Threshold Pot doesn't work

[Carl-NC]

Minelab uses multi-period PI to achieve iron rejection. Even then, it is only partly effective, not the same as VLF discrimination.

You are wanting to combine two completely different technologies and that will be somewhere between difficult and impossible. If you want to play with a system that is similar to what you want and already working then I suggest looking at the Voodoo project.

[h9361]

Thanks.
Please see GoldScanIV schematic.
If understand correctly, is it trying to discriminate via different delaying?!

[Qiaozhi]

Thanks.
Please see GoldScanIV schematic.
If understand correctly, is it trying to discriminate via different delaying?!
[ATTACH]56593[/ATTACH]

You have to understand that there is a big difference between rejection based on target conductivity and the way a VLF discriminates. Using target conductivity does not provide reliable ferrous discrimination.

I think the so-called ferrous rejection in the Goldscan IV works in the same way as the TDI. That is, it hijacks the ground balance sample to create a "hole" in the target response which corresponds to the conductivity of small ferrous targets (such as nails).

[h9361]

Yes, i know VLF method and its difference with PI.

[h9361]

Dear Carl, i have request.
I want to build your Off-Resonance inside of p. 37, IMD book. But i'm going to change its TX schematic with the attached (raptor TX).
See attached,
1- Should i use 5V or 9V?!
2- Should i R3 with 5K pot or it's OK? (R3 should be adjusted for maximum amplitude at the collector ofQ1.)
Thanks

[Qiaozhi]

Dear Carl, i have request.
I want to build your Off-Resonance inside of p. 37, IMD book. But i'm going to change its TX schematic with the attached (raptor TX).
See attached,
1- Should i use 5V or 9V?!
2- Should i R3 with 5K pot or it's OK? (R3 should be adjusted for maximum amplitude at the collector ofQ1.)
Thanks
[ATTACH]56594[/ATTACH]

That won't work.
The original off-resonance oscillator is designed such that the bias voltage is dependent on the oscillator frequency. As a consequence, the bias voltage is also sensitive to changes in coil inductance. This is not the case with the Raptor TX.

[h9361]

Thanks dear Qiaozhi.
Please read attached, it's Off-Resonance explanation.
As you see, it's written that we can replace Colpitts oscillator
Actually, i want to use only a single coil. Is it possible to guide me how to change the Colpitts for the Off-Resonance?
Thanks

[Carl-NC]

Here is an example circuit using a Colpitts. I do not guarantee this circuit will work (I think I built it many years ago) and it will certainly have some temperature drift. Technically none of these are "off-resonance" but rather something called "energy theft."

[h9361]

Here is an example circuit using a Colpitts. I do not guarantee this circuit will work (I think I built it many years ago) and it will certainly have some temperature drift. Technically none of these are "off-resonance" but rather something called "energy theft."

[ATTACH]56607[/ATTACH]

Thanks for your kindness.

[h9361]

Hello
Dear Carl
Please forgive me for my amatory questions.
I want to add a Voltmeter in your HH1 so that it shows 0 number for no detecting metals. As soon as detecting, the number is increased. Do you think it's possible?

[Carl-NC]

Yes, I think we have already discussed this.

[h9361]

Yes, i used an analog VU meter and works very nice.
Now, i want to replace a digital VU meter instead of it.
Unfortunately, i can not find a digital numeric VU. So, do you think is there a method that be able to use a regular digital voltmeter for it?
Dear Carl, is it possible to read the explanation about disc. in PI and tell me your opinion?
https://www.lammertbies.nl/electroni...metal-detector

[Carl-NC]

Replace the VU meter with a resistor and connect the voltmeter across the resistor.
I don't see anything new in the link. PI can only do pseudo-discrimination.

[h9361]

Thanks for your guiding.
Is it correct?

[Carl-NC]

Yes