Building the Geotech Barracuda Rev A (from silverdog)

[Qiaozhi]

output ne5534 with different values using the dumping tool. in the picture nr 3 i have the best air results. is this signal correct?

[ATTACH]39225[/ATTACH]

Image #1 shows a critically damped waveform.
Image #2 is somewhat underdamped.
Image #3 shows some ringing before it settles down. This signal is very underdamped.
You should use either setting #1 or #2.

It is conceivable that setting #3 may get better results in an air test, but it will all go horribly wrong when you test it in the field.

[Qiaozhi]

Quiaozhi, thanks for the info, I give you some details of my coil. I don't have acess to an scope.

I put details of the coil
Type of coil, mono coil, 10inch diameter, made out of 0.4mm insulated copper wire.
Inductance: 436uH
resistance: 2.67Ohm (What is DC resistance? how do I measure that?)

With an inductance of 436uH, it is very unlikely that the correct value for the damping resistor will be as high as 1k6.
The value you measured for the coil is the DC resistance.

I will buy a small cheap oscilloscope to get the things right, what about this one? I'm sorry if I ask too many stupid questions, as I don't have any idea if what I'm asking is stupid or not xD Thanks for your help and patience

If you need more data of the coil, tell me, I gave you the only information I got out of an lcr meter that I bought.

The scope you linked to only has a single channel. I have no personal experience with that unit, so perhaps someone else can chip in. However, I think you would be better off looking elsewhere.

[azigta]

why do you not want to report us about in CHINESE TOYS? why here? http://www.geotech1.com/forums/showt...2-Chinese-toys

Are you asking me to write a report about what I just bought? Or did I get the message wrong? I don't fully understand, sorry If you are asking me about writing about what I bought and how it works etc, I will do it, for sure

[kt315]

I finally decided to buy a cheap oscilloscope, I bought a JYEtech DSO150, I read someone suggesting this one on this forum, it comes with the smd presoldered. This way I'm sure I will build the metal detector the right way. I had to buy it from the very beggining, but I read very bad reviews about this stuff and I was very unsure, but I ended up thinking what user homefire told me from the beggining, even a bangood is better than no scope... I will post images when I have it working. I'm sure this will speed up the process a lot.

For someone that knows about scopes: I have some cheap multimeter test leads, could I attach them to the alligator clips to bnc converter that comes with the DSO or do I have to buy test leads?

why do you not want to report us about in CHINESE TOYS? why here? http://www.geotech1.com/forums/showt...2-Chinese-toys

[azigta]

I finally decided to buy a cheap oscilloscope, I bought a JYEtech DSO150, I read someone suggesting this one on this forum, it comes with the smd presoldered. This way I'm sure I will build the metal detector the right way. I had to buy it from the very beggining, but I read very bad reviews about this stuff and I was very unsure, but I ended up thinking what user homefire told me from the beggining, even a bangood is better than no scope... I will post images when I have it working. I'm sure this will speed up the process a lot.

For someone that knows about scopes: I have some cheap multimeter test leads, could I attach them to the alligator clips to bnc converter that comes with the DSO or do I have to buy test leads?

[kt315]

output ne5534 with different values using the dumping tool. in the picture nr 3 i have the best air results. is this signal correct?

[ATTACH]39225[/ATTACH]

note resistor value for every pic. N1 is near to a result, but not good.

[ionut_mtb]

output ne5534 with different values using the dumping tool. in the picture nr 3 i have the best air results. is this signal correct?

[azigta]

Just to muddy the waters I like putting the Damping resister in the coil connector. That way every coil is set up it's best for that detector. If you want to use the coil on another detector it's a easy fix. Snip and Replace.

HF

Yes, I noticed that when I had to remove the damping resistor that I had, to install the damping resistor tool. I will put that resistor in the coil connector too. Thanks

[azigta]

Quiaozhi, thanks for the info, I give you some details of my coil. I don't have acess to an scope.

I put details of the coil
Type of coil, mono coil, 10inch diameter, made out of 0.4mm insulated copper wire.
Inductance: 436uH
resistance: 2.67Ohm (What is DC resistance? how do I measure that?)

I will buy a small cheap oscilloscope to get the things right, what about this one? I'm sorry if I ask too many stupid questions, as I don't have any idea if what I'm asking is stupid or not xD Thanks for your help and patience

If you need more data of the coil, tell me, I gave you the only information I got out of an lcr meter that I bought.

[homefire]

Just to muddy the waters I like putting the Damping resister in the coil connector. That way every coil is set up it's best for that detector. If you want to use the coil on another detector it's a easy fix. Snip and Replace.

HF

[Qiaozhi]

Would it be a good idea to set the damping resistor tool as a permanent adjustable tool accesible from the control box just like the delay or threshold pot for when I go to the beach or to the mountain?

Absolutely not.
The damping resistor tool is only required to find the optimum value (critical damping) for that particular coil on your detector, and does not need to be adjusted to suit the ground conditions. Also, the resistors and pot in the tool are only specified for intermittent use. If you fit it permanently, one of the components will more than likely fail.

[Qiaozhi]

With the damping resistor tool adjusted to the best value, that turned out to be 1.614Kohm (I noted the value as accurate as possible with all the digits xD).

Presumably you didn't adjust the damping resistor tool by looking at the preamp output on an oscilloscope?

The value of 1k6 for the damping resistor seems exceedingly high for the Baracuda, and I suspect that a scope would show that it's not critically damped. What are the parameters of your coil? i.e. inductance, dc resistance, diameter, winding topology, etc. An image of the signal at the preamp output would be illuminating, if you can get access to a scope.

[azigta]

Idea is OK, but its proper realization in most cases of very variable terrain situation, can be very time consuming.

There are terrains with very fast changing in soil mineralization and attempt to ongoing settings of damping R was impractical.

This is case of settings, where we need to come to terms with some sort of acceptable settings approximation.

In general, it is better to setup damping R, to one heavy terrain, than to very mild one.

Ok, then I'll set the value testing it on the beach, as that will be what I'm going to be using it for primarily, and if I have some problem on the mountain, then I will find the correct damping value, and put a switch with 2 damping resistors to switch between them for using the detector on the mountain or beach, if it is that much of a variation in mineralization.

[WM6]

Idea is OK, but its proper realization in most cases of very variable terrain situation, can be very time consuming.

There are terrains with very fast changing in soil mineralization and attempt to ongoing settings of damping R was impractical.

This is case of settings, where we need to come to terms with some sort of acceptable settings approximation.

In general, it is better to setup damping R, to one heavy terrain, than to very mild one.

[azigta]

Yes, but this is valid in first line for air setting.

Soil alone, (depend on amount of mineralization), damped target eddy current as well as coil fly-back too,
so damping R at soil max setting, should be different than damping R setting in air.
In mild soil less in highly mineralized more.

Oh, that's interesting... Would it be a good idea to set the damping resistor tool as a permanent adjustable tool accesible from the control box just like the delay or threshold pot for when I go to the beach or to the mountain? I could adjust the damping resistor depending on the mineralization of the ground. As I guess the mountain will be very different from salt watered wet sand, and therefore the damping resistor could be adjusted to perform better on the go, just do a test on the on the field, adjust the damping resistor, and hunt. I plan to go places where I don't know what's like the mineralization of the ground, so Maybe that would be a good idea. What do you think? is it a good idea?