Voodoo Main Discussion

[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]

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/foru...metal-detector

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

[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]

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]

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

[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.

[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

[Carl-NC]

From recollection:
TX = 540uH
RX = 15.7mH

[Repwoc]

Thanks Carl.

[Carl-NC]

It's basically the same coil windings as the MXT/DFX/V3 coils but without the extra compensation components and a different connector. You can run a Prizm coil on a DFX and vice-versa but the target IDs are a bit off.

[Repwoc]

So it looks like it could work I think. George tested a range of different coils and the inductance of the White's RX coil is similar to the Tesoro one George tested (15.36 mH). I think the inductance of the White's TX coil should be OK.

To get the RX coil to resonate at ~10.5 kHz would need a 14.6 nF capacitor. The nearest I have is a 10 nF which would give ~12.7 kHz or a 22 nF which would give ~8.6 kHz, or I guess I could put 10 nF and 4.7 nF caps in parallel. But it doesn't look like the RX resonant frequency is critical from what George wrote in the book.

[phred01]

G'Day
I wish to alter the pcb rev-c
1) Make the width of the pcb 100 mm wide as commercially
available boxes are generally accommodate pcbs 100 wide
2) Make the board longer to accommodate better connectors
3) Improve the signal input stage better op amps with different
cct configuration to improve cross modulation characteristics
To cut down reverse engineering effort
Is there a net list available or better still a complete cct rather
create a cct from the bits and pieces in the book?

[Qiaozhi]

G'Day
I wish to alter the pcb rev-c
1) Make the width of the pcb 100 mm wide as commercially
available boxes are generally accommodate pcbs 100 wide
2) Make the board longer to accommodate better connectors
3) Improve the signal input stage better op amps with different
cct configuration to improve cross modulation characteristics
To cut down reverse engineering effort
Is there a net list available or better still a complete cct rather
create a cct from the bits and pieces in the book?

The PCB was designed using Easy PC.
I've attached the design files.

Ivconic also redrew the schematic using a different editor. I'm not sure what editor he used, but I've attached that as well.

[phred01]

G'Day Qiaozhi
Thanks for the files REV-C.zip file only contains Gerber files to make the pcb. The zip doesn't contain the schematic that were used to create the Gerber files
Ivconics sch file is not compatible with KICad it is either Protel or Eagle

[phred01]

Just had Ivconic's sch image printed on A3 sheet.....nice. Looked carefully @ the circuit noticed unconventional 2 x 6 LCD configuration. Normal use powering +5v on pins 2, 15 with 0v gnd on pins 1, 16 Here the module is powered 0V GND on pins 2,15 WITH -5V on pins 1,16......never seen the use in this way. Will have draw the cct in KICad