composit video signal aplifier

Discussion in 'The Projects Forum' started by ladybreaker, Jul 29, 2010.

  1. ladybreaker

    Thread Starter New Member

    Jul 29, 2010
    2
    0
    Hi every one,
    I have been searching a forum to assist me on one of my project for month, and hope someone can help

    I have installed a backup camera on my car (non factory) and it is connected to the navigation screen in which it shows the rear of the car when I reverse and of course the picture is in full color.
    Then I decided to insert between the camera and the monitor a control unit which shows overlayed graphic lines to assist for parking. But once the uint is incerted , the image on the monitor is in black and white !
    Now I have managed to borrow an original Backup camera specific for the car and if connected in place of my after market camera I do get a color image.

    I measured the video signal of the after market camera an it is around 1.2Volt.

    But the video signal of the car specific camera is around 2.2Volt.

    So I have reason to belive that the signal of the first camera is weak to reach the monitor to have full color, therefore ,will i get good result if I use the AD828 or better.

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yep, sounds like you need an amplifier.

    The AD828 could work out quite well, if you're careful with your board design and take care of voltage transients. Note that with automotive electrical systems, you can get spikes of up to 60v; you need to plan for those.

    You might use one of the amps for video, and the other to establish a "virtual ground", since you won't have a dual supply available.
     
  3. ladybreaker

    Thread Starter New Member

    Jul 29, 2010
    2
    0
    Thank you for replying and giving your opinion.
    I had in mind to use the tipical circuit as per data sheets of AD828 and maybe you can advise me of any changes for improuvements on the attached diagram.

    With regards to the power supply I will be using the 5V regulated supply from the control unit used to supply the camera.

    Thanks
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you are planning on using a single 5v supply, you will need to AC couple the input and output, and will need to use the 2nd amp to provide a virtual ground. Otherwise, you will not get any output at all.

    Here's an example schematic:

    [​IMG]

    [eta]
    Ignore the pin numbers for the AD811; it's a single amplifier, and the AD828 is a dual amp. I just didn't have the AD828 already in a library.

    C3 and C5 allow the inputs and outputs to be AC coupled instead of DC coupled.

    R2 and R3 provide a "virtual ground" reference for the 2nd video amplifier, which is connected as a voltage follower. It would be a good idea to add a cap from the junction of R2 and R3 to ground, to keep things quiet.

    R6 keeps the input biased at Vcc/2 (2.5v), while not significantly loading the input signal.

    X1 and X2 are your video jacks.

    C1 is the main cap. C2 goes directly across your video amplifier's +V/-V pins. If you wish, you could use two caps instead; one from +V to the virtual ground, and one from -V to the virtual ground.

    Keep your board as small as possible.
     
    Last edited: Jul 29, 2010
    ladybreaker likes this.
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