Author: Dan Maloney

3297 Articles

Satisfy Your High-Voltage Urges With This Printable Flyback Transformer

April 13, 2025 by 10 Comments

Sick of raiding old TVs and CRT monitors for flyback transformers to feed your high-voltage addiction? Never fear; if you’re careful, a 3D-printed flyback might be just the thing you’re looking for.

To be fair, it’s pretty easy to come by new flyback transformers, so building your own isn’t strictly necessary. But [SciTubeHD] was in the market for a particularly large flyback, in a good-natured effort to displace [Jay Bowles] from his lofty perch atop the flyback heap. And it’s also true that this project isn’t entirely 3D-printed, as the split core of the transformer was sourced commercially. The secondary coil, though, was where most of the effort went, with a secondary form made from multiple snap-together discs epoxied together for good measure. The secondary has about a kilometer of 30-gauge magnet wire while the primary holds just ten turns of 8-gauge wire covered with silicone high-voltage insulation.

To decrease the likelihood of arcing, the transformer was placed in a plastic container filled with enough mineral oil liquid dielectric to cover the secondary. After degassing in a vacuum chamber for a day, [SciTubeHD] hooked the primary to a couple of different but equally formidable-looking full-bridge inverters for testing. The coil was capable of some pretty spicy arcs — [SciTubeHD] measured 20 amps draw at 35 volts AC input, so this thing isn’t to be trifled with. STL files for the core parts are coming up soon; we trust schematics for the power supply will be available, too.

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Brush Up On Your Trade Craft With This Tiny FM Bug

April 11, 2025 by 19 Comments

Would-be spooks and spies, take note: this one-transistor FM transmitter is a circuit you might want to keep in mind for your bugging needs. True, field agents aren’t likely to need to build their own equipment, but how cool a spy would you be if you could?

Luckily, you won’t need too many parts to recreate [Ciprian (YO6DXE)]’s project, most of which could be found in a decently stocked junk bin, or even harvested from e-waste. On the downside, the circuit is pretty fussy, with even minor component value changes causing a major change in center frequency. [Ciprian] had to do a lot of fiddling to get the frequency in the FM band, particularly with the inductor in the LC tank circuit. Even dropping battery voltage shifted the frequency significantly, which required a zener diode to address.

[Ciprian] ran a few tests and managed to get solid copy out to 80 meters range, which is pretty impressive for such a limited circuit. The harmonics, which extend up into the ham bands and possibly beyond, are a bit of a problem; while those could be addressed with a low-pass filter, in practical terms, the power of this little fellow is probably low enough to keep you from getting into serious trouble. Still, it’s best not to push your luck.

While you’re trying your hand at one-transistor circuits, you might want to try [Ciprian]’s one-transistor CW transceiver next.

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Making Liquid Oxygen: Far From Easy But Worth The Effort

April 9, 2025 by 26 Comments

Normally, videos over at The Signal Path channel on YouTube have a certain vibe, namely teardowns and deep dives into high-end test equipment for the microwave realm. And while we always love to see that kind of content, this hop into the world of cryogenics and liquid oxygen production shows that [Shahriar] has other interests, too.

Of course, to make liquid oxygen, one must first have oxygen. While it would be easy enough to get a tank of the stuff from a gas supplier, where’s the fun in that? So [Shahriar] started his quest with a cheap-ish off-the-shelf oxygen concentrator, one that uses the pressure-swing adsorption cycle we saw used to great effect with DIY O2 concentrators in the early days of the pandemic. Although analysis of the machine’s output revealed it wasn’t quite as capable as advertised, it still put out enough reasonably pure oxygen for the job at hand.

The next step in making liquid oxygen is cooling it, and for that job [Shahriar] turned to the cryocooler from a superconducting RF filter, a toy we’re keen to see more about in the future. For now, he was able to harvest the Stirling-cycle cryocooler and rig it up in a test stand with ample forced-air cooling for the heat rejection end and a manifold to supply a constant flow of oxygen from the concentrator. Strategically placed diodes were used to monitor the temperature at the cold end, a technique we can’t recall seeing before. Once powered up, the cryocooler got down to the 77 Kelvin range quite quickly, and within an hour, [Shahriar] had at least a hundred milliliters of lovely pale blue fluid that passed all the usual tests.

While we’ve seen a few attempts to make liquid nitrogen before, this might be the first time we’ve seen anyone make liquid oxygen. Hats off to [Shahriar] for the effort.

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Better Bearings Take The Wobble Out Of Premium Scroll Wheel

April 9, 2025 by 12 Comments

Sitting in front of a computer all day isn’t exactly what the firmware between our ears was tuned to do. We’re supposed to be hunting and gathering, not hunting and pecking. So anything that makes the computing experience a little more pleasurable is probably worth the effort, and this premium wireless scroll wheel certainly seems to fit that bill.

If this input device seems familiar, that’s because we featured [Engineer Bo]’s first take on this back at the end of 2024. That version took a lot of work to get right, and while it delivered high-resolution scrolling with a premium look and feel, [Bo] just wasn’t quite satisfied with the results. There were also a few minor quibbles, such as making the power switch a little more user-friendly and optimizing battery life, but the main problem was the one that we admit would have driven us crazy, too: the wobbling scroll wheel.

[Bo]’s first approach to the wobble problem was to fit a larger diameter bearing under the scroll wheel. That worked, but at the expense of eliminating the satisfying fidget-spinner action of the original — not acceptable. Different bearings yielded the same result until [Bo] hit on the perfect solution: a large-diameter ceramic bearing that eliminated the wobble while delivering the tactile flywheel experience.

The larger bearing left more room inside for the redesigned PCB and a lower-profile, machined aluminum wheel. [Bo] also had a polycarbonate wheel made, which looks great as is but would really be cool with internal LEDs — at the cost of battery life, of course. He’s also got plans for a wheel machined from wood, which we’ll eagerly await.

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Dozens Of Solenoids Turn Vintage Typewriter Into A Printer

April 8, 2025 by 16 Comments

An electric typewriter is a rare and wonderful thrift store find, and even better if it still works. Unfortunately, there’s not as much use for these electromechanical beauties, so if you find one, why not follow [Konstantin Schauwecker]’s lead and turn it into a printer?

The portable typewriter [Konstantin] found, a Silver Reed 2200 CR, looks like a model from the early 1980s, just before PCs and word processing software would sound the death knell for typewriters. This machine has short-throw mechanical keys, meaning that a physical press of each key would be needed rather than electrically shorting contacts. Cue the order for 50 low-voltage solenoids, which are arranged in rows using 3D printed holders and aluminum brackets, which serve as heat sinks to keep the coils cool. The solenoids are organized into a matrix with MOSFET drivers for the rows and columns, with snubber diodes to prevent voltage spikes across the coils, of course. A Raspberry Pi takes care of translating an input PDF file into text and sending the right combination of GPIO signals to press each key.

The action of the space bar is a little unreliable, so page formatting can be a bit off, but other than that, the results are pretty good. [Konstantin] even managed to hook the printer up to his typewriter keyboard, which is pretty cool, too.

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Simple Antenna Makes For Better ESP32-C3 WiFi

April 7, 2025 by 42 Comments

We’ve seen tons of projects lately using the ESP32-C3, and for good reason. The microcontroller has a lot to offer, and the current crop of tiny dev boards sporting it make adding a lot of compute power to even the smallest projects dead easy. Not so nice, though, is the poor WiFi performance of some of these boards, which [Peter Neufeld] addresses with this quick and easy antenna.

There are currently a lot of variations of the ESP32-C3 out there, sometimes available for a buck a piece from the usual suspects. Designs vary, but a lot of them seem to sport a CA-C03 ceramic chip antenna at one end of the board to save space. Unfortunately, the lack of free space around the antenna makes for poor RF performance. [Peter]’s solution is a simple antenna made from a 31-mm length of silver wire. One end of the wire is formed into a loop by wrapping it around a 5-mm drill bit and bending it perpendicular to the remaining tail. The loop is then opened up a bit so it can bridge the length of the ceramic chip antenna and then soldered across it. That’s all it takes to vastly improve performance as measured by [Peter]’s custom RSSI logger — anywhere from 6 to 10 dBm better. You don’t even need to remove the OEM antenna.

The video below, by [Circuit Helper], picks up on [Peter]’s work and puts several antenna variants to further testing. He gets similarly dramatic results, with 20 dBm improvement in some cases. He does note that the size of the antenna can be a detriment to a project that needs a really compact MCU and tries coiling up the antenna, with limited success. He also did a little testing to come up with an optimal length of 34 mm for the main element of the antenna.

There seems to be a lot of room for experimentation here. We wonder how mounting the antenna with the loop perpendicular to the board and the main element sticking out lengthwise would work. We’d love to hear about your experiments, so make sure to ping us with your findings.

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Buyer Beware: Cheap Power Strips Hold Hidden Horrors

April 7, 2025 by 84 Comments

We’ve got a love-hate relationship with discount tool outlet Harbor Freight: we hate that we love it so much. Apparently, [James Clough] is of much the same opinion, at least now that he’s looked into the quality of their outlet strips and found it somewhat wanting.

The outlet strips in question are Harbor Freight’s four-foot-long, twelve-outlet strips, three of which are visible from where this is being written. [James] has a bunch of them too, but when he noticed an intermittent ground connection while using an outlet tester, he channeled his inner [Big Clive] and tore one of the $20 strips to bits. The problem appears to be poor quality of the contacts within each outlet, which don’t have enough spring pre-load to maintain connection with the ground pin on the plug when it’s wiggled around. Actually, the contacts for the hot and neutral don’t look all that trustworthy either, and the wiring between the outlets is pretty sketchy too. The video below shows the horrors within.

What’s to be done about this state of affairs? That’s up to you, of course. We performed the same test on all our outlets and the ground connections all seemed solid. So maybe [James] just got a bad batch, but he’s still in the market for better-quality strips. That’s going to cost him, though, since similar strips with better outlets are about four times the price of the Harbor Freight units. We did find a similar strip at Home Depot for about twice the price of the HF units, but we can’t vouch for the quality. As always, caveat emptor.

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