Mail Archives: geda-user/2012/12/15/12:19:18

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Subject: Re: [geda-user] pcb fundamentals
From: John Doty <jpd AT noqsi DOT com>
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Date: Sat, 15 Dec 2012 10:17:37 -0700
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On Dec 14, 2012, at 6:03 PM, Peter Stuge wrote:

> John Doty wrote:
>> In pcb you cannot do anything simple,
> I agree with various other things you've written, but I disagree with
> this, I think the simplest task is to draw lines between components
> on a board, and drawing lines is rather straightforward. Click the
> line button, click on the canvas to start, see where the line goes,
> click to make corners, hit ESC (maybe right click) to stop the line.
> I also think that it's very straightforward to create footprints.
> It's popular to use scripts, but I actually create most of mine
> manually. Sometimes tedious, but I do "get to know" the footprint
> well.
>> and you cannot deconstruct complexity to understand it.
> Hm, what are some examples of complexity?
>> Complex objects are not constructed of simple objects.
> Hm? Footprints are constructed of pins, pads, and lines.
>> There are no simple objects.
> Hm? I think of at least lines, pins, pads and vias as simple objects.

These are not simple. They are complex aggregates of simple objects.

>> Object properties are immutable and inscrutable.
> Hm? For "my" objects that's not true, I can change e.g. size of stuff
> with a keypress, names with another, and I can move things around
> by clicking and dragging them around.

But there are many other properties an object might have. Consider a truly simple object, e.g. a rectangle. What's it made of? Copper? Nichrome? Teflon? Vacuum? Does it belong to a net? Does it belong to a composite object of fixed geometry (via, footprint, subcircuit, ...). How thick is it?

Objects in pcb don't have inspectable/mutable properties in this sense. Instead, they have built-in magic.

It's very useful when learning a drawing application to be able to inspect the properties of an object. But hidden magic is a barrier to comprehension.

There's a whole class of questions that show up on this list of the form "How do I draw an X made of Y with affinity Z". But since the material and affinities of objects are not mutable, the usual answer is "you can't".

Consider blind vias, buried vias, and buried components. These are not any more complex geometrically than other things pcb can draw, but because they are not specifically implemented in the code, and pcb cannot generally construct aggregates from simple primitive objects, they cannot be drawn.

John Doty              Noqsi Aerospace, Ltd.
jpd AT noqsi DOT com

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