GOLD coil hunter

[green]

And ... at such short sample delays you will start to pick up the ground itself, especially in areas where gold nuggets tend to be found. This requires the detector to have some form of ground balance, which none of the PI designs on this forum currently have.

A chart comparing a 10usec sample starting at 6, 10, and 14usec for a US nickel(TC=10usec) and ground with a slope of -1.0 and -1.33. Was expecting to see a bigger difference.

[Tibuck19]

Tibuck19,

You live in a great international city. After visiting a company called Matrox in Dorvall on many business trips, I really enjoyed Spring and Summer in Montreal, the outdoor dining and wine drinking.

The key to making progress with electronics technology is to gain an understanding of the fundamental electronics principals and experiment to see how these principals interact. To experiment you need a few general tools that are a good investment, even if used and in good working order.

1. A digital volt meter
2, A signal generator that goes up to 2MHz or higher.
3. A 20 MHz bandwidth oscilloscope with 10x probes to reduce the load on sensitive circuits being measured or observed.

For pulse induction metal detectors you need to understand time constants both for the coil charge and discharge time constants as well as target time-constants to appreciate how much energy is being absorbed into the target metal mass as well as how much time that energy will last while discharging itself. It is only during the target discharge time that the Receive mode of the PI detector is capable of detecting a target. Small targets release their stored energy very quickly that is why the shorter the delay, the smaller targets you can detect.

Qiaozhi is right about short delays being more sensitive to mineralized ground typically found where gold is found. Using smaller coils and probes is one way to minimize mineralized ground. Ground balancing samples two ground signals and treats one as positive and the other as negative and cancels out the slowly moving ground signals while letting the faster moving target signal to sound a target.

The ITMD book will get you involved with building your own circuits, measure and observe various circuits, make changes and modifications to optimize for your favorite targets and hunting environment. Learning by doing is a highly effective and efficient way to learn. However, it takes published knowledge, tools to observe, and motivation to stay involved.

You have found the best Internet metal detecting forum to ask questions and obtain directions to make progress in your chosen metal detection directions!

Joseph J. Rogowski

Matrox has since down sized their operations dramatically, I had a few buddies working there, sadly for most circuit board companies around here, 90% of the work now gets done in China beside prototyping , If know Matrox, you surly know Electropac which was once in Point-clear, I worked there for a few years, Summer in Montreal is a great place to be, heck we have, great wines ,great food, beautiful woman, nice mild weather And last but not least F1 races hahaha, If you ever make your way back down this way, Id 'gladly offer you a drink. I have to totally agree with you and the best way to learn is to bite down hard and learn learn learn. I know more today about this subject then I did yesterday and I ll keep at it till I can talk the talk and walk the walk. I do like this forum you all seem to be a great bunch of guys willing to help and share knowledge.

[Tibuck19]

You have that wrong.
It's all to do with the time-constant of the coil (plus other parasitics that reduce the decay time). You want the current in the coil to reduce to near zero in as short a time as possible. i.e. way before the eddy currents in the target have died away. If you have a slow coil, the target response will have disappeared before you are able to sample.
Have you read ITMD? -> Inside the METAL DETECTOR - Second Edition - Published 2015

Are you the author of this publication ?

[Qiaozhi]

Are you the author of this publication ?

The Geotech website is owned and financed by Carl Moreland, and Carl and I are the administrators.
Over a number of years we have both searched for and collected numerous technical books and articles concerning metal detectors, and it is surprising how few of these can truly be called "technical". Most only cover the subject very superficially, or are essentially just project-based. Operational theory is rarely covered in any detail.

After meeting on the Geotech forums, we discovered that we were both in the process of writing a book on this very subject, and (after some discussions) decided to pool our efforts. Edition 1 of Inside the METAL DETECTOR was subsequently published in 2012. After struggling to get any serious attention from established book publishers (who wanted us to expand it into a more general electronics book) we decided to self-publish. We did not want to attempt to teach basic electronics, as there are many other books available that cover these concepts. We have made the assumption that you already know Ohm's Law, those of Kirchoff, transistor basics, opamps, filtering and some trigonometry. ITMD is essentially aimed at the sort of people who post in the Geotech forums.

Edition 2 of ITMD was published in 2015. This is an updated version to fix a few errors and inconsistencies that were in the first edition, include extra helpful information, and clarify certain areas. We also removed the chapters on Long Range Locators and the Pistol Detector to make it more focussed on real detecting technology. ITMD edition 2 is only available through Amazon, so we no longer have the joy of stuffing books into jiffy bags. I can assure you that the novelty soon wears off. Note that ITMD edition 1 is out of print and sold out. ITMD edition 2 is the replacement.

So, in answer to your question, "yes".

[WM6]

Best MD technical book ever.

Hope we will see ITMD #2 too - soon.

[Tibuck19]

The Geotech website is owned and financed by Carl Moreland, and Carl and I are the administrators.
Over a number of years we have both searched for and collected numerous technical books and articles concerning metal detectors, and it is surprising how few of these can truly be called "technical". Most only cover the subject very superficially, or are essentially just project-based. Operational theory is rarely covered in any detail.

After meeting on the Geotech forums, we discovered that we were both in the process of writing a book on this very subject, and (after some discussions) decided to pool our efforts. Edition 1 of Inside the METAL DETECTOR was subsequently published in 2012. After struggling to get any serious attention from established book publishers (who wanted us to expand it into a more general electronics book) we decided to self-publish. We did not want to attempt to teach basic electronics, as there are many other books available that cover these concepts. We have made the assumption that you already know Ohm's Law, those of Kirchoff, transistor basics, opamps, filtering and some trigonometry. ITMD is essentially aimed at the sort of people who post in the Geotech forums.

Edition 2 of ITMD was published in 2015. This is an updated version to fix a few errors and inconsistencies that were in the first edition, include extra helpful information, and clarify certain areas. We also removed the chapters on Long Range Locators and the Pistol Detector to make it more focussed on real detecting technology. ITMD edition 2 is only available through Amazon, so we no longer have the joy of stuffing books into jiffy bags. I can assure you that the novelty soon wears off. Note that ITMD edition 1 is out of print and sold out. ITMD edition 2 is the replacement.

So, in answer to your question, "yes".

Excellent,

[Tibuck19]

Not to jump to far off topic , id R2 the damping resistor for the Surf Pi and even better question, is R2 always used for this for the damping resistor for most board you guys make on here ?

[Qiaozhi]

Not to jump to far off topic , id R2 the damping resistor for the Surf Pi and even better question, is R2 always used for this for the damping resistor for most board you guys make on here ?

The designation "R2" is commonly known as the reference designator. It could just as well be "R202". The ref des is simply a unique identifier for each component in the design. PCB designers generally renumber the reference designators to run across the board in stripes from left to right. This makes it easier to locate a component. "R" is used for resistors, "C" for capacitors, "Q" for transistors,"M" for MOSFETs, "U" or "IC" for integrated circuits, etc.

[Tibuck19]

The designation "R2" is commonly known as the reference designator. It could just as well be "R202". The ref des is simply a unique identifier for each component in the design. PCB designers generally renumber the reference designators to run across the board in stripes from left to right. This makes it easier to locate a component. "R" is used for resistors, "C" for capacitors, "Q" for transistors,"M" for MOSFETs, "U" or "IC" for integrated circuits, etc.

HAHAHA im a newbie yes but not that new, But fantastic answer nonetheless. Just to be sure if I read other post right the value of R6 is the damping resistor for the Surf correct ?

[Qiaozhi]

Just to be sure if I read other post right the value of R6 is the damping resistor for the Surf correct ?

Correct.