[sdiy] KiCad early success: guide dots for drilling homemade PCBs

[Robin Whittle]

I am exploring the open source Kicad schematic - PCB - Gerber system and
so far am most encouraged by its ease of use, functionality and
documentation:

  http://en.wikipedia.org/wiki/Kicad
  https://launchpad.net/kicad

Thanks to Veronica Merryfield and others who wrote to this list about
their KiCad experiences - including Eric Brombaugh who wrote a great
comparison of KiCad and gEda, the two most prominent complete
open-source schematic-PCB systems:

  http://dropmix.xs4all.nl/pipermail/synth-diy/2011-February/030929.html

It is my impression that the documentation is is well-written,
well-illustrated and generally up-to-date with the software.   The
documentation is in PDF files.  (Eagle documentation is all text - no
graphics!  LabCenter Proteus is another commercial PCB system with
documentation which I think is seriously lacking - just Windows help
files which are very difficult to print, with no PDF versions.)

I worked through most of the "Getting Started in Kicad" document and was
able to make a schematic, with my own additional components, then a
netlist and a single layer PCB design with my own additional footprints
(PCB patterns of copper and holes).

I just wrote to the authors of this guide with some suggestions for
bringing the guide totally up to date with the current version of KiCad.
 If anyone wants to use this guide I can send you my notes which might
save you some headscratching.

The guide only covers making Gerber files for an external company to
make the PCBs.  I suggested they include a new section on home-brew PCB
making and suggested they link to the Homebrew PCB Yahoo group:

  http://tech.groups.yahoo.com/group/Homebrew_PCBs/

Below is the rough text I suggested for a section which explains how to
print or generate files for phototools or other home-brew toner transfer
techniques.  Except for people with their own CNC drilling machines, we
need a guide dot in the middle of each pad or via so we can center our
drill bit.

 - Robin      http://www.firstpr.com.au/pcb-diy/



For making PCBs at home, it is necessary to generate phototools - or a
similar pattern of toner or ink on the PCB itself as an etch resist -
which are 100% final size and which have a small dot in the centre of
each via and pad, to guide the manual drilling operation.

Frequently it is desired to replicate a small PCB design several times
on the one phototool.  This can be done in PCBnew by left-click dragging
around the entire original design, moving the mouse cursor outside that
area and right clicking to use the Copy option.  This can be repeated
several times so the total design contains an array of exact copies of
the original design.

There are two ways of creating the desired artwork.  In these examples
we assume that the board is single-sided, so only the B.Cu layer needs
to be output.

The first approach starts with File > Print with just the B.CU layer
selected.  The X and Y scale adjustments which would normally be set to
1.0 but could be used to correct for printer scaling errors.  The "Black
and White" and "1 Page per Layer" options should be selected.  "Mirror"
can also be selected.  "Drill Pad Opt" should be set to "Small mark" to
create the drill-bit aligning dot in each pad and via.   This drives the
printer directly, though many systems have printer drivers which can
create PDF files.  This approach does not directly allow the negation of
the image, so it is not appropriate if white tracks are required against
a black background.  (File > Export SVG has negation but lacks small
drill marks.)

The second approach allows this negation: File > Plot > SVG.  This can
also be used to generate a Postscript file which can be processed with
software such as Ghostscript to create a PDF file.  SVG files can be
loaded into vector graphics programs - for instance Inkscape, which with
suitable configuration can print them at exactly the right size, perhaps
after further manipulation, tiling, addition of other images etc.
There are options for Mirroring, Negative, and Small Drill Marks, but
not for scaling.  This method can also be used to generate a drill file
for home-based shops with CNC drilling facilities.