Threshold Pot doesn't work

[h9361]

I designed this audio circuit for the Bipolar PI, which uses the battery's negative terminal as ground. Your current detector, which you're building, uses the battery's positive terminal as ground, so this circuit won't work for you without some modifications. First, D15 needs to be reversed for it to work with your current detector. You could also remove this diode. In any case, several modifications are necessary, including the supply for the LM386, etc. It's better to use the audio section of the GS5 Lite, since it uses the battery's positive terminal as ground, just like the detector you're building. That solution will solve your problem.

Thanks dear eduardo

[h9361]

OK, I see. As long as the circuit isn't actually oscillating then it might work. All I can say is try it and see.

Dear Carl
My PI ( based on polarity ) is working nice but i tested it for ferrous and non-ferrous metals.
Unfortunately, i have the same pitch for all metals, while your video is high/low pitch for different metals.
Do you have any suggestion for checking?

[Carl-NC]

If you probe point "A" in your schematic, does it increase for one type of metal and decrease for the other?

[h9361]

If you probe point "A" in your schematic, does it increase for one type of metal and decrease for the other?

I checked the "A" point on scope, no difference. All targets first increase.
My GB is working, but no disc on Audio.
My coil is mono, 500uH+680R.

[eduardo1979]

Your timing settings might be incorrect, or the connections to the CD4066 synchronous demodulator are likely wrong. At point A—with the GEB potentiometer set to a mid-range position—high-conductivity metals should produce a response opposite to that of low-conductivity metals. In my opinion, you should check point A first, just as Carl suggests, before looking for the problem in the audio circuit.

[h9361]

Your timing settings might be incorrect, or the connections to the CD4066 synchronous demodulator are likely wrong. At point A—with the GEB potentiometer set to a mid-range position—high-conductivity metals should produce a response opposite to that of low-conductivity metals. In my opinion, you should check point A first, just as Carl suggests, before looking for the problem in the audio circuit.

Dear edurado
TGT = 10us
GB=10us
EFE1=320
EFE2=340
All sample width is 20uS
I attached scope for GBdelay (9.5)
My testing targets are a foil and Iron hammer.
My coil size is 10cm, it is small for testing.

[h9361]

If you probe point "A" in your schematic, does it increase for one type of metal and decrease for the other?

Do you think it can be because of my damping resistor (680R)? Maybe the value is high.
Should I change the value of this resistor to 330 ohms and use a new inductance?

[Carl-NC]

I checked the "A" point on scope, no difference. All targets first increase.

What targets are you using? This method does not discriminate between ferrous & non-ferrous, but between low conductor and high conductor. Try a small piece of aluminum foil.

[h9361]

What targets are you using? This method does not discriminate between ferrous & non-ferrous, but between low conductor and high conductor. Try a small piece of aluminum foil.

I tested with :
an Iron nail, Hammer and Pliers
1-euro coin, small and big foil, copper glass,

No difference in audio. GB is working nice, but disc audio is not work.

[h9361]

What targets are you using? This method does not discriminate between ferrous & non-ferrous, but between low conductor and high conductor. Try a small piece of aluminum foil.

Dear Carl,
During capturing video for Bipolar, do you remember your coil inductance and damping resistor?

[Carl-NC]

No difference in audio. GB is working nice, but disc audio is not work.

If you are getting the same response for all conductivities, then GB is probably not working.

During capturing video for Bipolar, do you remember your coil inductance and damping resistor?

300uH and ~470Ω. This is not your problem. All you need to do is make sure the preamp is no longer saturated when the first sample starts.

Look at TP5 and TP6. For any target they should have opposite polarities. For a small (25mm square) foil target TP5 should be stronger than TP6. For the hammer TP6 should be stronger than TP5.

[h9361]

If you are getting the same response for all conductivities, then GB is probably not working.



300uH and ~470Ω. This is not your problem. All you need to do is make sure the preamp is no longer saturated when the first sample starts.

Look at TP5 and TP6. For any target they should have opposite polarities. For a small (25mm square) foil target TP5 should be stronger than TP6. For the hammer TP6 should be stronger than TP5.

Thanks.
I captured two videos from my scope.
Ch1 = TP5
Ch2 = TP6

Video 1 : target was a foil.

https://drive.google.com/file/d/1YZRWF_9agj9ffYhEovbbcnvlaNjXN6PM/view?usp=sharing

Video 2 : target was a iron hammer

https://drive.google.com/file/d/1r401KEAQdRbpZXkI1-V0aiTMzuCGiuDr/view?usp=sharing

Both target has the same action.

Please see my 5532 inputs,
my input signal is connected to pin3 (+), whereas Mr. eduardo1979 advice me to change it. It should be connected to (-).
Do you think this problem is because of it?

I read Ivconic's posts, he had my problem too (his post).

[h9361]

If you are getting the same response for all conductivities, then GB is probably not working.



300uH and ~470Ω. This is not your problem. All you need to do is make sure the preamp is no longer saturated when the first sample starts.

Look at TP5 and TP6. For any target they should have opposite polarities. For a small (25mm square) foil target TP5 should be stronger than TP6. For the hammer TP6 should be stronger than TP5.

I checked my PCB more and more, the only difference was 4066 pins (3,4,10,11).
I attached final schematic.


See following, it is U7: pin8 and pin7 output when Iron and foil are in front coil. Both target form is the same.
Ch1 : U7: pin 8
Ch2 : U7: pin 7


I tested my GB, it is working very nice.

[Carl-NC]

Your videos show that both sides are doing the exact same thing. One side should do this:



And the other side should do this:



My guess is that your demod timing isn't right. What are you using to test GB? Because those videos tell me that GB can't possibly be working.

And, no, whether the preamp is inverting or non-inverting won't make much difference.

[h9361]

Your videos show that both sides are doing the exact same thing. One side should do this:



And the other side should do this:



My guess is that your demod timing isn't right. What are you using to test GB? Because those videos tell me that GB can't possibly be working.

And, no, whether the preamp is inverting or non-inverting won't make much difference.

OK.
Please tell me your suggestion for timing (TGT, GB, EFE1, EFE2) and i will test it.
Do you remember your timing for Bipolar?