When I get a magnet, generally I think it’s fairly strong, like those from a hard drive, or pretty weak, like normal refrigerator magnets. Though I have some vague sense of what is an effective magnet, this wasn’t good enough for Anthony Garofalo, AKA “Proto G,” an electromechanical engineer who lives in South Florida.
In fact, measuring the field strength on the surface of a magnet wasn’t even good enough for him, as his device, which he shows how to build on instructables, uses two Hall effect sensors. One measures the magnet’s pull on (or very near) its surface, while the other is spaced at 3/8″ away from the surface that the first rests on, giving a measurement of the magnet’s strength at a distance as well. This is important, as a larger magnet may not seem that powerful on its surface, but will pull for a longer distance.
If this is a new concept for you, Garofalo recommends this article for a little more background on how this works. As for how he was able to pick up on this information, he says that:
There’s not much difference in the theory of a dipole antenna and a dipole magnet. I design antennas so the relationship was easy for me to pick up on. Larger, more powerful magnets can actually have a lower surface field reading than a smaller, weaker magnet.
Besides the dual-meter design, another really clever thing about this meter is that it has no no visible on-off switch. Instead of a traditional button, it cleverly uses two reed switches to cycle power. One in the middle of the sensor’s round portion turns it on, while another, near where the handle meets the circular area, turns it off.
Once on, the unit measures the field strength with the two Hall effect sensors, then displays the surface reading, the 3/8″ reading, and an average on its tiny OLED display. As Garofalo notes in the video, field strength isn’t linear, the average of the two isn’t the entire picture, but it should still give a useful number for comparison.
Garofalo notes that:
The hardest part for me was finding a suitable sensor. Most gauss meters I could find information on used inferior hall effect sensors like Allegro’s A1302 which can only measure up to 1690 gauss. The best linear sensor I could find with the largest gauss range is Diodes Incorporated’s AH49HZ3-G1.
Electronics aside, the actual device was nicely 3D printed, and looks almost like something you could buy at a store. You can see him making a 3D model of it in Autodesk Inventor in the video below, then printing it. His process didn’t end there though, as he spray painted it black, then wiped away certain areas with acetone to create a dual-color effect.
He also used brass inserts to allow for easy attachment of each side of the 3D printed meter. Though I’ve tapped threads into 3D-printed objects, I can’t imagine they would hold up very well. Using an insert like that is definitely a good idea to remember when dealing with materials that aren’t really suited for repeated screw use.
On another stylistic note, if you think that this looks like something out of science fiction, that’s not entirely a coincidence. According to Garofalo, he did some research on gadgets from science fiction to get some ideas. He wanted it to have a “futuristic” look to it.
Probably a good reminder to all of us that style matters, at least a little bit in DIY/maker videos. Many times I, and I’m sure many others, get things marginally working, then move on!
If you’d like to build your own, STL files, a bill of materials, an electrical schematic, and the Arduino program that runs the device are available on the instructables page linked earlier.
If you’d like to see more from Garofalo, be sure to check out his High Voltage EEPROM Man featured on Make: in 2016. Or check out and maybe even subscribe to his YouTube channel to see even more interesting experiential builds!