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I'm looking to build a little pcb that boots my main PC over wifi with a ESP32. Because yes, no wake on lan or other fancy methods available.

Looking through motherboard specs, I couldn't find a maximum amperage supported for front panel pin header. Is there any standard for them?

The board itself will only have the esp32 and a transistor to act as a button. And a push button, of course, to power the thing on manually when required.

1amp should be enough. So my question is.

Could I power the board from the sw_pwr pin without problems?

As far as I understand, that pin is always giving 5v and I would prefer to not fiddle with psu wires, I think the best approach is to just use the sw_pwr header.

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    \$\begingroup\$ What's sw_pwr pin? On which motherboard? Is that pin one of the two pins that connect to power button? \$\endgroup\$
    – Justme
    Jun 19, 2020 at 21:13
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    \$\begingroup\$ @Justme exactly, that pin. I dont have at hand the motherboard model, but I looked at the data sheets at home and it's not specified. Which is weird. \$\endgroup\$
    – David P.
    Jun 19, 2020 at 21:56
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    \$\begingroup\$ That's an input to motherboard that senses the pushbutton, so it is grounded when pushbutton is activated. It can't be used for powering anything. Most likely it's not even pulled up to 5V, on a 20 year old ATX motherboard it's pulled up to standby 3.3V supply that's made from standby 5V. \$\endgroup\$
    – Justme
    Jun 19, 2020 at 22:01

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The sw_pwr is a pushbutton switch input for the power button. Pushbutton grounds that pin when it is pushed, and to sense that it is not pushed it is weakly pulled up to some supply voltage with a resistor that limits the current to few milliamperes. It can't be used to power anything, and it may not a 5V signal either, but whatever the chipset uses as IO voltage.

If you have USB headers with standby 5V available, that could work.

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  • \$\begingroup\$ Oh, that's a bad new. I have measured it and its pulled to 4.98v. But the ma limit is a burden. \$\endgroup\$
    – David P.
    Jun 19, 2020 at 22:21
  • \$\begingroup\$ Going to try the unused usb headers of the front panel! I hope they give current when the motherboard is off \$\endgroup\$
    – David P.
    Jun 19, 2020 at 22:22
  • \$\begingroup\$ OK, so the switch input pin might be pulled up to 5V standby voltage, but do note that the pushbutton shorts it to ground when pushed, so it will be at zero volts. And you might need to set up some jumpers to provide 5V standby supply for USB. \$\endgroup\$
    – Justme
    Jun 19, 2020 at 22:33
  • \$\begingroup\$ My understanding of that pair of pins was wrong start to end lol. I thought it was a simple vin directed to an input pin, not a pin pulled and then grounded. If the usb header make the trick, you have your correct answer! \$\endgroup\$
    – David P.
    Jun 19, 2020 at 23:50

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