Raspberry Pi as FM transmitter
Use the Raspberry Pi as an FM transmitter. Works on Raspberry Pi boards up to 4 (RPi 5 uses different peripherial chip).
Just get an FM receiver, connect a 20 - 40 cm plain wire to the Raspberry Pi's GPIO4 (PIN 7 on GPIO header) to act as an antenna, and you are ready for broadcasting.
This project uses the general clock output to produce frequency modulated radio communication. It is based on an idea originally presented by Oliver Mattos and Oskar Weigl at PiFM project.
To use this software you will have to build the executable. First, install required dependencies:
sudo apt-get update
sudo apt-get install make build-essential
Depending on OS (eg. Ubuntu Server 20.10) installing Broadcom libraries may be also required:
sudo apt-get install libraspberrypi-dev
After installing dependencies clone this repository and use make
command in order to build executable:
git clone https://github.com/markondej/fm_transmitter
cd fm_transmitter
make
After a successful build you can start transmitting by executing the "fm_transmitter" program:
sudo ./fm_transmitter -f 100.6 acoustic_guitar_duet.wav
Notice:
Other options:
After transmission has begun, simply tune an FM receiver to the chosen frequency, and you should hear the playback.
On Raspberry Pi 4 other built-in hardware probably interfers somehow with this software making transmitting not possible on all standard FM broadcasting frequencies. In this case it is recommended to:
make GPIO21=1
echo "powersave"| sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
hydranix has came up with simple method of using transmitter as an general audio output device. In order to achieve this you should load "snd-aloop" module and stream output from loopback device to transmitter application:
sudo modprobe snd-aloop
arecord -D hw:1,1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 - &
Please keep in mind loopback device should be set default ALSA device (see this article). Also parameter "-D hw:X,1,0" should be pointing this device (use card number instead of "X").
In order to use a microphone live input use the arecord
command, eg.:
arecord -D hw:1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 -
In cases of a performance drop down use plughw:1,0
instead of hw:1,0
like this:
arecord -D plughw:1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 -
You can transmitt uncompressed WAV (.wav) files directly or read audio data from stdin, eg. using MP3 file:
sudo apt-get install sox libsox-fmt-mp3
sox example.mp3 -r 22050 -c 1 -b 16 -t wav - | sudo ./fm_transmitter -f 100.6 -
Please note only uncompressed WAV files are supported. If you receive the "corrupted data" error try converting the file, eg. by using SoX:
sudo apt-get install sox libsox-fmt-mp3
sox example.mp3 -r 22050 -c 1 -b 16 -t wav converted-example.wav
sudo ./fm_transmitter -f 100.6 converted-example.wav
Or you could also use FFMPEG:
ffmpeg -i example.webm -f wav -bitexact -acodec pcm_s16le -ar 22050 -ac 1 converted-example.wav
sudo ./fm_transmitter -f 100.6 converted-example.wav
Please keep in mind that transmitting on certain frequencies without special permissions may be illegal in your country.
Included sample audio was created by graham_makes and published on freesound.org