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

[Aashif]

Hi Detectorist#1 and @GeoMac,
I cannot thank you both enough for taking the time to review my schematic. As a learner, getting guidance from experts like you is a huge privilege, and your practical insights are literally saving this project!

Detectorist#1:
I have carefully followed your instructions and updated the design:
1. Power Supply: Removed C1 to C8. Kept only C9 (4700uF/35V Low ESR) and added a 100nF/50V ceramic capacitor in parallel.
2. L1 Inductor: Replaced L1 with a 1 Ohm (0.5W) resistor.
3. MOSFET: Swapped the Drain and Source connections so they are now correctly routed.
4. Damping Resistor (R: Replaced the single 330-ohm resistor with three 110-ohm (3W) resistors connected in series to handle the flyback voltage safely.

I just have two small doubts:
* R9 Resistor: In my schematic, R9 is a 10K pull-down resistor at the MOSFET gate. Did you mean a different resistor to be divided, or should I leave this 10K as it is?
* D1 & D2 Diodes: I still have the back-to-back 1N4148 diodes at the gate. Should I completely delete them so they don't clamp the gate voltage?

@GeoMac:
You are absolutely right, and I completely missed that flaw! Using a standard BJT (Q1) to switch the delicate sampling signal was a rookie mistake on my part.
I would love to learn the right way to do this. Should I be using an Analog Switch IC like the CD4066 or a specific JFET instead? Your expert advice on how to properly wire this sampling stage would be incredibly helpful.

To make things easier, I am attaching both the updated PDF and the EasyEDA source file (.zip) to this post.
If you spot any more silly mistakes, please let me know. Also, if it is easier for you to explain the sampling logic by directly tweaking the source file, please feel free to do so! I am here to learn from the best.

Thanks again for being so patient and supportive!
Best regards,
Aashif

[Detectorist#1]

Hi Aashif,
My remarks continue:
- What is the purpose of the capacitor connected in parallel of TX coil? And the working voltage of this capacitor have to be more than 2000V - not 630V
- Used type of SIC transistor is not suitable for this design - he needs +20V pulse on gate for 6A Drain current. If you not want to use SMD type transistor - use IMWH170R450M1 type. The case is TO-247-3 and the Ron=450moHm at +12V pulse on the gate for 10A Drain current. This will allow to NOT use +15V stabilizer especially for controlling of the SIC transistor.
- The connection of gate driver is wrong - no connection to GND. Also the name of pin7 have to be "NC".
- It is not good to use for power ground and for minus 12V supply the same symbol despite the different name.
- GeoMax is right - for sampling is good to use J113 unipolar transistor instead of bipolar 2N3904 type. Also it is not possible to control the base of 2N3904 from pin6 of U10 - this is input, not output of 4011.
Further will be more remarks...

[pechkata]

[Detectorist#1]

Hi Aashif,
Your schematic have to many mistakes and some of them are too general to be easy corrected. The total structure of the detector is wrong and is not suitable for the design of the PI detector with "Brutal" TX power with 24V power source.
I will propose to you an other structure more suitable for your purpose instead of write many remarks. Soon, I will draw the schematics with the building blocks and you will have possibility to try to draw the full schematic as an exercise.

[Aashif]

Hi Detectorist#1,
Thank you so much for your honest feedback! I completely understand and agree.

I am very excited and grateful that you are willing to draw a proper structure for my 24V "Brutal" TX power goal. I will happily drop this flawed design and wait for your proposed building blocks. It will be a fantastic learning exercise for me to draw the final schematic based entirely on your expert guidance.

Take your time, and I will be eagerly waiting for your schematics!

Best regards,
Aashif

[GeoMax]

Hi Aashif,

You should take a look at the schematic for the PI-Polones, as it's very similar to your circuit design. The only difference to your design lies in the audio section and the transmitter control. Your approach for the transmitter, however, is a bit overkill.

Furthermore, you should know that PI-Polones is a modernized version of Sandbanks PI from 1979. You can find the project details and how the circuit works in the download section of Geotech or attached below. I would recommend checking-out this first before continuing to design your circuit. Once you understand how the circuit works, you can then convert the detector to 24V and/or modify the audio section.

Sandbanks article from 1979: sandbanks300.pdf
PI Polones schematic:

[Aashif]

Hi @GeoMac,
Thank you for pointing out the PI-Polones / Sandbank connection and sharing the PDF!

I have downloaded it and will definitely study the core principles. It will be great homework for me while I wait for Detectorist#1 to share his proposed building block schematics for my 24V goal.

Reading this theory will surely help me understand his upcoming schematics much better. I really appreciate the guidance from both of you!

Best regards,
Aashif

[pechkata]

Hi @GeoMac,


Reading this theory will surely help me understand his upcoming schematics much better. I really appreciate the guidance from both of you!

Best regards,
Aashif

Practice is the mother of knowledge.

[Detectorist#1]

I just start to draw the schematic with right building blocks as base to the design of the real "BRUTAL" power PI detector. I know for one old solution with kilowatts power detector ( and big size antenna) mounted on the airplane for searching of the goods under the ground. The new solutions have to be better! 10 meters deepness (for big size targets) have to be possible with now days electronics parts and huge power of Lipo accus! Just be aware from war mine reach zones! This is one new challenge for us! There is only one problem - the hidden big treasures are very rare in the world - but the Esperance stays last!

[Aashif]

Hi Detectorist#1,
Wow! Reading your message just gave me goosebumps! 10 meters of depth for large targets sounds like an absolute dream come true.

I am incredibly thrilled and grateful that you have taken this up as a new challenge and started drawing the building blocks. I have a lot of heavy-duty electronic parts and massive LiPo power ready for this "BRUTAL" build.

And don't worry, no war mine zones here—just pure dedication and hoping to find that rare hidden treasure because, as you perfectly said, "Esperanza stays last!"

Take all the time you need. I am fully ready for this challenge under your expert guidance!

Best regards,
Aashif

[Detectorist#1]

Hi Aashif,
The right project of very high TX power PI detector capable to use different coils with sizes from 1x1ft to 4x4ft (or most probably 6x6ft), as you want, will need additional parts for ensuring of safety work of the Tx power switch (high voltage SiC type transistor). This transistor have to be protected from over-current and over-voltage states. This task will need more design time but this challenge is excited.

[Aashif]

Hi Detectorist#1,
Take all the time you need! Safety and reliability for those massive 4x4ft or 6x6ft coils are definitely the top priority.

I am very happy that you are enjoying this design challenge. It is better to wait for a perfect and well-protected design rather than rushing it.

I will patiently wait for your masterpiece! Take care.

Best regards,
Aashif

[Aashif]

Hi @Detectorist#1,

Hope you are doing well and having a great week!

Just dropping by to say hello. I know that engineering the protection circuits and building blocks for the "BRUTAL" 24V setup takes a lot of careful thought and time, so please take all the time you need.

I am just eagerly holding on to my tools, looking forward to your masterpiece whenever it's perfectly ready!

Best regards,
Aashif

[Detectorist#1]

Hi Aashif,
The project of "High TX Power PI Detector" is in progress. I want to make some tests of the included modules before posting of the schematic of the first variant. Today, I buy all parts of the schematic except the materials for building of the search coil. The first variant of the search coil will be with 3ft diameter coil mounted in widely sold hoop for gymnastics convenient to be ported with the individual car. This variant of the coil will be suitable for searching of the targets in 10-15ft deeps. Further, the following variants of the designed search coils will be suitable for deeper and more big targets.

[Aashif]

Hi Detectorist#1,
Wow! I am absolutely speechless. I cannot believe you actually went out and bought the parts to physically build and test the modules yourself!

This level of dedication and professionalism is just mind-blowing. Thank you so much for investing your own time, money, and effort into this "BRUTAL" project.

The idea of using a 3ft gymnastic hoop for the first variant is brilliant and very practical. And 10-15 ft of depth with it sounds absolutely incredible!

Please take all the time you need for your physical testing. I will patiently wait for the results. I am incredibly grateful to you!

Best regards,
Aashif