Emergency compass

[airdale]

... The iPhone default compass app indicates direction relative to true north. ...

To do that using the phone's magnetometer, I think it would have to know your location (GPS) and either know the local declination or use its data connection to look it up, no?

Re using a cell phone magnetometer compass as a backup, I have tried several Android compasses and none worked very well while standing in my front yard away from metal. Near metal, I have had even car compasses with significant errors that could not be corrected by adjusting the correction magnets. So I'd be skeptical about using a cell phone magnetometer as a backup.

The ground track from a GPS, including the cell phone GPS, would seem to be more useful. Many GPS apps actually show TRK on a compass face. And that would have to be true, unless again the device had some way to look up declination.

Maybe I should, but have you been paying attention to the junk this dude has so arrogantly been writing ever since he joined the forum? It's just hard to believe...even by internet standards. And he shows no sign of improvement or humility.

Agreed. I wonder if he's familiar with the old quotation attributed to Abraham Lincoln: "Better to remain silent and be thought a fool than to speak out and remove all doubt."

 

[Jim Logajan]

Flux gate magnetometers are subject to EMI that permanent magnets are not.

You don't even know what kind of sensor is being used in mobile devices.

 

[MAKG1]

You don't even know what kind of sensor is being used in mobile devices.

Firsthand, no.

But I do occasionally work with solid state sensors.

No solid state device that is sensitive to magnetic fields is immune to EMI. Whether it's a Hall sensor or a simple pickup coil or a flux gate or whatever. Hall sensors in particular are sensitive to ELECTRIC fields in addition to magnetic fields, which will be real fun to avoid in a device that uses RF for essential functions.

 

[airdale]

You don't even know what kind of sensor is being used in mobile devices.

Probably magnetoresistive devices these days. http://en.wikipedia.org/wiki/Magnetometer#Mobile_telephones and http://spectrum.ieee.org/semiconductors/devices/a-compass-in-every-smartphone

Also, more than you wanted to know: http://www.sensorplatforms.com/understanding-smart-phone-sensor-performance-magnetometer-2/

 

[petrolero]

The new iphones also have a barometer, which portends interesting things.

 

[kgruber]

Android phones have had barometers for years.

 

[petrolero]

Android phones have had barometers for years.

Do any flying apps use it as any kind of quasi altimeter?

 

[Sac Arrow]

Do any flying apps use it as any kind of quasi altimeter?

Not sure but who cares. The real function of the barometer is for when cumulative elevation is being tracked. Absolute GPS elevation is accurate enough for most purposes but the positional errors multiply in cumulative elevation tracking.

 

[RotorAndWing]

FWIW I have got my iphone 4 out on long trips on the Airbus and play with the compass mode on it. Flying along it was very close to what the aircraft was showing.