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Title       : 	Raspberry Pi FM radio transmitter with Buttons
Author      : 	Remy van Elst
Date        : 	04-02-2015
URL         : 	https://raymii.org/s/articles/Raspberry_Pi_FM_Radio_With_Buttons.html
Format      : 	Markdown/HTML
![PiFM 1][1]
The [PiFM][2] project allows you to use a Raspberry Pi to send out a WAV file on
the FM band.
This is awesome because every normal radio then can receive your music/podcast
without expensive (sonos) equipment. It also allows you to listen in any car
without the need for a radio that handles USB or Bluetooth.
I've used a [lasercutter][3] to craft a new top plate for my Pi which has room
for three buttons. These are hooked up to a python script which allows me to
start and stop the transmission, and skip or go back songs. It also allows me to
shut down the Pi instead of just pulling the power cable.

I'm developing an open source monitoring app called Leaf Node Monitoring, for windows, linux & android. Go check it out!

Consider sponsoring me on Github. It means the world to me if you show your appreciation and you'll help pay the server costs.

You can also sponsor me by getting a Digital Ocean VPS. With this referral link you'll get $100 credit for 60 days.

Please do note that transmitting radio like this might be restricted in your
country. In The Netherlands this setup (on FM bands 87,5 to 108 MHz) forbidden
because it has too much transmission power. Transmitting on those frequencies is
allowed if your transmittor has a maximum capacity of 50nW, and this setup has
way more than that. [Source: Agentschap Telecom][5].
### Video
A small demo, shot with a phone and an Android app for lack of better equipment:
### The Case
![Short Crust][6]
The base of my case is a [Short Crust][7] case for the Model B. I initially
bought this case because it reroutes the USB power to the front of the Pi. I
mostly used it as a server back then, so having a power and a network cable at
one side of the device is quite nice. The case also looks beautifull. I bought
my case at [Pi Supply][8].
Initially I wanted to use a 3D printer to make a case because I [have some
experience with that][9]. My hackerspace, [Revspace][10] has a [Lasercutter][3]
and I'd never used that before.
I decided to replace the default top plate on the Short Crust with my own PMMA
version which should have place for the three buttons and easy access to the
GPIO. I don't find a flat ribbon cable easy access. After receiving the
instructions and doing a few test cuts in plywood I fired up Inkscape and found
myself a good ruler. I'd also never used Inkscape before but that is quite easy
to figure out after some fiddling around.
The SVG file of the top case can be downloaded [here][12]. It was cut at power
60% and speed 1.5. Below is a PNG version of the SVG:
![Top Plate][13]
My first attempts were not that great. Some measures were gambled the first
time, as you can see in the below picture.
  * A: the rounding on the corners was way off
  * B: the big access point to the GPIO pins was in the wrong spot
The holes for the screws were also a gamble, but, that was a lucky one, the are
in exactly the correct spot. The button holes were measured up and since it are
three standard [R13-57][15] buttons that was easy.
After two attempts and correct measurements I succeeded in printing the correct
top plate. It also has my website logo in it, the resistor symbol. That is just
a nice touch.
### The Buttons
I used three R13-57 push buttons for the input. They have wires soldered on to
them and a few pieces of electrical tape so that they do not short the Pi. There
is little space in the case.
The buttons are wired up to GPIO pin 18, 23 and 24 (and ground of course). I've
used the built in Raspberry Pi Pull Up resistor. If you are using another board
of some kind please check if there is a pull up/down resistor built in,
otherwise you need to place one in between the button and your GPIO pin, you
will get drifting otherwise.
![PiFM 2][17]
### The Python Script
You can find the [Python script in my github][18]. It is inspired by the [Pirate
Radio][19] script frome Make Magazine.
The only part used from that script is the config and the ffmpeg to pifm
converting. That script has no concept of a global playlist so implementing
start, stop and skip functions in it would be harder.
I've used GPIO callbacks to handle the button input. The button functions are
listed below, where bottom is where the network and USB ports are:
  * Top button: Previous Song
  * Middle button: Stop / Start playing
  * Bottom button: Next song
If you first press the Middle (Stop) button and then the Top (Previous) button
the Raspberry Pi will shut itself down using the `shutdown -h now` command.
After a few seconds you can safely disconnect the power of the Pi without
corrupting your SD card.
![PiFM 3][20]
### Setup Instructions
  * Wire up three buttons to GPIO pins 18, 23, 24 and ground.
  * Wire up a simple wire on GPIO pin 4 for the antenna.
  * Load up Raspbian on your SD card.
  * Install `ffmpeg` and `python3`.
  * Create a folder `/rasplayerfm/` and place all your music there.
  * Place a config file there:
        # /rasplayerfm/rasplayerfm.conf
[rasplayerfm] frequency = 101.0 shuffle = False repeat _all = True stereo_
playback = True music_dir = /rasplayerfm
  * Place the compiled `pifm` binary and the `RasplayerFM.py` script there as well.
  * Add the following to `/etc/rc.local` (above the `exit 0` line):
        /usr/bin/python3 /rasplayerfm/RasplayerFM.py &
  * Mark the `/etc/rc.local` file as executable:
        chmod +x /etc/rc.local
  * Tune your FM radio to the frequency set in the config file.
  * Reboot the Pi.
  * Wait a few moments.
  * Enjoy.
When you boot the Pi up it will automatically start playing on the set
frequency. With the buttons you can start, stop and skip music as described
This was an interesting project for me because it upped my knowledge and
experience with a Lasercutter, Inkscape, GPIO, soldering and Python programming
with callbacks and external inputs.
All the code (plus SVG file) from this article is released under the GPLv3. The
images are Creative Commons BY-NC-SA.
   [1]: https://raymii.org/s/inc/img/Pi_FM_1.png
   [2]: http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
   [3]: https://revspace.nl/Lasercutter
   [4]: https://www.digitalocean.com/?refcode=7435ae6b8212
   [5]: http://www.agentschaptelecom.nl/gsearch/vergunningsvrije%2Bradiotoepassingen
   [6]: https://raymii.org/s/inc/img/Short_Crust.jpg
   [7]: http://shortcrust.net/
   [8]: https://www.pi-supply.com/
   [9]: https://raymii.org/s/articles/3D_modelling_a_real_world_object_in_OpenSCAD.html
   [10]: https://revspace.nl
   [11]: https://raymii.org/s/inc/img/Lasercutter.jpg
   [12]: https://raymii.org/s/inc/img/Pi_Crust_Laser.svg
   [13]: https://raymii.org/s/inc/img/Pi_Crust_Laser.png
   [14]: https://raymii.org/s/inc/img/Pi_FM_4.png
   [15]: https://www.google.nl/search?q=R13-57&rct=j
   [16]: https://raymii.org/s/inc/img/R13-57.jpg
   [17]: https://raymii.org/s/inc/img/Pi_FM_2.png
   [18]: https://github.com/RaymiiOrg/rasplayer-fm
   [19]: https://github.com/Make-Magazine/PirateRadio
   [20]: https://raymii.org/s/inc/img/Pi_FM_3.png
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