My quest was simple: Have the output of my iPod transmit to my car’s FM radio. I tried a number of devices which worked to some degree. However, either the signal drifted with temperature or the signal was so week that it barely made it the 2-3 feet to the radio antenna. After being frustrated time after time with commercially available transmitters, I discovered the NS73M FM transmitter chip and associated breakout board from SparkFun electronics.
This project takes a NS73M breakout board and adds a PIC micro-controller controlled by a thumb switch to set the frequency. I built the entire transmitter inside a battery case that normally holds 4 AA batteries. The result? Awesome performance and no more signal drift or weak signals.
Check out the project details to learn how to build a NS73M based FM transmitter.
Update (11/20/2011): I realize that better commercial alternatives exist now (Bluetooth or crystal controlled transmitters), but my DIY transmitter continues to give great service at an out-of-pocket cost of under $20.