Mounting with magnets

Is it safe to mount an Arduino using magnets? I'm planning on doing this with a Raseberry Pi, and other Arduino variations as well. It's basically a weak magnet tapped to the Arduino that attaches to another magnet on the mounting surface. It seems like an easy way to detach the Arduino if I need to.

I have a wind speed sensor (anemometer) that I attach to its mount with large and very strong magnet. The anemometer has a stand alone 328 with NRF24 wireless tranceiver. Everything works just fine.

Magnetic fields do not affect electronics. With the exception of electronics that are designed to detect magnetic fields that is.

Grumpy_Mike: Magnetic fields do not affect electronics. With the exception of electronics that are designed to detect magnetic fields that is.

Stationary magnetic fields do not affect electronics, moving ones may, e.g. induced currents. My pacemaker is certainly affected by moving/variable magnetic fields. That's why I'm not allowed to go through the metal detectors at airports.

Henry_Best: My pacemaker is certainly affected by moving/variable magnetic fields.

Well, two things actually. Clearly a low frequency magnetic field (up to a few hundred Hz) can induce spurious signals similar to those it is designed to monitor and that could be a problem. I was warned that if I had a defibrillator fitted, I would not want to take up electric welding as it could have unpleasant consequences. :o

Secondly, it has a static magnetic sensor which simply disables it when a strong magnetic field (and I do mean, strong!) is applied. We use a magnet placed over the pacemaker to disable it during surgery, so that it is not affected by the diathermy and LigaSure™ instruments (even though the pacemaker is supposed to be relatively immune by design). The Harmonic Scalpel on the other hand should be quite safe.

VERY strong magnetic fields can even induce unconsciousness in the healthiest of humans as it stops the brain working. Fields of this strength are excedingly rare though and start at about a quarter of a ton (without the power supply)

Assuming you don't use one of these to mount your arduino, I think you'll be safe.

Very strong impulse fields, that is.

No problem with the static field of a 3T MRI.

Paul__B: No problem with the static field of a 3T MRI.

Pft, You call that strong? That's nothing. I'm talking about the 91.4 tesla kind. Even when static they'll halt the electrons in your neurons. :)

KenF: Pft, You call that strong? That's nothing. I'm talking about the 91.4 Tesla kind. Even when static they'll halt the electrons in your neurons.

I strongly suspect femoral traction here.

Paul__B: Well, two things actually. Clearly a low frequency magnetic field (up to a few hundred Hz) can induce spurious signals similar to those it is designed to monitor and that could be a problem.

By 'designed to monitor', I guess you're talking about the signals used to adjust my pacemaker whenever it's tested and the signals that tell how much battery life is left and the record of its activity.

I was warned that if I had a defibrillator fitted, I would not want to take up electric welding as it could have unpleasant consequences. :o

Yes. I was similarly warned. Not that I've ever intended to take up arc welding! I presume electric spot welding might have similar consequences. I did a little of that many years ago, but have no need nowadays.

Henry_Best: By 'designed to monitor', I guess you're talking about the signals used to adjust my pacemaker whenever it's tested and the signals that tell how much battery life is left and the record of its activity.

No, I am not aware of how the programming interface works though now you mention it, it must be HF wireless so that could be a problem with general broadband (arc) interference.

Henry_Best: I presume electric spot welding might have similar consequences. I did a little of that many years ago, but have no need nowadays.

Spot welding should be no great problem as it is primarily resistive - it is arc welding which generates the (very) broadband RF.

So I guess the conclusion has to be: Only mount your arduino with magnets if you don't have a pacemaker, but you should be OK spot welding it in place :)

KenF: So I guess the conclusion has to be: Only mount your arduino with magnets if you don't have a pacemaker, but you should be OK spot welding it in place :)

Yeah, that might do. ::)

Paul__B:
No, I am not aware of how the programming interface works though now you mention it, it must be HF wireless so that could be a problem with general broadband (arc) interference.

When I go for a check-up, they put a mouse shaped box over where it is and put the wire round the back of my neck so that it hangs in place. I assume that it is just a coil sending and receiving magnetic signals to and from the pacemaker. If it was HF radio there surely would be no need to have it so close.
What amazed me was, when I went for a check-up last month, I was told there had been a 3 second glitch in my heart rate on the 22nd of November last year! What size memory must it have to be able to retain that much historical data? I certainly can’t recall what I was doing almost a year ago.

KenF:
So I guess the conclusion has to be: Only mount your arduino with magnets if you don’t have a pacemaker, but you should be OK spot welding it in place :slight_smile:

A 6" nail through the centre of the board would be easier. :slight_smile: :slight_smile:

Henry_Best:
When I went for a check-up last month, I was told there had been a 3 second glitch in my heart rate on the 22nd of November last year! What size memory must it have to be able to retain that much historical data? I certainly can’t recall what I was doing almost a year ago.

It could be that it only stores the anomalies. Assuming normal function since, it may be the only data it has needed to store.

KenF: It could be that it only stores the anomalies. Assuming normal function since, it may be the only data it has needed to store.

That would be correct.

The Holter Monitor with which I am to be fitted again tomorrow morning uses a memory card - I will check, but I think it is about 2 or 4GB - to record about two channels of ECG for 24 hours though it can be set for a few days IIRC. Will try to recall the details as they set it up.

Beats cassette tapes.

And - you probably could do this with an Arduino (and an op-amp)!