Houston...I have a problem! (bandido coil)

[Geo]

Thanks people!!!
First thing i am gonna do is to make pcb and rest.....Later i'll post my experiences...
Best regards!!!!

Hi Ivconic . Why to make the bandido. It is about 90% the same with CL3. It is a little better at discrimination and cl3 is a little better at sensitivity.
Total weight .....the same
I say this because you are professional at CL3 construct.
Regards

[ivconic]

Like i thought...


Thanks people!!!
First thing i am gonna do is to make pcb and rest.....Later i'll post my experiences...
Best regards!!!!

[chemelec]

MAX, That 50 Hz sounds like a Line Frequency Being Picked up "by the COIL".

Gary

[Qiaozhi]

Qiaozhi can you tell us the diameter of every coin ???
Victorian Penny = ????mm
Liberty Dollar =
Dime =

Victorian Penny = 30mm
Liberty Dollar = 24mm
Dime = 18mm

[Geo]

Qiaozhi can you tell us the diameter of every coin ???
Victorian Penny = ????mm
Liberty Dollar =
Dime =

[Qiaozhi]

It sound also with iron (and rarely with steel) sometimes...but at few cms and with big masses (tools, hammer...).
So it's not perfect discrimination in my unit.

Question: have bandido total disc vs IRON ? I don't know.
Maybe it depends only of capacitors used.

With my original Bandido (not umax) I could detect the following:

Victorian Penny at 30cm
Liberty Dollar at 27cm
Dime at 23cm

These readings were taken with the detector set to maximum sensitivity, and were taken at a point where the signal was (just) consistent. So these are max depth readings in air. Sorry - no Euros were available for testing.

The Bandido totally discriminates against iron.

[Max]

I Totally AGREE with the Flux Removal.
Contrary to Manufacturers Claims, Flux is a Conductor in Sensitive Circuits.
(My PI Detector Also requires the Flux be Removed, Especially around Q4.)
Personally I use a Kester 331 Solder, "Its Flux is removed with JUST WARM WATER".

I'm using my Split PCB and I don't seem to have the Noise problems. (Maybe the Two PCB's Back to Back is helping this.)
I can Design a Double sided PCB and even etch them, but the Plate through holes is a PROBLEM.

As to External Pickup by the detector, A Metal Box should Prevent that. I also don't seem to have that Problem.
(Do you have a lot of Florescent Lighting?)

You MIGHT also Put a Few .001 uf Disc Type caps Across the Supply Lines at Various Points on the board to Supress Any RF in the circuit.

**Ferrite Beads Could also be Placed on the Wire Ends of Some Resistors, Where you think RF is a Problem.

Just some Possible Suggestions, Hope this Helps.

Take care.....Gary

Hi Gary,
thanks for the hints.

"Contrary to Manufacturers Claims, Flux is a Conductor in Sensitive Circuits."
Totally agree with you. I always remove any flux in this kind of circuits. I use (outdoor) solvents based on acyclic hydrocarbons. I have in spray and also in small bottles...using some cotton with. They are little dangerous, if one knows what to do and precautions. Never used kester331: I'll try it if I find here.

"I'm using my Split PCB and I don't seem to have the Noise problems. (Maybe the Two PCB's Back to Back is helping this.)"
Don't know. Maybe I have too electrical noise around. But no fluorescent lamps in all the house. I don't like them. Too UV for me (eyes stress)...sadly...workplace has a lot of them...

"I can Design a Double sided PCB and even etch them, but the Plate through holes is a PROBLEM."
Same problem. Can't do this way. I can impress photo-sensitive films both side...but then I've to manually connect layers...(tried only one time...waste of time..."butcher's work").

"You MIGHT also Put a Few .001 uf Disc Type caps Across the Supply Lines at Various Points on the board to Supress Any RF in the circuit."
"**Ferrite Beads Could also be Placed on the Wire Ends of Some Resistors, Where you think RF is a Problem."
Tested a lot of these...no way...I have 50Hz noise. No way.
Tested too inductance filters on power lines...no way.
Tested too hi-value caps (up to 50000uF) to prevent noise from supply ripple...no way.
Tested with battery, no way, it's external noise.
After trying a lot of things...I've realized that I can't suppress totally EM noise at 50Hz without proper shielding.

Maybe is just my situation...workshop...workbench...(too noise here?) don't know.
Never had such problems before. Think that huge amplification make things go worse if too noise present.
LM393 has 200V/mv voltage gain typ (open loop)...so saturation will occurrs here at about 45microvolts differential...
on single comparator and I had much more from noise before installing the shield.

So, I suggest anyone making bandido to look at noise levels before giving up and playing with hammer if something
goes wrong.

Best regards,
Max

[chemelec]

Hi all,
I think I've solved the problem in a cheapy way. My bandido seems works now.

What I have from tests in disc mode using a near-to-extrem setting of the disc pot:

- 1 eur coin at about 30cm
- 2 eur coin at about 32cm
- 1 half crown (diameter 32mm) at more than 35cm
- 1 small gold ring (1.5grams) at 24-25cm
- 1 copper cilinder thick 0.5mm, diameter 46.5mm, height 12mm at 42cm
- 1 silver coin (diameter 30mm) at 22cm

That seems pretty good... and like what I expect from Bandido.

All tests where made with fast object movements relative to the coil, tring to simulate
1m/s swings.

It sound also with iron (and rarely with steel) sometimes...but at few cms and with big masses (tools, hammer...).
So it's not perfect discrimination in my unit.

Question: have bandido total disc vs IRON ? I don't know.
Maybe it depends only of capacitors used.

Now the solution, I've used:

- eliminate as much noise as possible
Noise is really subtle.
I've done using semi-encapsulation of some part of the circuit board using a thin aluminum
sheet (insulated with plastic foils) shaped to cover upside of components/pcb. On the copper-side
I've used another PCB (single side copper downside), not etched, connected to circuit pcb using
screws and plastic spacers to give 4mm of distance from circuit copper-side.
Both metallic shields connected with a wire to a unique GND PCB trace.

This cutted out more than 95% of 50Hz noise...and now I have two symm signals at inputs of
comparators (IC8a-IC8b).
This way I get output nearly flat, at a small negative voltage, that rise when an imbalance
occourrs thus giving the audio signal to show-up.

I've noticed that bandido circuit is very sensitive to external noise also if one use (like I did)
fiberglass pcb...using solvents to remove flux after soldering etc...and that's expecially true for
the disc signal path starting at c20/c21.

Only thing to solve and avoid big troubles is Faraday shielding sensitive parts.

So, other good solutions can be using Gary's pcb with a huge upper GND layer and RF guards or use the germany
group pcb or another that have a good, wide gnd screen.

I think that Gary's PCB is very good for testing but, if one can do, to have the best he must add a second
upper layer of copper (double side) to give it a good GND plane and maybe also built in "jumpers".
Unfortunately, I can't do double or multiple side PCBs at this time... so I'll continue with metallic shields,
at least for now.

Other easy solution is insulate everything in a metallic box connected to GND - if a removable cover
present is easy enough to open and connect probes etc for testing.

IVCONIC, TRY SHIELDING AND LET ME KNOW.

Thanks again to all.
Best regards,
Max

I Totally AGREE with the Flux Removal.
Contrary to Manufacturers Claims, Flux is a Conductor in Sensitive Circuits.
(My PI Detector Also requires the Flux be Removed, Especially around Q4.)
Personally I use a Kester 331 Solder, "Its Flux is removed with JUST WARM WATER".

I'm using my Split PCB and I don't seem to have the Noise problems. (Maybe the Two PCB's Back to Back is helping this.)
I can Design a Double sided PCB and even etch them, but the Plate through holes is a PROBLEM.

As to External Pickup by the detector, A Metal Box should Prevent that. I also don't seem to have that Problem.
(Do you have a lot of Florescent Lighting?)

You MIGHT also Put a Few .001 uf Disc Type caps Across the Supply Lines at Various Points on the board to Supress Any RF in the circuit.

**Ferrite Beads Could also be Placed on the Wire Ends of Some Resistors, Where you think RF is a Problem.

Just some Possible Suggestions, Hope this Helps.

Take care.....Gary

[Max]

NOW IT WORKS !

Hi all,
I think I've solved the problem in a cheapy way. My bandido seems works now.

What I have from tests in disc mode using a near-to-extrem setting of the disc pot:

- 1 eur coin at about 30cm
- 2 eur coin at about 32cm
- 1 half crown (diameter 32mm) at more than 35cm
- 1 small gold ring (1.5grams) at 24-25cm
- 1 copper cilinder thick 0.5mm, diameter 46.5mm, height 12mm at 42cm
- 1 silver coin (diameter 30mm) at 22cm

That seems pretty good... and like what I expect from Bandido.

All tests where made with fast object movements relative to the coil, tring to simulate
1m/s swings.

It sound also with iron (and rarely with steel) sometimes...but at few cms and with big masses (tools, hammer...).
So it's not perfect discrimination in my unit.

Question: have bandido total disc vs IRON ? I don't know.
Maybe it depends only of capacitors used.

Now the solution, I've used:

- eliminate as much noise as possible
Noise is really subtle.
I've done using semi-encapsulation of some part of the circuit board using a thin aluminum
sheet (insulated with plastic foils) shaped to cover upside of components/pcb. On the copper-side
I've used another PCB (single side copper downside), not etched, connected to circuit pcb using
screws and plastic spacers to give 4mm of distance from circuit copper-side.
Both metallic shields connected with a wire to a unique GND PCB trace.

This cutted out more than 95% of 50Hz noise...and now I have two symm signals at inputs of
comparators (IC8a-IC8b).
This way I get output nearly flat, at a small negative voltage, that rise when an imbalance
occourrs thus giving the audio signal to show-up.

I've noticed that bandido circuit is very sensitive to external noise also if one use (like I did)
fiberglass pcb...using solvents to remove flux after soldering etc...and that's expecially true for
the disc signal path starting at c20/c21.

Only thing to solve and avoid big troubles is Faraday shielding sensitive parts.

So, other good solutions can be using Gary's pcb with a huge upper GND layer and RF guards or use the germany
group pcb or another that have a good, wide gnd screen.

I think that Gary's PCB is very good for testing but, if one can do, to have the best he must add a second
upper layer of copper (double side) to give it a good GND plane and maybe also built in "jumpers".
Unfortunately, I can't do double or multiple side PCBs at this time... so I'll continue with metallic shields,
at least for now.

Other easy solution is insulate everything in a metallic box connected to GND - if a removable cover
present is easy enough to open and connect probes etc for testing.

IVCONIC, TRY SHIELDING AND LET ME KNOW.

Thanks again to all.
Best regards,
Max

[Max]

Thanks man!! Reading these lines here many things come clear to me now. I made Bandido according to Gary's "huge" pcb and it is working....Of course i couldnt find original op-amps, instead i put TLC272,271 and simillar.....just to experiment.....Pretty simillar experiences.
One thing is clear; Gary's pcb is good and working...although very large for my taste.....But there is splitted pcb also form Gary somewhere here.....i am wandering if is it good, tested???
If it is, than i'll make another on that pcb....Gary...is it good?
Cose somewhere i saw that you claimed it has some minor mistake on it...is it?
About present; it is working...not perfect but i guess it is beacause of op-amps....Coil; well i tried to make one but with simillar problems explained here....These days i'll try again with a lot of help from here...
Thanks!
regards!

Hi ivconic,
I confirm that Gary's full-size PCB is OK. I've checked before mounting components and all electrical connections are OK. So I think split-version is OK too (because it's just the two halves version + some minor adds), but don't checked it till now.

I've noticed that two caps C20/C21 gets different ammount of noise because they are in different places in the PCB and don't share the same gnd point.

There is something about 4 cms from one to another and that creates small
noise asymmetry, that become great after amplification and can be measured at pins 5 and 3 of IC8 BUT if a good ground shield is added facing the copper-side at about 3-5 mm away from it noise is greatly reduced.

Anyway, I've reduced noise...but still I have a continuos commutation of comparators IC8a/IC8b that give me some square-like signal at R57/C34 junction...100Hz frequency...about from GND to -2.5V.

Here comparators are really sensitive and small differences in signals from the two channels are greatly amplified --> I suggest you check too at output of IC8...if you see anything not flat...well, same problem there.

If 50Hz noise is much higher than small signals variations there is no-way to have a good response but DISC works only at great imbalances. Proble is that I can't compensate asym by a nulling pot or something...one idea could be wiring the 2caps near...but don't tested. I've tested with battery, thinking that my supply was involved in noise... but problems are really similar...performance is poor too. So main part is external 50Hz noise.

This way DISC works but with very poor performance. I can reject iron and detect gold...but at not more than 8-10cm max from bottom of the coil.

And I have TLC2262s and MC33078s at now.

I've noticed also that foil is unuseful on my coil former and graphite-spray must be used. If every coil can be shielded individually maybe also foil could be used. But then one have to null after shielding coils...

But I think all the troubles here are not from coil or op-amps (at least for me--> I have only 33078 different and >1mVpp nulled coil) BUT having a flat GND-near signal at R57/C34 ...I can't get till now though using a good shield under the pcb... to have desired "bought-like" performance.

Any idea ? Any suggestion welcome...

Best regards,
Max

[chemelec]

Thanks man!! Reading these lines here many things come clear to me now. I made Bandido according to Gary's "huge" pcb and it is working....Of course i couldnt find original op-amps, instead i put TLC272,271 and simillar.....just to experiment.....Pretty simillar experiences.
One thing is clear; Gary's pcb is good and working...although very large for my taste.....But there is splitted pcb also form Gary somewhere here.....i am wandering if is it good, tested???
If it is, than i'll make another on that pcb....Gary...is it good?
Cose somewhere i saw that you claimed it has some minor mistake on it...is it?
About present; it is working...not perfect but i guess it is beacause of op-amps....Coil; well i tried to make one but with simillar problems explained here....These days i'll try again with a lot of help from here...
Thanks!
regards!

YES, My Split PCB IS OK.

My Mistake was Not balancing the Coil. STUPID MISTAKE.
The PCB is Fine.

All current Info is HERE:

http://www3.telus.net/chemelec/Projects/Bandido-Split/

[ivconic]

Thanks man!!!


Thanks man!! Reading these lines here many things come clear to me now. I made Bandido according to Gary's "huge" pcb and it is working....Of course i couldnt find original op-amps, instead i put TLC272,271 and simillar.....just to experiment.....Pretty simillar experiences.
One thing is clear; Gary's pcb is good and working...although very large for my taste.....But there is splitted pcb also form Gary somewhere here.....i am wandering if is it good, tested???
If it is, than i'll make another on that pcb....Gary...is it good?
Cose somewhere i saw that you claimed it has some minor mistake on it...is it?
About present; it is working...not perfect but i guess it is beacause of op-amps....Coil; well i tried to make one but with simillar problems explained here....These days i'll try again with a lot of help from here...
Thanks!
regards!

[Max]

Hi all,
think I found the problem with disc...but don't know how to solve.
I found that signals at pins 3 and 5 of IC8 (lm393) are different...in amplitude.
I get two sine waves that are
- 50mV peak to peak
- 85mV peak to peak
- frequency is for both : 50Hz ---> it's noise...

so noise propagation is different and stronger in a halve!

The IC8 shuts at 100Hz down to -2.5V the "control" line that go to pin 5 of IC3/b and so blocking any sound ! Where the "control" line (pin5 IC3) must be at gnd potential for good operations...

So...I have a little noise problem here...I think.

Any idea ? Any suggestion welcome.

Kind regards,
Max

[Max]

Hi Max,

Gary is correct, but I think you have missed one subtle point here.
The coil construction article you attached says "I have measured the frequency obtained when I connect the RX coil on the detector oscillator."
In other words, Mike is saying that the RX coil was connected in place of the TX coil and then the frequency of the oscillator was measured. This is completely different to measuring the frequency across the RX coil with the TX coil connected. In this latter case it must be the same as the TX frequency, as there is no other frequency being transmitted. The only difference will be the amplitude of the signal at the RX coil.

Hi Qiaozhi,
yes I have only 10KHz when rx-rx1 coils are on rx pads and TX coil oscillate at 10Khz, like Gary said it's an air core transformer.
No problem here.
My actual problem is with poor DISC performance. I see a doubling pulse when I turn DISC pot fully CW. But now I see phase shift on all the analog gates control pins when I use DISC pot (the first gate on top) and GND pot
(the two gates below).
Don't know why I get only few cm depth when in DISC mode; in all metal mode I get 2 eur at 28cm...seems ok.

Think I have a problem in disc section but can't find anything worse till now.
Maybe capacitors ??? Values are right ???
I've used Carl's values but have different in Gary revised schematic and start to think I have to replace something.
Don't know.

Best regards,
Max

[Max]

Please, see this revised schematic based on Carl's schematic and Gary components. Also, list of materials.

Hi Esteban,
Thanks for the update. I've solved the phase mistake...stupid mistake on the scope...I was tired and leave the trigger in "vert mode"...wow

But now, that I see phase shift using DISC pot...I had another problem...that is a kind of double peak when pot is completely turned CW. Don't know why.

Performance is still poor in DISC mode.

Any idea ???

Best regards,
Max