One more variant to create PI MD with reliable Fe reject

[Detectorist#1]

Hi all PI MD enthusiast!
The patent of Carl Nelson US6853194 expired at 25 Nov. 2021 and this allow to all DIY people to make some experiments and post the schematics at this remarkable site!

[Detectorist#1]

The project is based on information from coil's guru Joseph Rogowski and the patent of Carl Nelson for gradiometer design of PI MD

[Detectorist#1]

At the first design, the air test with static coils and waving of the targets all results was excellent, but on real test on the ground, when the target is static and the coil sensor is moving - surprise! - amplifying have to be reduced
10 times for avoiding of false signals! This reduces the recognize distant essential. To avoid this problem I was forced to modify the design - to use bipolar pulses.

[Detectorist#1]

My final goal is to design PI MD for small gold nuggets for searching small natural gold pieces - searching of coins and other old artefacts in historical places in my country -Bulgaria is strictly prohibited for hobbyists!

[Detectorist#1]

This project is targeted for the recognize of pieces on max 50-60cm depth. No body agree to dig holes at 1meter depth all day.

[Detectorist#1]

Differential scheme of the receiver allow recognition of one grain targets at two inches and for US quarter coin from one food and for bigger targets (beer can) from two foods in the ground.

[Detectorist#1]

Also, it is essential that this design have possibilities for reliable Fe targets reject - especially for bottle caps at first 6 inch of the ground - this reduces essentially digging efforts on the field.

[Detectorist#1]

This my project is not "ready to copy". The modules of the project have to by modified from experienced DIY peoples. The project uses only hardware parts. No microprocessor and software. I think - this is very important
for DIY people! All parts are situated on two boards - they are fastened to the bottom and to the top of the PVC box.

[lxs17757414132]

My brother, this is good news. Looking forward to your work

[Detectorist#1]

The solution of power supply is very important for every electronic project. In this case, have three options: 12V lead accu, 11.1V lithium accu or 8xAA alkaline batteries.
The first variant is too heavy. The second variant is not convenient - this variant needs special charging unit with equalizing charge of the cells capabilities.
The third variant also suffers from problems - the capacity of AA size batteries is very limited. Only solution is to reduce current consumption of the MD under 100mA to reach at least 20 hours of work with one set of the batteries.

[Detectorist#1]

For recognize of small targets, the first delay time have to be 2 to 5 microseconds. When you try to use these short delays, the result is that connecting cable is more sensitive to near hands than search coils.
Using of coaxial cable to the coils not solve the problem. Only solution is to situate the final TX switches and first RX stage inside the coils' unit. This also generate new problems. In gradiometer design, the board with
this parts have to use strong symmetrical disposition of the parts for eliminating of the difference of inducted signals in the board - this board is situated in very strong electromagnetic field of the TX coils!

[Detectorist#1]

Attached is the schematic of Sensor Board for this project. AD8429 instrumental amplifier is used as lowest noise instrumental amplifier

[Detectorist#1]

Hi all DIY enthusiasts!
Attached is full scheme of bipolar PI metal detector with true passive magnetometer mode for 100% reliable Fe separation.

[Orbit]

This is best done with a dynamic magnetometer, I tried this type of discrimination a long time ago, it worked smoothly without problems, the best with smaller coils, it only made mistakes on alloys, but it discriminated nails and other iron waste very well, only when I disconnected the transmitter while the magnetometer was working and the indication was before the led diode, after I connected a separate oscillator tone for iron .It had a switch that turns on the operation of the magnetometer and turns off the tx from the pi detector so that they would search in the pi mode and if I wanted to see what it was, whether it was iron or a precious metal, I would just click the switch to switch the mode, and if the iron was ice, it would light up or a low tone would be heard if it was not iron, there was no reaction to precious metals.I don't even know why I didn't use it after that, I probably wanted something new and new.

[Detectorist#1]

Hi Orbit,
This unit works exactly at the same way - in the magnetometer's mode TX coils not work.
When you wаnt to know the material of the target - just click the switch to Fe mode.