I am using a 3.3V Pro Mini for a solar project where the 12V source is run through a buck converter to power the Pro Mini and other bits. (The 12V is needed to power a pump). I want to debug in the IDE while running the system off of the 12V power. I tried just removing the 3.3V connection from the FDTI board to the Mini but fried the FTDI in the process. Is what I am trying even possible? Did I just do it wrong somehow?
It’s probably due to surge from the pump-side of things…how were the GNDs for all 3 wired?