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Thread: power on/off for video monitor

  1. #1
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    power on/off for video monitor

    I have a video monitor that I wired directly to the battery, in order to remove some background alternator noise that was causing horizontal lines to scroll up and down the screen. Wiring the monitor directly to the battery (as opposed to the circuit board) worked great and removed all of the electrical noise. My question is: is there such as a thing as a switch that can be put into the power line between the battery and the accessory that will automatically switch of the accessory when the car is turned off (ie. something that will do the same thing as a 12V ACC accessory wire, without tapping into the ignition harness)?
    Thanx for your help!
    - Scott

  2. #2
    Constant Bitrate
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    You can do a relay or a on/off switch.

  3. #3
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    Hmmm. Well, the on/off switch was something that I was trying to avoid. The monitor already has an on/off switch; I was trying to get it to turn itself off automatically. I'm not great with electronics, so I'm not sure what kind of relay that you mean. Can you refer me to a particular part?
    It's doesn't seem to be very uncommon to connect an electric device directly to the car battery, in order to avoid alternator noise, so I've got to admit that I'm a little surprised to be having such difficulty finding a switch of some sort to automatically turn off the device when the ignition is turned off (ie. something that will perform the same function as the 12V ACC accessory wire).

  4. #4
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    You can accomplish that fairly easy with a Relay. The quick version of what you need to do is install a relay in the +12VDC line running to your monitor, and power the relay off the ACC line.

    What a relay is, is nothing more than an electrical switch that is controlled by another electrical source. In this case, the Relay would be normally Open (IE, no power flowing to the monitor) but when you apply power to the proper side of the relay (IE, 12VDC from the ACC line) the Relay will close, thereby providing power the the monitor.

    Likewise, when you shut the car off (ACC off) The relay is denergized and the Circuit opens back up again thereby killing the power to the monitor.

    Relay's are fairly easy to work with. The following link is a great resource "http://www.the12volt.com/relays/relays.asp"

    It should be able to answer your questions. If not, keep posting and someone with be sure to help out

    Also, if you are powering your CarPC with a 12VDC-12VDC regulator you also have the option (which is what I did) to power your monitor off the computer itself.

    One last thing, if you do not wish to tap into the ignition harness for the ACC line, all you have to do is probe the wiring harness for your OEM stereo. One of those wires should be +12VDC only when the ignition is ON/ACC


    Trench

  5. #5
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    Trench -
    Thanks for your reply. As I mentioned before, I not great with electronics But, if the monitor receives power from the ACC line when the relay is closed, I'm thinking I'll probably still have the same original problem with alternator noise (the video monitor gets electrical noise, specifically horizontal lines travelling vertically up the screen, when it's connected to the fuse box and the car is turned on. Since the ACC line is fused, I've assumed the same thing would happen if I wired the monitor off of the ACC). I've tried filters, but they don't seem to work. The only thing that has worked so far is powering directly off the battery.

  6. #6
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    Quote Originally Posted by dipdog View Post
    Trench -
    Thanks for your reply. As I mentioned before, I not great with electronics But, if the monitor receives power from the ACC line when the relay is closed, I'm thinking I'll probably still have the same original problem with alternator noise (the video monitor gets electrical noise, specifically horizontal lines travelling vertically up the screen, when it's connected to the fuse box and the car is turned on. Since the ACC line is fused, I've assumed the same thing would happen if I wired the monitor off of the ACC). I've tried filters, but they don't seem to work. The only thing that has worked so far is powering directly off the battery.
    Have you tried powering it off your computer? If you have a DC-DC regulator, that should filter most flucuations out.

    But, in regards to using the relay. If you wire it up properly, then the power for your monitor is indeed coming straight from the battery. The relay is just switching on/off as per the ACC line

    here is abetter description of how a Relay operates http://home.howstuffworks.com/relay1.htm

    Here is a picture I just drew up that will hopefully help you understand just what is happening.


  7. #7
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    Well, that shows you what I know (not much!) That's exactly what I was looking for. Thanks so much for your help! I'm not sure if I was wording things wrong, but I've been looking/calling around for that answer for a while now, and had a really hard time finding it. I'm looking forward to hooking this up.
    Regarding the CarPC, I wasn't familiar with that term until I looked it up. Looks like there's some nice projects out there. What I'm using though is just an HDD enclosure with media outputs. I bought it on Ebay from China; it accepts a 40gb laptop harddrive that you can load with movies and music. It has audio and video outputs, and plays back the media with firmware included on the chip. It was very cheap and works great. But there's no OS. It came with a cigarette lighter adapter, and I have it powered through the fuse box. I have two video monitors; one is powered off of a cigarette lighter adapter, and it shares a dual socket cigarette lighter adapter with the HDD enclosure (dual socket cigarette lighter adapter connects to the fuse box). The other monitor connects directly to the fuse box (no cigarette lighter adapter), and this seems to be the one creating the noise (ie. if that monitor is unplugged, the other monitor runs fine; when both monitors are plugged in, then both have noise). So, are you saying that if I ran the 2nd monitor (no cigarette lighter adapter) off of either of the other two power adapter lines (with cigarette lighter adapters), than one of the other two lines would filter the noise? If so, that would probably be an even easier fix. Or if I just purchase a cigarette lighter adapter for the 2nd monitor. Do the cigarette lighter adapters usually having filtering built into them?
    Anyhow, thanks again for your help!

  8. #8
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    Quote Originally Posted by dipdog View Post
    Well, that shows you what I know (not much!) That's exactly what I was looking for. Thanks so much for your help! I'm not sure if I was wording things wrong, but I've been looking/calling around for that answer for a while now, and had a really hard time finding it. I'm looking forward to hooking this up.
    Regarding the CarPC, I wasn't familiar with that term until I looked it up. Looks like there's some nice projects out there. What I'm using though is just an HDD enclosure with media outputs. I bought it on Ebay from China; it accepts a 40gb laptop harddrive that you can load with movies and music. It has audio and video outputs, and plays back the media with firmware included on the chip. It was very cheap and works great. But there's no OS. It came with a cigarette lighter adapter, and I have it powered through the fuse box. I have two video monitors; one is powered off of a cigarette lighter adapter, and it shares a dual socket cigarette lighter adapter with the HDD enclosure (dual socket cigarette lighter adapter connects to the fuse box). The other monitor connects directly to the fuse box (no cigarette lighter adapter), and this seems to be the one creating the noise (ie. if that monitor is unplugged, the other monitor runs fine; when both monitors are plugged in, then both have noise). So, are you saying that if I ran the 2nd monitor (no cigarette lighter adapter) off of either of the other two power adapter lines (with cigarette lighter adapters), than one of the other two lines would filter the noise? If so, that would probably be an even easier fix. Or if I just purchase a cigarette lighter adapter for the 2nd monitor. Do the cigarette lighter adapters usually having filtering built into them?
    Anyhow, thanks again for your help!

    What circuit did you tap into in the Fuse box? It sounds as if you may be overloading it with all the accessories you are running through it.

    The best thing to do is power everything straight from the battery (making sure it is fused). That should eliminate your problems.

    Is this what you bought? http://cgi.ebay.com/PORTABLE-CAR-HDD...QQcmdZViewItem

  9. #9
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    close. it's this:

    http://cgi.ebay.com/2-5-Multimedia-H...QQcmdZViewItem

    the one you found looks like something newer. works great. very simple, hard to break. and never have to bother with scratched dvds again. which is a nice thing with 3 kids! my only regret is that it doesn't have a "shuffle" function. otherwise, it's perfect.

  10. #10
    FLAC
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    I only read about 70% of what was posted here, just skimmed through the rest, but you might be in risk of killing your monitor.
    1. Depending on the type of monitor, it likely needs a regulated power source meaning something between the battery and the monitor to prevent power spikes. One good spike on cranking and your monitor is done. This can be done by a DC-DC power supply and a molex connector which it sounds like you may have done initially. You say you had it wired to the circuit board, I can only assume you mean the power supply.
    2. The lines or noise in your monitor picture are likely due to bad grounds or interference from other wires being too close to your video cables. I would have addressed these possibilities first.
    Ampie Case
    2.5" Hard Drive 80GB Samsung 5400RPM
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    M2-ATX-HV

    2005 Honda Civic

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