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Thread: Motherboard on/off

  1. #1
    Low Bitrate Crav4Speed's Avatar
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    Motherboard on/off

    Instead of having seperate switches for the LCD and mobo, is it possible to connect a mobo's on/off jumpers to the on/off button of the LCD? Since there are no ways of having the screens automatically turn on (except by removing the board and jumping the wires) and you are forced to press the LCD on/off button all the time, you could have the LCD and mobo turn on by pressing one button. I'm not an electrical enigineer so maybe you guys can help me out. Thanks

  2. #2
    Raw Wave Defiler's Avatar
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    How bout setting the MB BIOS to boot after power fail and set up a relay for both.
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  3. #3
    Low Bitrate Crav4Speed's Avatar
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    ok, say i did do that... when i shut the car off, will windows shut down gracefully? Plus, I would still have to hit the power button on the LCD unless the relay was momentary.

  4. #4
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    Here's some ideas:

    The on/off on the system board is a simple ground loop (pressing the button feeds ground supplied by one pin to the other pin that usually rests at 5v).
    It is possible that the monitor operates the same way. Just use a meter on it to test. If they work the same way, you could set yours up the same way I have my on/off. And Windows will shutdown (I use hibernate) gracefully.

    You'll need one 5v micro-relay (Radioshack 275-240), one 12v micro-relay (Radioshack 275-241), one 4.7uf cap.

    Acutally, depending on your setup you might not need the 5v relay (I'm not using a Via ITX board, and mine does not support have an auto power-on after power loss).
    The 5v relay is connected to the 5v standby wire from the power supply (supplies 5v to keep the memory on, when using S3 standby). It allows the ignition through when the 5v is active. The 12v relay is triggered by the ignition, and loops ground through to the on/off input of the system board. To create a pulse, put the relay inline with the ground of the relay coil. It will give a pulse when the ignition is on, and a second pulse when the ignition is off (you must use the ignition, or a source that goes 12v when on and ground when off, typically the ignition wire does this).
    So there you have power on when key is on, and graceful shutdown when key is off.

  5. #5
    Low Bitrate Crav4Speed's Avatar
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    Well, I'm really not looking to have and kind of circuit shut windows down on its own. I don't think I would feel comfortable. I would rather be the one to shut it off. The last thing I need is to come out one morning and find my battery dead. So how could I let the mobo and the LCD power on and off just by pressing the LCD button?

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    Quote Originally Posted by Jonjonr6
    To create a pulse, put the relay inline with the ground of the relay coil. It will give a pulse when the ignition is on, and a second pulse when the ignition is off
    You lost me on this part. I would like to do something similar, but I don't understand how you generate the pulse.

  7. #7
    FLAC Pudge's Avatar
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    Quote Originally Posted by Crav4Speed
    So how could I let the mobo and the LCD power on and off just by pressing the LCD button?
    Part of what jonjon said was

    Quote Originally Posted by Jonjonr6
    The on/off on the system board is a simple ground loop (pressing the button feeds ground supplied by one pin to the other pin that usually rests at 5v).
    It is possible that the monitor operates the same way. Just use a meter on it to test. If they work the same way, you could set yours up the same way I have my on/off.
    So if your monitor has the same way of starting (the ground loop jonjon mentioned) you could probably splice the wires from your monitor switch to lead to your computers power switch pins. That way, the switch is sending the same signal to your monitor as your computer. This is IF they have the same method or starting.

  8. #8
    Variable Bitrate telekineticfool's Avatar
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    Quote Originally Posted by Crav4Speed
    Since there are no ways of having the screens automatically turn on (except by removing the board and jumping the wires) and you are forced to press the LCD on/off button all the time
    I have my screen set to always on...aparently this won't work for you. But if it will, you could feed 12V power to the screen from your power supply through one of the molex connectors. Then it would turn on and off with the computer.
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  9. #9
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    Sigma,
    To make a relay do a pulse, you use a typical electrolytic cap. In this case, you connect the trigger input (12v from ignition) to the one of the relay coil inputs. On the other side of the coil, you series the capacitor (if the caps is a poplarize cap, be sure to connect the positive side to the relay) and ground the negative side of the cap. Usually, people will also tell you to put a resistor in parallel witht he cap, to bleed off the stored power, but int his case, we need it to store the power so it will re-trip the relay when the ignition goes to ground.

    ign ===== + relay - === + cap - ======ground

    Not much of a diagram, but I think it helps if you look at the === as being wire, and the + and - is the polarity of the input on the device the wire is going to.

    The large the cap, the longer the pulse. 4.7uf should work fine. I've tried a 4700uf, and the pulse is longer, but still very short.

  10. #10
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    Crav4Speed,
    you could install a dual-battery isolator and a second battery for your computer. This way, the second battery will only get drained and you can still start your car. The isolator is about $30 and a small motorcycle battery is about $40.

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