Extra Wire in Shield Circuit Model

I have designed a shield using the Arduino UNO (Rev 3) part in order to define the pin header spacings so that I can connect the shield PCB to the actual Arduino UNO (Rev 3) sitting below the shield PCB.

The shield circuit model passes the Design Rules Check.

However, in the PCB Window, the Fritzing software automatically placed a wire from the Arduino part Pin A5 up to the Arduino Pin, two pins to the left of Arduino Pin AREF on the top side of the Arduino part.

I did not draw this wire . Fritzing drew the wire. See this wire in the PCB Window of the attached file, “Shield”.

If I take out the wire as done in file, “Shield, No Wire”, then the brown wire from Arduino Pin A5 disappears as shown in the Bread Board and Schematic Windows of this file.

When I connect the brown wire in these two windows, the extra wire reappears in the PCB window.

Is this extra wire, which appears in the file “Shield” PCB Window, required to complete the “Shield” design?

Since the “Shield” file appears to require this extra wire, and passes the DRC check, I assume that Fritzing will prepare the correct Gerber file for the shield PCB build. Is this correct?

Shield.fzz (59.4 KB)

Shield No Wire.fzz (57.5 KB)

This wire is redundant (and in fact incorrect as it produces a loop if pcb view was correct which it is not.)

There is an internal connection between A5 and SCL as shown by the green wire here. The yellow points are caused by left clicking on a pin which shows all connections to that pin.

When I delete the wire between R5 and A5, routing remains complete like this:

indicating the wire is redundant. However deleting the other wire between SCL and R5 causes this problem:

There is one route left to be routed (indicated by the message at the bottom of the screen) which in turn is caused because there is no connection to A5 (the pad is red indicating no connection, instead of green)

clicking on the end of the wire above the pad and moving it down a bit causes the wire to connect and routing to become complete and correct.


Thank you Peter. The more I use Fritzing, the more I learn about how missing some “minor” layout points can cause rather major problems.