Questions Regarding "Wandering" Sensitivity Setting.

[ToddB66]

I have a Cen-Tech Hand Held Metal Detector #97245 that I use as a pin-pointer, but the Sensitivity setting has to be re-set too often.

I also have a Velleman K7102 Metal Detector Kit and plan to build the circuit board and then morph it into a pin-pointer with plastic case and pin-pointer tube. Admittedly, you can't expect too much from these "cheapie" units, but I'm wondering if there is a fix for the "wandering" Sensitivity setting.

Maybe the re-tuning is necessary as I move to different areas of the Park where ground mineralization type and/or saturation has changed. Do you think this is possible ?

Could the problem be amended or ameliorated by adding some kind of electronic component to the circuit ?

Thanks in advance for any help you can give.

ToddB66

[Silver Dollar]

Well drifting is the nature of the beast. If you look here Davor is trying to come up with a circuit that
"autotunes" itself to eliminate this problem....

http://www.geotech1.com/forums/showt...n-chain/page16

[ToddB66]

Well drifting is the nature of the beast. If you look here Davor is trying to come up with a circuit that
"autotunes" itself to eliminate this problem....

http://www.geotech1.com/forums/showt...n-chain/page16

Silver Dollar,

Thanks for the above link, but I can't get it to work. From it's color, it appears to be hyperlinked, so I don't know what could be wrong.

Maybe if you just give me the names of the forum, the thread and title of Davor's post(s), I might be able to navigate there straight-forward.

Otherwise, if you have any suggestions, please let me know.

ToddB66

[Nupi]

Hi, the thread is.

" Can pinpointer detecting thin chain? "

On the tech Forum.

[ToddB66]

Hi, the thread is.

" Can pinpointer detecting thin chain? "

On the tech Forum.

Thanks Nupi !

I'm mostly reading parts of that thread that Davor wrote and replies to him from other members, yourself included.

I haven't reached the bottom of the thread yet, but my impression is that this is way over my head. I was hoping the "wandering sensitivity" could be fixed with a component or two added to the existing circuits of the Centech 97245 and Velleman K7102. Sounds like it would require a total re-design and build of these cheapie circuits. I'll just use these two units "as is".

Thanks again for trying to help !

ToddB66

[Nupi]

@ToddB66
I can understand that you're saying "that this is way over my head" but you do not have make it so extensively
Like the example as Davor describes. What Davor tried to do is a highly sensitive, stable and very good pinpointer,
the nupi-PP (which is much more sensitive as the Garrett pro pointer and the most PP) to make even better.
And I am convinced that Davor is the only one I know of Geotech Forum who can do it.
That's why I asked him if he wanted to improve the NUPI PP.
But if you would build the NUPI PP mini, than you would, for about $ 10 a PP which is more sensitive than the Garrett, Minelab and many more.
And that's the truth (though some people do not like that) but I do ..........
On the thread you can find videos where you can see the Functioning of the PP and a comparison test with the Garrett. The method of detection is the same as the "top" brands. but better.
Read the thread quietly through and try to ignore my nonsense I tell occasionally.

good luck,
nupi

[chemelec]

A considerable amount of this wandering is a result of Very Minor, Self-Heating Temperature changes of the transistors, affecting the Gain of them.
That is why they tend to Stabalize better after a few minutes of operation.

[ToddB66]

I've been running and re-running, etc., etc., etc. back over this thread, trying to find the FINAL version of Nupi's Pinpointer schematic. I kept moving down the thread into April and then the site program throws me back to the first thread-starter post. I've copied several pre-final versions already, but then comes along another corrected version.

Can someone help.......my neck is killing me !

ToddB66

[Nupi]

***You are absolutely right, I've messed up.***

I often (I mean to frequently) made mistakes.

I think I'm the mistake man.


If Qiaozhi would give a award to those who make most mistakes than I win a prize for sure.

Do not worry, I care that tomorrow everything put together and post it. I hope that it is without error.

Have patience, I am a very old man.

[ToddB66]

***You are absolutely right, I've messed up.***

I often (I mean to frequently) made mistakes.

I think I'm the mistake man.


If Qiaozhi would give a award to those who make most mistakes than I win a prize for sure.

Do not worry, I care that tomorrow everything put together and post it. I hope that it is without error.

Have patience, I am a very old man.

Dear Nupi,

I apologize that my post got so melodramatic; you didn't deserve that. It's apparent that you have/are working hard to figure out the pin-pointer circuits, all the while accepting critique with good humor while sharing your creative brilliance in electronics with us.

When you feel that your work is completed, circuit designs finalized, testing finished and you are satisfied with the results, please direct me to your post(s) showing the final schematics and any other relevant photos and specifications.

Thank you Sir !

ToddB66

[Nupi]

Hi ToddB66,

If you want to build the good working PP (two versions) that can you already do.
You will find all the necessary data, with no errors, on #410 on this link.

http://www.geotech1.com/forums/showt...n-chain/page17

If you want to build the "on and go" PP then you'll have to wait
until we built ourselves the PP with the additions of Davor and tested.

regard, nupi

[sinclairuser]

sorry to dig up this old thread but i post here for completeness, the op was asking about the wandering on the centech pinpointer, i have been playing with three of these i got in a job lot, two of them are the same as the ones that have schematics posted a search of the forum brings up that and pics.
the third is the same circuit but has the extra parts populated, a vibro motor and a thermistor the basic two dont have that ntc, and drift alot, the third though has and is more stable, so the answer to the op's question is to do the baum7154 modifications in the Harbor Freight Centech Model 97245 Pinpointer Modifications. thread.
or just add the 10k thermistor, but the boards are identical so the silkscreen tells you what to put where so upgrading is trivial, i know some scoff at these simple detectors but the centech is cheap, relatively well made and works.