Is my Baracuda operating as expected?

[Frank_Schwab]

Hello Forum,


I’ve assembled a Baracuda Kit from Silverdog and now I’m in the process of setting it up.


The coil I’m using has a diameter of 25cm. It’s made of 0.5mm enameled copper wire with 23 turns (iirc). Resistance is 1.6 Ohms. As I don’t have access to a signal generator I can’t measure the inductivity. Power is supplied by 3 18650 laptop cells.


At first sight it’s seems to be working. I’ve adjusted the offset (middle position of normal potentiometer, no multi turn) in a way that I can detect a 2 Euro coin at around 15cm. I’ve not played with the delay setting yet.


The figures I see on my Oscilloscope are looking different to the ones posted in the forum so I’m wondering if my Bara operates as expected.


Pin 6 of NE5534 is looking like that:


With Pin 2 of 40106 additionally:


Zooming in:



Is that how it is supposed to look like or is there something wrong with my assembly?
Any tips about how to improve (double?) detection performance? I have expected to come a little closer to 30cm....

That's how the board is looking like: and bottom:

Thanks a lot in advance!
Frank

[bernte_one]

Hello Frank,

it can work like this
https://www.youtube.com/watch?v=tnlPWCxfztI

try this
for Offset simple trimmer no multiturn - easier to adjust (adjusting to 0V on ne5534 give wrong results- adjust for best Performance)
delay off-board pot 20k better for field adjustment
treshold off-board pot

main cap not 6800µf or 4700µf better try 2200µf or 3300µf

tip127 or irf9640? use tip127 like in original Setup

damping resistor - it depends on coil resistance and inductivity so try to install a wire pot 5w with a Minimum resistor value in Serie then adjust the wire pot for best results or watch the damping curve on scope shot if you find the best value deinstall the hole Arrangement and measure the total resitance you ahve adjsuted with wire po and the preinstalled ressitor then replace this by the next value you can find of normal resistor e12 or e24 line better some ohms higher than too low

but thank for the scope shots
good luck

[Frank_Schwab]

Hi bernte_one,

thanks for the tipps. Very helpful!

I'm currently using a irf9640. Just ordered a TIP127...

I'll give it a try and post my results when done. But it takes a couple of days...

BR
Frank

[bernte_one]

Hello Frank,

any News about your Project?

[Frank_Schwab]

Hello bernte_one,

I have ordered a TIP127, 2200uF capacitors and a 1k poti and while waiting for them to arrive I was working on the rod and coil housing.

Today I got the TIP and the 2200 capacitor. I’ve also connected an off board delay potentiometer (threshold was already off board and offset was already replaced with a simple trimmer).

But this setup does not show any difference in the behavior. I’ve noticed that the TIP127 runs pretty warm, if not to say hot. I seem to remember that the irf9640 did not get so hot but I might remember that wrongly.

When comparing scope shots of other baracudas (e.g. this one: http://www.geotech1.com/forums/attac...9&d=1309516746 from post #141 of the Baracuda Legend thread in Schematics) with mine, the NE5534/6 signal looks completely different. After the falling edge, the raise of the signal is happening quite fast. Depending on the delay setting, this happens before the raising edge of 40106/2. In my setup the raise of NE5534/6 happens significantly later. See a12.png above.

I don’t know if this causes problems but at least it’s an obvious difference.

Any idea which components are influencing the raise of NE5534/6?

BR
Frank

[Frank_Schwab]

Finally some good news...


During holidays I read "the book" (ITMD). The 2nd edition was available right in time. Thanks to Amazon, it arrived one day before we were leaving


Back at home I've again tried to find the problem (after preparing a better coil). While measuring several several OpAmp outputs etc. I have lifted the coil from the desk and noticed that the picture on the oszilloscope is changing heavily. It was morphing into the the figure I was aiming for:


Stupid me! I should have noticed earlier that there is a metallic construction under the plate of the desk I was working on


So finally everything seems to be working fine.


Only one thing: I've connected a 1k/5W potentiometer as damping resistor. While changing the value one from 200 to 1k I did not notice a change in the oscilloscope picture.

[Qiaozhi]

Only one thing: I've connected a 1k/5W potentiometer as damping resistor. While changing the value one from 200 to 1k I did not notice a change in the oscilloscope picture.

Have a look at page 155 of ITMD (Edition 2), which describes a damping resistor adjustment tool. This is a better solution than simply connecting a potentiometer, as it is quite likely that the pot may be damaged when adjusted to the lower resistance end of the range.

[Frank_Schwab]

Have a look at page 155 of ITMD (Edition 2), which describes a damping resistor adjustment tool.

Yes, I remember the damping resistor tuning assembly. I'm anyway going to order a couple of components in the next days so I'll build one of these tools too.


After a second look at the oscilloscope screenshot, I've noticed that there's still a difference to the other pictures: It takes about 50us until the signal starts raising from the lower saturation to 0V:




In other pictures, this is closer to 20us. This makes more sense as the minimum delay on the original Baracuda was 22us.

Is this difference caused by the coil (e.g. too high capacitance)?
Or is there any other known reason?

Thanks!
Frank

[Qiaozhi]

Is this difference caused by the coil (e.g. too high capacitance)?
Or is there any other known reason?

Thanks!
Frank

I haven't built the Bara, so I don't know what minimum sample delay is expected. However, assuming it's supposed to be around 20us (which sounds reasonable for a beach detector) and your coil is critically damped (or slightly underdamped) then the finger of suspicion points to the coil.

[jladre]

Found something good today.. By using tlo72, irf9640, 6800uF cap., 340-360 uH coil i really improve my depth up to 10cm. Before i able to catch thin and small silver ring at about 22cm but now even at 35 cm whesper and 33cm strong.

[6666]

340-360 uH coil

What size ?

[jladre]

What size ?

22cm.

[Koala]

irf9640 was found to have more depth but lost the crude iron tone. Also on some builds static search does not work.

[jladre]

Anyway the crude iron tone is confusing. Object size and form will be a factor.. For example a silver coil will have a strong sound while nails is broken sound but a coin form iron will also give same response to a silver.