Thread: mobo does not support resume on power loss

Thats what I found on the net...

The push button sends a 5-volt signal to the power supply to tell it when to turn on. The power supply also has a circuit that supplies 5 volts, called VSB for "standby voltage" even when it is officially "off", so that the button will work.

So does it mean the pins where the power button is connected, has 5volts across and the power button either shorts it when pressed or its already shorted and the power button opens the ckt when pressed? My understanding may be flawed, I don't know. I tried to measure resistance of the power button(thinking its simple switch), but I got infinite resistance in both states. I'll check the voltage across the switch and resistance tomorrow.

I hope somebody here knows how this stuff works.

ATX motherboards, as long as their power supply is powered, and attached to the motherboard (and the switch on the power supply is in the "ON" position), indeed are powered. Most of them have some sort of LED on them to indicated that they have power, and some also indicate that they are in standby mode.

The power switches for ATX's are just momentary close, normally open switches. All it does is short the pins, which signals the power supply to turn on. To tun it off, the motherboard sends another signal to the power supply that indicates "turn off now!!" , or you can hold down the same power button for a few seconds, and it will also turn off.


I haven't researched this much, but you might look in the section called "power supplies," they probably talk about good ways for turning them on and off automatically.

If you just want something simple, you could have a relay from your on or accessory switch, and when energized, it will start a timer to close the power button circuit for a short time (half a second), and then open the circuit right after. And of course, when you turn the car off, cut the power to the computer...unless you're running windows or something, in which case you would need to find some shut down controller (again, search in the power supply section) to safely shut down the machine.

Hopefully this will help some.

Thanks Nic,

I did check the voltages and all and found out the functionality of the power switch the hard way. I'll probably mount the power switch somewhere in the dash. But as you said if I could use the relay, that'll be super. I'm still searching. But if you have any info on it pls let me know.