Carl's fluxgate Gradiometer ckt.

[damiafix]

Hi Sparky,
from my point of view, it's a great project very useful for understand as a fluxgate mag work, but I think that it's unusable in field, because it's much unstable; moreover the alignment of the sensors is really hard and it's necessary with the temperature variations.

Best wishes.

D.

[sparky]

Did you ever get it going? I was going to buy one of these kits a few years ago but it seemed a lot of people was having problems with it then.
I want to buy one now but am having second thoughts since I hear they are so hard to do the final alignment of the sensors.

[Krzysztof]

Hi Nicole95.7
So. You are right .
I greet in this difficult (MAG) forum.
I use existing algorithm now especially they would enlarge tenderness.
Not touching you expand during calibration the MAG the range of tenderness.
Best regards Chris.

[Geo]

Hi Chris.
Pin 16 has 0.8 to 3.2V, it is about 0.8V bigger than the tension at pin14_15.
So... with 0v ... 2.5V at Pin_14 i have 0.8..3.2 at Pin_16 and about 1.5... 5.9V at pin_4 (output) of the LM3900 (if i will suply with 6V and replace the 820K with 680K). With this tension i have at the out of the CD4046 a signal with frequency 50Hz ... 1800Hz.
It is very good but i don't like the Low frequency (50Hz).
Maybe i will replace it with something else. Maybe a compination between Carl Vco and LM3900 to be the best solution.

Regards

[Krzysztof]

Hi Geo.
Congratulations.
Just write what you have around Pin16. What is the voltage now enters the op_amp?
Normally, the DAC should be something tense between Pin16 and Pin14/15, in the original catalog is a short circuit.
Pin16 is therefore within the limits of 0-2.5 V.
Each additional element (resistor or connector p_n) raises the voltage drop.
Appropriate reference voltage is Pin14/15.
Schodky I suggested two diodes, because the measure zero (I / V) characteristics of the knee voltage (Schokley) have the lowest current polarization. This could keep you in the slightest error signal near zero.
Best regards Chris.

[Geo]

Hi Chris.
Here is the schematic....

Regards

[Geo]

Hi Chris.
I will try tonight or tommorrow to find free time so to draw a schematic of the modifications.
My Gradiometer works opposite from yours. At zero signal i have 50Hz and at max i have 850Hz. I will change the feedback of the DC amplifier so i believe my VCO to run at 1500Hz.

Regards

[Krzysztof]

Hi Geo.
Give a little diagram of your work so you can deal with the problem.
You're right, I believe digital audio to be annoying.
In my zero signal is 4kHz and the max is 16Hz.
But in the beginning when the signal increases, a rapid decrease of 4 kHz to 600 Hz.
You can easily hear the response of the instrument.
At high frequencies can not hear the sharp waveform.
Miniature transmitter(piezo).
I do not totally switch to an analog signal, and therefore such a reversed scale.
Best regards Chris.

[Geo]

Hi.
Damiafix, thank you.
Now i want a simple schematic to remove from the VCO frequency one fixed 40Hz frequency, (something as mixer but without filters). With this way i want to take a minimun frequency 5..10 Hz because the 50Hz that gives (minimum) the 4046 is a little annoying if you hear it for big time.

Regards

[damiafix]

Wow! Good lucky!

All the best, D.

[Geo]

Hi Chris.
Same problems.
At low DAC out the tension on the emmiter of Q1 is low (0.45V).
Anyway, i found a solution. I made a DC amplifier wit h gain about 1.5 and now is OK.
I used a Norton op_amp (LM3900) and now is OK. The VCO (with 4046) works from 0.01V to 2.5V (or 0.8 to 3.5 from pin16) and gives a frequency from 50Hz to 850Hz. I must give it a little more upper frequency and i am OK.

Regards

[Krzysztof]

Hi Geo.
Yes!
But the output voltage from the emitter Q1!
Chris.

[Geo]

Hi Geo.
I see two roads.
1_ Pin16 addition 10Kom resistor to Vcc.
May be problems with the smallest values of tension.
2_ To get the voltage from 1.4 V to your other VCO:
Rather than give the R6 -> 2 diodes in series as above.
Leavin Q1.
Leavin R4 and R5.
1Kom collector of Q1 to Vcc.
Of course, C5, Q2, IC3 disconnected.
Then the emitter voltage of Q1 you have requested.
Best regards Chris.

Hi Chris.
With "Rather than give the R6 -> 2 diodes in series as above" do you mean to replace the R6 with 2 diodes in series??

Regards

[Krzysztof]

Hi Geo.
I see two roads.
1_ Pin16 addition 10Kom resistor to Vcc.
May be problems with the smallest values of tension.
2_ To get the voltage from 1.4 V to your other VCO:
Rather than give the R6 -> 2 diodes in series as above.
Leavin Q1.
Leavin R4 and R5.
1Kom collector of Q1 to Vcc.
Of course, C5, Q2, IC3 disconnected.
Then the emitter voltage of Q1 you have requested.
Best regards Chris.

[Geo]

Hi Chris.
I will try it today and i will inform you

Regards

Hi Chris.
I tried it without results. When the tension at pin 14=0.01 ...1.2 then the voltage at pin16 is 0.6v bigger. If the voltage at pin14 is 1.1v or bigger then the voltage at pin16 is 1.2v bigger. I have the lm393 out of the socket, R6 and R4 are unconnected. I did not unconnect the Q1 and Q2 (is there any problem?).
Any idea??

Regards