jummama/ArduiNES — comment on commit 1d8c2b206ad2cfdc6d9f133dfffc87d6f91e7f4c
File:  line 0
By jummama:

You can omit the diode if you want, but if you do, be sure to have the NES running before plugging the USB end in, otherwise the NES power light will come on and the system will crash on boot, and it's probably not good for the hardware. Like any other similar project, do this at your own peril.