SMT Bandito Info/Build

[Koala]

Yep I would go with that the three successful builds on here Firebox Hugo and ashefr10 used a 2N3906 PNP wounder how bernte_one got on

[Silver Dollar]

I'm still unclear on the mistake for the pass transistor on the output of the negative supply.
Chemlec showed a PNP with the emitter to the output then corrected it to a NPN with the
emitter going to the input. I found a picture on the WEB of a capacitance multiplier with
a NPN with Emitter to the output but I'm not sure if this being a negative supply changes
things....



I found the answer! If you have a negative supply it goes this way;

[Silver Dollar]

I thought the thin ones were more stable as they are on a silicon substrate. As long as they are
1% it doesn't matter to me. You can always coat the finished PCB with conformal coat to protect
it from the elements.

I did a few more tweaks to the new layout today. I added a couple of pads so you can select the
diodes you want for sound. I also added a couple of mods from the attached schematic. One is two
20 meg resistors (oops more values to buy!, those are for the PP mode and helps ground balance
I think. And an option to jump the sensitivity pot to -5v through a resistor. Some used that one the
Golden Saber to get closer to the noise floor. You can still stuff the original resistor and use it per
the original design.

[Koala]

You have been busy

Done some more reading and thin film may not be suitable for a detector thin film resistors are susceptible to moisture Thick film resistor elements become glasslike after firing, which means they are inherently impervious to moisture

So going for thick film things get much easier 1% ±100ppm/°C in 1206 size which is the same spec as the cheapest thin film are easy and much cheap to find

[Silver Dollar]

Yow some of those are expensive! I just completed a new layout. I fixed a problem with an ungrounded cap
and changed the TX to the Minelab one. I also added a MIC5207 LDO setup for the main 5V and another for
the TX itself (I have these handy).
Here's a picture;
Note with the Minelab you don't need the 1.2K , 12K and 20K!

[Koala]

1x 20 RNCP1206FTD20R0CT-ND $.09
1x 100 RNCP1206FTD100RCT-ND $.09
2x 150 RNCP1206FTD150RCT-ND $.09
1x 200 RNCP1206FTD200RCT-ND $.09
6x 1K RNCP1206FTD1K00CT-ND $.09
1x 1.2K RG32P1.2KBCT-ND $.65
2x 2.2K RG32P2.2KBCT-ND $.65
2x 4.7K RG32P4.7KBCT-ND $.65
5x 5.1K RG32P5.1KBCT-ND $.65
8x 10K RNCP1206FTD10K0CT-ND $.09
1x 12K RG32P12.0KBCT-ND $.65
8x 20K RNCP1206FTD20K0CT-ND $.09
1x 27K RG32P27.0KBCT-ND $.65
4x 47K RG32P47.0KBCT-ND $.65
1x 82K P82KBCCT-ND $.79
10x 100K RG32P100KBCT-ND $.65
1x 150K RG32P150KBCT-ND $.65
5x 200K RG32P200KBCT-ND $.65
1x 430K RNCF1206DTE430KCT-ND $.55
1x 470K RG32P470KBCT-ND $.65
2x 620K P620KBCCT-ND $.79
4x 1M MCA1206-1.00M-CFCT-ND $,53
2x 2.7M 311-2.70MFRTR-ND thick film $.003

[Koala]

going to plod along with digi-key

The right size resistors in thin film are 1/4 of the price

just had a quick look and they have all the IC's and diodes except TLC22262?

If they have 90% of everything then there will only be one delivery charge then get the rest from eBay.

[Silver Dollar]

Well it looks like you can use 0805's in a board designed for 1206's. They are a bit more
available and a little cheaper. So maybe an option?

[Silver Dollar]

0805's seem to be more prevalent. I think they might work as this show they are close in size;

1206 3.0x1.5
0805 2.0x1.3

Ebay has a wider selection of these...

I have some pcb's and some of each type I'll take a look and see if it's workable...

[Koala]

Ya Mouser has some for $0.07, those are 1% and $0.01 nice! 0805 though I wonder if they would work?
I wonder how the guys in china get 5% parts? Maybe they are 1% that don't meet spec?

A lot of people have built SMT boards where did they get the components?

These guys have 1% for $0.10 you could get all 70 needed for $7 but probably $10 for shipping...
http://www.electron.com/resistors/sm...ors-size-1206/

Nice does not mention if they are thick or thin film

Digi-key have some thin film 1% at $.09 here not checked if they have every size have to go out now

[Silver Dollar]

Ya Mouser has some for $0.07, those are 1% and $0.01 nice! 0805 though I wonder if they would work?
I wonder how the guys in china get 5% parts? Maybe they are 1% that don't meet spec?

A lot of people have built SMT boards where did they get the components?

These guys have 1% for $0.10 you could get all 70 needed for $7 but probably $10 for shipping...

http://www.electron.com/resistors/smd-resistors/smd-resistors-size-1206/

[Koala]

http://www.taydaelectronics.com/resistors/smd-chip-resistors/0805.html

1/8W 1% 0805 SMD Chip Resistors only $0.01 min order of 10.
will be thick film though

Keep finding thin film 1206 for around $0.07 available individually but only in one or two sizes. Someone must have a full range ?

would be easy if you need 5000 of each as most only supply on a reel.

[Silver Dollar]

Yes I had a look on Ebay and came to the same conclusion around $20 for the required kit
to have all the values you need (and hope you don't need more than 10 of each).

Hmm these should be dirt cheap. The problem is handling. 100 should be the same cost
as 10 just the cost to package and ship adds up.

This is the closest I can get $12 for 90% of them.

http://www.ebay.com/itm/1206-5-SMD-S...item5d49493178 Oops 5%!

You might want to make sure you need all those values as I thought I checked and you don't need 430K.
There are 3 schematics floating around. I'm still working on a perfect list...

I'm using 4.99K for the 4.7K and 5.1K and have a mod to the 620K's so can make them 680K or 1M. I have a few
old boards hanging around I can steal parts from and can get most of the oneses from work but it's still a problem.

[Koala]

using thin film comes out very expensive £19.61 just for the resistors

1x 20 660-RN732BTTD20R0B25
1x 100 660-RN732BTTD1000B25
2x 150 660-RN732BTTD1500B25
1x 200 660-RN732BTTD2000B25
6x 1K 660-RN732BTTD1001B25
1x 1.2K 71-TNPW12061K20BEEN
2x 2.2K 71-TNPW12062K20BEEN
2x 4.7K 71-TNPW12064K70BEEA
5x 5.1K 754-RG3216P-5101-BT5
8x 10K 756-PCF1206R-10KBT1
1x 12K 71-TNPW120612K0BEEA
8x 20K 756-PCF1206R-20KBT1
1x 27K 754-RG3216P-2702-BT5
4x 47K 754-RG3216P-4702-BT5
1x 82K 667-ERA-8AEB823V
10x 100K 756-PCF1206R-100KBT1
1x 150K 756-PCF1206R-150KBT1
5x 200K 660-RN732BTTD2003B25
1x 430K 667-ERA-8AEB434V
1x 470K 754-RG3216P-4703-BT5
2x 620K 71-CRCW1206J-620K-E3 thick flim
4x 1M 660-RN732BTTD1004B25
2x 2.7M 71-CRCW12062M70FKEA thick film

might have to go for plan B there is no plan B

[Koala]

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.

Had a look at some of the SMT resistor kits very little in the descriptions but tolerance are either 1% or 5% so guessing they are thick film

http://www.ebay.co.uk/itm/0805-SMD-SMT-Chip-Resistor-Assortment-Kit-177Values-4425pcs-/191138428275?pt=LH_DefaultDomain_0&hash=item2c80bcf573

I will stick to plan A and start getting part numbers for Mouser if something better comes along it no big loss