HDD molex conenctor.
Use the yellow wire for +12v. The red is +5v.
I would like to know how you have wired the power cable to your LCD screen? In my case this is Xenarc 10" and Via Epia motherboard. For the past 1 year LCD got +12V from ignition... the same wire I use to connect to white connector on M1/M2-ATX (ignition). In that case every time that I remove the key, LCD went off, and I haven't seen what computer was doing (hibernating...). Now I decided to use standby instead of hibernation. And I wanted to wire +12V from somewhere from my motherboard or powersupply. 1 reason is that it would be more stable souce, 2. reason, I would like that LCD turns off when computer turns off. I tried to wire it to P4 connector from M1/M2-ATX, but unfortunatelly I realized when computer goes to standby, powersupply still has +12V on this P4 connector. I was searching and looking where on the motherboard is a +12V signal that goes off (to 0V) when standyby mode is on?
I tried with this too.. but molex also has +12V and +5V when standby mode is active?! It is strange because HDD turns off, but I checked twice... HDD still has all values (12V, 5V on molex), is it possible that HDD "knows" that it has to turn off from IDE cable?
Do you also know is it possible to turn of powering all USB tools when standby mode is active? And my CPU cooler on my Via Epia is also still on...
The best thing I'd do is wire a Molex connector like DarquePervert said.
For the reason of it being a clean 12V power (does not skip from 11 to 14).
Then, on the yellow (+12V) wire, I'd put a relay and have it turn on and off based on the accessory wire (much like your amp/PSU turns on when you turn the key).
It's a bit more complicated, but you can cut the 5V power to the USB devices in a similar manner.
Ok, but in this case, LCD will turn off when I remove the key. The only advantage of it is that in this case I have stable +12V from CarPC.
About USB - is there any wire on ATX connector that can be cut (by relay) for USB power?
Here's an experimental method you could use:
An USB optical mouse always has its light on when the computer is on.
When the computer goes to standby, the LED turns off.
If you could have a small relay feed off that ~5V (probably between 3 and 5 volts) to turn on/off your major accessories (like the LCD, amps, etc.), then it would work for you.
Ok, I figured it out By default S1 was selected in BIOS and even if I've changed it to S3, standby mode behafe the same. It was because I didn't restarted Windows (hibernation was on). Now everything powers off, except ram and USB. Now I have to use this "relay" to power off USB when standby is active.
It cannot be done on USB integrated on motherboard, but if I use 2 other USB connectors, I have all USB pins avaiable... I can use 2 USB hubs then on those 2 USB ports that is enough for 8 devices and everything will power off.
But I would like to ask you if it is enough if I cut only USB+5V pin and connect it to relay? USB pins are: USB+5V, USB_P-, USB_P+ and GND. Only first pin matters?
you should be able to use a relay on any device that completely turns off in standby mode.
use a multi-meter to test for power on the device chosen, before you start splicig or anything.
to use a relay, you will need to have both a positive and negative for your switch (in the relay)
see bottom of this post for an example
I'm using the usb as an example of this because you mentioned it earlier.
read the documentation coming with the relay to make sure that you hook it up correctly.
also, any 12v source for your relay should work, assuming that (1)there is high enough rated fuse and wiring to power your monitor, and (2) it's always "hot", or getting power, even when your key is removed.
cigarette lighters are usually good examples, however sometimes are switched with the ignition.
if there is no docs that come with it, use a multi-meter to test for conductance, by using the ohm setting. when you get a reading similar to touching the two probes together, you're in business.
that is, assuming you have a SPST relay. if you go to radio shack, they should be able to help you (although, recent personal experiences say the people working there don't know squat about electronic components)
this is the url for a relay that SHOULD work no matter where you decide to tap into on your computer, either 12v or 5v.
it also has a diagram painted on to the relay, helping to ensure proper connection.
I hope that this is helpful.