A Couple of New PI Coils

[Silver Dollar]

I decided to make a 10" "DD" Pi coil. I wound up some awg 24 PVC wire 24 turns for each coil.


Then attached them with hotmelt glue to get them in just the right position. Next will be the
epoxy to hold them solid. The housing is covered in graphite spray with a drain wire embedded.
I'll coat the epoxy to make a full cage then some fiberglass resin to finish.


I also made a 300 uh center tapped PI coil by winding two wires at the same time for 12 turns;


Dropped them in the housing;


Then epoxied and fiberglassed them in. No shielding this time as the CT should kill the noise;


I finished off with a clear hose for the wires to run in;


Anyone have a schematic for a differential front end for the center tapped coil?

[Koala]

Wow you been busy

Nice looking coil shells are the homemade

well done look very professional

[6666]

SD where did you get the housing ?

[Silver Dollar]

Those were some I got a while back on Ebay. I think they came from Bulgaria...

[6666]

Those were some I got a while back on Ebay. I think they came from Bulgaria...

Ok thanks.

[WM6]

SD where did you get the housing ?

http://www.geotech1.com/forums/showt...t=coil+housing

Available on eBay too.

[Silver Dollar]

Well on that link the guy seems to want you to buy 10. They don't seem to be available on Ebay anymore.
There's one that looks like the Tesoro but it's $18 + $10 delivery. I paid $17 delivered...
http://www.ebay.com/itm/Metal-Detect...item33919fff53

[Silver Dollar]

I did get some similar ones off DBFlowers;


Here's a link;
https://sites.google.com/site/dbcoil...10-inch-shells

[Koala]

I did get some similar ones off DBFlowers;
[ATTACH]31439[/ATTACH]

Here's a link;
https://sites.google.com/site/dbcoil...10-inch-shells

That's a good price.

Did find this http://crazy-tech.net/index.php?rout...tegory&path=17 with a Google search of "metal detector Bulgaria coil shells"

Don't know anything about them but did notice a nice 3 piece "S" shaft including bolt

[Davor]

Moodz did several designs with differential front end, see http://www.geotech1.com/forums/showthread.php?17320

[Silver Dollar]

Well I have schematics like this;


But their a bit tough to read...

[Davor]

There are 2 ways to go about it. You may use a microphone amplifier chip, such as those from THAT company, and you can instead build your own discrete front end in form of a Cohen amp or something similar. By modest investment compared to a mic amp chip you can get down to and below 1nV/sqrt(Hz) with garden variety BJTs in differential mode, and ~4mA of bias current through them. Things you should pay attention to are frequency responses, as you need to transfer ~100kHz of bandwidth for a decent PI.

[Silver Dollar]

New pictures of the DD. I epoxied the coils into a housing that was already painted with graphite
and had a drain wire melted into the plastic. Then I painted some more graphite to make a
faraday cage. I kept some painted areas from the first painting from getting epoxy on them so
they could merge into the second painting and it worked!

I RVT'ed the wire into the strain relief to keep water out. Next I will connect the wires then flood
it with fiberglass resin. I hope it's not too heavy...