Netlist changes as footprints are moved

I am trying to layout a Mega 2560 daughter board. The side footprints are fine (comm, analog, low digital). The problem is with the 2x18 connector. Specifically, I want to have parallel 2x18 holes - common to mega daughter boards.

First, I tried two 2x18 pin headers connected on a bus. Problem is, each individual 2x18 connector footprint had evens connected with odds (1-2, 3-4, etc) even though they were not connected.
I then broke the 2x18 into individual 1x18 connectors. J1 is 1:1 with J2; J15 1:1 with J16

Problem is: when I put J1 next to J2 (and J15 next to J16) (ordered J1-J2-J15-J16) they are connected (eg netlist) as I expect. But when I order them J1-J15-J2-J16, J1 is connected (netlist) to J15 && J2 to J16

I normally use my work account, but this is my personal account, so I cannot attached the schematic and PCB files (yet - technically, I am a new account).

Are you sure? Did you check using the highlight net tool? Sometimes the ratsnest can look as if there should be a connection if multiple lines overlap. (I think there are plans that in future the ratsnest does not use straight lines in such cases to make it more easily visible what really should be connected. Not sure how far along this is.)

Again check with the highlight net tool. (or simply try to make one of these connections which will also highlight what should be connected.) This could simply be a graphical artifact resulting from overlapping ratsnest lines.

Something else to keep in mind is that the ratsnest always shows the shortest connection.

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The netlist (actually ‘ratsnest’) is OK still.
A line is drawn from J1 to J2 and another line is drawn from J15 to 16 as expected.
But, because the ratsnest is drawn by inverting the background, where the lines are on top of each other between J15 and J2, the lines cancel and appear to not be there.
If you moved a connector vertically temporarily, you will see that the ratsnest is still connected correctly.
Been there, done that! :slight_smile:


(from my work account)
I will try moving the two connectors.
The weird thing was it did it on a 2x18 connector where I did not expect issues.
But - yes - the ratsnest for two co-linear traces can cancel themselves out.
I will be able to get back to this next weekend.


A couple of points:

  1. Ratsnest lines are ray traces. What appears as a single white line may be several and there is no obstacle avoidance, just direct lines. With the horizontal component alignment in you example posts, you may be seeing artifacts of the rendering method.

  2. The ratsnest does not necessarily show ALL connections, just the closest perhaps. Select a component and move it around in a big circle and watch the ray-traces jump. Your connectors may not be the best choice for this example.

  3. The way to tell if the netlst changed is to compare the actual netlist files before/after, not the graphical interpretation. I seriously doubt it is changing. Make a copy of the netlist file and use an editor to read it and see what it says for just 1 or 2 nets.

I suggest you intentionally misalign the jacks or have schematic connects of J1-15 to J2-14 and then convince yourself of what is going on.

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