I have the 5V/16 MHz Pro Mini from sparkfun
It looks like it can be powered from the FTDI breakout or the VCC pins. Is it OK to attach both at the same time?
Yes - but if your Vcc source is higher, you may end up backdriving the USB source.
Probably better off with low voltage schottky diodes in series with both sources to prevent reverse driving:
Do I need voltage on the FTDI 5 V pin? If it just feeds Vcc, I can simply break the 5v connection to that pin.
You don't want the FTDI unpowered while its IO has active signals on it. That's bad for the IO protection diodes. IO pins should not be more than 0.5V above VCC or below Gnd.
The FTDI will be powered by USB, I will just break the connection to the Vcc pin on the "BLK/GRN" connector to the mini.
That'll work.
Just for the record, yes it did.
Cool.
Thanks for the advice, Crossroads.