Updated Mirage PI (Ex Hammerhead)- Mono Coil, DD Coil or Super D Coil Options

[Elliot]

godigit1, what was the blue spike in your 3 pictures of the preamp ?

See posts #20 and #23. I'm hunting for a better psu design that is not TX frequency dependent -like the original Hammerhead design. Having the ability to tweak the Tx frequency is a good idea when detecting in various areas (as per the current design. When the integrator/cro takes an average sample, it tends to wash itself away, but I like to show the real world results here - warts and all (no hiding stuff like others do, I'm sure). Am trying a few mods for existing pcb's as well and will publish them here if they prove worthwhile.

[6666]

Having the ability to tweak the Tx frequency is a good idea when detecting in various areas

1200 PPS is a good place to start because you can divide it by 50 and 60 Hz

[godigit1]

godigit1, what was the blue spikey pulse in your 3 pictures of the preamp in post #56 ?

Hi 6666
Thats the coi flyback pulse. on MPP rev d , running at almost 2 khz
You could even add a couple Us to this coil if i was measuring from the fet to sample time. as has been stated by Carl.
I didnt know to measure there until recently.
Curious where sample time is on your small gold coil if you have tested it?

Hi Elliot ,
The coil in the picture is slower than yours. and has more capacitance.
Thats why Im interested in gold sensativity on your coil.
The coil is a folded eight mono coil designed and sold for digger john ( formally razorback coils) and Jimmy Sierra sells the exact coil but a bit larger than the Digger John .
Your coil stats are not that bad with a dual amp and op amp upgrade I think it could be a fully shielded 10 us coil. It would be interested to see after a amp upgrade.

Of my current test coils Ive only hooked one up. It should be the slowest one as its the highest inductance of the five coils. the rest of the stats are pretty close.
Currently its sampleable at about 6us from fet shut off, its not packaged up though so it will be interesting to see how much time is lost to shielding and cable shielding.




Ha ha on the gold filling Ive actually found one gold filling and two gold teeth and a silver crown between sled runs and sports fields ive hunted.


I use a 1.2 gram nugget tested at 20karat as one of my test targets. Probable close to your filling as far as TC. On the folded 8 coil on a the Mpp its about three inches as well.

[dbanner]

Has anyone come up with a design for a cleaner power supply for the +5V and -5V supplies. Using an NE555 timer to generate voltages adds small spikes to the power supply, and this gets amplified along the path. The attached photos show the following:

- Average voltages (+5V and output of pre-amplifier) - they look nice and clean
- Voltages by Time - lower trace shows the jitter as well
- Voltages by snapshot - can see the noise in the 5V transfers directly to the output of the pre-amplifier

Has anyone tried using a Low Drop Out (LDO) chip to smooth things out?

I came across this circuit, maybe can be tinkered with.

[godigit1]

Hi Elliot,
Mg Chemicals has nickle shield product called Super shield and also carbon sprays I grabbed the one called total ground its more for work surface so it has additives that make it abrasion resistant.
I was thinking it might hold up better at connection than the regular carbon paint.
I dont know if you can get them in Au though. I would think they would be all over the Au market as well.

I was running the max412 but telano turned me on to the 4562 so I have to give credit where due.
thinking you will gain more than a couple us with the double amp set up and then another couple by using a 412 or 4562 over the 5532.
These shots are just swaping amps on a MPP same coil folded 8 mono.
[ATTACH]47404[/ATTACH][ATTACH]47405[/ATTACH][ATTACH]47406[/ATTACH]
Stats on your coil are similar to the folded 8 mono I have for the TDI except your Capacitance is way better than the pro coil it has 2.1 ohms 280 uh 361pf 500Khz srf.

Im wondering if you have target tested any small gold with it. Curious if it gets gram size and at what depth?

Ive been looking at low loss forming similar to waht is done for radomes. Using a polyurathane foam can be almost invisible to the coil. There is no Diapole allignment in polyurathane or polystyrene. Pvc or abs on the other hand have instantainious switching of the diaploes as sonn as its hit with current.
My thinking is the foam as a form reduces capacitance pcv is good for the shell even though it increases capacitance it positive diapole allignment in my mind propagates signal admittance.
A example of this construction can be seen in the coiltek nugget shooter coils.
I was allready working this way when 6666 provided a link to their advertisement. It does not spell things out the way Im putting it together but to me that is exactly how those coils are made. And coiltek uses a proprietary shell material Polycarbonite. I think that also is diaploe reactive. cant find tests yet. And I think they put anti static aditives in it Not sure.
So wheather Im right or not Im still testing but thats my reverse take of a fast coil.

Here is the actual link that was provided in the spiral Pi thread by 6666.
https://www.nuggetfinder.com.au/spiral-wound-coils

After looking at it again I was wrong they are using ABS for their shells and the polycarbonate for the clevas mount.
The foam is closed cell vinyl foam.
Basically a expanded pvc material. So I was wrong about the foam they use as well.
Here is a link to some dialectrics for various plastics.
https://passive-components.eu/what-i...tic-materials/
I dont see expanded pvc it should be better than plasticized.

dialectric Testing is ongoing. on this product

https://www.brenntag.com/media/docum...h_brochure.pdf
I dont mean to side track your thread just thought that I needed to correct my bad.
Maybe Im overthiking the value of polarized vs non polar plastcs and dialectric within the coil.
Sorry for the missinformation.

[MartyJ1963]

Hi all,,,,Finally completed my 2 new Mirage Ultra MDDSD Ver 1.1 boards from Elliot. Big thanks to Elliot for all nagging I gave him in the countless emails I sent him during my build,,Great bloke and totally happy with the build. Just a couple of pics I thought I'd post of my 'Crivit hiking stick' detector shaft,,,Thanks,,,Regards,,,Marty

[godigit1]

Hi Elliot,
Im wondering if you or anyone else here has come up with a easy solution to the power supply noise yet?


Ive been playing with some filters and inductors and have cleaned it up pretty well I think.
Im no engineer so could someone here possibly take a look at this to see if its a viable solution.
Ive added a common mode choke wired in series with itself and in series with a 2.7 K resistor.
I tried conventional hook ups and inductor cap combos but this was the cleanest Ive gotten so far.
Following are scope shots from +18 at D9. Before and after wave form and zoom shots of the noise.

The filter was hitched inline on the positive rail only. Im not sure how this would act under load and I know its not proper use of a commn mode choke to wire it in series and all but it seems to be working.
The choke is two 188uH coils .



D9 +18 Test point before and after filter.





D9 Zoom of the noise spike.



Zoom of noise after filter.



Starting voltage was 17.50 after choke is 17.46.
My thought was to add this fiter inline to the output of the 555 hopefully to cleanup the +and -5 rails as well.
Is This a Bad Idea?
Is there a better way?
Thanks again.

[Elliot]

Hi Godigit1,
Your approach certainly appears to have cleaned up the power spikes. I'd suggest that you're onto a winner there!

[Sean_Goddard]

I made a suggestion for ULTRA fast coils a long time ago winding between two wooden plates but like this;

Firstly, decide which gauge wire you are going to use (litz is best) then look through a fishing products website for FLOUROCARBON fishing line which is the SAME DIAMETER as your wire. Now simply lay your wire side by side with the fishing line and wind a spiral coil. What you get is;

O = Wire
X = Flourocarbon Fishing line
- = Shield

------------------ ---------------------
XOXOXOXOXOX XOXOXOXOXOXOX
------------------ ---------------------

If you use "Guitar Shielding" (spray carbon) you will end up with a lightning fast coil that can sample as low as 5us.

Give it a try let me know what results you get, I built one for my modified Surfmaster and it is great at finding thin gold rings and chains at around 36cm in wet sand

[godigit1]

Hi Godigit1,
Your approach certainly appears to have cleaned up the power spikes. I'd suggest that you're onto a winner there!

Im thinking of winding a custom choke in a figure eight pattern. Eliminate the resistor. Thats why the common mode filter worked resistor just smooths it a hair but doesnt really lower amplitude any further so its not really needed.
With just the ckoke their should be no current drop.

[Elliot]

I made a suggestion for ULTRA fast coils a long time ago winding between two wooden plates but like this;

Firstly, decide which gauge wire you are going to use (litz is best) then look through a fishing products website for FLOUROCARBON fishing line which is the SAME DIAMETER as your wire. Now simply lay your wire side by side with the fishing line and wind a spiral coil. What you get is;

O = Wire
X = Flourocarbon Fishing line
- = Shield

------------------ ---------------------
XOXOXOXOXOX XOXOXOXOXOXOX
------------------ ---------------------

If you use "Guitar Shielding" (spray carbon) you will end up with a lightning fast coil that can sample as low as 5us.

Give it a try let me know what results you get, I built one for my modified Surfmaster and it is great at finding thin gold rings and chains at around 36cm in wet sand

I've been racking my brain about best to space the windings, and this is a brilliantly simple idea. I wonder what the dialectic constant is for fluorocarbon fishing line?

[godigit1]

A one wire space is the best Ive found so far .
At 1 wire space you get a nice reduction in capacitance with some loss of inductance.
At 2 wire space the capacitance gain is very little in comparison to the induction loss. I ve done six different coils with no spacing to two wire spacing.
They are in the spiral pi thread I have to target test them still.
You can wind a spiral and space it on double sided tape. just three 40 or so inch lengths of wire to lay in as a spacer then leap frog the last wire forward and peel out all the spacer wires at the end you get air as a dialectric. then transfer the coil to urathane foam.

I havent been able to find a way to make a spool as Sean suggests where I can remove the spacer but if a good dialectric and proper diameter is used it should be fine I would think.
Currently working on a 3D ss dd for the mirage.

[surfdetector]

Been trying to post a simple 555 power mod to stop the hash ripple but forum is acting up

Any chance that you could try again to post this mod that you are referring to?
Cheers

[surfdetector]

Any chance that you could try again to post this mod that you are referring to?
Cheers

BUMP........

Hi 6666,
I am interested in seeing the mod that you were referring to in post #25.
Cheers

[6666]

BUMP........

Hi 6666,
I am interested in seeing the mod that you were referring to in post #25.
Cheers

Its just a hash filter for 555 power rail.