Bipolar PI MD with GB and DD Coil

[GeoMax]

Hi,

You need to use the latest files that Detectorist#1 posted a few days ago. PCB's are for that latest design is also available on eBay.de

[pechkata]

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).

Speculation is detected.
There is no ethics—everything is a market economy.

Stay healthy.

[Detectorist#1]

Hi pechkata,
Speculation is when conclusions are drawn that are not based on facts. When there is complete documentation and the possibility of verification, it is not speculation.

[Detectorist#1]

Additional information for the assembling of this project.
Further will be posted time-diagrams of the signals for the two variants (Hybrid and Standard Pulse) and recommendations for settings of the resistor-trimmers on the boards.
Now, I prepare the videos from real work on the field ( it is not easy to make the movies first time in the life).

[Detectorist#1]

Information for the timings of the signals in "Dual Tone Pulse Detector Rev.B".

[Detectorist#1]

This is the diagram that explains the reason for not possibility to use standard "Ground Balance" feature in pure PI detectors when the first delay is under 12us.

[Ruben2000]

Information for the timings of the signals in "Dual Tone Pulse Detector Rev.B".

Great job, Detectorist #1, and thanks to Geomax for this fantastic project!

We appreciate your work and dedication in sharing this project with us. I don't know much about metal detectors, but I see that it has all the details necessary for any metal detector enthusiast to build it. I'd love to see how it performs in the field.

[Orbit]

This is the diagram that explains the reason for not possibility to use standard "Ground Balance" feature in pure PI detectors when the first delay is under 12us.

I simply cannot believe that you have gone so far from the initial knowledge as you wrote yourself in a year. As if you copied somewhere. Apart from the fact that you won't get any benefit, the biggest benefit will be the copywriters who supposedly have companies and have never joined Geotech.

[GeoMax]

I simply cannot believe that you have gone so far from the initial knowledge as you wrote yourself in a year. As if you copied somewhere. Apart from the fact that you won't get any benefit, the biggest benefit will be the copywriters who supposedly have companies and have never joined Geotech.

Hi Orbit,

I can assure you that Detectorist#1 did not simply "copy" the design from somewhere else. From the initial schematic to the final version, at least ten major circuit modifications were incorporated—changes that can only be identified through actual circuit testing. Furthermore, a total of four different PCB layouts for the mainboard and three for the power board were created before the designs were finalized. The entire development process, from the initial concept to the fully tested detector, took approximately 16 months.

The actual PCB design is a combined "standard" or "hybrid" version. It depends on what you want to populate it with. I suggested the idea of a combined PCB design for standard or hybrid applications to him.

[algan]

Hi,

the PCB's for the Dual-Tone Bi-Pulse Detector project are available in the catogory "Metalldetektoren" on eBay.de

.Hello GeoMax.Can I get a link to eBay? Thanks.

[eduardo1979]

.Hello GeoMax.Can I get a link to eBay? Thanks.

https://www.ebay.de/itm/128018846245...Bk9SR6SxzeGAaA

[algan]

Thank you Eduardo, I will wait for the video that the Detectorist#1 promised. If it has an impressive depth compared to other pulse detectors, I would buy a few boards. I am curious what objects it captures in the ground at 80-90 cm.

[Detectorist#1]

Hi algan,
Read please again #189 and the information for the sensitivity. The PI detectors for 80-90cm depth use other size and type of search coils - this have to be known from you as you are on GURU level.