Can pinpointer detecting thin chain?

[jakob leo]

Pcb please

[gurdal]

All Hi,
My Nupim Test

https://youtube.com/shorts/gZ23SDKe6rM?si=taQy8rnMFlDLh9xw

[hadireyhani]

good job

[MartyJ1963]

Thanks Getsa! Much appreciated! Regards, Marty.

[getsa]

The PCB is perfoboard. The schematic is the modified one (page 24). Turns are 208/69.
Greetings!

[MartyJ1963]

Hiya Getsa, I viewed your video,,,,Great result! Which schematic and pcb layout did you use and what are is your coil data please? Thanks, Regards, Marty.

[getsa]

Hello everyone,
Here is my result with Nupi ...

https://www.youtube.com/shorts/Tnj76--DixU

Greetings!

[Polymer]

It's the definition of all induction-based metal detectors. Target eddy currents induce an EMF in the RX coil; for IB/VLF that's a dedicated RX coil, for PI it's the same coil as was used for TX 10us ago, and in proximity detectors (BFO, energy theft) it's the same coil as is continuously transmitting.

I re-read the math section, and I'm pretty sure there are major errors. Eq 6 does not look at all right, and Eq 7 & 8 are definitely not the derivatives of 6. If I get time I will try to grind through it and see what it should be.

Thank you again Carl!

If I have comprehended this right, basically all metal detectors are in the "near field" and inductively-coupled ...?
As compared to say a radar which is "far field" and "reflectively" evaluated.

I am sure there must be other methods too. I spoke with a R&D guy of ultrasound products about the possibilities of ultrasound to image the sea floor in salt water,
with a resolution in the low millimeter range (chains/rings) and a resonable depth as to recognise the shape of denser objects in the substrate, without all the issues that PI/VLF have in sea water.

The conversation went quite well and I was excited until the question was asked "what particulate size" ... Me: ???
"In the water". Oh my, theres always stuff swimming around and the relevant sizing was u-meter range if I recall properly.
So that was that. I could have gotten testing done for my specs ... would have cost around 6000 USD.
Since I just want easier detecting and not jumping into starting a new company, I left it at that.

Perhaps someone else is deeper into this.

I read an article about a type of GPR around 25-30 years ago. It was military and in the testing phase for "looking" into the ground for mines. Geometric recognition also.
It was interesting and apparently it worked. Drawbacks: it needed liquid nitrogen for cooling, cost a fortune and weighed a helluva lot.
I sort of tried following it up, but never found anything about it again.

Gosh, Ive digressed.

More questions on the NUPI pinpointer to come - I have a soft spot for this simple device.

[Cazavor]

I use PP capacitors for the 33nF & 1nF capacitors. It looks like all the box capacitors you are using are PE, they are smaller than the PP ones.
Instead of a ceramic for C4 I have used a PE capacitor. Not sure if these components make such a difference.

What definitely is very different, is the ferrite I now use.

Breadboarding and having the coil wires flopping around also makes it more unstable.
Cant find the file right now, I have been using a printout which has been in the box "to do" for years now.
See if you can find the schematic from Chemelec.

I know how frustrating and amazing the NUPI pinpointer is. Dont give up.

I will build another one the next few months and hope to achieve similar results hoping this one is not some random luckiness.

As you can see, I do not fully understand this myself yet.

The transistors I used are 2n3904 and 2n3906, nothing special.

Ha, the patent you posted is from Whites ... perhaps Carl might like to comment.

The yellow capacitors I bought from aliexpress named "Polypropylene correction safety plastic film capacitors" with no datasheet. Who knows what they really are. I measured them at 0.3 ohm ESR and no significant leakage.

I built a perfboard version of the original NUPI circuit so board is not the problem. Attached a few pictures including some of my finds with solely this pointer.

I might revisit this project in the future but not at the moment. I have my hands full with a PI detector and also currently I'll get by with my two 20? pinpointers from China, one is PI and the other energy theft.

[dbanner]

Oh dear God, radians per second. I'm outta here!

[dbanner]

Further down, Q is taken at the resonant frequency, fine, but the equation for W ??? Shouldn't it be 1 divided by the square root of L*C ?
I probably arose on the wrong side of the bed this morning. Need coffee.

[Carl-NC]

Thank you Carl.

Have read the patent and am puzzled by something written on page 2 / lines 32-37 ... "These eddy currents produce a secondary electrical field ..."

Is that not the definition of a PI detector? At least thats how I understand it.

It's the definition of all induction-based metal detectors. Target eddy currents induce an EMF in the RX coil; for IB/VLF that's a dedicated RX coil, for PI it's the same coil as was used for TX 10us ago, and in proximity detectors (BFO, energy theft) it's the same coil as is continuously transmitting.

I re-read the math section, and I'm pretty sure there are major errors. Eq 6 does not look at all right, and Eq 7 & 8 are definitely not the derivatives of 6. If I get time I will try to grind through it and see what it should be.

[Polymer]

@Cazavor

Forgot to mention: The new coil I made for this pinpointer is shielded.

[Polymer]

Thank you Carl.

Have read the patent and am puzzled by something written on page 2 / lines 32-37 ... "These eddy currents produce a secondary electrical field ..."

Is that not the definition of a PI detector? At least thats how I understand it.

[Carl-NC]

Ha, the patent you posted is from Whites ... perhaps Carl might like to comment.

The patent describes a method known as "energy theft" or "loaded oscillator." It is in a family I call "proximity methods" that includes BFO and off-resonance. White's used this in their Coinmaster TR model in the 1980s:

http://www.treasurenet.com/forums/today-s-finds/47468-found-mail-old-white-coinmaster-tr.html

In reality, it is not a TR. Targets create a load change to the oscillator which alters the frequency, amplitude, and DC offset. In this case, the offset is the biggest contributor to detection. In most other energy theft methods I've seen the output of the oscillator is rectified and amplitude changes are used to drive a separate VCO or other audio oscillator. The patent shows a very clever way to get the audio from the coil oscillator using a divider and then recombine it with the output offset to drive a comparator.

The patent is exceptionally well-written and exactly describes what is happening, and even has some light math if you want to understand it at that level. You don't find many patents written as well as this one. Hirschi was a pretty smart guy, I looked through some of his old engineering notebooks when I worked at White's.