Mail Archives: geda-help/2012/01/03/15:31:48
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Chetan,
Is it possible that you are finding some confusion between symbols and
footprints? Symbols are the familiar elements of scematic: two parallel
lines for a capacitor, a triangle for an op amp, and so on. Footprints are
the shapes that must be on a PC board for components. A through-hole
resistor will have two holes a certain distance apart, a surface-mount
resistor two pads, and an op amp in a DIP package will need eight holes
(with sorrounding copper) for its pins.
Thus, a component is represented by two things: a symbol in gschem and a
footprint in PCB. In order to completely describe a component, it needs a
symbol on the schematic in gschem, and that symbol needs a "footprint="
attribute that will tell PCB which footprint from its library to use.
Some symbols is gschem's library and on gedasymbols.org have footprint
attributes already included. Others do not, and you must add the footprint
attribute yourself. This is especially helpful for symbols such as
resistors, which come in a dizzying variety of shapes and sizes, and
perhaps less helpful for certain chips that come in only one package. Even
a simple through-hole resistor can be mounted in either a standing or a
flat position, each of which requires a different footprint.
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<p>Chetan,</p>
<p>Is it possible that you are finding some confusion between symbols and f=
ootprints?=A0 Symbols are the familiar elements of scematic: two parallel l=
ines for a capacitor, a triangle for an op amp, and so on.=A0 Footprints ar=
e the shapes that must be on a PC board for components. A through-hole resi=
stor will have two holes a certain distance apart, a surface-mount resistor=
two pads, and an op amp in a DIP package will need eight holes (with sorro=
unding copper) for its pins.</p>
<p>Thus, a component is represented by two things: a symbol in gschem and a=
footprint in PCB. In order to completely describe a component, it needs a =
symbol on the schematic in gschem, and that symbol needs a "footprint=
=3D" attribute that will tell PCB which footprint from its library to =
use.</p>
<p>Some symbols is gschem's library and on <a href=3D"http://gedasymbol=
s.org">gedasymbols.org</a> have footprint attributes already included. Othe=
rs do not, and you must add the footprint attribute yourself. This is espec=
ially helpful for symbols such as resistors, which come in a dizzying varie=
ty of shapes and sizes, and perhaps less helpful for certain chips that com=
e in only one package. Even a simple through-hole resistor can be mounted i=
n either a standing or a flat position, each of which requires a different =
footprint.<br>
</p>
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