Help with building CCO?

[nabiul]

I know yhl already has a thread on this, but seeing as how his threads go nowhere...

I'm trying to build the CCO metal detector(http://www.geotech1.com/forums/attachment.php?attachmentid=12218&d=1274640067) but the plans don't really mention anything about the coils. It says 50 turns but is that 50 turns in a single row, ie a flat coil with 50 'layers'? Or is it 50 turns with however many rows and layers as you want, as long as the coils are the same? It also doesn't mention if the coils should be bent into D shapes like on IB.

I also have a question about the 200k pot, I wasn't able to find one of that value and instead got a 500k pot. The schematic shows that the middle lead of the pot should be wired to one of the side leads for the variable resistor configuration, but from my understanding does this not really become two 200k resistors in parallel (with one being variable)? I.e. their real maximum resistance is then 100k?

I'm trying to replace the 200k pot using some 470k resistors in parallel; wiring the two leads of the 500k and then putting three of the 470k in parallel should give me 96k in theory, would this be a proper replacement for the 200k pot?

[WM6]

It is 2x50 turns (two coils in DD or OO form).

See this illustrated instructions from same author (other detector but same principle to building coil):

http://www.geotech1.com/pages/metdet/projects/matchless/matchless150c.pdf

[nabiul]

Again that doesn't really show how the coil should be wound, it just shows two bundles of wires in circles. Should it be a single layer 50 row 50 turns? Single row, 50 layer 50 turns? Or just 50 turns randomly made and then taped together?

Maybe this picture will illustrate my dillemma, the author of that article kind of assumes that you already know how to make a metal detector.

[WM6]

Or just 50 turns randomly made and then taped together?

It can be randomly made and then taped together.

If you wind in orderly layers you can get more parasitic capacitance between layers which is unwanted.

[Qiaozhi]

Have a look at Figure 8 in this article to get an idea of the coil construction -> http://www.geotech1.com/pages/metdet...an_md2_150.pdf
You will need 2 similar coils. Place them so that they overlap slightly. By adjusting the overlap you can set the sensitivity on the CCO. You can probably leave out the electrostatic shield in the first instance while you are experimenting.

[nabiul]

Circuit is soldered, still missing a 12v power source and the coils. Need to buy the wire and I'm trying to recharge one of those small lead acid batteries for the power source. Is it critical to have 12 volts, could 9 volts run this?

Hopefully I didn't burn any components (30W iron that I leave sitting for too long so it gets very hot), fingers crossed that this works later.

[yhl]

MW radio / how and CCO connection?

MW radio / how and CCO connection?

[yhl]

There is no specific production plan

[nabiul]

Augh, could you please write in normal size text and stop making single sentence posts. Edit your post to add new information.


I'm not using the circuit with the medium wave radio connection, but I think this is how it's supposed to be.

[maikl]

Most AM radio has a ferrite antenna. Thus, the author recommends "crocodile clip".This is what you want to go doing the following:5 row * 10coil windings = 50 coil windings, it can be randomly made and then taped together. "OO form". 200k can be found in old radio receivers ... Sure to put a shield (a thin aluminum foil).Will function at 9V but weaker.Here's the picture with the coil in this pdf.

[Qiaozhi]

Here's another version without the AM radio.

[maikl]

This is BB (old version) not CCO. BB(Beat Balance Metal Detector) at a critical position of the winding.CCO is not as critical position of the winding (but need a bit of effort for the best performance). Experiments to find the direction of winding rotations. CCO better detected by BB (the greater the distance detected coin).If an interested, on this picture is a newer version of BB metal detectors:

[Qiaozhi]

This is BB (old version) not CCO. BB(Beat Balance Metal Detector) at a critical position of the winding.CCO is not as critical position of the winding (but need a bit of effort for the best performance). Experiments to find the direction of winding rotations. CCO better detected by BB (the greater the distance detected coin).If an interested, on this picture is a newer version of BB metal detectors:

These circuits are basic regenerative receivers. There is an oscillator adjusted on the edge of starting to oscillate. When a metal target upsets the coil balance, the oscillations start. It is the huge gain derived by this setup that makes them so sensitive.
http://en.wikipedia.org/wiki/Regenerative_circuit

[maikl]

Here's another BB metal detector by the same author.There are more details for beginners.

[Qiaozhi]

Here's another BB metal detector by the same author.There are more details for beginners.

This is the one I was searching for to show nabiul the coil construction.