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Help on circuit layout

Discussion in 'Electronic Basics' started by Chris, Nov 6, 2004.

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  1. Chris

    Chris Guest

    I have drawm up a power supply on eagle, on bread board it all works
    fine, but when i did a single layer pcb it didn't. Now one thing i
    noticed if i use autoroute the current doesn't seem to take the same
    path as it does on breadboard, it seems to run here and there... does
    this matter?


    Board Layout:
  2. Graham Knott

    Graham Knott Guest

  3. Clarence

    Clarence Guest

    Your AC input, "X1" should be connected to pin 2, not as shown on pin 3!
  4. Clarence

    Clarence Guest

    Just curious:
    If your qualified to write a (really) basic book on electronics, shouldn't you
    at least be able to trouble-shoot a simple power supply?
  5. Graham Knott

    Graham Knott Guest

    He didn't ask for help troubleshooting!
    This is what he asked if you read carefully.

    the current doesn't seem to take the same
    Try to be more positive with you criticisms and life can only get better.
    Best regards.
  6. Clarence

    Clarence Guest

    Other than the lines should probably be a little wider so a Power Supply to
    minimize resistance it should have only a minimal effect?

    " I have drawn up a power supply on eagle, on bread board it all works
    fine, but when I did a single layer pcb it didn't."

    Sounds like a trouble shooting problem to me.
    Also, the Schematic showed the input AC connector connected wrong!

    Besides it was a valid question, not criticism.

    While we are at it, why are 'YOU' so RUDE?
  7. Clarence

    Clarence Guest

    I see that I was not replying directly to the OP due to the poor cropping of
    the post you replied to with a curt "NO". Sorry about that. and your tag line
    was in the way. Checking it made me question the need for the original post. I
    see now that your RUDE response was because you missed the problem and wanted
    to strike out in anger at someone.

    I didn't mean to get in the line of fire.

    BTW, there are a lot of GOOD books for beginners!
  8. Graham Knott

    Graham Knott Guest

    Oh dear,another troll.
    I always give my best regards to trolls hoping that it makes their life
    just a little bit happier.
    Best regards Clarence.
  9. Clarence

    Clarence Guest

    No, I'm not, but I know one when I encounter one!

    You seem to have a problem relating to people.
  10. Printlayout is almost an art in itself and an autorouter is all but an
    artist. This print is bad in two ways: The placement of some components is
    wrong and the traces are improperly drawn and to thin. I don't want to
    cover the whole print but I'll give some examples.

    - The trace from the cathode D1 branches. One trace goes to the capacitors,
    the other to the regulator. That's wrong. The trace should go from the diode
    to the capacitors and then from the capacitors to the regulator.
    - The 100nF decoupling capacitors should be near the regulators. Especially
    a 7912 can go oscillate like hell when not carefully decoupled. Check the
    datasheets for it.

    An autorouter is not the correct tool to design printed circuit boards like
    this. Its rules do not care for the rules of even this simple power suply

    petrus bitbyter
  11. Clarence

    Clarence Guest

    My name is Graham Knott and I teach Electronics and Microcomputing in a third
    rate school at Cambridge Regional College, situated in the city of Cambridge,
    England. I need you money so send me $20 USD for my little reader.

    Send money to:

    Graham Knott 27, Edinburgh Road Cambridge CB4 1QR UK phone 01223 502751

    Graham, Did I understand this right?
  12. Chris,

    Some observations:

    1) Your schematic and board don't seem to match. For example there are 6
    diodes on the board and only 4 on the schematic. Also, the input power
    connector seems to have all three pins connected on the board and only 2
    connected on the schematic.

    2) Have you verified the schematic and layout pin connections for all the
    library components you have used against the component data sheets for the parts
    you are using? It might seem strange, but I have seen an error here cause lots
    of problems.

    3) As some of the other responders have indicated, you should be using larger
    traces for a power supply. You would also have better luck keeping the traces
    short, by manually routing something this simple. You might have to add a wire
    jumper here or there, but that is better than letting the autorouter run a trace
    all around the board as it did for the input to your 7812. If you really must
    use Eagle's autorouter, you should define a Net Class for your power traces
    before turning the autorouter loose.

    4) You might also try the Eagle news groups ( or
    eagle.userchat.eng). Since your circuit isn't a top secret design, consider
    posting copies of your Eagle .brd and .sch files to make it easier for other
    Eagle users to help you. At least that way, one could turn off the silkscreen
    layer to see where the traces really go.

    Good luck. I'd be interested to hear what the problem was when you find it.
  13. I've long since permanently killfiled him. When I get to read him quoted by
    others, though, I continue to see the sharp wisdom of that decision.

  14. David Harmon

    David Harmon Guest

    On Sat, 6 Nov 2004 17:26:21 -0600 in sci.electronics.basics, "James T.
    This strikes me as very odd. In my experience, that's the sort of thing
    Eagle gets right 100% of the time. You draw the schematic, then tell
    Eagle to "create board from schematic". It gives you a created board
    file with all the parts, and airwires for all the net-connections.
    However you proceed to move the parts around and route the connections,
    the airwires don't go away until you are done.
  15. Clarence

    Clarence Guest


    That is funny. I kill filed him and haven't seen him until I cleared my Kill
    file after the election.

    But he is so sure I can't see him, because he was so objectionable.

    So he is still being a jerk? Right?
  16. First, I see an error on the schematic - the AC ground should come
    from pin 2 of the connector, not pin 3.

    The board layout seems to have six diodes, but there are only four on
    the schematic???

    The board layout is poor - the capacitors at the input and output of
    the regulators should be placed very close to the regulators - you
    want short fat tracks between the hot side of the capacitors and the
    regulator, and between the ground side of the capacitors and the
    regulator. I can't see how you get from C2+ to IC2-in.

    Autorouters can be useful, but they can also seriously mess up the
    routing - things may be connected, but the tracks will go all over the
    countryside. Strangely, they will often do a worse job on a simple
    board like this than on a more complex board.

    I don't know if Eagle has an auto-placer - but if so, don't bother
    with it. Autoplacers were invented to appease the marketing
    department, and rarely do anything useful, even on high-end CAD

    I don't know what currents you expect to have on this board, but as a
    matter of course, I would use .050, or even .100, tracks in a power
    supply. There is lots of room on the board for Really Big tracks.

    A comment on schematic drawing conventions - I consider it Bad
    Practice to have 4-way junctions on a schematic - if the connection
    dots go fuzzy (as they will after a few photocopies), it will be
    unclear whether C1- and C5+ are just connected to each other, or if
    they are also connected to ground. I would move the whole -12
    regulator section right one grid position, so that you only have 3-way
    connections - that would make it perfectly clear that C1- and C5+
    connect to ground.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
  17. Graham Knott

    Graham Knott Guest

  18. JeffM

    JeffM Guest

    3)As some of the other responders have indicated, you should be using
    A lot of good stuff from James.
    There is a school of thought on etching PCBs
    that says the less copper you etch away, the more ecomomical the design;
    make 'em as fat as clearance allows. (Your etchant lasts longer.)
    Beefier copper is rarely a bad idea.

    BTW, the EAGLE Autorouter never impressed me
    --not even on a shortest-route basis.
    As petrus said, to do a good job,
    an autorouter has to know a lot of rules about physics
    and the more you do before turning it loose, the better it does.
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