Practical Sensors: The Hall Effect

Measuring a magnetic field can be very easy with some pretty low tech, or it can be very high tech. It just depends on what kind of measurement you need and how much effort you want to expend. The very simplest magnetic sensors are reed switches. These are basically relays with no coil. Instead of a coil, an external magnet gets close enough to make or break the contacts in the reed. You see these a lot in, for example, door alarm sensors.

Then again, there’s no real finesse to a reed. It changes state when it sees enough of a magnetic field and that’s about all. You could use a compass with some sort of detection on the needle to get some more information about the field, but not much more. That was, however, how early magnetometers worked. Today, you have lots of options, including the nearly ubiquitous Hall effect sensor.

You might use a Hall effect to measure the magnetic button on a keyboard key coming down when you press it or the open and closed state of a valve. A lot of Hall effects see service as current monitors. Since a coil generates a magnetic field proportional to the current through it, a magnetic sensor can estimate the current in a coil of wire without any physical contact. Hall effects can also watch a magnet go by in a linear motion system or a rotating system to get an idea of position or speed. For example, check out this brushless motor controller that uses three sensors to understand the motor’s position.

History

Edwin Hall identified the effect in 1879. The basic idea is simple: an electrical conductor carrying current will exhibit changes due to an external magnetic field nearby. These changes show up as voltage you measure across the conductor. Normally, the voltage across a conductor will be nearly zero, but with a magnetic field, you’ll get a non-zero reading in proportion to the magnetic field strength in a particular plane, as we’ll see shortly.

Hall effect sensors are just one type of modern magnetometer. There are many different kinds including those that use inductive pickup coils that may or may not rotate or a fluxgate, which is a special type of coil. Some use a scale or a spring to measure force against another magnet — sometimes microscopically. You can even detect a magnetic field using optical properties like the Kerr effect or Faraday rotation.

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River Cleanup Aims To Expand In Earnest To Tackle Plastic Pollution

The Great Pacific Garbage Patch is just one of a number of pollution disasters affecting the world’s oceans. All over the globe, huge amounts of plastic enter waterways every day, causing havoc in delicate ecosystems.

Heading up the charge to deal with the problem, The Ocean Cleanup have been working on a variety of projects to help clean up plastic pollution. Chief among these is their river cleanup efforts, aiming to stop plastic pollution from reaching the ocean in the first place. The non-profit group intends to rapidly scale up its efforts, partnering with Finnish industrial manufacturer Konecranes in order to put its latest river cleaning design into series production.

We last reported on the group’s efforts in 2020, with their Interceptor craft operating in rivers in Malaysia, Indonesia, and the Dominican Republic. They’ve since refined the design for better functionality and easier deployment. Let’s jump in and see what they’ve learned and how their hunt for plastic pollution is shaping up.

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Do You Really Own It? Motorcycle Airbag Requires Additional Purchase To Inflate

If you ride a motorcycle, you may have noticed that the cost of airbag vests has dropped. In one case, something very different is going on here. As reported by Motherboard, you can pick up a KLIM Ai-1 for $400 but the airbag built into it will not function until unlocked with an additional purchase, and a big one at that. So do you really own the vest for $400?

Given the nature of the electronics and computer business lately, we spend a good bit of time thinking of what it means to own a piece of technology. Do you own your cable modem or cell phone if you aren’t allowed to open it up? Do you own a piece of software that wants to call home periodically and won’t let you stop it?  Sometimes it makes sense that you are paying for a service. But there have been times where, for example, a speaker company essentially bricks devices that could work fine on their own even though you — in theory — own the device.

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2021 Hackaday Prize Hack Chat; Join Us Live On Wednesday

Join us on Wednesday, May 19 at noon Pacific for the 2021 Hackaday Prize Hack Chat with Majenta Strongheart!

At this point last year, we probably all felt like we’d been put through a wringer, and that things would get back to normal any day now. Little did we know how much more was in store for us, and how many more challenges would be heaped on our plates. Everything that we thought would be temporary seems to be more or less permanent now, and we’ve all had to adapt to the new facts of life as best we can.

But we’re hackers, and adapting to new situations more often than not means making the world fit our vision. And that’s why the 2021 Hackaday Prize has adopted the theme of “Rethink, Refresh, Rebuild.” We want you to rethink and refresh familiar concepts across the hardware universe, and create the kind of innovation this community is famous for.

The 2021 Hackaday Prize will have it all. As in previous years, the Prize will have several specific challenges, where we set you to work on a creative problem. There will also be mentoring sessions available, $500 cash prizes for 50 finalists along the way, with $25,000 and a Supplyframe Design Lab residency awarded to the Grand Prize winner.

We know you’re going to want to step up to the challenge, so to help get you started, Majenta Strongheart, Head of Design and Partnerships at Supplyframe, will drop by the Hack Chat with all the details on the 2021 Hackaday Prize. Come prepared to pick her brain on how the Prize is going to work this year, find out about the mentoring opportunities, and learn everything there is to know about this year’s competition. It’s the Greatest Hardware Design Challenge on Earth, so make sure you get in on the action.

join-hack-chatOur Hack Chats are live community events in the Hackaday.io Hack Chat group messaging. This week we’ll be sitting down on Wednesday, May 19 at 12:00 PM Pacific time. If time zones have you tied up, we have a handy time zone converter.

Click that speech bubble to the right, and you’ll be taken directly to the Hack Chat group on Hackaday.io. You don’t have to wait until Wednesday; join whenever you want and you can see what the community is talking about.
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Telemetry Debate Rocks Audacity Community In Open Source Dustup

Starting an open source project is easy: write some code, pick a compatible license, and push it up to GitHub. Extra points awarded if you came up with a clever logo and remembered to actually document what the project is supposed to do. But maintaining a large open source project and keeping its community happy while continuing to evolve and stay on the cutting edge is another story entirely.

Just ask the maintainers of Audacity. The GPLv2 licensed multi-platform audio editor has been providing a powerful and easy to use set of tools for amateurs and professionals alike since 1999, and is used daily by…well, it’s hard to say. Millions, tens of millions? Nobody really knows how many people are using this particular tool and on what platforms, so it’s not hard to see why a pull request was recently proposed which would bake analytics into the software in an effort to start answering some of these core questions.

Now, the sort of folks who believe that software should be free as in speech tend to be a prickly bunch. They hold privacy in high regard, and any talk of monitoring their activity is always going to be met with strong resistance. Sure enough, the comments for this particular pull request went south quickly. The accusations started flying, and it didn’t take long before the F-word started getting bandied around: fork. If Audacity was going to start snooping on its users, they argued, then it was time to take the source and spin it off into a new project free of such monitoring.

The situation may sound dire, but truth be told, it’s a common enough occurrence in the world of free and open source software (FOSS) development. You’d be hard pressed to find any large FOSS project that hasn’t been threatened with a fork or two when a subset of its users didn’t like the direction they felt things were moving in, and arguably, that’s exactly how the system is supposed to work. Under normal circumstances, you could just chalk this one up to Raymond’s Bazaar at work.

But this time, things were a bit more complicated. Proposing such large and sweeping changes with no warning showed a troubling lack of transparency, and some of the decisions on how to implement this new telemetry system were downright concerning. Combined with the fact that the pull request was made just days after it was announced that Audacity was to be brought under new management, there was plenty of reason to sound the alarm.

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Hackaday Links: May 16, 2021

With the successful arrival of China’s first Mars lander and rover this week, and the relatively recent addition of NASA’s Perseverance rover and its little helicopter sidekick Ingenuity, Mars has collected a lot of new hardware lately. But while the new kids on the block are getting all the attention, spare a thought for the reliable old warhorse which has been plying Gale Crater for the better part of a decade now — Curiosity. NASA has been driving the compact-car-sized rover around Mars for a long time now, long enough to rack up some pretty severe damage to its six highly engineered wheels, thanks to the brutal Martian rocks. But if you think Curiosity will get sidelined as its wheels degrade, think again — the rover’s operators have a plan to continue surface operations that includes ripping off its own wheels if necessary. It’s a complex operation that would require positioning the wheel over a suitable rock and twisting with the steering motor to peel off the outer section of the wheel, leaving a rim to drive around on. JPL has already practiced it, but they predict it won’t be necessary until 2034 or so. Now that’s thinking ahead.

With all the upheaval caused by the ongoing and worsening semiconductor shortage, it might seem natural to expect that manufacturers are responding to market forces by building new fabs to ramp up production. And while there seems to be at least some movement in that direction, we stumbled across an article that seems to give the lie to the thought that we can build our way out of the crisis. It’s a sobering assessment, to say the least; the essence of the argument is that 20 years ago or so, foundries thought that everyone would switch to the new 300-mm wafers, leaving manufacturing based on 200-mm silicon wafers behind. But the opposite happened, and demand for chips coming from the older 200-mm wafers, including a lot of the chips used in cars and trucks, skyrocketed. So more fabs were built for the 200-mm wafers, leaving relatively fewer fabs capable of building the chips that the current generation of phones, IoT appliances, and 5G gear demand. Add to all that the fact that it takes a long time and a lot of money to build new fabs, and you’ve got the makings of a crisis that won’t be solved anytime soon.

From not enough components to too many: the Adafruit blog has a short item about XScomponent, an online marketplace for listing your excess inventory of electronic components for sale. If you perhaps ordered a reel of caps when you only needed a dozen, or if the project you thought was a done deal got canceled after all the parts were ordered, this might be just the thing for you. Most items offered appear to have a large minimum quantity requirement, so it’s probably not going to be a place to pick up a few odd parts to finish a build, but it’s still an interesting look at where the market is heading.

Speaking of learning from the marketplace, if you’re curious about what brands and models of hard drives hold up best in the long run, you could do worse than to look over real-world results from a known torturer of hard drives. Cloud storage concern Backblaze has published their analysis of the reliability of the over 175,000 drives they have installed in their data centers, and there’s a ton of data to pick through. The overall reliability of these drives, which are thrashing about almost endlessly, is pretty impressive: the annualized failure rate of the whole fleet is only 0.85%. They’ve also got an interesting comparison of HDDs and SSDs; Backblaze only uses solid-state disks for boot drives and for logging and such, so they don’t get quite the same level of thrash as drives containing customer data. But the annualized failure rate of boot SDDs is much lower than that of HDDs used in the same role. They slice and dice their data in a lot of fun and revealing ways, including by specific brand and model of drive, so check it out if you’re looking to buy soon.

And finally, you know that throbbing feeling you get in your head when you’re having one of those days? Well, it turns out that whether you can feel it or not, you’re having one of those days every day. Using a new technique called “3D Amplified Magnetic Resonance Imaging”, or 3D aMRI, researchers have made cool new videos that show the brain pulsating in time to the blood flowing through it. The motion is exaggerated by the imaging process, which is good because it sure looks like the brain swells enough with each pulse to crack your skull open, a feeling which every migraine sufferer can relate to. This reminds us a bit of those techniques that use special algorithms to detects a person’s heartbeat from a video by looking for the slight but periodic skin changes that occurs as blood rushes into the capillaries. It’s also interesting that when we spied this item, we were sitting with crossed legs, watching our upper leg bounce slightly in time with our pulse.

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Should I Automate This?

The short answer to the question posed in the headline: yes.

For the long answer, you have to do a little math. How much total time you will save by automating, over some reasonable horizon? It’s a simple product of how much time per occurrence, times how many times per day it happens, times the number of days in your horizon. Or skip out on the math because there’s an XKCD for that.

What’s fun about this table is that it’s kind of a Rorschach test that gives you insight into how much you suffer from automatitis. I always thought that Randall was trying to convince himself not to undertake (fun) automation projects, because that was my condition at the time. Looking at it from my current perspective, it’s a little bit shocking that something that’ll save you five seconds, five times a day, is worth spending twelve hours on. I’ve got some automating to do.

To whit: I use pass as my password manager because it’s ultimately flexible, simple, and failsafe. It stores passwords on my hard drive, and my backup server, encrypted with a GPG key that I have printed out on paper in a fireproof safe. Because I practice good cookie hygiene, I end up re-entering my passwords daily. Because I keep my passwords separate from my browser, that means entering username and password by cut-and-paste. There’s your five seconds, five times per day. Maybe two seconds, ten times, but it’s all the same. It shouldn’t take me even as long as twenty minutes to whip up a script that puts username and password into selection and clipboard for one-click pasting. Why haven’t I done this yet? I’m going to get on it as soon as I’m done with this newsletter.

But the this begs the question. If you spend up to twelve hours on every possible 25-second-per-day savings, when will you ever get your real work done? Again, math gives us the answer. One eight-hour workday * 25 seconds * 12 hours (pessimistically) of labor = 1.58 years before everything that needs automating will be. Next week’s newsletter might be a little bit delayed.

What do you see in the XKCD “Is it worth the time” table? Automate more, or step back from the cliff edge?