KarKomp: Car Computer

KarKomp Updates Software Power Control TV out Pictures

ATX Shutdown Controller

This is the Original Schematic that I started with.
I made some changes, so here's my Modified Schematic
I used a second 7805 voltage regulator in place of the 3k and 1k resistor on the Vacc in. This was about the same cost as 2 1watt resistors.
I also added a radioshack 6amp diode to let me plug in with the 12V adapter and get power on without needing a switch.
Here's a copy of the original page I got the ATX shutdown controller from.
I also used a bosch automotive relay with a wiring harness from parts express.

Circuit Behavior:

The first time power is applied at all, it will power on the relay! After that... When power is applied to the Vacc in(car turned on), the relay is closed. (System boots). When power is removed from Vacc in(car turned off), the power switch is pulsed closed. Then after a time, the relay is powered off. I'll leave it to you to play with this to your preferences.

To get the Mini-itx mobo to behave with linux and this setup:

Install ACPI support in the kernel.
Then install acpid from the acpi project at sourceforge.
Add this to an event config file(/etc/acpi/events/power):
event=button power.*
Also, set the bios option to reboot in case of powerloss.
With this motherboard it will only reboot when power is applied if power was cut to the system. If you halt the board(power off) it will not reboot when power is reapplied.
So, modify /etc/rc.d/init.d/halt. (this is for Mandrake 8.2)
Comment out the last line(at the very end of the file):

HALTARGS="-i -d -p"
if [ -f /halt ]; then
HALTARGS="-i -d"
#eval $command $HALTARGS

This way, when the machine is halted, it won't power down the motherboard, but it will still be a clean shutdown. Note that this will make you unable to reboot the system via software!