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Video ADC

Discussion in 'Electronic Design' started by h200, Dec 14, 2012.

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  1. h200

    h200 Guest

  2. h200

    h200 Guest

    ---------------
    You are correct, PAL is mostly used and I will take this as base.
    I was thinking to take any analog camera, maybe some cctv camera,
    connect the BNC output of this camera to my portable device and transfer
    the data over rf. Maximum distance is around 20 meters.

    Camera --> video ADC ---> RF transfer ---> video DAC ----> monitor/ TV.

    I can not use USB because this should be some kind of camera adapter an
    it has to be portable.

    TW9900 looks like very good solution.
    What do you think, can i use it in my project ?
     
  3. h200

    h200 Guest

     
  4. h200

    h200 Guest

    ------------------------------------------------------------------------
    OK. I will use TW900 as ADC.
    How would you construct the DAC part ?

    I didn't calculated the data rates but i was planning to do this after
    i'v done the ADC / DAC part. You see, the transmit part should be fully
    adaptable to all kind of transfer options.
     
  5. whit3rd

    whit3rd Guest

    The PAL composite format is intended to be simple to transmit/receive
    over RF carriers. So, why convert it to something digital, which is NOT
    simple to transmit/receive? Put your PAL decoding at the
    endpoint, not the origin, of the RF transmission.

    Digital transmission over RF is very noise-sensitive, and the kind of
    error-correction that digital TV does nowadays is beyond the
    scope of most 'project' work.
     
  6. h200

    h200 Guest

     
  7. Guest

    Simple modulation systems are actually multipath sensitive, even if
    the average field strength is quite high.

    For this reason DMT/COFDM systems are typically used.

    For a point-to-point link with direct line of sight (LOS) path, the
    laser is a good solution and it might be enough to amplitude modulate
    the laser with the baseband signal. However, this requires that the
    transmitting laser is aimed _exactly_ towards the receiver, thus. any
    portable/mobile applications are more or less out of the question.
     
  8. Nico Coesel

    Nico Coesel Guest

    I'd convert the video to streaming MPEG so you can transport it
    anywhere you want. Wireless? No problem, just setup a Wifi bridge.
     
  9. h200

    h200 Guest

    ---------------
    I was thinking about streaming MPEG but i dont know if this could be the
    solution. Maybe it cauld be because this is standard for something like
    this.

    I dont want to use WIFI. There are bunch of problems regarding this kind
    of transfer. I'm in cctv security line of work and trust me,
    wifi is not something that you want to use. Of course there are some
    quality solutions but they cost like hell.

    Back to the subject :)

    What kind of video ADC and video DAC would you use to make the encoding
    / decoding ?

    TW9900 is for me still the best solution for video ADC but i dont know
    how to decode this digitalized signal.
     
  10. Guest

    While in an uncompressed format, loosing a few pixels, perhaps some
    lines or even a whole frame is no big deal, since the next frame will
    contain valid data, hiding any transmission errors.

    However, in any delta-modulated systems (such as JPEG) loosing some
    pixels will propagate along the line. In MPEG, any bit errors in the
    I-frame will propagate through the P and B frames (typically 0.5 s).

    Thus, in an uncompressed (analog/digital) video stream some random
    errors are acceptable, however, if you are going to use some
    compressed format, a 100 % reliable transmission path is required
    (such as TCP), but of course, the latencies can be anything.
     
  11. Ralph Barone

    Ralph Barone Guest

    One Hz of bandwidth is not required to transmit 1 bps of information. It
    all depends on your SNR.
     
  12. Nico Coesel

    Nico Coesel Guest

    I doubt some self made solution is going to cut it if you want low
    cost. Developments costs can rise quickly. If cost is an issue I'd go
    for commercially available network camera's with Wifi like the ones
    from Axis. Proprietary wireless connections are prone to jamming
    without people knowing it. If someone jams the wifi frequencies it
    will get noticed.

    Come to think of it. AFAIK one of my customers sells a high resolution
    (several Mpixels) wifi or wired security camera which records video
    and audio locally if the connection is not available. They also have a
    central storage facility where people can access the recordings
    through internet. Its a pretty neat package and relatively low cost.
    Like others pointed out: if you don't know about the wireless link
    then it is no use to look into coding/decoding. Besides that PAL
    signals are already intended to be transferred over wired and wireless
    connections. I'd concentrate on transferring PAL over wirelles or
    wired connections. This is old and well known technology.
     
  13. h200

    h200 Guest

    ----------------
    Let's forget about the transfer... for now.

    How would you make the encoding / decoding part.
    From my pov TW9900 would be the best solution but how to make decoding.
    Do you now some HW solutions that use MPEG as base for ADC ?
     
  14. Nico Coesel

    Nico Coesel Guest

    Thats not entirely true. H264/MPEG based transmission systems like the
    ones used for DVB-T allow some errors without distorting the entire
    frame.
     
  15. Nico Coesel

    Nico Coesel Guest

    You can connect the output of the TW9900 to a SoC (chip with ARM cpu
    and peripherals) and use that to encode the video stream into MPEG for
    transfer over a network or decode/scale it for displaying on a screen
    (direct LCD panel connection, RGB analog, VGA, composite or HDMI).
    Most SoCs have hardware accellerators to do this. You don't need a
    state of the art SoC to do this. It will require some software
    (Linux).
     
  16. Guest

    For JPEG with 8x8 DCT block, a corrupted low order coefficient will
    corrupt the whole 8x8 block, with clear visual impact. A corrupted
    high order coefficient will have much less visual impact, since the
    error will appear as high frequency low amplitude noise across the 8x8
    block.
     
  17. josephkk

    josephkk Guest

    Have a link to a data sheet?

    ?-)
     
  18. josephkk

    josephkk Guest

    You can do that analog as well. OK, they were fiber optic. Want some old
    model numbers?

    ?-)
     
  19. josephkk

    josephkk Guest

    That will work, but for more free space applications i would put an FM
    modulated carrier to the laser. Several advantages. For that matter,
    even for FO connections.

    ?-)
     
  20. josephkk

    josephkk Guest

    There isn't much "decode" at that point; is nearly raw digitized SMPTE-170
    at that point, shove it to an appropriate video DAC and it is analog
    again. Well there are some caveats here, but if you understand the tech
    it is nearly this simple.

    MPEG-2 and MPEG-4 and h.264 IP cameras are readily available from a bunch
    of vendors, why deal with the compression in your own hardware except as a
    learning exercise?

    ?-)
     
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