Day: August 31, 2026

What’s Mu Metal?

August 31, 2026 by 28 Comments

If you tear into old TVs or recording equipment, you may see shields made from some exotic-looking metal. Old timers will tell you it’s called mu metal, and its purpose is to — sort of — shield things from magnetic fields. The qualification is important. Unlike a conductive RF shield, mu metal doesn’t really stop a magnetic field. Instead, it gives magnetic flux an easier path to follow around whatever you’re trying to protect.

What’s In The Metal?

Mu metal belongs to a family of soft magnetic nickel-iron alloys. A typical modern formulation is about 80% nickel and 15% iron, with molybdenum and a few other elements making up most of the remainder. What makes it useful is its extremely high magnetic permeability. Commercial material can have relative permeability around 100,000 or more, and some specialty alloys can reach even higher.

You can think about reluctance as the magnetic equivalent of resistance. Put a high-permeability shell around something sensitive, and magnetic flux would much rather travel through the shell than through the space inside it, just like current tends to take the path of least resistance.

This works particularly well for DC and low-frequency fields, exactly where your usual copper or aluminum EMI shield isn’t much help.

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Digital “Film” For Your Pi Camera

August 31, 2026 by 2 Comments

The formula of a Raspberry Pi camera is such that it’s almost a self-assembly kit of parts. Over the years we’ve seen a lot of attempts to make one that’s more impressive, usually due to a different take on a case design. It’s not often we see something genuinely out of the ordinary, and perhaps [Strange Inventions] has made one. He’s produced an instant camera where the “film” is a removable cartridge containing a color e-paper display.

It’s a straightforward enough idea: the camera writes the image to the display, and since these displays are persistent, there it stays. The displays connect via headers, and the cartridge slips in in a similar manner to a console game cartridge. They’re not cheap, but at least unlike a Polaroid or Instax cartridge, they are reusable.

You’ll have to pay up if you want to download the files, but it’s not outrageously expensive if you really want to build one. But perhaps the key here is that it’s not something beyond the abilities of the average Hackaday reader to make their own. We’re sure this idea will be expanded upon by others in due course.

Meanwhile, if it’s simpler instant photography you crave, you can always print the real thing.

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A Flip Disc Display That Does It Slow And Steady

August 31, 2026 by 9 Comments

Flip disc displays can be quite a task to drive, what with having some sort of actuator mechanism for each and every dot in the display. [Zimm] has built an altogether different kind of flip disc display, though, which gets around this with a complexity all its own.

The idea behind the build is simple. There is still an array of discs, in this case, 37 x 18 square discs that are black on one side and blue on the other. However, they’re not actuated by magnets or any kind of per-disc flipper. Instead, a CNC machine is charged with flipping them one at a time. There’s a tool head that scans through the array, and uses a color sensor and LIDAR to identify which pixels to flip and how far to push them. It’s not fast, by any means, but it’s a perfectly cromulent way to build a flip disc display, as it turns out.

If you so desire, you can draw or upload images to be displayed on PAR yourself, right from your browser. The project reminds us quite a lot of various plotters we’ve covered over the years, perhaps more than a traditional flip disc display, even.

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