kopia lustrzana https://github.com/markondej/fm_transmitter
91 wiersze
4.7 KiB
Markdown
91 wiersze
4.7 KiB
Markdown
# FM Transmitter
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Use the Raspberry Pi as an FM transmitter. Works on every Raspberry Pi board.
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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.
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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](http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter) at [PiFM project](http://icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter).
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## Installation and usage
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To use this software you will have to build the executable. First, install required dependencies:
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```
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sudo apt-get update
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sudo apt-get install make build-essential
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```
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Depending on OS (eg. Ubuntu Server 20.10) installing Broadcom libraries may be also required:
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```
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sudo apt-get install libraspberrypi-dev
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```
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After installing dependencies clone this repository and use `make` command in order to build executable:
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```
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git clone https://github.com/markondej/fm_transmitter
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cd fm_transmitter
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make
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```
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After a successful build you can start transmitting by executing the "fm_transmitter" program:
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```
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sudo ./fm_transmitter -f 100.6 acoustic_guitar_duet.wav
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```
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Notice:
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* -f frequency - Specifies the frequency in MHz, 100.0 by default if not passed
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* acoustic_guitar_duet.wav - Sample WAV file, you can use your own
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Other options:
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* -d dma_channel - Specifies the DMA channel to be used (0 by default), type 255 to disable DMA transfer, CPU will be used instead
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* -b bandwidth - Specifies the bandwidth in kHz, 100 by default
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* -r - Loops the playback
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After transmission has begun, simply tune an FM receiver to chosen frequency, you should hear the playback.
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### Raspberry Pi 4
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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:
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1. Compile executable with option to use GPIO21 instead of GPIO4 (PIN 40 on GPIO header):
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```
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make GPIO21=1
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```
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2. Changing either ARM core frequency scaling governor settings to "powersave" or changing ARM minimum and maximum core frequencies to one constant value (see: https://www.raspberrypi.org/forums/viewtopic.php?t=152692 ).
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```
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echo "powersave"| sudo tee /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
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```
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3. Using lower FM broadcasting frequencies (below 93 MHz) when transmitting.
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### Use as general audio output device
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[hydranix](https://github.com/markondej/fm_transmitter/issues/144) 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:
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```
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sudo modprobe snd-aloop
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arecord -D hw:1,1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 - &
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```
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Please keep in mind loopback device should be set default ALSA device (see [this article](https://www.alsa-project.org/wiki/Setting_the_default_device)). Also parameter "-D hw:X,1,0" should be pointing this device (use card number instead of "X").
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### Microphone support
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In order to use a microphone live input use the `arecord` command, eg.:
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```
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arecord -D hw:1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 -
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```
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In cases of a performance drop down use ```plughw:1,0``` instead of ```hw:1,0``` like this:
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```
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arecord -D plughw:1,0 -c 1 -d 0 -r 22050 -f S16_LE | sudo ./fm_transmitter -f 100.6 -
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```
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### Supported audio formats
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You can transmitt uncompressed WAV (.wav) files directly or read audio data from stdin, eg. using MP3 file:
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```
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sudo apt-get install sox libsox-fmt-mp3
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sox example.mp3 -r 22050 -c 1 -b 16 -t wav - | sudo ./fm_transmitter -f 100.6 -
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```
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Please note only uncompressed WAV files are supported. If you receive the "corrupted data" error try converting the file, eg. by using SoX:
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```
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sudo apt-get install sox libsox-fmt-mp3
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sox example.mp3 -r 22050 -c 1 -b 16 -t wav converted-example.wav
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sudo ./fm_transmitter -f 100.6 converted-example.wav
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```
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Or you could also use FFMPEG:
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```
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ffmpeg -i example.webm -f wav -bitexact -acodec pcm_s16le -ar 22050 -ac 1 converted-example.wav
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sudo ./fm_transmitter -f 100.6 converted-example.wav
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```
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## Legal note
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Please keep in mind that transmitting on certain frequencies without special permissions may be illegal in your country.
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## New features
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* DMA peripheral support
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* Allows custom frequency and bandwidth settings
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* Works on every Raspberry Pi model
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* Reads mono and stereo files
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* Reads data from stdin
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Included sample audio was created by [graham_makes](https://freesound.org/people/graham_makes/sounds/449409/) and published on [freesound.org](https://freesound.org/)
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