Homemade gold detector?

adrian ss wrote:That's about when I last turned my D Smith special on. .......Would you believe that the forum would not allow me to type Smithies first name.

Tried the lower inductance un shielded coil this morning (348 uh x 2.5 ohm) and result is less sensitivity than the 714uh 6.9 ohm job. Although it is more stable and less effected by EMI.
I obtain similar result by turning down the sensitivity of the of the 714 combination.

Mannn I must be getting old.  When I reconnected the big coil the bloody thing would not work and after ten minutes of trying to find a bad connection and a bit of cursing I discovered that I had turned the flippin delay fully ccw. 

Adrian,
Info on the web suggests the original coil provided for the SMPro was 230uH @1.37R

Geotech recommends between 300-350uH

Also they strongly recommend that each coil should be individually damped to minimise ringing.
From http://www.geotech1.com/forums/showthread.php?22116-How-do-you-determine-the-value-of-the-dumping-resistors-for-a-balanced-coil-without-an-oscilloscope&highlight=damping+resistor
"The bottom line is that you need to make the damping resistor adjustable:
10k pot + 200R series resistor, both in parallel with 1k2 resistor.
Adjustment range is between 171R and1k1."

and (using an oscilloscope) adjust the signal at the preamp output for critical, or very slight under-damping.

Trying some braided copper shield tape on another 11 inch  coil. It seems to be working well at reducing EMI when used in conjunction with the screened twin core cable. (Not coxial). 

Tecta is finished and working fine. It is a bit fussy about EMI. Is best suited to beach detecting.
Also this unit will operate with coils up to 1 sq mtr

Adrian,
Neat looking unit
Which coil did you end up using..... and also what did you use for the lower shaft?

The lower shaft is an old Vsat  part. The elbow cuff is from Dean at Gold Search Aust. The upper stem is a plastic covered  22 mm metal broom handle from Bunnings.
The coil is a home made job 10.5 inches Un shielded.....It needs to be shielded because EMI response is a bit tragic with this one. The coil upper housing is from  a bloke in Bulgaria (Ebay)The coil lower plate is particle board coated in clear epoxy resign. The bits and pieces for the control and battery boxes are from Jaycar Electronics. The HPs are just an old set of 8 ohm stereo jobs. The upper handle and stem is  also from the remains of the broom handle cut in half and joined with a plastic pipe T Piece joiner and I have actually forgotten what I made the handle out of.  But it is plastic and wrapped in black foam and electrical insulation tape......That bit might not last very long.


A bit later this morning.

Took the detector out for a test run and it is ok. It is not a sand Shark or Infinium but does all right. It can locate 1 and 2 dollar Aussie coin at 12 inches in wet or dry river sand with the 27cm coil (just) and breeezes through rocks that stop my safari.
     The threshold is slightly jittery but can still be set to just on audible and still pick out the weak signals. The auto re tune is a bit rapid and can tune out weak signals after a few sweeps over the target, so it is necessary to pause momentarily between scans when pinpointing weak signals.
     The detector does detect the Earth's static magnetic field but is only noticeable if the coil is raised rapidly above the ground while facing N or S and standing on one leg while pickin yer nose, or if you spin it around through 360 degrees of  compass headings........Not often that a detectorist needs to do that Hey!  Unless he is pissed. 

     The rim of the coil pinpoints well in tight spaces.

I tried it in the water and it would appear that my attempts at WP ing the coil has been successful for shallow water (6 inches deep approx )detecting.
     There was no noticeable change in the threshold when going from the dry into the river water. 
At the moment I can see no reason why it would not perform well over salt water beaches and even in some lightly mineralised gold fields. The detector does not respond well to sub gram up to 2 grams gold nuggs.  Therefore at the beach I doubt that it will detect gold chains below 6 or 7 grams all that well, if at all.

The way I have made the coil has created a sand trap so I will either have to make cut outs in the bottom cover plate or attach some light plastic over the top of the coil.

     Over all I am satisfied with this detector for an outlay off around 200 dollars tops which includes enough bits and pieces left over that will go towards another coil and another detector that I have in waiting.

Adrian,
A good summary, thanks.
Let me guess..... you tested it at Pine Island? I used to live at Bonython

Yep. Pine Island it was.
I have been detecting the Canberra picnic grounds and parks since 91 with a wide array of tectas and still keep finding stuff, even after every other man and his dog has been and still is, doing this place to death. 

Thank you, your information was very helpful. Greetings from Uruguay

Hi Eduardo1173.
Welcome to the forum.
Glad to have been of assistance.

Does anyone have details like schematic or manual for the detector kit built by Adrian and Bicter above? eBay links dont work, seller is no longer around, and can't find any references to it online.

Specifically looking for a kit with Sensitivity, Volume, Delay, and Threshold control, but my Baracuda does not have all of that.

Thanks
Luke

eLuke455 wrote:Does anyone have details like schematic or manual for the detector kit built by Adrian and Bicter above? eBay links dont work, seller is no longer around, and can't find any references to it online.

Specifically looking for a kit with Sensitivity, Volume, Delay, and Threshold control, but my Baracuda does not have all of that.

Thanks
Luke

Here you go, this is where I got my Surf PI Kit:

https://diydetector.co.uk/store/index.php?id_category=12&controller=category

I built the Surf PI longboard kit here are the details along with how to build your own coil and how to make your circuit boards:

https://golddetecting.forumotion.net/t6394-grant-s-diy-pi-detector

Hope this helps.

eLuke455 wrote:Does anyone have details like schematic or manual for the detector kit built by Adrian and Bicter above? eBay links dont work, seller is no longer around, and can't find any references to it online.

Specifically looking for a kit with Sensitivity, Volume, Delay, and Threshold control, but my Baracuda does not have all of that.

Thanks
Luke

Just about all the information you need can be found here: https://www.geotech1.com/forums/forum.php
The Surf PI that I built worked satisfactorily but the equinox left it for dead