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.

[azigta]

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.


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.

Yeah you are right ... damn I wish I could buy a real scope... Let's see if I can buy one from an institute of electronics, probably not, but I know they have a lot, maybe I can at least do my measurings there, will take lots of pictures if so...

edit: I cancelled the order, it's only one channel and it max voltage is 100vpp. I will try to look for a scope to do the measuring instead of buying one, maybe a friend knows someone, or I can get it tested for me. Can someone post an image of how does a trace look if the resistor is adjusted to its correct value?

[kt315]

Yeah you are right ... damn I wish I could buy a real scope... Let's see if I can buy one from an institute of electronics, probably not, but I know they have a lot, maybe I can at least do my measurings there, will take lots of pictures if so...

edit: I cancelled the order, it's only one channel and it max voltage is 100vpp. I will try to look for a scope to do the measuring instead of buying one, maybe a friend knows someone, or I can get it tested for me. Can someone post an image of how does a trace look if the resistor is adjusted to its correct value?

good book to read to begin from
http://www.geotech1.com/forums/forum...Published-2015

[ionut_mtb]

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.

my coil have 4.2ohms because i use 1.2mm pvc coated wire for the moment. maybe that's why i get so many ringings.

[kt315]

my coil have 4.2ohms because i use 1.2mm pvc coated wire for the moment. maybe that's why i get so many ringings. "critically damped waveform" mean correct? i don't understand.

you must understand the coil has SELF resonance and ringings is exhibition of it.
open your eyes.

[kt315]

[azigta]

Well maybe the original resistor that I putted there, that was 470ohm may not be the best value but I've been testing varying the delay pot and I managed to get good results with the euro coins, I didn't note them down but the 2€ coin was 20cm and the rest of them between 13 and 16. I have to be positive, I have no way to get an oscilloscope for the moment, but the detector works very well with the 470ohm resistor, So I'll move on with that. I'll see how it performs on real ground, but for now I'm going to stick to that value since at least it works decently. Might not be the best, but I'll give it a second thought once I test it on real ground. I'll buy a bunch of 2w resistors going from 200 to 500ohm and test in real ground if this doesn't make it, and I'll do what I can to get it working as nice as I can.

[kt315]

pi detector is more sensitive to ferrous, that 2 euro is from. you must sure clearly grasp which coin from what metal done.
keep a magnet nearly and check them.

[azigta]

pi detector is more sensitive to ferrous, that 2 euro is from. you must sure clearly grasp which coin from what metal done.
keep a magnet nearly and check them.

I also did the test with american 5cent and 1cent and I wasn't disappointed either, can't remember the distances but well, whatever, I'm going to use it primarily for the beach so presumably there will be euro coins, which perform well under the actual condition, and maybe rings. Tomorrow I'll test with a slim gold ring that I have from my grandmother and see how it does. I'll be happy if I detect lots of 2€ coins though xD

[ionut_mtb]

[ATTACH]39226[/ATTACH]

Thank you kt315, i adjusted the dumping resistor like you said and still have good sensibility for targets. Looks more stable now and delay working good. The coil i made is only for quick tests, i will make another. Question: adding 3 more 18650 batteries (paralel) will increase the depth? or this is required only for longer pulses?

Picture of

[homefire]

Adding Parallel battery will do nothing for Depth but sure will help your run time on batteries.

[kt315]

i had gave a pic, very clear pic. i also did show a reaction on metal. are you so blind??

[kt315]

files in P-CAD 2006 - schematic, pcb, gerber.

[kt315]

my library file

mine.zip

[azigta]

Hi, yesterday I recieved the copper sticky tape and today I wrapped the coil with it leaving a margin on the pigtails, I think maybe too much space, I connected the shield to one side of the coil, and then connected it to the board according to the image that is on the pdf. It just beeped and didn't detect anything. I decided to disconnect the shield from the coil, and it works like before... Am I understanding something wrong? What's happening?