maemo.org - Talk - Programming digital compass

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Re: Programming digital compass

Quote:

Originally Posted by gerdich (Post 981976)

I've spoken about the RECEPTION of electromagnetic fields.

Please describe the nature of this influence on reception that you are claiming and provide an example.

Quote:

Originally Posted by gerdich (Post 981976)

I've got to be more precise:
In the oscillators of the receiver and transmitter there are electrons moving.
Their movement is not only determined by the electro-magnetic field of the radio wave but also by the magnetic field of the earth (superposition).

In any case, what differences in the sound do you expect?

You do know that the volume of audio derived from an FM signal is based on the frequency of the signal and not its amplitude? (FM vs AM)

What is your proposed test signal, and how will its received (final audio) form change as the orientation in the Earth's magnetic field change?

Re: Programming digital compass

Quote:

Originally Posted by Flynx (Post 981986)

Assuming you are tuned to a frequency of 87.7 mhz, you would have to spin the N900 at an rpm of 87,700,000. For reference, that is 551,034,887 rad/s.

The RPM you have in mind is 60 times what you have written.

Re: Programming digital compass

Quote:

Originally Posted by javispedro (Post 981983)

Use any radio player app and "arecord" or parec. And good luck...

Not just any app...

AM I right in thinking you're the author of the c fm radio app? I installed it the other week, but haven't got round to using it due to misplaced headphones. Then it just so happened that I was messing about trying to get a webradio shortcut on my desktop and by mistake I put cfm Radio there (it has a title of Radio on the desktop shortcut).

Anyway the point being when I pressed the shortcut, cfm is the only app that actually plays the white noise when no headphones are attached. The others out there just mute it.

So have a go gerdich, install cfm radio and see if your hypothesis works. For the record I had a scan through the frequencies without an antenna, and couldn't pick any signal up. Maybe you could take your device near to the local radio station mast and walk round it to see if it really is imperative to have the antenna.

Re: Programming digital compass

Quote:

Originally Posted by Flynx (Post 981986)

I'm not sure the FM receiver will be sensitive enough to detect the magnetic field of the earth. But you can test it.

Tune the FM receiver to a frequency where there is no radio station (static).

Start recording from the FM receiver.

Now, SPIN the N900 at a frequency that corresponds to the FM frequency you are tuned to.

The FM receiver should see the magnetic field of the earth oscillating (because of relative motion) at the FM frequency it is expecting and you should hear a tone.

Assuming you are tuned to a frequency of 87.7 mhz, you would have to spin the N900 at an rpm of 87,700,000. For reference, that is 551,034,887 rad/s.

At those speeds, the N900 would experience G-forces on the order of 789-million Gs (assuming radius of about 10cm).

Be sure to let us know how it goes :)

I think it would definitely make some noises apart from the FM white noise, but probably not a pure tone, and not from the speakers :rolleyes:
For a point of reference, I reckon (assuming the N900 is more or less infinitely strong) it would take around 36TJ to get it to that speed, or around half the energy released by the A-bomb dropped on hiroshima.
(0.5*1/12*0.181*(0.1109^2+0.0598^2)*551034887^2=3.64e13)

To the OP: Good luck. I think you'll need it :)

Re: Programming digital compass

@Javispedro
Arecord was also my first idea.
But arecord -L gives me only -null and -default (probably mic).

mplayer is not compiled with ://radio support.

For the moment I am downloading vlc.....

The radio applications want an external antenna. That's not what I need.

Quote:

Please describe the nature of this influence on reception that you are claiming and provide an example.

Electrons are particuls with negative charge. They react on magnetic fields (e.g. Tube of brown.)

AM or FM is no question for me. I don't know the nature of the deformation. I know the difference since I had 8 years.

Re: Programming digital compass

.... but I didn't read exactly.

If cfm works really without external antenna, I can arecord from standard output.

Re: Programming digital compass

Quote:

Originally Posted by gerdich (Post 982048)

.... but I didn't read exactly.

If cfm works really without external antenna, I can arecord from standard output.

I don't know for sure, but you get the white noise and it turns the bluetooth on. Install it and see. Do you have another n900 or Itrip handy? If not your local radio station should have a mast which might be picked up if you get close enough.

Re: Programming digital compass

Quote:

Originally Posted by gerdich (Post 982024)

But arecord -L gives me only -null and -default (probably mic).

AND radio comes through mic. :p

Re: Programming digital compass

I did a quick ask-around to people who know much more about radio and electronics than me and the suggestion was that this idea might generate some data but not in any stable way.

An interesting link to follow might be this one:
http://en.wikipedia.org/wiki/Fluxgate_compass

So, to sum it up: electronic/digital compasses are available but to use the FM oscillator in the N900 to do it might prove hard. This would be on account of the FM-transmitters inability to act on really low frequencies.

So any data that would be registered would be overloaded on the FM frequency (as I understand it), in the MHz region, resulting in a violently spinning reading (in the region of 6000 RPM).