I have two arduinos (UNO - MEGA) connected by tx-rx (pins 0 & 1) (I have already connected the ground between both). The communication is bidirectional and perfect when the 2 USBs are connected to arduinos but when I change the USBs for batteries (7v - 11 v) it seems that the communication goes only in 1 direction (not exactly).
—>First message from MEGA to UNO:
<—Second message (answer) from UNO to MEGA:
The second message arrive perfect with connected USBs but with batteries arrive some strange characters.
Someone can help me?
Thanks in advance.