SMT Bandito Info/Build

[Silver Dollar]

Did a little testing with the Bandito II and various resistors for R1 in the oscillator;

1K-----10.1Khz TX-----10.7V P/P-----Gold 5 1/2"-----Silver 6"

1.3K-----10.2Khz TX-----10V P/P-----Gold 6"-----Silver 7 1/2"

2K-----10.3Khz TX-----8.8V P/P-----Gold 6 1/2"-----Silver 7 1/2"

2.49K-----10.3Khz TX-----8V P/P-----Gold 7 1/2"-----Silver 8 1/2"

These are all air tests not sure in the ground.....

[Silver Dollar]

So I tried a couple input mods to try and increase depth.

The first replaces one of the 5.1K input resistors with a cap for DC coupling and the 220K to
ground with 5.1K for input impedance matching. This failed to gain and actually lost depth!
No responce to silver and gold at 6" with this setup.

The second worked quite well. I removed the 220k to ground and shorted the 5.1K input
resistor thus allowing all the signal from the coil to get into the opamp. This netted
8 1/2" on gold and 9 1/2" on silver. As always this might not mean anything in the ground
but could gain a little...

[Silver Dollar]

I didn't have 620k resistors so had to use 681k. The 22n caps should change to match
the frequency we want out of the bandpass filters. So Tried 1Meg, 470K, 604K and 681K
and found the 604K gave the best response.

I tried a few values for the cap but 22n was best.

Also the 100n in the Threshold amp has been found to work better as 22n. With these mods I
get 9" on gold and 12" on Silver in air test. Here's a modified Schematic;

[Silver Dollar]

Oops one last mod. I found adding the diode to the bottom of the 4024 diodes gives about 1/2" more air test.
So here's the schematic for all mods;



Playing with the TGSL is weird. The Disc didn't work yesterday it was just widening and narrowing so I removed
the LF353 and put a socket. I used a TL072 and same failure. Well today I put the LM353 and it's sort of working.
It gets a null in the center at one end of the Disc and 3 pulses at the other but it slides back and forth like it should.
I took some pictures and just noticed my TX is 13.7 khz. I'll have to tweak that and maybe lower the TX level somehow
to kill those extra pulses....

[Silver Dollar]

I lowered the TX level fed to the comparitors and tweaked the frequency to 14.6khz
but now the Disc and GEB seem to be off by 90 degrees or 180 or something...

[Silver Dollar]

I put a low frequency signal through the RX input and followed it all the way through
everything looks good! I'm thinking the Disc and GEB are not in the right place, not
sure why? I tried another opamp for the LF353 and new caps. Maybe the 393 is bad?

It works now and better than before. A good signal is heard when a target is in normal
range but there is lots of falsing and chatter...

[Silver Dollar]

The falsing seems to be caused by a 100hz oscillation on the signals coming out of my OP07's
(replacement for the LM308's). Funny though when it's there I get more depth (silver to 12")
when it goes away the sound is solid but only 8" on silver. I saw it on both OP07's but only one
output of the LM358 (using a TL072 as my LM358 got damaged).

[Silver Dollar]

It seems to be a bad connection somewhere as pressing on the board makes it go away....

I'll try re soldering everything. I had some glitching and it seemed to be caused by the
center leg on the FET broke when I reinstalled it. A new FET cured that but now that
pecky oscillation...

[Silver Dollar]

Well I finally got it working. The best I could do for depth though is 7" on Gold and 8" on silver.
I had a little more at one point but lots of falsing. I'm not really sure where it came from but
it seems eradicated (for now)...

[Silver Dollar]

I measured the Disc and GEB signals to check them against my TGSL and have a picture;

These are vs TX so look funny as the RX is shifted (maybe 200 degrees? Can't tell as can't
see the RX!).

The Bandito acts much different than the SMT Bandito and TGSL. It has random noise at
high sens and clean strong signals and can detect silver to 14". The target signals look
different too;





Not sure why? The filters are a bit different with the negative feedback opamps and
some values are different too....

[Koala]

Aren't the coils designed differently for the Bandido vs the Bandido II µMax ?

reading this thread the original coil for the none µMax does not test that well for depth and a homemade coil surpasses it.

[Silver Dollar]

Well my Bandito is a Rev B non uMax 5 pin (coil) with 6 mh and 6.5 mh which I believe is correct for the
SMT Bandito II and also for the TGSL. I'm not sure if there is a Bandito II uMax that uses the 4 pin
1 mh and 10 mh coils?

Looking back the original Bandito didn't do so well in my first test but worked excellent in the last. Also I have
never run the SMT board on batteries, there might be a difference there. Also I need to get my front panel
made as there might be some effect from grounding the pots to the panel and PCB. I have the shape cut out
but need to learn a Cad or Drawing program to make a fancy panel graphic. I'd like to at least have 1 - 10 for
the Disc pot for repeatability and testing.

[Koala]

I am more confused than ever now. From the Tesoro site they only sell 2 types.

"It is very important that you select an accessory coil that is compatible with your detector. Our coils are divided into two series, the Delta and Epsilon. The Delta coils have 4-pin connectors; they are, also called H.O.T. (High Output Technology) coils. The Epsilon coils have 5-pin connectors and are designed for µmax coils. Check your detector to make sure you get the right kind of coil."

And elsewhere I read that the Eldorado can be used on the Bandido but if you use homemade TGSL on the Eldorado it does not work properly as the phase is out because it's not center tapped

So you have a 5 pin µMax coil on a none µMax Bandido from original. But if the thread about the Eldorado and Bandido is correct the phase will be out on your SMT Bandido because it's not center tapped. This is where I get confused Tesoro only sell one type of 5 pin coil that is advertized to work on all units ? Something does not add up. My head hurts.

Think I will have to make one of each and test.

"grounding the pots to the panel and PCB" I found on my IDX it did not make that much difference except depth testing wasn't consistent and by a few centimeters until everything was boxed

[Silver Dollar]

Well the uMax is just a micro doing the sound so I believe the coil is the same as the old technology units.

The 5 pin I have is the old brown 8" and it has no centertap on the RX. So unless the Eldorado used a special
coil it couldn't have been centertapped. There is a spare wire in the 5 pin so a center tap could be chosen
at the control end but they would have had to carry it through to my unit to make them all compatible.

Davor used his own center tapped coil on an IGSL and just had to add some extra capacitance to the Disc and
GEB phase caps so not a huge difference to make it work...

[Koala]

I was looking at this and this. Looking at the last diagram I would guess that the box of numbers to the top right were someones measured coil.


Also noticed on some of the other forums that some had tried a larger newer coil and it worked okay but others it caused chatter and require the sensitivity to be turned down that much that they go no deeper than the original brown coil