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ebay CCTV camera has "magic" auto iris and backlight switch

Discussion in 'Hobby Electronics' started by rowan194, Nov 26, 2007.

  1. rowan194

    rowan194 Guest

    Just had a colour CCTV camera delivered, I opened it up to see if it
    was just a standard module board that I could squeeze into a smaller
    case... to my surprise, I found the auto-iris connector only has V+
    and ground wired (no video or drive - is the lens supposed to guess
    how bright it is?) and the backlight compensation switch is mounted
    but it has NO wiring at all!

    The manual is a real hoot too, it's even worse than the usual chinese
    english (probably auto-translated)

    Video quality seems decent enough.

    I guess you get what you pay for. :)
     
  2. rowan194

    rowan194 Guest

    It gets better: when I pulled the supplied switching plugpack out of
    the socket the front broke off, exposing its internals and breaking
    off one of the mains wires. That's not quite so funny.......
     
  3. That's what I was going to ask, do the v+ and ground wires actually go
    anywhere? I guessed not...
    Some time back, our secretary at work said the solar thingy on her
    big-buttoned calculator wasn't working.
    After a few more probing looks, it appeared the calculator is just plain
    dead. I said the solar thingys aren't even connected, they're just slabs of
    plastic purely for looks.
    A subsequent disassembly and reconnect of the built-in battery fixed it.
    For what you paid? I've worked with cameras they actually _do_ use in CCTV
    applications, and there's a reason they cost what they do. Aside from an
    actual working iris, they give a better image too.
    You've got that right. :)
     
  4. rowan194

    rowan194 Guest

    No, an attached auto-iris lens *will* be powered, but it won't do much
    else without a signal output. :)

    Couldn't pin 3 (video) have just been wired in parallel to the
    composite output, or does it need buffering?
    I'm using it for some basic home security so it doesn't need to be a
    super good image. Size is also important which is why I was pleased to
    see there was a small module inside.

    I made up a simple page with a couple of pics of this...

    http://www.gadgetguts.com/cheap-cctv-camera/
     
  5. Then why would the Chinese spend money on iris functionality, a motor, and
    associated control circuitry, if it's not being used? Seems to me, they'd be
    by far more likely to have some "wire" connecting the two to make it *look*
    "right" rather than function.
    Like my solar calculator example, it's deception. You have only the price
    to go by.
    No, you just need the raw video output, pre-processed by the auto "software"
    level. Feed that to the iris (along with power of course), and the negative
    feedback (within the iris) takes care of the rest.
    Three wires. Gnd, +v, and video. Never seen any other implementation,
    though I haven't worked with a HUGE amount of cameras, just lots.
    I'm going to guess that's a CMOS camera rather than CCD, and I'll also
    hazzard a guess that the plugpack is NOT C-Ticked? :)
    There are other options where you can get just the CMOS video image element,
    (your choice of lenses too!) with a small board on the back (much like yours,
    but smaller). You have to supply power yourself, but comes with (short) cables.
    You can retro fit these into the "dome" covers, or even buy domes with
    cameras in them (at a higher cost). Would end up smaller and neater than that
    chunky box.
    For what you're getting, I really don't think it's the best value for money
    out there.

    (after looking at the AC adaptor) Yeah, that did it, now I'm scared.
     
  6. rowan194

    rowan194 Guest

    Right, so the module needs to support it. That probably explains why
    the backlight compensation switch isn't wired. I'd guess the auto-iris
    lens is still fed power to keep it in a consistent (either wide open
    or stopped down as far as possible) state.

    Here's the ebay listing, I don't know whether the seller is aware of
    this little "issue."

    http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=150184644969
     
  7. No, I can't see why. The backlight compensation does exactly what you think
    it does, it manually forces the iris (either the external auto-iris, or the
    internal gain) brighter to cater for the dim (relevant) parts of the image.
    Problem is, this is rarely something that can be handled by an on/off
    switch, you really don't know how far the brightness needs to be shifted to
    get a decent image in the non-bright area between one installation and the next.
    Regardless of this, real-life installers position the cameras in FRONT of
    light sources, so you don't get this problem in the first place.
    In other words, this backlight compensation function is mostly pointless
    even if it did work.

    And largely irrelevant to whether or not the external lens has a functional
    iris or not anyway.
    No, default (no power) is wide open.
    Aware? Who knows. Care? Definitely not.
     
  8. Guest

    I guess the seller saw this thread because he offered a replacement
    plugpack, or a $US2 (!) refund.
     
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