Monday, August 31, 2009

Trials and tribulations with my M2-ATX

For the most part it was fairly easy to assemble my first car pc.  I've got about 15 years of experience with building pc's, from my first IBM XT in the late 80's right up to my latest dual core Intel gaming pc.  The only relative unknown in this car pc is the automotive power supply (M2-ATX).

The power supply for a car pc is a little bit different than a standard ATX AC/DC power supply in a home computer.  Since your car's electrical system is 12V DC, there is no need to convert from AC obviously.  So the M2-ATX is a DC power supply that takes the 12V from your car and feeds it to your computer.  All of this is straight forward.  The "unknown" part to me was the additional shutdown logic in the M2-ATX.

One of the obsticles  in running a pc in your car is that there is some amount of time needed for a proper windows shutdown.  In your home, when you turn off your computer, typically you don't just pull the plug.  Usually you either shutdown through Windows, or your power button on your computer is configured to send the proper shutdown signal to your computer so that Windows can shutdown elegently.

This is no different in a car pc.  When you turn off your ignition, the M2-ATX has some logic that allows for your computer to shut down cleanly.  This logic is configurable via some jumper settings on the power supply.  Basically you can set your power supply to send the shutdown signal, then wait for a configurable amount of time before cutting the power to your computer, so as not to drain your car battery.

Now, when I first connected the M2-ATX to my motherboard, I connected the J8 on the power supply to the power switch pin header on my motherboard.  This allows the M2-ATX to power the computer on and off.  Then I connected my case switch to J9 on the M2-ATX.  This is to allow me to turn the computer on and off with the case power switch as an option instead of the cars ignition.

In the manual for the M2-ATX it states that you should not jumper any of the J10 pins if you want to use the psu in standard mode.   So I hooked it up this way since I wasn't planning on using the pc in the car just yet.  What I found was that the power supply would not turn on.  There are three posts on the power supply for prividing a power input.  POS, IGN, and NEG.  Where IGN is for switched power (ignition).  I had initially misunderstood the manual for the M2-ATX.  In order to use the M2-atx in standard psu mode, you should only connect the POS and NEG terminals, since you won't be using the timing logic.  Alternativly, you could jumper J10a which is the recommended mode and connected POS,IGN and NEG.  By doing this, your case power switch emulates your cars ignition.  Once Chris over at www.mo-co-so.com straightened me out on this, everything powered on and came to life!

One thing to note about the J8 and J9 pins on the M2-ATX.  Some question was raised about polarity.  It seems the consensus is that there is no polarity on these jumpers.  Here is a photo of how my J8&J9 are connected and it is working fine.  J8 is on the left, J9 on the right.










Here are a few more pictures of my setup so far.  I'm hoping the hi-res photos will be helpful for others at this stage.

36 comments:

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