Carl's fluxgate Gradiometer ckt.

[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

[damiafix]

Wow! Good lucky!

All the best, D.

[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

[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 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

[Geo]

Hi Chris.
Here is the schematic....

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.
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 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.

[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.

[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.