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My Home Built PI Detector
Posted by: Smitty II
Date: November 11, 2017 03:13PM
Greetings Everyone,

I have been detecting since the late 60s and probably have designed and built every type metal detector out there. That may be a bit of an over statement but at least the major types. My latest project is a PI machine. I thought at least some of you might be interested in it and how well it performs for me. Here are the basic specs.

It has a Pulse Frequency of 1250 Hz and can be adjusted about 10%.

The Coil Pulse Width is 70us

It has a Pulse Delay that is adjustable form 5us to 85us and has an Iron Test switch.

It has a Target Sample width of 10us and 30us, 10us for tiny gold targets and 30us for normal coin and jewelry.

It has a Gain (sensitivity) control with a range of 1 to 3.

It has a SAT (self adjusting threshold) with a range of 1.5sec. to about 5 sec.

Naturally it has a Threshold control.

I have two coils for it, a 8" and a 10".

I have built two audio versions of the detector, a VFO version and PVA (proportional volume audio) version.

It runs on 8-AA batteries that give it about 8 hours of operation time. It does have a battery test.

Enough specs, now does it actually detect anything. Air Testing it indoors using the 8" coil, the Gain at max, the Pulse Delay and minimum (5us) and using the Narrow Target sample width, it will detect my 3 grain gold test nugget (more of a flake) at about 4+ inches using headphones, and my gold wedding ring at 13+ inches. I have been using it in the field now for about a year now. It has really opened the door to finding tiny gold jewelry targets like ear ring studs, tiny gold baby rings and thin gold chains. It is not a prospecting machine since it does not have a Ground Balance channel but it still does pretty well here in the Colorado gold country mineralized ground using the SAT and Pulse Delay. I have also had it down to the Gulf of Mexico beaches. I recently found a nice ear ring stud with a 1/2k diamond in it about 5" deep in the sand. The detector does an excellent job for me at detecting coins, Jewelry and relics. It has really added to my play money account over the last year.

I have had a lot of fun learning, designing and playing with this project and a pleased with my results.

Have a great time detecting and HH.

Smitty II

Re: My Home Built PI Detector
Posted by: ewtaylor
Date: November 12, 2017 09:48AM
Sounds great. Do you have any pics or videos?

Re: My Home Built PI Detector
Posted by: ionut_mtb@yahoo.com
Date: November 12, 2017 11:47AM
At 5us without gb not detecting the sand?

Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 14, 2017 09:51AM
Greetings, Yes! at 5us the detector will detect ground mineralization and when you get within about 2 to 3 inches of the mineralized sand or ground you will start picking it up. I have found that by adjusting the SAT speed and using a smooth sweep speed you can work highly mineralized ground reasonably well. You can increase the pulse delay and eliminate the ground signal but you will loose the ability to detect tiny gold targets. As I indicated, I did not intend the detector to be a prospecting machine. I just wanted it to have better capabilities at detecting small gold jewelry targets and it does do that. At the time I started this project, I owned three commercial built machines and none of them would detect my 3 grain nugget (flake).

Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 14, 2017 10:02AM
Greetings, Actually I have tons of pictures but I am still learning how to get around in this forum and I need to reduce the size of about all the pictures that I have. I will work at getting a few pictures on here someway. The only one that I have been able to reduce the size is a picture of the detector. I sort of over did it but I will attach it anyway.




Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 14, 2017 10:44PM
Here is a few additional pictures of some of its finds. A better picture of the detector, some finds from the Gulf of Mexico, The test targets that I used and some other finds including some chains and small gold jewelry.

HH

Smitty II




Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 15, 2017 09:03AM
Here is another picture of some of the gold jewelry that I have recovered using the detector.

HH

Smitty II




Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 15, 2017 09:16AM
Here is a picture of the loaded PC Board that I had made for those that are interested in seeing it.

HH

Smitty II




Re: My Home Built PI Detector
Posted by: mschmahl
Date: November 15, 2017 10:32AM
Great work. Thank´s for the pictures. Can you post something about the coil´s?

Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 16, 2017 08:31AM
Greetings,

I have two coils for my detector, an 8" and a 10" coil. A friend of mine has built a DD coil and said that it worked fine and handled mineralized ground a bit better. It is a big coil so it was not all that good for small gold targets. I have attached some pictures of my coil building process.

HH

Smitty II




Re: My Home Built PI Detector
Posted by: hecbom
Date: November 16, 2017 12:26PM
Hello Smitty
what gauge wire did you use and how many strands? is it Teflon coated? How about the coil capacitance? I have several coils I made for my "home made" Pi using Litz wire 175/46 but I finally settled for a 6" Mono from Miner John. I get the best depth on a 3 gram nugget @ 3 to 4" The Miner coils is a 310uH @ 1.3 ohms.

Hector

Re: My Home Built PI Detector
Posted by: Smitty II
Date: November 16, 2017 02:49PM
Greetings,

I use #24 gauge stranded wire with Teflon insulation. It comes in 7 strands and 12 strands. I have used both and I don't think I can tell any difference in the coils performance. I have not ever used Litz wire. I know that several people have used it in their coils. The combination that I have been using works very well with my detector so I have not tried any other combinations. Using my 8" coil I can detect my 3 grain gold flake at 4+ inches using headphones when bench testing. My coil inductance is 270uh at the connector on the end of my 4 foot cable. I don't know the coils capacitance but I think I can measure it. I do know that the self resonance frequency of the coil is just a bit under 3MHz.

Re: My Home Built PI Detector
Posted by: Idefix
Date: November 23, 2017 10:34AM
Hello ,

Very nice job.
As as see, you have fully shielded your coil with a copper tape.
I think , because the shielding is close on itself, that you may have eddy currents in it. So, it is better to open , near the ground connection. as it does not make a full circle. So , the shielding makes a C, and not a full ring (O) .
(Difficult to explain without a drawiang )

If you try this, let us know your results. The noise will be lower I think.

Re: My Home Built PI Detector
Posted by: ionut_mtb@yahoo.com
Date: November 23, 2017 02:59PM
Quote
Idefix
Hello ,

Very nice job.
As as see, you have fully shielded your coil with a copper tape.
I think , because the shielding is close on itself, that you may have eddy currents in it. So, it is better to open , near the ground connection. as it does not make a full circle. So , the shielding makes a C, and not a full ring (O) .
(Difficult to explain without a drawiang )

If you try this, let us know your results. The noise will be lower I think.

You can see the gap on the opposite side of the coil connection.

Smitty, one thing i don't understand. does this coil in picture goes as low as 5us? with that shield? and the spiral wrap is pe or pvc?

Thanks

Re: My Home Built PI Detector
Posted by: Idefix
Date: November 23, 2017 10:21PM
Quote
ionut_mtb@yahoo.com
You can see the gap on the opposite side of the coil connection.

It is not a gap, but a piece of tape , I think.
It is what I see while zooming.
Put before potting with resin.

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