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NFC Antenna (Back Cover) can be magnetized and will affect compass

8th January 2011, 09:38 PM |#1  
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So I've been noticing that my compass would always misbehave (in terms of accuracy, not stability a la Sky Maps). I would get a pretty large static error (30 to 40 degrees obviously not declination); rotations would not be consistent (IE, a 180 degree turn would yield 100 degrees change.); and the magnitude of raw measurements was not like that of the magnetometer I got from Sparkfun.

Turns out the neodymium magnets I had near my desk actually latched onto my phone and magnetized the NFC antenna. I tested this by removing the cover and putting the magnet near the antenna and it sticks. :P Without the cover on, the compass worked much better.

I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.

If anyone is having problems with the compass overall accuracy, removing the back cover may help.
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9th January 2011, 01:15 AM |#2  
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Quote:
Originally Posted by chadrockey

Turns out the neodymium magnets I had near my desk actually latched onto my phone and magnetized the NFC antenna. I tested this by removing the cover and putting the magnet near the antenna and it sticks. :P Without the cover on, the compass worked much better.

I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.

Why did you have such strong magnets near your desk? lol

Quote:
Originally Posted by chadrockey

I've mostly demagnetized my NFC antenna now by doing some magnet sweeps and leaving it near the heater, but I've learned to keep the magnets away.

Phones + magnets = bad same as with hard drives, but I guess at least you don't loose files with magnets and phones that would suck...
9th January 2011, 01:26 AM |#3  
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I use them to test various things, such as magnetic interference on magnetometers in phones/compasses/inertial measurement systems. :P The magnets used to hold doors closed are very powerful and affect compass heading. Rare earth magnets are also extremely cool.

That's mostly a myth with the hard drives. Floppy disks/cassette tapes sure. I think it takes something like .2 to .5 Telsa to actually start affect hard drives. My largest magnet is only something like .1. In large spinning drives, they all contain a neodymium magnet in the center.

Mostly I was surprised that the NFC antenna could be imprinted by a magnetic field. I was getting a pretty significant field too. The change was something like 10 uT.

Sources:
http://www.pcworld.com/article/11657..._pc_myths.html
http://en.wikipedia.org/wiki/Neodymium_magnet
9th January 2011, 03:22 AM |#4  
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Quote:
Originally Posted by chadrockey

I use them to test various things, such as magnetic interference on magnetometers in phones/compasses/inertial measurement systems. :P The magnets used to hold doors closed are very powerful and affect compass heading. Rare earth magnets are also extremely cool.

That's mostly a myth with the hard drives. Floppy disks/cassette tapes sure. I think it takes something like .2 to .5 Telsa to actually start affect hard drives. My largest magnet is only something like .1. In large spinning drives, they all contain a neodymium magnet in the center.

I took apart several old hard drives and found those magnets, so I knew about it but they are exceptionally strong! the two magnets are near impossible to pull away from each other when stuck, you have to slide them I have since lost them though
28th September 2012, 03:37 AM |#5  
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Thanks for the tip here! Removing the back cover does indeed bring my compass back to sanity. However, I have no idea how to demagnetize the NFC antenna. What are magnet sweeps? Any suggestions?
28th September 2012, 10:35 AM |#6  
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Didn't saw this thread either.

Thanks will check it later if compass works fine without the back cover
1st October 2012, 01:47 AM |#7  
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Tried without cover and it works ok!

Now need to find a way to de-magnetize thus damn cover :-\
1st October 2012, 03:02 PM |#8  
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If you figure out how please let us know.
4th October 2012, 03:02 AM |#9  
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Google how to demagnetize metal...


Sent from my Nexus S 4G using xda app-developers app
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