AppleWatchAmmeter
github.com
github.com
(My learnings from almost getting sued for a simple hobby project like this)
That u0 is meant to symbolize μ_0 (mu zero, with zero being subscript) the vacuum magnetic permeability [0], in case you were wondering where that magic constant came from.
I'm quite surprised that nobody has made an app which can do some baseline calibration and produce real-time current measurements yet; it would just be a few hundred lines of code at most.
(Fun fact: this is another project that Sebastian Staacks of http://there.oughta.be worked(s?) on. You might remember his wooden Gameboy shell, the Gameboy interceptor to screenshare the Gameboy screen to a PC or his bullettime video booth.)
That surprises me. As soon as a sensor saturates, you can no longer use it for dead reckoning (integrating the acceleration values to know position).
13g is way below what you'd expect when tapping the phone against a solid object for example - that could easily reach 1000g briefly.
I was under the impression that a big part of iphone's superior GPS performance was down to the clever use of dead reckoning and re-calculating past datapoints in a way android manufacturers rarely do.
Instead I think the iPhone cheat a bunch, and use a mixture of step counting, magneto and gyro inputs to perform dead reckoning. The iPhone uses periods when you GPS is in use anyway to calibrate your stride length at different speeds, which when mixed with magneto data to estimate a course direction, would allow an iPhone semi-accurately perform dead reckoning, without needing high resolution, wide scale, accelerometer input.
In short, the iPhone cheats. It’s dead reckoning systems take advantage human bio-mechanics to simplify the problem of dead reckoning, at the cost of building a dead reckoning system that only works effectively in a handheld device that semi-permanently lives on your person. A perfectly reasonable assumption for a phone, but a terrible solution for a more generic dead reckoning system.
Big g-forces are bad if experienced for more than a few hundred microseconds. But very briefly, they aren't too damaging.
It’s not even easy to find. Few months ago I wanted a simple audio spectrogram app, downloaded some which wanted dubious in-app purchases, or had ads. I hadn’t come across it earlier, but Phyfox does what I wanted better and for free.
Submitters: "Please submit the original source. If a post reports on something found on another site, submit the latter." - https://news.ycombinator.com/newsguidelines.html
I imagine a smart warch with two 4mm banana-jacks isn't going to be the next big thing.
I highly recommend just getting that magnetic ring instead.
But wearing a ring, while convenient and safer, is not biO hAcKiNg. It gives no bragging rights.
This took me longer than it should have. Nicely put.
This does not happen as easily or frequently with stainless steel.
(There is still a risk of spontaneous rejection however )
Maybe the most fun, though, was just playing around and "picking up" paperclips and tiny screws by flicking my finger at them.
I'm only guessing.
Imagine the joy of getting an MRI and forgetting about that bit of biohacking.
I have tragus piercings where the rings are titanium but the balls were steel. It was missed that they were there.
I have surgical steel self-done implants in each hand.
I have a magnet in one of my fingertips
I have NFC chips in both hands.
I did not explode, nothing felt hot, the only sensation was my tragus piercings wobbling slightly.
This whole MRI thing ....
Likewise if you're more than about a meter away, the gradient has also dropped off and forces are much smaller.
Imagine a bubble around the entrance to the core: that's the danger spot where field gradients can be >3 T/m. Fun fact: take B^2/(2*u0) and you get units of Pascals. Magnetic pressure and fluid pressure can be thought about pretty similarly, except that free space is very impermeable and things like iron instead act like "holes" that can create strong flows between areas of different magnetic pressure. You can have a 3 T field separated from you by air, but if you stick a steel rod into it suddenly both ends of the rod will be at 3 T.
3 T works out to about 500 psi of magnetic pressure. If you have a small, 5 mm iron sphere in a 3 T/m gradient, the pressure difference across it is only ~2.5 psi. Size matters a LOT. 2.5 psi may be a slight tug; 50 psi may pull a wire straight through you. And 10 psi may be fine when it's embedded in you already, but given a distance to accelerate it can go pretty fast.
> The static magnetic field B_0 of an MRI machine attracts ferromagnetic objects and accelerates them toward the center of the bore of the MRI scanner. Ferromagnetic objects such as coins, hairpins, steel oxygen tanks or scissors can be accelerated or torqued by B_0 [4,10] and become dangerous projectiles [51]. The MRI safety program of the facility needs to warn about the misconception that larger objects will resist attraction to the field and need to emphasize the relationship between object size, material components, and projectile risk. Insufficient MRI safety training of ancillary medical personnel has led to fatal accidents when medical and other equipment was accelerated into the bore of the magnet [50,51].
X-rays would be no problem. Having something that is attracted by a magnet (such as another magnet) may cause an issue.
https://pubmed.ncbi.nlm.nih.gov/38128958/ has more on the "stuff flying into an MRI with concerning force."
Things like a 10p coin imbedding itself 0.5cm into ballistic gel. A spoon going in 3.5 cm is a bit more concerning.
Just go read straight from the source instead of linking research papers.
It has the warning of:
>MRI COMPATIBILITY WARNING The xG3 and all magnetic implant products should be removed before any MRI or magnetic imaging procedure. While our x-series transponders have tested as compatible with MRI machines up to 7T field strength, all magnetic products are incompatible with MRI machines and procedures.
> with people implanting rare earth magnets into the tips of their pinky fingers
And I was specifically referring to those rare earth magnets.
Your comment then:
> I have an implant and MRIs or Xrays cause zero issues.
You gave no indication about what type of implant you hand or its manufacturer, and replying to my comment I took it in context that it was a rare earth magnet.
Failing any information about the manufacturer, the information that I am able to provide to say "this can be dangerous" is research papers.
You have further clarified that you only have a RFID and NFC chip implanted and not any magnets ... and provided a link to another product (rare earth magnet implant) from the same manufacturer that indicates that it is indeed dangerous when near an MRI machine which agrees with the original comment.
Implants inside the body cannot accelerate freely. They are held in place by the surrounding tissue. A force will act on them, and this force can cause complications, but implants will not suddenly turn into projectiles.
>MRIs don't accelerate objects instantaneously.
See some of the videos below for evidence to the contrary. Large metal objects inside the room can definitely accelerate very rapidly and suddenly, and unexpectedly and has killed people.
https://www.youtube.com/shorts/2NNJrOsw8vs "Metal objects not attached to bone may not be safe"
https://www.youtube.com/watch?v=naAZVCxhEcI
https://www.youtube.com/watch?v=uDfwxoigZZk
https://www.youtube.com/watch?v=5KuzTyn45og
The only thing I strongly disagree with is the urban myth that MRIs turn implants into projectiles. I don't think that can happen. None of the videos you linked show anything of the sort.
Yes, objects can be accelerated to dangerous velocities; but only if they can move freely (eg. oxygen bottles on a cart, wheelchairs, small objects placed on a smooth surface). Objects embedded in tissue can not move freely and won't start tearing holes in your body like reverse bullets.
It can of course still be dangerous. One lethal case documented in the literature involved a metallic clamp inside the patients head. The MRI seemed to have moved or dislodged it causing cranial haemorrhaging. It killed him, but it did not shoot out of his head like a bullet.
Once after falling on ice, I had a chest x ray where my shirt was unbuttoned but didn’t need to be removed.
A very anxious tech came to me a few minutes later asking if I had been wounded when I fell, if there was something embedded in me, etc.
Very quickly figured it out when shown the images.
Incredibly comical, and obviously not an issue. (Nor related to implants)
On the two occasions I failed to remove the large steel/titanium item in a piercing that set off the scatter machine so I was taken to a room and searched.
But the steel in my hands, the LED, chip and magnet in my left hand, the Vivokey and chip in my right hand - nothing. Even the handheld scanner doesn't pick them up.
One of the NFC chips was useful on my last trip to the US. I was constantly pulled over by the TSA and they might have wanted to inspect my laptop. So I made a backup, saved the minimum I needed, encrypted it on another device and uploaded to a domain. Clean installed the OS. The NFC chip carried a long string which to me gave the directory structure (very nested, no / in the string) and the encryption key. It wasn't needed, but it was amusing.