The XIAO works only when connected to the COMPUTER’s USB mother port（It can send TX data in UART…).
After used DMM, the USB port of the PC is 5.17 voltage, and the USB port of the battery is 5.13 voltage.
Both provide more than 20mA of current, so why doesn’t the XIAO work in the battery module(Led can work, but cannot use UART to send data)?
The problem is not clear- UART to PC communication or ?
Do you use code "while (!Serial) {} " ?
UART to other MCU
The PC is only responsible for power supply
Yes, how do you know… Maybe it caused the mistake.
Try to delete the line.
" While(!Serial) { } "
If you have this code in your program, it will continue to loop until you connect to the PC.
In fact, I used while(!Serial1){}，not `while(!Serial){}. But I had deleted it now.
You can help solved the problem? https://forum.seeedstudio.com/t/why-does-xiao-abnormal-output-when-reading-multiple-adcs/263893
ADCs output is always inconsistent, why not output the same range of values
