Help with PCB Layout!

Discussion in 'The Projects Forum' started by Sgt.Incontro, Apr 21, 2013.

  1. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1
    Hi guys.

    I am working on a project at the moment; to build an analogue function generator. I have pretty much finalized the design, and the simulations seem to work as expected.

    I have come to the stage of drawing it up on EAGLE, to come up with a PCB design that I intend to get built. However, I am a total noob at PCB design, so I definitely need some help.

    I need to know what needs to change, any mistakes I have made etc, and just general guidance in general. I hope that this will serve as a valuable learning process for me.

    Constraints:
    * must be single sided only
    * minimum track size is 0.25mm (preferably larger if possible, as tracks this size lift off easily when soldering apparently)
    * silk layer must be turned off at the end, cannot be manufactured.

    The file is attached. (EDIT: Now removed.)

    Thanks.
     
    Last edited: Apr 22, 2013
  2. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    Hi.

    When designing in Eagle, a good tip/a must, is to use the ERC.

    And export your schematic as an *.png. Not all members have Eagle installed.

    This is the warnings I got when running the ERC:
    [​IMG]

    ... and there's more:

    [​IMG]
     
  3. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1
    Hi, thanks for your help.

    I have already used the ERC, and it picked up on a few mistakes that I missed, such as dodgy connections.

    I was planning to add the values soon.

    The main part I need help with is exporting it to the board. I don't really know what to do after that. (For example, there seems to be many crossing lines, is this normal? I thought copper tracks couldn't cross?)

    And for some reason the "Autoroute" button is missing in the tools menu??

    Thanks.
     
  4. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    I'd suggest that you make a proper schematic, with no errors, or warnings. Well, warnings are just warnings, but I don't like them.

    Then, you switch to the board design.
    This button switch to board design:
    [​IMG]

    And this starts the autorouter:
    [​IMG]
     
  5. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1

    Ok, so I have inserted the values now. I now have these errors. I think the first is a dummy error, as I cannot see anything wrong with the connection.

    Secondly, what does pad has no value mean? I thought pads weren't supposed to have values - aren't they just (external) connection points?
     
  6. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    There is no thing as a dummy error.

    There is something strange with the wire from IC1B pin 6 to LED1. When I removed it and connected a new wire, from the tip of pin 6 and to the corner, and added a junction, the error disappeared. The wire overlapped the tip of pin 6. It is important that you start/stop wires exactly at the start/stop. This time it went past the pin.
     
  7. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1
    Did what you suggested, and the error disappeared. Thanks.

    Now moving on,

    I am I supposed to give the pads values?

    And from here I click switch to board, yes, create from schematic and then what?
     
  8. nerdegutta

    Moderator

    Dec 15, 2009
    2,519
    786
    I'd give them values, so the warnings disappears. You also have to check your 19 approved warnings/errors.

    When schematic is OK, you move to the board design. Here you place/lay out the components, and route the traces.
     
  9. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1
    I placed all the components in the way they first appeared (chosen by the program). I then chose single sided by setting the preferred direction on one side to "N/A."

    The program was able to auto-route up to 68.7%, but then stopped. So what do I need to do from here?
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Drop back and punt.

    A single sided board is hard to do since you oft get connections surrounded by other connections, and the router does not have the luxury of stitching connections from one side to the other.

    The last connections must be made manually... though 30% seems excessive as these are the very hardest to add. To start see if you could move parts to make it easier to connect things. Do not worry about tossing away the work of the autorouter: save it under an different name, delete the traces, shift parts, autoroute it again.
     
  11. Sgt.Incontro

    Thread Starter Member

    Dec 5, 2012
    50
    1
    Thanks for the advice ErnieM.

    It actually got to around 74% (not that its much better); don't know why I said 68%.

    I will do as you suggested, and report back when I have given it a solid try. In the meantime, any more manual routing suggestions/advice are strongly welcome, as I have never done this before.

    Cheers.
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Do have the air wires of the netlist turned on so you can see where connections need go.

    You'll now be adding jumper wires, and these will need to be added to the schematic to get the pads into the net list. I don't know if Eagle lets you edit a common footprint for several parts, or if each needs it's own copy.

    Beyond that there's not much to offer... it's a look & feel thing you get when you've done it a few times and your intuition starts speaking up.
     
  13. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    DO NOT use the autorouter! Those things are CRAP! Totally useless--they ruin the design, they go against conventions and often their routings are completely illogical. It's MUCH better to just take the time and do the design yourself.

    Dave Jones, from the EEVblog, has something to say about autorouters: http://www.youtube.com/watch?v=6JYG49zgEio

    Please don't ruin your design by trying to use the autorouter.

    Matt
     
  14. tracecom

    AAC Fanatic!

    Apr 16, 2010
    3,871
    1,394
    I don't use Eagle, but in general, that's true for most auto-routers. I sometimes run the autorouter on the last stubborn net or two, just to get ideas. Then, I un-route the net or segment(s) and route it manually.
     
  15. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    I've done that once or twice but it hasn't helped me yet. The only thing I use autorouter for is when I have to mix metric and standard spaced components, and the grid is a little off. There are some tiny airwires on each of the pins, so I run the autorouter to fill in the tiny gaps. But not until I finish laying out the rest of the board.

    I always use Eagle, and the Eagle autorouter is just as crappy as every other one I've tried. Unless you're using it only to fill in the tiny airwires under a SMD pad or something like that, STAY CLEAR OF THEM!!!
     
  16. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    I don't know what autorouter Eagle uses--I think it's very sad that so many people are burdening themselves with Eagle--but the one that FreePCB uses does an excellent job. It is slow, though. I try to force myself to start it up and then go to bed and enjoy the result in the morning! But when I think of the hours of work it's saved me, I'd never give it up.

    I also have to admit that I've never tried a single-sided board and I don't know if the program would give any help in designing one. In one sense, the jumpers are "components", but you'd want to have the autorouter place them, and I wouldn't know how to do that.
     
  17. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Eagle has one of the better autorouters out there, but still does a poor job.

    Is there any chance you could send an image of one of your autorouted boards? I have the feeling it's very poorly routed and goes against almost every convention out there. People who are inexperienced with PCB layout and design will not realize how bad it really is, they think they can just hit the button and have everything done for them. That is completely untrue almost every single time.
     
  18. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
    224
    Sure, here's a fairly dense one.
    http://files.myopera.com/John98wbr/albums/661338/lcdpanel.jpg

    The one "convention" I feel as if I ought to have pushed would have been to keep the traces from the filter caps to the IC pins as short as possible, and as I recall I did hand route a few of them before unleashing the autorouter, though I could have done more. But for an all-digital microcontroller board with no analog parts except a negative voltage generator, you don't have to be very fussy. The board works fine.

    Now make a guess as to how long that board would have taken you to route by hand!

    Here are a couple of pictures of the same board with a few of its friends:
    http://files.myopera.com/John98wbr/albums/661338/panel.jpg
    http://files.myopera.com/John98wbr/albums/661338/pcb.JPG

    I paid Gold Phoenix for a single panel of mixed boards, and they sent more than twice the quantity I ordered!
     
  19. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    May I ask what autorouter you used?

    I'm seeing a lot of 90-degree traces and goofy angles, which should generally be avoided. I'm also seeing some traces that are running dangerously close to some others, though they're probably ok. If your manufacturer can handle it and you're not running any serious current through your boards, it should be ok. It's also fairly messy--you've got traces going in every direction. While that doesn't cause any real issues per say, it does make the board look very haphazard and would be extremely difficult to test or troubleshoot if something went wrong. Seeing a lot of loops and sharp angles as well, which should generally be avoided, because in some circuits they can create unnecessary inductance, capacitance, or crosstalk/interference.

    Just a few of the major reasons I do not use an autorouter. They just put out extremely sloppy boards, almost every single time.

    Matt
     
  20. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    John: which autorouter does FreePCB use? It sounds like the same one I use with Kicad: http://www.freerouting.net/ I used it on one rather complex board and was happy with the results, though I agree it is quite slow and do the same: start it just before bedtime.

    Autorouters are tools, and like any tool has strengths and weaknesses. I don't give them the entire design: parts are placed first, then power traces, then anything critical needing my human judgment.

    Only the "who cares" signal traces get handed to the robot.

    lcdpanel.jpg looks fine to me. I can't see any detail on the others.
     
    Last edited: Apr 21, 2013
Loading...