Deep Fission Wants To Put Nuclear Reactors Deep Underground

November 23, 2025 by 8 Comments

Today’s pressurized water reactors (PWRs) are marvels of nuclear fission technology that enable gigawatt-scale power stations in a very compact space. Though they are extremely safe, with only the TMI-2 accident releasing a negligible amount of radioactive isotopes into the environment per the NRC, the company Deep Fission reckons that they can make PWRs even safer by stuffing them into a 1 mile (1.6 km) deep borehole.

Their proposed DB-PWR design is currently in pre-application review at the NRC where their whitepaper and 2025-era regulatory engagement plan can be found as well. It appears that this year they renamed the reactor to Deep Fission Borehole Reactor 1 (DFBR-1). In each 30″ (76.2 cm) borehole a single 45 MWt DFBR-1 microreactor will be installed, with most of the primary loop contained within the reactor module.

As for the rationale for all of this, at the suggested depth the pressure would be equivalent to that inside the PWR, with in addition a column of water between it and the surface, which is claimed to provide a lot of safety and also negates the need for a concrete containment structure and similar PWR safety features. Of course, with the steam generator located at the bottom of the borehole, said steam has to be brought up all the way to the surface to generate a projected 15 MWe via the steam turbine, and there are also sampling tubes travelling all the way down to the primary loop in addition to ropes to haul the thing back up for replacing the standard LEU PWR fuel rods.

Whether this level of outside-the-box-thinking is a genius or absolutely daft idea remains to be seen, with it so far making inroads in the DoE’s advanced reactor program. The company targets having its first reactor online by 2026. Among its competition are projects like TerraPower’s Natrium which are already under construction and offer much more power per reactor, along with Natrium in particular also providing built-in grid-level storage.

One thing is definitely for certain, and that is that the commercial power sector in the US has stopped being mind-numbingly boring.

 

Saving A Rental Ebike From The Landfill

November 23, 2025 by 3 Comments

One of the hardest things about owning a classic car is finding replacement parts. Especially if the car is particularly old or rare, or if the parent company is now out of business, sometimes this can be literally impossible and a new part will have to be manufactured from scratch. The same is true of bicycles as well, and there are plenty of defunct bicycle manufacturers to choose from. [Berm Peak] found a couple old rental ebikes from a company that’s not in business anymore and set about trying to get them working again. (Video, embedded below.)

Of course, unlike many classic cars, ebikes are encumbered by proprietary electronics and software that are much harder to replace than most physical components. As a result, these bikes get most of their electronics pulled out and directly replaced. This bike also had a seized motor, so [Berm Peak] replaced it with another hub motor he had in his shop. Some of the other highlights in the build include a custom 3D-printed latching mechanism for the battery’s attachment point at the frame, a 3D printed bezel for the new display and control unit, and the reuse of some of the other fun parts of the bike like the front basket and integrated headlight.

There are a few reasons for putting so much work into a bike like this. For this specific bike at least, the underlying components are worth saving; the sturdy metal frame and belt drivetrain are robust and won’t need much maintenance in the long term. It also only cost around $500 in parts to build a bike that would take around $2,000 to purchase new, so there’s some economic incentive as well. And in general it’s more fun and better for the world to fix things like this up and get them running again rather than buying something new off the shelf. And while proprietary electronics like those found on this bike are ubiquitous in the ebike world, they’re not all completely closed-source.

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The synth in question in its acrylic case.

DIY Polyphonic Synth Sings In 8-Part Harmony

November 22, 2025 by 5 Comments

There’s just something about an analog synthesizer. You’d think that for electronic music, digital sampling would have totally taken over by now, but that’s really not true. The world of analog synths is alive and well, and [Polykit] has a new, open-source polyphonic synthesizer to add to the ever-growing chorus of electronic instruments.

The analog part is thanks to the eight identical voice cards that plug into the machine’s mainboard: each one has a voltage controlled oscillator to generate tones, an envelope generator, multiple voltage-controlled amplifiers, and even a pole mixing filter which is also, yes, voltage controlled. Each voice card outputs stereo, and yes, there are controllable mixing circuits for left and right output.

All that voltage control means a lot of lines from digital-to-analog converters (DACs), because while this is an analog synth, it does have a MIDI interface, and that means that a microcontroller needs to be able to speak voltage. In this case, the brains are an ATmega2560. Instead of stacking the board with enough expensive DACs to interpret the MCU’s digital signals, [Polykit] is instead is using some clever tricks to get more work out of the one DAC he has. Some things get tied together on all eight voices, like the envelope parameters; other values are run through a demultiplexer to make the most possible use of the analog lines available. Of course that necessitates some latching circuitry to hold the demuxed values on those lines, but it’s still cheaper than multiple high-quality DACs.

It’s a well-thought out bit of kit, down to the control panel and acrylic case, and the writeup is worth reading to get the full picture. The voice cards, main board and control board all have their own GitHub repositories you can find at the bottom of the main page. If you’re into video, [Polykit] has a whole series on this project you might want to check out on Makertube; we’ve embedded the first one below.

If you want to get your toes wet in the wonderful world of synthesizers, this library of seventy synths is an amazing place to start, because it has great simple projects.

Thanks to [Polykit] for the tip!

Continue reading “DIY Polyphonic Synth Sings In 8-Part Harmony” →

Assistive Radio Tells You What You Can’t See

November 22, 2025 by 2 Comments

We think of radios as audio devices, but for people who are visually impaired, it can be difficult to tell which channel you are listening to at any given time. [Sncarter] has a family member with vision impairment and built a radio to help her. Unfortunately, it was difficult to replicate, so he decided to try again. The result is an FM radio that provides audible status notifications about power and frequency. Check it out in the video below.

This isn’t just some hacked-up commercial radio, but a ground-up design that uses a TEA5767 with an ATMega328 for control. There is an LCD for when someone else might use the radio and an audio amplifier. He built the prototype on a breadboard, but moved the finished product to a PCB.

It isn’t just the electronics and the sound that are assistive. The case has raised bosses to help the user find things like the switch and rotary encoder. The Arduino can speak frequency announcements, although the quality of the voice is something he wants to tackle in the next revision.

These radios on a chip give you many design options. These same ideas can be useful for audiobook players, too.

DIY TENS Machine Is A Pain-Relief PCB

November 22, 2025 by 19 Comments

Transcutaneous Electrical Nerve Stimulation (TENS) is one of those things that sounds like it must be woo when you first hear of it. “A trickle of current that can deal with chronic pain better than the pills we’ve been using for decades? Yeah, and what chakras do you hook this doo-hickie up to?” It seems too good to be true, but in fact it’s a well-supported therapy that has become part of scientific medicine. There are no crystals needed, and you’re applying electrodes to the effected area, not your chakras. Like all medical devices, it can be expensive if you have to buy the machine out-of-pocket… but it is just a trickle of current. [Leon Hillmann] shows us its well within the range of hackability, so why not DIY?

[Leon]’s TENS machine is specifically designed to help a relative with hand problems, so breaks out electrodes for each finger, with one on the palm serving as a common ground. This type of TENS is “monophasic”– that is, DC, which is easier than balancing current flowing in two directions through quivering flesh. The direct current is provided at 32 V to the digit electrodes, safely kept to a constant amperage with a transistor-based current limiting circuit. The common ground in the palm is pulsed at a rate set by an ATmega32U4 and thus controllable: 14 Hz is given as an example.

Obviously if you want to reproduce this work you’re doing it at your own risk and need to consult with relevant medical professionals (blah blah blah, caveat gluteus maximus) but this particular sort of medical device is a good fit for the average hacker. Aside from prosthetics, we haven’t seen that much serious medical hacking since the pandemic. Still, like with synthesizing medical drugs, this is the kind of thing you probably don’t want to vibe code.

A circular metal vessel is shown, with a symmetrical rotor of four vanes standing inside. At the bottom of the vessel are four loudspeakers.

Building An Acoustic Radiometer

November 22, 2025 by 5 Comments

A Crookes radiometer, despite what many explanations claim, does not work because of radiation pressure. When light strikes the vanes inside the near-vacuum chamber, it heats the vanes, which then impart some extra energy to gas molecules bouncing off of them, causing the vanes to be pushed in the opposite direction. On the other hand, however, it is possible to build a radiometer that spins because of radiation pressure differences, but it’s easier to use acoustic radiation than light.

[Ben Krasnow] built two sets of vanes out of laser-cut aluminium with sound-absorbing foam attached to one side, and mounted the vanes around a jewel bearing taken from an analog voltmeter. He positioned the rotor above four speakers in an acoustically well-sealed chamber, then played 130-decibel white noise on the speakers. The aluminium side of the vanes, which reflected more sound, experienced more pressure than the foam side, causing them to spin. [Ben] tested both sets of vanes, which had the foam mounted on opposite sides, and they spun in opposite directions, which suggests that the pressure difference really was causing them to spin, and not some acoustic streaming effect.

The process of creating such loud sounds burned out a number of speakers, so to prevent this, [Ben] monitored the temperature of a speaker coil at varying amounts of power. He realized that the resistance of the coil increased as it heated up, so by measuring its resistance, he could calculate the coil’s temperature and keep it from getting too hot. [Ben] also tested the radiometer’s performance when the chamber contained other gasses, including hydrogen, helium, carbon dioxide, and sulfur hexafluoride, but none worked as well as air did. It’s a bit counterintuitive that none of these widely-varying gasses worked better than air did, but it makes sense when one considers that speakers are designed to efficiently transfer energy to air.

It’s far from an efficient way to convert electrical power into motion, but we’ve also seen several engines powered by acoustic resonance. If you’d like to hear more about the original Crookes radiometers, [Ben]’s also explained those before.

RavynOS: Open Source MacOS With Same BSD Pedigree

November 22, 2025 by 21 Comments

That MacOS (formerly OS X) has BSD roots is a well-known fact, with its predecessor NeXTSTEP and its XNU kernel derived from 4.3BSD. Subsequent releases of OS X/MacOS then proceeded to happily copy more bits from 4.4BSD, FreeBSD and other BSDs.

In that respect the thing that makes MacOS unique compared to other BSDs is its user interface, which is what the open source ravynOS seeks to address. By taking FreeBSD as its core, and crafting a MacOS-like UI on top, it intends to provide the MacOS UI experience without locking the user into the Apple ecosystem.

Although FreeBSD already has the ability to use the same desktop environments as Linux, there are quite a few people who prefer the Apple UX. As noted in the project FAQ, one of the goals is also to become compatible with MacOS applications, while retaining support for FreeBSD applications and Linux via the FreeBSD binary compatibility layer.

If this sounds good to you, then it should be noted that ravynOS is still in pre-release, with the recently released ravynOS “Hyperpop Hyena” 0.6.1 available for download and your perusal. System requirements include UEFI boot, 4+ GB of RAM, x86_x64 CPU and either Intel or AMD graphics. Hardware driver support for the most part is that of current FreeBSD 14.x, which is generally pretty decent on x86 platforms, but your mileage may vary. For testing systems and VMs have a look at the supported device list, and developers are welcome to check out the GitHub page for the source.

Considering our own recent coverage of using FreeBSD as a desktop system, ravynOS provides an interesting counterpoint to simply copying over the desktop experience of Linux, and instead cozying up to its cousin MacOS. If this also means being able to run all MacOS games and applications, it could really propel FreeBSD into the desktop space from an unexpected corner.