bob prohaska <bp@www.zefox.net> wrote:

I turned on the compass utility on my old iphone6. It asked me to roll
a ball around a circle, which I did, then it asked me to turn off airplane mode or turn on WiFi. I did both, but the compass didn't find north.

Both questions surprised me. I always thought the compass used some sort of internal magnetometer and the ball-rolling was to establish a vertical datum.

What does the compass actually use to find north?

Thanks for reading,

bob prohaska

I don’t know how it works but I found it to be quite useful in setting up
my rooftop OTA antenna.

The elevation feature is useless though. Mine says my elevation is 20 feet,
yet I know where I’m sitting is 8.5 ft above sea level because I had to
have it surveyed for FEMA certification so I could get my flood insurance premiums lowered.

Makes me wonder if the compass is correct now…

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I turned on the compass utility on my old iphone6. It asked me to roll
a ball around a circle, which I did, then it asked me to turn off airplane
mode or turn on WiFi. I did both, but the compass didn't find north.

Both questions surprised me. I always thought the compass used some sort of internal magnetometer and the ball-rolling was to establish a vertical datum.

What does the compass actually use to find north?

Thanks for reading,

bob prohaska

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On 2023-09-13 19:16, bob prohaska wrote:

I turned on the compass utility on my old iphone6. It asked me to roll
a ball around a circle, which I did, then it asked me to turn off airplane mode or turn on WiFi. I did both, but the compass didn't find north.

Do you want true north or magnetic north?

There's a switch in settings to go between them.

I just turned on mine and it is easily within a few degrees of an
accurate true north.

Both questions surprised me. I always thought the compass used some sort of internal magnetometer and the ball-rolling was to establish a vertical datum.

What does the compass actually use to find north?

An IC that can detect the the Earth's magnetic field.

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bob prohaska <bp@www.zefox.net> wrote

What does the compass actually use to find north?

Good question... (which north - magnetic or true?)

True North: Settings -> Compass > Use True North -> ON (green switch)

You have a choice on the iPhone...
<https://youtu.be/4hhIIdGfPv0?t=45>

"Your iPhone has a device called a Magnetometer, which is basically
a compass. It not only uses the magnetic field to give you the
direction but also does one crucial thing ¡V measures the magnetic field."
<https://www.guidingtech.com/how-to-use-compass-on-iphone/>
That article covers in detail how to calibrate and why you might need to.

BTW, in terms of compass calibration, "In iOS 13 there is a privacy
setting to allow your compass to use location services to help
calibrate your devices compass. By default, this setting is disabled.
Enabling this feature is highly recommended for good compass accuracy."
<https://www.titanhst.com/improving-compass-accuracy-on-ios-devices/>

Hope this helps.
--
I'm on Usenet to learn from others and to teach others who want to learn.

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badgolferman <REMOVETHISbadgolferman@gmail.com> wrote

I don't know how it works but I found it to be quite useful in setting up
my rooftop OTA antenna.

Is this "OTA antenna" for Internet (WISP)?

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Wally J <walterjones@invalid.nospam> wrote:

badgolferman <REMOVETHISbadgolferman@gmail.com> wrote

I don't know how it works but I found it to be quite useful in setting up
my rooftop OTA antenna.

Is this "OTA antenna" for Internet (WISP)?

Over The Air antenna for local TV stations. I don’t have cable anymore but wanted a way to watch broadcast sports. I had to point the antenna at 193 degrees to get the four major networks.

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On 2023-09-13 22:16, bob prohaska wrote:

I turned on the compass utility on my old iphone6. It asked me to roll
a ball around a circle, which I did, then it asked me to turn off airplane mode or turn on WiFi. I did both, but the compass didn't find north.

Strange - was it stored in some oddball place subject to a strong
magnetic field?

To sort it out.

Face north (ish)

(AA)
Hold flat relative to the ground.
Rotate it slowly around each axis:
- roll
- yaw
- pitch

In any order, any direction.

Face east or west (ish).
Repeat (AA)

That should exercise it enough to sort it out.

Get the App: Sensor Log. It has a page that displays many sensor states/positions.
https://apps.apple.com/us/app/sensorlog/id388014573

Both questions surprised me. I always thought the compass used some sort of internal magnetometer and the ball-rolling was to establish a vertical datum.

What does the compass actually use to find north?

It uses a magnetic field sensor (magnetometer) which senses in 3 axis'.
Link below to such a device (not necessarily what is in any given iPhone).

The "ball rolling" thing I haven't had to use since iPhone 6.
(I have an iPhone 11).
If you do that "calibration" do it away from magnetic attracting metals.

Due to its tiny size, it is not esp. accurate. Expect any heading to be
no better than ±20° and occasionally worse.

My own experiments using local well known lines of bearing prove this
out. Some days is is withing a couple degrees, other days, wildly off.

Be sure it is in True or MagNorth mode as you need. Most maps are true
north up, but mag north isn't (mostly). It will use your position to
calculate the local mag var so True north is true. Ish. The Apple
Compass is crap as the True/Mag setting is under the system settings.
Most other apps correctly have the True/Mag selection in the app itself.

https://cdn.sparkfun.com/assets/2/2/4/d/6/MLX90393-Datasheet-Melexis_revision_003.pdf?_gl=1*p73k0n*_ga*MTA0ODg2MjIzMy4xNjk0NzE1NTE2*_ga_T369JS7J9N*MTY5NDcxNTUxNi4xLjEuMTY5NDcxNTUyMy41My4wLjA.

--
“If you torture the data long enough, it will confess to anything."
-Ronald Coase

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Alan Browne <bitbucket@blackhole.com> wrote:

Be sure it is in True or MagNorth mode as you need. Most maps are true
north up, but mag north isn't (mostly). It will use your position to calculate the local mag var so True north is true. Ish. The Apple
Compass is crap as the True/Mag setting is under the system settings.
Most other apps correctly have the True/Mag selection in the app itself.

I think you've hit the nail on the thumb. I carry the phone only for emergencies, with WiFi off and airplane mode on. The phone was
(unknowingly) set to true north, so it wanted to find its location
to make corrections.

Thanks for clearing up the mystery!

bob prohaska

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On 2023-09-14 22:17, bob prohaska wrote:

Alan Browne <bitbucket@blackhole.com> wrote:

Be sure it is in True or MagNorth mode as you need. Most maps are true
north up, but mag north isn't (mostly). It will use your position to
calculate the local mag var so True north is true. Ish. The Apple
Compass is crap as the True/Mag setting is under the system settings.
Most other apps correctly have the True/Mag selection in the app itself.

I think you've hit the nail on the thumb. I carry the phone only for emergencies, with WiFi off and airplane mode on. The phone was
(unknowingly) set to true north, so it wanted to find its location
to make corrections.

The compass doesn't need WiFi or any other transmitting radio to be on.
It will use its GPS for location. Though using cell towers may help it
compute location sooner - most GPS in smart phones lock within 15s or so.

That said, if it hasn't been used in a while, the GPS location may not
be where you are (doesn't have to be very accurate the mag var gradient
where I am, for example is about 1° per 40 NM - so over a 200 NM area it
will be more than accurate enough).

It's worth it to know the mag var where you are. There are tools online
where you enter you position (lat long) and it will spit out the mag var.

From there, if the variation is "West" then Mag north is to the left of
true north. ( Mag = True - magvar); west is negative.

Thanks for clearing up the mystery!

Not sure that I have. Did you get a more accurate reading?

--
“If you torture the data long enough, it will confess to anything."
-Ronald Coase

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Alan Browne <bitbucket@blackhole.com> wrote:

Not sure that I have. Did you get a more accurate reading?

Maybe not...

Just woke up the compass, it reports north as the way the phone is facing
(as in away with the home button close). That happens to be roughly correct, but the "compass card" is stuck (doesn't rotate as I rotate the phone) and there's no prompt to unstick it.

Went back into settings > compass and turned off the true north setting.
No change, the display is still stuck at 358 degrees. The phone is still
in airplane mode with WiFi and location services off. I'm indoors and my
cell service is voice only, no data. Still, the magetometers should work....

Thanks for writing,

bob prohaska


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On 2023-09-17 02:37:02 +0000, bob prohaska said:

Alan Browne <bitbucket@blackhole.com> wrote:

Not sure that I have. Did you get a more accurate reading?

Maybe not...

Just woke up the compass, it reports north as the way the phone is facing
(as in away with the home button close). That happens to be roughly correct, but the "compass card" is stuck (doesn't rotate as I rotate the phone) and there's no prompt to unstick it.

Went back into settings > compass and turned off the true north setting.
No change, the display is still stuck at 358 degrees. The phone is still
in airplane mode with WiFi and location services off. I'm indoors and my
cell service is voice only, no data. Still, the magetometers should work....

Thanks for writing,

bob prohaska

One of numerous Google search suggestions:

How to Fix Compass App Not Working on iPhone
<https://youtu.be/oxZV7CmHMsk>

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badgolferman <REMOVETHISbadgolferman@gmail.com> wrote:

bob prohaska <bp@www.zefox.net> wrote:

I turned on the compass utility on my old iphone6. It asked me to roll
a ball around a circle, which I did, then it asked me to turn off airplane >> mode or turn on WiFi. I did both, but the compass didn't find north.

Both questions surprised me. I always thought the compass used some sort of >> internal magnetometer and the ball-rolling was to establish a vertical datum.

What does the compass actually use to find north?

Thanks for reading,

bob prohaska

I don’t know how it works but I found it to be quite useful in setting up my rooftop OTA antenna.

The elevation feature is useless though. Mine says my elevation is 20 feet, yet I know where I’m sitting is 8.5 ft above sea level because I had to have it surveyed for FEMA certification so I could get my flood insurance premiums lowered.

Makes me wonder if the compass is correct now…

Today I looked at the Compass app again and now it’s reporting my elevation as 10 feet which is correct. The survey I had done reports the floor in my
den as 8.5 ft and I’m sitting down with the phone in my hand so that
accounts for the additional 1-2 feet.

I wonder why there is such a discrepancy between today and the other day. I haven’t done anything to the settings.

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On 2023-09-16 22:37, bob prohaska wrote:

Alan Browne <bitbucket@blackhole.com> wrote:

Not sure that I have. Did you get a more accurate reading?

Maybe not...

Just woke up the compass, it reports north as the way the phone is facing
(as in away with the home button close). That happens to be roughly correct, but the "compass card" is stuck (doesn't rotate as I rotate the phone) and there's no prompt to unstick it.

Went back into settings > compass and turned off the true north setting.

You want to leave it in Mag North - that way it does not have to know
its position to compute the mag var.

Also, do the procedure I outlined a couple posts back. Takes a minute.

No change, the display is still stuck at 358 degrees. The phone is still
in airplane mode with WiFi and location services off. I'm indoors and my
cell service is voice only, no data. Still, the magetometers should work....

Try it outdoors if you can - that way the GPS can update properly - and
then True North should also work.

As Your Name suggests (indirectly), restarting the phone may also help
(don't bother with the video).

--
“If you torture the data long enough, it will confess to anything."
-Ronald Coase

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