Threshold Pot doesn't work

[h9361]

Pin 2 goes to ground, not -5V.

Hello Dear Carl
As promised, i finished the DISC demod and captured a video on scope during moving a Iron hammer over DD-coil.
Frist i adjust sampling as follows:

Then i connected both preamp and Disc demod to scope

After that, i captured a video from scope with measured parameters during moving an Iron hammer. You can watch from the link:
https://drive.google.com/file/d/1PfH...ew?usp=sharing

I have a request, please see following picture.
Can you guide me, what schematic ( i remember that you told me that it can be a simple amplifier with gain pot as Iron sensitive pot) do you suggest me to add between the demod and 2n3904 for blanking audio ( inside the box)?
Thank you.

[Carl-NC]

Are you using a mono coil?

[h9361]

Are you using a mono coil?

No, I am using DD

[Carl-NC]

You need to find the correct pulse width and delay that will give you different signal polarities for ferrous and non-ferrous. A nail and a copper coin, for example.

[h9361]

You need to find the correct pulse width and delay that will give you different signal polarities for ferrous and non-ferrous. A nail and a copper coin, for example.

OK. Do you have a suggestion for adding good schematic in box for blanking audio?
For exp, do you think the attached is correct (between demod and 2n3904)?
Can you tell me your suggestion?
Thank you

[h9361]

You need to find the correct pulse width and delay that will give you different signal polarities for ferrous and non-ferrous. A nail and a copper coin, for example.

I again tested with different sampling,
The following sampling give me a different result in the measured maximum.
For Iron hammer, first goes up from its first values 2.89V to 2.95V.
And For a aluminum box, it first goes down from its first values 2.89V to 2.75V

[h9361]

You need to find the correct pulse width and delay that will give you different signal polarities for ferrous and non-ferrous. A nail and a copper coin, for example.

Dear Carl
Please accept my apology for my requests.
I hope you help me and tell me your suggestion schematic between Demod and 2N3904.
Now, all my schematic (micro for generating samples) +GB+Audio is finished.
The only part that is remained, it is the amplifier that i should put between DISC demod and 2n3904 for blanking audio.
Because first i have to to design my PCB and to test in real via blanking audio for finding best point sample DISC.
Thank you.

[Carl-NC]

I don't understand your waveforms and they do not look correct. Show me the waveform at the output of the preamp with (1) no target, (2) iron nail, (3) copper coin.

[h9361]

I don't understand your waveforms and they do not look correct. Show me the waveform at the output of the preamp with (1) no target, (2) iron nail, (3) copper coin.

OK, I tested with a big DD coil 60cm.
It may have noise, so i will make a small coil 20cm DD and i will take image from the outputs.
My DD coil was TX 500uH with 680R, RX 1mH with 680R.
About your following picture, do you remember inductance and damping resistor of your testing coil (RX and TX)?

[h9361]

I don't understand your waveforms and they do not look correct. Show me the waveform at the output of the preamp with (1) no target, (2) iron nail, (3) copper coin.

Today, i built a 20cm DD coil with TX 500uH+680R, RX 900uH with 680R. I also changed RX 680R with 510R, but i can not see any changing on tx like your picture.
Your testing picture:

No target:

Nail:

1euro coin:

About 500uH+680R (TX) and 1mH+680R (RX), i tested on my pi and my sensitivity is very nice.
If i remember, GPX series use 1mH inductance + 510R as RX and 330uH+330R as TX.
Do you think it can be because of high inductance for 1mH RX?

[h9361]

I don't understand your waveforms and they do not look correct. Show me the waveform at the output of the preamp with (1) no target, (2) iron nail, (3) copper coin.

Dear Carl
I again changed my nulling so that i have a split line at tip of preamp form.
Now, there is a different signal polarities for ferrous and non-ferrous.
See following:
No target:


Nail:


1Euro coin:


All of my testing was at 2cm distance than coil.

[Carl-NC]

It appears your coil is not induction-balanced. It must be IB for this scheme to work.

Edit: it occurs to me that you may not have the coils connected correctly. Please show the TX & RX circuitry and how the coils are connected.

[h9361]

It appears your coil is not induction-balanced. It must be IB for this scheme to work.

Edit: it occurs to me that you may not have the coils connected correctly. Please show the TX & RX circuitry and how the coils are connected.

Thank you.
I tested the DD coil even on HHD.
My method for nulling TX and RX, I will close RX to TX until form of my preamp is formed (TP4 in HHD).

Do you have any suggestion method for nulling?
IB coil needs to be null based on phase like following:

[Carl-NC]

I don't understand. What are the amplitudes?

[h9361]

I don't understand. What are the amplitudes?

Dear Carl, I am not using phase adjust for nulling RX and TX, the pic is from your book, not me.
my method, I connect TP4 (HHD) to scope.
Then, i close RX to TX and see to scope.
I keep to closing until my tp4 is formed.
I even built DD coil for GPX5000 and it works very nice with discrimination.
Do you have better method for nulling DD?