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

[Max]

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

Hi Satel,
yes I think too. You need to have something from e.g. 20mV to 100mV peak to peak at output of IC7a when no metal near. If you have more...
Sometimes I have 80mVpp, some other time I get less...
gain of ic7a is not so hi to have 0.6 volts...when things are going well.
So:
1. the coil is unbalanced
2. you have maybe wrong connection and much noise around

for 1. nothing to do with it (buy new one or build your homemade)
for 2. ...have you GND connection at one rx lead too ??? I found that , for me, only in this case I get good working.

Best regards,
Max

[Unregistered]

Hi Satel,
yes I think too. You need to have something from e.g. 20mV to 100mV peak to peak at output of IC7a when no metal near. If you have more...
Sometimes I have 80mVpp, some other time I get less...
gain of ic7a is not so hi to have 0.6 volts...when things are going well.
So:
1. the coil is unbalanced
2. you have maybe wrong connection and much noise around

for 1. nothing to do with it (buy new one or build your homemade)
for 2. ...have you GND connection at one rx lead too ??? I found that , for me, only in this case I get good working.

Best regards,
Max

Hi Max

I cheked connections several times and all looks like OK, yes one lead of RX is connected to GND and I tested my pcb in several rooms of my house, but nothing. I have original Bounty Hunter Discovery 3300, I tested it in my workroom, to see how it works, if there are noises, but nothing, it works OK.
In days I try to test Tesoro coil in other shematic to be see, is it really unbalanced (I dont understand, how original coil with no deformation can become unbalanced at all).
Thanks
Satel

[Max]

Hi Max

I cheked connections several times and all looks like OK, yes one lead of RX is connected to GND and I tested my pcb in several rooms of my house, but nothing. I have original Bounty Hunter Discovery 3300, I tested it in my workroom, to see how it works, if there are noises, but nothing, it works OK.
In days I try to test Tesoro coil in other shematic to be see, is it really unbalanced (I dont understand, how original coil with no deformation can become unbalanced at all).
Thanks
Satel

Hi Satel,
I agree with you. If no deformation is strange that the coil could be unbalanced. Maybe is balanced and working and the proble is in some other part , I mean in the circuit somewhere.
Anyway, I had an original white's coil that become unbalanced after fall down from 3 meters or so...never opened it. I think that maybe something inside moved. One day or another I'll try to open it to investigate and maybe adjust it.
If your Bounty Hunter works fine means it gets not too noise. So I think you need to check bandido's circuit for some subtle mistake.
Why don't you try to make an homemade e.g. DD coil (easy to do) and test if something different happens ? Could be a good idea and costs nothing but the wire and some time to align it.

Best regards,
Max

[Satel]

Hi Satel,
I agree with you. If no deformation is strange that the coil could be unbalanced. Maybe is balanced and working and the proble is in some other part , I mean in the circuit somewhere.
Anyway, I had an original white's coil that become unbalanced after fall down from 3 meters or so...never opened it. I think that maybe something inside moved. One day or another I'll try to open it to investigate and maybe adjust it.
If your Bounty Hunter works fine means it gets not too noise. So I think you need to check bandido's circuit for some subtle mistake.
Why don't you try to make an homemade e.g. DD coil (easy to do) and test if something different happens ? Could be a good idea and costs nothing but the wire and some time to align it.

Best regards,
Max

Hi Max

I tryd my Tesoro coil in other (Volksturm project) shematic and it saw too coil unbalancing.Yes, for me now two ways, balance the Tesoro coil or made new coil.
I opend it and still don`t understand, what is wrong in original coil.Inside looks like OK, nothing broken and nothing moveing.
Thanks
Satel

[Qiaozhi]

Hi Max

I tryd my Tesoro coil in other (Volksturm project) shematic and it saw too coil unbalancing.Yes, for me now two ways, balance the Tesoro coil or made new coil.

I opend it and still don`t understand, what is wrong in original coil.Inside looks like OK, nothing broken and nothing moveing.

Thanks

Satel

Yes - I have a Tesoro Laser coil that looks ok. Even the inductance and resistance values measure as correct, but it just doesn't work properly. This is a big mystery.
One day I will investigate this coil more closely, but at the moment it's a dud.

[Max]

Hi Max

I tryd my Tesoro coil in other (Volksturm project) shematic and it saw too coil unbalancing.Yes, for me now two ways, balance the Tesoro coil or made new coil.

I opend it and still don`t understand, what is wrong in original coil.Inside looks like OK, nothing broken and nothing moveing.

Thanks

Satel

Hi Satel,
yes it seems ok.
Don't know if can be in this case...but...maybe the problem is around cable guard or something else, not on woundings.
Sometimes cables broke in a subtle way...you have a lose and unstable connection and this may result in unbalace. I suggest to connect a digital ohm meter to tx and rx pins with stable contacts at connector then try to move the cable to see if any change in readings occourrs.
If so some broken cable causes problems.

I think that small mV variations could occourr also with no perfect connections between coils and circuit here.

Just an idea...other things seem ok...I mean positioning and epoxy layer.

Best regards,
Max

[Satel]

Hi guys,
I have a problem...with Bandido-coil
I've realized the Bandido circuit and I think something is wrong in the coil...

Let's explain:
I've used Mike's instructions to make Tesoro concentric starting from (30AWG):
- 110 turns for TX
- 175 turns for RX
- 22 turns for RX1
First I have to decrease TX turns to get 10KHz in tx osc. --> I've done using 105 turns , OK
Second I decreased RX and RX1 turns to obtain 10.5 KHz wiring RX+Rx1 to tx osc. terminals:
- used 156 turns for RX and 20 for RX1
Then I have to null the coil adjusting RX1:
- I have connected TX coil to tx osc. terminals
- I have connected 47nF ceramic cap to RX+RX1 to have a resonance of about 10KHz-->Ok

then connected channel 1 of the scope to tx osc. (to have the reference signal) and
channel 2 to RX+RX1+47nFcap

In few words I have:
- good looking 10KHz on channel 1 --> TX say 5Vpp (peak to peak)
- 2Vpp signal on channel 2 !!!

I think is too hi for RX to have 2Vpp with no metal near ...so I think I have a nulling
problem. I've tried to minimize this voltage decreasing RX1 turns to 18...but things go
bad...too signal again...
then I rewounded rx1 with 35 turns...then decreasing --> no way !

I've tested RX-Rx1 using the bandido circuitry...and seems something works...
but I have poor detection depth (1 200gr hammer at only 10cm ! 1 eur coin at 3cm !)

What's wrong ??? Seems problems originates from the coil...
What's the good nulling voltage peak to peak I've to expect ?

I've used a fixed rigid homemade coil former: pvc, abs plastic, some glue...that seems
good and leave me the freedom of wounding coils and then remove easy some turns.

Outer coils are on 20cm former, Rx is on 12cm - very well centered !

I have mc33078 and everything else like in schematic. I'm awaiting for delivery of
mc33178s but seems impossible that 33078 cause the problems of above. Negative rail is
at -3.9 volt...that seems ok too... I have the 3 seconds battery check beep...as expected...
etc... but things aren't so good about performance !

Any idea ?
Any suggestion welcome.

Best regards,
Max

Hi Max!

If You remember, at last I have a problem with nulling Tesoro Bandido coil (my original Tesoro concentric coil was not balanced).After little break, I return back to this detector, I made new coil, and the same story.I start thinking, that something in my nulling procedure is wrong.
Now my question is: When You balanced Your coil, ch1 of oscilloscope You connect to TX (collector of T1 by shematic Gary Lecomte)? and ch2 You connect to RX, (RX in parallel with 47nF cap and lead resistor 1k) directly(without shematic) or You connect ch2 to pin 7 of IC7A (by shematic of Gary)?
Sorry my long question and I hope, You understand it
Thanks,
best regards
Satel

[Max]

Hi Max!

If You remember, at last I have a problem with nulling Tesoro Bandido coil (my original Tesoro concentric coil was not balanced).After little break, I return back to this detector, I made new coil, and the same story.I start thinking, that something in my nulling procedure is wrong.

Now my question is: When You balanced Your coil, ch1 of oscilloscope You connect to TX (collector of T1 by shematic Gary Lecomte)? and ch2 You connect to RX, (RX in parallel with 47nF cap and lead resistor 1k) directly(without shematic) or You connect ch2 to pin 7 of IC7A (by shematic of Gary)?

Sorry my long question and I hope, You understand it

Thanks,

best regards

Satel

Hi Satel,
I connected tx coil to tx pads to have 10Khz oscillations on tx coil. Then measured rx-rx1 signal using 47nF cap and 1 Kohm resistor in parallel with rx-rx1 leads directly connecting with my oscilloscope probe.

In nulling I connected directly rx-rx1-cap-resistor to probe and not to rx pads on pcb. I'vent used ic7 at all for this. To avoid offset problems that may occourr if not balanced first...and mc33178/mc33078 haven't direct control on offset nulling - so, then too, it's nothing in schematics to do offset nulling on IC7.

You only need a scope and a probe to test for voltage null on rx-rx1 coil.

Someone used ic7 to do this nulling but I think is incorrect for the reason explained above.

Best regards,
Max

[Satel]

Hi Satel,
I connected tx coil to tx pads to have 10Khz oscillations on tx coil. Then measured rx-rx1 signal using 47nF cap and 1 Kohm resistor in parallel with rx-rx1 leads directly connecting with my oscilloscope probe.

In nulling I connected directly rx-rx1-cap-resistor to probe and not to rx pads on pcb. I'vent used ic7 at all for this. To avoid offset problems that may occourr if not balanced first...and mc33178/mc33078 haven't direct control on offset nulling - so, then too, it's nothing in schematics to do offset nulling on IC7.

You only need a scope and a probe to test for voltage null on rx-rx1 coil.

Someone used ic7 to do this nulling but I think is incorrect for the reason explained above.

Best regards,
Max

Great thanks Max!

Thats my mistake was-I tryed balance the coil in shematic.Shame me! I control again my original tesoro coil and its OK, null is 7mV.Now I can continue with my other parts of schematic.

Best regards
Satel