Retro Style VFO Has Single-Digit Parts Count

December 2, 2025 by Tyler August 9 Comments

Not every project has to be complicated– reinventing the wheel has its place, but sometimes you find a module or two that does exactly what you want, and the project is more than halfway done. That the kind of project [mircemk]’s Simple Retro Style VFO is — it’s a variable frequency oscillator for HAM and other use, built with just a couple of modules.

Strictly speaking, this is all you need for the project.

The modules in question are the SI5351 Clock Generator module, which is a handy bit of kit with its own crystal reference and PLL to generate frequencies up to 150 MHz, and the Elecrow CrowPanel 1.28inch-HMI ESP32 Rotary Display. The ESP32 in the CrowPanel controls the SI5351 module via I2C; control is via the rest of the CrowPanel module. This Rotary Display is a circular touchscreen surrounded by a rotary display, so [mircmk] has all the inputs he needs to control the VFO.

To round out the parts count, he adds an appropriate connector, plus a power switch, red LED and a lithium battery. One could include a battery charger module as well, but [mircmk] didn’t have one on hand. Even if he had, that still keeps the parts count well inside the single digits. If you like video, we’ve embedded his about the project below; if not the write up on Hackaday.io is upto [mircmk]’s typical standard.

People have been using the SI5351 to make VFOs for years now, but the addition of the round display makes for a delightfully retro presentation.

Thanks to [mircmk] for the tip.

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There’s Nothing Backwards About This Laser Cut Retrograde Clock

November 26, 2025 by Tyler August 7 Comments

It’s clock time again on Hackaday, this time with a lovely laser-cut biretrograde clock by [PaulH175] over on Instructables. If you’ve never heard of a ‘biretrograde clock,’ well, we hadn’t either. This is clearly a form of retrograde clock, which unlike the name implies doesn’t spin backwards but oscillates in its motion– the hands ‘go retrograde’ the same way the planets do.

The oscillating movement is achieved via a pair of cams mounted on the hour and minute shafts of a common clock mechanism. As the shafts (and thus cams) turn, the minute and hour arms are raised and drop. While that could itself be enough to tell the time, [Paul] goes one further and has the actual hands on pivots driven by a gear mechanism on the cam-controlled arms. You might think that that extra reversal is what makes this a ‘biretrograde clock’ but in the clockmaker’s world that’s just saying it’s a retrograde clock with two indicators: in this case, minute and hour.

It’s a fairly rare way to make a clock, but we’ve seen one before. That older project was 3D printed, which might be more your speed; if you prefer laser-cutting, though, [Paul]’s Instructable includes SVG files. Alternatively, you could take a different approach and use voltmeters to get the same effect.

The Zen Must Flow From Arrakis Sand Table

November 25, 2025 by Tyler August 22 Comments

In Dune, the Fremen people of Arrakis practice an odd future hybrid religion called “zensunni.” This adds an extra layer of meaning to the title of [Mark Rehorst]’s Arrakis 3.0 sand table, given that the inspiration for the robotic sand table seems to be Zen gardens from Japan.

The dunes on the tabletop version of Arrakis owe nothing to sand worms, but are instead created a rolling metal ball. With all workings happening below, it looks quite magical to the uninitiated, but of course it’s not magic: it’s magnets. Just beneath the tabletop and its sands, the steel ball is being dragged along by the magnetic field of a powerful neodynium magnet.

That magnet is mounted in a CoreXY motion system that owes more than a little bit to modern 3D printers. Aside from the geometry, it’s using the standard G6 belt we see so often, along with a Duet3D mainboard, NEMA 17 steppers, and many 3D printed parts to hold its aluminum extrusions together. Thanks to that printer-inspired motion system, the ball can whirl around at 2000 mm/s, though [Mark] prefers to run slower: the demo video below shows operation at 1000 mm/s before the sand has been added.

This build was designed for ease of construction and movement: sized at 2’x4′ (about 61 cm x 122 cm), it fits through doors and fits an off-the-shelf slab of coffee table glass, something that [Mark] wishes he’d considered when building version two. That’s the nice thing about jumping in on a project someone’s been iterating for a while: you’ve got the benefit of learning from their mistakes. You can see the roots of this design, and what has changed, from the one he showed us in 2020.

Naturally you’re not limited to CoreXY for a sand table, though it is increasingly popular — we’ve seen examples with polar mechanisms and even a SCARA arm.

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A PCB Can Be A Hydrofoil, If It Really Wants To

November 23, 2025 by Tyler August 10 Comments

You know those old cliche that the younger generations have begun to cynically despise: “follow your dreams!” “You can be anything you put your mind to!” — well, perhaps they are true on occasion. For instance when [rctestflight] had PCBs that dreamed of becoming a hydrofoil, he found a way to make that dream come true.

It’s kind of obvious in retrospect: printed circuit boards are made of FR4, which is a form of fiberglass, and you know what else is commonly made of fiberglass? Boats. So yes, the material is suited for this task. The fact that solder joints hold up to use in a little remote-control hydrofoil is less obvious, but good to know. It certainly makes for easier assembly for those of us who have developed an allergy to epoxy.

Ease of assembly wasn’t really the point here: the point was that by making the “mast” of the hydrofoil out of PCB– that’s the part that holds the underwater wing– [rctestflight] figured he could (shock!) print a circuit onto it. Specifically, a liquid-level sensor, and because microcontrollers are so cheap these days he went the “total overkill” route of embedding an ESP32 on each mast. He started with a resistive sensor, but since those self-corrode too quickly, the team switched to a capacitive sensor that doesn’t need to form a galvanic cell in salt water. Come to think of it, that might still be a problem with the solder joint between the PCBs. Good thing nobody will be riding this one.

Having such a sensor and brain close-coupled allows for a faster control loop than the sonar [rctestflight] had previously been using to control his hydrofoil’s altitude.. Pivoting each mast with its own servo made for a smooth flight over the water— well, once they got the PID tuning set, anyway. Check it out in the video embedded below.

We’ve seen PCB used for enclosures before, and even the chassis of a rover, but using it for a hydrofoil is a new hack. Continue reading “A PCB Can Be A Hydrofoil, If It Really Wants To” →

The synth in question in its acrylic case.

DIY Polyphonic Synth Sings In 8-Part Harmony

November 22, 2025 by Tyler August 9 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!

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DIY TENS Machine Is A Pain-Relief PCB

November 22, 2025 by Tyler August 37 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.

Wiring Up The Railway, All The Live-Long Day

November 21, 2025 by Tyler August 20 Comments

For those of you who haven’t spent time in North America around this time of year, you may be unaware of two things: one, the obligatory non-stop loop of “All I Want For Christmas Is You” retail workers are subjected to starting November first, and two: there is a strong cultural association between Christmastime and model railroading that may not exist elsewhere. That may down to childhood memories of when we got our first trainsets, or an excellent postwar marketing campaign by Lionel. Either way, now that Mariah Carey is blaring, we’re thinking about our holiday track layouts. Which makes this long presentation on Wiring for Small Layouts by [Chicago Crossing Model Railroad] quite timely.

There are actually three videos in this little course; the first focuses mostly on the tools and hardware used for DCC wiring (that’s Digital Command Control), which will be of less interest to our readers– most of you are well aware how to perform a lineman’s splice, crimp connectors onto a wire, and use terminal blocks.

The second two videos are actually about wiring, in the sense of routing all the wires needed for a modern layout– which is a lot more than “plug the rheostat into the tracks in one spot” that our first Lionel boxed set needed. No, for the different accessories there are multiple busses at 5V, 12V and 24V along with DCC that need to be considered. Unsurprisingly enough given those voltages, he starts with an ATX power supply and breaks out from there.

Even if you’re not into model railroading, you might learn something from these videos if you haven’t done many projects with multiple busses and wire runs before. It’s far, far too easy to end up with a rats nest of wires, be they DCC, I2C or otherwise. A little planning can save some big headaches down the line, and if this is a new skill for you [Chicago Crossing Model Railroad] provides a good starting point for that planning. Just skip ahead a couple minutes for him to actually start talking if you don’t want the musical cliff notes montage at the start of the videos.

If you don’t have any model trains, don’t worry, you can 3D print them. Lack of room isn’t really an excuse.

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