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add video to dc power and then later recover video

Discussion in 'Electronic Design' started by [email protected], Feb 15, 2007.

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  1. Guest

    Hi I'm hoping that someone out there can help me out and point me in
    the right direction.

    I have an application where I have a dc powered video camera. I'd
    like to add the video (composite) to the wire feeding the camera with
    power and then elsewhere in the system recover the video and feed it
    to a monitor.

    Is that possible ?
    How ?
    Is it easy ?
    What do I need to be aware of ?

    Any hint's or tips of what might be OK and what problems/issues to be
    aware would be greatly appreciated.

    Thanks in advance.

  2. Modulate the video and return it on the coax carrying the power. A
    simple filter should be able to seperate the signal from the DC at
    either end. I have a 'Channel 3' modulator used for feeding video into a
    TV set.
  3. Guest

    Hi Paul

    Thanks for the reply.

    I Should have told you a little more.

    The application is on an articulated truck/lorry. I have to use the
    existing wiring of the lorry. There will not be any co-ax - well at
    very small bit at either end.


  4. On 15 Feb 2007 13:24:05 -0800, in
    The other option to Pauls suggestion is to use cat5 cable, and a
    suitable interface, which if you google for CCTV cat5 will probably
    eventually give some almost useful hits
    is typical

  5. Video doesn't travel very well over plain old wires. You could try--
    put a 10mH choke at each end of the DC wire, couple the video to the
    wire in between with a pair of 1uF capacitors.

    You'll get *something* out, but it will be rather smeary, fuzzy, and
    noisy video.

    If you don't need a immediate real-time picture, you could use a
    webcam, and send the data using PPP over the wire, and get pretty good
    data. But I suspect you need the image right away, not three seconds
    later. Hard to back up a truck with a 3-second delay!
  6. Rich Grise

    Rich Grise Guest

    Must be mid-terms.

  7. On 15 Feb 2007 13:45:52 -0800, in
    then get a 2.4GHz video sender, check out campervan accesories for old
    gits who can't reverse properly

  8. Rich Grise

    Rich Grise Guest

    Then give up, or rewire the truck - you'll never get reliable video to go
    through ordinary truck wiring.

    Good Luck!
  9. Guest

    The lorry chassis is a bit of a hotbed of electrical noise as it acts
    like a substantial steel aerial. Also, the chassis loom wiring
    (electrically) looks like a mass of unterminated, high quality, open
    transmission lines/resonators that spend their lives singing gentle
    medium wave tunes to themselves in response to every single transient/
    change on the battery/alternator.
    Sending -clean- 1V video down unshielded wire from say the rear light
    cluster up through the Suzi connector and into the cab for inductively
    splitting off, looks a problem.
    Myself, I'd be looking at a seperate coax feed.
  10. Filter the DC out with an inductor.

    Try it and see if it works. Ideally you want a piece of coax cable.
  11. The problem with adding DC to the raw video is that video is DC coupled.
    The filter at the other end will take out the reference to the black
    level. One could build a circuit to recover it, but that would probably
    be more involved than RF modulation.

    BTW, Martin's idea for a 2.4 GHz wireless link would seem to be the best
    if one cannot modify or add to the truck wiring. 100% off the shelf
  12. It's a monitor - black level is not such a big deal.

  13. Guest

    Thanks for all of your suggestions/thought and comments

  14. One thing you could try is use a 74HC4046, set it to oscillate at about 20MHz,
    or higher if you can, connect the video the the VCO input, this will give you good
    linear FM.
    Add a small inductor on both sides of the supply line, and superimpose the 20MHz.
    On the receiving side use the same chip in PLL mode with the XOR phase
    comparator, and grab the video from the source follower output.
    Watch cable impedance, likely around 100 Ohm.....

    Actually in the olden days (1968) I used 2 x 74121 ones hots, byting their tail,
    with a video modulated current source at about 12 MHz, not the resistor.
    If you use a low frequency making a low pass will become more difficult.

    The FM method keeps DC component, but it will likely be H clamped anyways in the monitor.
    Works great for audio too.
  15. [ very clever idea]

    Well, you'll get a DC component, but it's very likely to wander a bit.
    True. Or you can restore the DC level with a diode and two
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