Threshold Pot doesn't work

[Carl-NC]

The Target channel is all metal, if there is a target (iron or not) it will be indicated. The Disc channel is ferrous/non-ferrous, there is no need to then compare this with the Target channel. You seem to want to use a method from VLF designs which is done there for a completely different reason, it does not apply to PI.

The comparator needs a pull-up resistor, maybe 10k. Because the comparator is powered from -5V and the NPN is grounded, you also need a diode, something like this:

[h9361]

The Target channel is all metal, if there is a target (iron or not) it will be indicated. The Disc channel is ferrous/non-ferrous, there is no need to then compare this with the Target channel. You seem to want to use a method from VLF designs which is done there for a completely different reason, it does not apply to PI.

The comparator needs a pull-up resistor, maybe 10k. Because the comparator is powered from -5V and the NPN is grounded, you also need a diode, something like this:

Thank you for your information.
Can i use 1N4148?

[Carl-NC]

Yes

[h9361]

Yes

Dear Carl
I have a question.
Today, i had a test and my result was strange.
As you know, i built the preamp+Demod (DISC part with LED) and could do my DD as induced-balanced.
The induced-balanced showed me as an almost straight line (like #577 post).

Today, i connected the same small DD (the same that i used for Iron disc) to my HHD and tried to do induced-balanced via TP4.
But what is interesting is that i can not reach to the almost straight line (#577 post)!
I even connected VLF coil of minelab to my HHD (added a damping resistor to its RX), but my TP4 is not straight line (see minelab VLF coil on HHD, TP4)!

Do you think this is because of gain of two preamp (My DISC gain 220, HHD gain 1000 )?

[h9361]

Yes

Sorry
Finally i could find the problem.
RX shield was problem.
Now it works very nice.

[h9361]

Yes

Dear Carl
I have a question about HHD.
I want to change the following values in HHD:
C17 and C18 from 100n to 470n.
R26 and R27 from 100K to 220K.

Do you think it can increase its sensitivity?

[Carl-NC]

All I can say is try it and see.

[h9361]

All I can say is try it and see.

Thank you.
I will test and tell you my result here.
Yesterday, i had a talk with a member of Russia group. He sent me a version of IDX with VCO Audio (attached).
But no one answered my simple question about this because most of them has built its simple one tone version.
My question is, please consider that i adjusted DISC pot so that it has removed Iron.
In this case, Does the VCO (4046) produce an different tone for Iron or it is silent (not any audio)?
Is it possible to see the schematic and tell me your opinion?
Thank you.

[Carl-NC]

It looks to me like it will blank the audio.

[h9361]

It looks to me like it will blank the audio.

Thank you.
So, i have to build the two tones model (attached).
Before designing its PCB, is it possible to check it for any error?
Thanks.

[h9361]

It looks to me like it will blank the audio.

Dear Carl
I already built Mr. Mickstv's Audio.
I want to connect my IRON output (LM393) to it for blanking audio.
Please see it, do you think this connection is true for blanking?
Thanks

[Carl-NC]

I doubt it, but I also don't see how this speaker driver works.

[h9361]

I doubt it, but I also don't see how this speaker driver works.

Now, i am using this schematic (Mr. Mickstv) with LM386.

[h9361]

I doubt it, but I also don't see how this speaker driver works.

Dear Carl
Please see #598, it is the same Mickstv's audio schematic with lm386 (audio driver).
I already built it for my HHD and it works nicely.
Now, can you tell me which point i can connect to collector of 2n3904 (out of my Iron DISC) for blanking audio?
Thank you.

[Carl-NC]

I think you will need to replace the 3904 with a 3819 and put it in parallel with Q2.