Bara sensitive to motion. How to solve that problem?

[Psyborg]

Hello every one.
I read the post where somebody have the same problem but nobody give an answer.
I shielded my coil. Try it outside.
If I adjust threshold pot im losing sensitivity depth. Has anyone have any idea?

[dfbowers]

Hello every one.
I read the post where somebody have the same problem but nobody give an answer.
I shielded my coil. Try it outside.
If I adjust threshold pot im losing sensitivity depth. Has anyone have any idea?

Sensitivity to motion would suggest that your secondary sample is not right as this cancels the magnetic field of the earth. Otherwise, you might have something large and metallic nearby that you cannot see..of course you can rule out #2 by going outside.

[Psyborg]

Can you explain?

If I adjust a barracuda with an oscilloscope,
will this error corrected


?

[kt315]

tell about how you shielded coil and enclosure. where is a point on sh-d connection at pcb.
analogically for enclosure. pics of all stages of shielding too.
why i must draw out this.

[dfbowers]

Can you explain?

If I adjust a barracuda with an oscilloscope,
will this error corrected


?

The Baracuda takes two samples. One set by the main delay and then a second sample much later. The clock signals for each sample are applied to the gates of Q3 and Q4. Then, both samples get passed to U4a (differential amplifier) and one sample is inverted by U4a pin 2. Since the earths magnetic field signal is almost constant over the entire cycle, it get's almost completely cancelled, but since a real target signal decays quickly, the second sample never contains it. This makes it important to have R7 and R8 closely matched so that the differential signals can be equal and opposite when it comes to rejecting the signal generated but the earths magnetic field. The coil from the Baracuda when in motion can act just like the windings of generator passing though a magnet! I don't think you can "adjust" this away but you can at least verify that you are getting both signals to the inputs of U4a. Just food for thought.
Now usually, the signal from the earth will make your Baracuda sound like it is "breathing" as you swing your coil if there is something wrong with the ground cancellation.
Don

[DOOLEY]

just been having another real close look at this version of the barracuda.

more at the sample timing delay part of it.

jpg below to illustrate.

not sure the first 2 delay caps should be joined together,
should the 2nd sample delay cap be AFTER the 1st 40106 ??

similar to the surf Pi arrangement.

also the values of the timing resistors screwed a little.......

original circuit had about 82uS delay to the 2nd sample start,
and a 902uS sample window !!

whereas the 1st sample window was about 3.7 uS

just done rough calculations,
but both sample windows should be the same size.

only a thought, just in case anyone's made the barracuda from this schematic.

[Psyborg]

Hi, here are pictures of previous work. I need to find a solution to the sensitivity of the coil to the movement. Is it problem connected with shielding , or with electronics on board?





I'm nowhere connected shield that is the coil. To shield I used aluminum duct tape. http://www.isover-technical-insulation.com/Products/Marine-Insulation/U-SeaProtect-Alu-Tape

[Davor]

You need to connect shield to Bara ground.

[Psyborg]

My coil have 410mH, magnet wire. Wrapped with electrical tape. At electrical tape is aluminum duct tape connected to neutral pole of battery. Coil air test is very god. I m very satisfied with baracuda, just when i moved around beeps. In air 1 meter over ground beeps. When move only coil (not box with bara ) beeps.

[Qiaozhi]

My coil have 410mH, magnet wire.

Did you mean 410uH?

[Psyborg]

Did you mean 410uH?

Sorry, yes that is correct.

[Psyborg]

So no one had this problem with barracuda?

[Koala]

i have only ever run mine on the bench but seemed pretty stable with no shield at all. Both with solid enameled copper wire or multi strand wire

[Qiaozhi]

Perhaps the Earth Field elimination is not working. That would account for it being ok on the bench (non-moving coil), but beeping when the coil is moved. Does it beep on the bench when a magnet is waved in front of the coil? Of so, then check the EFE part of the circuit.

[Psyborg]

The treshold is set high. I try to swing with small magnet in front of coil and it beeps.On the same length from coil i swing with metal and nothing.
Thanks Qiaozhi, i will now check EFE.