# Overton Coach Lighting



## Lemonhawk (Sep 24, 2013)

Since this is a short passenger car there was very little room for electronics. With the help of GunRunnerJohn I put together an LED lighting circuit with the CL-2 current limiter. You just don't realize how small these devices are until you try to solder them! I use the following parts
805 LED's
SMT perf board Mouser 854-SP1
100 uf 35v cap Mouser 647
0.5A bridge Mouser 512-MB8S
CL2N8 20ma current limiter Mouser 689
First picture is the LED light bar made from a PC tie
Second picture is the circuit that will fit in the coach
and the third picture is the coach with the 3d printed interior. I have to remove the seat in the upper left for the electronics. This is the first time I've dealt with SMT devices. Definitely need to get a small tip for the Hakko! The PC board will be the partition that appears to be the spot for a heater. There is no real prototype for this car. Now I need to power the trucks and paint the interior!


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## gunrunnerjohn (Nov 10, 2010)

You think those components are small? Solder a few of these boards up and get back to me.  And these are actually the easy ones...


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## gregc (Apr 25, 2015)

solder persons at work typically use scopes


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## gunrunnerjohn (Nov 10, 2010)

Yep, when you have unlimited funds, you can have such niceties.


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## gregc (Apr 25, 2015)

gunrunnerjohn said:


> unlimited funds ... niceties


the technology available to us as hobbyists is pretty amazing. At the same time I think people take for granted the technology in their mobiles.

Commercial product development is expensive and competitive.


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## Lemonhawk (Sep 24, 2013)

My $10 visor works fine for me, but is there some way to tack down the little bugs before I touch them with the solder? I tried using the liquid rosin to tack them down, but trying to get it just on the little pads seemed to not be that easy. I wonder if I could use some weights to hold the IC down before I tack it with the pencil. I'll have to research the how to's on hobby soldering SMT devices.


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## gregc (Apr 25, 2015)

i think in normal production they glue all parts onto the board before sending them thru a wave solder machine. you might try that rub on sticky glue


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## gunrunnerjohn (Nov 10, 2010)

I would NOT try to glue small SMT parts down, the glue will surely cause you all sorts of issues. The "glue" that is used for automated assembly is very special solder paste, it's actually the solder in a paste form. It's melts in the IR oven and solders the part.

What I do is put a spot of solder on one of the part's location pads, then use the tweezers to hold it and heat the solder and slide it into place. Make sure it's flat and aligned, then solder the other side. For multi-pin devices I do a similar thing, I tack one lead with the chip aligned. Then I tack one on the opposite side, and it's fixed in place, and I can solder the rest.

For really fine pitch multi-lead parts, which I avoid if at all possible, I actually just solder each side with a blob of solder, then use my solder sucker to remove all the excess, that leaves the part tacked down quite neatly.

When I design, I stick to SOIC chips (1.27mm spacing), and 0603 or larger sized discrete parts. The sensor picture I posted above adheres to those guidelines.


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## gregc (Apr 25, 2015)

gunrunnerjohn said:


> What I do is put a spot of solder on one of the part's location pads, then use the tweezers to hold it and heat the solder and slide it into place.


this is how a wire person at Bell Labs told me to solder (before surface mount). 
Tin both parts and leave a little extra solder so you can hold the part with one hand the iron with the other.


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## gunrunnerjohn (Nov 10, 2010)

For SMT parts, it's important to only tin one of the pads, you want to get the part positioned and flat, then solder the other side. But I agree for leaded parts and wire splices as well. I don't have three hands, so holding the part and the iron, I use up the full complement of hands.


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## Lemonhawk (Sep 24, 2013)

Wave soldering is for thru hole devices, as GTR says the SMT devices us a paste then are put in an IR oven to "flow" the solder. I think if I support my hands a little better I can hold down the part and then touch the part with the iron. I do shake a little if the hands are unsupported and while it not something that bothers me, these small parts really magnify the slight shake. On to painting the interior and powering the trucks - think I'll try the Kadee spring method!


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## gunrunnerjohn (Nov 10, 2010)

I always like to have something to lean my hand on as I do this.


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## DonR (Oct 18, 2012)

I have small spring clamps that hold the two parts
together for soldering.

Don


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## Lemonhawk (Sep 24, 2013)

I just never though I was that shakey, but Its probably the size factor also. Made the mod to the trucks to get power. First photo is gluing the Kadee springs on the truck, second photo is the completed truck and the third is a closeup of the modified Kadee spring. I use Philobond. I really should add a small screw, but didn't have any. I did run it around to see see how will it worked. Probably need a capacitor larger than 100 uf, but then again the occasional random blink may be more authentic.


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