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

[Max]

Which caps do you think are incorrect?

Hi Qiaozhi,

c9,c10,c14,c13,c16

They are all small pF values and I think there were problems in measures.
Can't say exactly what could be good values. Don't know what phase differences I have to expect exactly (is -37deg to +50deg correct at pin2 ic5 (goodrat values) ? because I think I haven't turning gnd pot.)

Best regards,
Max

[Satel]

Hi Max

I too started to built Tesoro Bandido and visit the same problems how You (-V, poor discriminate). I use original Tesoro concentric coil for this detector.
To get -5V I made some corrections: for IC1 and transistor T3 (in some circuits Q4, 2N3906) I give power supply 9V, then I increase R67 value to 2K and in emitter of transistor T7 (Q5) I get -5V.
In next days I try to solve discrimate problems.Please, can You give me Yours capacitance values of next components:C16, C10, C14, C13 and C18.
Thanks.

[Max]

Hi Max

I too started to built Tesoro Bandido and visit the same problems how You (-V, poor discriminate). I use original Tesoro concentric coil for this detector.
To get -5V I made some corrections: for IC1 and transistor T3 (in some circuits Q4, 2N3906) I give power supply 9V, then I increase R67 value to 2K and in emitter of transistor T7 (Q5) I get -5V.
In next days I try to solve discrimate problems.Please, can You give me Yours capacitance values of next components:C16, C10, C14, C13 and C18.
Thanks.

Hi Satel,
first I've used same Carl's values as in original schematic. Things were not so bad but I don't know if they were right.

Now I've substituted with these (as in Gary's revised schematic):

C16 : 39pF
C10 : 22pF
C14 : 8.2 pF
C13 : 10pF
C18 : 22pF

They are from Carl too, but measured OUT OF CIRCUIT. I think they are right.

And seems things are going well. No major differences in All-metal mode (just a bit faster response I think), but seems that in disc mode they work better than previous values.
I haven't now double pulsing or too distortion but sometimes it detects iron masses too.

"I give power supply 9V, "
I was thinking too using 9v line but I give up on this because it's not stabilized. When battery discharge you have voltage variations on V- rail that I think it's not good. Best to get mc33178 if you can; I'm still awaiting for delivery of these parts...not so easy.
Think that in worse case, one could use also a 12volt battery and an LDO regulator for 9v line.

Best regards,
Max

[Carl-NC]

To get -5V I made some corrections: ...

As a reminder, Tesoro didn't design the -V chargepump for -5V. I think it puts out about -3V or so. This should be sufficient for the circuit, i.e., -5V really isn't needed. Most opamps will run happily on unbalanced supplies.

On the caps, all I remember is having trouble getting stable readings on the LCR meter. I think I had pulled the caps out-of-circuit. So I make no guarantee they are right.

- Carl

[Max]

As a reminder, Tesoro didn't design the -V chargepump for -5V. I think it puts out about -3V or so. This should be sufficient for the circuit, i.e., -5V really isn't needed. Most opamps will run happily on unbalanced supplies.

On the caps, all I remember is having trouble getting stable readings on the LCR meter. I think I had pulled the caps out-of-circuit. So I make no guarantee they are right.

- Carl

Hi Carl,
yes not -5v ...one must consider also that there is a drop on last transistor, ,the Vcesat voltage, that will be about 1V, capacitive losses...too low frequency in charge pump...etc so maximum -4Volts on negative rail as best.
I think that with right components it will be fine anything from -2.8 to
-4volts.
MC33178 works and is fully characterized at, according to datasheet, +2.5/-2.5 volts (and so also for MC33078 but much current required).

"So I make no guarantee they are right."

I know - it's not easy to reverse eng. sometimes. I know from other experiences , expecially if it was an smt assembly.
I found second set of values is working better than first, so I think could be ok.

Best regards,
Max

[chemelec]

Hi Carl,
yes not -5v ...one must consider also that there is a drop on last transistor, ,the Vcesat voltage, that will be about 1V, capacitive losses...too low frequency in charge pump...etc so maximum -4Volts on negative rail as best.
I think that with right components it will be fine anything from -2.8 to
-4volts.
MC33178 works and is fully characterized at, according to datasheet, +2.5/-2.5 volts (and so also for MC33078 but much current required).

"So I make no guarantee they are right."

I know - it's not easy to reverse eng. sometimes. I know from other experiences , expecially if it was an smt assembly.
I found second set of values is working better than first, so I think could be ok.

Best regards,
Max

On my Revised design, I'm using the 7660 and the Minus rail is now -4.5 Volts.
But I also Agree that Even -3 volts is OK.

Yes, Carl said at the time that "He Did Remove the Caps to test them". He Also mentioned he was having a Bit of Problem getting "Stable Readings".
** Too Bad I don't have one of those Boards Here, So I could do some Very accurate Tests.
I have Three LCR Meters, One is a Sencore LC102, Capacitor/Inductor Analyzer.

I have now decided to put my Split board into a case with Proper controls and finish it off.
Maybe it will help me Solve some of the Problems mentioned here. (Trimpots are not easy to adjust when on both sides of the PCB and the board laying loose on the workbench.)

Take care....Gary

[Carl-NC]

I now remember that I was using an HP LCR meter, and great big expensive bench unit. Now I have a smaller, cheaper BK 878 handheld LCR meter, which is much more stable. So maybe I need to remeasure. Or, just use Gary's values.

- Carl

[Max]

...do it again...

Hi all,
anyone knows if bandido sounds with bricks/ceramics too sometimes ?

I had a response using disc mode and a piece of brick! And that shocked me !

I'm worried....

Qiaozhi, do you know if ceramics can be totally cancelled out by disc in Bandido ???

Maybe is just my circuit problem - not present in bought bandidos.

Best regards,
Max

[Qiaozhi]

Hi all,
anyone knows if bandido sounds with bricks/ceramics too sometimes ?

I had a response using disc mode and a piece of brick! And that shocked me !

I'm worried....

Qiaozhi, do you know if ceramics can be totally cancelled out by disc in Bandido ???

Maybe is just my circuit problem - not present in bought bandidos.

Best regards,
Max

Certain bricks seem to have some metallic content. In particular I noticed that blue engineering bricks can give a response. I also tested this with my Garrett GTAx1000, and this will detect blue bricks as well. So it's not a fault with the detector.

[chemelec]

How does this look?
Front panal is ABS with a Clear Mylar Decal.

The "Visual Detect" is an LED in series with R14.
It Works well.

Gary

[Carl-NC]

Hi all,
anyone knows if bandido sounds with bricks/ceramics too sometimes ?

Absolutely... bricks and pottery are often made from mineralized clays and can be detected. Here in the southeast US, the same red clay used to make bricks is really tough to detect in. Once at a construction site, I walked up to a large pile of red clay and my detector started wailing... nothing I could do would ground balance it.

Pottery that is fired at high temps can even be found with a magnetometer, because the heat aligns all the magnetic moments of the clay.

- Carl

[chemelec]

Here is a Rear View, Mostly all Wired up and ready for some testing.

[Max]

Hi,
thanks for your replies. Now I know that is normal to have some brick detection. It happens sometimes also with small fragments : I've tested a piece of about 5cmx8cmx7.5cm and sounds at 2-3cms in disc mode.

But I think is not a big problem like I had with GS4, where distances are much greater.

Gary, the prototype looks fine.

Best regards,
Max

[chemelec]

Some Coil Forms I made for my Coplanar coils.
These ones are 10 Inches and 5 Inches ID.
Make coil winding Much more uniform and Rigid.

If there was a reasonable demand for these in a Particular Size, I could get a small production of them done.

[Satel]

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