The blue line gets disconnected so that wouldn't help the serial ground.
Could the serial ground not be connected to the external power supply as well?
@user80288 started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
The blue line gets disconnected so that wouldn't help the serial ground.
Could the serial ground not be connected to the external power supply as well?