So, I decided it would be cool to try and sense Earth's magnetic field. Especially with the upcoming solar high, it would be fun.
The method I think would be the easiest to accomplish using an Arduino as the ADC/computer interface would be using a fluxgate magnetometer. For those that don't know what that is, well, it's basically two overlapping coils, one driven by an AC current, while the other produces a voltage proportional to the sensed magnetic field (if there is no magnetic field around the voltages cancel each other).
Sensing the voltage is the easiest part, what's driving me nuts is what exactly would be the best way to produce an AC current in the +/-2.5V to +/-5V range at frequencies from 50 all the way up to 1kHz to drive the primary coil.
I've never had to do anything similar, all my experience has always been DC only, so I'm lost. Any idea on how to accomplish this the easiest way or at least what exactly to Google? I tried a lot, but not knowing what to look for made all my search attempts a failure
That will give you 0-5V swings at arduino output.
Run it thru a 220uF capacitor to a 1K resistor to ground, the resistor/cap junction will look like +/- 2.5V
Run that thru an op-amp to boost to +/- 5V.
What sort of current do you need to drive the primary? What inductance is the primary. It may be that more current is needed than the arduino can supply directly. A more powerful circuit might be needed (such as an H-bridge).
If not, then simply use two pins in antiphase (they can be driven simultaneously if direct port manipulation is used). Flywheel diodes may be needed to prevent inductive spikes damaging the circuit, note.
CrossRoads, Thanks again, you really got me on the right track.
MarkT: To tell you the truth, I have absolutely no idea. All the references I've seen talk scarcely of the driving circuit and concentrate on the coils alone. They did mention that the pickup voltage is proportional to the primary, but by what factor is unknown. Even the frequency is stated to be anywhere between 50 and 1kHz, so I guess there's a lot of experimentation to be done. I already thought about an H-Bridge (I knew from my motor designs it can be used to reverse the polarity), but I'm not sure driving it at such high frequencies would work. And thank you too for your tips!
Looks like those who know how to get the design working obviously keep it for themselves and build commercial units But it's nothing so exotic that a bit of hacking and tinkering can't fix. It's a pre-WWII design, after all...