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Thread: M2-ATX ACC line instead of IGN?

  1. #11
    FLAC
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    well, im sure theyre all different... my xv791 has one, but even still it has door lock buttons and trunk buttons that arent even being used, and i figure one of those would work just fine too.

  2. #12
    Newbie
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    Apr 2010
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    Going from ACC to Ignition (Blue Screen Crash) M2-ATX

    El Camino hit on the key to my dilema, his explanation is the closest I can find to describing my problem.

    I have a M2-ATX white wire sensing line tapped into the ACC line in my stereo harness. Everything went well during tests while the key was in "ACC" mode, however I started the car from the "ACC" position to "Ignition" and the pc crashed. I was able to use the recovery console in XP to fix the MBR and CHKDSK, but I don't want to do that again...

    It has to have something to do with the short "disconnect" mentioned by El Camino and the voltage spike.

    Additionally, I don't understand why it didn't go into the 5 second shutdown sequence since it is set in P1 mode (5 second start up and shutdown, the suggested setting).

    Does anybody have any ideas? Suggestions? Wiring changes ro "P" setting changes?

    I could go with the rocker switch method, but I prefer to keep it tied to the key...

    Syrinx, FLW, MO

  3. #13
    Newbie Bmrbch's Avatar
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    Hey, I think I have a solution to your problem. This happened to me wiring my M2-ATX in my jeep. The computer would run fine, but anytime I changed the ACC on my car (starting or shutting down, even ACC to off w/o car running) it would restart or shut down my computer. I tracked it down to what I thought was a significant voltage spike. I've heard replacing a certain capacitor on the M2-ATX board fixes it, but what I did was put a resistor-capacitor pair to "shock absorb" right off the ACC wire and ground -- it works like a charm. Found a schematic online and set the time constant to about a second... which puts a second lag into shutdown and startup, but saves wear and tear... and makes it functional. I bet you could play with the timing and make that shorter

  4. #14
    Newbie
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    I have verly little micro elecrtonics experience and I learn as I go. I know the Capacitor temporarily stores the charge wich "cushions" the spike, but what is the purpose of the resistor?

    I have read many posts that elude to using some configuration of capacitors in the acc line, but I have not found any specific diagram (which I would need since I don't have the knowledge to pick my own parts specifications).

    What did you use?

  5. #15
    Newbie Bmrbch's Avatar
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    I hope this turns out 'cause i'm drunk: My circut is set up so that I have an on, off and acc selection:

  6. #16
    Newbie Bmrbch's Avatar
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  7. #17
    Newbie Bmrbch's Avatar
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  8. #18
    Variable Bitrate
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    Jan 2006
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    I think I'm having a similar problem. Sometimes, I'll have the car PC on but the car off, and then I turn the key to start the car, and the car PC shuts off (like pulling the power cable out) and starts up again. It's almost as if someone presses a reset button.

    I'll try that schematic the next time I get inside the dash. Any ideas about what types of capacitor/resistor to use? What values?

    And I still can't figure out why, when I press my power button to turn off my car PC, it hibernates properly and turns off and then turns on straight away. Any ideas?

  9. #19
    Raw Wave
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    As syrinx wrote, El Camino captured the main issue...
    ACC breaks when cranking (starting) the car.

    Otherwise as power sources they are equivalent.

    The common simple solution is a relay fed from the battery (fused! - for power to the load) whose coil/solenoid (#86) is connected via diodes to ACC and IGN.

    Then there are the usual latching methods, manual on & off & low-volts off that can be added to the above, but I won't repeat that boring verbose stuff.

  10. #20
    Newbie Bmrbch's Avatar
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    Cap and Resistor

    Meem, I put in the resistor capacitor pair from the diagram I posted and it fixed the same problem you speak of. I don't remember the values I used, but for about a 1 second delay (you can easily test shorter ones to see if they work), a 1mF Cap and a 1Kohm resistor should work. As for type, with that setup a 1/4 watt resistor with an electrolitic cap rated to 15v should be fine.

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