New Hammerhead Project

[KingJL]

my dear friend king jl very good setting.whats coil dia meter actually my requirment 12inch dia ms plat up to five feet.can you do this detect in free air ?.......rajesh

rajesh,
My coil housing diameter was/is 10 inches. Inside are two 8.37 inch diameter coils arranged in a DD configuration.

I seriously doubt that I can detect anything at 5 feet. I may try later, but don't hold your breath until you hear of positive results!!

Regards,
J. L. King

[rajesh]

hh

dear king jl i read a mail from chemelec form>for gold detecting>
Hi,
This is my first post here and I am happy to be involved.
My BIO -- I am a retired NASA electronic engineer and
also retired Naval Research Laboratory Acoustic engineer.
That is in my past and my hobby is electronics and astronomy.
Gold detection is not easy in the usual since unless one invest
in a 20000 dollar gold detector and then you still have to know
where to look.
However, I can supply some advice on gold detecting
on a few bucks. AM radio waves are very sensitive to gold.
Adjusting the tuning of the radio core and wire can pick up
gold and only gold at close range. Also the am radio
can be tuned to different freq. . Now this may sound
almost obvious , however it is presented for two reasons.
First , I think that the young people designing items on this
site can apply some old knowledge. Second, search for gold
and don't try to build a detector to find it all, just gold.
Also, shape of gold is everything. All shapes, rings, nuggets,
coins, and such are all totally different. I would use a 32 bit processor which would monitor slope detection of returned
signal decay from the affect an object has on the coil field.
The main point is to stick to finding only gold and the other
metal detectors will find all the other stuff.
Yes, The user is the key. No matter what detector you have,
it means nothing without many hours of field use.
Jeff

[erolunall]

Hello

İt is not easy to find a coin under 1 meter in soil like to sent space machine to mars for landing.

I cant understand this .

Best Wishes

Erol

[erolunall]

Hello

İt is not easy to detect a coin under 1 meter in soil like to sent
a space machine to Mars for landing.
But why I can t understand.

Regards
Erol

[bchampig]

King,

Nice work on this project. I am in the process of making something similar with the Hammerhead as my base design. I also wish to add a ground channel as I relic hunt in some highly mineralized red soil. I noticed on one of your schematics, you show the output of the 'ground' integrator feeding back to itself AND the main channel. I understand you are subtracting this signal from the main channel, but why are you feeding it back to the ground channel? On a later schematic you don't show this...you only show the output of the groung integrator connected to the main channel for subtraction. Could you please explain this?

Thanks very much for your postings...they have been very informative and helpful,

Best Regards,
Brian

[KingJL]

I noticed on one of your schematics, you show the output of the 'ground' integrator feeding back to itself AND the main channel. I understand you are subtracting this signal from the main channel, but why are you feeding it back to the ground channel?

That was an experiment that didn't quite work out... so I wouldn't do that!

On a later schematic you don't show this...you only show the output of the groung integrator connected to the main channel for subtraction. Could you please explain this?

That also was not quite successful. I had slightly more success rerouting the inputs for the ground channel so that the output was the inverse of the main channel and summing the outputs at the junction of +input of IC6B (each side has it's own .47uf HPF coupling capacitor). I did not pursue this any further. I decided to thoroughly study the Goldscan IV to understand it's principles and limitations. I think I now have a pretty good grasp of the GS IV. I would recommend study and simulation of the GS IV and then implement a similar strategy on your HH project if that is what you desire.

[bchampig]

Thanks for the info! I will spend some time studying the GS schematic.

Best Regards!

[bchampig]

King,

I think the problem you had with the HH ground balance scheme was that the subtraction will not work at the input to the diffrential integrator. I wonder if it would work properly with the output of your ground balance channel connected to an op-amp subtractor at the output of IC8a (Subtracting the ground signal from the main signal). The ground signal wouldn't need to be inverted I believe.

Does any of this sound reasonable?

Thanks for any advice/input,

Brian

[cko47]

RX&TX coils

How make (self) RX and TR coils for Hammer head project?
If it possible send me reply direct to my email [email protected], please.
regards cko47

[dfbowers]

How make (self) RX and TR coils for Hammer head project?
If it possible send me reply direct to my email [email protected], please.
regards cko47

DD or Concentric?

Interesting post here:
http://www.geotech1.com/forums/showt...ght=hh+dd+coil

Now, in reading this post, it suggest that polarity has an influence on target response (ferrous vs. non ferrous):
So then why not make all PI detectors with this coil configuration?????????



Hi Oscar,

Building a DD coil is not hard. In fact, it is quite easy since one can be sloppy even with the positioning of the windings. Fortunately, a PI will allow for less than perfect positioning of the two windings and still work fast and well.

Now, I normally use a 300 uh transmit winding and this is wound much like you would wind a mono coil. The receive winding can have a different inductance if so desired. I have used receive windings of 300 uh to 450 uh and they all have worked well.

I do recommend you install the receive winding damping resistor inside the coil, especially if you plan on using different coils on the detector. Typically, a resistor value of 1K to 1.5K can be tried as a damping resistance for initial testing. Just simply connect this resistor across the leads of the receive winding.

The windings are polarity sensitive so care has to be taken to assure the connections are correct. Now, when you are determining the correct polarity, make sure to use a non ferrous object.

So, wind your two coils, position them such that they have about an inch overlap to begin with and then connect them to the circuit. Pass a non ferrous object over the overlap to make sure you get a positive response. If you do not, then simply switch the connections on the receive winding and test again. You can switch the transmit windings also to obtain the same results. Just make sure that any winding shielding used be connected to the shield of the coax.

You will notice when testing that a ferrous object will give an opposite response than that of a non ferrous object, so if you try to set the polarity using a ferrous target, the signal will be incorrect.

If you are using a scope, you can position the receive winding such that you do get a minimum response or signal out of the coil or at the output of the preamp if you are trying to obtain the fastest coil. Fortunately, even if the windings are not "nulled" completely, a DD coil will generally be faster than a mono coil. In fact, I have deliberately built coils that are not nulled to assure a decent signal from a very small piece of gold.

Now, I have found that a round housing will generally work a little better than an elliptical if you are trying to reduce the ground signal. Also, the round housing will usually provide a little more depth than an elliptical also.
A good size is the 11" round housing such as that made by Bill Hays.

Now, as for connecting the windings, I do recommend you do try to keep the transmit and the receive separate in the coil. This includes the shielding of the windings and the coax. So, there will be no connection between the transmit and the receive except at the connector or pc board.

I also shield each winding separately and insulate the two windings from each other using something as simple as plastic electrical tape.

If you tie the shields together inside the search coil, you will find your coil will not be as fast as one where the transmit is isolated from the receive, so it is important.

Make sure each winding is wrapped such that the windings are not loose. I lace mine and use spiral wrap to assure they are very snug. If the windings are loose, they can vibrate when jarred and cause false signals.

I hope this helps a little. Don't be afraid to experiment a little to find what works best for you.

Reg

[cko47]

74HCT221 for Hammerhead PI MD

Thank You for your reply. But I have new question (for HammerHead PI MD).
In datasheet for 74HCT221 and 74HCT123 we have the following notes.
...Note for 74HCT221 ......It is recommended to ground pins 6 (2CEXT) and 14 (1CEXT) externally to pin 8 (GND).
and for 74HCT123 (1) For minimum noise generation, it is recommended to ground pins 6 (2CEXT) and 14 (1CEXT) externally to pin 8 (GND).

But Carl Moreland in own project not make this .
What You think about this notes (for Hammer Head PI MD)?
And second question. Better is mono coil or dual RX&TX coils (for low noise or another reasons)? If RX&TX coil then is better concentric or DD coil?
regards

[Qiaozhi]

Thank You for your reply. But I have new question (for HammerHead PI MD).
In datasheet for 74HCT221 and 74HCT123 we have the following notes.
...Note for 74HCT221 ......It is recommended to ground pins 6 (2CEXT) and 14 (1CEXT) externally to pin 8 (GND).
and for 74HCT123 (1) For minimum noise generation, it is recommended to ground pins 6 (2CEXT) and 14 (1CEXT) externally to pin 8 (GND).

But Carl Moreland in own project not make this .
What You think about this notes (for Hammer Head PI MD)?

The 74HC221 already has an internal connection in the chip between pins 6 and 14 to pin 8 (GND). Therefore (functionally) it doesn't make any difference to the operation of this circuit. Presumably the external connection helps to improve stability and prevent problems due to ground bounce.
There is however one good reason for adding this external connection in the HH design. If you are not using the differential integration feature, and have removed IC12a, then the main sample pulse generator ceases to function. This is because it relies on the internal connection between pin 6 and pin8 of IC12b to connect the lower pin of C26 to -5D. To overcome this problem you need to either add a wire between pin 6 of IC11 and pin 6 of IC12, or short pin6 of IC12 to pin 8.

[cko47]

74HCT221 for Hammerhead PI MD

Thank You very much for quick reply.
What You can say for second question (best coil - concentric or DD or mono coil)?
If I have mounted IC11 & IC12 using 74HCT123a chip then your suggestion is available for this variant?
Once again thank You.

[Qiaozhi]

Thank You very much for quick reply.
What You can say for second question (best coil - concentric or DD or mono coil)?
If I have mounted IC11 & IC12 using 74HCT123a chip then your suggestion is available for this variant?
Once again thank You.

If you have IC12 installed, then you will probably not notice any improvement in operation by adding the connections to GND.

The mono coil is the easiest to construct, and I would advise you to make your tests first with a mono. A DD coil will be better at pinpointing the target, as it has a narrow sensitive area from front to back, but there should be a slight decrease in depth due to the smaller transmit area - hardly detectable in practice. A concentric will provide even better pinpointing capability, but is the most difficult coil to construct. There is less depth than with a mono, because some of the transmit energy is used to null the receive coil.

[cko47]

74HCT123A in Hammer Head PI MD

I have measured resistance between pins 14 and 8 of microcircuit 74HCT123A. It is equal 5 Ohm. Between pins 6 and 8 of 74HCT123A the resistance is much less and equally 0,6 Ohm.
Once again
thank You
Best wishes