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Author Topic: Pulse Induction detector build  (Read 28620 times)
Cymro
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« on: September 05, 2015, 07:08:45 AM »

I'm building a PI metal detector which I was discussing/expounding on in this thread - just to save going over old ground again:

http://www.detectingwales.com/index.php?topic=24748.0

Thought the build may be of some interest to the folks on DW.

Bit of background to the detector I'm building. Having built a couple of detectors from scratch in the past with varying degrees of success, I bought what is supposed to be a working PCB from Bulgaria. I say supposed to be because I've not completed the hardware and therefore haven't been able to test it in any way, but it's *supposed* to be under guarantee anyway.

The Bulgarian connection is interesting because it, too was occupied by the Romans. Unlike the UK where they gradually shut down the operation and made a phased return home, they were apparently forcibly ejected by the Bulgarians, leaving all their villas as they were.

Couple of millennia later and the Romans' houses had all collapsed in on themselves, leaving little to no trace of where they had been. Under the houses, perhaps in cellars, there are alleged to be hoards of Roman gold - but they're out of reach of everyday metal detectors.

That's the story I've been told - I can't agree or disagree with it. But the Bulgarians want to be able to find this supposed gold and went to some lengths to be able to find it - or rather some lengths and breadths. They started using PI machines with huge coils - up to 2 metres square:

https://www.youtube.com/watch?v=f9ck24ibd7A

Now I don't intend using a coil of this size - I don't want to have to use a JCB to dig any finds - so I'll be using a conventional circular coil of about 11". The circuit board I bought is the same as the one used in the video so is capable of supporting different size coils.

I'll post a few pics of my build as it progresses if anybody would be interested?
« Last Edit: September 05, 2015, 07:05:12 PM by Cymro » Logged
Chef Geoff
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« Reply #1 on: September 05, 2015, 10:13:55 AM »

It will be interesting to see the finished unit I often have a read through the posts on the Geotech forum and know how popular and successful these self-builds are I've thought about making one myself but have to admit the lazy side of me decides not to bother.
Just have to pull you up on the Romans in what was Dacia they were evacuated (thrown out) by the advancing Goths not the native population and this was only the military the de romanization of the civilian population seems (from archaeology) to have been the same as Britain which incidentally was the second from last in and the second out Wink
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Cymro
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« Reply #2 on: September 05, 2015, 10:48:31 AM »

I'm on Geotech myself - it's a good source of information but things can get a little muddy with all the conflicting input.

I'm hoping to make a decent job of building the detector - I'm fundamentally a metalworker but enjoy making absolutely anything. Some of the skills transfer across to woodworking and other crafts - ultimately it's either hand work or machine work but the principles remain the same.

In my previous builds I've been disappointed with the hardware - I built what would have been a fabulous VLF machine, the 'Practical Electronics Magnum' in the early 90s which worked on the bench but I wasn't able to build a satisfactory shaft  for it. The recommended material was 3/4" plastic waste pipe but it was way too flexible and there weren't many accessible alternatives at the time. I also built a BFO machine before that which was enclosed in a plastic lunch box attached to a brush stick . . .

One of the contributors on Geotech, BernteOne, made a shaft and loop from 16 bar uPVC water pipe, so I tried that for my Barracuda (or Baracuda as they call them on Geotech . . . ) and for the Sniffer (current build) but found it too flexible - the coil  waves around too vaguely to be of any real use.

I'll post some pics of my solution to the perceived problems later.

Thanks for the history lesson - I'm no historian as you can see; I was just repeating the story as it was told to me  Wink



« Last Edit: September 05, 2015, 07:05:41 PM by Cymro » Logged
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« Reply #3 on: September 05, 2015, 10:56:23 AM »

Try fibreglass as used in Radio Antennas and fishing rods : http://www.sandpiperaerials.com

Lots of different choices, pullwound can also be drilled.

- Andy
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« Reply #4 on: September 05, 2015, 11:07:06 AM »

You can get carbon fibre tube very light and strong and drillable  i swopped the shafts on my explorer se with 1/2 " carbon fibre makes a bit lighter
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Cymro
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« Reply #5 on: September 05, 2015, 02:06:38 PM »

I was looking for this earlier when I started this thread - it shows the Delta Pulse 2 detector's depth capability. Just stopped for a coffee and found it:

https://www.youtube.com/watch?v=mvVq2XLSWWU

The Delta Pulse 2 is identical to the Sniffer XR-71 which I have and is sold by the same company. I make the depth on the tape to be +/- 1.5 metres (five feet in old money . . . )

For my own part, I have misgivings about digging Coke cans at 5' - or anything else for that matter  Undecided
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« Reply #6 on: September 05, 2015, 03:17:09 PM »

                           Using a pulse induction metal detector for general detecting on farmland sounds like a major nightmare in the making. When you first told me about building a PI machine and you weren't into beach detecting I was really puzzled. Now; having heard about the Bulgarian/Roman connection, I can see perhaps where you are heading.

                           As you already know, I used a C-Scope CS4PI on a beach that was used as an air-to-ground target range. Well with all that WWII scrap, eons of maritime scrap, and loads of tourist cast offs, the CS4PI had a great time. The bloody thing drove me crazy! Now that I have upgraded from the CS4PI and my EuroAce to a MineLab Safari, life on the beach has become a lot easier.

                          Recently I drafted in the PI machine to follow up on an interesting Safari find; just to see if the CS4PI was capable of sniffing out anything that the Safari may have missed in the small area where the find with the Safari was made. As happened, it didn't!

                         I'm guessing that it will be a good idea to draft in your pi machine to follow up on major clues in a specific area but await with baited breath to see how you progress.

                         As an aside.... an old friend and work colleague of mine who flew recognisance Spitfires for the RAF said they were told that if they were ever shot down in the Balcones they should surrender to the Germans and not the local military.   Shocked
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Cymro
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« Reply #7 on: September 05, 2015, 03:50:39 PM »

No Chris, you've got me completely wrong!! We are only casual beach detectorists, but as I said it's handy to be able to get on the beach when circumstances prevent us from detecting on land! I'm definitely not planning on using the Sniffer to detect on farmland - although I was wondering to myself today what we're missing by not digging iron. First time out in earnest one of us got a big deep signal and spent some time recovering it - it turned out to be a flintlock. Now we have more sophisticated machines we can completely ignore iron (in theory anyway . . . ) and just dig the 'good' signals. But what is a good or bad signal? It's something you want/don't want. I wouldn't mind finding more flintlocks, swords etc . . . Not necessarily valuable items in terms of money, but historically priceless to me.

One thing we have discussed is a ridge and furrow field we have permission on. I won't say we've cleared it of finds but we've pretty much done it to death, and nothing of any real age is coming up, so we wondered whether a PI might reach deeper than our machines do as there must be more history there than we're finding. And it's the next field to the one which produced the Edward III groat and the denarius . . .

My main motivation for building the PI is - because I can. Wink I enjoy working with my hands, making the tools to do a job (see later post . . . ) and using them.

Sorry if I've misled you! Chuckled at the pilot who was advised to surrender to the Germans  Grin
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Cymro
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« Reply #8 on: September 05, 2015, 05:42:59 PM »

Promised some pics - here they are, with explanations as necessary. Think I'll split them into smaller posts to keep things grouped together.

When I bought the Sniffer PCB I had to decide how I was going to use it - the original Bulgarian Sniffer is designed to be hung on a strap; you can actually buy a kit which includes the box, coil, PCB, battery, shaft (I think . . . ) but I wanted something that was more like a conventional metal detector and all self-contained.  The kit still uses the same control box but it's attached to the shaft and there's still an issue with housing the battery.

I looked at what I had and what I could buy - and it turns out I couldn't buy a box which would house both the PCB and the battery together. I'd already heat-formed the shaft in high pressure uPVC pipe, welded a handle to it, made a hand-grip and decided to mount the controls in a smaller box on top of the handle. The general arrangement is loosely based on my old Eagle Spectrum - 1st pic. But where to put the battery . . . ?

I made a box out of square rain-water pipe and placed it under the PCB housing so it would act as a 'stand' to keep the PCB off the ground and out of the water - see 2nd pic.

This was an ideal position, just under the handle as it caused the detector to achieve a neutral balance - the battery is pretty heavy but the detector handled quite nicely. The problem was that when I picked the detector up the shaft sagged at the ends and the movement of the coil was vague.

So as far as I was concerned, it was a failure and needed some improvement.


* Spectrum.jpg (128.31 KB, 922x691 - viewed 990 times.)

* Sniffer.jpg (119.4 KB, 922x691 - viewed 1154 times.)
« Last Edit: November 15, 2015, 07:51:02 AM by Cymro » Logged
Cymro
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« Reply #9 on: September 05, 2015, 06:02:03 PM »

The main problem was that the shaft was too flexible - but how to cure it? I had another think about the Spectrum and decided to make the shaft from aluminium tube - if it's good enough for Whites it's good enough for me . . . Sent for a metre of 25mm x 1.6mm aluminium tube from an eBay seller and set to.

This time I didn't set a goose-neck into the shaft, (I do have a hydraulic pipe bender capable of bending 3/4" - 3" steel pipe so could have done it . . . ) opting instead for a straight shaft. I cut a piece of it about 8" long, coped it to fit the main shaft at a 70 degree angle and aluminium brazed it on. See pic.Very strong joint, and quite neat in appearance. I first cut a hole in the main shaft so I could run wires up the handle and into the control box.

Quite pleased with the choice of aluminium - it's strong, rigid and light and I can braze, drill and tap it if I want to. IIRC it cost me 6.60 for the metre length. Thanks to the guys who suggested fibreglass and carbon fibre but this is a done deal now so I'm not going to change it.

While the upper shaft is aluminium, the lower part will be 20mm uPVC high pressure water pipe as originally intended with the MKI design, but since it's so much shorter there's next to no flex in it. As a bonus, I had already bought a 25mm - 20mm reducing compression fitting in plastic which still fits the 25mm upper shaft and after I bored the internal stop out in the lathe allows the shaft to telescope for adjustment.


* shaft.jpg (28.67 KB, 890x302 - viewed 440 times.)
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« Reply #10 on: September 05, 2015, 06:07:53 PM »

Ah ha, I stand corrected. Got ya now. Smiley

                     Looks like some very interested projects that you have in hand and I hope to see the fruits of your efforts real soon.

                     I often wonder about ignoring iron signals and when I first started detecting I dug pretty much everything. I believe that a lot of really good finds and hoards are found by beginners. They still have that "ooooh I wonder what this is?" freshness about them. Dave, an other caravan resident on our park, dug a lump of iron from the dunes and got himself a WWII hand-grenade! Shocked  He also got himself a rocket for digging in the dunes!  Roll Eyes

                     Looking forward to watching your progress.  Wink
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Cymro
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« Reply #11 on: September 05, 2015, 06:15:14 PM »

So now I had a viable shaft. Next I needed boxes to house the PCB and battery, and the controls.

I laid the PCB and battery on a sheet of paper and tried different arrangements until I had one that looked right, then when I knew what size the footprint needed to be I made a development so I could order the aluminium sheet.

I needed a sheet metal folder to make the box - which of course I didn't have. Looked at Machine Mart, eBay etc and decided to make one. I have an extensive pile of what my wife thinks is scrap from my days of contracting in engineering, so once again had a look what I had and how I could use it to make a folder. I've used them before in the dim and distant past but never took that much notice of how they were made, so I made it up as I went along.

The pic shows how it turned out. The main body is a chunk of rusty 3" x 3" x 3/8" angle, the movable 'jaw' is a length of 65mm x 65mm x 4mm steel box section with a flat plate welded to it and the handles are a half-shaft off a car. It's not pretty but it works and will take a piece of sheet up to 18" wide. I tried it on 16g steel sheet and although I broke a sweat nothing broke on the folder.


* folder.jpg (138.2 KB, 922x691 - viewed 500 times.)
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Cymro
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« Reply #12 on: September 05, 2015, 06:38:50 PM »

OK - I'd got the aluminium sheet and I'd got the folder. Now what . . . ? It had been many years since I'd used a folder and I only had one chance at it so it had to be right first time.

If you'll refer back to the photo of the Spectrum you'll see the form my box was going to take, with the 'base' attached to the shaft and the 'lid' underneath. With this arrangement, any rainwater will run right off without getting in with the electronics. I had a bit of a practice on some offcuts from the sheet and started making the base - see 1st pic. Turned out great (in my humble opinion . . . ) so I brazed the mitres on the corners to add strength and keep water out.

The lid has to be a neat fit inside the box, which is why the use of the folder was so critical. As you bend metal, one face is being stretched and the other compressed, and the radius of the bend eats up *some* material. Could I remember the formula? Could I ****! So I resorted to empirical methods and did a couple more trials on offcuts which told me how much narrower my scribed lines were to be than the finished box.

I'm pleased to say that it's a good fit, as I wanted, but have to admit it was probably more luck than judgement . . .
The result is in the 2nd pic.

The 3rd pic shows the completed box (in need of fettling) and the 4th shows how it will go together on the shaft. It's just sitting there for demonstration purposes at the moment so its position isn't yet fixed - depends on the balance.

That's as far as I've got up to now, but I'll keep updating this thread as and when I get anything done.


* Box base.jpg (53.52 KB, 862x567 - viewed 494 times.)

* Box lid.jpg (47.88 KB, 793x682 - viewed 356 times.)

* Box.jpg (45.48 KB, 900x590 - viewed 498 times.)

* assy.jpg (71.23 KB, 801x491 - viewed 1495 times.)
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Dryland
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« Reply #13 on: September 06, 2015, 12:04:55 AM »

Interesting read Cymro, can't wait for the next instalment
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« Reply #14 on: September 06, 2015, 10:54:59 AM »

Thanks, Dryland. It's a bit of a voyage of discovery for me - I do have a plan in mind but things tend to get made up as I go so it may evolve further yet . . .

I've discovered that some users have added a meter into the mix, but I'm still trying to work out whether there would be any advantage in having one. You can see some in the Delta Pulse 2 videos on YouTube. The PCB has the capability built in - I wrote to the Bulgarian seller who told me where it connects to. The ones I've seen are LCD bargraph panels  which presumably display the output from the VCO - i.e. a stronger signal gives higher tone audio output. The best way I can think of doing that is using a microcontroller like an Arduino or a Raspberry Pi, but although they're relatively small they still need space in one of the boxes somewhere . . . And power.

Remember the old PCs which used to down tools for a while and display a message saying, 'Thinking . . . . . . ?'

That's me right now!
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