My weather station project involves an Arduino Pro Mini. In the local station, power would normally be supplied to the Pro Mini from an FTDI USB connection which allows received data to be logged in Excel. In some circumstances it might be used as a stand-alone unit merely displaying received data on an LCD display. As a stand alone, power would be supplied to the Pro Mini from the on-board regulator. 180703-LWS-Circuit.pdf (55.0 KB)
Look at the ERC, type 3. Pin 9 of the Pro Mini (labeled VCC) is a power input. Likely pin 1 of the connector (O2) is a passive pin. So you have a net that has at least 1 power input but no power outputs to drive the net.
That is precisely the condition which would exist in reality in data-logging mode where the IS no connection between the regulator and the Pro Mini. So it is not actually an error - merely a factual report of an intentional situation. I guess the action is to ignore the error report and get on with building the PCB.
What does that have to do with anything? The connection between the connector and the Arduino is always there. Make the pin of the connector the correct type or add a power flag, exactly the same way you have dealt with this error many times already.
Although I would design it so that no “bridge” was necessary, but just connect or disconnect the FTDI board as needed.
I haven’t been able to figure out a way to do that. The problem is that if you have the Pro Mini powered from both the USB and the regulator things get very interesting. The two are mutually exclusive. Having a bridge (or not) was my only solution. I am all ears, so to speak, if you have another.