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I'm building a small circuit with an arduino bootloaded ATMega328 chip.

The project will be housed in a small box, and is intended to be stuck to the side of a fridge using a magnet.

Everything in my brain tells me that magnets and chips do not mix well. What is the likelihood that the sketch loaded onto the chip will become corrupted, or that something else will happen as a direct result of the magnetic forces, causing the chip to cease operation/ operate incorrectly?

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Magnets cause problems with magnetic storage (hard disks, tapes, etc). The AVR chips use flash, so won't be a problem.

Recently, I did some experiments with AVRs and hall effect sensors. I never saw problems from being near magnets.

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  • \$\begingroup\$ +1 I like the experiments... like to see those refined and see more results! Also, my brain was wrong - yay! \$\endgroup\$ – fearoffours Sep 30 '10 at 8:14
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    \$\begingroup\$ Toby - Your link is broken. \$\endgroup\$ – Michael Karas Jun 30 '13 at 10:41
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Joby hit it on the head as far as storage goes.

I would caution people experimenting with magnets and electronics (like reed switches) to be very wary of the filings that collect on powerful magnets. You'll get nearly invisible shorts when an iron filing that collected on the magnet falls onto your chip, embeds itself in some leftover flux, and takes down your system. Industry is worried about tin whiskers 10um in diameter and less than 1mm long - iron filings are just as dangerous.

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Magnets will not usually affect the chip. Magnets cause damaged to hard disks and floppy disks (remember those?) because they misalign the domains and destroy the data.

However, if you happen to have long traces on your PCB and strong (especially pulsating) magnetic fields, you could get induced voltage in these traces. This could range from a tiny bit of additional noise causing no harm to damaging the microcontroller from a voltage spike. This is only theoretical. You'd probably need MRI-level magnetic fields to induce any significant voltage.

As you are using a fridge magnet I do not see any of the above being a problem.

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    \$\begingroup\$ I think this should read "strong AND pulsating magnetic fields". A stationary magnet won't induce any voltages. A fast magnet (like a spinning motor), even if it has small magnets, can cause voltage spikes. \$\endgroup\$ – Kevin Vermeer Sep 29 '10 at 21:25
  • \$\begingroup\$ A moving magnet can cause problems, as can an electromagnet switching on. The magnet need not switch off to cause damage. \$\endgroup\$ – Thomas O Sep 29 '10 at 21:30
  • \$\begingroup\$ A stationary magnet would induce voltages if the wires move relative to it. A refrigerator door opening won't cause any problems, though. \$\endgroup\$ – endolith Sep 29 '10 at 21:42
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    \$\begingroup\$ If you have problems with a moving magnet near (but not right next to) a circuit loop, you will almost certainly have general EMI problems from ambient magnetic fields. If you have a PCB with a ground plane this is almost certainly not an issue. \$\endgroup\$ – Jason S Sep 29 '10 at 23:49

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