I am thinking of using the serial port to sense the ACC off and then turn the computer off, something that's used for UPS, as implemented for APC UPS in XP SP2 in power settings. So the scenario would be the power is on, when the key is removed, the signal on the serial port changes (one of the pins, that is), which computer interprets as request for shutdown or hibernation. If the computer gets stuck and does not shut itself off then the additional hardware (relays, capacitors and the like) shuts the power, ie pulls the plug. The advantage of this is that there's a chance for computer to exit graciously before its whacked by pulling the plug. If it is not gracious, then it gets whacked. Maybe then it learns, don't we all learn when whacked?
My question is this: is there a software that would look at the serial port and has the functionality to shut the computer off, or somebody solved it similarly (ie software). APC UPS software communicates with the UPS using modem protocol, so it is not simple to adapt for my purpose.
The software listed in that thread can now be purchased here:
If you're using Windows, there's something in the UPS options that'll let you do it. I did this about 4 years ago but decided not to go with it. Can't remember which pin but you have to run a constant 5V into it so I tapped it into a +5 from the PS and the shutdown sequence begins when you disconnect it from the serial port. Simple and effective but didn't suite my needs.
In XP select 'generic' > 'Custom' UPS. You can then select to have it shutdown on 5v or 0v
Use pin 8 on the comport.
The ultimate CarPC - Wow!
I have the ACC connected directly to pin 8 and generic ups switched on per laidback's post.
When the os is loading the UPS monitor is ignored.
Once the UPS service is started the port is monitored and looks for a drop in voltage. When the ACC drops significantly ( don't know how much ) it will begin the shut down. You can configure it to post a message, good for setup.
Note : starting the engine can drop ACC enough to trigger ups shutdown. An improvement would be to drive a relay with ACC and provide regulated 5 or 12 volts from your PSU.
Ok I hate resurrect dead post but can someone explain to me in a little more detail on how to fool Windows/UPS Service via the vehicle ACC. What I am looking for in specific is where to appl the voltage on the comport and where to apply the gound.