A system that takes analog audio as input via a phone connector, digitizes the input, modulates it onto a carrier and outputs the resulting FM signal on a pin. Even without connecting an antenna to the output, the audio signal can be received with a nearby FM capable radio.
The system consists of an MCU and an FPGA, where the MCU performs the crossover from analog to digital, and the FPGA performs modulation and output.
I built this project in the contex of a digital electronics lecture at ETH.