On my first project routing gives double traces?

Have you see this before?
Screen Shot 2022-01-14 at 9.42.51 PM

This appears to be an issue with single layer PCB.

The best bet would be to upload the sketch (the .fzz file, upload is the 7th icon from the left in the reply menu) and one of us will have a look. Assuming you were using autorouter it usually doesn’t work very well and you are better to manually route though.


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Here is my sketch. It’s the beginning of a full diode 16 keypad.
key16.fzz (29.0 KB)

Thank you!!

Autorouter appears to be broken (I am using Fritzing 0.9.9.) It also appears to have changed some (there were some fixes a version or two ago) which may make things worse. So first I re aligned schematic a bit to make sure it looked correct (which it appears to be) because if it is incorrect that will reflect in to pcb.

then in pcb I did Routing->Select all traces

then hit the delete key to delete them all leaving only rats nest lines like this

then clicked on the rats nest lines one at a time and manually routed the traces

first do all the traces that don’t overlap, then consider how to route the ones that will overlap. In the end to do that I needed to reduce the grid size from 0.1in to 0.05in by clicking Routing->Set grid size and changing it from 0.1 to 0.05 and clicking OK

that allows me to route it (without any jumpers) like this. Note the 0.05in grid size was needed to keep the top 3 traces circled in red in the bounds of the pcb. If you can increase the size of the pcb you don’t need the reduced grid size.

these changes are in this sketch.

key16-1-fixed.fzz (25.1 KB)

Now a suggestion, I would replace the 1n4001 diodes with this small signal part (the holes in pcb are smaller suitable for 1n4148 small signal diode which is all you need here.

As you note autorouter appears to have bugs which probably should be reported on github, but autoroute isn’t a high priority (there was discussion of removing it during the last set of fixes) so I don’t expect anything will happen soon.


Thank you for the thorough answer! I’ll look at the small signal diodes.


It is a known problem. This is the open issue in the bug tracker:

I added a reference to this thread so they know it is still an issue in 0.9.9. I expect it is low priority though.


I wonder if it is caused by using THT parts with a single sided PCB?

Doesn’t look to be that simple. I started with this

then autorouted with SMD on the bottom of the board

which works, then switched to tht (still single sided) and autorouted but it also worked correctly. There looks to be something more complex going on.