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

[Aziz]

Anyone is offering a better VCA? Nobody?

Well, I've soldered the VCA parts onto the bread-board. But due to pretty fine weather last days, I didn't finish it so far.

Cheers,
Aziz

[Aziz]

Take a peek: http://www.edn.com/article/520604-Us...entiometer.php

For VCA purposes it can be made even simpler.

Unuseable due to the critical demands for a low noise pre-amp stage. Too slow. Too noisy. Gain can't be below one (or zero).

The VCA I have presented is the best and cheapest solution (with matched BC337-40 transistor pairs) to the desired demands. And it is versatile.

Another solution?

Aziz

[Davor]

Take a peek: http://www.edn.com/article/520604-Us...entiometer.php

For VCA purposes it can be made even simpler.

[Aziz]

This is waaaay too complex for my taste.

BTW, since you played with a true discrete differential amp, here acting as VCA, it is a sacrilege wasting a perfectly good symmetrical input for ground connection.

There is a VCA solution with FET optocoupler that is supposed to work nice, and there are solutions with OTA. OK, your solution here is not unlike OTA, and is probably much better regarding noise. Then again - what noise? I'd go for OTA.

True, but...

the other solutions can't beat it in regards to noise, stability, accuracy, BW, AC capability... And you can use here simple matched transistor pairs too.

The VCA can achieve 1.2 nV/sqrt(Hz) input referred noise density in the configuration above.

I'm open for further suggestions. Any better solutions there?

Aziz

[Davor]

This is waaaay too complex for my taste.

BTW, since you played with a true discrete differential amp, here acting as VCA, it is a sacrilege wasting a perfectly good symmetrical input for ground connection.

There is a VCA solution with FET optocoupler that is supposed to work nice, and there are solutions with OTA. OK, your solution here is not unlike OTA, and is probably much better regarding noise. Then again - what noise? I'd go for OTA.

[Aziz]

Sharing Ideas Is Good!

Hi all,

this is the voltage controlled amplifier (VCA) I want to try out soon (see below). Notice, it is a small signal high gain VCA. A second amplifier stage is added and is sent to the right channel.
The controlling voltage is fed from the right line output channel of the sound card. Well, it is an AC controll voltage so I want to use the AC input. Note, positive control voltage disables the VCA (no collector current flowing) und is good for masking out unwanted signals.

Who wants to have the LTSpice-file to play with?
Cheers,
Aziz

PS: It is a low noise design. ;-)

[Davor]

Great link. I share the same views about patents, and for many years so far. The idea is not new, and interesting about it is that the most creative people of all tend to embrace it more often than not. Say, Don Lancaster http://tinaja.com/ - there is a whole patent avoidance library with down to earth explanation of the process, and all the rotten places to avoid.

[Aziz]

... very cool project AZIZ !!

Now im learning 55 pages from this thread and looks interesting.


If you are planning to sell some finished kit, then count on me.
I will buy one or more.

Sorry tjmlena,

I do not intend to sell anything.

This thread/project is for
- sharing experience
- education (if you find something valuable)
- entertainment
- stimulating ideas
- bashing and blaming patent trolls

http://devhumor.com/patent-chart/

Cheers,
Aziz

[tjmlena]

... very cool project AZIZ !!

Now im learning 55 pages from this thread and looks interesting.


If you are planning to sell some finished kit, then count on me.
I will buy one or more.

[Aziz]

VCA

Hi all,

I'll try a different pre-amplifier front-end: the voltage controlled amplifier (VCA) .

I do have a very low noise discrete VCA solution and want to try it. The controlling voltage is fed from the other sound card ouput line (instead of input compensation). Let's see how this works. Unfortunately, it doesn't fit into the PCB space. It requires more parts of course. This is just for my own curiosity.

Cheers,
Aziz

[Aziz]

This is what I mean with option #1. It's just a standard concentric co-planar coil with additional anti RX coil.

Aziz

[Aziz]

More Anti-Interference IB Coil Ideas

Ya wanna have more anti-interference IB coil ideas (or inventions)?
Stay tuned ...

Aziz

Ok, eat this:

#1 (main course, yummy, yummy):

Just exchange the coil position of RX+ and RX-/TX-Bucking coil bundle in the "top hat" coil design showed in post #1366 (http://www.geotech1.com/forums/showp...postcount=1366) and invert the winding orientation of the TX-Bucking coil so it opposes the TX coil winding orientation. This is a typical modified standard concentric co-planar IB coil with the anti RX coil placed above the coil embodiment. Fine balance with distance variation of anti RX coil.
That's an "old hat" idea and not a "top hat". Hey, but it's looking like a "top hat" coil again.

Anyway, it improves the standard concentric co-planar IB coil due to the fact, that the bucking coil turns count gets slightly lesser (not much, a tad). Full anti-interference feature due to identical RX+/RX- coils. This coil is easy to build and balance as well.

Modifying an existing concentric co-planar IB-coil doesn't make sense as the bucking coil therein needs a tad less turns count. But you could put an extra turn (or two) of TX coil outside the coil embodiment edge and could try the modification.

#2 (dessert):

Standard concentric co-planar IB coil with the anti RX coil placed apart from the IB coil (50 cm or less, or even more distance) but at the same vertical planar position (parallel to IB coil). That's an old idea. I have published it already somewhere.

Cheers,
Aziz

PS: Patent trolls, keep out please. You may use it too but you aren't allowed to patent it. Thank you very much.

[Aziz]

Ya wanna have more anti-interference IB coil ideas (or inventions)?
Stay tuned ...

Aziz

[Aziz]

Can ya see it? The "Top-Hat" coil?

But the beast is super quiet. I have to make it a little bit rigid.

Cheers,
Aziz

[Aziz]

World's First "Top Hat"-Coil Prototype Is Working

Hi all,

the world's first "Top Hat"-coil prototype is working as calculated & predicted!!!
(A big thank you to my magnificient coil software.)


Due to less coupling coefficient of RX-/TX-Bucking (when thick TX-wire is used), the TX-Bucking coil needs more turns count of course. One can wrap the TX-Bucking coil on top of the RX- coil to increase the coupling coefficient further (hence has slightly more diameter than RX- coil). The goal is to minimize the turns count for the TX-Bucking coil.

And it makes much sense to make rectangular type "Top-Hat" coils. Because this is much simpler to make the whole coil frame (wooden coil frame).

Cheers,
Aziz