Concept Design

[moodz]

I see.
So, the maximal sample number will determine the choice of ADC.
Carl would probably suggests even more than that! Much more samples as possible. Ok.
I circulate with questions about one and the same thing; what would be the minimum ADC specs that would get the job done here.
Carl said 18bit, maybe 16bit. Moodz and you said 24bit is the real deal.
But 4-8 channel, 24bit, with high(est possible) sampling rate... either there is none, they don't exist, or I didn't find them, or if they do exist;
they are probably very expensive and complicated to implement.
So...
In order to relax the criteria and in that way reach an existing ADC that would finish the job in full; first we need to clarify
if we really need high repetition rate TX?
25kHz according to Tony.
I understand why he demanded it.
But is it really mandatory?
We know of some detectors that successfully locate the smallest gold nuggets and yet do not have such a high pps.
How much in reality do we lose if pps is lower? What will we miss?
Another aspect; doesn't the influence of soil increase at higher pps?
Aren't the problems with mineralization drastically complicated, with the increase in pps?
What is the optimal measure? Which choice is the best? With the least complications and tradeoffs.

The GPZ6000 from minelab ( which is not cheap ) has 14 M HC4053 anlogue muxes and 2 at least texas instruments ADS131 4 channel 24 bit @ 128 msps.

The other option is multiple sampling integrators forming multiple separate channels each with its own filtering and amplfiction then feeding separate ADCs and all the scaling and subtraction etc is done in the CPU.

This will be more chips but say 8 channels minimum is certainly doable and could have a very wide input voltage range ( eg 40 volts ).

moodz

[Tinkerer]

I see.
So, the maximal sample number will determine the choice of ADC.
Carl would probably suggests even more than that! Much more samples as possible. Ok.
I circulate with questions about one and the same thing; what would be the minimum ADC specs that would get the job done here.
Carl said 18bit, maybe 16bit. Moodz and you said 24bit is the real deal.
But 4-8 channel, 24bit, with high(est possible) sampling rate... either there is none, they don't exist, or I didn't find them, or if they do exist;
they are probably very expensive and complicated to implement.
So...
In order to relax the criteria and in that way reach an existing ADC that would finish the job in full; first we need to clarify
if we really need high repetition rate TX?
25kHz according to Tony.
I understand why he demanded it.
But is it really mandatory?
We know of some detectors that successfully locate the smallest gold nuggets and yet do not have such a high pps.
How much in reality do we lose if pps is lower? What will we miss?
Another aspect; doesn't the influence of soil increase at higher pps?
Aren't the problems with mineralization drastically complicated, with the increase in pps?
What is the optimal measure? Which choice is the best? With the least complications and tradeoffs.

Do not confuse the PPS of a PI with the frequency of a VLF.

The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS

Roughly 2 times PPS = 2 times target signal amplitude after integration.

[Willy Bayot]

The GPZ6000 from minelab ( which is not cheap ) has 14 M HC4053 anlogue muxes and 2 at least texas instruments ADS131 4 channel 24 bit @ 128 msps.

The other option is multiple sampling integrators forming multiple separate channels each with its own filtering and amplfiction then feeding separate ADCs and all the scaling and subtraction etc is done in the CPU.

This will be more chips but say 8 channels minimum is certainly doable and could have a very wide input voltage range ( eg 40 volts ).

moodz

ADS131 4 channel 24 bit @ 128 msps.
should be read
ADS131 4 channel 24 bit @ 128 Ksps.

I thought that our goal in this project was to minimize the complexity of the analog part of the circuit by studying the DIRECT SAMPING mode.
What you describe is a multiple channel analog integration circuit (what the GPZ6000 is doing)

[ivconic]

Do not confuse the PPS of a PI with the frequency of a VLF.

The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS

Roughly 2 times PPS = 2 times target signal amplitude after integration.

Usually I like to do that , to confuse (P)ulse (P)er (S)econd and (C)ycle (P)er (S)econd.
Especially when I notice that it annoys someone!


...
(C)limate (C)hange (P)erformance (I)ndex !?!?
WTF!?


Joking aside, but I didn't follow many what's posted before, on those "CCPI" topics, so now I'm often confused by those abbreviations.
People of knowledge, people of science, like to complicate things with abbreviations.
But what does that have to do with us here? Can we adapt our vocabulary to the forum, the hobby, the vast majority of us here!?
There are actually many ways to generate a signal.
Signal procession.
Waveform.
And if we add some abbreviation to each method that will seem high-minded to others around us...
I suggest we reduce things to the simple vernacular. Ah, the good old days... when everything was so normal and easy...
...

"...The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS ... Roughly 2 times PPS = 2 times target signal amplitude after integration."

No, I don't understand this either. I'll have to go to school for a few more classes...



The Big Bang Theory... Sheldon often puts Howard down for being just an electronics engineer. And not a real scientist!
Screenwriters obviously visited this forum a lot!

[Willy Bayot]

Usually I like to do that , to confuse (P)ulse (P)er (S)econd and (C)ycle (P)er (S)econd.
Especially when I notice that it annoys someone!


...
(C)limate (C)hange (P)erformance (I)ndex !?!?
WTF!?


Joking aside, but I didn't follow many what's posted before, on those "CCPI" topics, so now I'm often confused by those abbreviations.
People of knowledge, people of science, like to complicate things with abbreviations.
But what does that have to do with us here? Can we adapt our vocabulary to the forum, the hobby, the vast majority of us here!?
There are actually many ways to generate a signal.
Signal procession.
Waveform.
And if we add some abbreviation to each method that will seem high-minded to others around us...
I suggest we reduce things to the simple vernacular. Ah, the good old days... when everything was so normal and easy...
...

"...The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS ... Roughly 2 times PPS = 2 times target signal amplitude after integration."

No, I don't understand this either. I'll have to go to school for a few more classes...



The Big Bang Theory... Sheldon often puts Howard down for being just an electronics engineer. And not a real scientist!
Screenwriters obviously visited this forum a lot!

CCPI = Constant Current PI
PPS = Pulse Per Second
One pulse for each cycle.

However, in CCPI, we have one decay curve each HALF-CYCLE or HALF-PERIOD because the system is BIPOLAR.

Simple, no??

[ivconic]

CCPI = Constant Current PI
PPS = Pulse Per Second
One pulse for each cycle.

However, in CCPI, we have one decay curve each HALF-CYCLE or HALF-PERIOD because the system is BIPOLAR.

Simple, no??

[ivconic]

What none of you noticed and I just now; where is Qiaozhi??
Our dear friend George.
What's going on with him?
Why isn't he participating here?

[moodz]

ADS131 4 channel 24 bit @ 128 msps.
should be read
ADS131 4 channel 24 bit @ 128 Ksps.

I thought that our goal in this project was to minimize the complexity of the analog part of the circuit by studying the DIRECT SAMPING mode.
What you describe is a multiple channel analog integration circuit (what the GPZ6000 is doing)

Sorry about the typo ... I was intending to write ksps .... the thing with the direct sampling is that above about 1 MSPS things start to get tight in the CPU with timing / DMA similiar to processing a video stream .... now I dont know many small CPUs that can process a 24 Mbit video stream. ( 24 bit sample X 1,000,000 ).

So I would be going for the AD7760 -> Small FPGA -> 32bit CPU

.... and there are FPGAs with an embedded ARM core ! eg zync

moodz

[Olly]

Sorry about the typo ... I was intending to write ksps .... the thing with the direct sampling is that above about 1 MSPS things start to get tight in the CPU with timing / DMA similiar to processing a video stream .... now I dont know many small CPUs that can process a 24 Mbit video stream. ( 24 bit sample X 1,000,000 ).

So I would be going for the AD7760 -> Small FPGA -> 32bit CPU

.... and there are FPGAs with an embedded ARM core ! eg zync

moodz

You can also use Xilinx’s soft core Microblaze processor in most of their modern FPGA range and my personal favourite is the tiny Picoblaze core which uses almost no resources if you’re happy programming in assembler. These are so tiny you can literally instantiate tens of them within the FPGA for parallel processing if needed..

[moodz]

You can also use Xilinx’s soft core Microblaze processor in most of their modern FPGA range and my personal favourite is the tiny Picoblaze core which uses almost no resources if you’re happy programming in assembler. These are so tiny you can literally instantiate tens of them within the FPGA for parallel processing if needed..

... I agree. :-)

[Tinkerer]

Usually I like to do that , to confuse (P)ulse (P)er (S)econd and (C)ycle (P)er (S)econd.
Especially when I notice that it annoys someone!


...
(C)limate (C)hange (P)erformance (I)ndex !?!?
WTF!?


Joking aside, but I didn't follow many what's posted before, on those "CCPI" topics, so now I'm often confused by those abbreviations.
People of knowledge, people of science, like to complicate things with abbreviations.
But what does that have to do with us here? Can we adapt our vocabulary to the forum, the hobby, the vast majority of us here!?
There are actually many ways to generate a signal.
Signal procession.
Waveform.
And if we add some abbreviation to each method that will seem high-minded to others around us...
I suggest we reduce things to the simple vernacular. Ah, the good old days... when everything was so normal and easy...
...

"...The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS ... Roughly 2 times PPS = 2 times target signal amplitude after integration."

No, I don't understand this either. I'll have to go to school for a few more classes...



The Big Bang Theory... Sheldon often puts Howard down for being just an electronics engineer. And not a real scientist!
Screenwriters obviously visited this forum a lot!

"...The resonant frequency of the CCPI is the same with 1000 PPS or with 25000 PPS ... Roughly 2 times PPS = 2 times target signal amplitude after integration."

No, I don't understand this either. I'll have to go to school for a few more classes...

SRF, the self resonant frequency of a coil is often used to describe the frequency a coil will resonate. See picture attached for AMX TX coil.
In a real hardware situation everything connected to the coil, like coil cable, coil shielding, cable shielding, Mosfets etc. including everything that is capacitively and inductively coupled to the coil, has some influence on the resonant frequency of the coil.

The Pulse Repetition rate per Second, PPS for the PI is how many pulses per second. Each pulse generates a Flyback and after each pulse there is a signal decay curve. We sample the decay and integrate the samples over a certain time. Integrating more samples improves the S/N (Signal to Noise ratio) and increases the final signal amplitude.
So, more pulses = more signal amplitude and better S/N.
Carl and George Overton have published an excellent book, "Inside the Metal Detector" where all these things and very much more is explained in detail.
I highly recommend you read this book several times until you understand what is going on inside a metal detector.

[Willy Bayot]

Sorry about the typo ... I was intending to write ksps .... the thing with the direct sampling is that above about 1 MSPS things start to get tight in the CPU with timing / DMA similiar to processing a video stream .... now I dont know many small CPUs that can process a 24 Mbit video stream. ( 24 bit sample X 1,000,000 ).

So I would be going for the AD7760 -> Small FPGA -> 32bit CPU

.... and there are FPGAs with an embedded ARM core ! eg zync

moodz

An STM32 @ 180MHz or a PIC32MZ @ 200MHZ are perfectly able to capture an ADC output @ 1MSPS under DMA
The only limiting factor is their max SPI clock, 45MHz and 50MHz.
I have calculated the max capture rate of the SPI with a data stream of 24 bits. I get in both cases a rate of approximatively 1MSPS.

I can put another choice on the table
ESP32-S3 is a dual-core XTensa LX7 MCU, capable of running at 240 MHz. Its SPI clock can go up to 80MHz.
Worlwide development support, many widely available and cheap development boards
All types of ESP32 can be programmed in C or C++.

It is now time for the 'boss' to make the main architecture decisions so that we get going with more details like defining circuits and selecting real components:

• Coil Assembly type
• XMIT model
• AFE model
• ADC
• CPU and development board

[Qiaozhi]

What none of you noticed and I just now; where is Qiaozhi??
Our dear friend George.
What's going on with him?
Why isn't he participating here?

Don't worry. I'm still here.
Just trying my best not to get involved with this project as I'm busy with other things.
Also, these so-called collaborative projects tend to fizzle out after a while, although this one may have a chance since Carl took over the reins.

[ivconic]

Don't worry. I'm still here.
Just trying my best not to get involved with this project as I'm busy with other things.
Also, these so-called collaborative projects tend to fizzle out after a while, although this one may have a chance since Carl took over the reins.

Now you know who is your true friend and who is thinking of you.
You haven't been on the topics for a long time.
Who thought to ask about you?
Just me!

Yes, past experience with ideas is not very great. Many ideas and none of them completed.
And this one here... after a long debate, we still don't have a consensus.
Carl and Willy have already declared themselves in favor of direct sampling.
I thought we were all going to vote.
I am for both; that both approaches develop in parallel.
For many reasonable reasons, which I would not repeat here, a lot has already been written about it.
I expected you to at least give your opinion on that.
There is still no definitive decision about the ADC. Nor about the MCU.
I'm afraid the whole story will come down to only two/three being able to work on the project going forward.
And the rest of us will be carried thirsty across the water...

[David_1]

im messing with PI at present but is the application of the signals similar across different design types ... what is best