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Home Made PI Detector

Smitty II

New member
Greetings to everyone,

It has been a long time since I have been on this forum. I have however, been busy and not idle. Quite some time ago I took on an educational project for myself. I decided to build a PI detector to better understand the technology and it's critical characteristics. Being a retired engineer and having been metal detecting since the late 60s and I have designed and built detectors of various types but never a PI machine. I spent several months researching as much information on the subject as I could find. I studied every circuit that I could get my hands on, circuits from Eric Foster, Carl Moreland, and other commercial circuits when ever I could get them. Anyway, I have been field testing my detector for the last 6 month and while it is not competitive with the top of the line machines on the market, I think it performs equal to or better than the average PI machine on the market. I want to say that during the development process, Reg Sniff provided a wealth of insight and technical information on PI technology, especially in the area of small gold detection.

I have attached several pictures. The one of the detector show it with an 8" mono coil installed and an 10" coil sitting on the floor. The picture of the pile of money is just to show that it is capable of finding coins with no trouble. The picture of the rings and nuggets give you a little indication of its capability in on the beach and in the gold field. The small 10K baby ring was found in a volley ball court and the mans 14 K gold ring was found on a swimming beach. Both of the gold nuggets were found down against bed rock. The largest one is about a gram and was found about 6" deep in a pocket in the bed rock and the smaller one is about 7 grains and it was about 3" deep in a bed rock crack on edge. The detector will detect a 5 grain nugget at about 3" in air and a 3 grain nugget at about 1 1/2" using the 8" coil. The larger of the two nuggets found produced a very good signal. The smaller one was weaker but still very clear. The dime is just for relative size comparison. The ground where I live has a fair amount of mineralization in it and the detector handles the bad ground very well.

Anyway, I am satisfied with the detectors performance and it has been a very useful project to keep this old mans mind working on all cylinders.

God Bless to all and HH.

Smitty II
 

Bob LI

New member
Reg is the best! He has bailed me out countless times when needed. Just built a clone baracuda from a kit. Still tweaking it some to get the best coil combination. No way can it see small gold like your unit. I'll mess around with it again when I get some time. Right now hitting the beach is more important. I rather be digging then tweaking at the moment.

Bob
 

Smitty II

New member
Bob,

Good for you in building your Barracuda clone. If I lived near the beach, I think my priorities would be in line with yours. I wound the coils for mine with #24 stranded Teflon insulated wire to keep the coil capacity as low as possible and the speed of the coil up as high as I could. Good luck on the beach.

God Bless and HH.

Smitty II
 

Smitty II

New member
6666,

It is a take off from Carl Moreland's Hammerhead. He said that his design was a good one to experiment with and I felt it was a good place for me to start. My circuit is similar, in that it has the same basic stages, but I changed a lot and added some additional circuitry. I had to make some significant changes to get it to detect small gold in the 5 grain range. Reg Sniff's inputs were really helpful here. I added some additional filtering, a gain control and improved the VCO audio response. I used different ICs in some places because they were locally available. As a result, I had to make some circuit changes to accommodate them. I came up with two final circuits, one with a VCO audio and one with conventional Volume Increase audio. The Volume Increase audio uses a somewhat different approach than Carl did and it sounds very much like commercial detectors. I also added a Low Battery alarm to let you know when it is time to change the battery.

I don't know how much interest there is in home made PI detectors and mine is by no means revolutionary. It is more of just another approach with some different ideas. It was a great educational experience for me and I am pleased with the way it performs in the gold field as well as on the beach. I am sure to Eric, Carl, Reg and other PI wizzards what I did is old hat but in my mind that is ok, fun is what is important. If anyone is interested in what I did I would be glad to pass it on.

God Bless!!

Smitty II
 

6666

New member
Hi Smitty
YES i would be very interested in your circuit designs
and I am sure other people around the world would be to, not everybody
has access to all modern components , so it would be interesting to see what
components you have used, its always good to see a working project
I will be watching, thanks smitty
cheers
6666
 

6666

New member
Hi Smitty
I see its been over a year now since you posted your project details
have there been any good improvements to your design ?
cheers
6666
 

Sven

Well-known member
Smitty and I got together. Made revisions, some corrections after I had PCB's made.
I posted bits and pcs. here as well as on my website.
http://www.treasurelinx.com/projects.html
They work great as a general purpose PI.

Smitty revisited the 2 stage pre-amp version, made some changes and had 10 PCB's made last month.
Three were recently sent to Smitty. We should be starting on them shortly, both of us have been pretty busy the past several weeks.
I just moved, so it's going to be about a week before I get organized to start building.
Intended results 20-30% deeper and more sensitive to smaller gold than previous version.
Picture of the news boards taken still sealed in plastic wrap below.
 

6666

New member
Hi Sven, thanks for the update, did you split the preamp into two low gain stages ?

If you have a spare PCB that I could buy, I would be interested in trying it out.
Cheers
6666
 

Sven

Well-known member
6666 said:
Hi Sven, thanks for the update, did you split the preamp into two low gain stages ?

If you have a spare PCB that I could buy, I would be interested in trying it out.
Cheers
6666
Smitty did do that for the new PCB.
Will PM you
 

WM6

New member
Smitty, Sven, where we are with "in field" testing of your device? Especially on smal gold sensitivity?
 

Sven

Well-known member
I just had the 2-stage amp PCB's made, 3 were sent to Smitty, he has been rather busy so he will start assembly sometime next month.
I got ambitious and started soldering away a couple nights ago. I'm at a standstill fro a few weeks, had to order several components to finish the PCB.
Sent one PCB off to 6666, so he can give it a whirl in OZ.
I am not going to release any more PCB's until I know the PI functions as planned no changes or corrections are needed to be made. So far everything looks good.
Will keep everyone informed.
 

Sven

Well-known member
Both my land and water units are very nice performing units. While living in North Bay, the main beach was three minutes away, hunted to death by the way.
I would use the land PI and VLF machines on the dry sand to pass the time. Did find using the 7" search coil worked wonders, didn't pick up the small tin foil like the VLF's.
Still picked up trash but, not as much as the VLF's. Actually a pleasure to hunt with the PI. Always wanted to try the PI at schools and parks, after reading how terrible they would be in trashy areas, non precise pinpointing resulting in digging huge plus, etc.... was reluctant to give it a try.

Well, moved to a much larger city, beaches are at least 1 hour away but, plenty of parks and schoolyards to dig in. Sold my Tek Omega, wife was using her Delta, the other old VLF machine was on the frits..............schoolyard was across the street.........hunted to death, very trashy with lots of foil, canslaw etc. Drives VLF machines nuts. One evening last week, thought that I would brave the challenge of using the PI in the trash. To my shocking surprise, it ran smooth and fairly quiet amongst the trash. Just needed a quick adjust of the frequency now and then to knock out some of the EMI. First three to four targets were coins. Thought the first was a large cent, it was a 50 Escudos Portuguese coin...........didn't take long to start really enjoying the PI in the trash. The 7" coil was precise in pinpointing, swore it was like using a VLF detector in that regard. The biggest thing I noticed is coins, rings to about 6" sound different 90% of the time than the sounds made by trash. Canslaw is getting so easy to tell now. Found a technique that actually works to ID it. Once the suspected canslaw is pinpointed, tilt the coil vertical over the target using only the backside edge and run it over the target. Canslaw gives off a longer target sound that is broken up. Coins will give a short tight sound. I constantly use the rear edge to pinpoint the target in plugs, it's dead on.
What I really like about the PI is the ability to ignore most pennies and the clad ratio to pennies has increased. Penny count is way down, higher denomination coins are up.

All I can say now is that I'll grab the PI machine more often. The places I hunted that were supposed to be hunted out, thought myself after hunting with the VLF machines are not. I hunted over the same areas with several VLF machines afterwards figured not worth hunting again. Bad thought, the PI found lots more and deeper amongst the trash. I am finding the PI is making a wonderful coinshooter as long as the 7" coil is on. Contemplating on taking it back out with the 10.5" coil for giggles. Just a side note, spent lots of time with the PI digging up all sorts of targets to get an idea what they sound like. There are enough variances to be able to distinguish good targets from bad if you take the time and learn the PI. Right now it's set up as basically turn on and go, with an occasional frequency adjust. It's not a miracle machine, just another tool in the arsenal. Now curious to see how the 2 stage pre-amp redesign PI is going to work.....

PS My nickel count is way up compared to other coins.

Some pictures below of finds for a few hours over two nights at the trashy hunted out schoolyard. Last picture is a picture of a previous beach hunt.
 

Sven

Well-known member
Getting a little closer every day to powering up.
Just have to add the IC chips, external pots, switches, speaker, battery, attach a search coil and it will be ready to power up.
Keeping my fingers crossed.
 

6666

New member
Hi Sven
here is a start, 18.88 khz from the powersupply 555,
I started the build last night, I would have been a bit more advanced but I did not relize the holes in the pcb are for machined pin ic sockets, my elcheapo's did not fit, which meant another trip to the store today.
cheers
6666
 

Sven

Well-known member
Just a quick update. Completed my PCB, added power...........packed it up and sent it off to Smitty for some debugging. He hasn't started is PCB yet.
He found I had soldered on two resistors that were the wrong value. My mistake, I grabbed two 27K instead of two 27R resistors. It was calibrated,
and works with an increase in depth, Smitty saw no increase in sensitivity to small gold over the orig. version.That's fine because it's sensitive enough.
Maybe able to get it into a housing and field test it before the ice and snow get here.
 

Mk2Brett

New member
Hello, i have been following this for a while and decided to join. Is there any progress with this design as i would really like to purchase one of these PCBs to create my own detector.
thanks
 

Sven

Well-known member
6666 said:
Hi Sven, thanks for the update, did you split the preamp into two low gain stages ?

If you have a spare PCB that I could buy, I would be interested in trying it out.
Cheers
6666
As you already know, we scrapped that PCB. Went back to the orig. PCB and made a few enhancements.
 

Sven

Well-known member
As we discussed, I am out of PCB's at this time and would need to order 10 to make it cost effective.
The best alternative, recommended for your first detector build would be the Surfmaster PI.
Easy build, no oscilloscope needed, respectable performance and a wealth of info and build support
can be found on Geotech. At age 17, you have a lot to learn, plenty of info out there and help as well. The Surfmaster
is a great learning tool.........Since 6666 lives in your neck of the woods. You can contact him thru Geotech which I provided you the link to.
I am sure he could give you advice as well.
 
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