# fluxgate compass, auto calibration, some math

• posted

It proved tricky to get 100 % correct calibration of the mag_pic fluxgate compass. And even then there is some thermal drift from day to night.

For something that actually moves, like a compass on a boat for example, it is possible to do auto-calibration that eliminates any offset and gain differences for the x and y channel. ( East West and North South channel). For those interested I found a nice website with a pdf that describes the math needed for auto calibration:

They have different kind of sensor for sale, and I am working on how those are designed, seems to me those sensors use a magnetic bias, as they are lower in frequency for north and higher for south sort of thing. Maybe just an LC oscillator with DC flowing in the coil around a high permeability core, Ic then provides the bias (wild guess). I did some lab test, I can make my own, but not get their sensitivity (yet). Anyways the 'auto calibration' procedure is universal, and I could not resist to try to write the C code. It has some interesting mathematical stuff in it, like Gaussian elimination for a n x n matrix, I found on some site. The C code now works with (their) test vectors, and parses mag_pic output, but is not finished in any way, but may be of interest to some.

• posted

On a sunny day (Wed, 15 Jun 2011 19:33:58 GMT) it happened Jan Panteltje wrote in :

compass.

differences for the x and y channel.

needed for auto calibration:

designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild

to try to write the C code.

a n x n matrix, I found on some site.

• posted

compass.

differences for the x and y channel.

needed for auto calibration:

designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild guess).

to try to write the C code.

a n x n matrix, I found on some site.

My Audi has an 8-point compass (as in "NW") in the mirror. The manual says I'm supposed to occasionally push some buttons and then drive around in a circle a few times to calibrate it.

Probably a few more hundreds of thousands of lines of code. I wonder how much code I'm actually hauling around in this thing.

John

• posted

On a sunny day (Wed, 15 Jun 2011 13:38:38 -0700) it happened John Larkin wrote in :

compass.

differences for the x and y channel.

needed for auto calibration:

designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild

to try to write the C code.

for a n x n matrix, I found on some site.

LOL

More every year I am sure.

• posted

compass.

differences for the x and y channel.

math needed for auto calibration:

are designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild

to try to write the C code.

for a n x n matrix, I found on some site.

He's probably got automatic updates disabled, so it should stay the same year on year.

• posted

compass.

differences for the x and y channel.

needed for auto calibration:

designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild guess).

to try to write the C code.

for a n x n matrix, I found on some site.

The iphone regularly pops up a message to "wave the phone in a figure of eight pattern" to calibrate the compass.

Like I'm going to do that in public...

```--

John Devereux```
• posted

compass.

differences for the x and y channel.

math needed for auto calibration:

are designed,

for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild guess).

to try to write the C code.

for a n x n matrix, I found on some site.

My Garmin asks me to slowly turn a few times (outside, away from ferromagnetic influences). Maybe if you scratch a pentagram in the dirt and step inside first it might get some attention?

• posted

On a sunny day (Thu, 16 Jun 2011 07:01:52 -0400) it happened Spehro Pefhany wrote in :

compass.

differences for the x and y channel.

math needed for auto calibration:

are designed,

frequency for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild

resist to try to write the C code.

for a n x n matrix, I found on some site.

I ment every year when a new car model comes out, more electronics. I do not like 'automatic updates', one of the reasons I burned my xp disk. I did read Firefox now also auto-updates, a bad idea.

• posted

On a sunny day (Thu, 16 Jun 2011 16:34:03 -0700 (PDT)) it happened " snipped-for-privacy@sushi.com" wrote in :

I do it this way (did, no correction ever needed normally): I select a suitable satellite, tune the right transponder and polarity (horizontal versus vertical) and set the symbol rate, select all PIDS mode for that transponder (get the whole transponder). You can get these things like sat position, transponder, frequency, polarisation, and symbolrate from many websites

for Europe is what I use). Activate the 'beep' modus on xdipo[1] (beeps wit ha higher pitch the stronger the signal). It is PC speaker beep, so I put a mike in front of it and amplify it with the hifi so I can hear it outside. Then I preset the motor of the motorised dish to the degrees of the sat I look for (motor has 2 buttons on it to move it). I loosen the bolts on the dish a bit so I can move it by hand, get the right elevation from the xdipo calculator, set it on the scale on the dish. and then move it around east to west listening for the beep. Adjusting the elevation a bit after each horizontal scan, scan the air like old analog TV scanning:

-------

-------

---.----

---*----

Here there are so many fields around, it is difficult to find a non magnetic place. Especially with a cellphone in you pocket. Throw it away!

[1] xdipo:
• posted

I have released version 2 of the auto calibration C program. It actually is now fully functional, and shows corrected output. It expects you to rotate the compass, and when it finds 4 data points (angles) that are far enough apart then it will use those values for calibration, and starts outputting the corrected heading in a log file format.

Website:

Program:

All still work in progress.

It should work with any device that outputs x and y values for north and south in the right format. You could lift the 'auto_calibrate()' function out of it no problem, but call it with a delay between each call, so the user has time to rotate the compass enough for calibration! Else you get milli degrees or some very small angle and the program will not accept (4) angles that close together, that would give very inaccurate results. Now I have the idea to put that delay in the program while it is in calibrating mode ... OK next version.

• posted

orizontal versus vertical) and set the symbol rate,

isation, and symbolrate

nger the signal).

the hifi so I can hear it outside.

look for

the dish.

ke old analog TV scanning:

to.

IIRC.

....

ng...

vbnet

ind it under driver ... apps/).

.

em is crap

tic place.

The trouble is on ku, there are often identically configured signals. That is, you park on the exact info as you mentions, you can still get the wrong bird. I'm really really good with the cammenga. ;-) I've used it in DFing transmitters. I also use it to get bearings on distant objects. With GPS coordinates and a good bearing, you can often find the spot on google earth or a topo map.

I have some USB satellite receivers. PC connection is the only way to go for satellite. I am just amazed at how cheap the gear is given the level of technology. Then again, a uP is a cheap bit of high tech gear.

As you probably know, there is quite a bit of linux software out there for data stream analysis. You can also make the videolan player decode a satellite if you use command line parameters.

• posted

orizontal versus vertical) and set the symbol rate,

isation, and symbolrate

nger the signal).

the hifi so I can hear it outside.

look for

the dish.

ke old analog TV scanning:

to.

IIRC.

....

ng...

vbnet

ind it under driver ... apps/).

.

em is crap

tic place.

Nobody would use satellite internet if they had a wired scheme available. The only subscriber I know has a motor home. You should try Skype over satellite. Might as well use the word "over" like in HAM comms.

In rural areas, I see a lot of Ka band gear for instrumentation, i.e. telemetry. These guys could care less about the latency. There is always a GPS antenna on the box for timing, so they just time stamp the telem data.

In the US, a lot of gas stations run satellite data systems. This always seemed overkill to me, but perhaps the system predates the internet. Does Chevron really need to count it's money second by second?

• posted

On a sunny day (Fri, 17 Jun 2011 14:49:20 -0700 (PDT)) it happened " snipped-for-privacy@sushi.com" wrote in :

Yes, that is why I wrote, that I then select some PIDs for an actual TV channel, and see if that works..

I have a compass somewhere, had one in te hcar too. Used it once at night when I was lost to find approx. north... Kept driving until the next directio nsigns. The Netherlands is so small that you will cross a main road with a sign within ten minutes :-) VERY difficult to get lost here.

I agree, I have 2 PCI cards, old SkyStar1 (hardware mpeg2 decoder, also has analog TV out), and a Hauppauge win nova. The last one delivers true .ts, the first one has a TI chip that makes .pva format and is not usable for hacking streams.

Well, the new system we have now, DVB-S2, is really at the edge of the Shannon limit. I do not have one yet (but I think my Samsung HD TV has a cable S2 decoder, not sure). Most HD stations here now use DVB-S2. Personally I do not give a dime about HD TV, but as monitor it is cool t odisplay an xterm on it with teh smallest font. That TV has 3D too, but I have declined to buy a 3D DVD player or write the soft for it until now. No good movies in 3D yet.

The Videolan player is one of those pieces of softwar I never could get to work on my system. Either did not compile, or just did not work, last time I tried was some month ago.

I think my own stuff is much better, I pipe the streams through little programs I wrote,for example teletext display xvtx-p ^ teletext pages | satellite -> xdipo -> jpfilter -> jpvtx -> xine eye several PIDS program related PIDS audio vide PIDS ear or program ID

Becaue from xdipo it is all stdout to stdin of the next 'filter', you can make a script that combines things to do anything you want. And you only need to write small modules, not modify a huge piece of code. It is the 'Unix' way.

For terrestrial I have 2 Hauppage USB receivers (on in use, the other in storage). Those even work with the eeePC. TV on the eePC :-) Had to install a separate kernel for that (dual boot),

What I would like to find is a cheap DVB-T modulator (chip or unit) for the home network.

• posted

It's for credit/debit card authorization. The store is effectively down when it is down.

-- Les Cargill

• posted

fluxgate compass.

example,

gain differences for the x and y channel.

the math needed for auto calibration:

those are designed,

frequency for north and higher for south sort of thing.

permeability core, Ic then provides the bias (wild guess).

(yet).

resist to try to write the C code.

elimination for a n x n matrix, I found on some site.

output,

I'll bet that there is over 100 KLOC in the radio alone. Maybe that much in the heater-defroster-A/C as well.

--

• posted

Pefhany

Larkin

fluxgate compass.

example,

gain differences for the x and y channel.

describes the math needed for auto calibration:

those are designed,

frequency for north and higher for south sort of thing.

high permeability core, Ic then provides the bias (wild

sensitivity (yet).

not resist to try to write the C code.

elimination for a n x n matrix, I found on some site.

output,

disk.

It is on by default. It even tries to shove Firefox 4 at an old Win98 laptop i have; where it just won't work or even install properly. I always cut updates back to notify only.

--

• posted

hannel,

ithin ten minutes :-)

as analog TV out),

va format and is not usable for hacking streams.

annon limit.

r, not sure).

odisplay an xterm on it with teh smallest font.

he soft for it until now.

o work on my system.

month ago.

ograms I wrote,for example

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0tele= text display

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0xvtx=

-p =A0

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= ^ teletext pages

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= |

=A0-> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0jpvtx =A0 =A0 =A0 =A0 -> =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 xine =A0 eye

=A0 =A0 program related PIDS =A0 =A0 =A0 =A0 audio vide PIDS =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 =A0 ear

make a script that combines things to do anything you want.

.

storage).

he home network.

Your own modulator? Hell if I know, but let me know if you find one.

I've never compiled videolan. I just use the repository. It's not that I never compile programs, but rather I try the repository versions first. A great deal of the time, they do the job.

Videolan is simply amazing if you study all the tweaks it can do. You can even rip DVDs with it.

• posted

That makes sense. I gather there is one satellite that handles all the major bank cards, or does the satellite go back to say Chevron HQ and then they farm out the requests?

• posted

On a sunny day (Sat, 18 Jun 2011 11:11:31 -0700 (PDT)) it happened " snipped-for-privacy@sushi.com" wrote in :

Well OK, maybe I will try a binary again one day. But rip DVDs?????? Do you know you can just do: cat /dev/dvd > image.iso?

Burn it again to an other disk like: growisofs -speed 3 -Z /dev/dvd=image.iso as many times as you like

Check for any write errors, full byte by byte compare: dvdimagecmp -a /dev/dvd -b image.iso

mplayer IIRC plays dvd, and will dump audio and video with the -dumpaudio or

-dumpvideo flag.

I sometimes use mplayer. transcode will also rip video, see man transcode, and make it into any format and size you like, great for youtube, and for my portable media player that wants xvid, my cellphone 3gp videos are made with ffmpeg... mplayer is partly based on ffmpeg. For the difficult things I use the mjpegtools, including the filters I wrote for that. Transcode has filter subtitler (that I wrote) mjpegtools has subtitler-yuv (that I wrote), Both are full picture manipulation programs (can do animation), If you want to author dvd you can use DVDauthor, I contributed the subtitles and multiple audio to it :-) tcmplex-panteltje is a multiplexer with DVD output. More here:

and for DVD specifically:
Been ten years or so since I wrote that stuff, it lives on in many 'derivative works'. Was fun. I still use it.

• posted

It's the usual satellite data backhaul arrangement - there's nothing "credit card" about it. 20 years ago, it was just any sort of thing over X.25, at least for Amoco ( which may have been bought by Chevron - not sure ). A T1 then it was a heck of a lot - if you could get it at all out on an exit off I95 or something.

There's a local "Race Track" store I trade at quite a bit, and when they lose their backhaul, they are *down*. Nobody much uses cash any more. Last time this happened, they said "It's the modem again", which surprises me - I'd bet on the media over the modem.

-- Les Cargill

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