Serial.print and battery powered pro mini

[peerv]

I want to test my battery powered pro mini sensor.
Is there a way to hook up the pro mini to the USB port and not using the USB power.
It is just for seeing the debug prints.

[manutremo]

@peerv do not connect the vcc pin. Gnd might be necessary to keep the reference common. Keep in mind that your usb will expect to see logic levels related to 5v, so if your arduino is 3.3v you might need a logic level converter.

[gohan]

If you have one of those ftdi adapters on Red pcb, just let it set to 3.3v and as said before leave just vcc disconnected. You could also set up a child ID that sends the values you are interested, I do it quite often because they get recorded in the controller and I can see a nice graph

[peerv]

Thanks.
I am using a 5V pro mini with a "red" FTDI adapter.
After disconnecting VCC between FTDI and 5V pro mini and the FTDI not (yet) connected to PC when connecting the battery to RAW also the power light on the FTDI adapter is lit.
So the power led on the FTDI gets power from the battery.
Is this not conflicting when I connect the FTDI to the PC USB?

[manutremo]

@peerv I don't use one of those "red" adapters but mine does the same and it seems to be no problem. Just test it, at worst case there might be some communication problem but that's all and I don't think it should even actually happen.