The Earth’s magnetic field plays an important role in the livability of our planet, and yet we really don’t pay much attention to it because we can’t see it. You probably don’t even think about its existence until you need to use a compass. But that doesn’t mean it’s not interesting if you have a way to measure it. Over on Instructables, AndresR145 has a tutorial that you can follow to build your own electronic field mill to take those measurements.
While the orientation of the Earth’s magnetic field remains constant — at least until it flips every half a million years or so — its intensity can fluctuate significantly. There is plenty of debate about the effect those fluctuations have, and the only way to get more information is to study them. To do that, you’ll need a way to measure the intensity of field over time, and AndresR145's e-field mill design can do that for you.
The magnetic field is enormous and extends thousands of miles into space, but it’s also very weak. To measure it, this design utilizes a conductive disk made from a copper PCB to gather a static charge. That is then channeled to a charge collector capacitor, where it can be measured. An Arduino takes those measurements, and then records them. From second to second, those readings should remain fairly consistent. But, over the course of a day, or many days, large fluctuations can be detected.