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

[Aziz]

Basic Schematics for the Quiz-Game.





Now try some frequencies, duty cycles and capacitor values. C1, Cs, and the optional capacitor ain't that much. Try for C1, Cs 10-100 times of the tunning capacitor value.
The mosfet pulse on duty cycle is defined by the tuning capacitor and the TX coil inductance (like in the original TEM TX).

Good luck to you.
Aziz

PS: {L} being the TX coil inductance. LC1 is a choke. CB3 is a bipolar elco (1000µF - 4700µF)

[Aziz]

Hint, Hint, Hint

Hi all,

I think you all deserve the new transmitter. Look at the TEM principles. We are going to make the TEM2.0 transmitter.
And look at the Class-E amplifier principles. We are going to make the Class-E-TEM transmitter.

And we finally will see, that TEM2.0 and Class-E-TEM are the same thing.
I'll publish soon the very trivial "invention". Shame, I wouldn't even call it as "invention".

Both transmitters can stimulate large targets more efficiently. It supports boost-mode at the expense of more power consumption. The basic principle is: leave some TX coil energy back and invest it into the next pulse. You can even do without energy recovery and invest all the energy in the coil into the next TX pulse (super-boost).

It supports TEM-PI/Hybrid VLF principles too. More oscillating sine-waves will stimulate the targets better. It's a wideband transmitter with the option of increasing the low frequency section.

It's so simple: one n-mosfet, one inductor (like in the TEM TX), two tuning capacitors (unipolar, high voltage).
By varying the pulse frequency, duty cycle and the capacitors value, one can setup the operating mode.

Can you see the forest for the trees? It's a good quiz game. I'll give you some time to figure it out.
(I'm sure, it isn't novel. But it is a KISS-masterpiece. Patent-trolls: keep quiet!)

Aziz

[Qiaozhi]

ce site étonnant et très intéressant

Please read the forum rules ->

http://www.geotech1.com/forums/showthread.php?10526-Basic-Rules-of-the-Forums

and make your posts in English.

[mazari31]

ce site étonnant et très intéressant

[Carl-NC]

It's a nice, fuel-efficient driver; I've been using a similar circuit for the past year. I tend toward bipolar, they run at a lower supply, and I have a 2-F option. I also designed (separately) a multi-waveform TX driver; it is quite the trick to switch between full PI, triangle, and sine wave.

[Aziz]

I would suggest "Really Good VLF/LF Oscillator Detector Controller Circuit" as the name. I doesn't do multifrequency. Or have a boost mode. Or do triangle waves. Or pulse induction. Or truncated half-sine. When you get all that incorporated, then we'll consider "Ultimate."

Ok, my bad Carl. Ultimate was meant, that I have finished the VLF/LF journey and it is the final schematics on this topic.
But I might give a little add-on option trick to the circuit above to make it multi-frequency capable. It would make the real ultimate option possible then.


Cheers,
Aziz

[Carl-NC]

I would suggest "Really Good VLF/LF Oscillator Detector Controller Circuit" as the name. I doesn't do multifrequency. Or have a boost mode. Or do triangle waves. Or pulse induction. Or truncated half-sine. When you get all that incorporated, then we'll consider "Ultimate."

[Aziz]

The Ultimate(tm) VLF/LF Oscillator Detector Controller Circuit

Hi all,

I'm releasing the Ultimate(tm) VLF/LF Oscillator Detector Controller Circuit (and zipped spice files for your convenience). As you can see it below, I have changed the battery polarity (Battery + = GND !!!). The preferred n-mos fets being used for the center-tapped TX coil (low Rdson, more power efficient). Everything is trivial and I have found some spare time to finish it finally. You can implement the "World's Best VLF/LF Detector"(tm) if you want (yes, you can!).

Here is the final schematics:



Here is the zipped spice file (LTSpice):
VLF-OSC-Detector-Controller-2013-02.zip

Ok, I have finished the VLF/LF Oscillator project and have kept my promise to publish it. It's up to you to code the software part now.

Have fun.

Cheers,
Aziz

[Aziz]

What happened to the LM48511 chip? Was it good? Just curious.
Aziz

[Aziz]

http://www.ti.com/lit/ds/symlink/lm48511.pdf.

..beats FCC class B requirements with no EMI suppression added. I say let the guy try the circuit ... That's what this forum is about ...

I'm not preventing anyone from trying this.. I appreciate it even.
Go ahead guys.. but don't forget to report it back.
Aziz

[moodz]

Oh yes, every coil is a low-pass filter of 1. order when pushing some current through it.
But it won't help us further. There will be huge noise (PWM modulated current).
Aziz

http://www.ti.com/lit/ds/symlink/lm48511.pdf.

..beats FCC class B requirements with no EMI suppression added. I say let the guy try the circuit ... That's what this forum is about ...

[Aziz]

not strictly true Aziz ... Filterless class D has been around for some time now whereas earlier class D did have a low pass filter on the output, nowadays the LR of the speaker itself forms the low pass filter effectively. The EMI suppression filter is not required except under strict EMI compliance. .... Just Google "filterless class D" ... There are many learned articles on the subject.

Oh yes, every coil is a low-pass filter of 1. order when pushing some current through it.
But it won't help us further. There will be huge noise (PWM modulated current).
Aziz

[moodz]

Hi Ken,



that's pure marketing. We can't use the amplifier without any filter in our application. I would even say, that such amplifiers will produce more noise. Better to use a simple class AB amplifier or one of the detector controllers here.




The loudspeaker is an inductive coil. When it is switched in the amplifier (PWM modulation), the loudspeaker leads also carry the current, which radiate a high frequency EMF during the switching transitions. The fundamental frequency (260 kHz) and multiple of it called the harmonics (where is PJ? ) will be emitted and radiated.



If you want to make a good detector, the answer is yes. You have to process the signal across the TX coil as well.
Either for
- synchronising onto an external clock or
- for demodulation of a signal given by an external clock or
- recognition of external noise to eliminate it from the signal or
- external battery voltage tracking (low battery detection, on/off detection, etc.)
...

I for one wouldn't use this amplifier type. It will produce a lot of noise. A clean class AB amplifier would do it much much better.

I'll publish new and improved detector controllers next year.


Cheers,
Aziz

not strictly true Aziz ... Filterless class D has been around for some time now whereas earlier class D did have a low pass filter on the output, nowadays the LR of the speaker itself forms the low pass filter effectively. The EMI suppression filter is not required except under strict EMI compliance. .... Just Google "filterless class D" ... There are many learned articles on the subject.

[Humanise]

Thanks for your answer Aziz,
Since I already have it and since I need something to give reasonable power while only using USB power supply, I will continue with it. If it causes problems, I will either have to do more filtering or find something else.
Regards
Ken

[Aziz]

Hi Ken,

The parts that I didn't understand were

1) Why the data sheet for the chip itself says that this is "filterless"? If this chip still requires a filter, on the board or otherwise then it is not "filterless".

that's pure marketing. We can't use the amplifier without any filter in our application. I would even say, that such amplifiers will produce more noise. Better to use a simple class AB amplifier or one of the detector controllers here.

2) Why the only reference to a filter, near the end of the data sheet, says it "reduces EMI of around 1 MHz and higher" when the oscillator frequency is only 260khz?

The loudspeaker is an inductive coil. When it is switched in the amplifier (PWM modulation), the loudspeaker leads also carry the current, which radiate a high frequency EMF during the switching transitions. The fundamental frequency (260 kHz) and multiple of it called the harmonics (where is PJ? ) will be emitted and radiated.

I don't follow what you mean here. Are you saying that we need to read back to an input of the sound card the actual voltage waveform across the coil? I notice that you were doing this with one of your designs earlier in this thread. Why do you think that this is needed here?

If you want to make a good detector, the answer is yes. You have to process the signal across the TX coil as well.
Either for
- synchronising onto an external clock or
- for demodulation of a signal given by an external clock or
- recognition of external noise to eliminate it from the signal or
- external battery voltage tracking (low battery detection, on/off detection, etc.)
...

I for one wouldn't use this amplifier type. It will produce a lot of noise. A clean class AB amplifier would do it much much better.

I'll publish new and improved detector controllers next year.


Cheers,
Aziz