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121 Articles

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.

Measuring Local Variances In Earth’s Magnetic Field

February 17, 2025 by 11 Comments

Although the Earth’s magnetic field is reliable enough for navigation and is also essential for blocking harmful solar emissions and for improving radio communications, it’s not a uniform strength everywhere on the planet. Much like how inconsistencies in the density of the materials of the planet can impact the local gravitational force ever so slightly, so to can slight changes impact the strength of the magnetic field from place to place. And it doesn’t take too much to measure this impact on your own, as [efeyenice983] demonstrates here.

To measure this local field strength, the first item needed is a working compass. With the compass aligned to north, a magnet is placed with its poles aligned at a right angle to the compass. The deflection angle of the needle is noted for varying distances of the magnet, and with some quick math the local field strength of the Earth’s magnetic field can be calculated based on the strength of the magnet and the amount of change of the compass needle when under its influence.

Using this method, [efeyenice983] found that the Earth’s magnetic field strength at their location was about 0.49 Gauss, which is well within 0.25 to 0.65 Gauss that is typically found on the planet’s surface. Not only does the magnetic field strength vary with location, it’s been generally decreasing in strength on average over the past century or so as well, and the poles themselves aren’t stationary either. Check out this article which shows just how much the poles have shifted over the last few decades.

You Can 3D Print Yourself Some Simple Magnetic Switches

August 22, 2024 by 9 Comments

Permanent magnets aren’t typically switchable. They’re always doing their magnet thing. However, if you align them with a bunch of other magnets in just the right way, you can create a permanent magnet that you can effectively switch on and off. [Andrew Klein] has done just that with his 3D-printed magnetic switch design.

The concept is simple enough. The design consists of a 3D-printed housing in two parts, top and bottom. When set into one orientation, the housing holds two arrays of magnets in opposite orientations. This effectively cancels out their magnetic fields and allows you to move the assembly around as if it’s pretty much not magnetic at all. However, rotate the device to its alternative orientation, and the magnets poles are aligned. This effectively combines their magnetic fields and makes the assembly act as one big large magnet.

These devices are useful if you want to create magnetic clamps or fixtures that can be attached and detached at will from ferrous surfaces. Being able to effectively “switch the magnet off” is much easier than trying to wrench a powerful magnet from a metal plate, after all.

You can do something similar with electromagnetic techniques, too! Video after the break.

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Print Your Own Magnetic Connector

July 27, 2024 by 22 Comments

If you have a late-model laptop, you’ve probably seen how the chargers magnetically snap into place. In theory, this should be easy to recreate for your own purposes. But why reinvent the wheel when [DarthKaker] has already done the work for you — assuming you only need two conductors.

The 3D-printed shells take the usual round magnets. Obviously, the north pole on one part should point to the south pole on the other part. In addition, if polarity matters, you should also have each housing contain one north-facing and one south-facing magnet so that the connectors will only mate one way.

It appears the project uses wires soldered or spot welded to the magnets. Heating magnets sometimes has bad effects, so we might try something different. For example, you could solder the wires to thin washers affixed to the magnets with epoxy, perhaps. Or use the magnets for alignment and make a different arrangement for the contacts, although that would take a different shell design.

We have talked about magnet soldering for connectors before. Don’t forget that you can build magnets into your prints, too.

Electromagnetic Actuator Mimics Muscle

July 26, 2024 by 11 Comments

Most electromagnetic actuators are rotating motors, or some variation on the theme, like servos. However, it’s possible to do linear actuation with electomagnetics, too. [Adrian Perez] demonstrates this with Linette, his design of a linear actuator that he was inspired to build by the structure of our own muscles.

The design uses a coil of copper wire in a 3D-printed plastic housing, surrounded by a claw full of strong magnets. When the coil is activated, the magnets are pulled towards the coil. When the coil is not energized, the magnets fall away. [Adrian] demonstrates the actuator under the control of an Arduino, which switches power to the coil to move it up and down.

He also notes that the design is similar solenoids and voice coil style actuators, though unlike most his uses discrete magnets rather than a single monolithic magnet. It’s possible to get more capacity out of the Linette design through stacking. You can parallelize the actuators to get more pulling force, with neighboring coils sharing the same magnets. Alternatively, you can stack them in series to get longer stroke lengths.

[Adrian] hasn’t put the design to a practical application yet, but we could see multiple uses for robotics or small machines. We’ve seen some other neat DIY magnetic actuators before, too. Video after the break.

Swapping Vinyl For Cardboard With This ESP32 Turntable

June 30, 2024 by 15 Comments

Cardboard is a surprisingly durable material, especially in its corrugated form. It’s extremely lightweight for its strength, is easy to work, can be folded and formed into almost any shape, is incredibly inexpensive, and when it has done its duty it can be recycled back into more paper. For these reasons, it’s often used in packaging material but it can be used to build all kinds of things outside of ensuring that products arrive at their locations safely. This working cardboard record player is one example.

While the turntable doesn’t have working records in the sense that the music is etched into them like vinyl, each has its own RFID chip embedded that allows the ESP32 in the turntable’s body to identify them. Each record corresponds to a song stored on an SD card that instructs the ESP32 to play the appropriate song. It also takes care of spinning the record itself with a small stepper motor. There are a few other details on this build that tie it together too, including a movable needle arm held on with a magnet and a volume slider.

As far as a building material goes, cardboard is fairly underrated in our opinion. Besides small projects like this turntable, we’ve also seen it work as the foundation for a computer, and it even has the strength and durability to be built into a wall or even used as shelving material. And, of course, it’s a great material to use when prototyping new designs.

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Spinning Magnets Do Your Dice Rolling For You

June 28, 2024 by 6 Comments

Dice are about the simplest machines possible, and they’ve been used since before recorded history to generate random numbers. But no machine is so simple that a little needless complexity can’t make it better, as is the case with this mechanical spinning dice. Or die. Whatever.

Inspiration for the project came from [Attoparsec]’s long history with RPG and tabletop games, which depend on different kinds of dice to generate the randomness that keeps them going — that and the fortuitous find of a seven-segment flip-dot display, plus the need for something cool to show off at OpenSauce. The flip-dot is controlled by an array of neodymium magnets with the proper polarity to flip the segments to the desired number. The magnets are attached to an aluminum disk, with each array spread out far enough to prevent interference. [Attoparsec] also added a ring of magnets to act as detents that lock the disk into a specific digit after a spin.

The finished product ended up being satisfyingly clicky and suitably random, and made a good impression at OpenSauce. The video below documents the whole design and build process, and includes some design dead-ends that [Attoparsec] went down in pursuit of a multiple-digit display. We’d love to see him revisit some of these ideas, mechanically difficult though they may be. And while he’s at it, maybe he could spice up the rolls with a little radioactivity.

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