Author Topic: HD video link for RC model FPV  (Read 7464 times)

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Offline Psi

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HD video link for RC model FPV
« on: May 24, 2013, 12:07:10 am »
I've been thinking of a project for a while to try and build a HD video link for RC model FPV flying.
It would be quite an undertaking and i'm not sure i will try but i though a thread on the idea might be interesting.

Currently there are very few solutions for HD video on a RC model. The products that exist are too expensive for the hobbyist.

It's not crazy complex if you ignore the RF side of things. People have been flying FPV for years with uncompressed standard definition video links. Compressing and uncompressing a HD signal with some error correction should be possible.
Even a simple MJPG codec might work, though MPEG would be better.

The only way i see it working is to use the RC radio link as a feedback system so the plane knows the error rate for received video on the ground. This would allow it to lower the resolution/bitrate on the fly to keep the signal solid.
Fly too far away and the picture quality just keeps dropping, but at least you can see which way is up and fly back into range.
When in close range you'd get a nice HD video signal.

The biggest problem to the project would be the RF side. Ideally it would use an existing RF transmitter/receiver module instead of making one. (Since most FPV video links are in the ghz range for bandwidth reasons and i'm no RF engineer)

Any ideas?
« Last Edit: May 24, 2013, 12:09:43 am by Psi »
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Offline marshallh

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Re: HD video link for RC model FPV
« Reply #1 on: May 24, 2013, 12:32:39 am »
Both the widely known Broadcom SOC used on the fartberry pi and the Freescale i.MX5 series do 720p encode and 1080p decode. Then the problem becomes your wireless link. Probably the easiest would be to repurpose an existing 2.4ghz all in one frontend chip (with DAC/ADC)
I looked into this some time ago but obviously you can't do it for anywhere as cheap as the chinese SD video links.. It is possible but you need to know what you are doing
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Offline Psi

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Re: HD video link for RC model FPV
« Reply #2 on: May 24, 2013, 06:09:14 am »
Probably the easiest would be to repurpose an existing 2.4ghz all in one frontend chip (with DAC/ADC)

Yeah, that occurred to me too.  Try and modify an existing cheap FPV analog RX/TX and use it's RF transmitter section.
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Offline RCMR

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Re: HD video link for RC model FPV
« Reply #3 on: May 24, 2013, 07:34:53 am »
You'll have two problems:

1. latency
2. RF link bandwidth

Using a decent silicon-based codec you can get the latency down to an acceptable level but the bitrate for good HD will still be very high - far beyond that offered by most of the existing low-cost digital Tx/Rx chip systems.

I looked at this a while ago and decided that while it was a great goal, the technology was not simple enough for a DIY solution -- yet!
 

Online Rasz

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Re: HD video link for RC model FPV
« Reply #4 on: May 24, 2013, 08:55:49 am »
rpi model a + camera module + usb wifi adapter + 2 handmade sector panel antennas for 360' coverage around model
Wifi link locked in 30Mbit mode, 40MHz channel to get the most sparse modulation (qpsk) and lowest error rate. It should be enough for 15Mbit h264 stream.
2 sector antennas at the base station should be good up to 10km LOS using ordinary 2.4GHz wifi and cheap AP/card.

Latency might be a problem, probably around 500ms end to end?


Another option is 808 #16 + microcontroller using SPI to pretend that its an SD card. This would be tricky to implement, no idea if 808 can be convinced to work in SPI mode (maybe it expects 1 or even 4 bit bus mode to work), not to mention its possible that camera buffers a lot in internal ram before sending data to SD so latency might be terrible. Of course this doesnt solve wireless link problem (about 7Mbit).

Another idea for wireless link -  US army went cheapass and used DVB-S for their drones in Iraq. Someone figured it out and freedom lovers started using Sat tv cards to intercept video feed.

DVB-T:

http://febon.blogspot.com/2012/09/dvb-t-transmitter-tx-usb-dongle-of-dvb.html
This chinese dude is really into TV transmission http://febon.blogspot.com/

You already have mpeg4 stream from the camera, the rest of dvb-t stream is just some bit shuffling and padding (multiplexing). RPI  might have enough umpf to do SDR modulation = you would only need USB DAC + amp to transmit DVB-T.
This chinese dude used IT9507FN/AX Commercial grade baseband transmitter for digital TV with USB and TS interfaces

product using this chip
http://www.hides.com.tw/product_cg74469_eng.html#310685
http://www.idealez.com/ES/hides/product-detail/en_US/69859

$170, you will need RF amp, aerial and portable DVB-T TV
« Last Edit: May 24, 2013, 09:29:36 am by Rasz »
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Offline amyk

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Re: HD video link for RC model FPV
« Reply #5 on: May 24, 2013, 10:04:19 am »
This would allow it to lower the resolution/bitrate on the fly
:D

How about a Wi-Fi network camera? Is this too expensive? http://www.amazon.com/Dropcam-Wi-Fi-Wireless-Monitoring-Camera/dp/B006P88VSE
 

Offline muvideo

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Re: HD video link for RC model FPV
« Reply #6 on: May 24, 2013, 10:37:03 am »
Hello, happy to see more pepole with the RC virus around  :)

just curious, since the tx is moving, how about DVB-H ?
As I understand it is targeted to handhels devices.

If I'm understanding correctly the situation is that there are
plenty of decoders for receiver side, since it's an huge market,
but very few encoders for transmitter side. And the fact that the
transmitter needs to  be light and low power it's even worse.

But i'm totally lacking rf education, let alone digital video links, I'm only
curious because I like to record onboard videos on my rc planes.

By the way, Psi, if you want HD video just for recording it, I've read
that there are RC video recorders that can record HD video and put
out SD composite signal for the video TX at the same time.

Ciao!
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Offline Psi

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Re: HD video link for RC model FPV
« Reply #7 on: May 24, 2013, 10:43:45 am »
How about a Wi-Fi network camera?

Anything involving wifi requires a transceiver in each device instead of a simple transmitter on the plane and receiver on the ground.
It complicates things and takes too long to re-establish a connection.


Another idea for wireless link -  US army went cheapass and used DVB-S for their drones in Iraq.

DVB would be perfect as it's intended for long range high bitrate video transmission and designed to avoid multipath.
However from what i can tell it's so complicated that the gear required is just too heavy.

But those USB modules are interesting. Perhaps coupled with a cutdown smartphone it could work.

if you want HD video just for recording it, I've read
that there are RC video recorders that can record HD video and put
out SD composite signal for the video TX at the same time.

Ultimate goal is to FPV with the oculus rift.
This kind of requires HD because the pixels are so spread out that a SD signal looks awful.
« Last Edit: May 24, 2013, 10:51:37 am by Psi »
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Online Rasz

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Re: HD video link for RC model FPV
« Reply #8 on: May 24, 2013, 11:48:12 am »
Wifi is not that terrible, as long as you have Line of sight you are good up to couple of kilometers without any problems.

btw:
http://bellard.org/dvbt/

http://www.oz9aec.net/index.php/gnu-radio/gnu-radio-blog/361-simple-dvb-with-gstreamer-and-gnu-radio
doable with SDR, but 10 sec latency :o

Now that I think about it US Army might of tolerated high latencies since drones are point and click controlled.

Wifi seems the easiest, cheapest and doable option so far.
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