Voodoo Main Discussion

[Math]

Ok thanks Qiaozhi i will get cracking!
Performances will vary largely depending on the coil used/built?
I use Explorer/Etrac FBS coils on my modified Minipulse..
I think the lower inductances, higher Fres/faster Rx makes them ideally suited for PI iron disc
Early used 10.5" and later 11" pro coils (with bust lugs) are plentiful and cheap
they can be had for 50GBP or less as can the smaller coils.. the 8" and Detechs 8x6 SEF which is a very good coil
I know these are all DD/~OO but i find the narrower detection zone better for target seperation..
Im not sure if this will apply to the Voodoo design being based mainly around concentric type coils?

[MartyJ1963]

Thanks George,,,but what I wanted to know is would 208ma be enough to charge a battery pack or would I need one with more current output? I'm wanting to put a battery pack beneath the armcuff on my detector shaft and not in the same enclosure as the pcb,,so I can swap out battery packs in the field. Thanks, Marty.

[Qiaozhi]

Hi Qiaozhi my copy of Voodoo Project arrived today, I think its great
Is the TX pps set at 1khz and is it possible to add adjustment to the menu?
Thanks

Yes, that would be possible, but at the moment I'm waiting for someone to replicate the project before there are any discussions about modifications.

[Qiaozhi]

Thanks George. The only 24v AC charger I have only outputs 208ma but that wouldn't be enough would it? Thanks, Marty.

Actually, if you connect the 24V DC adapter to the circuit it should still work. It won't even matter which way round you make the connections.

[Math]

Hi Qiaozhi my copy of Voodoo Project arrived today, I think its great
Is the TX pps set at 1khz and is it possible to add adjustment to the menu?
Thanks

[MartyJ1963]

Thanks George. The only 24v AC charger I have only outputs 208ma but that wouldn't be enough would it? Thanks, Marty.

[Qiaozhi]

Now the Rx coil needs damped to a pre value. the final damp will be at final assemble with a damping resistor set up.
Here is the Rx coil damped alone.

There is no requirement to damp the RX coil for Voodoo. It just needs to be induction balanced to the TX coil.

[Qiaozhi]

Hi George,,,Can you recommend a brand/Model of 24v adapter for the battery charger pcb and what amperage please? I have 2 x 24v adapters here. One is 24v @1500ma,,and the other is 24v @208ma. I also have a 23v adapter @400ma but I suppose that would be too low wouldn't it? Thanks, Regards, Marty.

The input to the charger is 24V AC, and is expected to come from a mains transformer. As suggested on page 90, you could use a fairly standard mains transformer with two 0-12V outputs in series. The charger should also work with 24V AC from a power adapter with sufficient current capability.

[MartyJ1963]

Hi Godigit,,,Really amazed at the results of your experiment. I for one will defnitely be having a go at it amongst the other coil variations I have already made templates for. I have all the materals/components to begin but I'm having to do it all in between some major repairs to the house that need fixing before Winter arrives. I should hopefully be starting soon though. Thanks again for all the details you posted. Regards, Marty.

[godigit1]

Attachments are working again

This is the rx coil pre damp to 966 ohms


So the way I balanced this coil was to hook it up without the damping resistors to a signal gen then do the final balancing.
I found that on the Mpp I could not really get the null where I wanted. After connecting to the S.G it balanced out well and almost 3/4 a inch apart from where it balanced on the mpp.

Here is the null on the genny


Here is the Pic of the Rx coil at preamp out


I forgot to check the output at the integrator but will make sure its good.
The coil operates with a nice steady threshold. there seem to be some unique attributes to this coil so far.

So far the two nuances Ive noticed are
The first Low edge sensitivity , I think will help with less target overlap and allow closer searching to metal objects such as volleyball net posts.

Secondly all the coils were noisy in my test area when tested alone and the threshold was erratic due to noise the 18" loop was picking up some 7mhz waveform it all was pretty noisy and I thought there may be a problem.
But after all was said and done the coils acted as quite as the shielded coil I made.

I'm not sure yet but think the outer coil Has somehow partially isolated the Inner Rx coil maybe through its own inductance.
Maybe its the benefit of the dual field arrangement as per the patent the inner coil is separated by its inductance from the outer coil and must be damped on its own merit.
I'm reaching for it here a little S.W.A.G at it anyway.

Marty
I hope you and others do decide to give this coil a go It would be great have the help of you and others to perfect and diagnose this coil for any real benefits .
If this coil goes full depth on the Voodoo in Pi mode and operates well in Disc mode its ill say the deepest coil I've built for small gold rings so far.
I thought I Would loose smaller gold with such a big coil but that doesn't seem to be the case.

So The Dual Field DD coil is born .
Hope it grows .

Best Regards All

[MartyJ1963]

Hi George,,,Can you recommend a brand/Model of 24v adapter for the battery charger pcb and what amperage please? I have 2 x 24v adapters here. One is 24v @1500ma,,and the other is 24v @208ma. I also have a 23v adapter @400ma but I suppose that would be too low wouldn't it? Thanks, Regards, Marty.

[MartyJ1963]

Hi Godigit,,Thanks for the details and great photos/explanation of your coil experiment,,Wow! You've been really busy with it! You can tell you like doing these coil experiments,,,I can't wait to start mine as I love coil building too. Thanks again for posting your results etc,,Regards, Marty.

[godigit1]

Just wanted to add ,
A unforeseen benefit to this coil arrangement is very little coil edge sensitivity.
A beer can has to be within 4 inches to respond.

This may really help for target separation in a small version of the coil.

Be Well

[godigit1]

This coil damped out at 1391 ohms.
Here is a shot of the final damp of the dual field portion.

final damp was at 1391 ohms.

At this point I did some target testing and increased my on time to the coil to 190 us.
Wow as 18 dual field this thing is pretty fast and deeeeeeeep its hitting a small gold band at a easy 12 inches and a good response you would not pass up.

Now the Rx coil needs damped to a pre value. the final damp will be at final assemble with a damping resistor set up.
Here is the Rx coil damped alone.

Sorry guys all the sudden I cant add any photos it goes to upload then nothing will try to finish later
sorry sucks almost all my posts screw up some how and it takes me way too much time to post.

ANyway the coil works good as a dd just slightly less depth than as a dual field.

[godigit1]

Hi Marty,

Glad you got your power supply working.
I'm just getting ready to start building I side tracked on coils a bit much.

I was able to get the dual field DD coil up and running on a mpp.

Here is what I did it could be adjusted better for the voodoo but i just wanted to see if it worked before saying it was good just by balancing it with my genny.

The outer coil is 17.5 inches in diameter, its verticle stack basket weave coil.
I used 30 strand 26 awg tin plated silicon insulated wire( on ebay BNTECHGO brand)
120uh
1.86 Ohms

The DD coils are on 10 inch forms the tx is the same wire and the RX is 40/46 30awg litz.

Tx D=
170 uh
1.57 ohms
The dual field portion combined
333uh
3.43 ohms

Rx D=
514uh
7.05 ohms
here are the DD coils,



For the DD forms I made a stack of hardboard to hold the coils level when overlapped.
here is a side shot of the form and coils .

this is the form with the sides cut back for overlap.


Once the coils are wrapped and finished the d portion needs to be glued down.
I used super glue on the litz and natural silicon on the silicon wire

Here is a shot of the coil done and balanced .


Steps to Damp and tune the coil ,

First the tx D coil needs to be damped by its self.
Just hook it up and damp as normal Start around 300 ohms on your resistor set up.
Here is the Tx d Coil Damped at 390 ohms.


Then the Outer coil and damping resistor are installed as for a normal dual field coil and the whole thing is damped as a assemble.


not sure of the # of attachments I can have so continuing on next post.