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

[chemelec]

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

According to Your Schematic, The Ground Balance Control is a 3.5 Turn Potentiometer.

According to the Manual, it Must be at Least a 5 Turn Pot.
(For Preliminary Testing, The Manual Says: Turn it Counter Clockwise a full 5 Turns, than Clockwise 2 Turns.)

But How Critical is this adjustment?

I'm just using a Single turn pot at the moment, But I haven't done any Tests Outside yet.

Gary

[Max]

Hi Max

Today I increased oscillator transistor R1 value to 3k and get correct sinus signal under TX coil (I lost little amplitude) and pulse now not with duble peaks.But in pin 6 of IC 4D (R34, C1, the pulse is deformed, it looks-like saw tooth.Can You tell me, what signal You have in pin6 and what is Your TX oscillator signal amplitude?
Thanks

Hi Satel,
do you mean maybe IC5a in Carl's schematic...at output (for me pin 1) I get a square-like signal.
It's a zero-crossing detector and switch at every crossing with saturation of comparator lm393. If you have little deformation of the square signal it is normal due to load applied on this output.
At r34/c18 junction you must have something like previous but not square ...equals to capacitor charge-discharge curve in r-c circuit (it is an rc). I have it, fast charge-discharge signal and it's OK to have it this way.

TX amplitude is fully Vcc related. Many volts. Big amplitude...but current in osc. is not so big...so I was thinking modifing R1 at first to avoid double pulsing...then used second set of values and double pulsing disappears. I have R1=1.2K as in schematics and circuit works fine.

Little problem could be some brick/ceramic detection in disc mode too...but at very few cm...so it's not a real problem.

Best regards,
Max

[Max]

Hi,
have some more info.
I've measured TX pulse on my circuit and is 10.2 volts peak to peak, as expected.
I have a tx coil with about 21.4 ohm resistance.

Data I have for tx gives it at 22ohm and rx+rx1 coils also 22ohm, for tesoro concentric
(data are from kt315 old post present in the archive - and are correct).
If you use original coils please post here your values -> if they are different you could
end up with different tx amplitude and also frequencies.
Other important things could be Q factor...and internal shaping.

You need to measure tx value as about double of your +V (about +5volts), peak to peak.
Also you have to check that it's not too deformed. Need a near to perfect sine wave.

I use poly caps for C1,C2 and noticed that needs about 1 minute to stabilize after switch-on.
Same thing for TR1 (2n3906) and other components in tx section.

Another thing to check is using 2 or 3 different, to test what's best, 4066 because some,
I noticed, work better than others...I think is due to resistance of gates in on state and
thresholds values that differs from one ic to another.
E.g. I have some older ones (ceramic case) and doesn't work any well...are SGS HCF4066 (from 80's, but new) --> don't work at all !

Other important things are bias currents, noise, etc in replacement ics for tlc2262. Now I have good
tlc2262, but before I have tested a number (I have a good collection) in one afternoon... :
TL072/82 --> good, but too consumption
TL062 --> desperate choice...not so good due to hi consumption, AVOID
TS272 --> good, but too consumption
TS27M2CN --> good, much like original tlc2262 but they are a bit noisy
LM158/358/1458 --> not so good but work too, rel. low consumption
LS204 --> really good, if you have, also for mc33178 replacement
LF353 --> BAD, don't use them
MC4558 --> BAD, don't like low supply

I was thinking also at ne5532 but never tested (no good due to enormous consumption!).

IC3 isn't critical...you could use what you want, but IC6 and IC10 are !

But you need mc33178, mc33078 or at least ls204 in IC7 and IC9 sockets. If not, circuit could
work too with other ics...but not really stable and with few performance.
I'm using 33078 at now for all measures...and works ok...but them need 10mA extra from
voltage converter. I'm still awaiting for real MC33178.

Best regards,
Max

[Satel]

Hi,
have some more info.
I've measured TX pulse on my circuit and is 10.2 volts peak to peak, as expected.
I have a tx coil with about 21.4 ohm resistance.

Data I have for tx gives it at 22ohm and rx+rx1 coils also 22ohm, for tesoro concentric
(data are from kt315 old post present in the archive - and are correct).
If you use original coils please post here your values -> if they are different you could
end up with different tx amplitude and also frequencies.
Other important things could be Q factor...and internal shaping.

You need to measure tx value as about double of your +V (about +5volts), peak to peak.
Also you have to check that it's not too deformed. Need a near to perfect sine wave.

I use poly caps for C1,C2 and noticed that needs about 1 minute to stabilize after switch-on.
Same thing for TR1 (2n3906) and other components in tx section.

Another thing to check is using 2 or 3 different, to test what's best, 4066 because some,
I noticed, work better than others...I think is due to resistance of gates in on state and
thresholds values that differs from one ic to another.
E.g. I have some older ones (ceramic case) and doesn't work any well...are SGS HCF4066 (from 80's, but new) --> don't work at all !

Other important things are bias currents, noise, etc in replacement ics for tlc2262. Now I have good
tlc2262, but before I have tested a number (I have a good collection) in one afternoon... :
TL072/82 --> good, but too consumption
TL062 --> desperate choice...not so good due to hi consumption, AVOID
TS272 --> good, but too consumption
TS27M2CN --> good, much like original tlc2262 but they are a bit noisy
LM158/358/1458 --> not so good but work too, rel. low consumption
LS204 --> really good, if you have, also for mc33178 replacement
LF353 --> BAD, don't use them
MC4558 --> BAD, don't like low supply

I was thinking also at ne5532 but never tested (no good due to enormous consumption!).

IC3 isn't critical...you could use what you want, but IC6 and IC10 are !

But you need mc33178, mc33078 or at least ls204 in IC7 and IC9 sockets. If not, circuit could
work too with other ics...but not really stable and with few performance.
I'm using 33078 at now for all measures...and works ok...but them need 10mA extra from
voltage converter. I'm still awaiting for real MC33178.

Best regards,
Max

Hi Max
I mesaured my coil parameters with MASTECH MS 8201H and get this results:
TX-23,9 Ohm 6,29mH and RX 22,9Ohm 6,92mH.
Yes, I think signals on IC5a pin 1 and after R34/C18.I think, that this signals are same with Yours.My IC-s are the same, what writed in shematic, but at that moment I dont know, what is wrong. In discrimination mode sensitivity is 2cm (for Al plate 3cm*3cm) and in All metal mode its generated periodicaly signal, but no metal is near. My TX amplitude is 7V from peak to peak (after increasing R1 to 3K, because my sinus signal was little damaged).
Ok, I continue to check my PCB.
Thanks to You

[Max]

Hi Max

I mesaured my coil parameters with MASTECH MS 8201H and get this results:

TX-23,9 Ohm 6,29mH and RX 22,9Ohm 6,92mH.

Yes, I think signals on IC5a pin 1 and after R34/C18.I think, that this signals are same with Yours.My IC-s are the same, what writed in shematic, but at that moment I dont know, what is wrong. In discrimination mode sensitivity is 2cm (for Al plate 3cm*3cm) and in All metal mode its generated periodicaly signal, but no metal is near. My TX amplitude is 7V from peak to peak (after increasing R1 to 3K, because my sinus signal was little damaged).

Ok, I continue to check my PCB.

Thanks to You

Hi Satel,
I think you need to check at pins 5 and 3 of IC8 (lm393). I solved the poor disc problem cutting the 50Hz noise that I can see there, just shielding.
But what's strange is periodic in all-metal. Seems some feedback signal...have you checked that +V / -V remain stable when it sounds ? sometimes current increase transients are detected as signal by amplifiers if supply is not well regulated and stable.

Best regards,
Max

[Satel]

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

Hi Max
I am now in the same position, how You was, all metal working (2cm coin 22cm), but discrimination is bad (50 Hz noise in legs 3,5 IC.Problem was in minus supply voltage, in my version it is -2,3V and it not must be -5V.
Can You post here pictures from Yours shielded Tesoro pcb-s?
Thanks

[Max]

Hi Max
I am now in the same position, how You was, all metal working (2cm coin 22cm), but discrimination is bad (50 Hz noise in legs 3,5 IC.Problem was in minus supply voltage, in my version it is -2,3V and it not must be -5V.
Can You post here pictures from Yours shielded Tesoro pcb-s?
Thanks

Hi Satel,
if noise is a problem like in my case, just shield using a metal box with removable cover...it's easy.

Sorry,I have no pictures at now and also my camera...(my brother has it) but I've made really easy. A singleside pcb facing copperside (copper of shielding pcb downside not against solders !) and a thin al sheet shaped on top on sensitive components part of pcb. Then two small cables soldered at same point on gnd trace. Really easy. But metallic box is easier I think.

Solve the noise asymm and you will have happy disc too.
But is hi motion behaviour and fast speed relative required (>1m/s).
On V- rail...well also -2.8 volts could be ok. Anything else say -3, -3.5 etc will be better but this is not a real problem if you have at least -2.8, -2.9 V.
You can increase easy a bit voltage on V- reducing also R5 and R6 from 10K to something lower e.g. 8.2K or 6.8K or lower (both the same always), but taking care you haven't too much negative voltage then and proceding from step by step reducing by small values (first 8.2, then 6.8 etc). This way you'll get more than your -2.3V but current consumption increases too...some mA.

Where have you find your original coil? Do you know any supplier of used tesoro coil?

Best regards,
Max

[Satel]

Where have you find your original coil? Do you know any supplier of used tesoro coil?

Best regards,
Max[/quote]



Hi Max

I found the coil accidentally from Finland ( was some electronic shop), it situated 80 km from my country.Time to time I visit this country.

Best regards
Satel

[Max]

Where have you find your original coil? Do you know any supplier of used tesoro coil?

Best regards,
Max

Hi Max

I found the coil accidentally from Finland ( was some electronic shop), it situated 80 km from my country.Time to time I visit this country.

Best regards
Satel[/quote]

Hi Satel,
I've asked to you because I've done concentric coil myself...and works well and I think I can shield too but I'm worring about finding a good coil housing for it...that all this requires time and work.
I think maybe I could find somewhere an original one without too much expenses, saving time and work. Actually I have not much time for my MD hobby.

I have found a lot of dealers around the world...but all of these sell new parts...but why buy a new coil...if one have an homemade detector...?
Too expensive and at the end not required...I think. I'll take a look around to find something inexpensive...e.g. on ebay.

"Finland" yes I know, is a beautiful place...I know a girl from there...she showed to me some pictures of her country...and she's interesting too. But don't know if she understand what is a coil....I think not. Bad luck.

Best regards,
Max

[Unregistered]

Hi Satel,
I've asked to you because I've done concentric coil myself...and works well and I think I can shield too but I'm worring about finding a good coil housing for it...that all this requires time and work.
I think maybe I could find somewhere an original one without too much expenses, saving time and work. Actually I have not much time for my MD hobby.

I have found a lot of dealers around the world...but all of these sell new parts...but why buy a new coil...if one have an homemade detector...?
Too expensive and at the end not required...I think. I'll take a look around to find something inexpensive...e.g. on ebay.

"Finland" yes I know, is a beautiful place...I know a girl from there...she showed to me some pictures of her country...and she's interesting too. But don't know if she understand what is a coil....I think not. Bad luck.

Best regards,
Max[/QUOTE]

Hi Max
I agree with You.When I end my Tesoro MD, I want to built Fisher 1266, for this MD I try to find ready coil too,but if not, then I hope to collect coil parameters from this forum.
Best regards
Satel

[Max]

Hi Satel,
I've asked to you because I've done concentric coil myself...and works well and I think I can shield too but I'm worring about finding a good coil housing for it...that all this requires time and work.
I think maybe I could find somewhere an original one without too much expenses, saving time and work. Actually I have not much time for my MD hobby.

I have found a lot of dealers around the world...but all of these sell new parts...but why buy a new coil...if one have an homemade detector...?
Too expensive and at the end not required...I think. I'll take a look around to find something inexpensive...e.g. on ebay.

"Finland" yes I know, is a beautiful place...I know a girl from there...she showed to me some pictures of her country...and she's interesting too. But don't know if she understand what is a coil....I think not. Bad luck.

Best regards,
Max

Hi Max
I agree with You.When I end my Tesoro MD, I want to built Fisher 1266, for this MD I try to find ready coil too,but if not, then I hope to collect coil parameters from this forum.
Best regards
Satel[/quote]

Hi Satel,
bandido seems a good vlf. Don't know fisher 1266 ...is it better than tesoro ?
Yes, here are much coil parameters e.g. :

http://geotech.thunting.com/cgi-bin/...oils/index.dat

Best regards,
Max

[Esteban]

Tesoro coil for uMax:

http://cgi.ebay.com/Tesoro-7-Search-...ayphotohosting

You can find near 50 items regarding Tesoro coils (include coil cover) in ebay.com for "buy it now!" items.

[Max]

Tesoro coil for uMax:

http://cgi.ebay.com/Tesoro-7-Search-...ayphotohosting

You can find near 50 items regarding Tesoro coils (include coil cover) in ebay.com for "buy it now!" items.

Hi Esteban,
thanks for the hint.
I'll take a look there.

Best regards,
Max

[Satel]

Hi Max and other guys

I lost my head.I building Tesoro Bandido, I used original coil, but it did´nt work.In pin 7 IC7b (by Carl schematic) is signal with amplitude 0,6V.Looks-like coil not balanced.It is used coil but outside view is OK (not opened).In all metal position (with switch S1, auto-tune connected) it detects 2cm coin at 22cm, but if I open S1, it detects coin only at 2 cm.Can You give please some ideas?
Thanks
Satel

[chemelec]

Hi Max and other guys

I lost my head.I building Tesoro Bandido, I used original coil, but it did´nt work.In pin 7 IC7b (by Carl schematic) is signal with amplitude 0,6V.Looks-like coil not balanced.It is used coil but outside view is OK (not opened).In all metal position (with switch S1, auto-tune connected) it detects 2cm coin at 22cm, but if I open S1, it detects coin only at 2 cm.Can You give please some ideas?
Thanks
Satel

Yes I would say your coil is not balance perfectly.
Too much un-balance will give a Square wave at that pin.

I use Pin 7 of IC7b to get Zero balance on my coils, also using the TX Signal from the bandido.

Seeing as IC7 has quite a bit of gain, it Works well this way to get Maximum Cancellation.

I also Tune the Recieve using parallel caps to C15 to get Peak Resonance.

Gary