EXTRA_EXTRA_DEEP DISCRIMINATING DETECTOR

[Tinkerer]

Tinkerer,

I think you would be better served by using the arduino platform rather the PIC. It was developed to
be simple enough for kids to use. It has simple hardware and software and is inexpensive.

Are you projects aimed at finding gold or just general detection?

I am a retired engineer, and am trying to learn the ins and outs of metal detecting.
I would like to develop and build one of my own.

Best Regards,

Paul

Hi Paul,

You are looking at an old thread, but I am still here and if you want to give it a try, I am willing to help.
My knowledge of programming never went very far, but I do know how PI detectors work.
What kind of gold do you want to find?

[Tinkerer]

Are you projects aimed at finding gold
---
gold does the people crazy.

I agree

[toolnuts]

Tinkerer,

I am looking to build a reasonable PI machine that can find .3g nuggets and up.

I have no interest in finding anything else. If I lived in Europe, I suppose, I
might like finding old coins.

I have read all of George Overton's books, but he is not targeting gold, and
does not give many PI details for gold, especially in mineralized soils.

Can you point me to information that would provide a good foundation
for the direction I want to head?

I have a good electronic shop, and a machine shop. My electronics
background is quite dated. I worked in controls, for Boeing, but I
retired 26 years ago. I am trying to get back into electronics, but
it is slow going.

Best Regards,

Paul

[waltr]

Tinkerer,

I am looking to build a reasonable PI machine that can find .3g nuggets and up.

I have read all of George Overton's books, but he is not targeting gold, and
does not give many PI details for gold, especially in mineralized soils.

Can you point me to information that would provide a good foundation
for the direction I want to head?

Best Regards,

Paul

Small gold has a short time constant (TC) therefore require the Sampling to happen very soon after the TX pulse stops. There are many, many threads in Geotech discussing how to obtain early sampling.
Check the threads by 666 and Green for starts.

[kt315]

ITMD is good book to begin a way in the dirtysht background electronics basics. IMO.

[green]

Tinkerer,

I am looking to build a reasonable PI machine that can find .3g nuggets and up.

I have no interest in finding anything else. If I lived in Europe, I suppose, I
might like finding old coins.

I have read all of George Overton's books, but he is not targeting gold, and
does not give many PI details for gold, especially in mineralized soils.

Can you point me to information that would provide a good foundation
for the direction I want to head?

I have a good electronic shop, and a machine shop. My electronics
background is quite dated. I worked in controls, for Boeing, but I
retired 26 years ago. I am trying to get back into electronics, but
it is slow going.

Best Regards,

Paul

Like you I'm trying to make a PI to detect gold. I've never done any metal detecting but would try detecting for gold if I could make a PI that would have a chance to find some nuggets. Lately I've been trying to detect #9 lead shot(Carl replied in another thread #9 shot is similar to a .5grain nugget). 4.6 grains(.3 gram)should be easier to detect. Maybe #4 lead shot would be a good test target for a .3 gram nugget. Maybe some one that knows could suggest a different size lead shot. Including some charts.

[Qiaozhi]

Tinkerer,

I am looking to build a reasonable PI machine that can find .3g nuggets and up.

I have no interest in finding anything else. If I lived in Europe, I suppose, I
might like finding old coins.

I have read all of George Overton's books, but he is not targeting gold, and
does not give many PI details for gold, especially in mineralized soils.

Can you point me to information that would provide a good foundation
for the direction I want to head?

I have a good electronic shop, and a machine shop. My electronics
background is quite dated. I worked in controls, for Boeing, but I
retired 26 years ago. I am trying to get back into electronics, but
it is slow going.

Best Regards,

Paul

Try the Minipulse Plus REV-E project -> https://www.geotech1.com/forums/show...PP-Beach-REV-E

As it says at the start:
"Here is the latest incarnation of the popular Minipulse Plus design. Although this revision is referred to as MPP Beach, there is nothing to prevent the various settings being adjusted to detect lower conductivity items such as gold nuggets."

The only problem may be the lack of ground balance if you're planning to hunt in heavily mineralized soil.
However, here -> https://www.geotech1.com/forums/show...586#post206586
KRinAZ modified a REV-C board to operate in the high iron mineralization of the gold bearing areas of Arizona (or Australia).

Some of the modifications made by KRinAZ subsequently found their way into the later REV-D and REV-E versions.

Also, there is waltr's HH2 project, which does have ground balance:
https://www.geotech1.com/forums/show...ake-on-the-HH2

[Tinkerer]

Tinkerer,

I am looking to build a reasonable PI machine that can find .3g nuggets and up.

I have no interest in finding anything else. If I lived in Europe, I suppose, I
might like finding old coins.

I have read all of George Overton's books, but he is not targeting gold, and
does not give many PI details for gold, especially in mineralized soils.

Can you point me to information that would provide a good foundation
for the direction I want to head?

I have a good electronic shop, and a machine shop. My electronics
background is quite dated. I worked in controls, for Boeing, but I
retired 26 years ago. I am trying to get back into electronics, but
it is slow going.

Best Regards,

Paul

Paul,

since you like the Arduino, we should give the "Arduino Nano Pulse Induction Metal Detector Project - Published March 2021 in Technical Books, Papers, and Literature" a closer look.
I like the idea that it is "fully open source" and has a book with all the details explained.
It sounds like a good platform to start with.
Can it be tweaked to become a nugget finder? Probably, but I need to buy the book to really look at it.
Buying the book and a kit from Silverdog would be a good start. Build that to get familiarized and to have a reference for the next version where we would make changes to make it more specific for nugget hunting.

[green]

Paul,

since you like the Arduino, we should give the "Arduino Nano Pulse Induction Metal Detector Project - Published March 2021 in Technical Books, Papers, and Literature" a closer look.
I like the idea that it is "fully open source" and has a book with all the details explained.
It sounds like a good platform to start with.
Can it be tweaked to become a nugget finder? Probably, but I need to buy the book to really look at it.
Buying the book and a kit from Silverdog would be a good start. Build that to get familiarized and to have a reference for the next version where we would make changes to make it more specific for nugget hunting.

surfdetector has a kit completed on the bench. Maybe he could try to detect a piece of #4 lead shot if #4 shot is a good test target.

I wonder why we can't set a goal and then define what might be required to accomplish the goal. Do we need GEB? Is #4 lead shot a good test target? What distance do we want to detect the test target(GEB on and GEB off)?

If we need GEB, there is going to be a hole. Where would we like it?

[Qiaozhi]

surfdetector has a kit completed on the bench. Maybe he could try to detect a piece of #4 lead shot if #4 shot is a good test target.

I wonder why we can't set a goal and then define what might be required to accomplish the goal. Do we need GEB? Is #4 lead shot a good test target? What distance do we want to detect the test target(GEB on and GEB off)?

If we need GEB, there is going to be a hole. Where would we like it?

#4 lead shot has a diameter of 3.1mm, so from calculation:



in this case the current implementation of the Arduino Nano detector should not be able to detect #4 lead shot. This is because the minimum main sample delay is 10us. Since 5 * 1.39us = 6.95us, the eddy currents will have died away long before the main sample occurs. The 10us minimum delay is caused by the software overhead due to setting up the timer register and entering and exiting the interrupt routine. However it should be possible to get below 10us if the delay is produced without relying on the timer. Of course this would still require a suitable coil, and possibly a reduction in the TX pulse width.

The actual position of the target hole will depend somewhat on the soil conditions, and consequently the TC you're trying to ignore.

Is #4 lead shot a realistic target to use for testing?
Carl has previously said: "If you can detect a #9 lead shot, then you can detect most 1/2 grain nuggets".
Calculating the tau of #9 lead shot gives 579ns. Which means that the eddy currents have vanished after only 2.9us.

[bbsailor]

#4 lead shot has a diameter of 3.1mm, so from calculation:



in this case the current implementation of the Arduino Nano detector should not be able to detect #4 lead shot. This is because the minimum main sample delay is 10us. Since 5 * 1.39us = 6.95us, the eddy currents will have died away long before the main sample occurs. The 10us minimum delay is caused by the software overhead due to setting up the timer register and entering and exiting the interrupt routine. However it should be possible to get below 10us if the delay is produced without relying on the timer. Of course this would still require a suitable coil, and possibly a reduction in the TX pulse width.

The actual position of the target hole will depend somewhat on the soil conditions, and consequently the TC you're trying to ignore.

Is #4 lead shot a realistic target to use for testing?
Carl has previously said: "If you can detect a #9 lead shot, then you can detect most 1/2 grain nuggets".
Calculating the tau of #9 lead shot gives 579ns. Which means that the eddy currents have vanished after only 2.9us.

George,

Why not also add what we need to fully stimulate these small, low TC targets? Theory tells us that the TX pulse discharge slope determines how fully the desired target size is stimulated. This discharge slop depends on the value of the damping resistor and any other resistance in parallel with the damping resistor such as the first amplifier stage input resistor value while the clamping diodes are conducting. Visualizing this forms a discharge slope with a kink at the point where the clamping diodes stop clamping and are open.

A good discharge slope mental model is formed when you take the coil value in uH and divide this value by Rd or damping resistor value. The 1.39 uS target would need an Rd of 1.39 divided by 5 or .278 uS with a 300 uH coil needing a 1079 ohm damping resistor to fully stimulate the 1.39 uS target. 300 uH coil divided by a Rd of 1079 is .278 uS.

This now gets down to needing a very creative coil construction technique to keep coil wire from retaining any eddy currents and looking like a target. Using Litz wire or very thin coil wire is required. The coax wire joint to the coil wire and/or the shield is another challenge to keep this solder joint from looking like a target.

The main point that I am trying to make is that at very low delays the coil construction techniques needs to focus on techniques to reduce coil and circuit capacitance and keep any physical parts of the coil from looking like the small targets you are trying to detect.

I hope this gets a discussion going in this direction.

Joseph J. Rogowski

[Tinkerer]

surfdetector has a kit completed on the bench. Maybe he could try to detect a piece of #4 lead shot if #4 shot is a good test target.

I wonder why we can't set a goal and then define what might be required to accomplish the goal. Do we need GEB? Is #4 lead shot a good test target? What distance do we want to detect the test target(GEB on and GEB off)?

If we need GEB, there is going to be a hole. Where would we like it?

"set a goal and then define what might be required to accomplish the goal"

this is the way to go.

[green]

#4 lead shot has a diameter of 3.1mm, so from calculation:



in this case the current implementation of the Arduino Nano detector should not be able to detect #4 lead shot. This is because the minimum main sample delay is 10us. Since 5 * 1.39us = 6.95us, the eddy currents will have died away long before the main sample occurs. The 10us minimum delay is caused by the software overhead due to setting up the timer register and entering and exiting the interrupt routine. However it should be possible to get below 10us if the delay is produced without relying on the timer. Of course this would still require a suitable coil, and possibly a reduction in the TX pulse width.

The actual position of the target hole will depend somewhat on the soil conditions, and consequently the TC you're trying to ignore.

Is #4 lead shot a realistic target to use for testing?
Carl has previously said: "If you can detect a #9 lead shot, then you can detect most 1/2 grain nuggets".
Calculating the tau of #9 lead shot gives 579ns. Which means that the eddy currents have vanished after only 2.9us.

What I think, not saying it's correct.

The actual position of the target hole will depend somewhat on the soil conditions, and consequently the TC you're trying to ignore. The grounds I've measured have the same R decay slope. Tx time and profile effect decay slope, maybe others. Don't think soil condition effects hole location. Tx time and profile + delay and sample times do.

Don't know if a piece of #4 lead shot is a good test target for toolnuts .3grain nugget. https://www.geotech1.com/forums/attachment.php?attachmentid=53833&d=1606672927 a chart I made for another thread. The #4lead shot is harder to detect than the 4grain nugget(reply #51)so maybe a larger shot would be better. #4 was the largest I have to test, will get correct size if we can define the size. There was only one of the seven 8mesh nuggets(reply #51)that detected farther than #4 shot.

Since 5 * 1.39us = 6.95us, the eddy currents will have died away long before the main sample occurs. TC isn't the only thing that effects signal strength. #9 shot and a 10mm square piece of regular strength aluminum foil have a similar TC but the foil has a signal strength about 100 times the shot.

[Tinkerer]

What I think, not saying it's correct.

The actual position of the target hole will depend somewhat on the soil conditions, and consequently the TC you're trying to ignore. The grounds I've measured have the same R decay slope. Tx time and profile effect decay slope, maybe others. Don't think soil condition effects hole location. Tx time and profile + delay and sample times do.

Don't know if a piece of #4 lead shot is a good test target for toolnuts .3grain nugget. https://www.geotech1.com/forums/attachment.php?attachmentid=53833&d=1606672927 a chart I made for another thread. The #4lead shot is harder to detect than the 4grain nugget(reply #51)so maybe a larger shot would be better. #4 was the largest I have to test, will get correct size if we can define the size. There was only one of the seven 8mesh nuggets(reply #51)that detected farther than #4 shot.

Since 5 * 1.39us = 6.95us, the eddy currents will have died away long before the main sample occurs. TC isn't the only thing that effects signal strength. #9 shot and a 10mm square piece of regular strength aluminum foil have a similar TC but the foil has a signal strength about 100 times the shot.

The surface area delivers most of the target response amplitude. Take a lead shot and knock it flat and see how the target response amplitude increases. Still the same mass of lead, but much more amplitude.
Gold nuggets are nearly always more flat than round. Often like flakes for very small nuggets.
There is a relationship of target response amplitude with coil diameter and ampere turns and di/dt. Green, your 133mm diameter coil can see the #9 lead.
What is the peak coil current?
di/dt?
Ampere turns of your TX?
Surface area of your TX coil? In this instance it is a bit more complicated, as the TX coil is oval.
An EXEL spreadsheet with these calculations would be a very useful tool.

[green]

The surface area delivers most of the target response amplitude. Take a lead shot and knock it flat and see how the target response amplitude increases. Still the same mass of lead, but much more amplitude.
Gold nuggets are nearly always more flat than round. Often like flakes for very small nuggets.
There is a relationship of target response amplitude with coil diameter and ampere turns and di/dt. Green, your 133mm diameter coil can see the #9 lead.
What is the peak coil current?
di/dt?
Ampere turns of your TX?
Surface area of your TX coil? In this instance it is a bit more complicated, as the TX coil is oval.
An EXEL spreadsheet with these calculations would be a very useful tool.

fig8 coils133_spread sheet I used when I made the coil.
gold detector1_scope ground, analog ground(2.5V above -PS). CH1, volts across .5ohm resistor from -PS to Mosfet source(reason shows current only in avalanche) recordings of differentiator out with different targets(#4 shot 500mV/div)(#9 shot 100mV/div)
gold detector2_picture of #9 shot and #9 shot flattened.

Delay and sample times from nuggets2 where different than todays recordings. Tx current was 1A peak current constant rate instead of not controlled 2A peak.