Voodoo Main Discussion

[Repwoc]

Thanks Carl.

[Carl-NC]

From recollection:
TX = 540uH
RX = 15.7mH

[Repwoc]

I'm looking for a coil for a potential voodoo build. I found someone selling a White's 9" spider coil at a reasonable price, but I don't know anything about this coil other than it is for a Coinmaster / Prizm. Does anyone have any knowledge they can share?



Thanks!

paul

[Qiaozhi]

R30 is the null-offset adjustment for the preamp.
This is a generic method of nulling the offset by applying an offset current to the non- inverting input of U3a.
Using an oscilloscope connected to the output of U3b (TP3), R30 should be adjusted so that the voltage dc voltage level is close to 0V.

I would suggest using the default settings for the sample widths.

[Levin]

thanks
oh sorry I mean R30. And how do you know what the correct sample width is?
best regards Levin

[Qiaozhi]

Hello
I have two questions in setting the voodoo detector. How do you set R6 correctly. And how do you select the Puls induction sample width
thanks for answers and best regards
Levin

R6 is the 1R0 resistor in series with Q1. There is nothing to adjust here.

The pulse induction sample widths are set via the menus.
The pulse widths you require depend on the coil you're using and the desired target.

[Levin]

Hello
I have two questions in setting the voodoo detector. How do you set R6 correctly. And how do you select the Puls induction sample width
thanks for answers and best regards
Levin

[Qiaozhi]

Why is this approach not used in commercial detectors? Why do they rely on target conductivity instead?

Chapter 1 in the book discusses the current state-of-the-art regarding PI and VLF detectors, and the different attempts that have been tried to build a PI/VLF hybrid.
The Voodoo Project is subtly different to previous attempts and (as you can see in Don's video) the ferrous discrimination really does knock out iron.

Inspired by the Voodoo Project, Don has also been working on his own version using some different ideas ->

https://www.geotech1.com/forums/forum/technology/pi-technology/424331-new-project-mps-pi-iron-discriminating-metal-detector

You would have to ask the metal detector manufacturers why they don't have such a detector in their arsenal.

[sndchaser]

The Voodoo Project does not reject iron using target conductivity, but uses true ferrous/non-ferrous discrimination. Voodoo is a hybrid detector with features of both a PI and a VLF.

https://youtu.be/8dC6jkkSNBo

Why is this approach not used in commercial detectors? Why do they rely on target conductivity instead?

[Qiaozhi]

Is the general concept behind this detector the same approach used by the TDI series of detectors?

With the White's TDI you can hijack the ground balance control to create a notch that can 'sort of' reject small iron nails. This concept is based on target conductivity, and therefore any other targets with a similar conductivity will also be rejected. It also means that you cannot ground balance as well as reject small iron. Other ferrous targets will tend to lie outside of the notch and will be accepted as good targets.

The Voodoo Project does not reject iron using target conductivity, but uses true ferrous/non-ferrous discrimination. Voodoo is a hybrid detector with features of both a PI and a VLF.

https://www.geotech1.com/forums/forum/technology/technical-books-papers-and-literature/16690-the-voodoo-project-published-october-2020

https://youtu.be/8dC6jkkSNBo

[sndchaser]

Is the general concept behind this detector the same approach used by the TDI series of detectors?

[Qiaozhi]

Hi George

For the non-electrolytics would you recommend film-poly, ceramic or something else? I read ceramics can drift?

Film capacitors have a lower drift and are more stable. However, none of the book designs use critical components, and I've fitted both film and ceramic caps without any problems.

[BigDutch]

Hi George

For the non-electrolytics would you recommend film-poly, ceramic or something else? I read ceramics can drift?

[BigDutch]

I am creating Excel based BOMs (mostly Digikey at the moment) for the Voodoo PI, Arduino PI and Arduino VLF if anybody is interested. I know part numbers may change but the electronic suppliers are good at substitutes. Its quite a tedious process creating these as you have to check the correct package types for IC's etc.

[BigDutch]

Many thanks George!