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| Magnetometer IC readings skewed by adjacent circuitry? |
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| HwAoRrDk:
I was playing around with a magnetometer breakout board (using a QMC5883L chip - a licensed clone of the Honeywell HMC5883L) today, and noticed something strange. I have the aforementioned breakout board and an accelerometer breakout board (MMA8452Q) hooked up with some short jumper wires to make the I2C connection to an Arduino. The jumper wires are so that I can move the breakout boards around freely while observing the changing readings. They are working well, with the exception that I noticed that when I move the magnetometer sensor near to the accelerometer, the readings from the magnetometer are skewed by a varying amount. For example, calculating the azimuth from north is roughly correct (well, as far as I can ascertain when comparing to a little hand-held needle compass and an app on my phone :)), but when placed nearer than an inch or so from the accelerometer board, the bearing from north is skewed and no longer correct. :( What would be causing this? It's troubling because I was going to mount both breakouts right next to each other, as daughterboards onto a main board, and if one is going to interfere with the other, that complicates my plans. Could it perhaps be something to do with inductance in the hookup wires I'm using when testing? |
| Kleinstein:
Ferromagnetic materials can influence a magnetometer sensor. Some parts (especially LEDs and connectors) can be magnetic. It already needs quite some DC current to have a significant effect compared to the earths field. If in doubt it is a good idea to keep the loop area small to keep the magnetic field local. |
| rhb:
Lots of through hole parts use tin plated steel leads. If the field is from current flow, removing the power from the accelerometer board will test that possibility. Steel leads seem more likely. |
| HwAoRrDk:
Hmm, I did use the 0.1" headers that were supplied with the breakout boards, and checking them with a magnet shows that they are magnetically attracted. I don't know though, it seems unlikely to me that current flow in this situation could induce a magnetic field, because the chips on these break-out boards have stated power consumption measured in microamps. :-// I will try with the accelerometer unpowered and see what effect that has. |
| amyk:
--- Quote from: HwAoRrDk on June 18, 2018, 11:05:33 pm ---I don't know though, it seems unlikely to me that current flow in this situation could induce a magnetic field, because the chips on these break-out boards have stated power consumption measured in microamps. :-// --- End quote --- ...and the strength of the Earth's magnetic field, which these sensors are designed to measure, is a few tens of microteslas. |
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