I've just uploaded a picture of a very early board I did with this
'scratching' process. I've called it the Eagle Scratch process, and made a
new photo album in the Yahoo Groups Photo section with this picture in it.
Some things to look at: the connectors on the side of the board are standard
.100 double row connectors. That gives you an idea of size. You'll note that
the board was over-etched. Also, the copper board I used for this test run
was very scratched. The big problem with my process so far is that the
scratch tip is not perfectly moved by the plotter head, so that when it
starts making concentric polygons around the nets in opposite directions, it
will leave little bits of copper on the board. These do not affect the
electrical properties of the board, but are really ugly. I am currently
working on better software to compensate for this and make much cleaner
scratches.
The etch tip is round.
Let me know if you have any questions. I can also upload HPGL plot files if
your interested.
∗Brian
> -----Original Message-----
> From: Stefan Trethan [mailto:stefan_trethan@...]
> Sent: Tuesday, May 13, 2003 2:02 AM
> To: Homebrew_PCBs@yahoogroups.com
> Subject: Re: RE: [Homebrew_PCBs] HPGL output (was PCB design software)
>
>
> ah i see, i see.
>
> if you have this very handy function in eagle this makes the
> thing a lot easier.
>
> i think this may also be there for making copper plains,
> determining design rule violations, etc.
> this would simplify the overall thing.
> my thought was the whole time how the hell can i tell that 2
> arcs, different sizes are from one pad and
> not 2 differtent pads. also when calculating the coordinates
> this would not be too easy to tell.
>
>
> which shape has the tip of your scretching tool?
>
> have you any results ready to meke a picture?
> i would be very interested in it.
>
> regards
> stefan
>
> 12.05.2003 22:25:44, Brian Schmalz <brian.s@...> wrote:
>
> >> nice to see there has one done the "scratch 'n etch" tool i
> >> asked a few days ago.
> >
> >Yes, it does work OK - and for me I only need OK, not great. Super
> >easy/cheap way to try out a board to get all the bugs out.
> >
> >> how do you detect when a line is on the outside of a
> >> trace/pad and when a line/arc is the outermost?
> >> so you can tell what actually is the outline?
> >
> >I had to use some really crazy tricks of the ULP (User
> Language Program) in
> >Eagle. What the program does is use a command in Eagle that
> will draw lines
> >around all of the existing traces. You pass this command a
> 'distance', and
> >it computes the correct lines based upon that distance from
> the nets. So my
> >ULP calls itself repeatedly (recursion) with increasing values of the
> >'distance'. So if I want at least 50mils of space around
> each net, and my
> >scratch tip is 5mil wide, the program will call itself 9
> times, starting
> >with a distance of 2.5 mil, and advancing up to 47.5 mil for
> the distance,
> >generating a whole series of lines each run. I just execute
> for 'x' number
> >of times, and that gives the proper number of concentric lines.
> >
> >> i first thought of plotting the layer with the drill drawing
> >> on it to get the holes "punched".
> >> i'm really wondering how you can tell when a line is only a
> >> fill line and when it is a outline.
> >
> >To me there's no difference. I never 'plot' the real artwork
> in any way -
> >the ULP just goes through the Eagle database of nets and
> draws lines around
> >each net. The nets are never drawn into the HGPL file, so
> there's never a
> >need to know the difference. I understand your question, I
> think, and if I
> >was starting with just plain artwork (like what a printer
> would print from
> >what's on the screen of a board file) then you're right, I'd
> have a big
> >problem.
> >
> >> how is the match on the edges of tracks? i know one in
> >> australia who has written a similar tool but for
> >
> >Ahh. Now there's the rub. ;-) The match is terrible because
> the scratching
> >tip is drawn along by the plotter, and so is always
> 'following' the desired
> >point of contact. So what I do is I draw each 'line' twice,
> without lifting
> >the pen from the board between lines. (Each 'line' is
> actually a long series
> >of lines that forms a closed polygon that totally rings each net.)
> >
> >∗Brian
> >
> >
> >
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> >
> >
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>
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