FM Radio Transmitter with RPI Pico – 16/07/2025

I have created an FM radio station with a Raspberry Pi Pico.

I first flashed this .uf2 file to the Rpi Pico (hold BOOTSEL while plugging pico into PC, then copy the .uf2 file onto the Pico).

The Pico then reboots to the PC automatically as a sound card. When sound is played through this output, it is actually transmitted over 87.9FM.

Note: by default you will get a bad signal. To improve this, attach a wire to GPIO Pin 21. I simply taped a wire to it. The Pin numbers should be labelled on the back of the pico.

I then made a python script to be run on a Rpi 4 (running 32-bit Raspberry Pi OS Lite), with a Rpi pico connected. It plays the songs in the Music directory in a random order. Ensure the songs are placed in a parent directory named “Music” from the python file. The songs must also be in WAV format. See Mp3 to Wav converter

See python code

I made it run on boot automatically with crontab (crontab -e) and adding the line at the bottom of the file:

@reboot /usr/bin/python3 /home/USER/code.py

Replace USER with your actual user.

I’m using it to play songs on my bike radio. It is connected to a 10,000 MaH battery which should give 5+ hours of playtime.

The range is by default not very far, however I noticed that by moving my finger closer to the Rpi Pico the range gets better and there is an increase in quality. It turns out that my body is actually becoming an antenna for this!

To get good quality while riding, I put the device in my pocket, with the Pico facing towards my leg. This seems to work just fine even while riding at relatively fast speeds.

!NOTE! There are possible health risks to using your body as an antenna for this. While the power is so low that it is extremely unlikely to cause any harm, do this at your own risk!!!

One last thing to note is that a Rpi Pico W may have issues as the WiFi/BT chip may interfere with the FM radio signals.

I hope you enjoyed this project!