Building Metal Detector

[Sherlene Holloman]

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Building your own metal detector is fun and educational. While building a traditional metal detector may require a kit (or in depth knowledge of electrical circuits), you can create simpler versions with household devices. The fastest way to detect metals is to use the magnet field on your smartphone. A more well known method is to use a calculator and a radio to make a metal detector.

I'm new here but been hunting since 1964. I'm an Radio Frequency Electronics Engineer. I design and build all kinds of Radio Frequency devices. I have been thinking about building my own pick up loop coils. I built some years ago when I worked for a fledgling metal detector company back in the MetroTec Days. If I recall correctly it was for a BFO type detector. I am now working with VLF Motion Detection and Descriminate type detectors, and a few Pulse Induction (PI) units. Most units operate between 3.0 and 40.0 KHz. Any input would be appreciated. Thank you ? Laurin the old SwampFox

Regarding the possibility of making a coil, on-your-own, to compete with a manufacturer coil : This endeavor might have been possible back in the 1960s. When the hobby (in-so-far as individual coin hunting) was concerned, was in its infancy. And when electronics were crude (by today's standards). But the problem now is that the super fine-tuning exactness, to eek out the absolute depth and optimum performance, is SO exacting, that a zillionth of an inch off in your windings, can make for the difference of good vs poor depth/performance. It's now done with computerization, and assembly line exactness (where every single coil coming off the line is exactly the same ).

I've always wondered if you could correct any sloppy windings with some tunable electronic circuit installed as well. Anyways, I always encourage others to try whatever they want to accomplish. Some of the best things invented come from tinkering around and trying unconventional or inspirational ideas. Good luck SwampFox on your endeavor. Are you located in the US by any chance. SwampFox was related to the Rev war I believe.

Ive built a few dozen coils for myself over the years, hardest ones to try are the CC and DD types, where distance and sizes between the 2 loops for tuning, sensitivity and depth purposes are the most critical parameters. Obtaining the inductance and resistance values for said loops is the 1st step. Shielding method is the 2nd. Correct parts (shell, cable, connector and wire) are very type specific too. Lots to think about when you first start out.

Steve's list above is as good as it gets. Note the size of the coil, should be your starting point depending on your preferred target size and depth of your ground. See Searchcoil size from the lists Steve has given above.

I am located in the US and in Northern Georgia to be exact. The name was given me by an old gentleman who I often encountered in the Mountains of North Georgia while hiking, camping ? and fishing ?. I've always been an outdoors person from young childhood. When I was 4 years old a friend and I spent most of our preschool days outside weather permitted. We continued that into adulthood in Scouting. I since raised 3 kids that way and they are raising their children the same. Of course Metal Detecting and Gold Panning are a part of that.

The figure 8 or BigFoot is one of the designs that I want to try, since they are no longer in production. There are a lot of detectors out there that people are still using and would like accessories for besides the newest out of the box. Sure if ya got megabucks you can buy the newest, but many folks want to start detecting without spending a fortune, others like the detector that they have and would welcome some add-ons for their existing machine. ? so I'm looking into producing some coils. Yes I heard the guy who said I could never equal what the factory built. But as an Electronic Engineer I know for a fact there are many products that are built to the minimum standard and can always be tweaked for maximum performance by not just hitting the minimum and shooting it out the door!

Don mentioned that I could epoxy the empty voids or fill it with scrap material. I chose to fill the voids with epoxy as it would allow for a pretty good watertight seal. He warned however that when using epoxy one needed to be careful of the heat it gives off when curing, as it could potentially melt the plastic! Being one to go for cheap and not buy slow curing stuff, I just purchased some epoxy at home depot and decided to figure out the heat problem later.

*if you notice I have pictures with and without the cable gland installed. This is because I did this 2x and so the pictures were taken after I figured out the best streamlined process for building these shells.

On my metal detector, I used RG6 coax cable for connecting the metal detector circuitry to the coil. Because of this, I found that the PG7 cable gland which was supplied was too small for the coax cable. I needed to use my PG9 cable gland reliefs which meant drilling out the PG7 indentation on the upper coil housing larger than it was intended (as he used a PG7 size connector to form the coil housing). I realized it needed more strength for support, and filled the void with epoxy as well. I recommend epoxying the main shaft ears first, then once that cures, epoxy the cable gland area so you can level the housing to get the epoxy to cure level.

While waiting for the epoxy to cure, I moved on to prepping the tape which will hold the coil stationary. I had some gorilla double sided tape laying around and used that on the lower portion of the clam-shell housing. I left the backing on so I could spray the graphite directly on top of it, and just peel it off later. Go do something else now, since you need to wait for the epoxy to fully cure.

Its now time to remove the double sided tape backing and stick the coil onto the bottom half of the coil housing. Be mindful of where your run of grounding wire is to have it come as close to the coil leads as possible. It will aid in soldering them together.

The other day when I was searching instructables I come across on interesting and simple circuit for metal detector. It is build with 555, coil and few other components. Instructable that inspire me to do this project was this one. Main debate was: does it really work? After quick research I found this video that proof it works. That was the time when I decided to make my own metal detector.

I do believe, that before you start working on metal detector you should read more about metal detectors and how they work.

I am not hold responsible for any damage that occurred during reproduction.

The most difficult part is making coil. In great help was web calculators for air coils. With them, I calculated that with coil 90 mm width I need about 250 windings and with diameter 70 mm 290 windings that inductance can be 10 mH. You can also buy already made coils online.

I made coils core from cardboard. Coil is made from lacquered copper wire which is 0,2 mm in diameter. I did 260 turns. Before soldering, you must clean up both ends of coil. You can do that with help of sandpaper.

To accomplish these goals, I will have to use quite a few pictures and drawings. Rather than have you jumping back and forth from the text here to the photos below, I will explain each photo and drawing in detail in a box to the right of each. I can assure all of you that you have never seen a Metal Detector Test Garden like this one and even if you are not inspired by it enough to build one as extensive, you should at least pick up some good ideas for making an adequate basic one for yourself. Keep in mind as you view this one, that the design can be customized at any time to include whatever additional high-value targets you are more focused on.

IMPORTANT NOTE: If you decide to build your own Test Garden, MAKE SURE that the ground you choose to put it in has no other metal readings in it that could interfere with the results of your own detector testing. If it does have other metal signals in its soil and you are limited in choosing a different spot for the Test Garden, then be sure to dig every target detected on your metal detector in that area to be used before proceeding further.

Dorian Cook is a native of Huntington, West Virginia, and spent the greater part of his childhood growing up in the Appalachian Foothills near the small town of St. Albans. From age 10 to 17 much of his time was spent exploring those foothills and the old cabin ruins they contained, as well as fishing and trapping along the Coal River.

He currently resides with his wife, on a small farm in the foothills of the Appalachian Mountains in Northeastern Kentucky and remains active in metal detecting historical sites and sponsoring a Civil War history and relic hunting group on social media.

A DIY BFO Metal Detector project is a project where individuals create their own metal detector using a Beat Frequency Oscillator (BFO) circuit. This type of metal detector is commonly used for finding metallic objects in the ground.

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