VLF MD (by Sascho - Varna)

[Leto]

Greetings to all.

I'm back after months just to find out that everyone seems to be occupied with LRL circuits these days at Geotech.
Good Luck guys.

Here is reposted Sashos circuit design not available at original thread
https://www.geotech1.com/thuntings/s...ad.php?t=12617
Coil configuration is the same as Grozdio Grozdev REBEKS metal detector design. Built in Bulgaria 30 years ago.
Original Grozdevs designs were put on forum by Georgi - Nexus designer:
https://www.geotech1.com/thuntings/s...t=nexus&page=2 post#33
Another simmilar project could be found here:
https://www.geotech1.com/thuntings/s...ead.php?t=7763
Another one:
http://www.md4u.ru/forum/viewtopic.php?t=1312

Why building this one?
* I never made any of 'REBEKS' yet.
* Very good Saschos design: NE5532 at input, 4007 sinchronous demodulator, VCO ad-on
* I'd like to play with coils tunned in full resonance for which I belive this is ideal project.

Qiaozhi you seem to be only conversant person with a copy of Nexus circuit - as you'll probably not attach shematic here,
could you please check folowing?
Does Nexus use adjustable RC network connecting RX-TX coils for nulling purposes?
ANY suggestions welcome.

[Max]

Greetings to all.

I'm back after months just to find out that everyone seems to be occupied with LRL circuits these days at Geotech.
Good Luck guys.

Here is reposted Sashos circuit design not available at original thread
https://www.geotech1.com/thuntings/s...ad.php?t=12617
Coil configuration is the same as Grozdio Grozdev REBEKS metal detector design. Built in Bulgaria 30 years ago.
Original Grozdevs designs were put on forum by Georgi - Nexus designer:
https://www.geotech1.com/thuntings/s...t=nexus&page=2 post#33
Another simmilar project could be found here:
https://www.geotech1.com/thuntings/s...ead.php?t=7763
Another one:
http://www.md4u.ru/forum/viewtopic.php?t=1312

Why building this one?
* I never made any of 'REBEKS' yet.
* Very good Saschos design: NE5532 at input, 4007 sinchronous demodulator, VCO ad-on
* I'd like to play with coils tunned in full resonance for which I belive this is ideal project.

Qiaozhi you seem to be only conversant person with a copy of Nexus circuit - as you'll probably not attach shematic here,
could you please check folowing?
Does Nexus use adjustable RC network connecting RX-TX coils for nulling purposes?
ANY suggestions welcome.

Hi Leto,
nice to see here again. Take a look at TGS thread too... we made "little" progresses with it.

Kind regards,
Max

[Leto]

PCB ready

Thanks Max,

I have checked TGS thread - became realy fat.
I'm quite interested in Vladimirs TGSL PCB designs (excelent work) and also have Silver Sabre project to finish; maybe even Barracuda now with Geo involved...
But it wouldn't be quite my way to work ''linear'', seems that I need few unfinished projects sitting on my desk.
So back to Saschos design.. PCB just finished.

[ivconic]

Leto welcome back!
Dobrodosao...gde si bio do sada?
Usput...najlepse zelje za Bozic i novu godinu!
Keep in touch!

[Leto]

VCO part

Thanks Ivconic
bio sam kao neki borg na cjevčicima u polikliniki.. sada sam ok
Sve najbolje zelje i tebi.

Forgot to attach VCO audio part... here it is.

[N@SKO]

Another shematic of Grozdanka.
But I think have a mistakes in shematic.

[N@SKO]

I have problem with upload shematic.
Give my a mail adres to send shematic!

[Qiaozhi]

Qiaozhi you seem to be only conversant person with a copy of Nexus circuit - as you'll probably not attach shematic here,
could you please check folowing?
Does Nexus use adjustable RC network connecting RX-TX coils for nulling purposes?
ANY suggestions welcome.

There are some simularities between this circuit and the Nexus, and there are also a lot of differences. However, the TX circuit is the correct configuration to use for testing resonant coils.
There is no RC network in the Nexus for nulling the coils.

In case you're wondering - when I first used a Nexus, I commented to Georgi on the erratic meter movement. After that I designed a new meter circuit that is now used in the later models. That's why Georgi gave me access to the circuit diagram. And no - I won't post it here.

[kt315]

I have problem with upload shematic.
Give my a mail adres to send shematic!

can use http://tinypic.com/
thanking in advance

[N@SKO]

[Leto]

Big question

There are some simularities between this circuit and the Nexus, and there are also a lot of differences. However, the TX circuit is the correct configuration to use for testing resonant coils.
There is no RC network in the Nexus for nulling the coils.

In case you're wondering - when I first used a Nexus, I commented to Georgi on the erratic meter movement. After that I designed a new meter circuit that is now used in the later models. That's why Georgi gave me access to the circuit diagram. And no - I won't post it here.

Thanks Qiaozhi, I'll not ask any more detailed questions about Nexus but am curious about one thing: main adversity of Rebeks, as I heard, is bad temper on mineralized ground. How is doing Nexus in this respect?

Thanks also to you N@SKO for posting another version of this design. First one I seen with 555 sound and LED indicator.

As I see main differences in circuit are at demodulators - seems that first models were made with transformers (to obtain low voltage levels?) and diode demodulator and later with FET or switching ICs as 4066 and 4011 synchronous demodulator. Saschos design with 4007 looks like the most elegant.

Sascho (are you here?) did not appoint transistors and few resistors values. My PCB is designed for TO-5 transistor packages and TO-220,225.. at TX but probably almost any transistor will work.

Tomorrow missing parts will be purchased and then the big question: will it work?

[Qiaozhi]

Thanks Qiaozhi, I'll not ask any more detailed questions about Nexus but am curious about one thing: main adversity of Rebeks, as I heard, is bad temper on mineralized ground. How is doing Nexus in this respect?

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

[N@SKO]

Missing values of resistors is 10k and potenc. SENS. is too 10k.
Transistors may be BC557 ,but I'm not sure of this!
Any body have a information where is fit resonance capacitators?
In search head (coil) or PSB?

[Leto]

values

Missing values of resistors is 10k and potenc. SENS. is too 10k.
Transistors may be BC557 ,but I'm not sure of this!
Any body have a information where is fit resonance capacitators?
In search head (coil) or PSB?

I was thinking about same resistor and pot values.
On audio section I will probably use BC107,BC177 and BC517-darlington simply because of frequent use in Saschos design. I'm sure also BC547-550, BC557-560 pair would work. For TX part I'll probably use something in to-220 packs: BD136, TIP32, PN200 maybe BC640.

You will need to adjust only capacitator marked * at RX coil for tuning the coil.

If you need to alter TX frequency than change caps or resistors in cross coupled RC oscillator.

[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.