Voodoo Main Discussion

[ivconic]

I found it to be very important because the first couple of oscillations will go into saturation and will not be useful to sample there unless gain is decreased unnecessarily. You can get very good sensitivity even at very low gain if everything is nulled.

Thanks!
I see.
...
Dunno... concentric coplanar coils were always hardest for me to make in my modest home made conditions.
Only because of the delicate balancing procedure.
"DD" were easiest.
Yet... "DD" is not most suitable coil arrangement for this kind of detectors.
What's next best trade off?
For experimental workbench purposes; i think the easiest would be "Omega" coil.
I draw 3D elements for it, for 3D printing. To make my life more easier while experimenting.
For those interested:

[lamoiz]

Thanks!
I see.
...
Dunno... concentric coplanar coils were always hardest for me to make in my modest home made conditions.
Only because of the delicate balancing procedure.
"DD" were easiest.
Yet... "DD" is not most suitable coil arrangement for this kind of detectors.
What's next best trade off?
For experimental workbench purposes; i think the easiest would be "Omega" coil.
I draw 3D elements for it, for 3D printing. To make my life more easier while experimenting.
For those interested:

[ATTACH]54236[/ATTACH]
[ATTACH]54237[/ATTACH]
[ATTACH]54238[/ATTACH]
[ATTACH]54239[/ATTACH]

maybe, but my tests with an omega give very poor results. I think the cancellation on the indoor loop limits the PI mode a lot. It works, but the detection area in hybrid mode is very small. In my application on the wet sand of the ocean, it is like looking on a small stretch of beach, it is not good for me.

[ivconic]

maybe, but my tests with an omega give very poor results. I think the cancellation on the indoor loop limits the PI mode a lot. It works, but the detection area in hybrid mode is very small. In my application on the wet sand of the ocean, it is like looking on a small stretch of beach, it is not good for me.

Omega type coils never were deep anyway.
What i am expecting from it is to be "comfortable" to experiment with in workshop.
Should be good for precise detection of smallest items, should be good in discrimination.
And yet... maybe i am just daydreaming, will see.
In the past i used larger room upstairs as my workshop, having lot of space and comfort for these kind of works.
Last several years situation has changed and now my workshop is 1x1 square meter, piled up with parts, tools and instruments.
Not to mention hums and interferences.
That's why i am forced to minimalize testing conditions, coils etc.
No harm done, this is just an attempt.

[lamoiz]

Omega type coils never were deep anyway.
What i am expecting from it is to be "comfortable" to experiment with in workshop.
Should be good for precise detection of smallest items, should be good in discrimination.
And yet... maybe i am just daydreaming, will see.
In the past i used larger room upstairs as my workshop, having lot of space and comfort for these kind of works.
Last several years situation has changed and now my workshop is 1x1 square meter, piled up with parts, tools and instruments.
Not to mention hums and interferences.
That's why i am forced to minimalize testing conditions, coils etc.
No harm done, this is just an attempt.

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.
best compromise, surface, discri and depth ...

[ivconic]

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.

I haven't tried such coil so far.
Balancing seems too complicated for me.
Even "CC" coil is too complicated to balance... in these conditions.
Truth is; the other day i prepared former for CC coil.
I had enclosure from before, i only 3D printed former for RX and former for bucking coil.
Enclosure is big enough to fit 25-27cm TX coil.
And dimensions of RX and bucking former are on the pics:

[MartinB]

While waiting for my PCB and PIC to arrive I decided to build a concentric except I went for a more conventional 360uH TX and 6.9mH RX coil. To test it I attached it to a modified Surf PI Pro with a split TX and RX. To my amazement it worked great for a disc channel but required reduced gain. So I figured why not just build a separate disc channel and have an analog version of the VooDoo? I am just using the existing PI channel as an equivalent GB channel and borrowed some of George?s idea from the VooDoo project. I am just merging the two channels just like the Raptor, TGSL or Whites classic with a pair of LM393s. The only real challenge was getting the frequency response of the GB and disc channels close to the same. Also.. Resonant frequency of the RX channel doesn?t seem to matter much as long as the sample delay and sample pulse can be adjusted to sample at the correct time.
Too many ideas from on George?s books to post here but I can show that it works.
https://youtu.be/9aqxGrFK9fo


So, here is a little demo of how it works. It deals with the ground signal quite well and can disc iron with an analogue meter.

Hi Surf
Which cable do you use for winding your coils?
I see that like me you have some interference before and after the signal. Is this capacitive from the coil?
Thanks

[6666]

this will work, but it is true that for me the "discrimination" area is too small for the ocean range. the omega was my first test on the voodoo. after I did the dd and the super d. I have come to the conclusion that the pancake is the best idea. I tried .. I didn t succeed .. impossible to nulling .. I had no luck. so I persist on the super d, it is the only one that has a performance as good in PI as in hybrid on the voodoo circuit.
best compromise, surface, discri and depth ...

Which/what coil are you calling "pancake" ?

[MartinB]

That mogami coax looks nice at least the connectors and the outside of the cable doesn't look like that cheap shiny plastic so then i assume just remove the ends and replace with 5 pin connectors [ATTACH]54234[/ATTACH]

Nice looking cable but it does have a conductive PVC sheath which may affect performance

[SilverSurfer17]

Yeah ive done some checking around and it has problems im going to try a few things and see what happens maybe even make my own

[ionut_mtb]

I haven't tried such coil so far.
Balancing seems too complicated for me.
Even "CC" coil is too complicated to balance... in these conditions.
Truth is; the other day i prepared former for CC coil.
I had enclosure from before, i only 3D printed former for RX and former for bucking coil.
Enclosure is big enough to fit 25-27cm TX coil.
And dimensions of RX and bucking former are on the pics:

when i print coil former i do it from two pieces, and after i glue together with superglue. In this way i don’t need to scrap the overhang support structure, which i find annoying and the surface of the part is not smooth. Also i keep the layers thickness about 1.5mm resulting in less weight(anyway this willbe covered in epoxy). Coil housing is from BG, i did not print them yet.

Thank you all for your involvment.

[lamoiz]

Which/what coil are you calling "pancake" ?

Yes . 3 superimposed coils Rx- / Tx / Rx +. I made one for the test. But not had good functioning. failed to make the Rx "invisible" on the oscilloscope. If anyone here knows this method, I'm very happy if he explains how to do it, or what I've done wrong ... but for voodoo it would be a good idea.

[ivconic]

when i print coil former i do it from two pieces, and after i glue together with superglue. In this way i don?t need to scrap the overhang support structure, which i find annoying and the surface of the part is not smooth. Also i keep the layers thickness about 1.5mm resulting in less weight(anyway this willbe covered in epoxy). Coil housing is from BG, i did not print them yet.
Thank you all for your involvment.

Yes sometimes i do the same. Magnetometer enclosure i did from several pieces and glued together.
...
This turned out surprisingly well, it took me half an hour to remove supports though:

[SilverSurfer17]

Anybody know where you can find these shells this is the only one i could find and all the links don't work https://picclick.com/8-Metal-Detecto...776327553.html thanks for any help

[surfdetector]

Anybody know where you can find these shells this is the only one i could find and all the links don't work https://picclick.com/8-Metal-Detecto...776327553.html [ATTACH]54257[/ATTACH] thanks for any help

dfbowers (member here) produces very good quality shells.

[SilverSurfer17]

The only concentric shell i could find was all closed in and one hole in the center and i wanted a open one like in the picture ill have to figure out how to hunt him down on here lol