Custom High-Power 24V Pulse Induction PI Detector Circuit Review

[GeoMax]

Hi Aashif,

I’ve read through your document and have a few comments. It comes across as though it was created—or at least heavily assisted—by AI. At the very least, the document's structure is typical of AI-generated content. Is that the case? No developer would choose that kind of phrasing; it reads like something an AI would write by simply parroting back things it has "learned." It seems the AI possesses some basic knowledge but lacks genuine understanding.
Let me explain why I get that impression. A few days ago, I wrote a project description for a new deep-seeking metal detector design myself, focusing on completely different aspects. I described the individual circuit sections in terms of their intended function rather than just their component makeup—referencing other detector circuits I studied, for context. Your text, by contrast, feels overloaded with superfluous details about individual components and IC pins—typical AI behavior. And finally, there are those precise source citations that only an AI produces.

Please do not misunderstand my comments—of course, you can use AI, but it is not suitable for absolutely everything. It would be more useful to describe your project differently and list some technical specifications for the detector. These could include parameters such as the TX pulse width, the pulse delay range, the sampling method, specific integrated functions (if applicable), and the type of controls or fixed settings on the detector. All this information is missing from your document.

[Detectorist#1]

Yes, it is strange that have noticeable difference between too detailed description of the connection of the pins of used integral circuits in initial idea and so raw (almost missing) information for the general structure of the project. But this is the future - will be serious competition between AI and the human experience.

[Aashif]

..

[Aashif]

Hello guys,
Haha, you caught me! I admit, I used AI to help structure my document and translate my thoughts into clear English. Since I am building this complex 24V PI system step-by-step in EasyEDA, writing down every single pin connection was mostly a way for me to not get lost in my own wiring while translating the design. The AI just made it look a bit too robotic and polished! But the passion, the soldering, and the actual build are 100% human and mine.

I completely agree that the core technical parameters were missing from my initial text. Here are the specific details of the architecture I am aiming for:

* TX Pulse Width: I am designing the NE555 timer stage to have an adjustable pulse width, roughly between 100µs to 300µs. I will likely keep it around 150µs for normal operation to balance depth and power consumption on the 24V supply.
* Pulse Delay Range: Since my main goal is to hunt for deep, larger targets and ignore small surface trash/ground mineralization, I plan to make the delay adjustable from about 15µs up to 50µs.
* Sampling Method: It will be a classic PI Sample-and-Hold setup. I plan to use an analog switch (like the CD4066 or similar) to sample the signal from the receiver op-amp (NE5532) just after the back-EMF spike collapses, feeding it into an integrator stage.
* Detector Controls: The front panel will have standard PI analog controls:
1. Delay (To tune out ground noise/small iron)
2. Sensitivity / Gain
3. Audio Threshold (To set the background hum)
4. Pulse Width (Might keep this as an internal trimmer on the PCB, or external if needed).

Right now, I am literally in the middle of drawing the schematic in EasyEDA (just finished wiring the +15V, +12V, and the LT1054 -12V rails based on your excellent suggestions). I will upload the complete schematic you were asking for by tomorrow evening. Once the visual schematic is fully drawn, the whole structure will make much more sense than my text document.

Thank you both for the reality check and the guidance. The competition between AI and human experience is real, but I'm here to learn from the human experts!

[Aashif]

Hi guys,

First off, big thanks to @GenoMan and Detectorist#1 for the solid advice in my last post. Taking your points about IGBTs and PI design into account really helped me structure this better.

I should mention that this is actually my very first time manually drawing out a full schematic from scratch. I’ve spent some good time in EasyEDA learning the ropes and finally put together this first draft.

I started with the capacitor bank and worked through the main power and analog sections. I intentionally left the battery charging and management circuit out for now, just to keep the schematic clean and focus on the core detector design.

I've attached a PDF and an image so you can take a quick look.

I’m also attaching the EasyEDA project (.zip) file. Since this is my first schematic and a high-power 24V setup, if you guys spot any missing protection components, routing errors, or design flaws, please feel free to open the file and edit it directly.

I really value your practical experience, so any technical feedback is highly appreciated. Let me know what you think!

Thanks for your time,

[GeoMax]

Hi Aashif,

I’ve taken a look at your schematic. To be honest, this drawing certainly won’t win any design awards. It’s quite a jumble with no discernible layout logic. But that’s okay—you’re here to learn, and we want to give you a few tips on how to improve it. First of all, you need to realize that reading a schematic is very similar to reading a book. In my part of the world, you read a page of text from left to right and then from top to bottom. A schematic should be structured the same way. I’ve attached an example of how I draw schematics; other experienced designers here on the forum use a very similar style. I usually start at the top left, where the signal is received or the TX signal is generated. Next come the receiver, any integrator circuits, and/or amplifiers, etc., depending on your design. Then comes the audio section, usually positioned on the far right. The timing and sampling circuitry is typically placed below the receiver. I draw the power supply unit next to that—or underneath it for larger circuits. These functional blocks fit neatly onto a single page, making the schematic easy to read and very organized. Just take a look at the example circuit for the PI-Polones; its structure is similar to that of your detector.

[Aashif]

Thank you so much for the detailed feedback and the example, GeoMax! I really appreciate you taking the time to explain the proper layout structure. Since I am still learning, this left-to-right and top-to-bottom approach makes a lot of sense. I will definitely apply these tips and try to organize my next schematic much better.

[Carl-NC]

Also notice the use of implied connections. You don't need to literally connect everything with wires, you can use ground and power symbols (and even signal symbols) to make connections, and it makes it far easier to read. Here is one of mine, notice how it's broken into several pieces:

[Aashif]

Thank you for jumping in and sharing your expertise, Carl-NC! Your 'Hammerhead' schematic is a great example of how clean and readable a design can look when broken into logical blocks.
I now completely understand the point about "implied connections." Using ground, power, and signal symbols instead of routing long wires everywhere makes a huge difference. This will definitely help me clear up the mess in my current drawing.

By the way, could you please tell me which software you used to draw this 'Hammerhead' schematic? I am currently using EasyEDA, but I really love the clean and professional look of your drawing. Which software would you recommend for making such neat schematics?

Thanks again for the guidance!

[GeoMax]

Hi Aashif,

I would recommend KiCad. It is quite powerful—comparable to professional PCB software—and also free.

[GeoMax]

Also notice the use of implied connections. You don't need to literally connect everything with wires, you can use ground and power symbols (and even signal symbols) to make connections, and it makes it far easier to read. Here is one of mine, notice how it's broken into several pieces:

Hi Aashif,

Carl's example schematic for the Hammerhead is another great example of how to create a clear and readable schematic. Always try to divide the entire schematic into circuit blocks and connect them using labels. This makes troubleshooting easier later on should any problems arise. It also makes it simpler to redraw a circuit block or swap it for a different version without having to redraw the entire schematic.

[Carl-NC]

That particular schematic was done in Microsoft Visio which is a generic drawing program, not a schematic capture program. I usually do all my formal schematics in Visio (such as all the ones in ITMD3) because it gives me more control over the appearance. For real schematic capture, get KiCad. It's free and quite good.

[Aashif]

Hi everyone,
A huge thanks to GeoMax, Carl-NC, and @Datatrust#1 for the high-level guidance. I took your professional advice to heart and have completely upgraded the schematic design.

Here is what I have implemented in this new version:
1. Professional Layout: Structured the entire circuit with a clean Left-to-Right signal flow.
2. Clean Wiring: Replaced all long wires with standard Netlabels/Netports for power and signal lines.
3. Modular Blocks: Organized the schematic into functional sections with dashed boundaries and clear titles.
4. Capacitor Bank: Cleaned up the parallel capacitor representation (8x 4700uF + 8x 104).
5. Completed the standard Title Block.

I am attaching both the updated PDF and the EasyEDA .zip source file. I am really proud of how clean and systematic it looks now!

Since you guys have the practical, hands-on experience with this specific PI design, I’d highly appreciate it if you could run an expert eye over the final wiring and component values. If you notice any technical nuances or connections that could be optimized, please feel free to tweak the attached .zip file directly.

Let me know your thoughts before I jump into the PCB routing stage!

Best regards,
Aasif

[Detectorist#1]

Hi Aashif,
My initial remarks on your schematic3:
1. No need of so many capacitors 4700uF 35V in the power supply part. The internal resistance of LiPo accus is very low. Will be enough only one 4700uF/35V capacitor of "LOW ESR" type on the place of C9 with parallel ceramic capacitor 100nF/50V. All capacitors C1-C8 have to be omitted.
2. On the place of L1 have to be used 1oHm 0,25-0.5W resistor.
3. The connection of SiC transistor is wrong - the Drain and Source ends have to be exchanged.
4. The resistor R8 have to be divided in 3-4 serially connected resistors - every one is for 500V working voltage if their power is 2-3W.
5. The same think have to be made with resistor R9.
In my next post I will continue with remarks - now I have to go for lunch.

[GeoMax]

Hi Aashif,

I think the logic circuit for the timing and sampling is flawed. How can the output of a gate switch the transistor? I think you definitely need to revise this part—and why are you using a transistor to switch the sampling signal, anyway?