New Project - MPS PI - Iron discriminating metal detector.

[dfbowers]

To answer MartinB's question. The way that the project is presented, the MPS PI will present a high tone on non ferrous targets and a high- low tone on ferrous targets. Your choice on what to dig. The design goals did not include iron infested sites but parks, yards and open fields. You can now use a PI in a lawn without digging up nails and bobbypins everywhere.

However, I think It could be adapted to iron infested area by:
Flipping the polarity of the RX coil.
Rebalancing the RX coil null.
Turning off the PI channel audio.

That would present a single low- tone on non ferrous targets, much like the VooDoo was designed to do.

To take it a step further, the recovery speed could be changed. But , you are on your own there.

Weaknesses. Yes, every detector has one. If you noticed, there is no ground balance on the PI channel. The whole project can fall apart in heavy ground minerization. The project depends on a quiet PI channel as it's also working as THE ground balance channel. With that said, this project works fine in Central Pennsylvania dirt, which is pretty bad to begin with. VLF detectors loose 1/2 their depth here in DISC mode. To make this project serious, it would need the addition of a GB sample, a couple more integrators, bigger board, more parts etc.

I have tested several versions in a clay fired brick bed and it struggles to correctly ID things, but my Nautilus DMC11B and Troy X5 can't ID a nickel under a single brick here either. It DOES stand a chance by using a DD coil in this environment but as I mentioned in the previous post, I have not been able to get a DD coil to work to my satisfaction. But.. it DOES go a long way with ground rejection.
Don.

[Detectorist#1]

Hi Don,
Your answer: "However, I think It could be adapted to iron infested area by:
Flipping the polarity of the RX coil.
Rebalancing the RX coil null."
Why flipping the polarity of Rx coil - in Vioodoo project have possibility to flipping of the polarity of PI channel?
How you imagine to rebalancing of RX coil's null on work table?

[Detectorist#1]

Yes, this hybrid PI-IB projects are very interesting area for experiments. Now have 3 variants for additional DISK channel:
- sample of the RX signal after TX pulse (by Voodoo project)
- sample of the RX signal during of the TX pulse ( by Don)
- adding of "resonance" capacitor to RX coil (by Eduardo)
Wide field for experiments!

[dfbowers]

The purpose of flipping the polarity of the RX coil is so you can hear non ferrous targets on the iron DISC channel instead of ferrous targets. In iron infested areas hearing all the iron would drive Ya nuts!
While sampling an induction balanced receive coil while "TX ON" , the extracted signal will show opposite change in polarity between ferrous and non ferrous targets.
The DISC channel will never trigger the comparator otherwise.
We found out that flipping the polarity MAY require the null position to be adjusted slightly by moving the fine tuning end of the bucking coil in order for it to work properly.

[Qiaozhi]

Yes, this hybrid PI-IB projects are very interesting area for experiments. Now have 3 variants for additional DISK channel:
- sample of the RX signal after TX pulse (by Voodoo project)
- sample of the RX signal during of the TX pulse ( by Don)
- adding of "resonance" capacitor to RX coil (by Eduardo)
Wide field for experiments!

The problem with adding a resonance capacitor to the RX coil is that this also affects the TX signal.

[dfbowers]

Hi Don,

In this case the important question is - how to setup correctly frequency response and the gain of the DISK cannel depending of PI settings?

If you stick with this project as is, all should work fine. Frequency response and gain of each channel is already figured out.

[eduardo1979]

Hello Eduardo!
It would depend on what type of hotrock. In our area, the ground is littered with natural graphite( I think) that looks like coal but is as conductive as thin aluminum foil. It can be rejected easily with a main PI sample delay of around 17uS.

I think the disc channel could be easily adapted to almost any PI circuit assuming the frequency response and the gain of the channel is setup correctly. My original idea was to team two Surf PIs together but a good friend of mine ,Cyril is a wiz at designing and build his own PIs. I did a proto board on one of his designs and it worked so he finished the artwork.
The main challenge is going to be the concentric coils though. I have made dozens and they all work great.
I'm wondering of something like a Minelab Commader DD coil might
work.
Don.

Hello Don.
Thank you for answering my questions. The hot rocks we have in our area are a kind of rock that contains ferrous metal, so if you put a magnet near it, it sticks very easily. Regarding the Minelab DD coil, I cannot give an opinion, because I have never had one to see the parameters it has and I also do not know if that kind of coils have a cancellation point like the VLF-IB coils. I think it would be better for you to build your own concentric coil and thus ensure the correct operation of the detector. By the way... I really like the idea of joining two Surf-PI detectors to achieve ground balance. If you have the finished work of the two SURF-PIs coupled together, I would like to see a demonstration video.
Best regards,
Eduardo.

[dfbowers]

Here is an example of a school yard hunt with the MPS-PI.
Cyril ( Who layed out the PCB and designed the PI section)
sends me pics like this all the time.

[Carl-NC]

I'm surprised any pencils register as iron since the ferrules are aluminum. What are the 3 red things in the non-iron pic?

[dfbowers]

Carl. The red things are some sort of cast metal. One thing about the MPS, it's really good at identifying any ferrous content, like bottlecaps. Some pencil erasers do have ferrous content, checked with a magnet.

[dfbowers]

More testing with the MPS-PI today.. I originally did not have high hopes with this design when it comes to salt beaches, just because it's a "hybrid". But.. I was pleasantly surprised to find that It's100% at home in the salty surf. No noise or false signals on either the PI or iron disc channels in the surf! In fact, I ran my iron disc reference pot at 0V (max sensitivity). I was fooled by one very deep bottle cap and one piece of steel wire on edge but otherwise was nearly 100% accurate on iron ID. I didn't find much other than a handful of corroded coins, fish hooks, Bobby pins and fence wire (I dug everything for a sanity check). Ocean City Maryland...

[dfbowers]

Another successful build (for his son) by CBS, who did a lot of the board design for this project. This will be the 7th or 8th successful build of the MPS PI. We have been favoring the Hammond aluminum enclosures for this project.

A question for the Geotech community.. What would make this project more attractive or increase interest? What might impede hobbiests from undertaking this project?
Don..

[ivconic]

10 years ago, I would have made a dozen by now!
But one gets fed up. Age takes its toll. It is time for the younger ones to continue.
I will make it, but maybe only in the winter. Right now, I have a dozen started and not finished works on my desk. I work very poorly and rarely.
There is no special reason... except mileage and oversaturation.
I watched the video and I like the behavior.
But I can't suggest anything constructive until I build it and try it myself.
Anyway; great job Don, as always!

[Qiaozhi]

A question for the Geotech community.. What would make this project more attractive or increase interest? What might impede hobbiests from undertaking this project?
Don..

Release the details as a book on Amazon, like The Voodoo Project, Arduino Nano Pulse Induction Metal Detector Project, and Arduino Nano VLF Metal Detector Project.
It helps a lot of constructors if they have instructions to follow with a detailed explanation of how the design works.

I used LibreOffice Writer to create the above project books. It was a relatively easy task to upload the completed manuscript to Amazon KDP.

[bernte_one]

I am nearly at the end with my freetime. So Life gets hard with two children, a wife and a full time Job.
Far away these times where i build detectors. But hope they come again. Maybe ten or more years when my boys leave the Home Hotel managed by Mom.