Let's make a closely MXT like detector!

[Carl-NC]

I noticed the later versions of the STM32 software give a warning message about using cloned stlink dongles ( aka chinese ) and would not program the chip ...

Interesting... I have several of those clone dongles but haven't used one in years.

OK so now I'm going to maybe open a huge writhing can of worms in asking all interested - stick with 13.8khz TX RX (as the single frequency)? Seems to work beautifully in the MXT and I'm happy with it.

If you are wanting to design a detector that mimics MXT performance, then using an MXT coil at the MXT frequency eliminates 2 variables when performance is falling short. Furthermore, I would duplicate the MXT's TX circuitry. Once you have firmware running that achieves performance, then you can entertain other changes like coils or frequencies. As you point out, there are still a lot of MXT/DFX/V3 coils out there, even with aftermarket vendors. A problem with the MXT coil is that the L_RX = 15.7uH which is quite high and doesn't work well beyond 15kHz. It took quite the effort to make it work on the V3 (@22.5kHz).

So now to look at Bluetooth modules for the STM32...

ST has a broad portfolio of wireless MCUs, many of them dual core with a pretty hefty main processor. You could easily put the whole metal detector on one chip. This has already been done with the ESP32 but (IMO) the STM is still the better path.

A thought - if the 8 bit PIC running 8mhz was enough processor and resources to run the MXT it seems like even the slowest STM32 would be overkill - so is a H series really needed? Would the L low power / the least powerful be enough if there is one with the needed peripherals? It seems like all the STM32 variants have more flash and memory than will be needed, at least to my - still learning the STM32 lineup - mind.

The MXT was written in assembly language and barely fit in the 16C76's 14k memory space. The MXT Pro required more memory which is why we jumped to a new chip. When you write the code in C, it will invariably take more memory than hand-optimized assembly. Probably you could fit a C-version of the MXT in 32k with little problem, but why limit yourself? Memory is now dirt cheap, and a micro with 512k-1M barely costs any more and you don't have to worry about how you write code. Also, more flash == more RAM so you can play with way-too-big arrays. Same thing with processor speed -- yes, you could get it to work at 8MHz but... why? Speed is also dirt cheap.

Although I have used PIC16/PIC18/DSPIC in the past I am pretty much exclusively using ST micros now. This was a choice we (me and a co-worker) made years ago at White's after evaluating pretty much all the leading micros at the time. STMs had clearly better timers and other peripherals were as good or better. It was a good choice as ST has largely been outrunning their competitors ever since. I've used L0, L4, G0, H7, and U5 families. Currently using the U5. Yes, the H7 has massive horsepower but if you are driving a graphics display the extra horsepower is good to have.

All that said, there is also the comfort factor to consider. That is, what micros and tools you already know well.

[KRinAZ]

Interesting... I have several of those clone dongles but haven't used one in years.



If you are wanting to design a detector that mimics MXT performance, then using an MXT coil at the MXT frequency eliminates 2 variables when performance is falling short. Furthermore, I would duplicate the MXT's TX circuitry. Once you have firmware running that achieves performance, then you can entertain other changes like coils or frequencies. As you point out, there are still a lot of MXT/DFX/V3 coils out there, even with aftermarket vendors. A problem with the MXT coil is that the L_RX = 15.7uH which is quite high and doesn't work well beyond 15kHz. It took quite the effort to make it work on the V3 (@22.5kHz).



ST has a broad portfolio of wireless MCUs, many of them dual core with a pretty hefty main processor. You could easily put the whole metal detector on one chip. This has already been done with the ESP32 but (IMO) the STM is still the better path.



The MXT was written in assembly language and barely fit in the 16C76's 14k memory space. The MXT Pro required more memory which is why we jumped to a new chip. When you write the code in C, it will invariably take more memory than hand-optimized assembly. Probably you could fit a C-version of the MXT in 32k with little problem, but why limit yourself? Memory is now dirt cheap, and a micro with 512k-1M barely costs any more and you don't have to worry about how you write code. Also, more flash == more RAM so you can play with way-too-big arrays. Same thing with processor speed -- yes, you could get it to work at 8MHz but... why? Speed is also dirt cheap.

Although I have used PIC16/PIC18/DSPIC in the past I am pretty much exclusively using ST micros now. This was a choice we (me and a co-worker) made years ago at White's after evaluating pretty much all the leading micros at the time. STMs had clearly better timers and other peripherals were as good or better. It was a good choice as ST has largely been outrunning their competitors ever since. I've used L0, L4, G0, H7, and U5 families. Currently using the U5. Yes, the H7 has massive horsepower but if you are driving a graphics display the extra horsepower is good to have.

All that said, there is also the comfort factor to consider. That is, what micros and tools you already know well.

Great advice on the first point - I'll just focus on making a detector as MXT like as possible. I'm finding those Eclipse and compatible coils are getting more scarce. I've also read a bunch of quite bad experiences with the Detech coils, glad I don't have any. I may take a shot at a hand build of a 4x6 or 6x10 DD that meets or exceeds the Eclipse coils - if so I'll make a separate thread...that would of course be after I read the Coils section of your ITMD3 that I'm waiting on...

And...wow the world of micros has changed in a hurry - I spent the day today getting up to speed on the STM32 Families and Series within the Families, and then better understood the differences between the 9 current production Nucleos. Finally at the end of all that I searched for prices and had quite a laugh. I expected them to cost more and there to be a big price difference from lower to higher performance. I found the lowest end Nucleo was around $12 and the highest end Nucleo was...you guessed it!...around $12. So, now I see what you mean - we now get crazy amounts of processing power and peripherals and all for very little $ and it's silly to buy the low end when the high end is so cheap. And these things are far less $ than the much less capable Arduino Nano (I love the Arduinos but you gotta admit you get a lot more from any of the Nucleo's per dollar). I can see myself also just using ST Micros going forward.

So, it's quite possible I'll want to run a chip that isn't on a Nucleo - especially if I find a STM32 (or higher) with built in Bluetooth and OLED driver. How does the hobbyist implement bare micros? Is there a socketed breadbord that you can plug processors into so you don't have to solder the micro in place? Something like a Nucleo with a socket instead of a soldered micro? My SMD soldering skills aren't yet up to soldering and unsoldering micros...at least without destroying things haha...

EDIT - ok there are more than 9 current production Nucleo's, and probably STM32 Families I haven't discovered yet...

[KRinAZ]

I've officially fallen down the ST Micro rabbit hole...blue pill, black pill boards, just discovered a whole additional section of ST Micro's web site with the WB family of Nucleo's...looking amongst them for Bluetooth audio support.

I've also found lots of articles on how to diy a STM32 PCB - is that what you folks who run bare STM's do - design your own PCB for each project? Forgive me for asking but I come from the through-hole DIP and breadboard world...have done my share of wire wrap...

[moodz]

For prototypes you can most always find the CPU you want on some little board with 0.1 inch headers for everything. ( Alibaba :-). )
Before you choose your CPU ... one plan is to determine what the signal flow / main blocks are and how much grunt ( code wise )
is required to do the heavy lifting.

There is nothing worse than choosing your CPU and finding down the track you are missing that extra PWM, or DMA, or the interrupts wont fit into your DSP cycles.

Rule of thumb is go big or go home. If you find you oversized your CPU ... you can downsize it much more easily than upsizing it.

[Aziz]

Hi all,

I for one would like to see the STM32 family solution.
Look at the new N6 generation:
https://www.st.com/en/microcontrolle...n6-series.html

Huge horse power. Huge neural network inference horse power. Post-signal processing is possible with neural network (AI) solution.
This is sure overkill.

Choose a right one:
https://www.st.com/en/microcontrolle...rtex-mcus.html

Aziz

[Carl-NC]

Look at the new N6 generation:

Unfortunately all BGA and all use external flash. Tougher for the hobby crowd.
For me:

• H7: High horsepower/graphics
• U5/C5: Medium horsepower
• L0/G0/C0: Low cost/low power

[KRinAZ]

For prototypes you can most always find the CPU you want on some little board with 0.1 inch headers for everything. ( Alibaba :-). )
Before you choose your CPU ... one plan is to determine what the signal flow / main blocks are and how much grunt ( code wise )
is required to do the heavy lifting.

There is nothing worse than choosing your CPU and finding down the track you are missing that extra PWM, or DMA, or the interrupts wont fit into your DSP cycles.

Rule of thumb is go big or go home. If you find you oversized your CPU ... you can downsize it much more easily than upsizing it.

Nice block diagram, that could be the 60k foot view diagram for this project.

Between you and Carl and everyone haha I'll just throw a huge micro at this project - that is mostly just spinning nops - but who cares if there's no price or power penalty. Back in the day, good design required disciplined product selection without waste or excess, but back then there were very much both power and price penalties. Anyway big horsepower and resources it shall be...not ready for a specific micro selection yet though.

Will be continuing my discovery of the whole ST-M ecosystem in the background and will ocassionally bring up a specific micro or nucleo or dev kit for this project.

I think, in the background for starters, I'm going to get a cheap Nucleo F or H and setup the ST CUBE system, and redo some projects on the Nucleo - just to get used to the STM tools.

If I find there are socketable STM32s - can also see myself making a socketed nucleo board in KiCAD where I can plug in a range of STM32's and experiment.

[KRinAZ]

Hi all,

I for one would like to see the STM32 family solution.
Look at the new N6 generation:
https://www.st.com/en/microcontrolle...n6-series.html

Huge horse power. Huge neural network inference horse power. Post-signal processing is possible with neural network (AI) solution.
This is sure overkill.

Choose a right one:
https://www.st.com/en/microcontrolle...rtex-mcus.html

Aziz

Exploring these links - and - there is a N6 Nucleo! The NUCLEO-N657X0-Q, in stock, a mere $58, would fit the bill of big horsepower big resources...but it's not time yet for specific micro choices...

[KRinAZ]

Unfortunately all BGA and all use external flash. Tougher for the hobby crowd.
For me:

• H7: High horsepower/graphics
• U5/C5: Medium horsepower
• L0/G0/C0: Low cost/low power

I have to look into the H, C, and U families and learn more about them. The H7 Family keeps coming up as a contender for this project.

And ah, but that tantalizing NUCLEO-N657X0-Q though with neural and computer vision capability. Laugh now, but imagine a detector that SEES (spectral analysis) the rock with a target ID and says to you; Nah mate that's just a hot rock, or, Hey mate I'm seeing gold there

[Hristo]

Hi, you have my suport voice for STM32 H7 series: High horsepower/graphics. This is sure overkill but today we can aford it. My MXT concept is with not one microcontroler design two , tree and many chips design with ewery one with dedicated specific task to do for example this most powerful will engage only display keyboard or touch screen - capacitive input and perhaps jesture and mimic of face control example with blinc an move on the eye with dedicated stereo 3D video cam two or tri in triangle configuration and other separate die for audio and so on for everi task distributed computing network paralel processing arhitekture design. s Multiple Instruction Multiple Data (MIMD) parallel computing design.

Now serious, the MXT circuit use analog TX generator design this avoid digital jitter with Tx signal if is generated with Microcontroller and microcontroler generate phase with zero and 90 degree ofset signals for demodulator in quadrature like software radio design SDR in modern design chip without clasic demodulator with diode in radio circuits state of the art of now days. this function needs of smal pic microcontroler enough fast to do the job with phase control on demand with ground eliminating and zerro salt adjust for reactive and resistiwe components X,Y Q I and so on have many names to confuse ewery one who hope to andarstend anithing more than notning.

And for audio separate processor who is responsible of audio sound managing already says

lest but no least left most important processor in this project this is heart of MXT design is the discriminator had find chip master CPU who control all other co-processors in this multi CPU design. This may be classic ordinary old PIC Microchip and assembly codded control software with tremendius responce time ot I/O pins contrary to modern fast STM32 H7 with jitter and delay on all of them I/O pins.

[ivconic]

There is too much talk about various powerful processors (which 70% of the world cannot get easily and cheaply) and that is unnecessary.
If you looked at the schematic any more seriously; you will see that the detector does not require a powerful processor.
The processor does a very simple task in MXT. Even the Atmega328P can do the job. Not to mention ESP32. STM32 blue pill too.
And those are 3 processors that anyone on the planet can easily get.
ESP32 can do the most. ADC on ESP32 is not the best. Linearity is not the best. But it certainly may use some cheaper external ADC.
The ESP32 has an integrated DAC. I'm not advocating ESP32 here, just stating some of my personal experiences.
Instead of talking about the choice of processor; first of all, a "scenario" should be made about what will be done from MXT and in what way?
Personally, I am attracted to the analog part of the device. Although there are details that I do not fully understand on the schematic.
This seems to be another one of those threads where everyone will say what they want and eventually the thread will stagnate and disappear.

[Hristo]

so who will redraw mxt ANALOG front end on PCB module with separate dedicated A/D chip and SPI or I3C interface to display and STM32H7 or ESP32 separate board modul construction with one Analog and other display and control board with integrated audio and who ever like other things.

[ivconic]

I may do that in next few weeks. First I will need some clarifications. I will prepare some questions directly for Carl. But now I have to go on short trip.
If somebody else is willing to to that; my hat down and thanks!

[KRinAZ]

I may do that in next few weeks. First I will need some clarifications. I will prepare some questions directly for Carl. But now I have to go on short trip.
If somebody else is willing to to that; my hat down and thanks!

I'm working on that also and going over the schematic, would prefer to work together rather than by myself so maybe we can team up when you get back? I'll have some Q's for Carl also...soon...
One note - I'm not so sure an external ADC is needed, nor more than one micro needed. More on that soon.
I think it would be wise to start simple and only add more complexity if testing proves it necessary. Some of the higher end STMs may have the resources we need internal, it's late in my time zone, more soon.

[Hristo]

Also like to add to MXT circuit and MXT2 (makro2 circuit Technetic T2 hardware clone) for reference and compare Garrett AT Max original circuit from FCC ID: https://fccid.io/DBD the only one there who is official aviable free.