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.
Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.
I don't suppose it's any more than a few mW - Ofcom don't seem to be interested in / able to remove the many high-power pirate radio stations, often with awful dirty signals, dotted around the UK (particularly London) so this would be a long way down their list of priorities! Even in rural Yorkshire, I get the "delights" of Phatt 100 and others every weekend.
Agreed though - anything throwing unwanted noise onto the RF spectrum is a Bad Thing, however low-power it is (see powerline networking).
Hams solved all the issues I saw mentioned in the article 100 years ago.
In the USA, it will be easy to break laws with this device. However, since the 1980s there has not been field enforcement by uncle Charlie (the FCC). Licensed users must complain a lot to get a response.\
For example, several times in CA police radio repeaters have been cross patched into HAM radio bands. No prosecution.
Now, all that being said, jamming is the worst sin a radio operator can commit. Please be careful if you start transmitting. Not out of fear, but out of being a good operator.
The replies to this comment are missing your point. It's not just the power of the FM signal, it's the amount of extraneous junk outside the FM band that will be a problem. This is a very dirty signal generator.
Nah, they sell small FM transmitters you hook up to your MP3 in order to get the audio on your car audio system, this is kinda similar I guess (link is down for me at the moment).
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.
Yes, but it isn't practical or effective. You would be re-inventing 802.11 very poorly.
1) You could use the given technique to create the MOdulation side of a modem[1]. You would have to solve the receiver and DEModulation side. Not likely to be do-able with a bare Raspberry Pi so you will end up adding a receiver and probably a demodulator (software demodulation is theoretically within the grasp of a Raspberry Pi).
2) Your data rate would be dependent on how well you implement your modem. Assuming you limit yourself to audio range frequency modulation (i.e. 10-3000Hz), you will have a hard time exceeding 300 baud using frequency shift keying (e.g. modulate with two tones, one indicating '0' and the other indicating '1'). If you use phase shift keying, you may achieve 2400 baud, but (a) I really doubt that a Raspberry Pi can do phase shift keying, (b) demodulating PSK is much more difficult that frequency shifting, and (c) in my limited experience, attempting phase shift modulation on top of a FM carrier doesn't work for crap (FM can be viewed as a type of phase shift modulation, so you end up phase shift modulating a phase shift modulator which doesn't demodulate + demodulate reliably into your baseband signal).
Higher data rates over phone lines encode multiple bits per baud (signaling unit), making the encoding and decoding tasks go through the roof if done in software. Getting to e.g. 56Kbaud of the end-of-the-road phone modem is impossible - 56Kbaud only worked when the phone company digitized the phone audio, and rather iffy even then.
There are UHF radio modems that are commonly used for radio telemetry for amateur UAVs (typically RC planes or multi-rotors), transmitting on 900MHz or 433Hz using spread-spectrum technology.
Based on HopeRFs HM-TRP module, they present a serial port, either TTL, or as a virtual COM port over USB using a (defacto-standard) FTDI USB to serial chip. You can use two serial, two USB, or one of each - the radio modem in them is identical, it's just the presentation that differs.
Line-of-site range depends on the data rate, but is in the region of 1 - 2km, but up to 24km is possible with amplification. The data rate is up to 128kb/s.
Lots of technical details can be found on the ardupilot wiki[1].
They were designed as a lower cost, longer range alternative to Xbee [2]. Xbee support ZigBee, multipoint, mesh and other protocols, but not the 433MHz frequency legal in Europe.(900MHz is fine for the US, but the alternative, 2.4GHz, is the same frequency commonly used for spread-spectrum radio-control, so risks interference or reduced range.)
They can be purchased in the US for $75 a pair [2]. Clones can be found can be found from Chinese suppliers for less than $40 a pair [3].
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?
Thanks for that link. The PiHAT page does a much better job of explaining the details of how this works to me (as someone with a lot of hardware experience but not a lot of familiarity with the Broadcom SOC on the Pi).
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"
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.
[+] [-] ChuckMcM|13 years ago|reply
[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|13 years ago|reply
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.
[+] [-] bhousel|13 years ago|reply
Unlicensed broadcasts on the FM broadcast band (88 to 108 MHz) are limited to a field strength of 250 µV/m at a distance of 3 meters from the antenna. This is equivalent to 0.01 microwatts.[2] Emissions must be kept within the 88.0 to 108.0 MHz band under Part 15 rules.
[+] [-] andyking|13 years ago|reply
Agreed though - anything throwing unwanted noise onto the RF spectrum is a Bad Thing, however low-power it is (see powerline networking).
[+] [-] lifeguard|13 years ago|reply
In the USA, it will be easy to break laws with this device. However, since the 1980s there has not been field enforcement by uncle Charlie (the FCC). Licensed users must complain a lot to get a response.\
For example, several times in CA police radio repeaters have been cross patched into HAM radio bands. No prosecution.
Now, all that being said, jamming is the worst sin a radio operator can commit. Please be careful if you start transmitting. Not out of fear, but out of being a good operator.
[+] [-] mark-r|13 years ago|reply
[+] [-] Adirael|13 years ago|reply
[+] [-] lifeguard|13 years ago|reply
[+] [-] unknown|13 years ago|reply
[deleted]
[+] [-] darkarmani|13 years ago|reply
[+] [-] Joeboy|13 years ago|reply
http://www.joebutton.co.uk/blog/baremetal-midi-lv2-raspberry...
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|13 years ago|reply
[+] [-] mgunes|13 years ago|reply
[+] [-] gvb|13 years ago|reply
1) You could use the given technique to create the MOdulation side of a modem[1]. You would have to solve the receiver and DEModulation side. Not likely to be do-able with a bare Raspberry Pi so you will end up adding a receiver and probably a demodulator (software demodulation is theoretically within the grasp of a Raspberry Pi).
Ref: http://en.wikipedia.org/wiki/Modem
2) Your data rate would be dependent on how well you implement your modem. Assuming you limit yourself to audio range frequency modulation (i.e. 10-3000Hz), you will have a hard time exceeding 300 baud using frequency shift keying (e.g. modulate with two tones, one indicating '0' and the other indicating '1'). If you use phase shift keying, you may achieve 2400 baud, but (a) I really doubt that a Raspberry Pi can do phase shift keying, (b) demodulating PSK is much more difficult that frequency shifting, and (c) in my limited experience, attempting phase shift modulation on top of a FM carrier doesn't work for crap (FM can be viewed as a type of phase shift modulation, so you end up phase shift modulating a phase shift modulator which doesn't demodulate + demodulate reliably into your baseband signal).
Ref: http://en.wikipedia.org/wiki/Modem#Narrow-band.2Fphone-line_...
Higher data rates over phone lines encode multiple bits per baud (signaling unit), making the encoding and decoding tasks go through the roof if done in software. Getting to e.g. 56Kbaud of the end-of-the-road phone modem is impossible - 56Kbaud only worked when the phone company digitized the phone audio, and rather iffy even then.
Ref: http://en.wikipedia.org/wiki/Modem#Using_digital_lines_and_P...
[+] [-] scoot|13 years ago|reply
Based on HopeRFs HM-TRP module, they present a serial port, either TTL, or as a virtual COM port over USB using a (defacto-standard) FTDI USB to serial chip. You can use two serial, two USB, or one of each - the radio modem in them is identical, it's just the presentation that differs.
Line-of-site range depends on the data rate, but is in the region of 1 - 2km, but up to 24km is possible with amplification. The data rate is up to 128kb/s.
Lots of technical details can be found on the ardupilot wiki[1].
They were designed as a lower cost, longer range alternative to Xbee [2]. Xbee support ZigBee, multipoint, mesh and other protocols, but not the 433MHz frequency legal in Europe.(900MHz is fine for the US, but the alternative, 2.4GHz, is the same frequency commonly used for spread-spectrum radio-control, so risks interference or reduced range.)
They can be purchased in the US for $75 a pair [2]. Clones can be found can be found from Chinese suppliers for less than $40 a pair [3].
[1] http://code.google.com/p/ardupilot-mega/wiki/3DRadio
[2] http://www.digi.com/xbee/, http://en.wikipedia.org/wiki/XBee
[3] http://store.diydrones.com/category_s/13.htm
[4] Try: http://RCTimer.com, http://AliExpress.com, http://GoodLuckBuy.com and search for 3DR
[+] [-] sp332|13 years ago|reply
[+] [-] bokchoi|13 years ago|reply
http://en.wikipedia.org/wiki/ALOHAnet
[+] [-] DoubleCluster|13 years ago|reply
[+] [-] StavrosK|13 years ago|reply
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?
[+] [-] emaste|13 years ago|reply
[+] [-] ck2|13 years ago|reply
[+] [-] mark-r|13 years ago|reply
[+] [-] mynegation|13 years ago|reply
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|13 years ago|reply
http://www.griffintechnology.com/itrip
[+] [-] john61|13 years ago|reply
[+] [-] StavrosK|13 years ago|reply
[+] [-] 0x0|13 years ago|reply
[+] [-] yuvadam|13 years ago|reply
[1] - http://sdr.osmocom.org/trac/wiki/rtl-sdr
[+] [-] antonb2011|13 years ago|reply
[+] [-] shaddi|13 years ago|reply
I like this because they are using the rPi itself as a radio -- that's a pretty neat hack.
[+] [-] IgorPartola|13 years ago|reply
[+] [-] jobigoud|13 years ago|reply
[+] [-] lifeguard|13 years ago|reply
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|13 years ago|reply
[1] http://www.wired.com/underwire/2013/01/mf-decentralized-danc...
[+] [-] jaykru|13 years ago|reply
[+] [-] neya|13 years ago|reply