VLF MD with digital signal processing : Bee-Buzz 1

[Marchel]

Yes, I work for FTP (Bounty Hunter, Teknetics, Fisher).



It is both. You can't get high performance results with low performance hardware, no amount of software can fix a bad ADC. However, it is often a useful step to start out with lower ambitions and simpler hardware and work your way up. For a 'why' see my next comment.



You can talk about the process for months on end, but the most valuable step is to build a circuit and get it working. For that, all you need is a TX driver, preamp, micro, and coil. Build it, make it work! You'll learn a whole lot more from that than continuing to talk about it. This thread is now 11 pages long and your very first post was a reasonable plan of what you should do.

I also think that until hardware is made and real tests and measurements are done, the theory is worthless.

[Marchel]

If the prototype design were up to me, I would build it on this STM32H7 board, which also has a 16bit ADC and a small LCD that is enough for common information. On the top side of this board, I would connect a board with a few buttons and on the bottom side, a board with TX, RX and an audio amplifier.

https://vi.aliexpress.com/item/10050...Cquery_from%3A

[moodz]

If the prototype design were up to me, I would build it on this STM32H7 board, which also has a 16bit ADC and a small LCD that is enough for common information. On the top side of this board, I would connect a board with a few buttons and on the bottom side, a board with TX, RX and an audio amplifier.

https://vi.aliexpress.com/item/10050...Cquery_from%3A

Hey that board looks OK and could do the job .

But seriously Carl is right there needs to be less talk and more action. Like at least a diagram of the signal flow. Following this thread is like listening in to a a crowd at the pub .. everyones got an opinion but you cant find them when its their turn to buy a round of beers.
I know Carl does not like it but you really do need to choose a better CPU than the blue pill ( which name sounds like it needs to be inserted somewhere LOL ).
Also I think Carl also wont like it but you need to model some of this stuff as well ... as it will help other people understand what is going on ... rather than trying to interpret a huge block of obscure code in a undersized platform like the blue pill.

So my 2 cents ( and there are many ways to skin a cat - so this is not the only way ).
Get on a Matlab trial ( you have 30 days for free ) and you can get 20 hours a month on line access for free also.

1. Draw your model and run it in simulink- heres the IQ demodulator


and here is what is in the IQ block


2. You can edit the params in each block like frequency / phase etc as much as you want. Add or delete blocks as required.

3. Now right click on the IQ block and select generate code. Done the C code for the IQ demod is autmagically generated.

4. You can even get Matlab to squirt the code into your chosen platform. ( you WILL have to put more bits into it though )

If you have your model all this takes less than a minute.
I can post the model too ... but maybe you should learn by doing.

PS I have not used MATLAB for years ... its come a long way.

moodz

[Marchel]

It looks pretty cool but I've never worked with Matlab but I can try it. The biggest problem is that Matlab will never replace real tests because a metal detector behaves completely differently on the ground than in the air and it's best to do all the tests on the ground with real equipment.

[moodz]

It looks pretty cool but I've never worked with Matlab but I can try it. The biggest problem is that Matlab will never replace real tests because a metal detector behaves completely differently on the ground than in the air and it's best to do all the tests on the ground with real equipment.

In order to do the real tests you have to devise the real circuit ... my experience is that most people apply lots of tweaks to circuits that they think will work.
If there is an understanding of how the different variables change then the correct modifications can be made to the circuit so that it will do what you want in real testing. Potentially you could simulate a full ground / coil / detector in matlab however that is not the intent that I meant. Its more of a case of quickly generating the code harness that can then be tweaked in the real testing and also a way of communicating the model so people can contribute. Its a top down modular approach to solving the problem rather than starting at the bottom ... building a circuit then making it work.
My experience with top range detectors is that the air test and ground test dont show a huge difference in target ranges ... this is in contrast to "home built" detectors which usually dont get the ground balance / cancellation right.

[Altra]

If the prototype design were up to me, I would build it on this STM32H7 board, which also has a 16bit ADC and a small LCD that is enough for common information. On the top side of this board, I would connect a board with a few buttons and on the bottom side, a board with TX, RX and an audio amplifier.

https://vi.aliexpress.com/item/10050...Cquery_from%3A

How do you load the hex on a board like this? A USB bootloader or dedicated programmer? I like this board and it would be good way for me to get familiar with the STM micro family.

Thanks

[Marchel]

How do you load the hex on a board like this? A USB bootloader or dedicated programmer? I like this board and it would be good way for me to get familiar with the STM micro family.

Thanks

There are many ways to upload firmware for this board, I personally use HID bootloader and upload firmware directly to keil ARM via this bootloader. You can upload bootloader easily via USB using STM32CubeProgrammer. Check out these files on GitHub and you will find everything you need there.

https://github.com/WeActStudio/MiniSTM32H7xx

[Altra]

Thanks Marchel

[ivconic]

I don't want to derail a topic that has started to develop in an interesting direction,
I just wanted to give a small update to my previous thoughts here: https://www.geotech1.com/forums/foru...time-of-change

[Atul Asthana]

It's great to see the interest in developing a direct sampling VLF metal detector using a highly constrained core device. I truly appreciate all the suggestions for improving the device, as well as the advice on refining my product development methodology and enhancing my skills and expertise.

I understand that many are eager to see a prototype and that the current discussions often encourage me to build one and then work on improving its performance. However, I am currently engaged in (more thsn) full-time work unrelated to electronics, software, engineerng maths or signal processing. My available time for metal detector research is limited to some of my travel time. And my technology friends, who have agreed to assist with building the prototype, won’t be available until the end of the financial year (end of March or early April).

I am also not in a rush to create a prototype until I feel confident that my research has yielded atleast a few solid, promising outcomes, that exceed my expectations and vastly surpass my 30 years old knoeledge.

I've explained most of the concepts in the initial paper and subsequent discussions, so it should be fairly straightforward for those with the necessary resources to develop working prototypes over a day or weekend.

That being said, I encourage anyone interested to create their own version of this design. There have been many suggestions for improvements, alternatives, and redesigns, and there are experts here with the resources to build, simulate, and test such a device far more efficiently than I can.

I invite you to create your own prototypes and share your designs, observations, and learnings on this forum for the benefit of everyone.

So, are there any volunteers to build the first prototype? it will be great to see a prototype over this coming weekend.

[Repwoc]

How do you load the hex on a board like this? A USB bootloader or dedicated programmer? I like this board and it would be good way for me to get familiar with the STM micro family.

Thanks

I use this mini STLink board: https://vi.aliexpress.com/item/10050...yAdapt=glo2vnm

It works with the STM32Cube programmer and the STM32CubeIDE debugger.

[Altra]

[Aziz]

Hi all,

great topic. I enjoyed taking a quick look at it.

You guys don't need soldering iron and can immediately start coding using a Tablet PC + USB sound card. Either Android or Windows OS.
Just plug in a TX-Coil and RX-Coil into the line-out and line-in terminals.
You never imagine, what can be done.

Cheers,
Aziz

[Atul Asthana]

Hi all,

great topic. I enjoyed taking a quick look at it.

You guys don't need soldering iron and can immediately start coding using a Tablet PC + USB sound card. Either Android or Windows OS.
Just plug in a TX-Coil and RX-Coil into the line-out and line-in terminals.
You never imagine, what can be done.

Cheers,
Aziz

Great
Any exploratory examples of the working code for android phone/tablet that I can download and use?

[Aziz]

Great
Any exploratory examples of the working code for android phone/tablet that I can download and use?

Hi Atul,

I'm sure, there are many source codes in the internet available (open source, look at the required parts only). I haven't done on android platforms. But on Win32 using C/C++ code. Only experimental code.

BTW, external USB 2.0/3.0 sound cards support now sampling 32-Bit at 192 kHz SR and above. Some good sound cards have 114 dB dynamic range at the line inputs.

I'm thinking of to try the 32-Bit sample bits at 192 kHz SR. Or at least the 24-Bit @192 kHz. But I have not found a good and cheap external sound card yet. Most vendors don't publish true technical specs. And this makes it difficult to find one. The Sound BlasterX G6 seems to me interesting at the moment. I hope, they don't band limit the input signals up to 24 kHz. I had some sound cards, which they did. Even they sampled at 96 kHz (sic! ).

Cheers,
Aziz