[MayeulC]

interesting, one could probably power it from the motherboard itself pretty easily, too!

One of the pins of the power switch is probably 5V (though possibly high impedance if a pull-up is used, so not much power).

But I think I'll rather look into one of these Pi-based "ilo" with HDMI in and USB gadget support to get remote access to the BIOS as well. It may also be useful for remotely debugging computers of family members :)

[myself248]

Yes, it is powered from the motherboard. The mobo's WOL header, if present, contains +5VSB, wake, and ground. It's intended to power the NIC since the motherboard's slots aren't powered when the machine is off. (At least, ISA slots weren't, and PCI added standby power in a later revision.)

Or, you can just tap the +5VSB line from the ATX wiring directly. It's the same as on the WOL header. USB-equipped boards tend to power the USB ports from standby too, to support USB wake events, whether from keyboards, modems, or whatever. Plenty of options.

If I were doing it again, yeah, I might use an ESP chip. That would give me power, reset, and serial, and I can always enable a serial console in my OS. I wonder if the ESP32's camera peripheral could read HDMI...