@dodiyez I am perfectly calm, I'm just trying to point out to you that in order for us to give you meaningful and specific answers we need to have some minimum information about what you are doing.
The library/framework-independent answer is "use the UART to output debugging text". But that is not very helpful, as it doesn't really tell you how to do it -- and that is dependent on the library/framework.
Ok, I managed to solve it (or rather the cause was found).
Problem was not in PSU but in an not powered arduino attached to tx/rx pins (and pershaps the sensors at D3 D4 pins - becuse I moved them as well). I cant really tell what was going on, but having arduino rx/tx pins attached to mini's tx/rx stops it from booting properly (a reset is required) - importatns is that removing the arduino fixed the issue (it was not powered since it's not used yet an I use mini's serial as debug rather than a communication port).
When my project will move to the next phase I'll need that uart connection to work - but in the meantime - skipping "not yet used" arduino works.
Thanks for help.
yes, solar panel goes directly to USB charging port, and this scheme has been working for more than 8 months.
do not ask me why it has not burned down yet. i do not know, probably i have lucky ;)
datasheet TP5410 tell that this chip can accept up to 10 volts input, and this one still work...
Do you have a multimeter or, better an oscilloscope to see what is actually happening between that charging module and the battery shield? Can you measure the voltage and current that it is giving? I suspect the LED is not really blinking, but instead the battery shield is simply resetting due to inadequate or noisy power.
would you please use three backticks next time you include something like code or an error log.
The code part in question is inside of "esp8266_peri.h", which will be included from "Arduino.h", which in turn will be included before "Music_WEMOS_D1.ino.cpp" or any other sketch will be opened.
This also explains the smiley, as *) will be shown as *) in this forum.
I downloaded the original code, named "Visualizer_Program.ino" and compiled it with no error. I also suggest to post your code here ( please do not forget the backticks ). Maybe we can help then.