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I'm assembling a new computer from components. It's something I've done quite a few times, but now I would like to skip the case. Except for some structural integrity and LEDs, the only technical necessity the case supplies is the power button that tells the motherboard to start.

I know I can buy generic power switches, but I have no idea which, exactly, to get, and how they should be interfaced with the motherboard. Can anyone help out?

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The requirements for the switch are not severe. The switch will be pulling down a current-limited 5V signal. It should be normally-open and momentary (non-latching).

The motherboard manual will have diagrams of the pin headers; two of those pins will be for the power switch (one side for the signal, the other for signal return / ground).

A reset switch is always a good idea too - the same sort of switch will do (momentary, normally-open).

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Okay you can use any push button to power the board, yes. I used a screwdriver more than once while testing a board just to short the pins.

But the hacker solution is to use a capacitor (some µF). For electrolytic type: Minus (-) goes to GND (ground). This will switch on the board once the ATX power supply is connected to mains.

Modern BIOSes should have that functionality too (full on on power connect).

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  • \$\begingroup\$ Won't the switch stay high if you use a capacitor? And won't it interpret that as a command to force off? Or does it need to see a falling edge before it will register the switch held down? \$\endgroup\$ – AngryEE May 5 '11 at 1:14
  • \$\begingroup\$ The high state of the signaling pin just means "switch open" and does nothing. \$\endgroup\$ – Turbo J May 5 '11 at 7:46
  • \$\begingroup\$ Ah, opposite of what I thought. That's pretty cool then. \$\endgroup\$ – AngryEE May 5 '11 at 11:27
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    \$\begingroup\$ Even with a capacitor, you still need a switch, to turn off in case of a complete halt. Also, some Intel motherboards need a long press to turn on in certain situations. \$\endgroup\$ – Lior Bilia Jan 4 '15 at 17:11
  • \$\begingroup\$ To turn off completely you can always just disconnect the power plug... \$\endgroup\$ – Turbo J Jan 4 '15 at 17:14

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