Grant's DIY PI detector

Hi All,

So what do an old broken clock, a broken games joystick, a mouse pad, a piece of electrical conduit, and a curtain rod holder have in common?

They are all components in my latest project a DIY PI detector. I only just started it today.

Anyway here are some first photos. I will keep updating the thread with my progress.

I am going to base it on the Baracudda design on geohunting.







Regards,

Grant

.

God fencejumper, looks like another 3 pages coming up.

i'll take 2

Hi All,

Just a quick update on where I am at with this, I am making up some test coils while gathering the parts I need to make the PCB for the control box.

I am going to to use a Double D type coil for the induction balance it provides which will help in highly mineralised soils.

Here is how you can make your own coils the process is the same no matter what type or shape of coil you want to make.

Step 1: Build coil making jig from old board some cup hooks an old Pizza tray and an old camera stand I had laying around:



Step 2: Begin winding coil



Step 3: First stage complete two test coils



Step 4: Add faraday shield, its just aluminum foil you use in the kitchen cut into approx. 2cm strips



Step 5: Coil with shield now in place making sure you leave a space at the end of the shielding or you wont get the faraday shield effect



Step 6: Wrap a bare wire around the shield to give you a good connection to the shield for soldering to the plug later



Step 7: Make sure the shape is a D and then wrap the coil in cloth, this is used for strength and to bond with the expoxy later when we put the coil into the coil mould we are going to vacuum form later using a home made thermoforming machine :-)



Step 8: Completed coil ready for wiring



Step 9: This is how the coils will eventually sit in the coil mould note the overlap in the middle the spacing of this is critical when we come to tune the coils later in order to get them to null each other out so we only get real targets



The whole process took me about an hour which included making the coil making jig.

Well thats it for now, hope this is of use to somebody.

Regards,

Grant

G'day Grant

That looks impressive already for a home made job.

I have a question as I know nothing about the inside of a coil except to say that I understand the difference between a Mono and a Double D type,which is what your making. Now back to the question: how come you only have the faraday shield on one half of the coil, or is it just that it's not finished yet?

cheers dave

Hi Dave,

Yes I only did the one so the other one is not finished yet as I was just using it to show the process and to show how it will be laid out in the coil.

There is not much more that goes into a coil unless you want to put some dampening on it to compensate for ground effect in which case it would have a small circuit added to the coils with a few resistors and a diode in it. The Double D coils dont need this, which is why I chose this type, as the overlap and tuning of the coils already null each other out and remove a lot of the ground effect. Not much to coils really.

The only thing people seem to be confused about with them is they call them antennas when they are not they are inductors. The difference is that the antenna is there to receive a signal from an outside source which is miles away. ie. a radio or tv station whereas the inductors are looking at the near-field region for magnetic field distortions. i.e. when a lump of metal sends the tuned coils out of sync with each other.

Regards,

Grant

Hi All,

Worked on the main cable today:

I am trying to setup my home made detector so I can use commercial coils later if I want to so I am attempting to replicate the Minelab pinouts for this cable.

Step 1: Time to wire up a Female Microphone plug to go into the control box male plug. I found these diagrams that explain the pinouts for the minelab plugs so I wired the plug according to these. Using bits of wire I had laying about I used separate wires for each pin and then joined the two wires for 3 and 4 and then joined this to a single wire.So I wound up with four wires coming out of the plug. Ensure you do a continuity test using a multimeter on each wire for each pin on the plug.





Step 2 Join the main recieve (RX) and transmit (TX) coil cables up to the plug.Note the microphone cable I was using had 2 cores (white and blue) and a shield. I joined the shield to the blue cable and then wired them up. As per the diagram the blue and shield wires were joined to the black cables which go to pins 1 and 5 respectively.







Here is a closeup of the soldering of the black cable to the blue and shield wire:



Step 3: Use zip ties to join the two coil cables together to form a single cable. I chose to use two separate microphone cables with 2 core and a shield instead of just getting a cable with 5 core shielded in it. I wanted to ensure that the two coils wires do not interfere with each other and that they are shielded separately from each other. It is also a lot cheaper than the 5 core wire.



Step 4: Make sure that you have marked each wire at the other end to indicate which coil they go to. It can be worked out later on using a multi meter but this will just save you time. Ensure you do a continuity test using a multimeter on each wire for each pin on the plug.



I will be putting a male plug on the control box for this cable to plug into.

Now I just have to sort out the coil end of the cable.

Hope this helps somebody.

Regards,

Grant

top post there grant,great detail and very clever.i guess the over-all principle is reasonably basic is the impedance? etc shown in the diagram and it will match up correctly to the control box? reckon you may have a market there if the cost is reasonabe =$$$$$,s great ideas and knowledge on this forum thanx to all. cheers

Great project Grant, it's like a good book, can't wait to see what comes up next...

Hey Goldslugger / Costasdee,

> i guess the over-all principle is reasonably basic is the impedance? etc shown in the diagram and it will match up correctly to the control box?

Yes, sort of. The control box is just a timing circuit, actually its usually two timing circuits or oscillators as they are known. There are many designs all with their pros / cons, PI (Pulse Induction) is just the latest craze but it too is not without its pros/cons. I am going to have to wait for a kit from overseas for my PI detector.

So while that is happening I will build an Induction Balance (IB) control box and try that out with the coils, from all my research the IB's should be able to detect down to half a meter in mineralised soil with little ground effect using a Double D coil. The IB's can also discriminate between ferrous and noble metals and ignore to a large extent the iron and tin.

I am building the metal detector so I can swap out the control box and try out different circuits to see which one works best with different coil types.

The real key to a metal detector is the coil, after all if the coil can't detect a signal and isnt sensitive enough then there isnt a benefit.

This document can explain how the coils work better than I ever could, just ignore all the techy stuff and read it to the end it is a good read and explains why some coils do better than others:

http://www.google.com.au/url?sa=t&rct=j&q=geotech%20coil%20basics&source=web&cd=1&ved=0CB4QFjAA&url=http%3A%2F%2Fwww.geotech1.com%2Fpages%2Fmetdet%2Finfo%2Fcoils.pdf&ei=UpqoTvCLJI-uiQekopz9DQ&usg=AFQjCNE6kvQ7JXmwBLIcPzxxDmixvLVIBg

I wasnt looking to market this in the end it just came down to not being able to afford / justify the cost (AU$900-$6000) of a decent commercial metal detector when I can build it myself for under AU$200. For me it also comes down to if I know how it is built I will be able to fix it, hopefully in the field rather than back at the workshop. When I make my first few finds and sell them then I may consider upgrading to a commercial one.

From all my research so far it seems a lot of the early gold prospectors were a self reliant lot who built a lot of their own equipment, so I am just following in that tradition. So I have decided to build a metal detector, a sluice and a pinpointer.

I also hoped that blogging about it here as I built these would inspire others to have a go and experiment with these themselves (so I dont end up as the only nong who tried this).

Regards,

Grant

Hi All,

Its time to make the printed circuit board (PCB) for the control circuit for the metal detector. In this case we are making an induction balance (IB) circuit while I wait for the PI kit to come from overseas. That kit will have everything including the PCB board but for now we will have to start from scratch and make our own PCB board.

Materials needed:
a. Etching Kit containing copper board and etching solution. Jaycar sell these for about AU$28.
b. Safety glasses
c. Safety mask
d. Gloves
e. Bucket of clean water
f. Acetone (thinners or nail polish remover)
g. Cotton wool
h. Photo paper and laser printer

Step 1: Using a laser printer print out the circuit board onto photo paper or a page from a glossy magazine.
Print out both the circuit and the component layout diagrams. Later on one of these goes on the top and the other on the bottom of

the PCB. Now cut the circuit diagram out of the printed page to match the single sided copper board. These boards are fibreglass

and have copper laminated on one side of them. Clean the copper board surface with a scouring pad but not a steel one. Place the

cutout over the copper side of the board face down with the printed side facing the copper. Use a couple of aligator clamps to

hold it in place. Now get your iron and set it to its maximum setting, when hot place over the paper and press this onto the paper

and hold it there for a couple of minutes. When it starts to stick to the copper start moving the iron around and then work the

ink onto the copper applying firm pressure. After 5 minutes remove the paper from the copper plate and you should have a printed

circuit on the copper surface. It make take a couple of attempts at this to get it right.




Step 2: The ink may not have fully transferred and there will be areas where it is light so trace over it with a black pen either

a felt tip or a calligraphy pen.




Step 3: Put on your safety gear as the etching solution is caustic, corrosive and poisonous. (a great combination, remember this

stuff will melt metal so imagine what it can do to your skin)
Mix the etching solution into a glass jar with 1/2 litre of hot water. It needs to be 50 degrees celcius.
Once mixed pour all of it into the bath tray supplied in the etching kit.
Using the tweezers from the kit place the copper board with the ink circuit on it into the bath tray.




Step 4: Gently move the tray from side to side being careful not to spill the contents. This will keep the solution moving over

the copper plate. The whole process is going to take between 15 and 30 minutes for the copper to disolve everywhere except where

the ink is. After about 5 minutes of moving the tray back and forth just let it sit.




Step 5: You will start to see the copper etch away. Its slow to start but when it starts it happens quite quickly. You can use a

heat gun or hair dryer to keep the water temperature up but be careful water and electricity dont mix well.




Step 6: Once you are happy that all the copper has gone and you are left with your printed circuit on the board take it out using

the tweezers and rinse it in the bucket of clean water. Leave it in there and stir it around for a few minutes to ensure that all

the etching fluid is off it. Then take it out and dry it off using paper towels.
Now you still have to get off the ink so put some acetone on some cotton wool and scrub the ink off the copper plate. It should

start to reveal the copper underneath. Here is the etched board.




Step 7: Using a dremel cutting wheel cut the board to size. Now use the dremel with its smallest drill size to drill out all the

pads (the round holes at the end of the lines that the components will go into)




Step 8: Now cut out the component layout diagram from the photo paper. On the fibreglass side of the copper plate glue the

component layout diagram onto the board ready for the circuit components to be soldered into place.



So there you have it, we now have a PCB ready for our control circuit. Now all we have to do is solder on all the components.

Hope this helps somebody.

Regards,

Grant

Intamaresting!!!!!!

G'day Grant

Thats truly amazing, keep on going this is really interesting stuff.

cheers dave

Hi All,

Time to work on the control box.

Introducing the MYLAB GC-4600

Its not finished yet, still wiring up all the controls.

I decided on a simple naming system for my metal detectors since I built it in my secret underground laboratory (the shed) its called a MYLAB I then added my initials and age and since its the first one I built this year its serial number is 00.



Heres the front view:



Heres the rear view:



I was originally going to run this off a 9 volt battery but I am changing the design I am using based on the original inventors suggestions for improvements, by adding a regulated power supply. I purchased a kit from JAYCAR for AU$16. That way I can run it on a 12 volt battery box and regulate it back to 9 volts which should improve the stability of the circuit and give a longer running life.

Here is the regulated power supply tweaked to 9 volts output installed:





Here I have added the Piezo buzzer and wired up the head phone socket. I am allowing the operator (me) to use a normal set of 3.5mm head phones or via the battery box the larger plug version. If the head phones aren't plugged in then the buzzer will sound instead.



Well thats where I am up to at the moment.

Hope this helps someone.

Regards,

Grant

Carn't wait to see it finished and working, it's a great little project by the looks of it.

cheers dave

jeez grant, it just gets better and better.inspirational stuff. well done, back to the days of inventiveness,ala popular mechanics magazine,etc.
i see the logic behind it, a basic principle and fairly basic? electronic components. plus the personal sense of achievement and satisfaction great project with great potential. thanx again for the informative posts and your willingness to share. good luck with it all. cheers p.s. trade in price on my BH discovery 3300?

Hi All,

I have changed my mind about having a brick on my back with a bulky battery box.

So after thinking about how to get a portable rechargable 12v power source for my metal detector this is what I came up with:



Bonus is it acts as a stand for the metal detector.

And here is my charging circuit



Hope this helps someone.

Regards,

Grant

Oh yeah!! now where talking!! the best thing one can do with Ozito products is find a use for them... other than that of which it was intended. They tend to function much better.
Well done gcause on finding a more appropriate use for this abomination which was marketed.... at a guess id say... a drilling tool.????

I used my Ozito jigsaw for an Olympic hammer....the electrical cord on many of these products are precisely placed, giving you, the end user a more comfortable grip when the time comes for correct placement way out into your paddock. And believe me....the time will come.....you will find a better placement which can be seen from the above post.


I also found better placement for a gift bearing the same name, i embedded the similar looking excuse for a tool in the pic above into a color-bond fence. The indentation left resembled the face of a demon.

Fortunately, i have but only one item left of my misguided tool buying, cant get a pin up my butt dollar saving collection of... which will in time be given new placement, and should leave an impressive crater on contact with whatever.

It was marketed as a metal cut off saw....and im under no illusions and bear no false hope..... it will fail this choir!!.

Hi Narrawa,

Yes the drill was an utter piece of @#$#$%#$ but I guess that comes with the cheap price tag however the battery was still good so it seemed a shame to waste it and it makes the ideal solution as a power source for my metal detector:

a. Its 12v which will be regulated down to 9v for long life and stability;
b. Its rechargable and I can easily carry spare batteries in the field;
c. No need to carry a bulky battery pack on my back and it really weighs bugger all;
d. It doubles as a stand for the detector; and
e. It will act as a counter weight to the coil and balance out the metal detector nicely.

So I would suggest next time you "repurpose" your equipment like that salvage the battery part it may come in use as a 12v power source.

Regards,

Grant

IT LIVES!!!! IT LIVES EGOR!!! IT LIVES!!! MUUUUHHHHHAAAAAAAHHHH!!!!

Well its finally all together and working, circuit is working a treat and the power supply I built is working out just fine its all wired up now so it can just be plugged into the back of the control unit just like the coil. All the tuning controls are working just fine.

Here is a picture of the unit:



Now there is only one small problem....it doesnt detect metal....DOH!

Problem is the coils I am getting intermittent signal from them so I have a dry solder joint somewhere in the coils.

These were just test coils I did up with 7 winds of 30 SWG on each.

The actual design calls for 70 winds on each coil so it will be way off at the moment.

I will have to wind some real coils and see how it goes.

But for now I have the machine that goes PING!!!

"Now there is only one small problem....it doesnt detect metal"....DOH!

Thats just a minor problem Grant I am sure it will when your finished it, I want to see it working.

cheers dave

Ok I got my kits from the UK and have built them now. I got 4 in total, 2 of each in case I stuffed them up. They are the Baracuda and Surf PI Pro.

My first two Baracuda's were a total failure and I had to send them to one of the members of the geotech forum who kindly agreed to fix them for me they are still with him but he got it working in the end so I am very grateful to him for that.

I just finished building a clone of the Whites Surf PI Pro, the clone has a few additional modifications for timing and you can also do a pinpointer with it but I havent added that modification yet. I have it working with my Coiltek UFO coil.

I am about to do some air tests to see how it goes but initial tests are looking good 20-30cm on a variety of targets.

Looking forward to more reports and pics.

cheers dave

Just picked up a Coiltek 14" Round Mono Solid from shandeemax its in really good condition. Plugged it into my home made metal detector tweeked the delay and tuning and away she went just like a bought one.

Just did some quick air testing of the coil and it can detect most small targets at about a rulers length roughly 30cm and my car keys at about 40cm.

Very happy with my purchase from shandeemax can recommend him as a good seller and a top bloke having spent quite some time talking to him tonight about his prospecting.

That is awsome, id love to see more pics and reports on your testing with it!

Here is the video of me air testing the home made metal detector.

Well done on getting your DIY project up and running and working.

cheers dave

Hi all, been lurking for a week being a newbie and and all and never knew what to post, but at the first site of electronics its bit hard to hold back.
Awesome work!!

Is there anywhere where, you can order a kit or circuit for a higher end detector?

Once again hello to all! I must add, been around some other forums and ive found this to be at the more serious end of detecting.

Cheers,
Greg

G'day Greg & welcome to the forum

I don't have any answer for you question about where you might a kit or circut and stuff for DIY detectors but I'm sure there is someone here who may be able to help you with that.

Good luck with any project that you have in mind.

cheers dave