I tried out all I could, but Im'getting a one way communication error between the Arduino ProMini and the ESP8266-03.
The ESP module is able to receive all AT commands from the arduino board, but when it sends replies it arrives just garbled text.
If I isolate the rx and tx of the ESP I can communicate easily with any usb to serial device with no problem. But once I connect it to the Arduino, the RX pin of the ProMini receives just unreadable AT text.
What can it be?
So let try to think in another way.
Rather than try to come up with the error, let's rule out what is correct for sure, see what is left, that could be wrong.
We know you have the units running on 3.3v, seems good here.
The communication is at 115200 at all units, that seems fine as well.
The RX and TX, does seem to be swapped, but connected correct (one way), also good.
-Do the units share the same ground of the power? (just asking to be sure).
-Serial communication on the ESP8266 with PC is good?
-Serial communication with Arduino Pro Mini and PC good?
-Normally RX and TX lines do not need any pull-up registers, do you use any?
-Do you have enough power from power supply, when both units connected?, could you power on their own (or is this the case?)
Thanks again Adam,
All serial connection are fine and there are not packet lost or other errors,
I use the same power supply. I tried to power Arduino either from a arduino Mega or USBasp programmer. But the result is the same
I did not measure voltage actually, but all less are bright and flashing as usual, but I will check that too.