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

[Max]

seems now happy !

Hi Max,

I have no experience with uMax or concentric coil making.
-> but anyway here are my thoughts:
*I would start testing the circuit with DD coil - you can achieve null easyier.
and you will have reference to that original coil you are making now.
If both coils will show bad results then should be problem on board.
Maybe you have already some appropiate scrap coils; hook them to the circuit:
1) null them in DD (OO) configuration.
2) with changing caps on Tx get appropiate frequency.
3) with changing caps on Rx search for highest amplitude.

*I found out that searching for highest amplitude on Rx coil works better than trying to get same resonant frequency (even if this should lead to same result)
Amplitude was measured on input pin of preamplifier (ic removed).
Rx coil driven by circuit.

Hi Leto and all,
I'd like to send many thanks to everyone for the useful help and for every hint.
Endly I've rewounded Rx and obtained a good null at less than 1mV peak to peak.
I found also a problem on PCB that was almost invisible without using a lens !
Was a little short due to a small solder metallic "ball" that was "glued" by flux
accross two pads...I've already washed out the excess of flux by a solvent...but
this little thing there was, as I say, almost invisible and impossible to find if
I wouldn't followed signall path using the scope, discovering the "little" mistake.
I have again 33078s as low noise op amps, not yet 33178s.
Much consumption BUT

Now, in ALL METAL wow ! it works fine...pretty good:

2 eur coin at 28cm ---> small output volume boost that is easy to ear in headphones

Like in other VLFs different alloys responds very different here...but:

- a small gold ring (1.5 grams) at 24cm that seems very good considering low tx power!

My coil is now very well nulled, and my actual "recipe" is:

104 turns for TX on 200mm id
155 turns for RX on 120mm id
25 and 3/4 turns for RX1 (0.25 of turn 26 shaped in the middle between tx and rx) 200mm id

(with my components is OK)

very good ! on TX osc I have (as in Mike's "recipe"):
- TX coil gives 10.022 KHz
- RX+Rx1 coils gives 10.506 KHz
- whole RX+RX1 nulled signal on 1Kohm load and 47nf cap is less than 1mVpp
Needs very good shielding too...I haven't at now on and capacitive is a huge problem.

All the stuff run in "motion" mode ...why the manual talk about non-motion ? where is it ?

Only disc doesn't work well till now...about 1/3 of all metal performances...no good!

Have to fix it, somehow...

Best regards,
Max

[chemelec]

YES, C15. Sorry

Your Recieve Frequency "MUST BE THE SAME as the Transmit Frequency".

These Coils make an Air Core Transformer.
The Frequency on the Recieve coil has Nothing to do with the Inductance or the Parallel Cap. It is the Same Frequency.

Probably your Frequency Counter is adding a Parallel Capacitance when Measuring the Transmit Signal, Resulting in a Frequency Change.
This Can't Occur on measuring at the Recieve Coil.

Take care....Gary

Hi Gary,
thanks for the help.
Maybe you mean C15 (parallel to the RX coil) not C16. In Mike's instructions there is something about + or - 4.7nF to try on the 33nF cap (C15).
My actual frequencies are:
TX = 10.155 KHz
RX = 10.530 KHz

TX was exactly 10.002 Hz before wounding RX1 then increased. Don't know why - maybe due to force applied by RX1 coil wounded on it.

I can see on another german post that other frequencies could be:
TX 10.15 KHz
RX 11.13 KHz

Are these fine too ? Anyone knows ?
How much critic are frequency ratio and values for TX and RX ???

Best regards,
Max

[Max]

YES, C15. Sorry

Your Recieve Frequency "MUST BE THE SAME as the Transmit Frequency".

These Coils make an Air Core Transformer.
The Frequency on the Recieve coil has Nothing to do with the Inductance or the Parallel Cap. It is the Same Frequency.

Probably your Frequency Counter is adding a Parallel Capacitance when Measuring the Transmit Signal, Resulting in a Frequency Change.
This Can't Occur on measuring at the Recieve Coil.

Take care....Gary

Hi Gary,
"The Frequency on the Recieve coil has Nothing to do with the Inductance or the Parallel Cap."

Yes, I know. But I mean using Mike's instructions for measuring resonance frequency of TX and RX coils when connected to TX oscillator.
TX must give 10KHz and RX+RX1 coils must give 10.5 KHz following this way to making these coils. Then when RX+RX1 are connected to RX pads they gives only same TX frequency (10KHz).
I've measured also with scope not only frequency meter.

Take a look at Mike's instructions, below.

Thanks again.

Best regards,
Max

[Esteban]

Some people of Europe has success with the Bandido (hope this is right because has finished the project). In the files there are the same coils, etc. In very detailled parts list you can find replacements, bla, bla, bla. This is the detector based on split PCB of this people (maybe you want all the info) PCBs are in Eagle program and all the documentation in .rar compressed files. You can compare with all has been done by you at this moment. Remember that the second TX coil is winding in reverse, so big TX and receiver are in the same orientation winding and secondary TX (bucking coil) is in reverse winding (or phase).

[Max]

Some people of Europe has success with the Bandido (hope this is right because has finished the project). In the files there are the same coils, etc. In very detailled parts list you can find replacements, bla, bla, bla. This is the detector based on split PCB of this people (maybe you want all the info) PCBs are in Eagle program and all the documentation in .rar compressed files. You can compare with all has been done by you at this moment. Remember that the second TX coil is winding in reverse, so big TX and receiver are in the same orientation winding and secondary TX (bucking coil) is in reverse winding (or phase).

Hi Esteban,
thanks but I've already the Germany-group's stuff and the one from Paul-Panzer...seem nice works.
I'm doing with Gary's pcb design to avoid too layers...at now.
My coil is ok now (nulled under 1mV peak to peak).

Now it's good in all metal but disc doesn't work like expected:

I've found something that seems wrong in the disc section.
I mean at IC7/b pin 1 I get a sinusoidal wave that have a phase shift respect to
the main TX wave, and that's ok.
BUT that phase shift seems fixed , I mean when I turn the DISC pot (100K) I get
ONLY AMPLITUDE VARIATIONS , NOT PHASE VARIATIONS
::confused:: then there is a zero-crossing detector, the comparator IC5/b that so always
switches at the same time intervals (respect to main TX wave) independent from DISC pot
position (because zero-crossing appears always at the same time too).

What's wrong ? I would expect a regulable phase shift there and so different timings of
the gate signal at pin 7 of IC5 not a fixed pulse-train!
I've checked four times...everything is like in schematic and I'm very confused now.

I think that IC7/b is intended as phase-shifter, isn't it ???

Any idea ? Any suggestion welcome.

Best regards,
Max

[Geo]

Hi Max.
If you connect the scope to the input of IC5b you must see a phase shift when you turn the disc poten.... But connect the scope to -input of IC5b, not at out of ic7b. If you have not a phase shift , then look for the problem. Yes the IC7b is a phase shift (how else to work the discrimination ????)

[Qiaozhi]

Hi Gary,
"The Frequency on the Recieve coil has Nothing to do with the Inductance or the Parallel Cap."

Yes, I know. But I mean using Mike's instructions for measuring resonance frequency of TX and RX coils when connected to TX oscillator.
TX must give 10KHz and RX+RX1 coils must give 10.5 KHz following this way to making these coils. Then when RX+RX1 are connected to RX pads they gives only same TX frequency (10KHz).
I've measured also with scope not only frequency meter.

Take a look at Mike's instructions, below.

Thanks again.

Best regards,
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.

[Qiaozhi]

Some people of Europe has success with the Bandido (hope this is right because has finished the project). In the files there are the same coils, etc. In very detailled parts list you can find replacements, bla, bla, bla. This is the detector based on split PCB of this people (maybe you want all the info) PCBs are in Eagle program and all the documentation in .rar compressed files. You can compare with all has been done by you at this moment. Remember that the second TX coil is winding in reverse, so big TX and receiver are in the same orientation winding and secondary TX (bucking coil) is in reverse winding (or phase).

Nice work Esteban!

[Esteban]

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

[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

[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]

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

[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!

[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/

[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