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**Davor** · 02-11-2016, 11:37 AM

You don't need metal housing, but if you use one, make sure it is connected to the device's signal ground in only one single point, and nowhere else. Say, a coil connector.

**kt315** · 02-11-2016, 01:56 PM

i asked peli on shipping price. microcase 1040. its expensive for me.

[email protected]

We can ship international. I would be happy to get a shipping quote for you, could you send me the full shipping address?

Hi John,

It looks like the cheapest shipping would be 47.97.

**kt315** · 02-11-2016, 01:58 PM

ikelite enclosure

http://www.ikelite.com/accessories/5...using-kit.html

**LukeJ** · 02-11-2016, 09:43 PM

Thanks for the replies...

I bought an Ibex case since the rubber seal is separate from the interior 'padding'. The Pelican and Ibex are roughly the same size. It is about the same size as a TDI SL housing, which is fine. I was just trying to get a more compact unit. Of course, the next issue is how do I connect the batteries and will they be inside the housing or outside. The latching waterproof case makes it easy, the battery could be inside with plenty of room to spare. I was considering the option of fabricating a housing out of ABS and then making the battery plug into the outside of it. Then the battery could be Velcro strapped to the underside of the arm cuff. It's interesting that when you buy a commercial detector you just generally take what you can get. In this scenario, I can have it any way I want and now I can't decide...

Not having to shield the board definitely makes things a bit easier.

Thanks,

Luke

**kt315** · 02-12-2016, 01:27 PM

you do not need to shield the housing if you hunt in salt water, or just your body part and coil touching the water.
salt water is a perfect current conductor.

**FatBob** · 02-12-2016, 08:20 PM

Hmm Eric Foster had this to say on another forum:

PI's for large objects buried deep, where the pulse delay is 50uS or more, can get away without coil shielding. The main purpose of the shield is to prevent spurious signals from coil to ground capacitance. This effect becomes more pronounced at short delays, as are used when hunting for small coins and thin rings. Also, the effect is worse on a salt wet beach than in fresh water or dry sand.

**LukeJ** · 02-13-2016, 03:36 AM

I was referring to shielding for the PCB. Which I guess is unnecessary.

I hunt in the deserts of Arizona. Not much salt water or any water where I'm detecting.
Looking for small nuggets, so I'm going for a short pulse delay.

It looks like I'm going to fabricate a housing first. If it doesn't turn out good, I'll modify the case I bought and use that instead.

**FatBob** · 02-13-2016, 11:26 AM

Oops I missed that it was the board housing you were talking about.

I've heard of people having trouble when touching the pots even with them
grounded to a metal panel and so they had to use plastic shaft pots.

Some also have had to shield the entire PCB to eliminate interference.

The front end has a lot of gain so may need shielding.

**LukeJ** · 02-18-2016, 05:34 PM

Okay. So I've decided to use the Ibex case I purchased, for now...

My next question is: Would it be better to leave the wires connecting the pots to the board a bit long or the cable that joins the board and the coil connection socket ???

The reason for this question is: I would like to mount the board to the top of the box, with the pots and the bracket that mounts to the shaft. I was thinking that it would be 'cleaner' and when I opened up the box the 'guts' would be on the lid. Problem with this is, I have to leave the coil connection wires long since the socket will be mounted on the front of the housing (toward the coil) and will be on the lower portion of the box. There is plenty of room in the box so I will be mounting the battery in the lower rear of the box.

If I mount everything in the bottom of the box, I'll have a bunch of longer wires to deal with (that connect the pots) when the box is opened to change the battery.

I would think that making all connections short as possible will help to reduce undesirable effects. So which one will give me the least problems ???

Thank You,

Luke

**LukeJ** · 02-26-2016, 02:33 AM

So here it is:

This was my first detector project. I am quite happy with how it turned out !!

I have to give a lot of credit to the thoughtful craftsmen who engineered the project. Well Done.

The way the board was populated and each step was more or less confined to it's little section of the board was great. This feature also made the soldering easier I believe.

I don't have, up till now, any experience with this level of electronics projects. I do however have more than a decade of manufacturing experience. Specifically, Machining.

I'm certain these skills made the project flow with little to no problems. I also just took my time. Wanting to get it done right more than just get it done.

I would highly suggest to anyone who wishes to build a MPP that they buy the kit the first time around. Then, once you have the kit, read through each step and put all the correct parts for that step in a sandwich bag. Number the bags for each step. This way you can verify much easier that you do in fact have all the parts and they have been correctly identified before assembly. Double check each component with a multi-meter as well. I used this method. It helps quite a bit.

I used an oscilloscope that I bought used for $50. It's an older analog model. I had little experience with it as well. There were a few steps that when finished, I wasn't sure I had done it right. Turned out, each time, it was how I was operating the scope or my understanding of what the scope was trying to tell me. By the time I got to the end of KRinAz's modifications, I was pretty familiar with the oscilloscope. It was a great learning experience.

The coil is a 7.25" OD basket coil. The picture shows 30AWG that I used to proof the winding pattern. I cut that stuff off and re-wound it with 26AWG Teflon insulated silver-plated stranded wire. It's 33 turns, 2 OHM, 290mH. It works really well. In fact, I found a couple nuggets with it and my White's SPP a couple weeks ago !! The basket wind is covered in two layers of medical paper tape and one layer of medical cloth tape. I went ahead and shielded this one since one I had made previously was still hearing the ground too much in a spot I've been hunting. Spiral wrapping the silver plated conductive tape seemed to solve the issue and didn't have any measurable negative effects. I've used this method of shielding on several bunch wound mono coils with favorable results.

The coil housing is a one of a kind. I watched some YouTube videos and made myself a little vacuum forming box. Then I made two molds, a top and a bottom, from 1/4" MDF. The bottom mold was made such that it would have a protruding lip that would accept the top piece. It took a few tries with the plastic temps but eventually I got one of each that I could trim up and fit together. Turned out much better than I expected.

I would like to additionally thank, Reg Sniff. He is a wealth of knowledge and experience and had quite a bit to do with helping me get started in winding my first mono coil. He pointed me towards this forum and the article "Making a Fast Pulse induction Mono coil" by Joseph Rogowski. Excellent article. Thank you !!

So here it is, my homemade metal detector.