SMT Bandito Info/Build

[Silver Dollar]

Well the electrolytics are through hole too but I have those so wasn't too worried about it.
Someone said you can buy an assortment of SMT resistors from China. I got some 1%
through holes a short time ago $6 for 600 resistors, a good deal I thought. I need to find a
deal like that on caps. My old junk box is getting pretty low these days.

[Koala]

Cheers mouser looks good slightly dearer but supply individually I can look up the part numbers and post here silly both doing the same thing

Used mouser before only place I could get a Whites coil connector.

[Koala]

there are at least 11 none surface mount capacitors mostly the larger sizes.

Quite a few different sizes of resistors

Farnell have every size in 1206 but in packs of 10

1x 20
1x 100
2x 150
1x 200
6x 1K
1x 1.2K
2x 2.2K
2x 4.7K
5x 5.1K
8x 10K
1x 12K
8x 20K
1x 27K
4x 47K
1x 82K
10x 100K
1x 150K
5x 200K
1x 430K
1x 470K
2x 620K
4x 1M
2x 2.7M

R65-??

[Silver Dollar]

Yes the thins are close tolerance and low drift. Now caps on the other hand...

It seems ceramic is OK for all of the SMT caps. If you notice the TX and RX caps are through hole.

Have you tried to find the chips yet? I ordered from Mouser a little while ago and found good prices and
a great selection. They even have a hobbyist shipping plan for $5.

I found a way to get the gerbers so I can have some more boards made. Anybody need a board?
I estimate $6 delivered. I may try to make a few slight changes, mostly to allow for a Dual Band ito.
It should be just a few extra holes for wires easily ignored. The Minelab TX should be added too if it
will fit and maybe a few regulator choices to allow for different power schemes?

[Koala]

The only resistors I can find in a good range of values are classed as
Chip?
Thick film
Thin film

Quoting the wiki

"The resistance of both thin and thick film resistors after manufacture is not highly accurate; they are usually trimmed to an accurate value by abrasive or laser trimming. Thin film resistors are usually specified with tolerances of 0.1, 0.2, 0.5, or 1%, and with temperature coefficients of 5 to 25 ppm/K. They also have much lower noise levels, on the level of 10–100 times less than thick film resistors."

So I take it thin film 1206 is what is required

[Koala]

Back from a day at the beach with the IDX. Had a good day plenty of finds. Kinda got it dialed in now

Will have a hunt around for a supplier that stocks most of the components. Metal film resistors and film capacitors aren't that common most are chip technology

I am normally late but not by years.

Yep that's a very nice bonus means 1x PP3 will give useful detecting hours vs the weight of 8x AAs it never dawned on me.

[Silver Dollar]

We it seems (from doing a little reading) that the negative supply can work fine down to 2.5V.
A side benefit is low current consumption 14 ma vs 36 ma for a TGSL with approx. 5V. That's
nice! I wonder if we could go to +- 2.5V and super low currents?

It looks like we are a bit late to the party as most of the work on these was happening a few
years back. Too bad I'd love to get a few more boards and possibly do a IGSL style Bandito
using 2 pcb's. We have the sprint files but just a viewer so can't get the gerber files....

[Koala]

I have decided to get this enclosure mainly due to the ease of making a waterproof cover.

I built a really nice enclosure for my IDX with a separate compartment for the battery but attached it under the stem this has made it very difficult to waterproof and also very easy to knock the controls. Have spent half an hour on the beach at night wondering why I had no signals before I realized that the disc was turned all the way up

Weathers is good tomorrow so a trip to the beach with the IDX not been out detecting for about a month.

[Silver Dollar]

Those photo's are good. I was just checking to make sure my docs matched. It looks like the circuit
matches the last schematic I attached. It uses a slightly different battery monitor.

For the components I have found some values are not easy to find in some sizes. The caps seem to
be different sizes depending on value. I have different sizes / values available at work so I can "try
before I buy" to make sure to order the correct ones. It's hard to tell from the pictures but the pads
seem larger to me. A too big component can be used but is hard to solder as the pads are underneath it.

Here's a link on pad sizes; http://en.wikipedia.org/wiki/Surface-mount_technology

Looks like 3mm x 1.5mm = 1206 for resistors
4.4mm x 2.1mm =1806 for caps

So 1206 should work for both

[Koala]

for the capacitors I take it that 1206 (3216 metric) is the best size

can only find a few metal film in either Polyethylene Naphthalate and Polyphenylene Sulphide in limited sizes

Same with the Resistor 0805 (2012 metric) can find some metal film but not every size

at Farnell and RS

Don't see the point in scrimping on components if there is a stabilizability advantage have to look elsewhere

[Koala]

Yes I have the silverdog PCB looks very good and much better than trying to etch my own.




Can take some better photos in daylight if you need them

97.5mm x 71mm

pads 3mm x 1.5mm approx for resistors
4.4mm x 2.1mm approx for caps


Yes I read also the original Bandido was very good. There were 4 Bandido's the most desirable ones were the original and the last. The last Bandido II umax was slightly deeper but the original had crisper sound on good targets and less chatter in iron infested ground.

[Silver Dollar]

Yes 2012 would be 0805 but the ones you linked were 1206. Did you get your pcb from SilverDog?
I am waiting for mine but would like to see the pcb (both sides) to plan my parts list and verify
which schematic we are working to. I found a German schematic this morning that uses the battery
check circuit that's in the layout. It's different from the original Carl one and Chemelec's.

I read the earlier models worked better than the Bandito UMax. Probably because of the power setup. My
plan was to build it into a housing from a Tracker IV. It already has 2 9V batteries so maybe some improvments
can be made? I wondered why they didn't use +-15V for the old op amps to get the max headroom. There is a
lot of dynamic range in the return signal. Instead they compress the heck out of it and then trigger on mv's.

The variation you talk about appears in most detectors. I think that's why some say each one is great
and some say each one stinks. I had a Radio Shack that worked pretty good but the coil was advertised
to be waterproof, well it wasn't and when I brought it back they exchanged the whole unit. The new one
just didn't work as well.

The coil will make a difference too. Ivonic said 1 out of every 4 coils he made was just not quite as good. The
beauty of making it yourself is you can tune it for a long time to make it the best it can be. The commercial
ones get a 1 minute test and then are off to be sold...

Here's that schematic;

[Koala]

Resistor pads are 3mm x 1.5mm does that mean 0805 (2012 metric) are going to be the best fit

Would this be a good choice

http://uk.farnell.com/panasonic/era8aeb102v/resistor-metal-1k-0-25w-0-1-1206/dp/1717745RL

metal film and available in quantities of 5 and quite a range of sizes

Looks like Tesoro did not use tight spec components

Quote from another forum

"and just how well it worked. That is the tricky part because I found there to be quite a variance between batches of Tesoro's of the same model. If I ordered in let's say 10 units of the same model, like the original Bandido, I might discover that 1 or 2 would be a bit wimpier than the average unit, and 1 or 2 might be a 'hot-performing' specimen. I was a Tesoro Dealer (obviously) at the time and I checked out every unit that came in prior to sale to ensure everything worked."

[Silver Dollar]

Well on the negative supply. I'd try to get as much voltage as possible just because it
seems right. At work we use similar circuits and we get 4.1 - 4.7 for the negative supply.

I'm going to use the schottky's to get a better output though on some units we put a diode
in series with the battery and use the far side as - 0.5v for just a tickle of negative voltage.

We clamp the signal at 0.6v at the second filter stage anyway so it might not matter much.

I had tried to come up with a way to drive the negative voltage generator with the direct TX
frequency. A question, why did they use a pass regulator when there is not enough voltage
available? Usually you use that to throw away excess voltage....

[Koala]

Some more information on this forum under the TGSL mode CMS tread including one mistake on the legend

http://www.geotech1.com/forums/showthread.php?19346-TGSL-mode-CMS&p=156787#post156787