fluxgate, some more experiments

Did some more experiments to see how I could interface a fluxgate coil assembly the best way to a microprocessor.

The original idea was to drive the 'drive coil' from between 2 pins of a PIC. The problem I ran into is that you need to drive the core into saturation, and that saturation point depends on a lot of factors such as permeability of the core material, and those factors have this tendency to change, So that sort of rules out driving from software with a *fixed* frequency. Of course I was appalled by the large number of analog components in designs I have seen, used mainly to generate sampling pulses for analog switches (in abundance too). So anyways trying to solve the constant saturation point problem, I considered using the PIC's comparator to, in an interrupt, switch the polarity of the drive voltage, the comparator used as current peak detector as in any switch mode. But the PIC also proved to not be powerful enough to drive the 100 mA or more current into the coils... So I needed 2 drive transistors anyways, But then why not leave it free running as in 'multivibrator'? Everybody seems to do that. So, OK, but then what to do with my nice peak current detector idea? Well that proved to be a stroke of genius (tm). By simply using a PNP in the supply to 'feel' the current peak that happens every half period that the core goes in saturation, and a simple resistor, you get a nice very small sample pulse EVERY HALF PERIOD, and then you only need ONE analog switch per channel (x, y, or z axis). Sensitivity proved absolutely great, stability too, added 22x gain with a LM324, output swings between +5 and 0 V for a magnet rotating north to south 20 cm away. I added a lowpass after the sample and hold cap to filer out some ripple from the multivibrator, but this likely can replace the sample and hold too. The PIC can make 1/2 U as 'zero' as there is only a +5V supply (PID has a programmable DAC output on pin 19), saves an other 2 resistors. So I think I have a working circuit, LCD works too, ADC software can be used from my other projects. Now for a real PCB and the other channel[s] (only tried North South). No complicated diodes and RC differentiators to get sample pulses, only ONE

74HC4053 for 3 axis, only ONE quad opamp (one for 1/2 supply voltage buffer, other three for x, y, z gain), And a 7805 for supply, NO SWITCHER, that magnetic field would cause havoc.

End of report.

DANGER DANGER PICTURE OF HAND DRAWN CIRCUIT DIAGRAM, LOOK AT YOUR OWN RISK.

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Filed under Usenet patent 001011110110ZZ fluxodecimal. Prior art you have seen it here,

All rights reserved. Donutted into the public (domain). Burn before reading.

Reply to
Jan Panteltje
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Sounds good as a learning experience. Is it cheaper and/or better than the Honeywell HMC6352 three axis magnetometer, eg from Sparkfun at under $30.00 ?

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Regards,

Adrian Jansen           adrianjansen at internode dot on dot net
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Reply to
Adrian Jansen

have seen,

polarity of the

mode.

current into the coils...

to do that.

every half period that

sample pulse EVERY HALF PERIOD,

LM324, output swings between +5 and 0 V

the multivibrator,

programmable DAC output on pin 19),

from my other projects.

74HC4053 for 3 axis,

z gain),

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Dear J.P.: that drawing has very low contrast; getting near Y rating; i spiffed it up some; see ABSE "fluxgate, some more experiments RESPONSE to J.P.".

Reply to
Robert Baer

On a sunny day (Mon, 23 May 2011 09:14:25 +1000) it happened Adrian Jansen wrote in :

Mine is cheaper (all parts in the box), can be reprogrammed, can be extended to 3 axis, can be made more sensitive (they give no sensitivity), is actually visible to the naked eye, will have a nice LCD display with heading in degrees, has RS232 interface (for control of a ship for example), etc etc etc, and the educational value is priceless. For the Usenet patent I expect to get a trillion. And diagrams like this sell for 25 $ or more these days :-) It is a win-win situation :-) And mine is in a nice transparent box.

Reply to
Jan Panteltje

On a sunny day (Sun, 22 May 2011 22:35:03 -0700) it happened Robert Baer wrote in : Dear J.P.: that drawing has very low contrast; getting near Y rating;

I love to see it, but no abse here. Anyway that can go on a website?

Reply to
Jan Panteltje

Tell me the "secret" of posting on some convenient and free site; will be glad to comply. Actually, if you could scan, rather than photograph the schematic, that would be far better.

Reply to
Robert Baer

On a sunny day (Mon, 23 May 2011 23:19:58 -0800) it happened Robert Baer wrote in :

You could email it to me, panteltje a t yahoo d o t com then I can put it on my server next to the original painting.

I would have to boot up win 88 for my Canon scanner.. trying to avoid that. And it is way to much work for every sketch I make:-) Already the diagram changed on a few points, to be more precise, after switch S1 now 1 k and 470 nF to 1/2 Ub (other side of NW coil), so the 10 nF cap and 22 k low pass are gone. I added a 470 nF between output and - input of the opamp, so integrator, to filter out some 50 Hz ripple here. I increased the op amp gain by changing the resistors to (IIRC) 22 k and 820 k, higher values to reduce load on the 1/2 Ub buffer, wired up the PIC ADCs, moved the whole thing from the lab to my living room so I can program it now in the evening at home. One important thing is the 470 nF cap to ground via 1 k after the switch. I was scoping the output and observed very slow variations, irregular. After thinking I was detecting the movement of earth's metallic core (LOL), really, found out that it was simply leakage effect in that 470 nF (I think those are ceramic) caps. I solved it by reducing the voltage over that cap by not connecting it to ground, but to the 1/2 Ub point. It seems one should test some caps, I tried a 1 uF MKH and that worked fine, but took a long tome to charge (ages). So a smaller but better cap should be tried too. Avoid ceramics, they suck in many ways. It is VERY sensitive, I now know that my cellphone has a magnet in it, and there is a steel bar under my desk... You can align it NS by turning it until the output is at zero... even with one coil, of course N and S could be reversed but then sun is always south here. I have an extremely precise reference to test it against, my motorised satellite can me moved to point to many satellites, for example: Europbird 9A 9 E Hotbird 13 E Astra 1 19 E Astra 3 23.5 E BADR2 3 25.8 E Arabsat 3A 26 E Astra 2 28.2 E Eurobird 1 28.5 E Sesat 36 E Hellas 2 39 E I use my own software to control the disk:

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Note that for example '13 E' stands for 13 degrees eat of due south. All sats are good for less than a degree in normal circumstances (they do drift a bit).

So, anyways things are constantly changing, I just grab in the box looking for some component 'this will do', so there is a chance factor too. It is fun that way.

Reply to
Jan Panteltje

imageshack.com Select file, click upload, copy the resulting URL into your posting. How much easier could it be?

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Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
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Reply to
Nico Coesel

Or Photobucket.

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Sign up, log in, click "upload now" then click "Select photos and videos" Then go to My Albums this will have thumbmails of all the pictures you have saved. When I'm going to upload a picture I usually save it to my desktop, that makes the file easier to find after I click "Select photos and videos" Mikek

Reply to
amdx

of NW coil),

ground,

south here.

satellite can me moved to

drift a bit).

Done; 2 versions sent.

Reply to
Robert Baer

On a sunny day (Tue, 24 May 2011 22:00:17 -0700) it happened Robert Baer wrote in :

The most enhanced version is on the site now:

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Thank you.

Reply to
Jan Panteltje

Jan Panteltje a écrit :

You should shot your scope pics on axis or you'll be having time warps problem soon :-)

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Thanks,
Fred.
Reply to
Fred Bartoli

On a sunny day (Sat, 28 May 2011 08:16:58 +0200) it happened Fred Bartoli wrote in :

The reason I took from an agle is that otherwise you'd see nothing but reflexions. I will not comment on timewarps at this moment.

Reply to
Jan Panteltje

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