CODEWITHSUNDEEP
iosobjective-ciphoneswiftmagnetometer
Ivan Nesterenko
Ivan Nesterenko

Reputation: 969

Using iOS device as teslameter (magnetometer discussion)

In my app I want to detect how strong surrounding magnetic/electromagnetic fields are. What I want to achieve is to measure magnetic field change to know if it's stronger than in control measurement or if it's lower. This is my code:

- (void)setupLocationManager {
    self.locationManager = [[CLLocationManager alloc] init];
    if ([CLLocationManager headingAvailable] == NO) {
        self.locationManager = nil;
    } else {
        self.locationManager.headingFilter = kCLHeadingFilterNone;
        self.locationManager.delegate = self;
        [self.locationManager startUpdatingHeading];
    }
}

// CLLocationManagerDelegate
- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)heading {
    CGFloat magnitude = sqrt(heading.x * heading.x + heading.y * heading.y + heading.z * heading.z);
    if (self.defaultMagnitudeValue == 0.f) {
        self.defaultMagnitudeValue = magnitude;
    }
    self.curentMagnitudeValue = magnitude;
}

Magnitude value reacts to the magnetic fields surrounding the device, the problem is that you need to be REALLY close to a source of such a field.

So, the question is: Is there any possibility for an iOS app to measure magnetic fields on distances more than 10-20 centimeters? If so, how?

P.S.: I have also checked the Teslameter App by Apple, it has nearly same code and totally same problems.

Upvotes: 4

Views: 2291

Answers (1)

Jonah
Jonah

Reputation: 17958

Sure you can, the magnetic field just has to be very strong!

Your first limit might be the hardware. As noted in In iOS, what is the difference between the Magnetic Field values from the Core Location and Core Motion frameworks? the range of those raw values may be limited. At some some hardware and iOS versions restricted them to -128 to +128 microteslas. On an iPhone 6 I can get microtelsa readings well outside that range but that doesn't necessarily help. Apple doesn't seem to provide any reference for the accuracy of magnetometer readings, we can measure values out to nanotesla but the results we get back might be meaningless noise.

Earth's magnetic field at the surface will be 25 to 65 microteslas. Any field you hope to measure is going to need to be measurably stronger than that at the desired measurement distance. What are you trying to measure, and is it really strong enough to move a compass needle at the distance you want to measure it?

Upvotes: 2

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