Bipolar PI MD with GB and DD Coil

[algan]

I think it refers to P-channel and N-channel MOSFET transistors. IRF740 and IRF9640. If we zoom in on the photo, we can see that the terminals are defined as GDS

Yes exactly IRF640 and IRF9640.

[Ruben2000]

[QUOTE=pechkata;n450736]

[Hello, Ruben.
Yes – a capacitor in parallel to determine the sweep.
The MOSFET doesn't matter—it doesn't consume power.]



Although I didn't quite understand your answers, I think you stated that you used the same Sascho coils. And as for the MOSFETs, you can use any type, even low-power ones.
Well, I don't have a clear answer. Thanks anyway!
What I noticed is that you placed two capacitors in the generator. Do you mean that these are in parallel with each MOSFET, which determines the sweep?
Here's an image that appears in your video!

[pechkata]

Although I didn't quite understand your answers, I think you stated that you used the same Sascho coils. And as for the MOSFETs, you can use any type, even low-power ones.
Well, I don't have a clear answer. Thanks anyway!
What I noticed is that you placed two capacitors in the generator. Do you mean that these are in parallel with each MOSFET, which determines the sweep?
Here's an image that appears in your video!

The video is a test version—to see what it does.
All my videos were filmed online—before that, I didn't know what I was doing.
Google Translate does not translate correctly.

[algan]

Here is a pdf of Altra you can test a bipolar generator

[pechkata]

[Ruben2000]

The video is a test version—to see what it does.
All my videos were filmed online—before that, I didn't know what I was doing.
Google Translate does not translate correctly.

Thank you so much, pechkata, for the details and for this last file!
I'm going to build this last Lay file you shared and see how it performs. It has parts I can get where I live. As for the coils, I'll use the ones Sascho mentions in his schematic; or do you have any other coil recommendations for better performance?

[Ruben2000]

Here is a pdf of Altra you can test a bipolar generator

Thank you so much, Algas, for sharing this file.

I didn't know this file existed; it explains everything in detail. I'm sure you've experimented with these types of generators.

I see that this file belongs to Altra, a member of this forum. Excellent research, and we look forward to sharing our experiences with everyone.

[pechkata]

Another option.

[Detectorist#1]

Hi DIY people,
After more than one year of experiments with different schematics of bipolar pulse metal detectors with DD coil, me and GeoMax made one design with focus on relative easy repeating of the construction from relative less experienced DIY people. This is the reason for using of ready DD coil from Bulgarian DETECH company , ready S-type stick from MINELAB and aluminum box from HAMMOND company.
Some additional information for this detector:
- Using of power, dual channel integrated MOS driver and low capacitance fast 600V 1A diodes ensures good symmetry of TX pulses beside of the big differences in the capacitance parameters of the power NMOS and PMOS switches transistors. The power MOS driver eliminates the differences in "input and reverse capacitances" and the additional diodes eliminates the differences in "output capacitance" parameters.
- Bipolar TX pulses eliminate 1/f noise and allow using of cheap IC in the first stage of the RX channel.
- Reduced 1/f noise allows using of low cut-off frequency in the filters in RX tract (1Hz). This make this detector as "slow motion" type.
- The schematic allows using of two variants of generate of the "Ground Balance" signals. The first variant is "classic" type with samples from RX signal after some microseconds after the main sample. The second variant uses "truncated half-sine wave" TX signals and GB signals taken after the peek of the half-sine signals. It is possible to make difference in "targets hole" feature between these two variants in real tests.
- Ground balance feature have to be used only for delays grater than 10-12us. The reason is explained in popular diagram for the polarity of the RX signals for "Fe" and "non-Fe" targets in the first 20us after the end of the TX signal.
- With delays more than 12us, this detector not react on ferrite and red bricks.
- For Fe/non-Fe discrimination, this detector uses RX signals taken during the first 10-12us of the rise of the TX current. For non-Fe targets, the sound tone is 1.5KHz and for Fe targets the sound tone is 600Hz. The volume of the sound is proportional to the the value of the received signal (in some borders, as in every radar sensor).
- Some words for the sensitivity of this detector. The 0.3g gold nugget - 5cm (at 5us delay), 1x1inch Al piece from the beer can - 60cm (at 5us delay). This project is not for big targets at big distances! (no one wants to dig big holes in hot summer).
- The main disadvantage of this detector is impossibility to react to the small target situated to near to the big target. This opens the space for further improvement of this project. Maybe the solution used in White's TDI MD with eliminating of "opposite" signals with J113 switches will help.
As a first step, the schematics, the BOM files and the pictures of the assembled used boards of this detector are attached. Further, I will post more and more information useful for repeating of this detector by DIY people.
The designs for the printed circuit boards used are the property of GeoMax; he will sell the two-board set on eBay at a reasonable price (if someone decides to order their manufacture independently, the cost would not be lower).

[Op04]

Congratulation Detectorist#1 & Geomax, thank you for this project!

[usefi5961]

Excellent project and congratulation,can you please detail about making DD coil for this project and What is the maximum depth detection of the devices?

[Detectorist#1]

Hi usefi5961,
As initial idea of this project, the DD coil used in this project have to be ready-made (made from DETECH company from Bulgaria in this case). The parameters of this search coil are very good (especially balance parameter is excellent). Maybe the details of making are secret (know-how) of this company. The maximum depth detection depends from the size of the target - but the deep detection isn't the target of this design. This design is oriented to be balanced between the size of the targets and the depth detection.

[usefi5961]

Hi usefi5961,
As initial idea of this project, the DD coil used in this project have to be ready-made (made from DETECH company from Bulgaria in this case). The parameters of this search coil are very good (especially balance parameter is excellent). Maybe the details of making are secret (know-how) of this company. The maximum depth detection depends from the size of the target - but the deep detection isn't the target of this design. This design is oriented to be balanced between the size of the targets and the depth detection.

OK,thank you very much for reply .good luck.

[Detectorist#1]

Hi,
Additional information for this project:
- The bipolar power supply allows to not use any pulse DC-DC converters. This allows to be achieved more signal to noise ratio with more simple GND traces and escape of using of special filters on the board. Not using of microprocessor for generate of timing signals also adds possibility to not warry from added digital noise in the detector. All this allows to use TX signals with less power (and less power consumption from the detector) for achievement of the same final results.

[karakus]

Thank you Detectorist and GeoMax, you really put in the effort and have good intentions.