Hello. one question.
I have olimexino 32U4 and ESP8266 UEXT.
Can i connect ESP8266 to UEXT with olimexino 32U4 in 5V?
You should download the MOD-WIFI-ESP8266 schematic, which is the ESP8266 for the UEXT port to see how Olimex protects the Rx and Tx pins. Power on the UEXT is 3.3V.
I've run many ESP8266 on Arduino without problems -> Power for the ESP8266 was 3.3V and the Rx/Tx pins were connected directly to the Arduino pins without resistors: no problems.
But you should use the Olimex method just to be safe.
Thnaks Lurch