BARACUDA-Legend-1

[Qiaozhi]

Well, I finished up the Barracuda project today and took it for a walk. It works fantastic!

I did have several problems that I needed to overcome though.

1. Point circuit prevents setting threshold correctly (omitting Q5 solves this problem)

2. The Barracuda is too sensitive to coil movement (through earths magnetic field).
I attempted to replace Q3, Q4 and 1k Ohm resistors with matched sets and the problem got worse!! More sensitive!! The only solution I could find was to reduce the value of R25 (1M Ohm resistor around U2) to reduce the gain a little. This solved my problem completely. Performance is now about the same as the Surf PI project. Oh well, such trade-offs Anyone else run into this one?

Don

To eliminate the effect of the Earth's magnetic field, you will need to add a secondary pulse sample (taken much later in the pulse decay cycle) and subtract this from the main sample. Have a look at the Hammerhead article.

[maikl]

Hi dfbowers. Nicely done detector. Have you had a problem only in salt water or everywhere? Did you put a shield and that (graphite, aluminum tape ...)?

[dfbowers]

To eliminate the effect of the Earth's magnetic field, you will need to add a secondary pulse sample (taken much later in the pulse decay cycle) and subtract this from the main sample. Have a look at the Hammerhead article.

Hi, Qiaozhi.

I was thinking that is what Q4 is for. It's a later sample into the non-inverting pin of U4a. If I monitor pins 2 & 3 of U4 they both swing the same way when moving the coil. But, a fast decaying signal does not show up on pin 3.
Don

[dfbowers]

Hi dfbowers. Nicely done detector. Have you had a problem only in salt water or everywhere? Did you put a shield and that (graphite, aluminum tape ...)?

Maikl,

I have not tried at the beach yet. I used metallized Mylar for shielding material.

[dfbowers]

hello don

"Performance is now about the same as the Surf PI project"

the most and also me get little better results as surf pi i think you could get 2-3cm more than surf pi with very little threshold sound and coil from insulated litz wire
i couldn´t reach the same with such coil at surf pi
try- i think you will not regret it

regards

As built per Silverdog's kit, it does get 2-3 cm more than the Surf PI kit. I used 7 strand silver wire with a teflon skin.

[Qiaozhi]

Hi, Qiaozhi.

I was thinking that is what Q4 is for. It's a later sample into the non-inverting pin of U4a. If I monitor pins 2 & 3 of U4 they both swing the same way when moving the coil. But, a fast decaying signal does not show up on pin 3.
Don

To be honest, I've not paid a lot of attention to the Barracuda circuit. But now I look at the schematic more closely, I think you are correct. Can you measure the delay time for each sample? i.e. monitor the gate signal for Q3 and Q4. The secondary sample (Q4) needs to be made significantly later than the main (Q3) sample.

[Tepco]

Well, I finished up the Barracuda project today and took it for a walk. It works fantastic!

I did have several problems that I needed to overcome though.

1. Point circuit prevents setting threshold correctly (omitting Q5 solves this problem)

2. The Barracuda is too sensitive to coil movement (through earths magnetic field).
I attempted to replace Q3, Q4 and 1k Ohm resistors with matched sets and the problem got worse!! More sensitive!! The only solution I could find was to reduce the value of R25 (1M Ohm resistor around U2) to reduce the gain a little. This solved my problem completely. Performance is now about the same as the Surf PI project. Oh well, such trade-offs Anyone else run into this one?

Don

Neither Surf or Barracuda detectors are sensitive enough to detect movement in Earth's magnetic field, even if they do, electrostatic shield will not help at all.
Most probable source of problem is either local EM interference, or mechanically unstable (microphonic) coil. Try it outdoors, on battery power, and coil must be mechanically sound enough, when you tip it, no response should be produced.

Issue whit static mode try to solve this way: remove R25 and short it, increase R37 to 1M (i don't have working board at hand, let someone try this, just an idea)

Surf and Barracuda are similar detectors, same "system gain" but different timing and time constants, changing few component values can turn each into another.
Best regards

[dfbowers]

Neither Surf or Barracuda detectors are sensitive enough to detect movement in Earth's magnetic field, even if they do, electrostatic shield will not help at all.
Most probable source of problem is either local EM interference, or mechanically unstable (microphonic) coil. Try it outdoors, on battery power, and coil must be mechanically sound enough, when you tip it, no response should be produced.

Issue whit static mode try to solve this way: remove R25 and short it, increase R37 to 1M (i don't have working board at hand, let someone try this, just an idea)

Surf and Barracuda are similar detectors, same "system gain" but different timing and time constants, changing few component values can turn each into another.
Best regards

Here's the thing that makes me believe that it's the earth's magnetic field:

If I orient the coil parallel to the ground and wobble the coil east to west (as if the coil were mounted on a North to south pointed axis) , very little noise. North to south wobble is noisy. It's the same indoors or outdoors.

[maikl]

In earlier posts, was asked why Q3 and Q4 are "not paired" the original Barracuda. So the answer: because of the influence of magnetic field of the Earth.

[Vortxrex]

Bravo ....Apberg and thank you for your work it is good in Geotech to help and experiment all kind of PI ....
If you find a Tip 127 : you will see a different kind of result !!! in the response in audio mode that you can distinguishing a little the iron response over the gold and silver response "a must for this time".......(for the most slow delay i think) ...
like you see with a good coil (450uH and 1R5 ) to mach exactly the original the damping resistor (330R)..... BARACUDA will be THE winner in performance to many other ACTUAL PI detector ....
See also the switch name Sw1 for the Fet Q5 ....and have you noted the "smooth " threshold adjust !!!
Also in the original board the Fet Q3 and Q4 are not matched one is 5485 and the other is Mpf 102 perhaps is for something ??? or this day they do not have stock but i was thinking why they did not place 5485 for Q7 and have Q3 and Q4 the same MPF 102 ??'
Have a good time
Alexis.

Isn't this the whole secret to how the Barracuda can discriminate ??

[Qiaozhi]

Isn't this the whole secret to how the Barracuda can discriminate ??

The Barracuda does not provide ferrous / non-ferrous discrimination, if that's what you're referring to.

[TH Jim]

DON I HAVE HAD THIS EXACT SAME PROBLEM WITH A SURF PI!!!!!

It turned out to be a digital radio transmitter on 212MHz hidden away on the roof of a hotel near the beach I work!!! Five miles further up the coast it works beuatifully - no problems at all.

Hope this helps,

Jim.

[dfbowers]

DON I HAVE HAD THIS EXACT SAME PROBLEM WITH A SURF PI!!!!!

It turned out to be a digital radio transmitter on 212MHz hidden away on the roof of a hotel near the beach I work!!! Five miles further up the coast it works beuatifully - no problems at all.

Hope this helps,

Jim.

My problem suddenly disappeared!! I have no idea where it was coming from but was directional. I incorrectly thought it was the earth itself, but now the Barracuda works great..

[Vortxrex]

The Barracuda does not provide ferrous / non-ferrous discrimination, if that's what you're referring to.

OK, now I am confused.... I thought the Barracuda does have some discrimination abilities related to the audio tone ?

Dave Frank

[Vortxrex]

DON I HAVE HAD THIS EXACT SAME PROBLEM WITH A SURF PI!!!!!

It turned out to be a digital radio transmitter on 212MHz hidden away on the roof of a hotel near the beach I work!!! Five miles further up the coast it works beuatifully - no problems at all.

Hope this helps,

Jim.

I tested my Surf PI (s) at the beach last spring (Oregon Coast) and I had some interference problems where to detectors would sound off when the coil swung in a certain direction.