Impulsowy wykrywacz metali

[Andi68]

Hello,
I have rebuilt this circuit - it works, but the sensitivity to gold, small parts is very bad.
What can I change, I ask for help.
Greetings and thanks

[waltr]

Small and Gold target have a Short Tau so must sample soon after TX off.
Lots and lots of threads about this.

Then that circuit is the most simple of PI detector circuits and may only be good enough to demonstrate the principles of a PI detector or just for large high Tau targets..

[Andi68]

Thank you.
Which components do I have to change for a short Tau, that's not clear to me.
I made R9 and R10 variable, but nothing really worked ...

[waltr]

The Coil and cable.

READ the many, many other threads. These answer your question.

[kt315]

http://www.geotech1.com/pages/metdet...can/index.html

direct hit? maybe... do not know...

[dbanner]

I build this detector, and made some mods now it works very good, not good for tiny gold but good for rings, coins at beach. very good depth penetration in wet sand. I changed R8,R9 to 22K, you can put trimmers on R8,R9 and adjust. Damping resistor use 1K, Coil wind 17 turns, 9 inch diameter(use 0.4mm-0.6mm wire). Here is original sandbanks article with mod instructions. you can use this as a guide.
Very important what chip use for preamp. I used ne5534 with some small changes to circuit as I did not have original lm709. What did you use? LM709 is good, LF357 is not good in this circuit.

[dbanner]

Also change C2 to 33nF, pulse rate now 500hz, this increases response speed, now detector is very fast response to target.

[Andi68]

Thanks a lot, Mr. Banner, and other guys, the modifications work well.
I use the LM 709, it was a bit difficult to organize.
The explanations in the construction manual of the sanbanks help me further

[bernte_one]

we want to see the results

[Andi68]

Damn, I just do not get any real depth with this circuit.

I think that's because of the operating voltage of 6V.

Does anyone have an idea?

[dbanner]

Here is old document, I build this one as well, it works very deep, it is same basis as all. i did some mods but cant remember details.
Maybe it will help with comparing some component values.

[6666]

Here is old document, I build this one as well, it works very deep, it is same basis as all. i did some mods but cant remember details.
Maybe it will help with comparing some component values.

Here is a translated copy of only the TEXT in English as done in google docs, I take no responsibility for the content of the translation.

[Andi68]

Thank you.

The Sanbanks mods I did at the circuit, works very well.

I suppose I'll have to start over completely, unless
to get even more depth with 6V operating voltage.

Difficult.....

[dbanner]

No, no. This is sandbanks too!. In fact, all these are SANDBANKS is the big momma matriarch.
I could show at least three other children of SANDBANKS. She was a naughty girl.

[dbanner]

Put small trimmer and change the pps and p width a little up or a little down and you will see huge difference in performance(depth). I learn this trick with sandbanks.
She has a sweet spot.