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Thread: Video Noise Issues / Camera Switching Problem

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    Video Noise Issues / Camera Switching Problem

    OK so I have a few problems with my CARPC after completing my install. First off I have a laptop as my PC along with a rear view camera in the trunk keyhole. Using a Liliput 7" LCD Touch screen as a display. It has a green reverse camera switching wire. The wire is connected to my reverse light signal wire. Problem is if I press the brake the screen wants to switch to VIDEO2 as if it quickly has a flash of voltage on the line. When this happens the screen goes black and then PC appears and my VGA comes back in view. The camera is switching fine in reverse but with the brake pedel its as if its getting a quick low voltage signal for a quick flash. Anything I can do to clean the line to only trigger on a full 12v?


    These are other people having the same problem as I am. links below.
    http://www.mp3car.com/lcd-display/14...n-braking.html
    http://www.mp3car.com/lcd-display/13...f-then-on.html

    My other problems are with the video noise on my screen. The Rearview camera appears clean signal with the car not running. With the car running I have lots of noise on the rearview camera picture. The video RCA is run right near my power cables for the vehicle. I know this could be a problem but i've grounded the RCA with a jumper to test it and the noise still remains. Should I reroute the cable if I can? any other solutions for this? is it common?

    My VGA has video noise with the car off but very slight, when the car is running it becomes worse.
    I've traced it to my laptop cigarette lighter adapter. With it unplugged the display is crystal clear. How could i clean the laptop charger signal safely?

    I hope to hear from you so i can finish off my project! Pics will follow in the show off forum.

    Thanks guys!
    Last edited by DodgeCharger; 07-07-2011 at 07:10 PM.

  2. #2
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    1. reverse camera issue:

    the easiest solutions are these:

    1a. a relay-- this would prevent small voltages from tripping the relay, which would prevent the screen from switching. shifting between gears could still cause it to switch though-- as you usually need to cycle past reverse to get to drive(if you drive a stick, then ignore this)..

    1b. a delay, like the 528t pulse timer might be the best option-- assuming that it is only a small voltage that passes through the reverse wire(small enough to not trigger a relay). setting the timer for about a 1 second delay would prevent gearshifts from triggering the switch, while still working correctly when you stay in reverse. this would add 1second to the amount of time it would take to see the reverse image though..



    noise issues:

    those are are symptoms of a ground loop, or dirty power.

    1. you said that your using the cigarette lighter adapter for power. these are notorious for having poor grounds and bad power, and is the exact reason why so many here recommend running a new dedicated power and ground wire. so this would be the first, and best step to removing your noise issues.

    2. you never mentioned how/where the camera is gettting power from, or where it is grounded. having the camera grounded somewhere else, or getting power from a separate wire then the carpc/screen can also cause noise issues.

    3. you also never mentioned how the screen is powered-- same as the camera, getting power/ground from other wiring can cause noise.

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    Soundman!!

    Thanks. I'll take a measurement of the reverse wire but I am sure its a low voltage triggering and yes your a right a relay should eliminate that problem. I will test this out with a voltmeter over the weekend. I will also test my rearview camera and laptop charger directly off the battery to see if it reduces or eliminates the noise! I will report back with my findings! Getting excited now as it seems these are common problems and should be easy fixes. Thanks again! talk to you soon.

    Edit: Added reputation.

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    Tested my camera directly from the battery. My camera was connected to the cigarette lighter wire in the back of the car. Put it directly to the battery and noise will still exactly as before. The camera is grounded to the frame using a factory ground point in the trunk. My screen is still powered direct from cig lighter socket up front. The VGA is showing clean when running off battery and the camera is always full of noise. My next step is to go directly to battery for the screen? Or will I have to re route my cables away from the power harness?

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    have you tried the screen and camera directly off the battery together? or powered from the same location? it sounds like you were still powering the 2 at different locations.

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    Soundman, I really appreciate the quick replys. I will try all 3 (camera, screen, laptop) directly on the battery and I will see the results. I've been reading and saw that the lilliput screen has an egg (regulator) on the DC power cable and that it's a poor design. And that sometimes the screen can ground out through the VGA cable. Lets hope directly off the battery solves it!

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    Here are my updates Soundman.

    Upon measuring the reverse wire in my car I found that when the brake pedal is pressed at any time the reverse wire picks up 0.4V to 0.63V. Like you said a relay would fix my problem which is true. I understand relays fairly well and made a quick diagram of my plan of action. Would this not work? it would be a lot less wires to add in if I were able to wire it like this. All I really would need to add is the ground wire. I haven't tested the relay yet but im assuming this low voltage will not trigger the relay.



    As to my noise issues. I mocked up a quick setup. Took an old 4 gauge power wire from a stereo system I had, attached it to the battery (factory location in trunk). In trunk I have camera wired directly to battery. I left the laptop disconnected for this test. Powered my screen upfront off of the 4 gauge power wire which runs directly from the battery along the outside of the car to the front seats and powered my screen off it through the cig lighter plug adapter simply by holding wires on to it. Used a ground point at the door which is directly to the frame. While doing this and running the car I had the exact same amount of noise as I had begun with. I did notice that when I removed the ground from the door, meaning the lilliput had a 12v source direct from battery but no ground attached that the sceen was still on! After removing the camera's RCA the screen shutoff immediately after. No where am I to look? camera? lilliput charger? ground the rca and vga cables?

    Hopefully this has happened to someone else here and im not alone

    Thanks again soundman!

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    you may have unhooked the ground from the door but you where still grounded through the shield on the rca from the camera, i'm assumeing was grounded also. have you tried the camera on something else, say a tv perhaps?

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    for now, focus on correcting the noise before correcting the reverse wire issue-- the noise is going to be more difficult, so adding the relay into mess is only going to make it more complex.. but that relay setup should work-- i would typically run a constant +12v to pin 87 instead of using the reverse wire, but that method would require more wire...

    Quote Originally Posted by smarty2 View Post
    you may have unhooked the ground from the door but you where still grounded through the shield on the rca from the camera, i'm assumeing was grounded also. have you tried the camera on something else, say a tv perhaps?
    yup.

    i service security cameras-- i see it a lot on negatively-fused power supplies-- the fuse blows, but the camera grounds through the video cable, and stays on, right until you take the cable off to see what the camera video output looks like...


    this is pretty much how you hooked it up right?:


    all i can think of is that you need to try a different ground point..

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    Yes thats how i wired up for my testing. Sucks that I am having all these problems. One thing after another. I will try other grounds but I don't see it correcting the issue as my grounds are soldered to terminals and connected to factory ground points. Is there no way to stop the screen ground from running through the RCA? Noise filter? I will start reading im sure other members have had this happen. My PC looks clear just faint noise, but im sure if i remove the RCA and get rid of the camera that all of a sudden everything will be grounding through the VGA cable. strange.

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