Re: [Paparazzi-devel] Wireless communications

[antoine . drouin]

Hi Filipe

Our cheapo solution consists in using a 2.4GHz video transmitter and transmiting
data in the audio channel. Onboard we use a CMX469 4800bps FSK modem. On ground
we feed the audio output of the receiver in the soundcard line input of the
laptop and demodulate with a programm called "multimon" that was adpated by
Martin.
This solution has a couple of advantages : it's cheap, very robust and you get
video/telemetry synchro for free if you record the sound along with the video.
But it is only unidirectionnal.

To achieve bidirectionnal datalink, we are evaluating some coronis "wavecard"
868MHz radio modem (http://www.coronis-systems.com/produit.php?id=WCA&lang=en
).
Theses devices are a little more than radio modems as they provide some neat
network functions that will allow aircrafts to talk to each other and even
relay frames.
On the desktop they work very well. We haven't tested them in the air yet due to
a problem of interferences with the 41MHz we use for safety radiocontrol. We're
working on it. The expected throughput of these device is maximum 19200bps - no
good for video.

A+

Antoine

ps: I felt inspired by this page ( http://www.lrr.in.tum.de/~acher/bga/ ) and
managed to solder some adxrs using a clothes iron and a hot air iron. I
have soldered a couple since and the method appears to work well.

http://www.nongnu.org/paparazzi/images/bga_solder_station.jpg
http://www.nongnu.org/paparazzi/images/adxrs.jpg
http://www.nongnu.org/paparazzi/images/adxrs_2.jpg
http://www.nongnu.org/paparazzi/images/gorazoptere.jpg
http://www.nongnu.org/paparazzi/video/gorazoptere_outdoor.mpeg

Selon Filipe Varela <address@hidden>:

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> Hey
>
> I'm developing a project for long range wireless communications for
> both telemetry+video downlink and simmultaneous control uplink.
>
> The idea is not to have an a/v transmitter + r/f receiver on the
> platform and r/f transmitter + a/v receiver on the ground but to
> merge these two "streams" together on a single long-range radio link.
>
> Now, has anyone experimented with radio-modems? My only doubt is
> whether it is feasable to multiplex a telemetry packet plus a video
> packet and transmit it to the ground and at the same time demux a
> control packet from the ground and still maintain real-time video.
>
> If course that multiplexing control, telemetry and video on a single
> channel requires transferring the pwm generation from an r/f
> "joystick" to the computer which is an idea i like a lot.
>
> I guess there is a pretty good alternative. Your standard
> unidirectional transmission of video+telemetry(audio channel) and use
> a cheap gsm module for emergency backup link to control the platform
> or override waypoints, maybe force a system shutdown, whatever.
>
> Basically my interest is achieving a specification for VERY CHEAP
> long-range bidirectional communications using a single link instead
> of r/f + a/v.
>
> BTW, by long range i mean 1Km to 10Km. Any more than that is not of
> any interest and should be addressed with propper expensive
> transmitters.
>
> To the paparazzi developer: what's your tried and tested max range
> for both telemetry/video transmission (air-to-ground) and control
> transmission (ground-to-air)?
>
> Thanks for reading,
> Filipe
>
>
> BTW To those looking for a cheap IMU, check this out:
> http://www.sparkfun.com/shop/index.php?
> shop=1&cart=281909&cat=1&itemid=406&
>
> It's a 6DoF for $399 ($339 no bluetooth) ASSEMBLED. Does not filter,
> but that should be done by the flight controller anyway. It's still
> expensive but a lot cheaper than rotomotions, cloudcap's, etc plus it
> IS asssembled with Analog Devices mems gyros and accelerometers which
> are, by the way, a real pain-in-the-ass to solder manually (i'd say
> impossible but i saw someone do it on a website)...
>
> Plus there's another cool thing. It's modular. You can order the
> carrier with either 1, 2 or 3 imu sensor boards (exactly the same).
> That way you can test it as you buy it and not pay $339 in a single
> payment. cool...
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