Compass Scanner, JE two board series (top Target ID/Notch board)

[Melbeta]

Very Interesting. I see the Rx and the Tx coil color wires are now in reverse from the Coin Magnum color scheme. But the Coin Magnum is a Axial coil. Your 6 inch is a concentric coil.

On the Coin Magnum they had the Tx in Red and Black, with the Rx in Green and White. I know a guy who wants one of those coils for his Coin Magnum and that was why I was trying to put a cap/Res/induct reading together for him. But the pin configuration is so close together, unlike the 13.77 scanner coils, that one has difficulty getting my alligator clips on the pins without touching together. I need some kind of sleeves to slip over without shorting out, so I can clip better. I pulled the connector out, but the pins are still to close together where the wires were soldered. On the Shield it has no color wire.
Melbeta

[Melbeta]

The Sprint 60 is a demo, but I will run it when I get some time, to see how it works.
Melbeta

[Melbeta]

Phil
You have any information on how to make a Compass DD coil? And perhaps on how to null it as well? I have a friend who wants to build one.
Melbeta

[turtlebowl]

I have alot of info on some Compass Coils including the DD but only on the Scanner and Challanger series. Not much at all on the other models Jerry, sorry.
Winding coils is a big topic and we could start a thread on building Scanner coils if there is interest in the Compass Scanner material being released lately.
FYI - I just started a related thread today on adding the Scanner Model AU2000 VCO to the Gold Scanner Pro here on Geotech.
Phil

[Melbeta]

Phil
I did not notice that related thread so far, let me know where it is located. On the VCO, I want to make sure I grasp and understand it. IT stands for Voltage Controlled Osciallator, and I think it may be related to the front end amplification method first used on the Compass Challenger X-100 metal detector? That way one can really throw the coal to the stove, or the metal to the pedal? Now I know they have Pre-Amplification at the very beginning of the Rx inputs, then the Amplification begins of this Pre-Amp. So is this a circuit with an adjustable pot, that throws more or less into the Pre-Amplificator?

Oh, I am really into learning about the Compass DD coil. I know some about it, but would like to learn it well. Yes, I would like to learn it for both the Challenger units and the Scanner units, and then could grasp that technology for the other models. I have never tried to make any DD coils as I did not quite know about how to do it. I have two O-scopes, and a LCR meter, along with some other equipment, so I think I could do it if I know what is going on.

So setting it to Zero Volts, you are setting it to the Base Line? Now I do not know exactly what that entails and how you do it. I can envision reducting the P-to_P down to the Base Line? That kind of sounds to me wrong. It would sound easier to use the voltage Multimeter and adjust to zero voltage.
Melbeta

[turtlebowl]

Good evening Melbeta, I see you found the Compass VCO thread over in the Modification forum and so we can talk about the VCO question over there.
Happy to talk a little about the Scanner DD coil here and answer your interest in that coil. Would be happy to talk more in depth in a thread dedicated to that topic if there is enough interest in sustaining that thread. It's Easy enough to get side tracked away from Davids thread centered on the upper TDI he drew out and shared and the related main circuit board schematic for the Gold Scanner Pro so we can bring the coil stuff over there.
But briefly, there really isn't much to tell on building a DD coil for the Gold Scanner. It's the same proceedure as most other brands. Tuning is very straight forward and pretty basic no matter what brand. These basics are Covered much better than I could tell over in the Coil section of this forum. What I just said is true if you are just making a "copy cat coil" OF THE SAME Size and configuration exactly. All you need are the electrical values of the coil , a peek inside to check shielding, configuration, and any extra parts, wire size, location of buck coil, etc.. basically you are just copying ..and start winding. The trick is in the care taken and especially the null has to be just right. But again a piece of cake nulling since your just copying the signal you saw on your scope of the real coil.
A whole different story all together if you are changing the size, shielding or style or anything else about the coil. In this case a person would do well to remember the article George Payne wrote on how much time and effort is involved in designing a coil for his machines. And that is why a design engineer almost always sticks with the same frequency and coils. A heck of a lot of work sometimes to design a new great coil. So a guy must be prepared to do a lot of experimenting and re-winding I have found when changing the size. For example you may have to experiment with wire size on the receive coil or change just slightly a coil diam so that it fits inside the shell you are using when you finally get it to null.
All stuff better suited to a different thread.
BUT,,, Rest assured that the 13.77 kHz Scanner DD Coil is a pretty easy coil to build and I can provide the build specs over in the coil section if someone is actually wanting to build one for their machine.
Take care Jerry, doesn't look like much interest in this old machine, Just you, me and David LOL. I don't know why as it is an excellent bad ground discriminator the way it sets. And much better with new chips. See you over at the VCO thread.
Phil

[Melbeta]

Well, the real interest is to learn all that one can learn, then make up a new board with SMT parts, put in smaller case, and go out and look for the deeper vintage targets. That is my goal. Another goal is to merge options of other detector models into one master model. I do not care what it looks like as long as it works better the the original unit.

I will study the 6" concentric and see what can be done for the Coin Magnum. Then perhaps make up one for the Challengers and Scanners as I do have some of them, even though I do not have a GSP model.

Not sure if you knew that Compass on the later Coin Magnum 2 model, removed the mercury shut off switch and the tone control, and inserted a LED into the negative side of the Good/Bad meter. So it was easier to see the meter deflection with the LED light.

I am going to have to get my Orcad schematic software out and begin to relearn it again, it has been so long I do not remember what to do in it again. Last time I used it was back in early 1990s. Right now I take out graph paper and begin to draw and I am really quick that way... But it does not look like the Orcad. And with the Orcad, it outputs Gerber files.

When I get some time I am going to redraw your schematic, so I can see everything and grasp it better. You said 11 parts, right now I do not know which are the 11 parts.
Melbeta

[Melbeta]

I do have a question on coils. If I try to take the Scanner concentric 6 " and use it for another Compass coil, for a different frequency model, do I use the same number of windings? I know I would have to change over the nulling part values to new values. Just trying to grasp the differences in the coils.

Another question. It popped into my mind, I wonder what would happen if one put an adjustable pot into the Tx side of the oscillator and give an option to change the amount of voltage current going down the coax cable into the Tx windings? Interesting concept. Did you ever think of that too?
Melbeta

[turtlebowl]

Melbeta the 11 part #'s for the VCO Mod are shown on the Schematic in the lower right corner. All parts #s in the 2000 sequence section 2000 . The component numbers are shown on the LAY file layout attachment where I show their placement on the PCB. You Gotta open the lay file to see the component placement. All that info over in that thread on the VCO mod. The value of each component is shown on the AU2000 PCB PHOTO. I will also go over there and add a component value list today.

http://www.geotech1.com/forums/showt...oldScanner-Pro

Short coil answer. - A GOOD working coil is designed specifically for A machine or family. And it must swap out easily with other diameter coils for the model without having to internally recalibrate the machine to change coils. The mis-matched coil will typically overdrive the RX preamp causing noise, clipping, and un-usable phase info. OR it under drives and has crappy sensitivity. The RX and TX relationship is everything. Gotta be just right. A coil calculator only gets you in the ballpark. The rest is trial and error when designing a coil from scratch. Pick a TX freq and design a good OS tank. Next wind a RX coil that self resonates at 2.5 times the TX. Adjust the RX windings and tuning cap to achieve proper sensitivity without overdriving front end. In a nutshell. 2.5 x TX is the formula Compass used for RX coil on the Scanner and X100 coils.
Best just to copy a known working coil until one learns all the coil design stuff and has the time, desire and patience to experiment. All the learning stuff needed is over in the Coil section of the forum.
Going to cut this short and keep this thread clean. One day I'll get together the Scanner DD coil building specifics and post them in the coil section. I have winding forms and patterns for a custom 9" Eliptical 13.77K DD Scanner.
Best of luck to ya Melbeta, Phil

[Melbeta]

I have not had time to look a the lay file, but saw the circuit schematic on that drawing. It takes the collector feed, runs through the circuit, outputs to pin 5 of a chip, Very interesting.

I wonder of a two or three tone device, would interface and give a
TID meter for the AU52/AU2000? For myself, a TID meter is very desirable to have.

Thanks for the coil information. I noticed that 2.5 was what George Payne said as well. I appreciate your taking the time to address some questions of mine. I don't understand everything, and I like to learn something new each day.
Melbeta

[DavidB]

Cleaned and corrected Scanner Main board schematic. This one is the XP-350 version but includes interface connections for other models.Scanner_XP_350.pdf

[DavidB]

Scanner notch circuit with signal description

[Melbeta]

David
I have an interesting question. On the Compass Challenger detectors, Compass used a CD4066 to handle Iron into the beginning for the silver quarter, then used a CD4016 to handle the higher range metals into the Silver Dollar.

Why did they do that?

One Op-Amp handles one better, and another Op-Amp handles the other range better? That is all I could guess which was the obvious.
Melbeta

[DavidB]

The CD4066B device is a quad bilateral switch intended for the transmission or multiplexing of analog or digital signals. It is pin-for-pin compatible with the CD4016B device, but exhibits a much lower on-state resistance. In addition, the on-state resistance is relatively constant over the full signal-input range.

This is your answer from the data sheet

[kt315]

4066 has more advanced structure. more modern.