Adafruit-Si4713-Library 
This is the Adafruit FM Transmitter with RDS/RBDS Breakout - Si4713 library
Tested and works great with the Adafruit Si4713 Breakout Board
These transmitters use I2C to communicate, plus reset pin, 3 pins are required to interface
Adafruit invests time and resources providing this open source code, please support Adafruit and open-source hardware by purchasing products from Adafruit!
Limor Fried/Ladyada (Adafruit Industries). BSD license, check license.txt for more information All text above must be included in any redistribution
To install, use the Arduino Library Manager and search for "Adafruit Si4713 Library" and install the library.