Let's made a PC-base metal detector with usb interface !!!

[Aziz]

Aziz, You must more often go out with the detector on the field. Not only 1 April.
Mrand

Brrrrrr, cold today, but fine!
My ultimate magic coil isn't finished however.
I'll do this soon.

------------

Ok guys,

I have just submitted the order list to get more parts. The pre-amplifier gain issue isn't fixed yet as we need more gain with the anti-interference coils now. A gain of 100x to 500x could be interesting range. The amplifier noise can not be neglected now and I am looking forward to test some new dual op-amps. (Damn!, I couldn't get the AD8022.) But I'll see soon, how much gain is necessary.


Cheers,
Aziz

[WM6]

Don't hurry Aziz, I am in 66 now and still very vital, so couple of years mean nothing.

[Mechanic]

Whip Crack C'mon Aziz, whats taking you???
I have now wound up a second rx coil form some old litz harvested from an old coil.
I used the preamp gain to null the tx(rx+) and Rx- and it seems to work, although it is difficult to tell in my house. The Rx- is 17" diameter, the Rx+ is 25". Will have to attach it up in such a way that I can test it out in my backyard. With an 11" DD in subtraction mode my detector runs sweet in the backyard, but not in the house Oh well, good to get outdoors once in a while

Cheers Mick

[Aziz]

Whip Crack C'mon Aziz, whats taking you???

V i a g r a Lot's of V i a g r a *LOL*

I have now wound up a second rx coil form some old litz harvested from an old coil.
I used the preamp gain to null the tx(rx+) and Rx- and it seems to work, although it is difficult to tell in my house. The Rx- is 17" diameter, the Rx+ is 25". Will have to attach it up in such a way that I can test it out in my backyard. With an 11" DD in subtraction mode my detector runs sweet in the backyard, but not in the house Oh well, good to get outdoors once in a while

Cheers Mick

Why don't you use identical RX coils? It's easier. It's better for EMI rejection too.
I'm going out now (walking with girl friend).

Cheers,
Aziz

[Mechanic]

G'day Aziz,

Well my rx+ coil is a commercial 25" mono coil. It would be very difficult for me to make another identical coil. That coil cable(coax) is impossible to buy unless it has a coil attached to it! If we can come up with a good way to null the coils without them being identical will be good, cause then we can all be a bit sloppy with the coil builds. The ML DD coils do not have identical windings, however when set to subtract it is so damn quiet. If it can be done with a DD it can be done with a Top Hat (TH coil).

Last time I tried to make 2 identical receive coils, damped them and connected them in parallel anti-phase, the tx coil was seeing them as a shorted turn and the response took a long time to decay. By sending each coils signal to a preamp and then adding or subtracting and varying gain thing become a bit more flexible. Sure the cct becomes more complex, but not really that much more. However I am not sure how this method will work for your induction balance of your rx coils to the tx/bucking coils.

Enjoy the walk with your girlfriend.....

Cheers Mick

[Aziz]

G'day Aziz,

Well my rx+ coil is a commercial 25" mono coil. It would be very difficult for me to make another identical coil. That coil cable(coax) is impossible to buy unless it has a coil attached to it! If we can come up with a good way to null the coils without them being identical will be good, cause then we can all be a bit sloppy with the coil builds. The ML DD coils do not have identical windings, however when set to subtract it is so damn quiet. If it can be done with a DD it can be done with a Top Hat (TH coil).

Last time I tried to make 2 identical receive coils, damped them and connected them in parallel anti-phase, the tx coil was seeing them as a shorted turn and the response took a long time to decay. By sending each coils signal to a preamp and then adding or subtracting and varying gain thing become a bit more flexible. Sure the cct becomes more complex, but not really that much more. However I am not sure how this method will work for your induction balance of your rx coils to the tx/bucking coils.

Enjoy the walk with your girlfriend.....

Cheers Mick

Hi Mick,

it is very very important, that both RX coil parts should be identical (same characteristics). The frequency response characteristics of both RX coil parts should be identical. Otherwise you will have a different frequency dependency and not all EMI noise can be cancelled out. And it is quite difficult to make it. So I do strongly prefer and propose identical RX coil parts. Different RX coil parts works in principle - but difficult to realise. We are bloody amateurs (particularly me) and we should do the easy things first.

By sending each coils signal to a preamp and then adding or subtracting and varying gain thing become a bit more flexible.

Too much risky due to high voltage induction. You need to clamp the high voltage. It is better to connect them in series not to deal with much high voltage flyback pulses.
BTW, I have done this in my dual channel detector as well (adding/subtracting in software). It works.

Cheers,
Aziz

[Aziz]

High Performance

Hi all,

I have compared the calculated performance of a magic cylinder IB-coil vs. standard concentric co-planar IB-coil.

Coil specifications:

Magic cylinder IB-coil:
10" diameter TX (outer coil diameter)
8" diameter RX+, RX-, TX-Bucking (inner coil diameter)
8" distance of TX/RX+ and RX-/TX-Bucking
TX-total: 300µH (TX + TX-Bucking)
RX+: 300µH
RX-: 300µH

Standard concentric co-planar IB-coil:
10" diameter TX (outer coil diameter)
8" diameter RX, TX-Bucking (inner coil diameter)
(BTW, this coil is performing better than the 5" inner coil diameter coils)
TX-total: 300µH (TX + TX-Bucking)
RX: 300µH


Magic cylinder IB-coil results:

Better sensitivity in the near detection region (up to 1 .. 2 times coil diameter detection distance) without the RX gain compensation (it doesn't require boys! ) -> better pin-pointing capability due to stronger signal.

The gain compensation is only relevant for deep detection distance and requires only two times more RX gain compensation to be equivalent to the other coil. The RX gain compensation can be done either with more RX turns (doubling the turns count for instance) or a higher RX front-end amplifier gain. The lower the distance of the RX+/RX- coils, the more RX gain compensation is required of course.

As the EMI cancellation factor is in the range of 20 - 30 dB (10x .. 32x), you have enough RX gain compensation range to improve and outperform the detection distance.


So, this is a magic and surprising result. Isn't it?

Cheers,
Aziz

[Aziz]

Ok guys,

you deserve more. I'll add the other equivalent coil type comparisons.

Eat this (and I'll eat more blue pills):


10" mono coil (the standard PI mono coil):
Requires only 4 times RX gain compensation to be equivalent to it.

10" DD IB-coil (10" total outer coil diameter):
Requires only approx. 1.5 times RX gain compensation to be equivalent to it.

That's magic.
Aziz

PS: BTW, did you patent trolls keep holding on your breath? If not, please hold on your breath now! Thanks for your valuable contribution to the mankind.

[Aziz]

How To Make Identical RX Coils?

Hi guys,

I'll give you a tip, how to make identical RX coils. Use a (thin) ribbon cable (3-6 veins or whatever you need) and a coil former (wood, polystyrene board, pot, etc.). Wind the ribbon cable strip tightly around the coil former (spirally). Fix it (hot glue, tape, epoxy resin, etc.), add a paper tape (insulation to shielding) and make a shield around the coil bundle. Connect the individual veins in serial. That's it.

Do this procedure for the second identical RX coil (same turns) and you have a perfect matching RX+ and RX- coil. The RX coil wire need not be a thick wire.

The ribbon cable strip RX coil is very easy to make.

Cheers,
Aziz

[Aziz]

Real Bargain Op-amps!

Hi all,

my ordered parts are on the way!
I have ordered some interesting cheap Japanese dual op-amps for the NE5532 replacement. They were known to be quiet.

NE 5532 A (note, this is the A-grade! Didn't test it.)
MC 33078 (alternate to NE5532, 4.5 nV/sqrt(Hz))
µPC 4570 (alternate to NE5532, 4.5 nV/sqrt(Hz))

Japanese:
NJM 2068 (0.5µV noise over a specified frequency range, have to look at the data sheet)
NJM 4580 (low noise alternate, ~3.5 nV/sqrt(Hz))
NJM 4556 (high output current: 70 mA!!, for the power supply splitter)

I'm looking forward to test them.
Cheers,
Aziz

[Aziz]

Ready For Big Entertainment?

Hi all,

I wonder how long it will take, that a patent troll will try to steal & lock our big coil invention (the magic cylinder coil)?

Are you ready for blaming this patent troll with tar & feather?


Keep watching. I'll do this too.
Let's look, how long it takes.

Aziz

[PATCHES JUNIOR]

Hi all,

I wonder how long it will take, that a patent troll will try to steal & lock our big coil invention (the magic cylinder coil)?

Are you ready for blaming this patent troll with tar & feather?


Keep watching. I'll do this too.
Let's look, how long it takes.

Aziz

You have nothing to worry about AZIZ. It will not work in the real world, sorry.

[Aziz]

You have nothing to worry about AZIZ. It will not work in the real world, sorry.

*LOL*
Did you do the Maxwell's equation calculations ? It will work better than an equivalent size mono coil. Comeon, do some math!
http://en.wikipedia.org/wiki/Maxwell's_equations
Or ask your mentor PJ!

Cheers,
Aziz

[Monolith]

You have nothing to worry about AZIZ. It will not work in the real world, sorry.

Don't let them stop you, Aziz.

Just keep up the good work and keep checking on new patents.

Monolith

[simonbaker]

Hi all,

I wonder how long it will take, that a patent troll will try to steal & lock our big coil invention (the magic cylinder coil)?

Are you ready for blaming this patent troll with tar & feather?


Keep watching. I'll do this too.
Let's look, how long it takes.

Aziz

I'll be interested in how you do with the coaxial coils, even though they do not seem novel to me. I saw a photo once on the web (I can't locate it now) of an MD with coaxials coils and the guy hunting near a fence under some power lines with a claim it reduced EMI. There have been some discussions on this site also of the idea, and I started experimenting with some EMI cancelling dual coil designs, first starting with co-planar because much easier to stabilize, but with intent to stack them coaxial also. The theory makes sense so let's see how practical they are to build and use (weight, vibration, etc.).

Note: need for more preamp gain suggests loss of S/N advantage...???

A long time ago I did a thumbnail analysis that suggested that such coils are worth it if lots of EMI around, but otherwise not. So useful in my neighborhood, yes!

One benefit of the top-hat design is that if there is more trash than treasure around, we can get part-time jobs filling the hat with gum wrappers and tin-foil and make an important contribution to our communities as trash pickers...

Cheers!

-SB