VLF MD (by Sascho - Varna)

[tiktak]

Hi

Hi,
Nice work Leto!
You got it!
Can you tell me what are other Transistors?
I will try to prepare a picture with labeled parts.So the things would be easyer.
If I wanna wind 20 cm OO coil for this detector with 0,3 wire how much turns should I try?
Thanks
I will try to make and try this one in next couple of days.

Za golemite maistori. Imate dumata za kritiki i opluwane.
sascho

[aft_72005]

Hi Leto
good work.
Please say more about performance.
Detecting range with 2cm coin and discrimination.

[Leto]

PCB

As promised here are PCB files. Original AutoCad (.dwg) drawing is included + some generated raster files. PCB dimensions are 15 x 6cm.

[Leto]

eagle has landed..

Hi,
I could not find that PNP pair so I tried with good old 2N2907 for TX transistors.
Coils made for testing have folowing params:
Tx ID-12cm, 128-Turns (64/32/32), 0.2mm wire
Rx ID-12cm, 128-Turns, 0.2mm wire
Resulting Frequency at first 779kHz
First I checked power: Voltages were not symmetrical (+3.2V,-4V), I removed 3k resistor to get voltages right from 393 voltage splitter - mistake in drawing?
40mA overall consumption.. Treshold can be adjusted to hear nice and very loud tone (25ohm speaker), meter circuit can also be adjusted - zeroed very well.
Further I tried to null the coils and when I had them in proper position frequency went to proper range - 5.85kHz. -> Quite strange, I never seen that before when adjusting coils? Also have to check those 150nF resonant capacitators..
IT WORKS!! From start? I actually did not belive my ears at first.
50EU cent - 26cm in the air with 12cm coils - pretty good as I even did not troubled myself with fine adjustments..
Things to do further:
Make better coils with thicker wire (0.3mm).
Attached is simillar oscillator - I have to figure out power control - more usable than sensitivity pot.

[tiktak]

Hi,

Hi,
Happy New Year!!!!!
How are you?
I wish everithing nice to all!

Thanks Leto!
Now I get it I just have to conect 2 wires one when I reach 25 and one when reach 50-th wind on L1 so I get 4 wires for L1.
You have explained this like I expected understandable.
So L2 is 100 windings and thats all?
What wire should I use?0,25 like for TGS?

Leto my hunch is that Pn4393 variant is better!
I still cant make my self a PCB for this scheme.
Please if you have time draw me such PLEASE I will remach to you somehow!

Have you finish this PCB on picture?

[Leto]

Hi,
Leto.
Thanks for the fast reply.
I am happy to hear that you are well now!
I have read this tread couple of times but because I dont have this kind of education I cant find my answer there buy my self.I am entusiast.Please explain about L1.
Thanks.
I wish you a happy new year.

Hi tiktak,
L1 is just normal coil with 100 turns of wire with two coil taps; first at 25th turn and second at 50th turn.
In other words: it is single round 19cm dia coil with 4 exit wires.
"Coil tap" is a point in a coil where you connect extra terminal likewise in transformers where you have taps on output coils for different output voltages.
Sorry, but my english language sux, hope it is understandable..
I do not have any formal electronics education also, but hired from small excavation team and slowly finishing study of archaeology this electronics stuff is just a BIG distraction for me. I trust other guys on this forum with more knowledge to assist me in case of problems, doubts etc..
This is the true reason why I started this thread.
Yes Max, you are one of those guys. BIG thanks.

[Max]

I did just that but no reply - possible vacations.?
Actually I dont mind. On Nexus webpage, Nexus Standard SE - product description text says: >>Its design offers versatile use on most inland sites and salt water beaches around the world including sites with heavy mineral deposits and black sand beaches.<<
Probably thats also the answer I'll recieve from Georgi. I adressed question to you as it would probably be more objective.

Of course lots of detector behaviour on mineralized ground depends on coil and coil shield quality.. also thinking to add Tx power conrol.

Electronics shops are closed for this year.. so I had to dig into my el. junque boxes.. no luck finding higher powered TX NPN transistor pair yet.

Hi Leto,
very nice work with PCB. I think many people here were awaiting for such a gift. Thanks !

About coils... well yes all right it's the disturbing point about these designs cause they need particular params and so contruction could be complex and take longer than with other kind of MDs.

I'll await for your tests on it !

For now... happy new year,
Max

[tiktak]

Hi,

Hi,
Leto.
Thanks for the fast reply.
I am happy to hear that you are well now!
I have read this tread couple of times but because I dont have this kind of education I cant find my answer there buy my self.I am entusiast.Please explain about L1.
Thanks.
I wish you a happy new year.

[aft_72005]

Hi Leto
I wrote for you about silver saber plus.
I don’t have any reply yet.
Please see silver saber plus thread .

[Leto]

tiktak,

i will atach PCB files when it is confirmed that it works.
Parts-layout picture will probably never be made by me, sorry. It would be just too much unnecesary work. Shematic is quite simple and you should be able (with help of assembled board photo) figure it out.
About L1 coil. Read carfully this thread:

https://www.geotech1.com/thuntings/showthread.php?t=11433&highlight=nexus

[Leto]

Hi,
Leto.
Where have you been?

Nice work again!You are ready with PCB!Greait!
But I think that we should try to build working unit of:
Metal detector with meter discriminating
Because this is working!!!
I have try to make a PCB layout but I dont understand so much!
Will you help me.
Look Sasho tells that this variant is BEST.
Good scale,and PN4393...............
Thanks

Hi tiktak,

I had misfortunate vacations at clinic hooked on tubes, etc..
With only one crowded cyber-caffe there was no way for geoteching. I'm well now and kicking.

I agree with you about other Saschos scematics - also very tempting but you should know that Rebecks with PN4393 are of older design (not saying worse) and I wanted to make something new.

My PCBs are made in AutoCAD - this is what I use at my job and do not know anything about other PCBsoftware and autorouting.

[tiktak]

Hi

Hi,
Leto.
Can you make a picture with the names and values of compnents please?
Like Vladmin and others.
Did you use sprintlayout?
I dont have a pc and internet now at home and cant work.
Thanks
p.s.how should L1 be wound?I see that this is composed buy 50w,25w and 25w???Never seen such?How this should be acomplished?

[tiktak]

Hi,

Hi,
Leto.
Where have you been?

Nice work again!You are ready with PCB!Greait!
But I think that we should try to build working unit of:
Metal detector with meter discriminating
Because this is working!!!
I have try to make a PCB layout but I dont understand so much!
Will you help me.
Look Sasho tells that this variant is BEST.
Good scale,and PN4393...............
Thanks

[Leto]

Shops closed

You should address this question to Georgi, the Nexus designer.
http://www.nexusdetectors.com/Contactus.html

I did just that but no reply - possible vacations.?
Actually I dont mind. On Nexus webpage, Nexus Standard SE - product description text says: >>Its design offers versatile use on most inland sites and salt water beaches around the world including sites with heavy mineral deposits and black sand beaches.<<
Probably thats also the answer I'll recieve from Georgi. I adressed question to you as it would probably be more objective.

Of course lots of detector behaviour on mineralized ground depends on coil and coil shield quality.. also thinking to add Tx power conrol.

Electronics shops are closed for this year.. so I had to dig into my el. junque boxes.. no luck finding higher powered TX NPN transistor pair yet.