VLF MD with digital signal processing : Bee-Buzz 1

[Aziz]

BTW,

the single frequency dft using the Goertzel algorithm is approx. twice efficient as the Lock-in Amplifier decoding. FFT makes only sense for wide band applications.
But you need windowing function for the samples. Odd frequencies of interest to the number of samples per frame/buffer at specific sample rate require windowing regardless of FFT, Goertzel, Lock-in amp or any other decoding algorithm.
https://en.wikipedia.org/wiki/Window_function

It is best to avoid windowing by taking harmonic frequencies (this means, that the frequency fits fully (0.. 2pi) into your sample buffer or is the multiple of it). No windowing is required and you save CPU time. You get very stable decoding output and you don't have to average it.
Just tune your TX to the harmonic frequency if it is a resonant TX system like a VLF design.
I can decode phase angles better than 0.001 degree.

You don't even need phase information. Just decode 3 harmonic frequencies centered at the resonant frequency. And take the magnitude decoding outputs (R = sqrt(I*I + Q*Q) ). These three magnitudes around the resonant frequency delivers enough information for resistive and reactive response.

Aziz

[Atul Asthana]

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

Aziz,

Great idea.
my research says that there is more to the target detection than the sound card, the contribution of sound card resolution and sampling rate start diminishing beyond a certain point, and that point is decided by system noise.

AIso you will actually need to penetrate the noise barrier to pull out the target signal.

but before you start testing your idea, do a lot of research. the difference between thoroughly researched approach and otherwise is the Brahmos and a sugar rocket.

my best wishes,
Atul

[dbanner]

"The Goertzel algorithm has a higher order of complexity than fast Fourier transform (FFT) algorithms, but for computing a small number of selected frequency components, it is more numerically efficient. The simple structure of the Goertzel algorithm makes it well suited to small processors and embedded applications."

Ok, dust off those Math textbooks.

[Atul Asthana]

"The Goertzel algorithm has a higher order of complexity than fast Fourier transform (FFT) algorithms, but for computing a small number of selected frequency components, it is more numerically efficient. The simple structure of the Goertzel algorithm makes it well suited to small processors and embedded applications."

Ok, dust off those Math textbooks.

and we are processing a single known frequency.

[Atul Asthana]

BTW,

the single frequency dft using the Goertzel algorithm is approx. twice efficient as the Lock-in Amplifier decoding. FFT makes only sense for wide band applications.
But you need windowing function for the samples. Odd frequencies of interest to the number of samples per frame/buffer at specific sample rate require windowing regardless of FFT, Goertzel, Lock-in amp or any other decoding algorithm.
https://en.wikipedia.org/wiki/Window_function

It is best to avoid windowing by taking harmonic frequencies (this means, that the frequency fits fully (0.. 2pi) into your sample buffer or is the multiple of it). No windowing is required and you save CPU time. You get very stable decoding output and you don't have to average it.
Just tune your TX to the harmonic frequency if it is a resonant TX system like a VLF design.
I can decode phase angles better than 0.001 degree.

You don't even need phase information. Just decode 3 harmonic frequencies centered at the resonant frequency. And take the magnitude decoding outputs (R = sqrt(I*I + Q*Q) ). These three magnitudes around the resonant frequency delivers enough information for resistive and reactive response.

Aziz

my submission is that what ever I do and whatever algorithms/signal processing methofology I use, I need to keep the microcontroller's processing power in mind as the biggest constraint.
so, I did a lot of research before deciding on various parts of the project.

thetefore, I should be able to complete the processing of the signal, administrative tasks and target identification etc in one single slot.
and deciding on stm32f103c8t6 bluepill was based on many factors : cost, availability and onboard peripherals.

[dbanner]

Looks like phase can be readily synthesized with Goertzel.

[Atul Asthana]

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

Great,

Feel free to develop your own version of the metal detector prototype using any processor or codec combination of your choice. There are no restrictions on how you approach the design, as I haven't imposed any limitations.

The design is essentially a detailed description and is fully open-source, encompassing all developments made thus far. I encourage you to build your prototype, test its performance, suggest enhancements, and share your results with the community. By doing so, we can all benefit from each other's insights and learn collectively.

After all, I am sure that Carl and others would agree with me, that fostering innovation and collaboration is what this forum is all about.

[Atul Asthana]

I encourage members of this group to introduce this VLF metal detector 'Bee-Buzz 1', project to college students, highlighting its suitability as an educational and hands-on project. This initiative offers students the chance to apply various technologies learned in the classroom to real-world scenarios, utilizing their mathematical and signal processing skills to tackle practical sensing and instrumentation challenges. It also provides an opportunity for students to interact with a community of experts beyond their academic environment, fostering parallel, out-of-the-box thinking to overcome the complexities that arise.

The project is particularly appealing due to its low costs and minimal hardware complexity, making it manageable and accessible for students. They will need to address real-life issues like analyzing target and ground responses, requiring clever thinking and a broad understanding of material and environmental properties. Furthermore, in more advanced iterations, students can integrate machine learning / neural networks, pushing the boundaries of traditional metal detection technology.

This project is an excellent platform for students to innovate and develop, with special encouragement for girls to participate and contribute their unique perspectives and ideas. By engaging in this project, students can develop their skills, gain practical experience, and play a pivotal role in evolving this technology into something truly remarkable.

[moodz]

I encourage members of this group to introduce this VLF metal detector 'Bee-Buzz 1', project to college students, highlighting its suitability as an educational and hands-on project. This initiative offers students the chance to apply various technologies learned in the classroom to real-world scenarios, utilizing their mathematical and signal processing skills to tackle practical sensing and instrumentation challenges. It also provides an opportunity for students to interact with a community of experts beyond their academic environment, fostering parallel, out-of-the-box thinking to overcome the complexities that arise.

The project is particularly appealing due to its low costs and minimal hardware complexity, making it manageable and accessible for students. They will need to address real-life issues like analyzing target and ground responses, requiring clever thinking and a broad understanding of material and environmental properties. Furthermore, in more advanced iterations, students can integrate machine learning / neural networks, pushing the boundaries of traditional metal detection technology.

This project is an excellent platform for students to innovate and develop, with special encouragement for girls to participate and contribute their unique perspectives and ideas. By engaging in this project, students can develop their skills, gain practical experience, and play a pivotal role in evolving this technology into something truly remarkable.

This is the real reason you insist on using the Blue Pill ... why was this not clear up front. This information would have saved alot of thinking time. LOL

[Atul Asthana]

This is the real reason you insist on using the Blue Pill ... why was this not clear up front. This information would have saved alot of thinking time. LOL

Yes sir,

this is the reason.

and 'the thinking time' was deliberately not meant to be 'saved'

Before involving students, it was important to ensure that there is a strong interest and support from the expert community, as proper guidance is crucial to keep students motivated. I also wanted the experts to evaluate the design to provide students with a functional metal detector design idea they can complete and proudly showcase, which could inspire their peers and lead to exciting treasure hunting adventures.

Building this metal detector offers students practical, hands-on experience in a project that many dream of undertaking/owning/using. It gives them the chance to explore a real-world challenge, enhancing their problem-solving skills and teaching them to maximize performance in constrained environments. The experience gained will significantly boost their resumes, showcasing their ability to work on complex, multidisciplinary projects.

Through this project, students will develop skills in electronics, instrumentation, mathematics, signal processing, and material sciences—skills that are essential in industries such as medical technology, space exploration, military applications, automotive, consumer electronics, and communications. My goal is to encourage students globally to expand their learning beyond the classroom and engage in innovative, interdisciplinary projects.

[boilcoil]

So, this project finished, or died?
Or was he still-born?

[Atul Asthana]

So, this project finished, or died?
Or was he still-born?

Great question.
Sir, if we want to quickly breathe life back into this 'dead' project, you could take the lead by writing the first version of the code. The hardware is already simple and low-cost—it's the code that's holding things up.

Given that every tiny component has been thoroughly explained, dissected, and analyzed, writing the code shouldn't be an issue. It's time to move beyond waiting for some one else to take the initiative and contribute directly to getting this project back on track.

[Carl-NC]

Sir, if we want to quickly breathe life back into this 'dead' project, you could take the lead by writing the first version of the code. The hardware is already simple and low-cost—it's the code that's holding things up.

I was under the impression you were going to write the code.

[dbanner]

I was under the impression you were going to write the code.

[moodz]

I have a feeling we are the ones who have been coded.