Bipolar PI design

[ivconic]

It is very difficult to find anything in the book that is not very interesting.
But I immediately decided on the Bipolar PI design as the first thing to focus on.
There are several reasons for that.
First, I like the idea of a "non-invasive" detection method because of the possibility of adapting this project for demining purposes.
Second, this approach is only the tip of the iceberg of possibilities for further development of PI detectors. That is my humble opinion, there are probably many who will disagree with me.
I have tried to participate in the AMX thread a long time ago but felt deprived of the vast knowledge that the other participants in the thread undoubtedly have.
Then I realized that I still have a lot to learn in order to be an equal interlocutor with others.
Luckily Carl's book is here, I have plenty of time to read and study. And now I'm slowly (after all, I'm quite old) starting to understand some things.
That's why I think Bipolar PI design is a good initial step and an introduction to some broader knowledge.
Carl offered very interesting solutions that "provoke" further thoughts.
There are two parts in particular that I really like. TX and audio. I wouldn't dwell on audio for now, because I think it is necessary to make it first and only then draw conclusions.
At this point I would focus on TX first.
Originally from the book Bipolar PI TX looks like this:

[ivconic]

But it's just a picture from a book, not a "living" thing to work with. That's why I redrawn that schematic in the software in which it's easiest for me to continue working (click to enlarge):

[ivconic]

And this schematic above is just a "picture" too, for all those who are interested, here is the schematic file.
The software that is needed is "ExpressPCB",
(don't get confused, it's a free installation package that during installation also installs a schematic part called "ExpressSCH" in which I mostly draw schematics)
and you can download it free from here: https://www.expresspcb.com/
And here is the sch file:

[ivconic]

Ok, now that I've got everything set up, let's just focus on the TX:

[ivconic]

In the book, Carl himself noted well that the use of the 4053 switch is "delicate" due to the high internal resistance in the "ON" state.
He further suggested mitigating that problem by using the 74HCT4053.
I still have parts of earlier debates from the AMX topic fresh in my memory and I know that such details are very important and that special attention should be paid to them.
I am 100% committed to building this detector. But I would like to improve some such "little things" in advance.
Of course, Carl himself "made it possible" by not giving the gerbers for the pcb yet. Otherwise, I would make the original version first, which is definitely recommended.


I apologize to everyone that I did not follow the numbering order of the components on the schematic according to Carl's original schematic.
I will try to correct that because it will be much easier to talk about the project further if the numbers match.
I also "broke" the quad opamp into dual and single opamps. I don't think this is a big problem.
But I will redraw the schematic and replicate the original.

UPDATE: I just corrected the enumeration and uploaded most proper drawing.

@Carl, small notice:
You have duplicated "IC8a" at Your schematic.
Not important, yet good to include it in "Errata".

[algan]

Yes, I'm also interested in this design, it would be nice if Carl posted a lay file or a Gerber file or a picture of the board, and if he doesn't, we should make it and test it, and maybe we can start with the TX first and experiment with what input signal TXN and TXP should be.
Ivconic, you're making a pulse star 2, I'd be curious if you use this model of the TX there, whether the penetration into the ground will improve and what the difference in depth will be compared to the original.

[ivconic]

PS2 timing is very complicated (that's why it works so well) and is performed entirely in the analog domain.
Here, things have been moved to a higher level, the timings are done digitally, which is good and guarantees greater accuracy.
Another thing, I wouldn't confuse a PS2 type detector with this bipolar PI detector, one of the last intentions on my list is "depth" with this project.
I suggest that we slow things down and don't start modifying right away, until we've made the original.
I would definitely make an original right away, but I'm waiting for Carl to sort out his work and publish the gerbers.
The only thing I would explore here, for now, is possibly replacing the 4053 with a better solution.
My main motivation here is to achieve as short a sampling time as possible with this type of TX.
In other words it means "fast" bipolar PI.
In other words it means; "depth is not important" but sensitivity to smaller objects.
I am not referring here to nuggets of gold and similar "particles" (AMX thread is dealing with such), but primarily to objects the size of a medium coin and larger.
...
Any further elaboration of the merits of this detector by me would be mere rewriting of what Carl otherwise brilliantly covers in his book.
I suggest that anyone interested should first buy the book and read it.
It would not be fair to the author to list here entire paragraphs with explanations of why what was done and how it was done.
...
I started this thread only because of a question about finding the best solution to replace the 4053 with a better solution.

[algan]

For example, instead of a 4053, you can use some kind of integrated circuit that is a high-side MOSFET driver. Here are some sample circuits with different integrated circuits.

[ivconic]

Yes, there were similar suggestions on the AMX thread.
But in my opinion, that would be a failure and a deviation from the concept and idea around which the book itself was written.
Carl seems to have followed the reactions of most members on the forum very carefully over the years and understood what the majority needed.
And in that spirit he wrote the book. Which, in my opinion, makes it even more valuable.
He used in most cases "old" components, which are everywhere and easy to get for anyone in any part of the world.
Specifically with this example of bipolar PI; he used 9640 and 740, mostly all chips are very easily available and everything makes the whole project even more interesting.
Of course, all this could have been done in a more "modern" way with new ultra-small SMD components and top-of-the-line specifications.
But that would turn off the vast majority of people, me in the first place!
I often refer to AMX, which I think is a fantastic project. But for exactly the same reasons I left the subject and I don't believe I will ever make one or do anything about it.
Because in some parts of the world (specifically, here, too) it is practically impossible ... or prohibitively expensive, to get most of the components.
Not to mention the working conditions and the impossibility of working with such small SMD components.
The good old "through-hole" way with DIL sockets; gives unprecedented freedom in further work and experimentation.
Of course, the performances between one approach and the other are clearly different and mostly go in favor of the "modern" SMD approach.
But here we are not talking about professional industry and production for wide markets. We have gathered here for hobbies and learning.
And for that purpose, the "classic" approach is second to none.
I believe that hardly 5% of the forum members have the approximate conditions to work easily with the top technology.
All the better for them, because what works well in the "classic" way - will work even better and easier in the "modern" way.
For this purpose, I think it is better to come up with a bipolar driver with discrete components instead of using some specialized chip.
And the understanding of the principles of work will be more complete.
In the specific case, I think it would be best to come up with such a driver with mosfets or BJT transistors.

[Carl-NC]

Yes, I'm also interested in this design, it would be nice if Carl posted a lay file or a Gerber file or a picture of the board...

I'm working on this now. Give me a couple of days to finalize.

[ivconic]

Carl... I just tried to find where to buy PIC16F18426... you won't believe it is not even on Aliexpress or Temu!???
Not to mention the local shops in the region! One has only the SMD version. Phew!
Carl where on earth did you find it! (rhetorical question)
You and the others from the AMX thread are top artists in finding literally all the components that I (and the rest of the "eastern part") can't find!
I have no choice but to port the code to some of the AVRs available to me.

[ivconic]

Once Trumpet is seated in the chair... I will call him personally (we are good friends, we used to roast the same chicks in our time) and I will ask him to finally solve this issue regarding the procurement of materials!
This took on too much momentum, it exceeded all measure! Can't take this anymore!

[algan]

where to buy PIC16F18426...
https://bg.farnell.com/microchip/pic...-14/dp/2857684
https://www.tme.eu/bg/details/pic16f...ip-technology/
You can tell your friend from Bulgaria and he will order it for you.

[ivconic]

Algan from now on You are my brother!

[ivconic]

Algan... you ar not my brother anymore: