Can anyone answer a Coil question?

[Mojave]

I am new, and I am trying to build a two box unit that is listed here:

http://geotech.thunting.com/cgi-bin/...eker/index.dat

I am trying to build this unit (I know I may be crazy, but it's my first electronic project).....I think I understand everything else, but the coil is really getting me confused. The coils are mounted on a square, flat piece of wood. Around the edge of the wood is supposed to be a strip of aluminum.

Now, I see that it says "jumble wound". Does that mean that the coil wires are turned around the strip (Top example) or does it mean that they are just a bunch of little coils "draped" around the strip (lower example)? Sorry about my poor drawing.....

I see, on every diagram, there is a "small" coil pictured to the left, and a bigger coil on the right, with a broken line in between. Does this mean that the smaller pictured coil goes "under" the strip? Also, why are there 3 coils pictured?

This coil (which is probably the easiest part) is really confusing me, and I probably sound dumb........

[Mojave]

I forgot to add a picture of the coil diagram

I would appreciate any help...The link above goes to the project....

[Qiaozhi]

The strip of aluminium around the edge of the wood is the coil. So there is one strip for the receiver and one for the transmitter.

If you look at the diagram of the complete receiver circuit (page 6) you will see one loop (the receiver) at the top left, and another loop (the transmitter) at the bottom right. The square parts labelled "LOOP" are the aluminium strips. To add some confusion, the author has called both the RX and TX transformers L1, whereas these are actually two separate items. It appears the reason is that the receive and transmit circuits are considered to be completely independent, and therefore several of the reference designators have been duplicated.

"Jumble" refers to the tidiness of the coil windings. i.e. they do not need to be wound neatly with perfectly overlapping layers. Just wind the wire on roughly until you have the correct number of turns. In other words, it's just a "jumble".

The three transformers are each wound onto a potcore (Philips type P18/11, 3H1 material). The purpose of the two L1s is to provide impedance matching between the circuit and the TX and RX loops (aluminium strips). The third transformer is also used for impedance matching between the RF amplifier and the following stage. So there are no windings on the wood formers as you've shown in your diagrams. All the windings are on the potcores.

Also look at the PCB component layout, where you will see 3 coils. The broken line on the coil diagram represents the ferrite core material. In the section entitled "Coil Details", the first coil connects to the transmitter, and the second connects to the receiver. The "small" coil to the left connects to the aluminium strip.

Hope this clears up the confusion.

[Mojave]

Thank you so much....

I appreciate it! I know this is probably not the best project to make my first, but I am learning alot. I appreciate your help! That makes alot of sense, now....

[Geo]

I appreciate it! I know this is probably not the best project to make my first, but I am learning alot. I appreciate your help! That makes alot of sense, now....

If you have found the cores then build it , it is a good project. I tried it with different cores and detector was no so sensitive and it was unstable. As Qiaozhi said the coils are a one turn loop. Good luck

[Mojave]

I'm going to try...

I am so used to calling normal metal detector loops "coils", that I wasn't thinking that loops and coils were 2 different things....I feel real stupid now.....Guess I must be more "technical" minded about all of this....I'm just very excited to build something..... Thanks again!

[Qiaozhi]

I am so used to calling normal metal detector loops "coils", that I wasn't thinking that loops and coils were 2 different things....I feel real stupid now.....Guess I must be more "technical" minded about all of this....I'm just very excited to build something..... Thanks again!

Good luck with the construction!
Please let us know how it performs in the real world. It's always a good idea to start with a simple project.

[Mojave]

One last question (hopefully)

In the picture below of the coil design, what does this mean (circled in red)? what does this tapping lead to?

[Qiaozhi]

In the picture below of the coil design, what does this mean (circled in red)? what does this tapping lead to?

It connects to the negative side of the battery.

[Martin]

Since I am also interested in building one of these detectors, I thought I would chime in here.

The 3H1 core material has been obsolete for some time. It's replacement is 3H3. Although any material with similar permeability should work. P18/11 3H1 cores were widely used in telephone circuits.

Geo I would greatly appreciate some further info on what core material you used.

The circuit, while realtivly simple, could have some stability problems like Geo said.

[Geo]

Hi Martin. I don't remember (and i don't know) what type core i used. I think that i took cores from TV (maybe from audio IF) and i winded them. The cores had shielding problem so the detector was very unstable (with sens from midle to max). I am sure that if you find the cores the project will work very good.
What to say...Good luck

[Martin]

Geo thanks for the info.

The replacement cores, for the Philips models used, are made by Ferroxcube. They are still listed in the data-sheets but are next to impossible to find at least in Europe :-( The cores are occasionall available but the rest of the parts including the shielding can and adjustment screw don't turn up anywhere.

Oh well I guess I'll have to look elsewhere for a 2 box unit that can be built with easily available components.

[Geo]

Hi Martin. You may build the following detectors
1. T/R Locator by Sevzirfo. A good and easy detector
2.Two Box Deep Seeking Metal Detector. A revision with transistors from Gary Chemelec. He has an easy pcb.
3.TM808. Very good and difficult detector. (look at technical forum the thread TM808 White's from Ivconic.
4. Buccaneer Ib Detector by Andy Flind.It is a ib detector but you can modify it to a 2box detector very easy. Very good and sensitivity detector
The choice is your.

[Martin]

Geo thanks for the info.

I am currently looking at the T/R detector design. It has a nice transmitter idea.

At the minute I'm just wading through translating all the Russian info with an online translator.

I built a Buccaneer years ago sadly I don't have the circuit anymore.

[Qiaozhi]

Geo thanks for the info.

I am currently looking at the T/R detector design. It has a nice transmitter idea.

At the minute I'm just wading through translating all the Russian info with an online translator.

I built a Buccaneer years ago sadly I don't have the circuit anymore.

Is this what you're looking for?