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

[moodz]

Yep, the old cassette tape (red/brown) consists of very fine grain maghemite. But it could be difficult to get these today.

BTW, some maghemite is also produced in red/brown bricks. It's the maghemite and magnetite (ferrimagnetic), that makes detecting difficult. Not the hematite (anti-ferrimagnetic).

I have choosen the Fe2+ wet oxidation path to produce the fine grain sized maghemite (nm to µm sized grains). Using tensides (washing powder ) help reducing the grain size.

The charcoal method is dusty, messy and hot.

Aziz

..you mean like this 3 KG jar I found under my bench ...

[Aziz]

..you mean like this 3 KG jar I found under my bench ...

Hey, what's this????
Looking like cacao powder...

[Aziz]

Hi guys,

did you ever see the frequency response of the real lightning storm? (You may even be 100's of km far away. BTW, the lightning can be seen as a very very large coil driven by a very very high coil current.)
It's a wide band frequency response.
I had the chance to see it three times. I have been waken up by the loud lightning storm and this was the chance to see the response.

PJ's infamous harmonics(c)(r)(tm) will help reducing it by using the out-band response propagation to the in-band frequency response.

Out-band is the frequency band you aren't interested in (0 Hz ... pulse frequency)
In-band is the frequency band you are interested in.

BTW, the solar caused EMI storm is of the same wide band response. The "coil" is much much larger than the lighting of course. This is something, one can't do it without being smart enough. Just trust in PJ's harmonics!!!
Long live the PJ's harmonics!!!

Aziz

[Aziz]

Sorry to be cyriptic here.
But the skilled in the art will know, what i mean.
Aziz

[Davor]

I played a bit with a CFIA and turned it single ended. The circuit is optimised for 6mH coil, 12kHz, and 12V supply, just as you often use. The op amp is NE5532, but in reality it can be just about any op amp with, say, 20nV/sqrt(Hz) or better - the work horse here is a BJT. LTspice model of a BC337 gives it Rbb higher than the 30ohm actual value, so the noise appears a bit higher than is really achievable with this circuit. A true noise limit is dictated by coil resistance, and it is about 0.8nV/sqrt(Hz).
C1 shifts the noise minimum, not amplitude resonance. In fact, to see the best of this circuit you must see the AC plot as well.

So, this is a true low noise pre made with garden variety components for almost free

[6666]

Aziz where did you put your blog ?

[Aziz]

I played a bit with a CFIA and turned it single ended. The circuit is optimised for 6mH coil, 12kHz, and 12V supply, just as you often use. The op amp is NE5532, but in reality it can be just about any op amp with, say, 20nV/sqrt(Hz) or better - the work horse here is a BJT. LTspice model of a BC337 gives it Rbb higher than the 30ohm actual value, so the noise appears a bit higher than is really achievable with this circuit. A true noise limit is dictated by coil resistance, and it is about 0.8nV/sqrt(Hz).
C1 shifts the noise minimum, not amplitude resonance. In fact, to see the best of this circuit you must see the AC plot as well.

So, this is a true low noise pre made with garden variety components for almost free

Hi Davor,

wow! Not that bad for it's simplicity. Particularly for a single frequency detector amplifier and one can shift the best parameters to the operating frequency of the detector.
I've have been using the transistors BC337 and BC327 already in a differential ultra low noise amplifier configuration using a cheap op-amp too. But this is a bit simpler.
Thanks for your contribution.
Cheers,
Aziz

[Aziz]

Aziz where did you put your blog ?

Looking after the WBGB? *LOL*

No, I haven't done yet.
Aziz

[Aziz]

Hey Davor,

your ultra-low noise amp is indeed brilliant. I'll use the dual op-amp NJM 2068 as the driving horse due to high current drive capability and low noise specs (and cheap too). I'll make a test circuit soon (very likely in combination with our magnificient VLF LC oscillator).
Thanks mate, this is really an useful circuit.

Cheers,
Aziz

[Davor]

I know

The fun part is that you can use just about any op amp that agrees with your supply voltage and have some nice low noise design, and broadband too. It works happily and with a very modest phase transition over a 1:2 bandwidth. phase transition can be further equalised by an additional op amp, but I did not bother to do so ... yet. Multi frequency rig was NOT my idea for this circuit purpose, but a no-brains solution for a tune-free single freq rig. Just plug some coil that is at hand and go.

[Aziz]

The Masterpiece VLF Oscillator Detector Controller.

Hi all,

coming soon... No! Coming right now:
The Masterpiece VLF Oscillator Detector Controller.
*LOL*
Getting most out of almost nothing using the legendary Aziz-Davor cross-coupled balanced LC oscillator.


Watch out for the most power efficient VLF oscillator detector controller. Either no batteries required (powered by stereo sound card output ) or using a low voltage battery (3 V or whatever you like). No amplifier required by using a high inductivity RX resonant coil (resonance frequency nearby the TX frequency). Set TX frequency whatever you prefer and adjust the RX frequency for your configuration.

Notice, that the demodulation must be done with the TX reference signal (right input channel). Receive signal is on the left input channel.

The full schematics:


The LTspice file:
SingleFrequencyOsc-VLF-passive-pnp-03.zip

Enjoy and have fun.

Cheers,
Aziz

[WM6]

Aziz, on schematic you have Sound Card Power Source on "Stereo Input". Is this correct, or have to be "Stereo Output"?

[Aziz]

Aziz, on schematic you have Sound Card Power Source on "Stereo Input". Is this correct, or have to be "Stereo Output"?

Referenced to the detector controller:
Lin, Rin (input): These input lines are connected to the sound card output line (stereo). Power comes in to the detector controller.
Lout, Rout (output): These outputs are connected to the sound card input line (stereo). Signals go to the sound card.
Aziz

[WM6]

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

[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