[sdiy] KiCad schematic and PCB techniques

[Robin Whittle]

From: Re: KiCad early success: guide dots for drilling homemade PCBs:

With KiCad the component appearance can be changed, by changing it or
making a new one in the the eeschematic (the schematic program) library.
 As far as I know, there is no possibility of altering the component in
the schematic, such as by moving pins around, altering the text for each
pin name etc.  This was possible with the old MSDOS Protel Schematic
(goes with Protel MSDOS AutoTrax) program from the late 1980s or early
1990s.  The Schematic program had a special library manager in which
library components were made and edited, but it could also be done with
a text editor with care.  The PCB program itself was used to make PCB
library components - footprints - including by "exploding to primitives"
an existing components, moving them around as ordinary objects etc. and
then selecting them to make a new library component.  I always found it
satisfying to explode something to primitives, rearrange and add to
them, and then make a new component.

The text font can't be changed - for eeschematic and PCBnew (the PCB
editor) - it is compiled into the binaries and would be difficult to
change.  However I am happy with it since it is fixed width, simple and
readable.

  https://answers.launchpad.net/kicad/+question/121048

The size of each item of text can be changed in the schematic.  It can
be rotated in 90 degree increments.  Each piece of text (not the text
for each pin in each component) can be made invisible.  (In PCBnew, text
made invisible is visible on a special layer which itself can be made
invisible.)

I think these changes need to be made one by one, but that it would be
possible to do it en-masse with a text editor in the schematic file
itself by finding and replacing the text which specifies the size.

I think the trick to making good schematics is something like this:

  Use a fixed width font.  With age our eyesight deteriorates and
  when reading proportional spaced sans-serif fonts we have trouble
  deciding whether there is one or two "i" characters side by side.
  Proportional width fonts such as Arial or Helvetica generally make
  the lower case L and upper case I look identical.  We need to be
  able to read every character explicitly, not just recognise whole
  conventional words as when reading prose.

  Make the components the way you like.  The library components will
  probably suck in fundamental ways with respect to this, since they
  were made by a bunch of people with different ideas.  I haven't
  tried to make my own set of KiCad schematic components yet, but I
  will probably make all complex parts have 100 mil (0.1 inch) pin
  spacings with pin number text which is readable at this spacing.

  Pin length is selectable with KiCad - I will decide on some
  standard.

  In the schematic itself it is vital that the font size used for
  all component labeling, net labels etc. be small enough that it
  can fit within whatever the usual wire spacing is, such as 100 mil
  without touching or overlaying the wires.

  In order to make the schematic look good it is vital to move the
  text with care using a much finer grid than might be used for the
  placement of components.  The "Getting Started with KiCad" document
  suggests using a 50 mil grid for schematics.  I think it is better
  to use a 100 mil grid when placing components and a finer grid, such
  as 10 mil, when moving text.  (In MSDOS Protel Schematic the grid
  was for component placement and was usually 100 mil.  I recall that
  this did not restrict text movement.)  I think the program could be
  improved by having separate grids for component and text placement.

  Text colours are no-doubt selectable.

  People who use rectangular resistors can use the space inside the
  resistors to label its value.  I prefer zig-zag resistors since they
  are instantly identifiable as such in a schematic which already has
  lots of right-angles and rectangles of various sizes.

  I will be making my own electrolytic capacitor schematic component
  with the positive plate empty and the negative one filled (full of
  electrons).


I haven't looked at hole size editing in the PCB program, but I think it
is vital to plan a systematic set of hole sizes in the PCB library to
minimize the diversity of hole sizes in the final board - this is for
external double-sided plated-through hole PCB manufacture.

There's a huge body of work learning a program, annotating the printed
out documentation (I can't imagine how to do this without annotated
documentation and personal cheatsheets), developing work procedures and
PCB standards appropriate to different methods of making PCBs, creating
your own schematic and PCB library, and then just becoming competent at
using it all.  I wrote for myself an entire 40 page Word document, all
comb-bound and updated and/or hand-annotated, just to remind me how to
do schematics and PCBs with the MSDOS Protel software.  I will refer to
this when I decide how to do serious work with KiCad.

I did this once around 1990 and haven't been designing PCBs since I
modified the 1993-96 Devil Fish board in 2004.  Now I plan to learn
KiCad.  It is like learning a whole new language (programming or
spoken/written).  It is a major investment to become proficient in one
of these packages.  I would not like to have to learn and use two such
systems at the same time.

This would happen naturally if I spent a large part of my time designing
PCBs, but I do many other things, so I will probably immerse myself in
it, write good cheatsheets (I tend to do this in HTML with Kompozer,
since it can so easily link to web pages, forum discussions etc. and
contain screen shots and photos - and be cleanly updated).  Months or a
year or more may go by where I don't think at all about PCB design.
Then I will rely on my cheatsheet, annotated documentation, mailing list
messages, libraries and previous projects to remind me how to do it again.

  - Robin


megohm quoted Tim Parkurst:

>> The process to add new parts and footprints is a little clunky, but 
>> I've managed to work with it (then again, maybe I need to read the
>> docs again).
> 
> Can you elaborate on this?
> 
> I have been using TinyCAD and FreePCB but would like to try KiCAD but,
> 
> I like to make my own footprints. Even simple things like resistors I
> make my own version of.
> 
> Also, I have never liked the look of KiCAD (or Eagle) schematics. Is
> this something that is set in stone or can you make your own symbols and
> change font sizes and stuff like that?
> 
> Thanks,
> p.