im new here , i bought sim808 and its work well for first , then the serial port shows no response at all even for AT Command only ! i thought the problem with arduino or sim808 module , then i tried ATD with my number and its call me and i can hang up by ATH !! so its work.
for that i got some application test the serial port and its response with special characters and unreadable thing as the picture.
i tried change baud rate and even use my desktop computer and laptop the same result.
if anyone has any idea or had the same problem advice me please.