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Offline leftfieldTopic starter
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« on: August 13, 2009, 08:49:17 pm »
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Hi There,

I stumbled across

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a while ago, and it seems like far too much fun not to try using my computer sound card as the basis for a metal detector. I have a  rusty background in electronics, though I excelled in it at the time (20 years ago). The plan is eventually to wind my own coils, write my own software, and make a VLF detector... or have fun trying.

For step one, I decided that getting a bunch of search coils, and using some free-to-try software (

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www.virtins.com
) would probably be a good idea - use heads that are known to work, and software that is known to work, and see if I can make them talk. After that, I'll change whatever seems to be the component most within my grasp.

On my desk right now I have on my desk three coils from a Garrett detector of unknown model and vintage. They all have a 4-pin connector... and first up I'd like to know what the 4 pins connect to - had no luck finding that out so far.

Next... some idea of the voltage levels and frequencies involved would be handy. I'm told the "Deepseeker" coil operates at 5.5kHz, but I should be able to confirm this using an LCR meter to determine the coil characteristics, and then calculate the resonant frequency - yes?

Any technical information about the Garrett coils would be handy - measuring the outer diameters, they are roughly 4.5 inch, 7 inch and 10.5 inch... but only the small one is labelled as "Garrett - the electronic prospector - Deepseeker" (all other labelling has worn off the other two).


And that's probably enough to get me started... aside from comments like "are you nuts?" or "that's far too easy - try this..." or similar.

Cheers,
Paul,
Auckland,
New Zealand.

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Offline leftfieldTopic starter
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« Reply #1 on: September 07, 2009, 05:19:31 pm »
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Thanks to useful discussion on the

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Garrett Groundhog ADS Schematic
thread, I have mostly resolved this.  What I found was this:

* I have three coils - a 3.5" co-axial, a 7.5" co-axial (?? - the phase response as I sweep an object suggests it is co-axial, not co-planar) and a 10.5" co-planar. I don't have a detector connected to them - I'm just looking at the properties of the coils themselves when hooked up to my computer sound card.

* the only way the three can be connected up the same way and give sane responses is if:
  Pin 1 = shield and Rx (signal ground?)
  Pin 2 = Tx
  Pin 3 = Tx
  Pin 4 = Rx

* Connecting up as per homefire's observations in the

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Garrett Groundhog ADS Schematic
thread gives a response... but not a consistent one that would let coils be interchangeable.

* Reversing the Tx/Rx circuits compared to what I've just described also gives a response, but a lower one... and I'm guessing you'd want to shield the Rx circuit more than the Tx

The pin numbers are what I read looking into the plug on the coils, and are numbered going counter-clockwise from left down then across up to the right.

Now I'm just left with this mystery: what is wired up inside that allows...
   * Interchangeability between co-axial (1 Tx coil, 2 Rx) and co-planar (2 Tx coils, 1 Rx), and
   * Gives a response when you cross the Rx/Tx circuits

I really like the response of the co-axial coils (simple phase relationship - easy to write software for) so if anyone knows the internals, I'd love to find out.

Paul.


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Offline homefire
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« Reply #2 on: September 07, 2009, 06:32:46 pm »
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What a Hoot!

I just opened up a busted up 14" coil and again Pin 1 and Shield .

I think your right.

They have 2 and 3 as TX and 4 as RX signal.

Why they split up the pairs?Huh?   

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« Reply #3 on: October 30, 2010, 02:00:10 am »
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Hi Paul,
Hope you can help me, have just bought a Garrett Beach hunter AT3 and think the coil might be faulty.
Could you please contact me, as I am also in Auckland, 2984619
Need some specs on the coil plug connection
Thanks
Noel

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Offline Paul A
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« Reply #4 on: October 30, 2010, 05:16:48 am »
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Hi,

The Shield wire is on Pin 1
Black wire is on Pin 2
Red wire is on Pin 3
White wire is on Pin 4

If there is a green wire it is not connected to anything, also if it is a 5 pin connector there is nothing connected to the center pin.

Best way to check for a "faulty" coil is with a field strength measurement.
Goldigger1950 put an easy field strength checker on here (which works really well)
Bu**ered if I can find it now though.......





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Offline GoldDigger1950
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« Reply #5 on: October 30, 2010, 03:00:18 pm »
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Quote:Posted by Paul A
Hi,

The Shield wire is on Pin 1
Black wire is on Pin 2
Red wire is on Pin 3
White wire is on Pin 4

If there is a green wire it is not connected to anything, also if it is a 5 pin connector there is nothing connected to the center pin.

Best way to check for a "faulty" coil is with a field strength measurement.
Goldigger1950 put an easy field strength checker on here (which works really well)
Bu**ered if I can find it now though...


This might be it, mate.

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http://thunting.com/smf/metal_detectors/transmit_coils_testing_procedures-t18215.0.html


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It's all about that moment when metal that hasn't seen the light of day for generations frees itself from the soil and presents itself to me.
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