SoR Kit assembly, Part 1

December 5, 2009

If you have purchased the SORKIT1 here at CircuitGizmos, or even if you purchased the parts somewhere else, you might be interested in the Gizmo build of the circuit board controller. The Society of Robots instructions here have a handful of steps for building the $50 robot. Steps 3A, 3B, and 3C have to do with making the electronics of the robot. Step 3B specifically is the step that has to deal with building the controller board. The Society of Robots step 3B also shows board assembly if you have a 10-pin AVR programmer, where here in this blog the 6-pin programmer is used.This blog entry will highlight steps that will help make your controller assembly a little more likely to succeed.

SoR Kit assembly, Part 2
SoR Kit assembly, Part 3

The SORKIT1 Controller Board:

sorkit00

The picture above shows the finished SORKIT1 board. You might note a few differences from the board built in step 3B on the SoR website. First, the AVR programming header is the newer 2 by 3 pin type, rather than the older 2 by 5 pin type. The newer 6 pin programming connection is now more common. The 10 pin programming connection can still be found on older programmers.

Second you might notice that the placement of the regulator and the power connections are different than the connections on the SoR board in step 3B. I made changes in the part placement, but the functionality remains unchanged.

SORKIT1 in a bag:

sorkit01

If you order the SORKIT here at CircuitGizmos, this is one of the bags that comes in the kit. The bag has the circuit board, or Printed Circuit Board (PCB), and other parts.

Top view of circuit board:

sorkit02

pcbtop

This is the PCB viewed on the top/component side. Note that the rows of 0.1 in spaces holes are labelled numerically and go from 1 to 25 (2-24 shown). The columns of holes are labeled alphabetically and go from A to O (B-N shown). These labels will help in parts placement. The top picture is a photo of the board, while the bottom picture is a graphic of a blank board. See this blog here for more information on these graphics.

Bottom view of circuit board:

sorkit03

pcbbottom

This is a picture of the PCB viewed from the bottom/copper/solder side, plus a graphic that represents the PCB bottom/copper/solder side. Some of the numbering is there in the photo. The graphic for the board bottom might help, as it duplicates the numbering and lettering. To follow the parts placement correctly you have to keep in mind that the board gets flipped over and the column lettering is flipped from left-to-right to right-to-left.

So here is something that you should note: the black smudges on the copper donuts. The donut that you will solder to is a thin layer of copper glued to the board. This copper is exposed to all the world, and as a result it gets dirty. Thing get on the surface of that copper that include oils from your fingers and whatever it was that caused the black smudge. When you want to solder to the copper, the solder is separated from the copper by this layer of gunk. That makes it tougher to solder.

Clean the board. It really helps to make the soldering easier.

Board Scrubber:

sorkit04

In the photo above I’ve used a non-metallic (nylon) common kitchen pot scrubber to clean the lower half of the board. It isn’t an hour’s worth of scrubbing – if you did that there would be no copper left at all – it only takes a few passes in each direction to make the copper shine. You have cleaned off the gunk and roughened the surface of the copper. Melted solder will LOVE to cover this surface.

Half clean circuit board:

sorkit05

You can see the half-cleaned board in this photo. The lower part of the board is shiny if you move it around in the light. It doesn’t photograph well, but you will see a difference. Finish cleaning the entire copper side of the board and avoid touching the surface with your fingers. Eventually the copper will get dull again. So move to the next step as soon as you can.

Flux pen:

sorkit06

Want to REALLY make it easier to solder? Once you have cleaned the board, “tin” it. Tinning is the act of putting a thin layer of solder over the copper. You put a little effort into tinning the board, and when soldering it parts the tinned surface heats well and certainly accepts solder well. This is a big step to making it easier and more reliable to solder together the controller board.

You will need to make an investment in solder flux. Flux is a slightly sticky chemical that you coat onto the clean copper. When heated by the soldering iron tip the flux sizzles and chemically cleans the copper. When you add solder the flux-cleaned surface draws copper onto it. Cleaned copper coated with flux helps you move from applying heat and solder to a surface and being annoyed at the copper resisting the melted solder, to being tickled that the copper is sucking up the solder that you apply.

Pictured is the flux in an applicator pen that I use, a 2331-zx by Kester. It is about $5 a pop. Well worth adding this to your toolbox.

I coated the copper of the recently cleaned PCB with flux much like drawing with a marker. Apply a generous amount of flux – all of the copper donuts should be wet.

Tinning the board:

sorkit07

Above I’m tinning the board. I melted a little solder onto a couple of the copper donuts and I’m spreading it around easily with the hot iron. Try doing that on an uncleaned board versus a cleaned and fluxed board. The difference will amaze you. Spread a thin layer of solder to all of the copper donuts on the entire board.

Tinned board on bench:

sorkit08

Here is a picture of the board completely tinned and setting on my bench next to a board that is half cleaned.

Tinned board:

sorkit09

desolder

A picture of a shiny tinned board. Again, photographing this board doesn’t show the shiny surface well. The finished tinned board will be silvery-shiny.

Some, a few, or a lot of your holes might be closed by excess solder. This happens. It isn’t a big deal, but it must be fixed. Another investment to go along with the flux pen is solder wick (solder braid). I borrowed the little picture above from somewhere on the Internet. It shows the use of solder braid. To fix a covered hole, place a new/clean section of the solder braid over the hole. Then apply heat using the soldering iron. The solder braid will heat up and also heat the solder below it (covering the hole). That melted solder will be sucked up into the braid. “Wicked” is also a term for that. Remove the iron and the braid at the same time and your donut should be uncovered.

To make the solder braid work better, add a little flux.

You can clean this board with a mix of Windex and rubbing (isopropyl) alcohol. Mix 50/50. Dip a spare tooth brush into the cleaner and scrub the board. Rinse under hot water and dry completely.

Man! Doesn’t that board look good?

You now have a PCB that is tinned and much easier to work with for making the controller board for the SoR $50 robot, whether you bought all of the parts individually or saved money and effort and bought the SORKIT1 from CircuitGizmos.

Next blog: Solderng parts onto this board.
SoR Kit assembly, Part 2
SoR Kit assembly, Part 3

=Gizmo=

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