b. Hardware connection

Hardware connection is very simple . Your device must send data at any TX pin as UART standard at any baudrate (OSD will detect baudrate as described here  a. Communication protocol simple )
We must simply made connection from TX pin of Your Device to RX pin of OSD .
GND (ground) must be also connected - elsewhere connection will not work .   
If Your Device and OSD is supplayed from one battery so already have common GND .

Samples on pictures :