Bandido II uMax - strange iron-copper disc

[Max]

Hi all,
I have my bandido II working...detecting gold, silver, bronze...and rejecting most of the iron...when in disc mode, but still it gets sometimes signals from big iron masses moving really close to the coil.

What's strange is that sometimes it seems to detect big iron masses (hammer, etc) better than copper....big copper objects !!!
Example at 3cm my hammer sounds...with fast movement but I can't detect copper , 20 cm diameter plate, moving !

Copper is diamagnetic...I know...

And it still detect gold and silver well...e.g. 1.5 gr gold ring at 18cm.

I think that's because of something wrong on phase shift section...maybe a cap or two need to be modified.

Any idea ???

Best regards,
Max

[Max]

bandido's gatings

Hi all,
I'd like to investigate bandido disc section so
I've made some pictures of bandido gating signals (gnd and disc gatings).

Channel 1 is ever signal (sine wave) at R30/R33 junction (20mV/div).

Channel 2 (5V/div) is (gating signals like square wave or charge/discarge) for:
1c. is gating for disc-channel1 at pin7 ic5 when disc pot fully ccw
2c. is gating for disc-channel1 at pin7 ic5 when disc pot fully cw
3c. is gating for disc-channel2 at pin1 ic5 when gnd pot fully ccw
4c. is gating for disc-channel2 at pin1 ic5 when gnd pot fully cw
5c. is gating for all-metal (geb) at juntion r34/c18 when gnd pot fully ccw
6c. is gating for all-metal (geb) at juntion r34/c18 when gnd pot fully cw

Timing is 50mS/div and trigger is always on Channel1.
Behaviour is that for ,both gnd pot and disc pot, when turning cw there is a shift to
the left referred to input sine wave. Shift is less than 1/2 square for disc pot , and about an half-square for gnd too.

These pictures were made using Carl's schematic values for everything (caps included).

Are the gatings correct ??? Anyone could confirm geb and disc are working ok ?

Any suggestion welcome.

Best regards,
Max

[Max]

Other pics ...not so easy to upload here !

[Max]

very slow...

[Qiaozhi]

Hi all,
I'd like to investigate bandido disc section so
I've made some pictures of bandido gating signals (gnd and disc gatings).

Channel 1 is ever signal (sine wave) at R30/R33 junction (20mV/div).

Channel 2 (5V/div) is (gating signals like square wave or charge/discarge) for:
1c. is gating for disc-channel1 at pin7 ic5 when disc pot fully ccw
2c. is gating for disc-channel1 at pin7 ic5 when disc pot fully cw
3c. is gating for disc-channel2 at pin1 ic5 when gnd pot fully ccw
4c. is gating for disc-channel2 at pin1 ic5 when gnd pot fully cw
5c. is gating for all-metal (geb) at juntion r34/c18 when gnd pot fully ccw
6c. is gating for all-metal (geb) at juntion r34/c18 when gnd pot fully cw

Timing is 50mS/div and trigger is always on Channel1.
Behaviour is that for ,both gnd pot and disc pot, when turning cw there is a shift to
the left referred to input sine wave. Shift is less than 1/2 square for disc pot , and about an half-square for gnd too.

These pictures were made using Carl's schematic values for everything (caps included).

Are the gatings correct ??? Anyone could confirm geb and disc are working ok ?

Any suggestion welcome.

Best regards,
Max

Here's a simple test you can do:

1. First connect a scope probe to IC4b pin4 (the output of the GEB [middle] channel analog switch) and adjust the GEB control until you find a null point.

2. Then move the scope probe to IC43 pin8 (the output of the DISC [top] channel analog switch) and adjust the DISC control until you find a maximum point.

If you cannot detect the null and maximum points, then the gate timings are incorrect.

[Max]

analog gates outputs

Here's a simple test you can do:

1. First connect a scope probe to IC4b pin4 (the output of the GEB [middle] channel analog switch) and adjust the GEB control until you find a null point.

2. Then move the scope probe to IC43 pin8 (the output of the DISC [top] channel analog switch) and adjust the DISC control until you find a maximum point.

If you cannot detect the null and maximum points, then the gate timings are incorrect.

Hi Qiaozhi,
thank for the useful hints.

I get a nearly to flat signal (like dc level) at output of analog gates due to filtering.

Levels are small and appears this way:

- for disc analog gate output (r37/c21 junction) I get from +25mV (disc pot fully ccw) to
-25mV (disc pot fully cw). So a symm level that pass through zero and have a maximum of +25mV.

- for geb analog gate output (r35/c19 junction) I get again a like to dc level but now
from -17mV (gnd pot fully ccw) to -13mV (gnd pot fully cw). So here I haven't a null, mean
a passage through zero of the signal: signal is ever negative voltage

Must I conclude I have bad values in GEB section ?
Or both disc and geb are affected ? What do you think ?

Best regards,
Max

[Qiaozhi]

Hi Qiaozhi,
thank for the useful hints.

I get a nearly to flat signal (like dc level) at output of analog gates due to filtering.

Levels are small and appears this way:

- for disc analog gate output (r37/c21 junction) I get from +25mV (disc pot fully ccw) to
-25mV (disc pot fully cw). So a symm level that pass through zero and have a maximum of +25mV.

- for geb analog gate output (r35/c19 junction) I get again a like to dc level but now
from -17mV (gnd pot fully ccw) to -13mV (gnd pot fully cw). So here I haven't a null, mean
a passage through zero of the signal: signal is ever negative voltage

Must I conclude I have bad values in GEB section ?
Or both disc and geb are affected ? What do you think ?

Best regards,
Max

In the Bandido design the top channel is DISC, the middle channel is GEB, and the bottom channel is ALL METAL.
What happens at the R36/C20 junction when you adjust the GEB control?

Both the GEB and ALL METAL channels should have a DC level that passes through zero. To balance the detector for an air test you need to set the control so the the DC level is at zero.
The DISC channel should have a DC level that passes through a maximum value. For the air test, set this to the maximum point. I don't have a BandidoII here to test, but you may find that the maximum voltage will be negative.

Have you tried reversing the connections on the RX coil? If that doesn't work, then recheck your component values.

[Max]

In the Bandido design the top channel is DISC, the middle channel is GEB, and the bottom channel is ALL METAL.
What happens at the R36/C20 junction when you adjust the GEB control?

Both the GEB and ALL METAL channels should have a DC level that passes through zero. To balance the detector for an air test you need to set the control so the the DC level is at zero.
The DISC channel should have a DC level that passes through a maximum value. For the air test, set this to the maximum point. I don't have a BandidoII here to test, but you may find that the maximum voltage will be negative.

Have you tried reversing the connections on the RX coil? If that doesn't work, then recheck your component values.

Hi Qiaozhi,
thank you very much for the useful informations.
On R36/C20 junction, at the output of middle analog gate, I get:
dc level with
-13mV when gnd pot is fully ccw
+2.5mV when gnd pot if fully cw
It pass through zero when near fully cw turned.

In disc analog gate output maximum is at one extrem and level passes to zero near pot in the middle. So maximum is not in the internal range of pot positions - but at one extrem I get maximum negative (absolute) -25mV.

If I expect a maximum not at extrem positions of disc pot I must conclude I need to change disc cap cause other components are ok.

I've tried many times reversing rx leads but I lose almost all performance, also in all-metal mode. Maybe because of wrong phase shift from gnd circuitry.

Think I need to test again with goodrat set of values (the ones in Gary's revised schematic, that I found working better than original schematic ones).

Best regards,
Max.

[porkluvr]

Disc pot

Hello Max - I saved an Oscillograph submitted by Goodrat that I believe was taken while scoping an honest to god working Bandito - although I can't say for sure - but it is very interesting.
Read the whole thread here:
http://thunting.com/geotech/forums/s...oto=nextnewest
From what you said about the direction of travel on your scope display, I believe your discriminate pot is wired backwards.
As the ground pot is moved Cw the ground reverence pulses should advance (move left). Turning the discriminate control CW causes the DISC reference to retard - moving to the right. (Thank you, Goodrat!)
Good luck

[pigeon]

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salut.hi
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voici mon email [email protected]
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[Max]

Hello Max - I saved an Oscillograph submitted by Goodrat that I believe was taken while scoping an honest to god working Bandito - although I can't say for sure - but it is very interesting.
Read the whole thread here:
http://thunting.com/geotech/forums/s...oto=nextnewest
From what you said about the direction of travel on your scope display, I believe your discriminate pot is wired backwards.
As the ground pot is moved Cw the ground reverence pulses should advance (move left). Turning the discriminate control CW causes the DISC reference to retard - moving to the right. (Thank you, Goodrat!)
Good luck

Hi porkluvr,
thanks for the infos. Seems really interesting stuff from goodrat.
I'll check my traces again and then try to figure out where the problem is.

Best regards,
Max

[Max]

Hi all,
I've substituted again caps...now I have again goodrat's values and now I get waveforms much similar to those present in the picture from him.
There are minor differences regarding initial phase but only in disc section. GEB section have the same timing of goodrat pictures.

I concluded (at least for now) that these are the right values.

I have also measured dc levels and now I get a maximum on disc analog gate output. I had inverted leads too on this pot, now is ok, and shift to right with cw movement.

fully ccw ---> -20mv
a bit cw ---> maximum of -25mV
fully cw ---> +25mV

Also geb dc signal pass through zero.

Seems everything ok now.

What to say...

Thanks to all,
Max

[Qiaozhi]

Hi all,
I've substituted again caps...now I have again goodrat's values and now I get waveforms much similar to those present in the picture from him.
There are minor differences regarding initial phase but only in disc section. GEB section have the same timing of goodrat pictures.

I concluded (at least for now) that these are the right values.

I have also measured dc levels and now I get a maximum on disc analog gate output. I had inverted leads too on this pot, now is ok, and shift to right with cw movement.

fully ccw ---> -20mv
a bit cw ---> maximum of -25mV
fully cw ---> +25mV

Also geb dc signal pass through zero.

Seems everything ok now.

What to say...

Thanks to all,
Max

The information from porkluvr is very interesting. In fact, it has reminded me that the DISC on the Bandido is set so that ferrous targets are already rejected at minimum discrimination. In this case the maximum (i.e. max negative voltage) will occur when the DISC is fully ccw. This is confirmed by the first oscilloscope plot. The third plot shows that the DISC control has an adjustment range of about 45 degrees (pi/2). So all this makes sense now, and your DISC pot was definitely wired back to front.
The GEB control only seems to have a very small adjustment range, probably about 10 degrees. The Bandido design is particularly sensitive to the GEB setting (hence this small adjustment) and must be tuned very carefully as it also has an effect on discrimination.

Is it working as expected now with good discrimination?

[Max]

The information from porkluvr is very interesting. In fact, it has reminded me that the DISC on the Bandido is set so that ferrous targets are already rejected at minimum discrimination. In this case the maximum (i.e. max negative voltage) will occur when the DISC is fully ccw. This is confirmed by the first oscilloscope plot. The third plot shows that the DISC control has an adjustment range of about 45 degrees (pi/2). So all this makes sense now, and your DISC pot was definitely wired back to front.
The GEB control only seems to have a very small adjustment range, probably about 10 degrees. The Bandido design is particularly sensitive to the GEB setting (hence this small adjustment) and must be tuned very carefully as it also has an effect on discrimination.

Is it working as expected now with good discrimination?

Hi Qiaozhi,
yes now with goodrat's set of cap values I have better disc than previous (I already know this because I've tested before these values...but now I have diagrams too to compare).
Yes disc on iron is definitely better than previous. I've inverted disc pot leads and now I have right shift as expected. But have maximum not at one extrem but really close to it : at extrem I get -20mV where at maximum I get -25mV then turning cw signal increase till +25mV at other extrem.
So I have now a maximum in the inner range of pot, but really close to the left extrem position.

Yes, geb has only few degrees of movement much like in goodrat diagrams.
My diagram now like much like in the picture.

Yes, iron is rejected at minimum disc too. But with big masses happens sometimes it sound briefly.

Do you think I need maximum at the extrem for disc ? If so I need to sligtly modify disc cap, 2 or 3 pF I think.

Best regards,
Max

[chemelec]

Hello Max - I saved an Oscillograph submitted by Goodrat that I believe was taken while scoping an honest to god working Bandito - although I can't say for sure - but it is very interesting.
(Thank you, Goodrat!)Good luck

1) What are "Goodrats Cap Values"?

2) Can "Goodrat" Confirm that these Scope Traces were taken from an Actual "Manufactured Bandido".

I Think this info Would be appreciated by all.

Thanks in Advance...Gary