Homemade gold detector?

Hi,

Just wondering if anyone has built their own metal detector? Just getting into gold prospecting and got the basic gear, however the prices for a reasonable detector to me seem way too exorbitant especially for the amount of hardware that's involved and the relatively simple technology used. I'm not too bad with a soldering iron and know a bit about electronics.

Looking to go gold prospecting with Dad to Hills End and will hire a GPX 4000 for 5 days (cost about $400) however will like to build my own down the track, anyone done this?

Cheers.

captpaul10101 wrote:

however will like to build my own down the track, anyone done this?

Cheers.

I think Minelab have built a couple

Hi Captpaul, do a search of "Grant's DIY PI Detector " cheers Pete.

ps I don't know how to do a link.

Here you go CaptPaul

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

Ok thanks for the link, looks like an interesting project.

Has there been any thoughts on making a detector that discriminates gold from other metals? Would save a
lot of time chasing nails, bullets etc

Cheers, Paul.

Hello CaptPaul

Last year I built a pulse induction metal detector named the wahc and is design by a russian. You can blank out iron objects and also has an identification tone on different metals. I use a Minelab 11" monocoil, but it is not spectacular on depth, but find it good to use at parks and at the beach. At the gold fields its useless as it has no ground balance. It can get unstable at times but can be reset with a press of a button. I also built a barracuda which is a simple beach pulse induction detector and with an external amplifier and a op-amp upgrade, goes deep on coins & rings. The wahc is a more involved project due to the atmega8 chip in which the hex file needs to be uploaded. You can purchase the kit from silverdog.co.uk, for a reasonable price. If you know how to build a avr isp programmer you can upload the hex file yourself using ponyprog2000.

http://fandy.vov.ru/Chance.htm
http://www.geotech1.com/forums/showthread.php?t=18079&page=3

I have bread boarded one of these http://www.ebay.com/itm/232173745361?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT and it works quite well. It is better suited to beach detecting but will find gold (0.3g and upwards)in tough ground.
It is not a depth giant but will find Aussie 20 cent coins at better than 30cm in an air test. I have no doubt it will go better than that in wet beach sand.
You will have to provide your own stem and control box, coil, head phones and battery (12vdc  gell cell or AA NiMH. even good alkaline AAs. The cct draws just 37ma so it is easy to make a power pack that will run the tecta for a good streatch.
     Ready made coils are avail. I opted for an 8 inch (Mono Only).
The tecta has Sensitivity, Volume, Delay, and Threshold control.
   

Assembly instructions are few and far between but the seller is very cooperative and will provide info as required and is fast to reply to emails.

This is what you will get if you purchase a ready made coil. You will have to provide everything else.

This kit cost approx 85 AUD. So after adding a coil, and other sundries you will be up for around 150AUD

Adrian,
I've built the same pcb but would like to buy a ready made coil to suit as I don't have the neccessaries to build my own.
Can you tell me who you purchased the 8" coil from?

Bicter What's your budget like, maybe you would consider the new detector who's name cannot be mentioned go http://www.goldsearchaustralia.com/our-products/interfacion-s-detectors.html

Or look for a used GPX 4000 minelab!

Dave

Dave,
I already use a GPX5000, an ATPro and a Safari. 
I'll only be using this home made job on the wet sands where I don't want to take the Safari(not waterproof) and the ATPro is too noisy.
Rather risk a $75 pcb than a $1200 minelab.
Regards

I got the coil from the cct board seller.

Some kits here.
http://www.ebay.com/sch/i.html?_odkw=pulse+induction+metal+detector&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.A0.H0.Xpulse+induction+kit+metal+detector.TRS2&_nkw=pulse+induction+kit+metal+detector&_sacat=0

The coils are actually easy to make. It is just a matter of whether you can be bothered to do it.
There are other coils on Ebay from Bulgaria and RUSSIA and from what I can figure , these other coils will work with this detector. It has a low pulse rate of around 700 pps although i am not 100% certain of the exact rate..

Starting to take shape...veeerrry slowwwly.

I know the thing works, so I will finish this one.

Looking good so far Adrian, be interesting to see the finished product. Keep up the good work.

Cheers.

Mike.

Almost done with the control box. It passed a dynamic test. Just a few minor details to take care of now. Like make the stem and decide where to put the battery box. but Most likely under the arm support. Will be running it from 8 x AA NiMH 1800mah. With a max current draw of approx 38mah they should drive it for 30 to 40 hours. If I get 30 I will be happy. 

Nice work Adrian, I ended up ordering the same kit/coil.
A couple of questions:
Did the coil come fitted with a plug as I see you're using a 5 pin connector similar to the minelabs connector. 
If same type as minelab can you advise where you purchased it? 
Also will you be trying it with a minelabs coil?

Terry

HI terry.
What you see in the first pic in this thread is what you get. No plug on the coil. You get the very bare essentials

The connectors and all the other stuff came from Jaycar. 

They have some of those older style two and 5 pin connectors which is great. I have been trying for yonks to find those. Just a couple of bucks ea.

No the detector will not work with ML coils. This tecta operates at around 700 pps (I have not taken an actual  pps reading yet, maybe tomorrow)and I thought it would not be much chop on small chains but it is better that anticipated

The coil performance is significantly effected by the type of coax used and needs to be very low capacitance and ohmic resistance. Not more than 2 ohm and preferably much lower.

I will post some coil winding info here in a day or so.

Thanks Adrian,
I purchased a ready made coil from Tacoma56 to use as a reference when trying various coils.
Have you investigated making a "fast" coil to improve the response to small gold?
I'm a bit surprised the ML coils wont work as they are generally around 300uH and <1R, may require changing the damping resistor.
Terry

N/T

N/T

Adrian,
Just a thought, are you suffering interference in your area which may affect your results?

The thread below gives an indication of improvements using a basket coil

http://www.geotech1.com/forums/showthread.php?22092-Please-tell-us-how-your-wonderful-deep-penetrating-Surf-PI-1-2-coil-is-made/page2&highlight=Smpro

Relevent Extract:
For your review!! And thank you Chet and all for convinceing me to finally try a basket coil out.

Basket coil#1 002.JPGBasket coil#1 001.JPGBasket coil#1 005.JPG


I just finished this basket coil for my Sm pro kit. I used 30 guage radio shack plastic coated wire.
I used the form provided on the Chance Pi coil thread . It is working the best of any of my coils so far. I am primarially looking for gold sensativity in my coils and use the earing in the pictures as my minimum acceptable target. (earing weighs .5 gram) Before this coil with regular fast coil design I could only get it at 3 inches with a 4 inch coil.

Super suprise when I got it all tuned to my Pi I can now hit the earing at about 4 inches with this 8 x10 basket coil.
I also changed out my 5534 for a max 410 and the differance was huge as far as waveform clarity. I will provide some scope pictures when I get it hooked back up. I removed it to put on my last wrap of teflon.

So here is my improvement to the basket design using small guage single strand wire and every 5 wraps I wrap two layers of teflon tape to increase spacing and dialectric and hopeing to reduce capacitance. Also the tape holds the windings in form on the coil form as the oval shape makes them want to pull out of form on the sharper corners.
I went 20 wraps but had to remove one I tried two but had to put one back 19 works well.

The rock in the pictures is a hematite chunk I use for a ground sample. the coil does pick it up slightly but with audio after you leave the target. And almost providing the boing sound that a vlf does on negitive cold rocks. I can place the sample in the center of the coil and it does not effect my depth. If I use it to shield the nugget I still get the nugget as positve response. This peice of hematite totally overloads my VLF detectors and the ground it came from was undetectable. I am no expert in coils and there may be inhearent problems with this coil I have not had it outside yet so that is still unknown. It does have slight sensativity to my hand so that may be a concearn and i may have to shield it.

Here are some of the depths and I have the sens and threshold almost completly silent, when I get outside Ill be able to crank it up and I cant wait to see
if the depth will be close in the ground.
1/2 gram earring 4 inches
1.2 gram nugget almost 7 inches
silver quarter 7 inches
silver dime 8 plus
nickel 10 plus
2 gram gold ring
10 plus
and these are good responses I can hear with my headphones not on my head but around my neck.
Also as Kt 315 has stated I think this design would lend itself for a dual wrap. notch the tabs in the center and wrap a tx or rx coil over the center coil Im not sure which would be on the inside.
you can bet Ill be playing with that...
Hope this can be of use!!

http://www.geotech1.com/forums/showt...-the-MPP/page1 KRinAZ has some improved Basket weave templates in the last pages

Yes a lot of EMI here. I am certain that performance will be better and threshold much smoother when I get the detector away from my place.

I have an unfinished 11 inch coil here somewhere. Will give it a try when I find where I hid it.

I could not get any of those links to work?

Adrian, the first link worked for me but the second failed. It may be that I was logged on, so will see if I can get the link to work for you

Edit: OK it looks like you need to register and be logged in toview the thread

Regards
Terry

Found the 11 incher.
600uh 6.8 ohm
Works fine.....and no coax or shielding. 

So I reckon you could stick a tyre rim on this thing and it would work 

This is the partly finished 11 inch mono.
Who said Womens undies clothes line hangars are no good for anything else. 

Here is some coil winding info for coils that will work with a lot of these Ebay detector kits.

They are all Unshielded coils.
I will put a shield around the 11 inch and see what happens. Have also tried a couple of different coax coil leads (from Jaycar) and cannot pick any performance difference between them when hooked up to the 11 inch.

18/02/17

Tried shielding the coil but can not get satisfactory performance with any of the coax leads that I have on hand. (0.3, 0.4, 0.5 nf ?
The shielded coil works fine with just plain unshielded twin cable.
Unshielded the coil works with any of the mentioned coax leads. I am getting best performance from unshielded coil and non coax cable.  
The coil has  minimal response to maghemite and iron stone and zero hand capacitance or salt  effect.  


22/02/17

Slowly coming together with 11 inch Shielded coil. and un shielded coil cable.
A bit of work still to be done on the coil
Seems to be working fine.
Will take it to an EMI quiet place tomorrow and do some air & in ground depth tests.

Adrian,
Looking good.
My order turned up the other day.
Some comments:
COIL - A bit light on the potting of the ears, as a result I think there'll be too much flexing in use, followed by possible premature failure of the housing. I've pulled it apart and now adding epoxy for more rigidity. Following that, and after testing and playing round a bit, I'm going to make sure it's fully sealed/waterproofed.
PCB assy - The board looks well made, main disappointment is the fact the schematic doesn't match with the PCB provided. One pot has been changed to 20k and the component designators don't match the schematic designators. The PCB doesn't have any version control or identifiers in place so theres no way of knowing of any changes that may have been implemented in consequent deliveries.

Regards
Terry

Agreed. The ears are tragic and the coil housing is  weak. A bit of a disappointment although mine does work ok.
The 11 inch is working fairly well and is strong but I am doing another one with lower inductance .359 mh and 1/2 the resistance of the first one , about 2.5 ohms. Will be interesting to see how much the performance differs.

Did you get the same cct board as per my pic at the start?
I did not have a schematic. If your board is the same as mine then I can tell you where each pot connects.

I got the same board, thanks for the offer but I've already sorted that stuff out and actually turned my Tektronics dual trace 100mhz on for the first time in about 7 years

That's about when I last turned my D Smith special on.  

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. 

Finally had time to play with the kit jury rigged on bench this morning.
Depth was approx 11" in free air on $1 coin
Settings were:
Volume - maximum
Pot R2 - set to 2.5k
Pot R10 -set as close to zero as possible without it taking off, approx 210mV
Threshold -
Delay - fully ccw (must be opposite to Adrians)
Sensitivity - fully clockwise

Mods
Audio O/P - fitted 1k/8R transformer and speaker
Fitted 100R in parallel with R34 (150R) to increase audio.(one of the recommendations is to swap Q6 (MPSA13) with MPSA14)

Now all I need to do is ensure the coil is closely matched to the PCB Assy to minimise ringing.