hall effect

46 Articles

Completely Scratch-Built Electronic Speed Controller

April 19, 2018 by 13 Comments

Driving a brushless motor requires a particular sequence. For the best result, you need to close the loop so your circuit can apply the right sequence at the right time. You can figure out the timing using a somewhat complex circuit and monitoring the electrical behavior of the motor coils. Or you can use sensors to detect the motor’s position. Many motors have the sensors built in and [Electronoobs] shows how to drive one of these motors in a recent video that you can watch below. If you want to know about using the motor’s coils as sensors, he did a video on that topic, earlier.

The motor in question was pulled from an optical drive and has three hall effect sensors onboard. Having these sensors simplifies the drive electronics considerably.

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High Speed Imaging Of Magnetic Fields

February 15, 2018 by 41 Comments

Some time before experimenting with MRI machines and building his own CT scanner, [Peter Jansen] wanted to visualize magnetic fields. One of his small side projects is building tricoders — pocket sensor suites that image everything — and after playing around with the magnetometer function on his Roddenberry-endorsed tool, he decided he had to have a way to visualize magnetic fields. After some work, he has the tools to do it at thousands of frames per second. It’s a video camera for magnetic fields, pushing the boundaries of both magnetic imaging technology and the definition of the word ‘camera’.

When we last looked at [Peter]’s Hall effect camera, the device worked, but it wasn’t necessarily complete. The original design used I2C I/O multiplexers for addressing each individual ‘pixel’ of the Hall effect array, limiting the ‘framerate’ of the ‘camera’ to somewhere around 30 Hz. While this would work for visualizing static magnetic fields, the more interesting magnetic fields around us are oscillating — think motors and transformers and such. A much faster magnetic camera was needed, and that’s what [Peter] set out to build.

Instead of an I/O expander, [Peter] re-engineered his design to use analog multiplexers and a binary counter to cycle through each pixel, one at a time. Basically, the new circuit uses two analog muxes for the columns and rows of the Hall effect array, a binary counter to cycle through each pixel at Megahertz speed, and a fast ADC to read each value. It is, bizarrely, the 1970s way of doing things; these are simple chips, and the controller (a Chipkit Max32) only needs to read a single analog value and clock the binary counter really fast.

With the new design, [Peter] is able to get extremely fast frame rates of about 2,000 Hz. That’s fast enough for some beautiful visualizations of spinning motors and transformers, seen in the video below. Further improvements may include three-axis magnetometers, which should allow for some spectacular visualizations similar to [Ted Yapo]’s 3D magnetic field scanner.

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Make Your Own Current Clamp Probe

January 27, 2018 by 11 Comments

If you want to measure AC or DC current with an oscilloscope, a current clamp is a great way to do it. The clamp surrounds the wire, so you don’t need to break the connection to take your measurements. These used to be expensive, although we’ve seen some under $100, if you shop. We don’t know if it was cost or principle that motivated [Electronoobs] to build his own current clamp, but he did.

This probe design is little more than a 3D printed case, an old power supply toroid, and a conventional alligator clamp to make the business end. The sensor uses a ferrite core and a hall effect sensor. The ferrite toroid is split in half, one half in each side of the clamp. An opamp circuit provides a gain of 100 to boost the hall effect sensor’s output.

In addition to building a homebrew probe, the video also shows a teardown of a Hantek current probe and explains the theory behind the different kinds of current probes, including some tricks like using a compensation winding to prevent core magnetization.

Does it work? You bet. After calibration, it did just fine. It’s not as pretty as a $100 unit, but beauty is in the eye of the beholder, and we are suckers for homebrew gear so we will say it is certainly more interesting. If you have a fair junk box (and a 3D printer), this probe could be made very inexpensively. The hall effect and a BNC connector are likely to be the most expensive parts. Even if you bought everything and used a non-printed case, we would be hard-pressed to think you’d spend more than $25.

If you want to see how the big boys do it, Keysight had a good break down last year. We’ve seen other homebrew builds for current probes and some of them are very accurate.

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Flying The Friendly Skies With A Hall Effect Joystick

January 18, 2018 by 15 Comments

There are plenty of PC joysticks out there, but that didn’t stop [dizekat] from building his own. Most joysticks measure position mechanically using potentiometers or encoders. Only a few high-end models use Hall effect sensors. That’s the route [dizekat] took.

Hall effect sensors are non-contact devices which measure magnetic fields. They can be used to measure the position and orientation of a magnet. That’s exactly how [dizekat] is using a trio of sensors in his design. The core of the joystick is a universal joint from an old R/C car. The center section of the joint (called a spider) has two one millimeter thick disc magnets glued to it. The Hall sensors themselves are mounted in the universal itself. [Dizekat] used a small piece of a chopstick to hold the sensors in position while he found the zero point and glued them in. A third Hall effect sensor is used to measure a throttle stick positioned on the side of the box.

An Arduino micro reads the sensors and converts the analog signal to USB.  The Arduino Joystick Library by [Matthew Heironimus] formats the data into something a PC can understand.

While this is definitely a rough work in progress, we’re excited by how much [dizekat] has accomplished with simple hand tools and glue. You don’t need a 3D printer, laser cutter, and a CNC to pull off an awesome hack!

If you think Hall effect sensors are just for joysticks, you’d be wrong – they work as cameras for imaging magnetic fields too!

Arduino + Geometry + Bicycle = Speedometer

March 9, 2017 by 9 Comments

It is pretty easy to go to a big box store and get a digital speedometer for your bike. Not only is that no fun, but the little digital display isn’t going to win you any hacker cred. [AlexGyver] has the answer. Using an Arduino and a servo he built a classic needle speedometer for his bike. It also has a digital display and uses a hall effect sensor to pick up the wheel speed. You can see a video of the project below.

[Alex] talks about the geometry involved, in case your high school math is well into your rear view mirror. The circumference of the wheel is the distance you’ll travel in one revolution. If you know the distance and you know the time, you know the speed and the rest is just conversions to get a numerical speed into an angle on the servo motor. The code is out on GitHub.

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Sensing A Magnet With Local Sourcing

December 8, 2016 by 48 Comments

I had a small project going on–never mind exactly what–and I needed to detect a magnet. Normally, that wouldn’t be a big problem. I have a huge hoard of components and gear to the point that it is a running joke among my friends that we can be talking about building something and I will have all the parts we need. However, lately a lot of my stuff is in… let’s say storage (again, never mind exactly why) and I didn’t have anything handy that would do the job.

Options

If I had time, there are plenty of options for detecting a magnet. Even if you ignore exotic things like SQUID (superconducting quantum interference device) there’s plenty of ways to detect a magnet. One of the oldest and the simplest is to use a reed switch. This is just a switch made with a thin piece of ferrous material. When a magnet is nearby, the thin piece of metal moves and makes or breaks the contact.

These used to be common in alarm systems to detect an open or closed door. However, a trip to Radio Shack revealed that they no longer carry things like that as–apparently–it cuts into floorspace for the cell phones.

I started to think about robbing a sensor from an old computer fan or some other consumer item with a magnetic sensor onboard. I also thought about making some graphene and rolling my own Hall effect sensor, but decided that was too much work.

Browsing

I was about to give up on Radio Shack, but decided to skim through the two cabinets of parts they still carry just to get an idea of what I could and could not expect to find in the future. Then something caught my eye. They still carry a wide selection of relays. (Well, perhaps wide is too kind of a word, but they had a fair number.) It hit me that a relay is a magnetic device, it just generates its own electromagnetic field to open and close the contacts.

I picked up a small 5 V reed relay. They don’t show it online, but they do have several similar ones, so you can probably pick up something comparable at your local location. I didn’t want to get a very large relay because I figured it would take more external magnetic field to operate the contacts. You have to wonder why they have so many relays, unless they just bought a lot and are still selling out of some warehouse. Not that relays don’t have their use, but there’s plenty of better alternatives for almost any application you can think of.

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3D Carver Makes Magnetic Fields Visible

November 19, 2015 by 10 Comments

The history of science is full of examples when a 3D physical model led to a big discovery. But modelling something that’s actually invisible can be tough. Take magnetic fields – iron filings on a card will give you a 2D model, but a 3D visualization of the field would be much more revealing. For that job, this magnetic field following 3D carving machine is just the thing.

What started out as a rapid prototyping session with servos and hot glue ended up as quick and dirty 3D carving rig for [Frits Lyneborg]. The video shows his thought progression and details how he went from hot glue and sticks to LEGO Technics parts and eventually onto Makerbeam extrusions for the frame of his carver. A probe with a Hall effect sensor is coupled to a motor spinning a bit that cuts into a block of floral foam. A microcontroller keeps the Hall sensor a more or less fixed distance from a rare-earth magnet, resulting in a 3D model of the magnetic field in the foam, as well as a mess of foam nubbles. Despite a few artifacts due to in-flight adjustments of the rig, the field presents clearly in the block as two large lobes.

Carving foam isn’t the only way to visualize a magnetic field in three dimensions, of course. If you’d rather have a light show based on the local magnetic field, try this 3D compass build we covered a while back.

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