My detector builds-so far.

[Guest]

This is the basic circuit I have been using. From Colin Mitchells Talking Electronics site.

This has on-off and a dual frequency switch. Two separate pairs of different capacitance Mylars are switched to earth. The transistor is precision mounted on the radio for maximum signal.
The adjustment is done via a 10 turn 100R pot (the knob). Very easy, not too touchy. This is in the coil-only circuit.

The wheeled coil started out as an inverted figure 8 coil, but after experimenting it was double looped, then made into a boomerang/arrow shape to fit under the board. The 6 inch has a groove cut around the 12mm ply with the .25mm enamelled wire wound into it. Coil covers are made from heat molded thin cutting boards from the cheap shop.

This is the same circuit doubled up to make a Beat-Balance detector.
The X spot and 10Ks haven't been tried yet-the detector below basically has a built in AM radio receiver and ferrite coil.

Coil shielding is shiny powdered milk packet. This coil was originally made and tested on a Matchless-shield requires no earth wire.

This is my Surf Pro DD in the box, with 3x18650 holder. The little boards sitting there are 1/2/3/x 18659 charge controllers, so I can plug it into the cig lighter to charge. And I have a 1w solar panel to mount on the detector as well, so it should basically never need charging!

This is the sniffer XR71-a complex beast that can handle up to a 2 metre square coil !!

I have bits and pieces arriving in the post all the time. My Matchless detector need a re-board( make my own PCBs) and the latest purchase is 10x TL074CN chips($2.74) for a different Scarborough BFO-super simple. I'll be trying all sorts of coils to get a the most out of the simplest circuits. Pulled the ML 10x5 apart when I got it to see how they tick.

 

[silver]

Thanks for sharing Tim,..I'm gobsmacked mate,... good on ya,.. I love it, all held together with ticky tacky,... keep us informed,.... I like how if the finds run out you could at least listen to the news or talk back radio too.

 

[kawman]

very interesting mate.. please keep this thread going so we can all learn a bit from your efforts..

 

[Mackka]

Great stuff Tim. years ago a mate of mine made is own and for the coil he used a Frizzbie and filled it with resin.
Cheers
Mackka

 

[Guest]

Cheers all. The radio jobby actually works quite well-110khz, smallish coil. Sometimes in the trash it's no advantage having a super-sensitive dooflanga.

Had a play with the old Garrett ADS the other day- I can get that old codger on par or better with the GMT. Now I'm in the process of getting a Groundhog with the 2 coils and all accessories and box.
Also came across an SD down the road today.(not sure which one yet) Old mate has a stuffed back and can't use it. He couldn't sell it for $900, now he wants $700, so I will have a look at that too.

 

[Guest]

Thanks for sharing Tim,..I'm gobsmacked mate,... good on ya,.. I love it, all held together with ticky tacky,... keep us informed,.... I like how if the finds run out you could at least listen to the news or talk back radio too.

Actually Silver on the 70khz setting I CAN listen to 801 5RM at the same time !!

 

[BigWave]

I loved building these machines. Built my first VLF at 17, but got hooked on PI technology. Built 2 PIs in 1965 (age 21). First one saw my elder brother go head first into a river with it. On repairing, it was shortened into a cave detector where I used it to detect beach-side caves in Perth. Found plenty of coins (pre dec and new) They were where the sand met the cave walls. The second is still with me (was used for detecting underground water pipes etc) pictured below. No idea how it stacks up against modern machines. The battery will be stuffed, but I've now got the itch seeing this forum to get it on its legs (hard for me these days).

Shows the electronics box (moveable for balance), the speaker and the Stanley Plane handle.

The coil was wound into a pool filter cover attached to the shaft.

The threshold was set by the pot on the front panel.
Will post how it stacks up against the 4500

 

[Dreamwalking]

Tim, I love the innovated design ... not only have you made it easy to run your coil around under your trolly ... but it also serves as a way to help you wheel your nuggets home .. hope the wheels can cope with any unexpected weight.

Cheers

 

[Guest]

She might take a bit of twiddlin' to match the 7000 though mate.
I posted these in "today I made" but I spose I should gather 'em all here.

The Surf Pro DD, with 1w solar charger(not pictured) and Li-ion charge control board alongside battery box.

This is the coil I made(Mono)-paint still drying- it was 290 uH, but with the milk packet shielding and lead wire it will be over 300uH. They recommend 300-350uH. The ML Commander(DD) was 380uH. It works good, but mine is less than half the weight, and is of comparable sensitivity. Still not up there with the GMT, but an excellent all-rounder all the same.

This is my next assembly- the Sniffer XR71. It runs at 450-500 uH and can take up to a 2Msquare coil, but I will attempt to set it up for small gold. It's a tight fit in this box- I had to slot it from the outside because I don't have a Dremel(yet).

 

[Guest]

Tim, I love the innovated design ... not only have you made it easy to run your coil around under your trolly ... but it also serves as a way to help you wheel your nuggets home .. hope the wheels can cope with any unexpected weight.

Cheers

Cheers Dreamwalking. I tested the little coil on the secohmmeter and it's 880uH- to much for a PI, but I'm hopeful the wheeled thing is less, so I may be able to use it on the Sniffer maybe.

 

[Dreamwalking]

Tim, that secohmmeter kit you acquired, have you test it against any commercial made meter, just wondering how accurate they are.

 

[Guest]

Nah mate- I don't have anything to test it against. It is preset for inductance and frequency, but there is a trimpot to calibrate capacitance. As this is my first PI build, and the first experience I have had with non pre-set values it is a learning curve, but I am relatively confident I can get close enough to the mark to make fine tunings via observation. I am yet to fine-tune the Surf. It was pre-tested, offset at 0v and R10 @ 2.2K, which is by definition the least resistance/ most sensitivity available at the coil. For a homebuilt board they say start at 3.3K and reduce to get most sensitivity, suggesting a 2.5K max.
I am reasonably sure the secohmmeters' inductance is accurate, and I probably could not improve the performance of the Surf anyway.
To be honest I am quite chuffed with the performance. It is on par with my Infinium- they are about $2 grand now. The built and tested board was $100+ postage, add a few sundries and a box and I'm still under $150.

 

[Dreamwalking]

Thank you for that info Tim, I had been looking at getting one of those BIY kits just to play with just so I could comment on it, if asked by someone "what do I think".
Now that you have done my homework I'll get a bit of extra free time to go for a swing.... LOL ..
I'll have to start watching under members finds for your results... Hope you step over a big one that calls your name real soon.

Might have to put our heads together (<<< that's a pun if I ever saw one) and create a better detection sound .. 5 voices warm... warmer... "BINGO"... colder... cold

Cheers

 

[Guest]

Another success story today- the Sniffer XR71 is up and away. Not assembled on a stem yet, but a goer.

All together after a few headaches- a very tight fit. Then I couldn't get anything but noise- one of the wires to a switch was touching one of the pots- pulled the top off, and away she went. And yes, that's the 300uH coil for the Surf there. Out of desperation I was trying that one when I pulled the top off again.
The beauty of having circuits with external pots/ adjustments is the range available for experimentation.
This one has the Li-ion charge controller, like the Surf, so can be charged from a cig lighter, 12v supply, or the 1.5 w solar panel I have for it also.
No paying some rogue for an exclusive charger with an exclusive plug people.

This is the 50x30 coil I made for it- 450uH-bugger me dead, it works on the Surf too!! Getting a dollar coin at 2 feet!!
All the brackets are made from pvc sewer pipe-same as my armrests. Cut, then flattened and molded with a heat gun- I'm getting pretty proficient with it now.
The windings are cat5 computer networking cable (from the cheap shop) with the internal wires joined end-for-end. The last 2 rounds are joined but the neg. is connected in there for the right impedance- I'm presuming the 2 open-ended rounds are acting as a shield of sorts.

 

[Tathradj]

The Xr71 has me real interested.
Can I have a link please. ?

 

[Guest]

Cheers Tath I dunno if I can do links, but they're on Ebay-bids start at $100US, which you can usually get them for, or his website is Crazy-tech (.com).
I quizzed him about the best one for small gold and he reckons the Vandal pulse2- it has 3 different operating frequencies you can select with a jumper. Much smaller than the Sniffer. Tomorrow I'll try the 880uH wheeled thingy just for interest.

 

[Tathradj]

Struth.
Operating from 120Hz to over 600hz.
That has me thinking. 8)
Many Thanks.
wonder if I can set up a small digi display as it uses a micro controller.
.
Cogs will run dry on this one. LOL

 

[Guest]

I'm pretty sure he has others there with digi displays, and an upgraded Vandal with one already. He sells the displays separately as well.

 

[Guest]

I've been out in the shed making pvc fitments for my detector shaft today. Just back inside having a fiddle. The wheeled thing(for my BFO) is 1161 uH- but it does work on the Sniffer. Likewise the small BFO coil. And the 3 PI coils I've made (so far) all work on the BFO as well. This opens a whole scope of mix'n'match versatility for me.
Not sure if any of the high inductance BFO coils will work on the Surf yet though-probably, as it also has adjustable delay/thresh/sense.
Down the track I may reduce the R on the volume of the Surf, but for now I am using the [volume controlled] headphones I fitted a mono plug to yesterday, and it screams through them.
The Sniffer I have worked out on the bench- despite having 7 knobs- most settings on zero (some are reverse wired so zero is max) noise-sens-grnd-gain. Tune for manual tuning, and [reversed] thresh full up for manual, but reducing for max sens when on auto.
Neither of these are gold beasties though, so it looks like the hunt continues there. I have a Tesla-style 6 inch coil wound from cat5 networking cable with the glue drying that may-or may not- give me the sensitivity I desire.

 

[blennus]

New to the forum here (just searched for prospecting on Facebook and found the group)... my family and I are about to move up to Ballarat (end of March) and one of the main things I've been looking forward to is a bit of prospecting... I've panned a bit... but got the idea it could be fun to get a detector. Hadn't even thought about the possibility of making one until I saw this thread so thanks heaps Tim... I have a new DIY project to research and get stuck into (last one was making a home theatre projector). Looking forward to hearing of any gold you come across with your detectors.