short range wireless video

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alba800

Joined: 06 Oct 2003
Posts: 21
Helped: 1

19 Mar 2005 9:10 kd2bd modulator

Hi everybody,
I need to design a short range (4-5 meters) wireless connection from a camera to an 1/2VGA color LCD display. Which is the best way? analog transmission? digital with compression? bluetooth?
thank You for Your suggestions!

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

19 Mar 2005 10:46 wireless video shortrange digital

For this distance you should be OK with normal analog transmission using standard TV channels.
Examples here:
http://www.web-ee.com/Schematics/RF_Modulator/rf_modulator.htm
http://www.qsl.net/kd2bd/modulator.html
http://www.kwantlen.bc.ca/electech/FinalProjects/p2000/av_modulator.pdf

When you say VGA, have this screen also TV mode?
Otherwise, how would you convert standard baseband video to VGA?

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alba800

Joined: 06 Oct 2003
Posts: 21
Helped: 1

19 Mar 2005 11:05 short range wireless video transmission

so far my intention is to use a color TFT display, then I need to interface it with a controller. what about a digital transmission?

regards

IanP

Joined: 05 Oct 2004
Posts: 6490
Helped: 1542
Location: West Coast

20 Mar 2005 10:02 Re: short range wireless video

With digital video transmission you have to be familiar with advanced video compression technologies at the transmitter end and then de-comprassion procedures at the receiver end .. and it is to complicated for applicaton like yours ..

alba800

Joined: 06 Oct 2003
Posts: 21
Helped: 1

21 Mar 2005 13:11 Re: short range wireless video

Thanks for your suggestion, but I still think that a digital transmission could give me more security and flexibility. I can handle FPGAs for compression but I don't know what to choose for the communication.

thanks

ezpcb

Joined: 02 Mar 2005
Posts: 202
Helped: 5

22 Mar 2005 4:53 Re: short range wireless video

alba800 wrote:

TDA8722 works well for analog video transmition. The baud rate needed for digital video transmition is rather high. If cost is not a problem, use 802.11b card and you'll get 11Mbps. To reduce cost, Nodic nrf24e1 is a RF transceiver with built-in 8052 microcontroller and the speed is up to 1Mbps. Cypress' wireless USB solution is also an option for you.

mike

Buriedcode

Joined: 06 May 2004
Posts: 327
Helped: 34
Location: London

25 Mar 2005 2:48 Re: short range wireless video

Just thought I'd add my bit Smile

For comms you 'could' try using those 2.4Ghz AV modules. I've got a pair and its got 6Mhz bandwidth for analogue video, and 40Khz for stereo audio. These things are cheap and easy to setup. Considering the vast bandwidth of the compsoite video channel of these things, passing data through it shouldn't be a problem. It's design for NTSC/PAL 1v p-p, 75 ohm impedence, and if you're using an FPGA for something else, you could add pulse shaping to the baseband digital stream, so you might be able to get about 8MB/s out of it (at short range at least).

But these modules are designed for FM modulation, so you can't 'I/Q' the scenario, but you can have 4FSK (having 4 levels in the baseband), double your datarate at the expense of more 'noise' in the digital stream. It may seem messy, but your FPGA will probably have enough room for 'conditioning' the digital stream to be sent across an analogue channel. With compression, the bandwidth shouldn't be too big, so you might be able to get away with simply plugging your output baseband into the Tx module after reducing its amplitude to 1v p-p. Also DC balancing is an issue.

The Rx is just as simple, the reverse proccess (maybe with a dynamic 'data-slicer')

Probably doesn't help, but its a nice cheap way of doing things, you don't have to build any radio circuits. Smile

If money is no issue, just go with 802.11x.

Regards

BuriedCode.

alba800

Joined: 06 Oct 2003
Posts: 21
Helped: 1

25 Mar 2005 16:33 Re: short range wireless video

You mean that I could generate 4 analog levels to be sent to the TX module, then get them from the receiver module, convert these signals into digital symbols (ADC, comparator) and use them? Nice idea, especially if those AV modules are cheap.
Thanks a lot
Alberto

Buriedcode

Joined: 06 May 2004
Posts: 327
Helped: 34
Location: London

25 Mar 2005 20:00 Re: short range wireless video

Thats it! I'm not sure how many levels you can use before the system starts adding errors, but I think 4 would be a good start, and for a 'DAC' a simple 'R2R' ladder would do the trick - Again, simple and cheap! The ADC at the receiver would probably be harder, and the more resolution the more room for error you'll have. This setup should push most of the complexity into the FPGA, which can be a good thing, or a bad thing, however, there is plenty of info on the net, since 802.11 uses a similar sort of thing, although, with QPSK.

To be honest, I haven't got mine working yet, since they require 0.05" pitch connectors which are tiny and very hard to aquire here in the UK, but thats my fault for buying the ultra small modules that run on 5v and low current.

Most of the modules are probably about $30US (£20UK right here) for a Tx/Rx pair. And nearly all have an antenna connector 'built-in' and a nice convenient 0.1" standard header for power and singals. Most seem to run off 12V. Also they have a built in microcontroller, so channel selection will simple need a 4-way switch. The 2.4Ghz spectrum is crowded, and because these are analogue, no interference-protection is provided (DSSS, FHSS). So, I imagine they're not that great for analogue video, where noise in the channel would directly effect the video, digital should be far more robust.

Sorry to keep going on, but I'm gonna use these for digtal audio, because the S/PDIF signal is very similar to composite video (1v p-p 75 ohm etc...) so if you want to find a 'simple' interface, search google for 'ttl to S/PDIF" (or visa-vesa). These require a couple of inverter gates and a couple of passives, and according to some operate up to 6MB/s (note this is 2 signal levels and no pulse shaping, and is not 'true bit-rate', but the symbol rate, due to over-heads in your packets).

With this setup it should give you an idea of what speed it can operate at, and if you buy them and decide not to use them for this, you will have a simple wireless A/V system to watch DVDs elsewhere in your house Smile

I'm don't know where you live, so I can't comment on availability/restrictions. heres a good place to strat though:

http://www.lprs.co.uk/main/search.products.php?category=video

Hope this helps, google will have loads of matches for "2.4Ghz A/V module"

BuriedCode