This is librtty [/ˈlɪbərti/], an open source Arduino library for generating an RTTY bitstream to be fed into an FM transmitter. Uses a potential divider on the Arduino output pin, providing the correct voltages to set the frequency shift.

Call this line before setup():
RTTY rtty(radio_txd_pin, baud_rate, stop_bits, CHECKSUM_CRC16)

Then call the transmit() function with the string you wish to send, forex:
rtty.transmit("This is my string\r\n")

Library Functions:
Transmit a string:
transmit(string);

Set the transmission baud rate:
setBaud(50);

Get the current baud rate setting:
getBaud();

Set the checksum type to be appended to the transmitted string:
setChecksum(CHECKSUM_CRC16);

Get the current checksum setting:
getChecksum();

Written by Jon Sowman in 2010 and released into the public domain under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License.