coil

97 Articles

A Number Of Microphones… Er, Inductors, Rather

June 18, 2025 by 5 Comments

There’s a famous old story about [Charles Steinmetz] fixing a generator for [Henry Ford]. He charged a lot of money for putting a chalk X in the spot that needed repair. When [Ford] asked for an itemization, the bill read $1 for the chalk, and the balance for knowing where to draw the X. With today’s PCB layout tools, it seems easy to put components down on a board. But, as [Kasyan TV] points out in the video below, you still have to know where to put them.

The subject components are inductors, which are particularly picky about placement, especially if you have multiple inductors. After all, inductors affect one another — that’s how transformers work. So there are definite rules about good and bad ways to put a few inductors on a board.

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Illustrated scheme of Sam Ben Yaakovs concept

Leakage Control For Coupled Coils

June 5, 2025 by 3 Comments

Think of a circuit model that lets you move magnetic leakage around like sliders on a synth, without changing the external behavior of your coupled inductors. [Sam Ben-Yaakov] walks you through just that in his video ‘Versatile Coupled Inductor Circuit Model and Examples of Its Use’.

The core idea is as follows. Coupled inductors can be modeled in dozens of ways, but this one adds a twist: a tunable parameter 𝑥 between k and 1 (where k is the coupling coefficient). This fourth degree of freedom doesn’t change L₁, L₂ or mutual inductance M (they remain invariant) but it lets you shuffle leakage where you want it, giving practical flexibility in designing or simulating transformers, converters, or filters with asymmetric behavior.

If you need leakage on one side only, set 𝑥=k. Prefer symmetrical split? Set 𝑥=1. It’s like parametric EQ, but magnetic. And: the maths holds up. As [Sam Ben-Yaakov] derives and confirms that for any 𝑥 in the range, external characteristics remain identical.

It’s especially useful when testing edge cases, or explaining inductive quirks that don’t behave quite like ideal transformers should. A good model to stash in your toolbox.

As we’ve seen previously, [Sam Ben-Yaakov] is at home when it comes to concepts that need tinkering, trial and error, and a dash of visuals to convey. Continue reading “Leakage Control For Coupled Coils” →

Ender 3 Pro Gets A Second Job As A Stator Winder

June 2, 2025 by 10 Comments

Sometimes, you find yourself in need of a coil. You could sit around winding thousands of turns of copper wire yourself, but that would be remarkably tedious. Thus, instead, you might follow the example of [OJengineering] and choose to get a machine to do it for you.

This build first popped up on on Reddit, with [OJengineering] explaining that they had repurposed an Ender 3 Pro 3D printer to wind a stator for them. The reasoning was sound—a replacement stator for their motorcycle cost $1000 in their local area, so rewinding their own would be much cheaper. The idea was straightforward enough—the 3D printer was a capable motion control platform that really just needed to be retooled to drag wire around instead of squirting hot plastic. In a later update, they explained that they had created a Python program that spits out appropriate stator winding G-code from user-entered parameters. This G-code commands the 3D printer’s head to make rectangle winds around the stator core while moving up and down to appropriately distribute the wire. The device can be seen in action in a video on YouTube.

It’s a hacky build, but one that does nevertheless get the winding done. That’s the thing about 3D printers—they’re really just simple motion systems that can do whatever you tell them. You just need a way to generate the right G-code to do the job.

We’ve featured some other nifty coil winders before, too. Video after the break.

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Internals of ding-dong doorbell.

Wireless Doorbell Extension Features Home-Wound Coil

May 16, 2025 by 12 Comments

Today in the it’s-surprising-that-it-works department we have a ding dong doorbell extension from [Ajoy Raman].

What [Ajoy] wanted to do was to extend the range of his existing doorbell so that he could hear it in his workshop. His plan of attack was to buy a new wireless doorbell and then interface its transmitter with his existing doorbell. But his approach is something others might not have considered if they had have been tasked with this job, and it’s surprising to learn that it works!

What he’s done is wrap a new coil around the ding dong doorbell’s solenoid. When the solenoid activates, a small voltage is induced into the coil. This then gets run into the wireless doorbell transmitter power supply (instead of its battery) via a rectifier diode and a filter capacitor. The wireless doorbell transmitter — having also had its push-button shorted out — operates for long enough from this induced electrical pulse to transmit the signal to the receiver. To be clear: the wireless transmitter is fully powered by the pulse from the coil around the solenoid. Brilliant! Nice hack!

We weren’t sure how reliable the transmitter would be when taken out of the lab and installed in the house so we checked in with [Ajoy] to find out. It’s in production now and operating well at a distance of around 50 feet!

Of course we’ve published heaps of doorbell hacks here on Hackaday before, such as this Bluetooth Low Energy (BLE) doorbell and this light-flashing doorbell. Have you hacked your own doorbell? Let us know on the tips line!

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Satisfy Your High-Voltage Urges With This Printable Flyback Transformer

April 13, 2025 by 11 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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A Unique Linear Position Sensor Using Magnetostriction

February 18, 2025 by 16 Comments

To the extent that you’re familiar with magnetostriction, you probably know that it’s what makes big transformers hum, or that it’s what tips you off if you happen to walk out of a store without paying for something. But magnetostriction has other uses, too, such as in this clever linear position sensor.

Magnetostriction is just the tendency for magnetic materials to change size or shape slightly while undergoing magnetization, thanks to the tiny magnetic domains shifting within the material while they’re aligning. [Florian B.]’s sensor uses a side effect of magnetostriction known as the Wiedenmann effect, which causes a wire to experience a twisting force if a current pulse is applied to it in a magnetic field. When the current pulse is turned off, a mechanical wave travels along the wire to a coil, creating a signal. The difference in time between sending the pulse and receiving the reflection can be used to calculate the position of the magnet along the wire.

To turn that principle into a practical linear sensor, [Florian B.] used nickel wire stretched tightly down the middle of a PVC tube. At one end is a coil of copper magnet wire, while the other end has a damper to prevent reflections. Around the tube is a ring-shaped cursor magnet, which can move up and down the tube. An exciter circuit applies the current pulse to the wire, and an oscilloscope is used to receive the signal from the wire.

This project still appears to be in the prototype phase, as evidenced by the Fischertechnik test rig. [Florian] has been working on the exciter circuit most recently, but he’s done quite a bit of work on optimizing the cursor magnet and the coil configuration, as well as designs for the signal amplifier. It’s a pretty neat project, and we’re looking forward to updates.

If you need a deeper dive into magnetostriction, [Ben Krasnow] points the way.

Cool Kinetic Sculpture Has Tooling Secrets To Share

January 29, 2025 by 8 Comments

Occasionally, we get a tip for a project that is so compelling that we just have to write it up despite lacking details on how and why it was built. Alternatively, there are other projects where the finished product is cool, but the tooling or methods used to get there are the real treat. “Homeokinesis,” a kinetic art installation by [Ricardo Weissenberg], ticks off both those boxes in a big way.

First, the project itself. Judging by the brief video clip in the reddit post below, Homeokinesis is a wall-mounted array of electromagnetically actuated cards. The cards are hinged so that solenoids behind them flip the card out a bit, making interesting patterns of shadow and light, along with a subtle and pleasing clicking sound. The mechanism appears to be largely custom-made, with ample use of 3D printed parts to make the frame and the armatures for each unit of the panel.

Now for the fun part. Rather than relying on commercial solenoids, [Ricardo] decided to roll his own, and built a really cool CNC machine to do it. The machine has a spindle that can hold at least eleven coil forms, which appear to be 3D printed. Blank coil forms have a pair of DuPont-style terminal pins pressed into them before mounting on the spindle, a job facilitated by another custom tool that we’d love more details on. Once the spindle is loaded up with forms, magnet wire feeds through a small mandrel mounted on a motorized carriage and wraps around one terminal pin by a combination of carriage and spindle movements. The spindle then neatly wraps the wire on the form before making the connection to the other terminal and moving on to the next form.

The coil winder is brilliant to watch in action — however briefly — in the video below. We’ve reached out to [Ricardo] for more information, which we’ll be sure to pass along. For now, there are a lot of great ideas here, both on the fabrication side and with the art piece itself, and we tip our hats to [Ricardo] for sharing this.

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