VLF MD with digital signal processing : Bee-Buzz 1

[Atul Asthana]

I was considering whether we could explore using 2–3 different TX frequencies interleaved in adjecent time slots, frrquencies being on either side of the main TX frequency.

Our coils have a low Q and perform similarly good enough at 5800 Hz and 6200 Hz. With an op-amp filter bandwidth of ±400 Hz and precise control over the TX frequency, we can operate within these limits. Additionally, the signal processing in each TX slot is independent of the preceding or succeeding slots.

This allows us to transmit and process different frequencies in separate time slots: Slot 1 at 5800 Hz, Slot 2 at 6000 Hz, and Slot 3 at 6200 Hz. The received signals from these slots can be analyzed using the Goertzel algorithm to extract amplitude and phase data for each frequency.

To effectively process and display this multi-frequency data, we’ll need a new technique to consolidate these results into meaningful information for the user. Increasing the number of slots to 512 and reducing the sine wave cycles per slot from 16 to 8 may help accommodate the additional data.

I’m curious to know the advantages this multi-frequency approach might offer and what strategies could be employed to integrate and optimize these results for improved performance in the metal detector. Could this enhance target discrimination, depth estimation, or reduce ground noise interference?

please opine.

[Atul Asthana]

That's all hidden in code. However, based on patent US7579839 I assume Minelab is doing narrowband synchronous quadrature demodulation in software. Likewise, Noka has a patent (US11914095) on an asynchronous demodulation method.

great, I'll read up. but may not be able to directly use their patents in our design, due to patents.

[ivconic]

I became boring (to myself too) repeating this on forum many times; but author of FelezJoo PI has done a real little miracle with a minimalist approach.
That is enough proof that even with little a lot can be achieved.
Of course, just looking at the schematic doesn't say much in support of my claim.
But after a dozen DIYs and the final success of getting it right (there are a lot of strict conditions for success); FelezJoo PI becomes a real little wonder, very usable and competitive.
Of course, behind everything is a very smart approach to writing code. Everything is in the code.
That's why I said "The "trick" is not in the codec but in the DSP."
In the specific case, the author first relied on principes explained in patent No.5,506,506 (US5506506) by Candy.
In this case it is VLF I/B and not PI. (easier to do than PI imho)
I can't remember the exact patents, but I think Carl tried to include them all on this site...among them there are a couple of well written ones with detailed algorithms.
All it takes is to take some time and do a little research by reading some of the patents.
Some of the algorithms can be reduced to minimalism and successfully applied in your project.
I think Paul suggested the same thing only in a different way, by linking to the smart students project.

[moodz]

I would agree .. we had some discussions on this forum years ago about the KISS principle and you really need to make it simple.
A simple way to get a POC "proof of concept going" is these possible pathways / options.

1. Take a simple project off the web ( ie exists already ) that ppl can build and play without visiting the bank manager or the wife. Like the example I gave. Then make it better.
OR
2. Take some generic modules ( eval boards and cpu boards ) and connect them together with some glue bits ( power supplies , tx circuit )
OR
3. Just use the soundcard in an old laptop / computer with a simple RX / TX and write/download the DSP code and try things out.

Instead you are choosing the most difficult path of designing a custom detector from scratch using random chips and DSP blobs AND you already said it wont be very high performance ????? ( waste of time )
Building the custom unit is the step AFTER the POC is done !!

As an example I have gone down choice 2. and with an ADC7760 eval board and an XILINX spartan eval board and some glue bits ( about $150 ) I getting PI ( 1 meter detect ranges + ground cancel ) performance from a single frequency detector with no front end amplifier,
Best of all I have not committed my eval modules to a "soldered" design ... I can reuse them ( and bits of the code ) on something else. There are no amps or filters on the frontend and I did not try to use nice sounding DSP blocks I just kept what worked and threw out everything that didnt.
moodz.

[Atul Asthana]

I became boring (to myself too) repeating this on forum many times; but author of FelezJoo PI has done a real little miracle with a minimalist approach.

............
I think Paul suggested the same thing only in a different way, by linking to the smart students project.

--------------------

Ivconic,

I am currently taking my time to browse through some patents, and it may take me weeks to identify the relevant ones, comprehend their details, and extract the knowledge applicable to this project.

However, those of you who have already explored these patents or worked on creating similar devices could share your insights, practical applications, and any associated challenges on this forum much more effectively and quickly.

For instance, you could delve into the student project you recommended, thoroughly analyze it to extract the relevant knowledge, and compare its methodology and outcomes with the goals of our project.

From this comparison, you could evaluate whether the project is feasible using the resources and constraints of the STM32 Blue Pill, and propose any necessary modifications.

Additionally, outlining the advantages of these suggested changes would help us understand how they enhance the project's performance or efficiency, providing a clear path for improvement.

The truth is, direct suggestions and improvements from a group of knowledgeable experts are far more valuable than one individual painstakingly analyzing the technology or patents, some of which I might struggle to fully understand or interpret. Collaborative discussion not only accelerates the learning process but also enhances the quality of solutions we can collectively achieve.

[Atul Asthana]

I would agree .. we had some discussions on this forum years ago about the KISS principle and you really need to make it simple.
A simple way to get a POC "proof of concept going" is these possible pathways / options.

1. .......
As an example I have gone down choice 2. and with an ADC7760 eval board and an XILINX spartan eval board and some glue bits ( about $150 ) I getting PI ( 1 meter detect ranges + ground cancel ) performance from a single frequency detector with no front end amplifier,
Best of all I have not committed my eval modules to a "soldered" design ... I can reuse them ( and bits of the code ) on something else. There are no amps or filters on the frontend and I did not try to use nice sounding DSP blocks I just kept what worked and threw out everything that didnt.
moodz.

Dear Moodz,

Thank you for your input. As I mentioned earlier, I am not up-to-date with electronics and signal processing, having not explored these areas deeply in the past 30 years. It’s clear that my design approach may be influenced by older ideas.

To provide clarity on the objective and some details of the design, may I kindly request you to revisit posts #1 and #68? The fundamental goal here is to create a low cost simple to create metal detector—regardless of whose idea or design it is. As Carl pointed out in his post #97, there are already several commercial direct sampling metal detectors, like ths design, with far superior performance, but these come at a significantly higher cost.

If you still feel that using a $2 Blue Pill board, $1 op-amps, and $5–$10 worth of additional mechanical hardware, along with open-source DSP libraries optimized for this constrained environment, is not a viable approach, I would greatly appreciate it if you could suggest an alternative design.

Consequently, could you please propose a solution that stays within the same budget and uses a similar number of components? I am more than willing to adapt and follow your recommendation.

Your insights, along with contributions from others, would help steer this project in the right direction and ensure the chosen approach remains both cost-effective and practical for a general hobbyist to implement.

Best regards,
Atul

[ivconic]

Such projects require commitment and engagement. Mostly everything revolves around the author, that is, the one who has an idea and knows what he wants.
I break down and change my mind every day, and for months now I've been trying to force myself to sit down and create a complete concept.
I don't even know what I want, I don't have focus, I don't have time and I'm overwhelmed with obligations.
And I'm not getting any younger during that time. During that time, young and much smarter people than me are already working on their tenth such project.
Github is full of works.
I have Nucleo 144 and ESP32 as two potential candidates. My latest research tells me that the Nucleo 144 is the better choice.
Now I need to find time, sit down and design the rest of the modules (Paul was 100% right here, the project needs to be broken into modules).
Once I get the modules, I draw the PCB, I have to send it to China for manufacturing. Because I am not capable of soldering those tiny components myself.
It's all a process. An ongoing process. And there is no certain outcome.
We have already tried to work together on projects several times and always the same problem has held things back. "Incompatibility" in opportunities, free time and resources.
That's why something like this is still an individual job.
As for the help; it is difficult to give concrete help because each of us should have the same set of hardware and software in front of him on the table.
And the worst part of the whole story is that they finally managed to infect me with the PI detector virus... so a couple of years ago I completely gave up on VLF I/B ideas!
The main culprits for this are Carl, Moodz and Tinkerer.
I think I have a very easy and interesting project somewhere on disk that could help you. I'll try to find it.
It already exists on the forum but I can't remember the name.
I remember building it and it worked quite nicely.

[ivconic]

I have it!
It's called Quant. Here is the archive, you have everything inside.
I made it and it works very nice.
The best part of the story is that you can use a wide variety of stock coils without having to build your own coils.

[moodz]

A Conceptual Design for a Fully Digital VLF Metal Detector Using STM32F103C8T6

This paper outlines the concept of a fully digital Very Low Frequency (VLF) metal detector based on the STM32F103C8T6 microcontroller. The design prioritizes simplicity, low cost, and ease of construction for electronics hobbyists while leveraging the processing power of a 32-bit microcontroller running at 72 MHz. STM32F103C8T6 is about 20 times faster than popular 8 bit microcontrollers.


So above is the header from post #1 and it would seem then that cost and processor performance are a priority .. but not detector performance or new innovative solutions / techniques ?? I can tell you that from my experience on this board the later two are what people are looking for. Of course they want cheapness also and easy to construct and open source and they expect you to support them when they have problems. But overall they want to pay the organ grinder peanuts for a full orchestral symphony.

But just on processor performance ... the ESP32 blows the Blue pill out of the water on bang for buck ... it has WIFI too which can be linked to a smartphone app .. saving even more money on LCD s and controls !!
The development environment is easier on the ESP32 too.

Though in consideration the raspberry pi is way faster than either of these .... try demodulating 100 IQ streams simultaneously ... the RPi can do it with bags of room to spare.

[Atul Asthana]

A Conceptual Design for a Fully Digital VLF Metal Detector Using STM32F103C8T6

This paper outlines the concept of a fully digital Very Low Frequency (VLF) metal detector based on the STM32F103C8T6 microcontroller. The design prioritizes simplicity, low cost, and ease of construction for electronics hobbyists while leveraging the processing power of a 32-bit microcontroller running at 72 MHz. STM32F103C8T6 is about 20 times faster than popular 8 bit microcontrollers.


So above is the header from post #1 and it would seem then that cost and processor performance are a priority .. but not detector performance or new innovative solutions / techniques ?? I can tell you that from my experience on this board the later two are what people are looking for. Of course they want cheapness also and easy to construct and open source and they expect you to support them when they have problems. But overall they want to pay the organ grinder peanuts for a full orchestral symphony.

But just on processor performance ... the ESP32 blows the Blue pill out of the water on bang for buck ... it has WIFI too which can be linked to a smartphone app .. saving even more money on LCD s and controls !!
The development environment is easier on the ESP32 too.

Though in consideration the raspberry pi is way faster than either of these .... try demodulating 100 IQ streams simultaneously ... the RPi can do it with bags of room to spare.

Great,
I am following the KISS principle.

Sir, first, lets get the 'good enough', and then we will strive for the best.

I'd also switch to esp32, if an external adc becomes necessary.
lets once get this design going, I wont hesitate to use Axon or Raspberry PI or even x-86 sbcs if the design needs it.

[Atul Asthana]

I have it!
It's called Quant. Here is the archive, you have everything inside.
I made it and it works very nice.
The best part of the story is that you can use a wide variety of stock coils without having to build your own coils.

thanks ivconic.

[moodz]

Great,
I am following the KISS principle.

Sir, first, lets get the 'good enough', and then we will strive for the best.

I'd also switch to esp32, if an external adc becomes necessary.
lets once get this design going, I wont hesitate to use Axon or Raspberry PI or even x-86 sbcs if the design needs it.

Sorry .... about those suggestions .. didnt know you worked for ST.

[Atul Asthana]

Sorry .... about those suggestions .. didnt know you worked for ST.

instead,
I will try and get st to work for me

[Atul Asthana]

I would agree .. we had some discussions on this forum years ago about the KISS principle and you really need to make it simple.
A simple way to get a POC "proof of concept going" is these possible pathways / options.

1. Take a simple project off the web ( ie exists already ) that ppl can build and play without visiting the bank manager or the wife. Like the example I gave. Then make it better.
OR
2. Take some generic modules ( eval boards and cpu boards ) and connect them together with some glue bits ( power supplies , tx circuit )
OR
3. Just use the soundcard in an old laptop / computer with a simple RX / TX and write/download the DSP code and try things out.

Instead you are choosing the most difficult path of designing a custom detector from scratch using random chips and DSP blobs AND you already said it wont be very high performance ????? ( waste of time )
Building the custom unit is the step AFTER the POC is done !!

As an example I have gone down choice 2. and with an ADC7760 eval board and an XILINX spartan eval board and some glue bits ( about $150 ) I getting PI ( 1 meter detect ranges + ground cancel ) performance from a single frequency detector with no front end amplifier,
Best of all I have not committed my eval modules to a "soldered" design ... I can reuse them ( and bits of the code ) on something else. There are no amps or filters on the frontend and I did not try to use nice sounding DSP blocks I just kept what worked and threw out everything that didnt.
moodz.

mmodz,

It will be a grest idea if you could help and restructure this project on the principles and processes, you've proposed.

a much simpler design, based on your choice of cpu and adc boarfs etc, could be a better option, and we could all learn this principle, save efforts and the hassle oif experimentstion.

I think, we will wait till we have a better, more cost effective and more robust proposal from you.

you can let us know the estimate of time for the propsal and for the POC .

regards and best wishes
atul

[moodz]

Try the nano_vlf as a starting point .... however it uses two processors for some reason that I dont know. But you should be able to see there is fair bit of work in this project to achieve what it does.
https://www.geotech1.com/forums/foru...d-january-2024

However if you are going to get into developmental DSP you will need more powerful hardware than a blue pill for development work because there will be insufficient processing overhead for debugging code etc.
The rule of thumb is go hard or go home.
Once you have understood what the signal chain looks like and you have coded a working system or simulation ... then and only then should you try to port it to the blue Pill which may or may not be capable
In commercial development the only reason to use less powerful chips is to save money ( for the manufacturer ) however engineers usually hate this reason because it just creates headaches.

moodz