Voodoo Main Discussion

[scs-bg]

The best working hybrid detector is with a DD coil. Sound from a pulse induction channel. Discriminator with a meter with an arrow. Separate channel, signal when transmitting. Both channels without movement, with a reset button. Both channels work with a signal from the receiving coil. In this way, the influence of the ground is weak and a great depth is achieved. Frequency 220 hertz.

[scs-bg]

I made a hybrid pulse detector 20 years ago, long before Voodoo. It turned out that due to the influence of the ground, incorrect discrimination of deep-lying objects occurs.

[Voyager]

Hey kraimov, why are you using my signature?

[kraimov]

Good work thanks

[phred01]

Happy New yr to all.
There are 2 a ways to control the current in the TX coil. In the Voodoo case, the case it is source side of the power FET. What is across after turn on pulse is a ringing coil with a loading 1k and 2 diodes. In the MPS PI - Iron discriminating metal detector design the coil is on the drain side of the FET with 300 ohm permanently across it. The difference with the Voodoo case TX & RX coils are both used to receive echo signals from the target. Where as in the MPS-PI only the RX coil is used;. The MineLab metal detectors use a complex cct capacitor diodes to quench the back EMF to about 185 v The inputs of the receive op amps have 2 FETs to prevent of being fried. The only downside of the Voodoo design I see is the digital side is a little bit harder to debug in case of a problem. So far in my view the Voodoo approach is novel.

[Carl-NC]

Having studied the circuit noticed the whole circuit uses positive as ground like old British cars. Is there a logical reason for this approach?

In a typical PI, the battery voltage is applied to the coil and then, when it's removed, you want the coil to decay to ground potential. When using a low-side switch, if the coil is connected to ground then the switch must be connected to -V. The easiest solution is to just relabel the battery so the + side is ground.

[Qiaozhi]

Having studied the circuit noticed the whole circuit uses positive as ground like old British cars. Is there a logical reason for this approach?

Carl's Hammerhead design also uses battery positive as ground (0V).
In Chapter 2 it explains that the Voodoo Project started as an experiment to combine Hammerhead and Raptor (a VLF design from ITMD) as a means of providing ferrous/non-ferrous discrimination.
It's just a different power supply topology. The Arduino Nano PI Project (ANPI), for example, uses a more conventional approach.

[phred01]

Having studied the circuit noticed the whole circuit uses positive as ground like old British cars. Is there a logical reason for this approach?

[Qiaozhi]

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

The original EasyPC project, schematic and PCB are definitely contained in the zip file.
They have the extensions: prj, sch and pcb. Of course, you will need EasyPC to read them.

If you want to create your own version, then I would use KiCad.

[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

[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

[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
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?

[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.

[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.