Feel The Force With A Pocket Magnetometer

January 24, 2020 by Kristina Panos 12 Comments

With the rise of affordable 3D printers, we just don’t see the projects in Tic Tac boxes that we used to. That’s kind of a shame. Not only are you upcycling existing plastic when you use one, they’re decently sized component vessels for pocket builds such as [rgco]’s portable magnetometer, especially if you can get the 100-count box. Best of all, they’re see-through!

Sure, you could get a magnetometer app for your phone to test out the strength of your Buckyballs, but this is more fun, and you can use it in more places. This build doesn’t take much — an Arduino Nano reads from a Hall effect sensor and outputs the magnetic flux density in militeslas (mT) on an OLED. Fortifying the sensor by mounting it inside the body of an old (also see-through!) ballpoint pen body is a nice touch.

In order to calibrate it, [rgco] made a solenoid by wrapping a length of PVC with magnet wire. The code for this very portable and low-cost magnetometer measures the magnetic field 2000 times in under three-tenths of a second, and outputs both the mean and the standard deviation of these measurements.

Magnetometers can ID all kinds of things from submarines to Suburbans. Here’s an ESP8266 magnetometer that opens a driveway gate when it detects the car.

Spintronic RAM Gets A Little Closer To SRAM

January 7, 2020 by Al Williams 16 Comments

Sometimes it seems as though everything old is new again. The earliest computers used magnetic memory such as magnetic core. As practical as that was compared to making for example each bit of memory be a vacuum tube or relay flip flop, newer technology such as SRAM and DRAM displaced core and similar technologies. However, some of the newest technologies once again use magnetic fields. FRAM or ferroelectric RAM and magnetoresistive or MRAM both use magnetic fields to store data. Now Japanese researchers think they are on track to make MRAM more competitive with traditional RAM chips.

The Tokyo Institute of Technology researchers use new material combinations to make chips that store data based on the spin of electrons — the underlying reason for the way magnets behave. Their recent paper discusses USMR or Unidirectional spin Hall magnetoresistance and using this effect could greatly simplify the construction of MRAM cells.

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Better Simulators With Homemade Potentiometers

May 24, 2019 by Bryan Cockfield 22 Comments

Perhaps you’ve played a flight simulator before, using something like a mouse and keyboard. That’s a fine experience, but like any other activity you can get a lot more out of it if you put a little more effort into the experience. Some will upgrade to a joystick for a modest improvement, and others will build incredible accurate cockpit replicas down to the smallest detail. The builders of these “pits” are always looking for ways of improving their setups, and it’s from this world that we find a method of building specialized, inexpensive hall-effect sensors.

A hall-effect sensor is a circuit that outputs a voltage based on the presence of an external magnetic field. These can be used to make compasses, but with a permanent magnet in close proximity can also be used to create a potentiometer-like device at lower cost and with higher precision than a similarly-priced pot. There was a method of building these in the simulator world using the housing of a Bic pen and some strong glue, but [LocNar] has improved on this method as well. He repurposed some bearings and some stock metal tubing in order to fabricate a professional-level sensor at a fraction of the cost.

This build is essentially a solution for anyone needing a potentiometer that’s easier to build, less expensive, has higher precision, and interacts with a digital input in a much more predictable (and programmable) way. Certainly this has applications in the simulator world, but will work for many other applications. If you’ve never thought about the intricacies (and shortcomings) of potentiometers, some other folks have taken a deep dive into that as well.

Thanks to [Keith O] for the tip!

Three-Conductor Pivot For E-Textiles Is Better Than Wires

February 13, 2019 by Donald Papp 1 Comment

Pivots for e-textiles can seem like a trivial problem. After all, wires and fabrics bend and flex just fine. However, things that are worn on a body can have trickier needs. Snap connectors are the usual way to get both an electrical connection and a pivot point, but they provide only a single conductor. When [KOBAKANT] had a need for a pivoting connection with three electrical conductors, they came up with a design that did exactly that by using a flexible circuit board integrated to a single button snap.

This interesting design is part of a solution to a specific requirement, which is to accurately measure hand movements. The photo shows two strips connected together, which pivot as one. The metal disk near the center is a magnet, and underneath it is a Hall effect sensor. When the wrist bends, the magnet is moved nearer or further from the sensor and the unit flexes and pivots smoothly in response. The brief videos embedded below make it clear how the whole thing works.

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Teardown Shows Why Innovative Designs Sometimes Fail

January 7, 2019 by Dan Maloney 28 Comments

Some ideas are real head-scratchers from a design standpoint: Why in the world would you do it that way? For many of us, answering that question often requires a teardown, which is what [Ben Katz] did when this PCB motor-powered weed whacker came across his bench. The results are instructive on what it takes to succeed in the marketplace, or in this case, how to fail.

The unit in question comes from an outfit called CORE Outdoor Power. The line trimmer was powered by a big lithium-ion battery pack, but [Ben] concentrated on the unique motor for his teardown. After a problematic entry into the very sturdy case at the far end of the trimmer’s shaft, he found what looks like a souped-up version of [Carl Bugeja]’s PCB brushless motors. The rotors, each with eight large magnets embedded, are sandwiched on either side of a very thick four-layer PCB with intricately etched heavy copper traces. The PCB forms the stator, with four flat coils. The designer pulled a neat trick with the Hall-effect sensors needed for feedback; rather than go with surface-mount sensors, which would add to the thickness of the board, they used through-hole packages soldered to surface pads, with the body of the sensor nestled in a hole in the board. The whole design is very innovative, but sadly, [Ben]’s analysis shows that it has poor performance for its size and weight.

Google around a bit and you’ll see that CORE was purchased some years back by MTD, a big player in the internal combustion engine outdoor power market. They don’t appear to be a going concern anymore, and it looks as though [Ben] has discovered why.

[Jozef] tipped us off to this one. Thanks!

OpenSCAD Handles The Math In 3D Printed Holder For Magnetic Spheres

August 28, 2018 by Donald Papp 35 Comments

3D printed holder mounted to bike wheel, fitting precisely 38 magnetic spheres around its perimeter. Tedious math? Not if you make OpenSCAD do it.

Off-the-shelf components are great; the world and our work simply wouldn’t be the same without. But one of the constraints is that one has to design around them, and that’s what led [Antonio Ospite] to create a parametric design in OpenSCAD for a 3D printed holder which snugly fits a number of magnetic spheres around its diameter.

If that sounds a bit esoteric, it will become much clearer in the context of [Antonio]’s earlier work in making a DIY rotary encoder out of a ring of magnetic spheres. He found that such a ring in front of two Hall effect sensors was low in cost, high in precision, and thanks to 3D printing it also had a lot of potential for customizing. But hampering easy design changes was the need for the spheres to fit snugly around whatever shape was chosen for the hardware, which meant constraints on the encoder diameter.

In this case, [Antonio] wished to create an encoder that could be attached to a bicycle wheel but needed to know what outer diameter would best fit a ring of magnetic balls perfectly, given that the balls were each 5 mm. OpenSCAD did the trick, yielding a design that fit the bike wheel and spokes while perfectly nestling 38 magnetic balls around the outside edge with a minimum of wasted space.

OpenSCAD is a CAD program that’s really more like a programming language than anything else. For those who are not familiar with it, [Brian Benchoff] walked through how to make a simple object in OpenSCAD, and [Elliot] has sung the praises of a few advanced functions. Now that this project makes DIY encoders easier, perhaps they could be used to add intuitive new controls to OpenSCAD itself.

Magnetic Spheres Line Up For Rotary Encoder Duty

June 5, 2018 by Dan Maloney 21 Comments

When it comes to rotary encoders, there are plenty of options. Most of them involve putting a credit card number into an online vendor’s website, though, and that’s sometimes just not in the cards. In that case building your own, like this encoder using magnetic spheres, is a pretty cool way to go too.

If he’d had less time to spare, we imagine [Antonio Ospite] would have gone for a commercial solution rather than building an encoder from scratch. Then again, he says his application had noise considerations, so maybe this was the best solution overall. He had some latching Hall effect sensors lying around, but lacked the ring magnet that is usually used with such sensors in magnetic encoders. But luckily, he had a mess of magnetic spheres, each 5 mm in diameter. Lined up in a circle around a knob made from a CD spindle, the spheres oriented themselves with alternating poles, which is just what the Hall sensors want to see. The sensors were arranged so the pulses are 90° apart, and can resolve 4.29° steps. Check out the video below to watch it work.

Small, cheap and effective are always good things. But magnets aren’t the only thing behind homebrew rotary encoders. A couple of microswitches might do in a pinch, or maybe even scrapped hard drives would suffice.

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