JDY-16 Bluetooth Rx/Tx Connection
AT commands for the JDY-16 require '\r\n' termination.


'\r' = Carriage Return character (0x0D).
'\n' = Line Feed character (0x0A).


From page 10 of the datasheet: 


  "Special note: JDY-16 module serial port instruction AT need to add
  terminator \r\n".