Threshold Pot doesn't work

[h9361]

I did the change, but i put a 100K and 1M pots for the resistor.
Unfortunately, my voltmeter did not turn on until i changed value of the pot via rotating.
As soon as it turns on, it shows 5V and the number did not change by passing metal over coil.

[waltr]

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

Go back and re-read the thread "my take on the HH2".
I did add a small analog VU meter that is 'center Zero". This along with the GB method I used indicates high verse low conductive targets.
A digital meter is not as easy to quickly see trends (just a bunch of rapidly changing numbers verse see a needle switch in one direction or the other) as a analog meter.
Details of how to do this is in the thread.

[Carl-NC]

Your resistor is way too big. Try 1k-4.7k. Waltr is right, the voltmeter will be very sluggish as it does a lot of averaging. You will need to move the target slowly.

[h9361]

Go back and re-read the thread "my take on the HH2".
I did add a small analog VU meter that is 'center Zero". This along with the GB method I used indicates high verse low conductive targets.
A digital meter is not as easy to quickly see trends (just a bunch of rapidly changing numbers verse see a needle switch in one direction or the other) as a analog meter.
Details of how to do this is in the thread.

Thanks Dear Walter.
Your explanation:
Discrimination
Another addition is a meter on the Integrator output. This helps to determine target signal strength and for pin-pointing since the integrator output is Non-motion. I used an old VU meter with 500uA full scale. It is connecting from -5V and through a 20k series resistor to the Integrator output, -5V to +5V. This sets the meter to mid-scale with no target (5V/250uA = 20k). Then it goes to the left for high conductive targets (dimes, quarters) and to the right for low conductive targets (nickels) when the GEB is adjusted for 50-150usec - see posts above on target response with GEB adjustments.

See attached, Did I get it right?

[waltr]

Thanks Dear Walter.
Your explanation:
Discrimination
Another addition is a meter on the Integrator output. This helps to determine target signal strength and for pin-pointing since the integrator output is Non-motion. I used an old VU meter with 500uA full scale. It is connecting from -5V and through a 20k series resistor to the Integrator output, -5V to +5V. This sets the meter to mid-scale with no target (5V/250uA = 20k). Then it goes to the left for high conductive targets (dimes, quarters) and to the right for low conductive targets (nickels) when the GEB is adjusted for 50-150usec - see posts above on target response with GEB adjustments.

See attached, Did I get it right?
[ATTACH]56648[/ATTACH]

That's it. It picks off the integrator output.
Note the 20k is for a 500uA meter. Check or measure your meter and re-calculate the resistor value.
Here are the notes on my schematic:

Integrator output is +5V to -5V
referenced to ground (+VB)
This is 0 to 10V referenced to 5V-

600 Ohm * 500 uA = 300 mV to move meter full scale.
R90 forms a Voltage divider with a ratio of 0.3/10
So 600 Ohm /(.3/10) = 20k Ohm. A19.4k Ohm resistor is
close enough to move meter to Half scale whrn integrator outout is Zero.

[h9361]

Thanks dear Walter for your guiding.
As you know, i have built two versions of HH (1-HH1-Rev-D, 2-With GB).
Both of them works very very nice. About GB version, i changed its audio part and i added Mr. MickStv's schematic.
According to your advise, i have to use the VU+resistor in my GB version.
Is it possible to tell me which point of MickStv's schematic is the best for connecting to VU?
For more understand, you can read in attached Mickstv's explanation about his schematic.

[h9361]

Your resistor is way too big. Try 1k-4.7k. Waltr is right, the voltmeter will be very sluggish as it does a lot of averaging. You will need to move the target slowly.

I put a 5K pot and connected my Volmeter but it did not turn on.

[Carl-NC]

I put a 5K pot and connected my Volmeter but it did not turn on.

Hold the target steady over the coil where it gives a strong audio response. Adjust the pots until the voltmeter responds.
What you are trying to do is very impractical and will be almost useless.

[h9361]

Hold the target steady over the coil where it gives a strong audio response. Adjust the pots until the voltmeter responds.
What you are trying to do is very impractical and will be almost useless.

OK, i will stop it.
Dear Carl, i want to know your opinion about Lorenz method for discrimination (generate different ID for metals ), is it possible to tell me?
Thanks.

[Carl-NC]

I don't know anything about what they are doing.

[h9361]

Hello
Dear Carl
I have a question about motion and non-motion of HH1.
In motion mode, TH pot works very nice and i can hear pit ... pit and its sensitivity is very good.
But in non-motion mode (AT opened), i have a constant sound but TH pot doesn't work and i can not reach to pit ... pit.
Other words, my HH always is in silence and its sensitivity is half than motion mode.
I also changed R30 by different values, but nothing changed. Do you think it's normal?

[waltr]

Non-motion never worked for me so never used it.
In the field motion mode is best and is not hard to use to 'pin point' a target.

[h9361]

Thanks dear Walter.
My non-motion mode works stably for a short time (as mentioned in article ) but it's sensitivity is low and TH pot doesn't work in the mode.

[Carl-NC]

Non-motion mode requires an opamp (IC8b) with an exceptionally low input IB spec. With SW2 open the input IB flows through the SAT cap and the offset ramps up until the opamp rails out. For a decent TL072 this is less than 0.5mV/s at the input or 50mV/s at the output. This will mess up the threshold pretty quickly. To use this for more than a few seconds you need a 1pA IB opamp.

[waltr]

Thanks for the explanation Carl. That is why it doesn't work well.