
Turning the Raspberry Pi Into an FM Transmitter - trueduke
http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter
======
ChuckMcM
Heh, that blows away my AM morse code sender [1] using a PIC. One of the
things I did in the PIC and it would probably work here is to mush the data
into a sort of pre-encoded form (which is ready to be shipped out to the
transmitter) I expect you could do the same here by taking the wave file,
precomputing what the stereo deltas on the FM signal would be than then just
using that file (maybe a foo.efm for encoded-FM) then just DMA the pre-
processed file to the spectrum offset and voila, done.

[1] <http://www.mcmanis.com/chuck/robotics/projects/eelb.html> (and yes I'm
re-doing the web site not in Comic Sans which will eventually all be moved to
<http://robotics.mcmanis.com> but until then ...

------
meaty
I bet the FCC (or RCA in the UK) will love that :)

The amount of noise and harmonics that come off that sort of transmitter will
be horrible. At least chuck a bandpass on the end of it.

~~~
darkarmani
What is the power output of something like this? Would the FCC even care?

~~~
exhilaration
They say, _"This means that all you need to do to turn the Raspberry-Pi into a
(ridiculously powerful) FM Transmitter..."_ and claim it's transmitting at
least 50 meters away, which is far beyond what's allowed by the FCC. Not that
they'd care unless someone filed a complaint.

~~~
lifeguard
Wrong.

There are multiple rules for different spectrum.

Anyone can transmit for miles on FM in the 'green dot' / 'blue dot' spectrum.
The laws were written for business, but anyone can use them.

<http://en.wikipedia.org/wiki/Business_band#Overview>

~~~
teraflop
But that's not the band on which this is transmitting.

~~~
lifeguard
This can be configured in software. Pi can transmit up over 450 Mhz.

~~~
anthonyb
And with a paperclip antenna, it's leaking harmonics all over the place, not
just at 450MHz or 100MHz, or whatever.

------
Joeboy
Since there's a nerdy rPi post at the top of HN, I'm going to take the
opportunity to plug my new baremetal midi file player / lv2 audio plugin host:

[http://www.joebutton.co.uk/blog/baremetal-midi-
lv2-raspberry...](http://www.joebutton.co.uk/blog/baremetal-midi-
lv2-raspberrypi/)

When I get time I want to connect up a MIDI keyboard and audio input, so it
becomes a synth / guitar stompbox that'll use an open audio plugin format.

~~~
walshemj
Now that is cool will have to try that on one of my PI's

------
mgunes
An unreplied comment on a previous submission on HN was questioning the remote
feasibility of running TCP over FM with the Raspberry Pi. I too am curious
about the state of the art in general, if any, and how it might possibly be
exploited for long-range networking between small computers like the Pi.

~~~
sp332
Packet radio has increased in popularity in recent years.
[https://en.wikipedia.org/wiki/Packet_radio#Amateur_Packet_Ra...](https://en.wikipedia.org/wiki/Packet_radio#Amateur_Packet_Radio_Evolution)
Might be worth looking into, although I'm not sure how practical it would be
for the RPi.

~~~
ge0rg
It should be entierly possible to modulate packet radio using the GPIO hack,
however you would probably need a real-time kernel extension to ensure proper
transmission. Decoding is easily possible on the CPU as well, provided you
attach soeme RF demodulation circuitry, e.g. to a sound card input.

------
DoubleCluster
Just found PiHAT - Rasberry Pi Home Automation Transmitter:
<http://www.skagmo.com/page.php?p=projects/22_pihat>

~~~
StavrosK
That's fantastic, I discovered earlier that I had some plugs like those and
now I'm trying to make them work. I've managed to make them turn off easily
enough, but I can't for the life of me get them to turn on.

Would anyone happen to know how I can tune in to my remote's frequency (144.63
MHz, it says, even though the remote operates at 433.49 or something) and
listen to the tones it generates?

------
ck2
Back in the TRS-80 days, someone discovered they could make sounds through an
AM radio and a few games took advantage of that.

~~~
mark-r
I saw it done in the '70s with a PDP-8.

~~~
jlgreco
Back when I was doing z80 programming on my TI-83+, I would sometimes us an AM
radio as a very crude debugger. Programs stuck in busy loops would generally
have a very distinct sound, and you were often over time able to learn what
other parts of your program sounded like too.

~~~
meaty
That is one of those little stories which is just awesome.

That's when you KNOW the machine.

You just can't do that with anything these days. Even my HP50G calc is
personality-free in that respect.

~~~
jlgreco
Yeah, my understanding is that doing that became difficult even on the higher
end 83+/84+ series calculators as the clockrate went up, though I haven't
actually put that to the test.

------
mynegation
Oh, nice! Here is situation: I have a pretty old car with FM receiver and
single CD player, with no line input. Problem: I want to listen to the music
from my iPhone, hopefully with a distraction free interface. For that I need a
horrible contraption from car power splitter, USB cable to the iPhone that
usually doubles as GPS on the dashboard, audio cable back to FM transmitter
down there plugged into power outlet.

But now I can have a raspberry pi hidden somewhere, translating audio to FM
and possibly recognizing my voice commands while at it like "play We Are the
Void by Dark Tranquillity"

~~~
yesbabyyes
Or you could get an iTrip, but I agree that the RPi is way more fun.

<http://www.griffintechnology.com/itrip>

------
0x0
I wonder, would it be possible to do the same thing in reverse, i.e. use it as
some kind of radio receiver that dumps .wav to disk?

~~~
yuvadam
No, but rtlsdr [1] is a classical use-case for raspis.

[1] - <http://sdr.osmocom.org/trac/wiki/rtl-sdr>

------
antonb2011
Well, this is cool, but it would be cooler if they wrote an open source cell
tower for GSM phones running on Raspberry Pi.

~~~
IgorPartola
<http://wush.net/trac/rangepublic>

~~~
anthonyb
$5k for a dev box? Not really in the same league...

------
jobigoud
Fantastic, now we should combine that with a good text to speech engine so it
can read aloud e-books, blogs, and whatnot during daily commute.

------
lifeguard
I found this very exciting! Every Pi is now a potential pirate radio station!

I imagine that if a proper ground plane antenna were hooked up to it the pi
would transmit much farther.

Are FM transmitters still restricted for civilians in some parts of the world?

------
RaphiePS
I just read about Distributed Dance Party [1], a movement that uses an FM
transmitters and a bunch of boomboxes to power outdoor parties. Seems like
this would be perfect for parades or groups that need a cheap way to
communicate with a large number of people.

[1] [http://www.wired.com/underwire/2013/01/mf-decentralized-
danc...](http://www.wired.com/underwire/2013/01/mf-decentralized-dance-party/)

------
jaykru
[http://webcache.googleusercontent.com/search?q=cache:www.icr...](http://webcache.googleusercontent.com/search?q=cache:www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter)

------
neya
This is brilliant! Thanks for sharing!!

