In the 2015 workshop, a student had found some code that claimed to make the Raspberry Pi able to transmit an FM radio signal. It didn't work when we tried it on one of our Raspberry Pi B 2's, but it did work on earlier versions (B and B+).
On July 8, 2015, a Japanese web site published a version that works on the Raspberry Pi 2 along with an explanation of what was needed to make it work. Here is my rough translation of that article.
This new code is available in two slightly different versions, fm_transmitter-master.zip and pi2fm.tar.gz, both appear to work fine on Pi 2 and Pi 3's, but not on earlier versions.
I have yet to carefully study the working code presented in the Japanese site I translated, but clearly making it work involved knowing more about the Broadcom SoC architecture. Its code references a helpful 205-page Broadcom document from the Raspberry Pi Foundation and gives specific with page numbers.
A short (~15 cm) jumper needs to be plugged onto GPIO04 (header pin 7) (See GPIO pin layout) as an antenna. Keep in mind that an excessive length for the antenna can get you in trouble with your local radio communications authorities.
Last updated: June 30, 2016
