making hardware based on his experience both in the industry and in giving an intro-to-surface-mount workshop to maybe thousands of hackers over the years.

His main points are that the old “hardware is hard” cliche is overdone. Of course, working on a complicated high-reliability medical device isn’t child’s play, but that’s not where you start off. And getting started in hardware design and hobby-scale manufacture has never been easier or cheaper, and the open-source tooling gives you a foot in the door.

He tells the story of an attendee at a workshop who said “I kept waiting for the hard part to come, but then I was finished.”  Starting off with the right small-scale projects, learning a few techniques, and ramping up skills built on skills is the way to go. ([Kliment] is a big proponent of hand-placed hot-plate reflow soldering, and we concur.)

This is the talk that you want to show to your software friends who are hardware-curious. It’s also a plea for more experimentation, more prototyping, more hacking, and simply more people in the hardware / DIY electronics scene. Here at Hackaday, it’s maybe preaching to the choir, but sometimes it’s just nice to hear saying it all out loud.

The Birotary Engine Explained

December 28, 2025 by 25 Comments

Everyone generally knows about piston and rotary engines, with many a flamewar having been waged over the pros and cons of each design. The “correct” answer is thus to combine both into a single engine design. The resulting birotary engine comes courtesy of Czech company [Knob Engines] which makes their special engine for the aviation market. The workings of this engine and why it makes perfect sense for smaller airplanes is explained by [driving 4 answers] in a recent video.

Naturally, it’s at best confusing to call an engine a “rotary”, as this covers many types of engines. One could consider the birotary engine perhaps a cross between the traditional rotary piston engines that powered early aircraft and the Wankel rotary engines that would appear much later. The fact that both the housing and the crankshaft rotate reinforces this notion of a piston rotary, while it keeps the fixed ports and glow plugs on the housing that is typical of a Wankel-style engine. Having both the housing and crankshaft rotate is also why it’s called the ‘birotary’.

The claimed benefits of this design include a small size, low vibrations, reduced gyroscopic effect due to counter-rotation, no apex seals, and less mechanically complex than a piston engine. This comes at the cost of a very short stroke length and thus the need for a relatively high RPM and slow transition between power output levels, but those disadvantages are why small airplanes and UAVs are being targeted.

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Streaming Music To Cassette

December 28, 2025 by 8 Comments

In almost every measurable way, a lossless digital audio file is superior to any analog media. This doesn’t mean that analog audio isn’t valuable though; plenty of people appreciate the compression, ambiance, and other side-effects of listening to a vinyl record or a cassette tape despite the technical limitations. To combine the audio technology of the modern world with these pleasant effects of old analog media, [Julius] built a cassette-based media streamer.

The music playback device takes input from a Bluetooth stream of some sort, converts the digital stream to analog, combines the stereo signal into a mono signal, and then records it to a cassette tape. The tape is then looped through to a playback device which outputs the sound to a single speaker. This has the effect of functioning as a tape delay device, and [Julius] did add input and output jacks to use it as such, but in its default state it has the effect of taking modern streaming through a real analog device and adding the compression and saturation that cassette tapes are known for.

The design of the device is impressive as well, showing off the tape loop and cassette front-and-center with a fluorescent vu meter on the side and a metal case. Getting all of this to work well together wasn’t entirely smooth, either, as [Julius] had to sort out a number of issues with the electronics to keep various electric noises out of the audio signal. Retro analog music players are having a bit of a resurgence right now, whether that’s as a revolt against licensed streaming services or as a way to experience music in unique ways, and our own [Kristina Panos] recently went down an interesting rabbit hole with one specific type of retro audio player.

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A photo of the circuit on a breadboard

Retro Semiconductors: The Silicon Controlled Rectifier

December 28, 2025 by 5 Comments

Over on YouTube [Lockdown Electronics] reviews an old bit of kit known as the Silicon Controlled Rectifier (SCR). Invented in the 1950s the SCR is a type of thyristor and they were popular back in the 1970s. They are often replaced these days by the TRIAC and the MOSFET but you might still find some old schematics that call for them and you can still buy them.

The SCR is a three terminal electronic switch which latches on. You apply a signal at the gate which allows the other two pins, the anode and cathode, to conduct; and they continue to do so until power is removed. The silicon inside the device is comprised of three semiconductor junctions, as: PNPN. The P on the left is the anode, the N on the right is the cathode, and the P in the right middle is the gate.

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Photographing Cosmic Rays With A Consumer Camera

December 28, 2025 by 16 Comments

The reason photographic darkrooms are needed is because almost any amount of light can ruin the film or the photographic paper before they are fixed. Until then these things are generally kept in sealed, light-proof containers until they are ready to be developed. But there are a few things that can ruin film even then, most notably because some types of film are sensitive to ionizing radiation as well as light. This was famously how [Henri Becquerel] discovered that uranium is radioactive, but the same effect can be used to take pictures of cosmic rays.

In [Becquerel]’s case, a plate of photographic material was essentially contaminated from uranium by accident, even though the plate was in a completely dark area otherwise. Cosmic rays are similar to this type of radiation in that they are also ionizing and will penetrate various materials even in places we might otherwise think of as dark. For this artistic and scientific experiment, [Gabriel] set up a medium-format digital camera in a completely dark room and set it to take a 41-minute exposure. The results are fairly impressive and are similar to [Becquerel]’s experiment except that [Gabriel] expected to see something whereas the elder scientist was more surprised.

Like cosmic rays or radiation from uranium, there is a lot flying around that is invisible to the human eye but that can be seen with the right equipment and some effort. Although [Gabriel] is using a camera with a fairly large sensor that we might not all have access to, in theory this could work with more off-the-shelf digital photography equipment or even film cameras. A while ago we even saw a build that used UV to see other invisible phenomena like electrical arcing.

Create Aerated Concrete Using Xanthan Gum And Dishwashing Liquid

December 28, 2025 by 25 Comments

To make aerated concrete, add a foam-forming agent and stir in a significant amount of air. This serves to make the concrete significantly lighter, better insulating, and more resilient to fire. Making it can however be a bit of an issue, often requiring ingredients that aren’t purchased at the average DIY store. This is where [NightHawkInLight]’s method seems rather promising, requiring effectively only xanthan gum and dishwashing detergent.

For the small-scale demonstration, 15 grams of the thickening agent xanthan gum is mixed with enough alcohol to create a slurry. To this 60 mL of the detergent and 1 liter of water is added and mixed until the xanthan gum has absorbed all the moisture, which takes about 5-10 minutes. This mixture is then added to Portland cement with two parts cement to one part xanthan gum/detergent mixture and mixed for a while.

Of importance here is that this mixture will keep expanding in volume while mixing, so you have to have to keep an eye on the amount of air relative to concrete, as this will determine the strength and other properties of the final aerated concrete. If you continue past a certain point you will even create open-celled aerated concrete that’s completely porous, so you have to know what kind of concrete you want before you start mixing up a big batch.

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Cheetah 3d printer mobo

Cheetah MX4 Mini: A Pint-Sized 3D Printer Controller

December 28, 2025 by 28 Comments

There’s a seemingly unending list of modifications or upgrades you can make to a 3D printer. Most revolve around the mechanical side of things, many are simple prints or small add-ons. This upgrade is no small task: this 17-year-old hacker [Kai] took on designing and building his own 3D printer control motherboard, the Cheetah MX4 Mini.

He started the build by picking out the MCU to control everything. For that, he settled on the STM32H743, a fast chip with tons of support for all the protocols he could ask for, even as he was still nailing down the exact features to implement. For stepper drivers, [Kai] went with four TMC stepstick slots for silent motor control. There are provisions for sensorless homing and endstops, support for parallel and serial displays, and both USB-C and microSD card slots for receiving G-code. It can drive up to three fans as well as two high-amperage loads, such as for the heated bed.

All these features are packed into a board roughly the size of a drink coaster. Thanks to the STM32H743, the Cheetah MX4 Mini supports both Marlin and Klipper firmware, a smart choice that lets [Kai] leverage the massive amount of work that’s already gone into those projects.

One of the things that stood out about this project is the lengths to which [Kai] went to document what he did. Check out the day-by-day breakdown of the 86 hours that went into this build; reading through it is a fantastic learning aid for others. Thanks [JohnU] for sending in this tip! It’s great to see such an ambitious project not only taken on and accomplished, but documented along the way for others to learn from. This is a fantastic addition to the other 3D printer controllers we’ve seen.