in short, I'm looking to create a magnetic field meter, much like the popular Trifield TF2 meter. Or something close to it.
I'd like to be able to read a baseline magnetic field of a room, then when getting close to a strong magnetic field, the milligauss reading on screen will increase. Then decrease when moving away from the magnetic field.
My initial research led me to test out magnetometers for this idea. Specifically the QMC588L. I understand these sensors are mainly used for compass/direction applications because they are sensitive enough to read the Earth's magnetic field. And this explains why the example sketches that I've tried, gave me a wide range of readings. Such as the readings changing drastically when simply rotating the sensor. I realize that this is normal behavior since this is how these sensors are usually set up. But that's something I would definitely want to minimize in my final project
My question here is, can the sensitivity/range of these sensors be adjusted so that it can only detect nearby magnetic fields instead of the Earth's magnetic field? I do see some documentation on gain adjustment but not a whole lot. Just looking for some ideas or a place to start from someone who's more experienced than I am with these sensors. Or let me know if a different sensor would be better for this application. I've looked at hall effect sensors but decided against them as they seem like they don't have enough sensitivity or range.
Magnetic fields add as vectors, and a magnetometer measures the sum of fields due to all sources. For small sources like a refrigerator magnet, the field drops off very rapidly with distance.
With the very outdated QMC5883L, you can set the full scale sensitivity to either 2 Gauss or 8 Gauss. For reference, the Earth's magnetic field strength ranges from about 0.2 to 0.6 Gauss.
Gotcha, which explains why baseline levels on meters such as the trifield meter range from 0.2-.08. The readings I was getting from the output of the qmc, were in the thousands, which I assume is because it natively outputs in something like microteslas?
You mentioned that the qmc5883l is very outdated, is there a successor to the qmc? from what I could gather, the qmc was a successor to the hmc5883l and that was one reason why I chose it. but I'm definitely willing to try another sensor that is more reliable than the qmc or that just works better for this application
for a vector magnetometer, it is not possible to minimize the changes due to rotation. These are not errors, but a reflection of the directional nature of magnetic fields. However, If you measure all three components of the magnetic field you can construct a scalar magnetometer by taking the norm of these values which will have no directional sensitivity.
Gradiometers, as opposed to magnetometers, are most sensitive to nearby AC field changes and insensitive to the large DC changes and low-frequency drifts associated with the earth's field.
So, measuring the raw output of the sensor in all 3 axis, then I'm assuming by the "norm" you mean averaging the readings, and that should create a combined reading that has no directional sensitivity? I'm also wondering about the negative readings of the sensor? since the opposite pole would also be measured, it would give some negative numbers that would affect the calculation. I'm thinking that taking the absolute value of the readings would probably take care of that issue.
My application, believe it or not. making a paranormal investigating tool. other devices like the trifield meter are ridiculously expensive. So I thought I'd give it a shot trying to make something similar at a fraction of the price. Also seemed like a nice challenging project. And this would be specifically magnetic fields, rather than electric fields.
not quite, the norm would be sqrt(x^2+y^2+z^2). This has no directional sensitivity and is only sensitive to the magnitude of the field at a given position in space. The squaring gets around the negative values issue you mention.
sounds like fun. Hopefully, you will have something up and running for Halloween!
other devices like the trifield meter are ridiculously expensive. So I thought I'd give it a shot trying to make something similar at a fraction of the price. Also seemed like a nice challenging project. And this would be specifically magnetic fields, rather than electric fields.