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Discuss RTL-SDR and cheap software defined radio
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 Post subject: RTL-SDR+Arduino+OpenWRT?
PostPosted: Fri Jun 19, 2015 3:13 pm 
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While I see plenty of RTL-SDR projects using a Raspberry Pi, I see very few implementations incorporating an Arduino. Which is somewhat surprising considering how much SDR depends on the conversion of analog signals into digital information, for which the Arduino is especially well suited. Methods like audio piping might work, but it just seems like a temporary workaround when there are so many inputs and outputs possible through the serial-USB interface of an Arduino.
I'm guessing that part of the reason why Arduino/RTL-SDR combinations are difficult to find is the lack of processing power of the 8bit Arduino "Uno". This might also explain why the few projects I do find have rarely been updated since 2012, which is right around the time that the Raspberry Pi came out... The Raspberry Pi is an amazing device on its own accord, but one thing it was never meant to do is handle analog I/O with any kind of accuracy. Other single board computers like the Beaglebone Black, and the UDOO were designed as part RPi/part arduino from the beginning, but I've found that there's still a lot of room between what you can do with an 8Bit MCU and full blown PC... This is one reason why I've always been intrigued by things like the TP-Link WR703n router running OpenWRT firmware, about which an article recently appeared on this very site- http://www.rtl-sdr.com/running-an-rtl-sdr-on-openwrt/. The key component of the WR703n is the Atheros AR9331 processor which is powerful enough to run Linux/OpenWRT. A few years ago, the AR9331 started shipping as a standalone unit at very low cost. Platforms like the Dragino (http://www.dragino.com/) incorporated the chip into
a much more hacker-friendly design with open I/O ports. Most significantly, the chip was adopted by Arduino itself as the basis of the Arduino Yun (http://www.arduino.cc/en/Guide/ArduinoYun).

The Arduino Yun, is basically a standard 8bit Arduino combined with the OpenWRT processor on a single compact controller. What REALLY makes the platform so powerful however was the creation of a new "Bridge Library" to facilitate standardized communications between the Arduino microcontroller and the Linux processor. Essentially this means you can have your cake and eat it too!

I'm interested to see if the Arduino+Linux combo could be used to simplify a standard RTL-SDR workflow. As I've been using the RTL-SDR as an AIS receiver, I will use ship tracking as my initial use-case. According to the post at http://www.rtl-sdr.com/running-an-rtl-sdr-on-openwrt/, the RTL-SDR package is available in the OpenWRT package manager. As the link to the tutorial referenced in the article seems to be dead, I can only assume that the dongle connected to the WR703n router via USB. The same can be done via the dedicated USB port on the Yun's Linux side, and as such might well suffice as a simple embedded TCP server that could be directly attached to the antenna setup. A similar setup was documented at http://rtl-sdr.sceners.org/?p=40 (EMBEDDED RTL-SDR SETUP: RTL-SDR + OPENWRT = OMG!!)
Of course, such a setup only needs the Linux side and it seems like a waste of so much potential to bypass the Arduino completely! What if the Arduino made it possible to either enhance the antenna reception or even do away with the hardware antenna altogether?!!! (See:Electronically-tunable antenna for software-defined radio-- http://forum.arduino.cc/index.php?topic=240131.0)


Has anybody else used the RTL-SDR with OpenWRT or Arduino or both?


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PostPosted: Fri Jun 26, 2015 9:35 am 
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Joined: Tue May 19, 2015 5:49 am
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MCU with multiple cores and enough CPU power would be the future platform of SDR including RTLSDR.
That's not far away if you look at LPC4370.
For RTLSDR, it is very easy to get samples into the PC by USB connections. Once the data is in the PC, why we need MCU?
The cost of the raspberry pi is half of that of ArduinoYun. If you want to get wifi for the raspberry pi, it only costs 4 more dollars to get a very good one.


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