SMT Bandito Info/Build

[Silver Dollar]

Well I just measured and there's no centertap. Both TX and RX have one end grounded.
So maybe my RX wires are swapped?

Thanks for the info on front panels. I hadn't seen that thread (I thought I've read everything
on here).

[Koala]

Well I just measured and there's no centertap. Both TX and RX have one end grounded.
So maybe my RX wires are swapped?

Thanks for the info on front panels. I hadn't seen that thread (I thought I've read everything
on here).

Maybe there is a difference between the uMax coils. Tesoro only list two types of coil 4 pin Delta and 5 pin Epsilon.

Found this


Resistance looks quite different looks more like a normal coil with a finer wire and more turns on the RX compared to the TX

[Silver Dollar]

Well the new 4 pin coils are 1mh TX and 10 or 12 mh RX somewhat similar to the Minelab coil.
They require a different oscillator but put out a lot more field. Though I'm not sure it gains you much...

[Silver Dollar]

I'm not sure this is a problem as I didn't use a Sens or Threshold pot. I didn't think they were
necessary unless you wanted more depth.

So here's the inputs to the 393's;




The fixed input to compare to;


And the chattering output;

[Silver Dollar]

So there's defiantly a problem with my Bandito similar to the problem I had with TGSL.
The RX input is a differential amp but is fed from a single ended coil. I get a sound
when I probe to the grounded side of the opamp and see a 400mv signal out of
the first opamp. I didn't check on the original Bandito but I'm using it's coil...



I see a ring down on the output of the LM393 and am not sure if it's going through the
power rails or standard path. I can hear targets but also get an oscillating tone. I did
try to isolate the 393 using 10 ohm resistors and a 4.7uf cap on the plus and minus supplys.

On the TGSL I shorted out the 2 resistors on the plus input of the opamp and grounded the
4.7K/5.1K on the other side and that helped cure it. Maybe a cap across the 200k to ground?

I'm not sure about the 39pf cap. I measured all resistors and caps incircuit but the pf value caps
would not read...

[Silver Dollar]

Well it looks like the 39pf might not have been making a good connection.
So today I tested the original Bandito to the SMT one using the original
coil hung from the ceiling. I couldn't try the TGSL as it's still not working
(maybe later on tonight I'll work in it).

They were pretty close. The original sounded louder and here's the results;

Original SMT
Gold Ring ----6-7" -------7" Solid ----8" Intermittantly
Big Silver---- 5-5 1/2"--- 1" Solid---- 2 - 4" Intermittantly
Nickel --------6" ----------6 - 6 1/2 ---7" Gone
Bottle Cap ---6 1/2" -----6 - 6 1/2"
Penny --------6" ---------6"
Quarter ------5 - 6"------6"
Dime ---------4 - 5" ------5 - 6"

[Koala]

Big Silver---- 5-5 1/2"--- 1" Solid---- 2 - 4" Intermittantly

Does not like silver ?

[Silver Dollar]

Might be a ground balance thing. I was reading the TGSL threads again and with a bad ground
balance you will reject silver. I didn't balance the new board properly. I just got my 10 turn
GEB pot yesterday so will have to connect it up.

I just remembered I disconnected the PP function too while messing around so that might be
the problem with the chatters (not the 39pf)...

I worked on the TGSL too and found it works at close range (2-3") but just ticks at deeper
ranges. Not sure what's causing that....

[Koala]

You results seem to confirm what is said on the findmall.com forum that the II umax is slightly deeper but the original has sharper sound

Strange as you would expect gold and aluminum to be affected first. I take it the iron reject was good. Looking at some video of homemade Bandidos and they appear slightly better at large iron than the IDX

http://jb-ms.com/Carlsforum/Dec24-2006/1161873823.html does confirm that too positive ground balance will reduce detection range on silver air test.

Your problem with you TGSL sounds exactly the same as when the batteries are low on my IDX. Close to the coil beeps as normal but further away sound like chatter sort of a pop and spit type sound. But it still work fine in all metal mode.

Annoyingly I am still waiting parts. It's the parts I ordered first from China that I am waiting for. Solder wick,solder and the ground potentiometer. One from China has arrived today the connectors. Look to be of high quality amazing that 5 sets or 10 pieces equal one switcraft connector in price.


One SMT capacitor went on back order from Mouser no big deal but the estimated delivery is mid July got them to ship the rest and they are here.

Start working on some coils next week

Hope you can sort you TGSL as a direct comparison would be good. I will build the same size coil as I did for the IDX.

[Silver Dollar]

Thanks for the tip on the low batteries. I checked the TX and negative supply but didn't check each
chip. I had the GEB and Disc parts off the board and the 4024 was reconfigured. It basically works
but something isn't right. I work on it some more tonight.

It completely rejects a screwdriver, drywall screw and bolt with nut and washer. I'm not sure what I
have that is iron?

I got a 10 turn pot in yesterday which I think I ordered after you so those China guys are shipping faster!

That backordered cap is going to cost you as you have to pay shipping again. Hope everything gets in
fast!

[Silver Dollar]

I couldn't get the TGSL going. There seems to be a problem with the Disc. It gets wider
and narrower as you adjust the pot. I checked the Resistors and changed the Cap but
still acting weird. Maybe my LF353 is bad?

I checked the Original Bandito with big Silver today and got 8"! By ground balancing the
new one I got 8 - 9"! So they are about the same.

[Koala]

That back ordered cap is going to cost you as you have to pay shipping again. Hope everything gets in
fast!

Hope not email they sent me just says it will ship as soon as it's in stock E.T.A. JUL 23 if they do I will have to cancel and ebay the last part.

Been reading up on coils. Seems like a lower power TX but with more turns equals the same as using more power with less turns. So the Bandido has got the same ground penetration for less battery when compared to my IDX.

[Silver Dollar]

Well I thought the measure of a TX coil is ampere turns, so 1 amp with 1 turn is 1 amp turn, but 1 amp with 10 turns is 1/10 amp turn.
So for TX more turns equals less power. That being said I have read that a MD with variable TX power will sometimes get better depth
with less power. The problem is magnetism of course. A low power will drain off and possibly allow you to see behind it where a high power
will saturate the field and not allow further object id.

July 23? How about next week? They have to mine the ore to make it? Reminds me of the time Amazon backordered something and finally
sent it 6 months later! I didn't need it by the time I finally got it...

[Koala]

I read it at times not divide but I could be wrong http://compass-metal-detector-forum.548136.n2.nabble.com/Coil-field-strength-by-George-Payne-td6185238.html

[Silver Dollar]

Well I'm confused now, he says "Loop field strength is not related directly to the loop voltage" then says
"The sensitivity was increased by increasing the loop voltage about 2.5 times"?

Also if you have an oscillator and 2 coils, one with less turns and one with more, the oscillator will put
less current into the one with more turns as the resistance is greater. I guess that's what I was trying
to say. Same current more turns is better but same circuit more turns = less current so less power in coil.

It is more complicated as a special oscillator like an H Bridge will build up current in the coil and trap it there
so will draw say 4 ma but have 150 ma in the coil where a regular oscillator might draw 2 ma and have 30 ma
in the coil.

The big question is how much is enough current? It seems a depth equal to your coil diameter is about right
(although some companies can make a coil that goes 1 - 2" deeper than that).

The stock 5 pin Tesoro goes 6" with 30 ma and it takes 64x to go twice the depth so we should shoot for
around 2 amps into the coil to match the better MD's on the market at 12"? The H Bridge does around 150 ma
so it's a start.

I found with the stock oscillator on the New Bandito I used 1.2K for R1 and got 11V P/P but some distortion, I
tried various values and found 2.49K gives no distortion but only 8.5V P/P. Will the extra 2.5V gain you anything?
I'm not sure. Is the distortion bad? I don't know. We need some further testing to see.

(1.3K = 10.4V P/P
2.0K = 9.2V P/P)

(Original Bandito reads 1.8K incircuit and has 7.8V P/P)


I do believe the Minelab style coil will go deeper but will you give up better disc in trashy areas? Need to test more.
I also see some variation day to day even with the factory unit so it may be hard to determine what is better....

The newer 4 pin Tesoro's are very similar to the Minelab coil specs so I believe there is some merit to using those...