Reader [Mike Y] responded to our “What are you working on?” post with his stereo FM transmitter project. If you’ve ever used an FM transmitter for your portable audio, you know that even the best consumer level ones can be difficult to make sound decent.
He obtained an NS73M FM Transmitter module from Niigata Seimitsu Company, but it required a controller to handle pre-emphasis, modulation level, frequency, and power level. He decided on an Arduino which would also control his LCD.
His results were quite good, with decent range and superb audio quality. His total cost thus far is $35, but he still needs to put it in an enclosure. You can find complete schematics as well as source code and helpful tips on his site. You may also want to check out the regulations on broadcasting(pdf) as well.