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Please help with PCB layout

Discussion in 'Electronic Basics' started by Owen Lawrence, Jul 24, 2003.

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  1. Hi. I'm trying to design a circuit using a PIC and some home-grown
    H-bridges (i.e. 4 transistors each) to drive a bipolar stepper motor. There
    are few other things on the board, but my question is about how I should
    position the components. I'm using Eagle, and when I autoroute, it finds
    most paths it needs to, but the result is ugly. There are lines going under
    components all over the place, lines inbetween the pins of the IC, etc.
    Since I want to etch this board myself I'm not confident of the results if
    so many lines have to be close to each other.

    Do you have any advice about how I should do the layout? I started with
    the ratsnest view, and positioned components roughly where I thought they'd
    cause the least amount of positional interference. But now I've been
    fiddling with it for a couple of evenings, and while I'm making progress,
    I'm not sure this is the best way. I honestly thought I'd have it finished
    long ago.

    How much time does one usually spend working on the board layout, after
    the schematic is designed? I'm still adding things to the design. Also,
    what do you usually do with V+ and V-? I think these are the sources of
    many of the strange routes I'm getting, since so many components have to
    attach to them. Is there a layout technique you use?

    Thanks for your help.

    - Owen -
  2. I find that routing a design takes the longest unless you autoroute and
    trust the results. However I practically always ended up doing the routing
    manually since the autorouting results are quite often poor or/and
    inefficient (like using two layers when one suffices). I think practice
    makes it perfect, the more you do the layout and routing the more you get
    the feel for placement of the components, etc... What could work also is
    autoroute then ripup and manual route of the really bad/silly tracks.

  3. trust the results. However I practically always ended up doing the routing
    I have forced it to do only one layer.
    That's the direction I'm leaning to. I've already done a bit of manual
    rerouting after the autoroute, and now believe I'm quite capable of making
    it look much better. As long as I don't have to redo most of the board, I
    can live with this.

    It seems that my own experience is consistent with others', and there is
    no free lunch. Therefore, my new intention is to practice, so I can get
    enjoyably good at this.

    I also intend to finish my design. I wanted to do some routing at an
    intermediate stage before things got too complicated to handle, and I'm glad
    I did.

    Thanks for your advice.

    - Owen -
  4. Rich Grise

    Rich Grise Guest

    You didn't say if you're doing one layer or two, but I've done manual
    layouts, 2-sided, and even making boards by hand at home, it's not that
    much worse than single-sided. I took the tape-up to the photo guy, and
    it was no problem shooting it 6-up, registered. Then I just scotch(r)
    taped them together and slid the board between them. As far as style,
    I usually start with ground and power on the component side, and do
    as much of the signal stuff as I can on the other side. You don't need
    to make plated-thru holes, since you can use a component lead for a
    via, and you can make stand-alone vias with a tiny piece of wire.

    Have Fun!
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