Voodoo Main Discussion

[Qiaozhi]

Hi George,,I removed the 78L05 and the voltage at the cathode of D6 is 9.89v. Thanks, Marty.

In that case either the 78L05 is faulty or there's something loading its output pin.

[MartyJ1963]

Thanks George. I'll replace the 78L05 to see if it rectfies the problem. I don't understand what you mean about something 'loading' its output pin? Thanks, Marty.

[MartinB]

yes, I think it is, because it is an old spool of thread that I have had in my workshop for a very long time, and there is no longer the informative label. silicone and silver color.

Let me know how the coil performs. I have heard that the silver plating creates eddy currents and reduces coil performance

[6666]

Thanks George. I'll replace the 78L05 to see if it rectfies the problem. I don't understand what you mean about something 'loading' its output pin? Thanks, Marty.

Sometimes a fault will put such a high current drain (load) on the circuit the battery voltage drops

[MartyJ1963]

Thanks 6666,,,Learning something new every day! I've never had a problem like that with any of the power supplies of any other detector I've built so this is probably why I never knew what to look for,,Lol. I've changed the 78L05 now. Out of a new bag of 10 x 78L05's, the first 3 that I tried replacing were faulty too!,,Anyway, I now have my +5v and my -5v on TP14 and TP15,,,but, I only have 7.4-7.5v on the cathode of D6. Shall I change that diode too? Thanks again for the help and I hope your wife is recovering ok, Regards, Marty.

[MartyJ1963]

Hi All,,,I changed the diodes D6 and D7 but still didn't get 12v at the cathode of D6. I have +5v and -5v though so I'm lost what to do next? Thanks, Marty.

[Qiaozhi]

Hi All,,,I changed the diodes D6 and D7 but still didn't get 12v at the cathode of D6. I have +5v and -5v though so I'm lost what to do next? Thanks, Marty.

Since you have +5V and -5V you're OK to continue. The voltage at D6 is not going to reach exactly 12V. It only needs to be higher than 5V plus the dropout voltage of the regulator.

[MartyJ1963]

Thanks George. I can start sorting my Detector shaft and enclosure now so I can estimate the cable I'll need for the LCD then I can solder the LCD wires in and move to the next stage. Regards, Marty

[godigit1]

Were you able to zero this out?

Hi Lamoiz,
Thanks for posting the specs on your coil.
Are you balancing on detector?

[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.

[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]

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

[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.

[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.

[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