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By Joe Sz
I'm I want to use a FTDI Basic to program a 5V Pro Mini while the Pro Mini is being powered by a 5V power supply. The Pro Mini is controlling 2 150 SK9822 LED strips. Is opening SJ1 on the Pro Mini all I need to do to get everything together properly without damage or do I need to do something on the FTDI Basic? It looks like I should open both the 5V and 3.3V solder jumpers so no voltage goes from the FTDI Basic to the 5V Pro Mini. Is this correct? Thanks, Joe.
By jremington
My approach is to disconnect the Arduino from the gizmo, use power from the FTDI adapter while programming the Arduino, then reconnect the Arduino and the gizmo.

Your approach won't work, as the FTDI I/O section requires one or the other for power. Leave the jumper at 5V.
By Joe Sz
I'm not sure I made my point clear. The right hand side of the FTDI Basic schematic: ... v24-5V.pdf
shows a "SJ2" connection leading to "JP1" (the programmer connections). The Pro Mini schematic: ... ni-v14.pdf
has a Vcc connection on the FTDI Basic connector on the left side of the schematic.
FTDI Basic-Pro Mini.jpg
I still think I should cut/disconnect both the 5V and 3.3V connections on the FTDI Basic (SJ2). The FT232RL would still get power from the USB connection. The Pro Mini would still get power from my 50W supply. If I don't disconnect SJ2 (on the FTDI Basic) won't I have a two (possibly different) Vcc inputs ? One from the FTDI Basic and one from the 5V/50W power supply. Wouldn't two Vcc values cause a problem for one or both of the power supplies?
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By jremington
Yes, you made your point clear. Unfortunately, I evidently did not.

Check the data sheet for the FTDI USB-RS232 chip and the schematic for the Sparkfun board. The I/O section of the USB-RS232 chip is a separate chip power input that MUST BE provided with either 5V or 3.3V or it won't work at all. The 3.3/5 V jumper is connected to both on the Sparkfun board.

Your options are to
(1) leave the 5V jumper in place and ignore the possible slight voltage difference between the two 5V sources,
(2) cut the Vcc lead between the Pro Mini and the adapter,
(3) use my method.
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