What kind of cable do you use from the coil to the control box?

[SVEN1]

Since the mono coil has 3 wires, I can't use the standard coax.
What do you suggest?

[Chet]

Hi SVEN1

The circuit diagram may have you confused. Just place a short jumper on the bottom side of the board. Connect PL2 and PL4 center pins together. Then use a single coax to the coil.

Chet

[kt315]

[SVEN1]

Got it, thanks

[egonw3]

What defines "damn good cable" between coil and control box?
Should it be stranded or single core? 50okm or 75ohm? What are optimal parameters (core diameter etc)?

[SVEN1]

Stranded, tinned coax.
For starters solid core is not made for constant flexing or bending. Solid core copper can or will eventually heat hardern during flexing or bending and break.
Easiest to find in bulk is marine grade coax. And is is fairly flexible.
http://www.westmarine.com/WestAdvisor/Coaxial-Cable

You want the coax as short as possible from the coil to the controlbox.
I use RG58. 40-42" for control box rear mounted under the arm cuff. Less if mounted on top in front of the shaft of a s-handle.

[dotniet]

You want the coax as short as possible from the coil to the controlbox.

That's bad news. I wanted to mount the metal detector on my belt or backpack and have only the coil on the stick.

[dotniet]

Update: I just find out that the cable greatly influences the stability of the detector.
What if we just put the pcb close to the coil and use long wires for potentiometers?

[KRinAZ]

For my MPP I built my mono coil (a fast Self Shielding 3D) and I just use the wire for the coil right up to the control box - I used 600V rated PTFE (Teflon) coated wire - that is twisted the whole way - and it has to my experience so far the lowest capacitance & best specs. Simple and very low capacitance...

[aries1470]

Separate box and ideas

Update: I just find out that the cable greatly influences the stability of the detector.
What if we just put the pcb close to the coil and use long wires for potentiometers?

You just game me an idea.
What if there were 2 boxes?
One with the electronics, close to the coil, but not as close as to cause interference, and another either on you or closer to the handle or hip.
In this control box, you can have the batteries, and the required switches.
Here is an example:

Link to digital pot's (one of many manufactureres):
Maxim-IC / Dallas Semi:
http://www.maximintegrated.com/en/products/analog/data-converters/digital-potentiometers.html

They have both analogue and digital control. With the digital control, you have more options and more fine tuning, while with the analogue, you have simplicity, but not many "steps".

This is another company:
Microchip:
http://www.microchip.com/dac-digital-potentiometers/
then after you have browsed and got other nice ideas you can select "Digital Potentiometers", or just go directly there.
You may notice, that they do not have PDIP package available for their Up/Down while Maxim do. That may be an issue for people that can not solder surface mount, but adapters can be used and a toaster oven etc...

Using a DPDT with centre off, and 2 momentary pushbutton switches, you can use 2 DS1804-100's to control the reject and audio.

Here is one more company:
Intersil:
http://www.intersil.com/en/parametri...ometers--dcps-

There are plenty of options that are still available in PDIP here too
X9C104,
All that needs to be added to use them, is bounce elimination circuit if using switches directly and no microcontroller. The other good thing with them, is that they retain their memory when their is no power.

These are just ideas, and for playing around, you can use an Arduino for quick prototyping if you want to use a µC to control the chips, then you will have even more options.

Also, if a µC is used, some person brighter than me, might want to consider a TC9402 and do a F/V convertor, of which then the µC converts the voltage to a value and displays on screen so potential targets are not lost due to failing hearing... just saying.

Dear Mod, if you beleive that this reply would be better accomodated in a new thread or somewhere else, you are more than welcome to move it

[dotniet]

Or you could move only a part of the circuit (the receiver connected to the RX coil) close to the coil.