Analog Target Indicator for VLF

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I have left out CD4053 as it is not necessary. I have no interest in depth measurements, so I don't have to switch modes.
Thing are coming along nicely. I use old school method of drawing PCB layout by permanent marker!

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So I've found another analog target ID meter circuit.
This one has been right under the nose for years, but l never really noticed it before.
Compass XP-PRO full schematic. The target ID circuit is very interesting. And based on video, it works good. The meter is smooth and looks rock steady.
https://m.youtube.com/watch?v=fi7cln...&persist_app=1

[Nandor]

Im so glad . Nice documnets you have found there are so many good sources on this forum, big thanks for the administrators!

There is a part after the log amps from the Geb channel that triggers the treshold level when there is a metalic object only, its like a ground exclusion balance so the VDI does not indicates ferrite or soil effects. I have measured the output some times it's almost square sometimes distorted waves depends on the target response.

Sometimes I use "Ink paper" copy method and make my pcbs with marke it looks good and I feel good making something by hand.

This is the schematic on which I was working on and I would like to try.

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I don't have laser printer and the entire country is in lockdown. So toner transfer method is not an option for me at the moment.
Making a PCB is biggest obstacle, this is main impediment for experimenting. It takes too much time to go from drawing board to actual testing out a circuit. The whole process is demotivating.
Nevertheless, I will persevere.
I see you've designed a new circuit.
I'm trying to understand the Compass target ID circuit. Some clever things going on there. More on that later.
In your circuit, you use the White's log amps. After the difference amp, l see you vary the design. Extracted your schematic. I had almost forgotten about Express sch. Software.

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In White's design, after diff amp, there is a stage with a feedback diode, l not sure what it does. I did simulation of this stage standalone in Ltspice, l put 10khz square waveform input just to see the output waveform, it is a triangle waveform output, which l think is integration? There could be some math going on there. This stage combined with the previous log amps stages are doing something together perhaps critical to proper target ID function.
I think the entire circuit should be conceptualized in mathematical terms, to understand how it functions to extract target ID on the meter. That would be helpful to any possible changes or mods.
I will dig deeper.

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I don't have laser printer and the entire country is in lockdown. So toner transfer method is not an option for me at the moment.

There is always dead bug. or vero board.

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So at the output of the log amps there are log x and log y. Then after the difference amp we get
Log x - log y = log(x/y). So that's at the output of diff amp.

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Then comes the stage with the diode in the feed back loop, which I think is another log amp( whose output decreases with increasing amplitude), so now we end up with log( log(x/y) ? Somehow this all works out to present target info on meter. There is a little compensation and adjusting going on just prior to the meter, but that appears to be it.

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There is always dead bug. or vero board.

Yes, of course, I have few pieces of those, but it is no joy when the circuit is a little larger than a handful of components.

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I found some simulations of the whites circuit.
I remember this was discussed in the past.

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One curious thing I observed from the whites 5900/6000 schematic is that the Y channel feeds directly to filters and then into the y log amp. Whereas THE X CHANNEL IS INVERTED by an extra inverting amplifier stage prior to feeding into the X filters and then into the X log amp. It is clearly shown and labeled as" x channel inverted"
So therefore the the x channel signal ends up at the input to the x log amp as an INVERTED X.
The Y signal is not inverted.

Don't know why.

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This schematic shows x inversion after the demods.
Not sure.

[Nandor]

I told you before, if my way of understanding of this circuit is good than it is the ground balance. Thats why X channel is used, my first prototype has no ground balance and it shows ferrite like a good target. That part samples and holds the output of the signal difference and triggers only if a metalic object is detected because Disc channel reacts to soil and that signal phase difference is enough for the diff amp to produce an output.
I did not found these, before this topic I searched a lot here and on russian forums but did not found any simulations or working pcbs with meter indicator. You made it
Regards

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Big Bud metal detector has target ID meter circuit. There are few variations of the big Bud series. The circuit used to obtain target information looks very different than White's circuit. I see a lot of CMOS bilateral switches are implemented.

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The meter update drive circuit from the Whites 6000DI. The input is taken from the "G" channel. The circuit output is active high logic level.
I cut and pasted input V sources only to verify that the main circuit is electrically sound. Actual working conditions are not derived here. The 6000DI features full wave synchronous demodulators. Perhaps this has some relevance on how the target ID circuit was designed.