Physics Toolbox App (it is full of test and measurement tools)

[watchmaker]

I just found the app Physics Toolbox; was looking for an Android Magnetometer.

This thing is loaded.  Oscilloscope (w/ FFT), spectrum analyzer, sound meter, tone generator, g-force, accelerometer, barometer, gps, magnetometer, light meter.....

https://www.vieyrasoftware.net/

I spent $3 for the "pro" version.  While it will not replace test instruments, it provides another way to leanr how to use tools and the tools are useful for outdoor tasks.

[Sensorcat]

Interesting app! Glad they don't claim you can now throw away your instruments, but instead have education in mind.

Out of curiosity: Could you please test what range the magnetometer on your phone has?

Reason for the question: As an application for the magnetometer section of the app, they propose to do measurements with magnets. However, the magnetometer (usually 3D) in a smartphone is not designed for that, it is supposed to aid navigation by measuring the earth's magnetic field, which is on the order of 50µT. So one would expect the range of the magnetometer to be not much larger. Since modern rare earth magnets are stronger by 4 or more orders of magnitude, one would expect the magnetometer to be saturated in proximity of such a magnet.

Caution (not knowing which technology is used for the magnetometer in your phone): Some magnetometers, like GMR type, have a maximum tolerable magnetic flux density, perhaps 100mT, above which they are damaged. This limit should be outside the dynamic range, so it appears wise to stop bringing a strong magnet closer once saturation of the output signal has been reached.

[Dr. Frank]

Here's another Physics Tool Box, it's for free: https://phyphox.org/

It was developed at the II. Physics Institute of the RWTH Aachen by Sebastian Staacks.


When I made my diploma and PhD there, 35 years ago, I have developed PC based data acquisition for the institute, after the old PDP 11 was out of order, and we again had to use paper plotters instead. So there's a certain history on T&M

The electronics box of the M5 practical course on Ultra-Sound is still working: https://institut2a.physik.rwth-aachen.de/teaching/praktikum-physikmaster_versuche, after 30 years  .     

[watchmaker]

Interesting app! Glad they don't claim you can now throw away your instruments, but instead have education in mind.

Out of curiosity: Could you please test what range the magnetometer on your phone has?

Reason for the question: As an application for the magnetometer section of the app, they propose to do measurements with magnets. However, the magnetometer (usually 3D) in a smartphone is not designed for that, it is supposed to aid navigation by measuring the earth's magnetic field, which is on the order of 50µT. So one would expect the range of the magnetometer to be not much larger. Since modern rare earth magnets are stronger by 4 or more orders of magnitude, one would expect the magnetometer to be saturated in proximity of such a magnet.

Caution (not knowing which technology is used for the magnetometer in your phone): Some magnetometers, like GMR type, have a maximum tolerable magnetic flux density, perhaps 100mT, above which they are damaged. This limit should be outside the dynamic range, so it appears wise to stop bringing a strong magnet closer once saturation of the output signal has been reached.

I got to 200 uT and it was still counting.  Pixel 7.  Thank you for the warning.

[Sensorcat]

Meanwhile, I played with my smartphone and a magnet. The limits were at 3276.7µT and -3276.8µT, so the LSB unit is 100nT and it sends a 16bit word.

The phyphox app also tells which sensors it found. In my case, a Yamaha YAS539 magnetometer. Data sheet does not tell much, especially not the technology used! At least the specified range is 2000µT, and absolute maximum ratings include 500mT. So this sensor is in fact destructible by strong magnets, which means that it is not Hall, but probably GMR.

[RoGeorge]

It's hard to find a 500mT magnetic field.  That is very much even for the strongest magnets.

For example, I've measured once a permanent magnet clamp (measured the magnetic field with a piece of wire, a ruler, and a DS1054z oscilloscope ).  Found about 66mT.

[Phil1977]

A cellphone must tolerate quite strong magnetic fields.

A story from times of magnetic hard discs: Once the "Deutsche Bahn" (German railways) had chair tables that were fixed with a quite decent magnet in the upright position. Many travellers had data loss when they put their notebook with a non-solid-state hard drive on these tables.

Magnetic chargers have decent magnets to stay in place. People play with magnets and put them into their pockets.

Cellphones need to be tough enough to not lose functionality in these cases.

This is possible because smartphones use magnetoresistive sensors. They are not as sensitive as fluxgate sensors, but astonishingly cheap, precise enough for a compass with few degrees of angular resolution and quite robust. Some specify up to 10T in their absolute maximum ratings - that value is not even reached inside a MRI machine.

[Sensorcat]

It's hard to find a 500mT magnetic field.  That is very much even for the strongest magnets.

Look for Neodymium magnets (NdFeB). More than 1T is pretty standard today. If you put such a magnet directly on the phone, the Yamaha sensor I found in my phone would be damaged.

[Kleinstein]

For the magnets there is a theroretical strength with a closed magnetic loop - that may go a bit over 1 T. The field in the outside air or with a non closed magnetic path is much weaker. With some magnet configurations one can get at least a half closed configuration, but still far away from the theoretical limit.