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Thread: I have a weird wiring situation. Please read...

  1. #1
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    I have a weird wiring situation. Please read...

    I have an Audi A4 and I'm trying to figure out the best way to wire my LCD screen. First of all let me explain how the Audi handles the power to the stock HU. When the power is on the HU works (obviously), but when I turn off the ignition the HU powers off (this is obviously normal as well). After the car is turned off, however, I can push the power button on the HU and it turns on and my amps power up as well.

    Here is my question. I want to wire the LCD the same way. So when I push the on button on the screen (when the ignition is off) the screen works and also turns on my amps and sends the acc line to the shutdown controller for the computer. I'm not sure how to do this? It seems the HU has an ACC line and an always on 12v line. My amps remote wires are also hooked up to the HU.

    Can this be done?

  2. #2
    Raw Wave Rob Withey's Avatar
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    The headunit in my Corsa behaves in exactly the same way. I have it wired so that my PC comes on with my headunit. To do this I take the enable pin of the amplifier chip in the headunit and use it to switch on the pc. The chances are that there is a similar line inside your headunit, all you have to do is find it.

    Rob
    Old Systems retired due to new car
    New system at design/prototype stage on BeagleBoard.

  3. #3
    Maximum Bitrate BoraXP's Avatar
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    Quote Originally Posted by audrenaline
    I have an Audi A4 and I'm trying to figure out the best way to wire my LCD screen. First of all let me explain how the Audi handles the power to the stock HU. When the power is on the HU works (obviously), but when I turn off the ignition the HU powers off (this is obviously normal as well). After the car is turned off, however, I can push the power button on the HU and it turns on and my amps power up as well.

    Here is my question. I want to wire the LCD the same way. So when I push the on button on the screen (when the ignition is off) the screen works and also turns on my amps and sends the acc line to the shutdown controller for the computer. I'm not sure how to do this? It seems the HU has an ACC line and an always on 12v line. My amps remote wires are also hooked up to the HU.

    Can this be done?
    i have a jetta and it does the same thing,
    the being able to power on is just overriding the trigger wire.

    i did mine with a relay
    works well

    to find out wich pin is ignition, get a voltometer and test all the wires when the car is off, all the thinner ones, then go back when the car is on, if you find the one that is hot when on and cold when off then youve found the trigger, im pretty sure mine was on the opposite corner as ground and power

    cheers

  4. #4
    Maximum Bitrate none's Avatar
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    This is why I've avoided getting rid of my stock HU, but I think you want to go without a HU, right? What we need to do is find a 12v line inside the LCD that is only hot when the unit is on and tap into that for the trigger line. Will probably be harder than it sounds, actually, but I can do it It won't turn off automatically when you turn off the car, however, you will have to power it down. To keep that functionality, and still be able to use the system when the car is off, you would have to keep the stock HU.

    Next weekend should be good for me.

  5. #5
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    I'll plan on next weekend then. I've done most of the wiring and I have a spot for the computer. All we need to do is hook it all up.

    Is it possible we could just use a relay like the person above did? I'm not totally sure on how relays work and how they are hooked up.

    Quote Originally Posted by none
    This is why I've avoided getting rid of my stock HU, but I think you want to go without a HU, right? What we need to do is find a 12v line inside the LCD that is only hot when the unit is on and tap into that for the trigger line. Will probably be harder than it sounds, actually, but I can do it It won't turn off automatically when you turn off the car, however, you will have to power it down. To keep that functionality, and still be able to use the system when the car is off, you would have to keep the stock HU.

    Next weekend should be good for me.

  6. #6
    Maximum Bitrate none's Avatar
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    Quote Originally Posted by audrenaline
    Is it possible we could just use a relay like the person above did?
    We probably could, but from his description I'm not sure exactly what he did or what it accomplished.

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