Concept Design

[Willy Bayot]

I want to make a polling among the active (and also the read-only) members of this topic.
From the following list of micro-processor platforms, what is your previous experience with projects using them:

• STM32
• PIC32MZ
• ESP-32

Please, answer with the words : 'extensive', 'good', basic',' none'?

If your answer is not 'none', can you describe the development tools you have used and the type of application of your project?

We are ready to accept any help and recommendations before making a final decision on the CPU selection for this project.
This would also make the learning curve less steep as soon as we have collectively decided.

my own answers are:

• STM32 : extensive, STM32CUBE IDE, metal detection
• PIC32MZ: good, MPLAB IDE, metal detection
• ESP-32 : none but extensive on ARDUINO IDE, underwater drone, remote sea water surveys

YOUR turn now

[David_1]

We must have several different options there. Several different approaches.
Not only one, one that "must".
"My way or a highways" solution.

maybe a backplane with a common voltage rail to common connections to the micro, so each module connects to an I/O
so these modules can be mixed and matched.


Sort of something like this but it would need a little more thinking about rather than the five mins it took to draw this

[waltr]

Zadig?

Tried it --does NOT work..

[ivconic]

Only familiar with the internals of the PICs but both the STM32 & ESP32 seems to look good.

I have done some coding on the ESP's but used it strictly for the WiFi capability. I did run into a big problem after buying some ESP32-S3's---- the USB programming requires Windows 10 or higher. There are NO USB drivers for Win8.1. I was doing programming in the Audriuno IDE and lots of library functions available that worked. Then tried the ESP-IDF Eclipse and needed to write my own libraries for all sorts of things. Never did get finished code.

Actually the same with libraries for the PIC but this was just easier for me since I have written lots of PIC code and even libraries for the 16F (8bit) PICs only need slight mods for the PIC32's.

However, with the programming expertise here this in probably not a problem.

I agree with Carl that the circuit from coil to ADC has very critical constraints if desiring 18b or more of ADC resolution.
.

Zadig?

[waltr]

Only familiar with the internals of the PICs but both the STM32 & ESP32 seems to look good.

I have done some coding on the ESP's but used it strictly for the WiFi capability. I did run into a big problem after buying some ESP32-S3's---- the USB programming requires Windows 10 or higher. There are NO USB drivers for Win8.1. I was doing programming in the Audriuno IDE and lots of library functions available that worked. Then tried the ESP-IDF Eclipse and needed to write my own libraries for all sorts of things. Never did get finished code.

Actually the same with libraries for the PIC but this was just easier for me since I have written lots of PIC code and even libraries for the 16F (8bit) PICs only need slight mods for the PIC32's.

However, with the programming expertise here this in probably not a problem.

I agree with Carl that the circuit from coil to ADC has very critical constraints if desiring 18b or more of ADC resolution.
.

[Willy Bayot]

I've briefly looked at the ESP micro. I am concerned that it has very weak timer peripherals, both in number and capability. My goal is to support a contingency plan of 8 analog demod channels which requires a minimum of 9 timer outputs. Add to that the TX and audio and probably 1 or 2 system timers. The ESP micro would even be pushing it on the direct-sampling route.

Personally, I am inclined toward STM right now. I am also looking to develop a multifrequency platform in the future to support ITMD and it will also require a lot of timers. I would prefer to use at least a common micro family. But as I said before, this is a point where people can diverge and use different micros, assuming they know how to write code. And those who don't know how to write code probably won't care what micro is used.

The ESP32 system has timers with 6 PWM output with full Output Compare capabilities (MCPWM). They are even easier to program than the STM32 to generate pulses with programmable phase, duration and period (same as PIC32MZ).
It is true that would not be enough OC pins for an integrated sampling system but here, we talk about a Direct Sampling system, is not it?
In this project, we do not aim at building a general purpose platform able to support future technologies. We must give priority to easy building, programming and testing individual functional modules at as lower cost as possible.

My point is that the ESP32 family is giving the best tools to build highly modular systems at low cost using easy to use development IDE.

[Carl-NC]

I've briefly looked at the ESP micro. I am concerned that it has very weak timer peripherals, both in number and capability. My goal is to support a contingency plan of 8 analog demod channels which requires a minimum of 9 timer outputs. Add to that the TX and audio and probably 1 or 2 system timers. The ESP micro would even be pushing it on the direct-sampling route.

Personally, I am inclined toward STM right now. I am also looking to develop a multifrequency platform in the future to support ITMD and it will also require a lot of timers. I would prefer to use at least a common micro family. But as I said before, this is a point where people can diverge and use different micros, assuming they know how to write code. And those who don't know how to write code probably won't care what micro is used.

[Carl-NC]

That's the part I would like to see as separate module. Also I would like to see the schematic of it.
" A two-stage pre-amp" is the subject to further analyze and "negotiations".
We must have several different options there. Several different approaches.
Not only one, one that "must".
"My way or a highways" solution.
AD(A) type opamps are expensive, not affrodable in many areas etc.
Maybe I would like to use some from my batch?
That part must be "universal" and "portable".

The design has very specific goals. If we make it an "everything to everybody" design then it won't meet the intended goals. My intent is to propose a specific design that I believe will meet the goals. It very likely will require parts that are expensive, difficult or impossible for some people to buy, and probably SMT. Anyone can then substitute parts on their own, with the understanding that performance will likely be degraded.

[Carl-NC]

I would very much like to see a "bare bone" version of such a module.

Here it is reduced as much as possible:


It's also critical to pay close attention to the V2.5A supply.

[Willy Bayot]

That's the part I would like to see as separate module. Also I would like to see the schematic of it.
" A two-stage pre-amp" is the subject to further analyze and "negotiations".
We must have several different options there. Several different approaches.
Not only one, one that "must".
"My way or a highways" solution.
AD(A) type opamps are expensive, not affrodable in many areas etc.
Maybe I would like to use some from my batch?
That part must be "universal" and "portable".

It is not recommended to separate the receive module from the ADC.
I am not an ANALOG guy, I am an old DIGITAL guy, thus, you must ask the real analog experts on this forum for that type of question.
What I know is that the opamps to be selected for the pre-amp circuit are quite critical for the whole performance (SNR) of the system.
I do not see how that receiver module can be 'universal'.

[ivconic]

...There will be a coil interface, a two-stage pre-amp and an ADC driver (a specialized opamp) to connect to the differential inputs of the ADC...

That's the part I would like to see as separate module. Also I would like to see the schematic of it.
" A two-stage pre-amp" is the subject to further analyze and "negotiations".
We must have several different options there. Several different approaches.
Not only one, one that "must".
"My way or a highways" solution.
AD(A) type opamps are expensive, not affrodable in many areas etc.
Maybe I would like to use some from my batch?
That part must be "universal" and "portable".

[Willy Bayot]

I have reviewed the entire "family" of those ADCs before. Specs match. There's a lot going for it.
But I can't find anywhere on the net that someone worked with that ADC and gave an example of a small pcb with only the most necessary components.
The evaluation board offered by the manufacturer is "huge" and also has very expensive and delicate parts on it.
The whole design is done with their solutions and components.
I would very much like to see a "bare bone" version of such a module.
A module that would complete all the work we need. And that it has replaceable components and not from the same manufacturer.
I'm afraid that we will be "blackmailed" by additional purchases of their expensive components, in order to make that ADC work properly.
And we cannot accept the evaluation board for several reasons. It's too big. It has "excess" components. As such, it cannot be easily integrated into our project.
I don't have enough knowledge and experience to draw a "bare bone" schematic with such an ADC myself.
So I would like one of you to do it, who is 100% sure of what he is doing.
ESP32 is a good choice. There are so many modules that are cheap. I would choose the one that has the most derived pins. So far I have found one module with 38 pins.
The module is small and does not need any modifications, the entire module can be easily integrated into the device.

The schematic necessary to connect to the ADC and to support it will be part of the AFE work (TBD). This is the work of electronic experts on this forum. Tony has already given a first look at a potential receiver schematic but I think it still need some team work to finish it.
There will be a coil interface, a two-stage pre-amp and an ADC driver (a specialized opamp) to connect to the differential inputs of the ADC.

The connection and wiring of this external ADC is not complex. There are examples of it on the datasheet. We would not need to buy any evaluation board for it.
However, the PCB layout of the receiver module will be critical to clearly separate the analog, digital and power lines with proper ground planes.( The SPI clock is high frequency (45 to 80Mhz) and the signals coming from the coil are tiny)

[David_1]

I have reviewed the entire "family" of those ADCs before. Specs match. There's a lot going for it.
But I can't find anywhere on the net that someone worked with that ADC and gave an example of a small pcb with only the most necessary components.
.

I used pic's until the covid shortage, then looked very hard at ESP's built a few pcbs with access points but often tried the ADC's even setting a pin high while the accusation was talking place, setting pin low after... compared to a pic it was very slow, but yes fine for battery voltage, just nothing fast.

[Willy Bayot]

ADC on all the esp's seem much slower than the documentation so it would need an external one..

Yes, indeed, 100Ksps
That's what is planned
See post #174
Internal ADC can still be used for accessory functions like battery level,...

[ivconic]

I have reviewed the entire "family" of those ADCs before. Specs match. There's a lot going for it.
But I can't find anywhere on the net that someone worked with that ADC and gave an example of a small pcb with only the most necessary components.
The evaluation board offered by the manufacturer is "huge" and also has very expensive and delicate parts on it.
The whole design is done with their solutions and components.
I would very much like to see a "bare bone" version of such a module.
A module that would complete all the work we need. And that it has replaceable components and not from the same manufacturer.
I'm afraid that we will be "blackmailed" by additional purchases of their expensive components, in order to make that ADC work properly.
And we cannot accept the evaluation board for several reasons. It's too big. It has "excess" components. As such, it cannot be easily integrated into our project.
I don't have enough knowledge and experience to draw a "bare bone" schematic with such an ADC myself.
So I would like one of you to do it, who is 100% sure of what he is doing.
ESP32 is a good choice. There are so many modules that are cheap. I would choose the one that has the most derived pins. So far I have found one module with 38 pins.
The module is small and does not need any modifications, the entire module can be easily integrated into the device.