VLF MD with digital signal processing : Bee-Buzz 1

[Aziz]

Post #1732 states even 0.4 - 0.5 nV/sqrt(Hz).
Oh man, I'm getting old.

[Detectorist#1]

Marchel and Aziz,

Let's talk about new and more good possibilities if they are guaranteed by new ideas, not for tools. For end users is more important the end result at reasonable price.

[Aziz]

And you will also find a lot of information here

https://www.geotech1.com/forums/foru...ace-!!!/page3=

I have found the ultra-low-noise AC amplifier here:

https://www.geotech1.com/forums/forum/projects/usb-projects/5599-let-s-made-a-pc-base-metal-detector-with-usb-interface?p=175731#post175731

I hope it is the correct link for.
This is really a nice amp.
Aziz

[Marchel]

And you will also find a lot of information here

https://www.geotech1.com/forums/forum/projects/usb-projects/5599-let-s-made-a-pc-base-metal-detector-with-usb-interface?14102-Let-s-made-a-PC-base-metal-detector-with-usb-interface-!!!/page3=

[Marchel]

Here is some information about a PC-based metal detector and there should also be a link to the source code if you're good at it, you just have to register.

http://md4u.ru/viewtopic.php?f=11&t=3772

[Marchel]

Ok, I agree.

But you can make a detector, which is way beyond the scope of the current technology.

Once you have seen the possibilities, you won't going to do it the other way.

Aziz

Yes, I agree, it's definitely about something else, but I could imagine it on a Raspberry PI.

[Aziz]

The problem is that it is useless in the field, no one will carry a computer with them into the forest. In my opinion, the device must be light and compact.

Ok, I agree.

But you can make a detector, which is way beyond the scope of the current technology.

Once you have seen the possibilities, you won't going to do it the other way.

Aziz

[Aziz]

Hi Detectorist#1,

This sounds too good to be true. What is the type of OpAmp with 0.6uV/sqrt(Hz) at 5 to 45 KHz? 1000V Tx voltage at VLF MD is not serious! But the hope dies last.

no joke. Seriously.
The preamp is a discrete AC amplifier. Allready realised and tested here somewhere.

I have built Tx-Oscillators or drivers, which were capable of driving huge coil current. The Tx voltage rises according to L*di/dt. No joke.

But you dont really need much Tx current. You are dealing with more noise and other problems then.

It is better to go without anything in the first stage. A preamp can be added easily later.

The simple "naked" system (without amplifiers) would outperform most VLF detectors. With ease! No joke.
Aziz

[Detectorist#1]

This sounds too good to be true. What is the type of OpAmp with 0.6uV/sqrt(Hz) at 5 to 45 KHz? 1000V Tx voltage at VLF MD is not serious! But the hope dies last.

[Marchel]

Hi all,

just checked my old USB sound card band width:
24 Bit at 96 kHz SR, input and output signals up to 45 kHz. The sound card is Sound Blaster X-fi from Creative Labs (USB Audio Class 1 only).

Effective number of bits (ENOB) is 20 bit, -120 dB noise floor (average). 1 uV detection possible.

VLF up to 45 kHz, direct sampling digital fancy stuff! Who has any doubts?
Aziz

The problem is that it is useless in the field, no one will carry a computer with them into the forest. In my opinion, the device must be light and compact.

[Aziz]

Hi all,

just checked my old USB sound card band width:
24 Bit at 96 kHz SR, input and output signals up to 45 kHz. The sound card is Sound Blaster X-fi from Creative Labs (USB Audio Class 1 only).

Effective number of bits (ENOB) is 20 bit, -120 dB noise floor (average). 1 uV detection possible.

VLF up to 45 kHz, direct sampling digital fancy stuff! Who has any doubts?
Aziz

[Aziz]

The Tx power is enough. You can drive the Tx coil either differential or parallel output using the 2-ch stereo output. One can also take Earphone output instead of the line output, to increase the Tx-power.

Rx side can be rised with the capacitor (resonant Rx-tank) by at least 20 dB. No amplifier required.
Not producing any noise.

Oh well, we can add amplifiers too. But later.
On the Rx-side an ultra-low-noise preamp with 0.6 nV/sqrt(Hz) noise voltage density.

On the Tx-side, where the Tx voltage goes up to 1000 V if you want.
Aziz

[Marchel]

Now I did a current measurement because I wasn't completely sure of the current draw so the current at a frequency of 16.6kHz is 35mA in my electronics which I replaced in the X35 coil.

[Marchel]

Here are current measurements on the XP Deus X35 at two different frequencies.

[Marchel]

Is it this current is draw from Tx circuit or from total detector with processor and all other electronics?

In my case, the total current is the same with the processor and all the electronics. This figure varies depending on the frequency used, I think the maximum current I measured was 60-80mA.