Let's made a PC-base metal detector with usb interface !!!

[Aziz]

Do I hear a hint of FKK coil recognition? A new convert perhaps?
Welcome to the FKK covenant

Oooooh nooo!, sorry, but you really need the shielding. I can detect capacitive effects. These are more significant with more TX coil voltage and high operating frequency.

Better shield everything. TX & RX coil.

Aziz

[Davor]

Oh yes!, capacitive effects does not seem to affect the system. The coil isn't shielded.

Do I hear a hint of FKK coil recognition? A new convert perhaps?
Welcome to the FKK covenant

[Aziz]

*LOL*
The sound card power generation went up for Vcc from 2.5V to 4.5V.
The TX coil voltage is 28 V peak-to-peak.

Aziz

[Aziz]

BTW, I have forgot to mention, that I also have the "World's best VLF technology"!!!
*LOL*
Aziz

[Aziz]

Good News!

Hi all,

I have very good news for you:
You don't need neither an active RX-amplifier nor much power to the controller to knock out the VLF detectors.

Processing the TX reference signal and demodulating the RX signal from the TX reference signal gives incredible results.

I have made the higher Q coil and it reduced the power consumption from 80 mA to 30 mA @10V battery input. It's not the end and can be improved further (TX coils resistance is 2x0.4 Ohm, 2x10 turns wound spirally as D-shape). I have another loudspeaker cable, which I want to try it next time.

BTW, the VLF controller circuit does not need a low battery detection circuit as well. The low battery condition can be extracted from the TX-reference signal. So everything can be kept very very simple. That's really a KISS-masterpiece.


Oh yes!, capacitive effects does not seem to affect the system. The coil isn't shielded.

Cheers,
Aziz

[Aziz]

Great Aziz. So low Q? Coil is barely in osc. life.

What we can expect from higher Q of say 16 or 27?

You know, that a very big portion of the source energy is currently burnt in the low Q coil (in the coils resistance). High Q coil will improve the power efficiency and will cause more current circulating in the TX tank. This will improve the target banging and response.

We can expect more of course. But we don't need such a high Q coil. Just some figures up.
Aziz

[WM6]

My current TX coil Q:
Q = w*L/R = 2*pi*1kHz * 240 µH/2.5Ohm = 0.6
(This isn't indeed high enough.)

Great Aziz. So low Q? Coil is barely in osc. life.

What we can expect from higher Q of say 16 or 27?

[Aziz]

The VLF KillerApp(c)(r)(tm)!!!

Hi all,

it's the end of ... <you know what> *LOL*

Still with sound card output operated power source (=no battery connected) and the low Q TX coil (bad coil).

Now tuned the RX coil with resonant capacitor set around the TX resonance frequency. Wow . Incredible and remarkable sensitivity without the need for an amplifier, an external power source and a KISS masterpiece. The tuned RX tank has indeed enough gain.

My current TX coil Q:
Q = w*L/R = 2*pi*1kHz * 240 µH/2.5Ohm = 0.6
(This isn't indeed high enough.)

There is more potential left yet ... with high Q TX coil, high inductivity RX coil, battery operation, ....

Cheers,
Aziz

PS: Thanks tjmlena

[tjmlena]

Congrats Aziz

[Aziz]

New VLF Oscillator Prototype Working Fine.

Hi all,

I have finished the new cross-coupled, balanced Aziz-Davor(tm) VLF oscillator prototype and it is working fine. I have also built the power generation from the sound card output line using the transformator and rectifier section.

The power supply generation from the sound card output line delivers enough power to go detecting without batteries connected to the controller. The whole controller runs even down to a rectified voltage Vcc of 0.53 V (battery input voltage slightly higher due to forward voltage drop of the diode). At full sound card output power, Vcc is going up to 2.5V. It's going to happen even better, when I use a high Q TX coil. The TX coil I'm using at the moment has more losses (~240 µH, 2.5 Ohm resistance).

I'm going to test the prototype extensively soon. But I have to built a new IB coil for this awesome VLF controller.

The active version (with RX amplifier and battery input) will deliver high performance depth and sensitivity of course. But let's play with the simplified KISS version first.


Cheers,
Aziz

[Aziz]

Hi friends,

I want to mention, that there have been modifications and improvements of the cross-coupled balanced LC oscillator available on the other thread.

Post #156 and further:

http://www.geotech1.com/forums/showthread.php?19730-Balanced-VLF-Tx&p=160073#post160073

I'll try the very basic variant without an active amplifier implemented in the first place (1 emitter inductor, 2 BJT and center-tapped TX coil). I do also have another circuit with a low noise amplifier (Davor's magnificient LNA) for the case of I want more RX sensitivity. Due to the power supply splitting for powering the amplifier, I will use the full-bridge oscillator design (2 emitter inductors, 4 BJT, not tapped TX coil).

Let's see first, how the very basic and simple solution works (I'll leave the power generation from the sound card output line and I'll use a battery instead, which makes the circuit much simpler and cheaper of course).

But give me more time, I'm quite lazy.
Cheers,
Aziz

[Aziz]

Hi WM6,

the emitter connection of the transistors has the name "V+". Yep, the V+ node (I can refer to it as it has a name) is interesting to see the half sine waves. That's the reason, why I have given it a name. It isn't used elsewhere.

I'll leave the sound card power supply source (transformer, bridge rectifier) and use a small battery in the first place as it makes a lot cheaper and faster to make the prototype.

I'm sure, that this ultra easy thing will get remarkable performance for its simplicity and beauty. But the software coding is quite tricky as the receive signal must be decoded with the help of TX reference signal.
Aziz

[Davor]

That's the potential emitters are on. There is a choke between V+ and Vcc

[WM6]

Aziz, where, did you get V+ (at TX Osc.)? I cannot find this parameter in sim. Or this is alternate to Vcc?

[Aziz]

Thanks. What are CTx capacitances? Parasitic capacitance of TX?

LTX (a,b): Transmitter coil (inductance)
CTx: Transmitter resonant capacitor (note: CTxl, CTxr not required if you have a parallel CTx tuning capacitor, CTx directly placed nearby the TX coil)

Parasitic capacitances don't matter here. The tuning capacitances are much higher.

LRx: Receive coil (inductance)
CRx: Receiver resonant capacitor (set it nearby the TX resonant frequency or calculate using the formula in the circuit)
fres = 1/(2*3.1415*sqrt(LRx*CRx) )
(fres = resonant frequency)


Hey, this controller is a nice toy. I've made it because it's so beautiful simple. I'll make the prototype board soon (next week).

Aziz