[kur1977]

Originally Posted by j.p.s

The voltage levels would likely zap the port on the kindle.

Thank you. I just did some googling and find that the voltage on the PC serial port can be from -13 to +13V.

So I'm ordering USB to serial converter from Aliexpress now )))

I think, this will be fine https://aliexpress.ru/item/4000216010101.html

And I think, that it will be not required to solder VCC wire. Just Tx, Rx and GND