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you could use this to broadcast RDS, and then tell the other cars on the road that there is a blockade ahead, it would be like that Bruce Almighty scene, well maybe not...
It has enough range to cover your home, DIY drive-in movie, a high school ball game, or even a bike parade (depending on the stragglers).
Interesting idea... but wouldn't you need to increase the broadcast range for that to work effectively?
Maybe every car with the system could work as a re-transmitter?
You can also use a bare raspi (plus a couple passives...) as a 10mW QRP transmitter: http://en.wikipedia.org/wiki/QRP_operation
With the right software, plus favorable ionospheric conditions, you can get really, really good range. This guy did 7,600km, eastern Austria to south Florida: http://gerolfziegenhain.wordpress.com/2013/04/13/raspi-as-ws...
You also need a very, very good antenna for that sort of stunt.
QRP is tough. I'm a licensed HAM radio operator and my Tx has a 5 W final stage, so I fit right into the QRP limits. It's tough. You're at the mercy of the ionosphere all the time.
100 W amplifiers are cheap. :)
Plus he's doing QRSS using WSPR, which transmits at the breakneck pace of 1.46 baud. Supposedly WSPR works down to -28dB.
http://en.wikipedia.org/wiki/WSPR_%28amateur_radio_software%...
I use a WSPR transmitter that outputs around 200mW on 20m and am easily heard all over North Americdn and Europe. I've also had two South Pacific reports.
This was into a poorly tuned dipole at 35ft.
You also need a very, very good antenna for that sort of stunt.
For 10mW, sure, but I've done Michigan to France on 5W with a plain old 40m loop 15-20 feet off the ground. In hindsight, I should have tried it on 3W if only to get 1000mi/W on a cloud warmer.
There are some really good legitimate uses for this, but I'm concerned that it's going to turn into another Defense Distributed situation =-(
I'm not sure exactly how they compare, other than the fact that both have a potential for some form of misuse.
Exactly what concerns do you have?
As an amateur radio operator, I think this is fascinating, because they claim it can transmit on the 2m VHF band (144-148MHz) that's popular among hams.
But I have some concerns about its signal characteristics, since you're essentially abusing digital hardware (GPIO) to produce a modulated output it wasn't designed to produce. Someone with a spectrum analyzer should check to see if it produces any nasty harmonics, or similar noise, that could interfere with other stations.
It transmits ~10mW, though.
If you need a datapoint on how noisy those signals are: some people have combined a 144.6Mhz Raspberry Pi output with a narrow passive bandpass filter to generate a relatively clean and powerful 433MHz signal (the third harmonic, which is quite strong in a square wave): http://www.skagmo.com/page.php?p=projects/22_pihat
Yes, assuming there's strong harmonics (I'd be real surprised if there weren't), you should definitely put a bandpass filter between the Raspberry Pi and the antenna like these guys did.
Thanks for the link! That's a clever way of using harmonics to your advantage.
Recently I did a similar project in which a malicious hardware device leaks a victim's data (Password, credit card #, etc.) through a similar technique.
We used an FPGA though, so with a 100 Mhz fundamental frequency we had harmonics well into the 1.5 Ghz. We called it CPU-SDR. Video here:
https://sites.google.com/a/groundworkstech.com/index/blog/rs...
Bonus: Using mutiple PCB traces, you have a basic Yagi-like directional antenna. Feeding different traces you can modify the RF radiation pattern it in real-time.
You've indeed invented MIMO.
It's more like a Yagi, as currently I feed only one of the "antennas" and the modulation is very limited.
But messing with the phases should be possible.
Fellow HAM here.
I don't doubt that the spectrum coming out of that thing is pretty horrific. There are no filters, and who knows what the wave form is (rectangular?).
Hang a bandpass LC filter on the output then feed to a dipole?
Disclaimer: not an active HAM, used to clean seagull crap off 500KHz distress aerials on small ships in the last century.
I don't think a rectangular wave can propagate through the ether :)
Output from the digital pin is very rectangular. But you have many sinusoidal harmonics ready to be fired into the air if you plug a small antenna on it.
Of course it can. A square wave is just a series of discrete sine components, each of which will happily propagate through the air. If this were not true, WiFi wouldn't work -- it also relies on multiple, coordinated frequencies and complex modulation.
Right, in ideal hardware. The problem is that in order to transmit an ideal square wave, you need infinite bandwidth.
The problem being that any real circuit has a finite band it operates on. It will filter the components of the wave that are outside of its bandwidth, leading to 'ringing' artifacts (Gibbs phenomenon).
On the contrary. An ideal square wave's higher harmonics decline rather quickly:
http://en.wikipedia.org/wiki/Square_wave#Examining_the_squar...
In other words, there's enough energy to cause problems at 2, 6, 10 ... times f, but at rapidly declining levels.
Ringing artifacts are present in a system whose bandwidth rolls off abruptly. It's less significant in a system with a gradual drop-off in response, like a piece of wire acting as a broadband antenna.
A true square wave would require an infinite series of discrete sine components, wouldn't it?
Yes, in principle, it represents an infinite series:
http://en.wikipedia.org/wiki/Square_wave#Examining_the_squar...
But as you can see, the higher harmonics decline quickly in energy.
According to a guy named Fourier, a rectangular wave is really just a bunch of sine waves working together.
Totally of topic, but I think it might be interesting and new for some of the HN crowd: both Lagrange and Laplace, not the least of mathematicians, didn't believe that idea when Fourier presented it to the Paris institute. http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Four...:
"[...] a committee consisting of Lagrange, Laplace, Monge and Lacroix was set up to report on the work. Now this memoir is very highly regarded but at the time it caused controversy.
There were two reasons for the committee to feel unhappy with the work. The first objection, made by Lagrange and Laplace in 1808, was to Fourier's expansions of functions as trigonometrical series, what we now call Fourier series. Further clarification by Fourier still failed to convince them. As is pointed out in [4]:-
All these are written with such exemplary clarity - from a logical as opposed to calligraphic point of view - that their inability to persuade Laplace and Lagrange ... provides a good index of the originality of Fourier's views."
Doubt it's got much range. I'd be surprised if it goes 50ft. Most of the power is going to be lost unless you have a decent antenna on the end and something to decouple it from the host circuit. Bandpass wouldn't go amiss though.
I was able to pick up an indoor transmission from my car up to about 1000 feet away. However after losing the signal the car radio had to be within 400 feet before it locked on again.
Ouch that's pretty huge.
Yeah, it's nasty, but also gutless.
The winner of Make's 2014 Raspi contest does SSTV from a Pi:
http://www.instructables.com/id/Raspberry-Pi-security-Slow-S...
I used an RTLSDR to look at the spectrum. If you're plugged into the wall, you get ripple. Also the harmonics are pretty loud too. The WSPR example above shows the filtering they put in. In theory at low power like someone else said it isn't ideal, but wouldn't upset too many people so long as you didn't amplify before filtering.
After starting the broadcast: "Keep in mind that it'll take about 15 seconds to warm up"
What does that mean? What needs to warm up?
Boot up. It runs a full Linux stack, and the raspi CPU is not astonishingly fast.
I just rebooted my rapberripi running archlinux, It took ~2 seconds from the time I rebooted it to me being able to ssh into it.
The pi started to respond to ICMP packets in 19 seconds
http://pastebin.com/JQmCmHXH
Hmm, maybe a Raspberry PI could be easier and more reliable replacement to virtual machines?
(I love Vagrant/Virtualbox but sometimes, after putting the laptop to sleep, it stops working and I have to reboot).
They're not that fast. A single thread build of my python/c project (pillow) takes ~ 15 seconds on a vm, ~ 30 on an ancient core duo laptop, and ... still waiting on the raspberry. edit: 5:15. So 25 times slower.
I did an analysis of Mathematica benchmarks on the Raspberry Pi and found it to be 15x slower at best and much slower when there are CPU specific optimizations:
http://adereth.github.io/blog/2014/01/06/benchmarking-mathem...
Nice! Way back I did something similar in the AM band with one of the 8 pin PIC chips [1], didn't play music though, just sent morse code. The RPi version is much nicer, you could have it talk to you :-).
[1] http://www.mcmanis.com/chuck/robotics/projects/eelb.html
Make has covered it before: http://makezine.com/2012/12/10/raspberry-pi-as-an-fm-transmi...
Note that the news here is only the Make project on it, as this has been known and working for well over a year. The current PiFM software uses DMA from the userspace to play without clicks and without taking the whole CPU. The later versions also appear to support stereo, so I can't make much sense of this sentence in Make's tutorial (step 5):
If their pre-configured image is really doing this, it is doing it wrong, I think. Worth noting that the PiFM script is capable of reading from stdout, and not just play WAV files, so the possibilities go well beyond playing music off a SD card.
By the way, here is the original page in a Wiki (of which Make shows a screenshot, but I found no link): http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb...
edits: add information
Would it be possible to modify this to work at 125khz to use passive RFID?
Personal number station here we go!
It will transmit radio noise on many other frequencies. I played with this stuff when i was a kid to jam neighbor's TV's (they only used antennaes). Worked like a charm.
It's very hard and expensive to transmit signal on a single frequency. And very easy to pollute everything.
FM transmitters for MP3 players are cheap and work well (within a very short range, but that's their use-case), see for example http://www.amazon.com/FM-Transmitters-MP3-Player-Accessories...
So surely it can't be that hard or expensive - unless it changes when you try to broadcast to more than a few feet away?
If you can only broadcast two feet, who will care that you are flooding the spectrum?
So I don't think you can assume they are particularly clean transmissions.
If they meet FCC regulations then yes you can assume that. If they don't meet FCC regulations then they're illegal. I don't know how much policing goes on for that though.
I thought FCC regs involved a distance component? Like, they don't measure EMI right on the surface of the device.
If you're interested in getting into RF, I'd suggest getting a software-defined radio like bladeRF[1]. It allows you to make a lot of cool devices without being a hardware whiz.
The guys who run it are extremely knowledgeable about RF and there's some really cool stuff being done with it [2][3].
[1]: http://nuand.com/
[2]: http://bladerf.blogspot.com/
[3]: http://www.irrational.net/2014/03/02/digital-atv/
I wish they had put the $420 price of the basic model on the front page.
yeah. FPGA device prices are still up there unfortunately
Yes, it's not exactly in the raspi price range. That range is covered by the TV-tuner SDR receivers and other USB-stick receivers.
On the other hand, for what it does, that x40 is actually quite cheap.
I really want to learn more about this stuff! Is there a good book that introduces the basics? More technical introductions are good too.
Just blew my motherboard by updating the bios via one of dell's software updates and corrupted my bios. The board doesn't have a dual bios configuration so its corrupted so I can't pull the battery or reset the CMOS.
All of my research showed that most people just pony up and replace the mobo for $200. Unwilling to give up I kept researching and found that you can turn your Raspberry Pi into a flashrom to restore your bios. http://flashrom.org/RaspberryPi
Waiting on female to female GPIO connectors to come in mail before I can hook my raspi up to the SPI sockets on my mobo and reflash the bios. Got my fingers crossed, if this works it will be a great win!
It should work. If you have serious trouble with that then there are also devices like the Bus Pirate[1] that can do the same thing (Though I have yet to do it myself).
It's really neat how easy this kind of thing has become recently with all of the hobby electronics guys driving the market and opening up doors that 10-15 years ago looked bleak at the time (though that could just be my memory coloring it).
I have used similar stuff to fix up routers (though haven't had to interface with the flashrom directly) and install openwrt.
With BIOSes being serial flash these days, it's really easy to read/write them since all you need is something that can do programmed GPIO on a few lines at the right voltage. An Arduino, a parallel port on another PC, etc.
A lot of PC repair shops in China will reflash BIOSes really cheaply too; they usually use a clothespin-like clip to attach to the chip so they can do it quickly without having to solder anything.
Reminds me of Fabrice Bellard generating TV signals (analog and digital) with a VGA card.
http://bellard.org/dvbt/
This is awesome! Now what kind of bandwidth can we get out of this?
Hmm add a line-in, transform the signal, pipe it over to the transmitter and BOOM; silent disco!
There are two previous discussions of this that might also be worth reading:
https://news.ycombinator.com/item?id=5103031
https://news.ycombinator.com/item?id=4899505
Does anyone have the ISO or a torrent of it?
Why not just make one out of a single transistor and some resistors? #overkill
Great ! I just managed to transmit the FM signals, I used my micro USB cable stuck in 7th Pin
Is it possible to both receive and transmit FM simultaneously?
Could this be used to create a simple, low bandwidth wireless connection between 2 pis?