LOOKING FOR GOLDSCAN 4 Schematic.

[ivconic]

You haven't read my posts carefully (if at all) from the beginning.
That's not my goal, big coil and big depths... for that kind of thing I have Pulse Star 2.
My goal is good sensitivity on the smallest targets and good GEB.
Of course, the GS4 can also be set to work "slowly" and to work with a coil of 3x3 meters and larger!
I don't care one bit.

[Xtrem]

https://www.youtube.com/watch?v=tm9aABN7p5I

This is GS4 with very large coil, you can see that in the AM mode it has more sensivity.

[Jose]

I once tried to vary the width of the samples on the GS4 to more than 20 us, but it doesn't work, apparently the integrator stops working or I made some mistake, I don't know.
I also tried to reduce the time between both channels in order to obtain greater sensitivity when using the GB. The result is an unpleasant sound with some metals. In practice it can be reduced by about 5 us with some improvement in sensitivity.

[Detectorist#1]

Hi Krzysztof,

OK, ATMega328BP is 8b uP - sorry- , but this not change the difficult of discrimination in PI MD.

[ivconic]

Got it!
More or less I thought so.
But it's always better to get confirmation from someone in the know.

[Carl-NC]

You should look at the preamp output settling to see if there is any room for decreasing the sample delay. Or, if you build a fast coil, then you will want to decrease the delay. IMO, increasing the delay above 15us or so has no value so don't worry about losing the high delay values.

Hunting high conductor coins is a completely different setup than hunting small nuggets. You want an early sample delay, but a much wider sample width helps a lot. So does a higher TX width. Suggestion: start out by doing air tests with a variety of coins. For this, you don't need GB so run it in AM mode. Focus on TX width, frequency, and sample width (you should quickly see that a minimum sample delay is always best) and see what is optimum for the different coins. You will obviously need to compromise, or decide that you need to hunt the same ground in more than one mode (nugget hunters do this all the time). One you figure this out, enable GB and figure out the best Gnd delay & width for the least obnoxious target hole.

[ivconic]

That's much better, probably OK to leave it there for now.

What do you think; does it make any sense with these hardware to set the delay adjustment range something below 10uS?
As for other tweaking; all that's left is to separate TGT from GND in terms of pulse width and set GND a little wider.
Is it a matter of experiment or do you have any concrete recommendations regarding the pulse width for TGT and GND?

[Carl-NC]

3 channels will give you 3 sample points on the curve, which does 2 things. First, it gives you 2 slopes so you can ground balance without ending up with a target hole. Second, it lets you consider non-linear responses like iron, which is not strictly exponential, and perhaps can be used for ferrous ID. However, non-ferrous targets are only linear after 1 tau of decay, so even non-ferrous targets (especially high conductors) will appear non-linear in the normal region of sampling.

[pito]

That's why I said maybe, it is additional info which maybe can be used, again maybe.

[Carl-NC]

" what phase" in PI MD. =
You have two channels in GOLDSCAN 4, so there will be a phase shift between them,.....
Maybe that can be used for discrimination???

PI gives you a decay curve, and a 2-channel RX gives you 2 points on the decay curve. From this you can get a slope which can be used to estimate the conductivity of the target. However, this is only a resistive signal, you don't get a reactive signal like you do with VLF so you cannot distinguish ferrous from non-ferrous. Ferrous also has an eddy decay and, to a PI, looks similar to a non-ferrous target.

[Carl-NC]

I completely forgot to check RV2 and it was not completely closed, that's why shortest possible delay in previous case was "≥ 30uS".... WRONG!
Now when I turned RV2 to 0 resistance; situation has changed, actual shortest possible delay on original GS4 setup is "≥ 10uS" and that's now correct!

That's much better, probably OK to leave it there for now.

Also noticed one more thing, previous confusion about peaks of pulses... scoping only Q4 gives amplitude slightly over 8Vpp.
Adding second pulse (via 10k) is decreasing it to 6Vpp and so on. Q4 with all 4 other gives as on above photo 5Vpp.
And that part now is clarified. But Q8,Q7,Q6 and and Q5 still remains at ~1Vpp ???
I changed PPS down to 380Hz and nothing has changed, still all 4 are ~1Vpp. Misty??

The multiple resistors form a Thevenin voltage divider, the more legs you add on the smaller the pulse amplitudes. One pulse on the channel gives you full amplitude, 2 pulses (equal resistors) cuts the amplitude in half, 4 pulses will have 1/4 amplitude.

And there is another "intrigue" to solve, Carl you try to explain this; 1000PPS....all as you see on posted photos and yet overall power consumption with loudest detection is rock solid 150mA ???
How come?

As you decrease the overall pulse rate, you are also decreasing the TX pulse width. That's a drawback with using a 555. You can partially fix it by placing a diode in parallel with R7, see the Internet for examples.

[Krzysztof]

When he was explaining on another topic how easy it is to solve this kind of task; he said (I'll paraphrase, it's not verbatim): "I'll choose a mcu that has at least 8 to 16 timers and that's it..."

8b uP ATMega328BP -> 3 x timers 16b (T1,T3,T4)

[Detectorist#1]

Hi pito,

Yes, phase shift is used in hybrid MD in last years in attempt to combine PI and VLF principle in metal detecting. Good primer is Voodoo project from Carl. This idea is copied from some other hybrid detectors in geotecg1 site.
This idea works, but my hope is that have to be possible to make pure PI with stable discrimination.

[Detectorist#1]

Hi Krzysztof,

Do you really thing that using of more powerful ( with more timers) 32bit uP for generating of of 6-8 pulses with simple relationships will solve the fundamental problems of PI MD?

[Detectorist#1]

Hi pito,

If the real world is dual - analog and digital - and metal detecting use VLF and PI - our hope is that have to be way to make stable discrimination in PI MD also. Our attempts continues!