Published: December 16, 2025

← Back to Home

Every year I set up a simple Grinch decoration that looks like it’s taking the lights off the house. It is “Fully festive with minimal effort” - it does the job with almost no fuss, but one year we decided to make it a little more theatrical by adding a tiny FM radio broadcast that plays the Grinch song in a perpetual loop.

This is how I did it using an older Raspberry Pi 3, a short length of wire on GPIO 4, and a small open-source project I forked: https://github.com/dahln/PiFmRds.

Hardware & repo

• Pi: Raspberry Pi 3 (older, perfectly fine for this)
• Repo: my fork of PiFmRds — follow the README to install dependencies and build.

Photos:

Preparing the audio

I purchased the Grinch song I wanted to transmit and copied it to a Music folder on the Pi (I created the folder myself):

mkdir -p /home/pi/Music
scp my-grinch.mp3 pi@<pi-ip>:/home/pi/Music/

PiFmRds accepts WAV audio, but I like keeping the original MP3s. To avoid permanently converting files I stream a live conversion using sox and pipe the WAV output into the transmitter binary.

The command I run

From the Pi’s home directory (the PiFmRds binary lives in PiFmRds/src after building):

while true; do \
  sox -t mp3 /home/pi/Music/*.mp3 -t wav - | sudo ./PiFmRds/src/pi_fm_rds \
    -freq 107.3 -ps GRINCH -rt 'GRINCH' -pi GRCH -audio -; \
done &

Notes:

• sox converts the MP3(s) to WAV and pipes them to pi_fm_rds.
• -freq 107.3 sets the transmit frequency to 107.3 MHz; adjust to a clear local frequency.
• -ps, -rt, and -pi set RDS station name and text.
• The while true loop keeps the song playing in a continuous loop.
• Run the command inside an SSH session; after it starts, press Enter a few times and then exit — the process will continue in the background.

Build & wiring summary

1. Clone my fork and follow the README to install dependencies.
2. Build with make (run in the PiFmRds directory).
3. Attach a short wire to GPIO 4 (this acts as the antenna). Keep the wire short and away from people.

A couple of practical reminders

• Check local regulations before transmitting; unlicensed FM transmission rules vary by country.
• Keep power and volume low; this is a small, low-range transmitter intended to cover a yard, not a whole neighborhood.
• If you want to change the song, replace the file(s) in /home/pi/Music and the loop will pick them up on the next iteration.
• Disclaimer: I am not responsible for any damages; proceed at your own risk.

Keep shining!