We are using an Arduino Nano for simple serial comms to fire a relay from a Windows 10 PC.
Initial issue we had was windows not recognizing the device (COM Port) when the pc is powered off (as per this link: Arduino Nano - USB not present after reboot ) so we powered the arduino nano over a 5V pin and now when Windows starts up the device is recognized.
However, as I'm learning with these chips, nothing is ever that simple. Now the relay that we are firing does not work with external power, but if you unplug the external power then the relay does fire (powered over USB)
The units are at a mine and at the moment and I believe that the problem is that the serial chip is now not responding as per this - from the official Arduino Nano page:
The FTDI FT232RL chip on the Nano is only powered if the board is being powered over USB. As a result, when running on external (non-USB) power, the 3.3V output (which is supplied by the FTDI chip) is not available and the RX and TX LEDs will flicker if digital pins 0 or 1 are high.
Note - I included the above from another question but this no longer appears on the official arduino nano page (can't past link as it's my first post)
The question is how can we get the digital pins on the arduino nano to fire using an external power source and input from a Windows PC?