I have a system in which I have no access to the power button, so I need it to power on automatically.
I have set the 'restore on AC Power Loss' option and it works fine when I turn off the system abruptly but if I shutdown the system properly (start, shutdown...), there is no way to start it up unless I press the power button.
I have some computers for digital signage (aopen DEx4502) that acts just in this way. Is there any way to replicate this behavior in my system?


this depends on the options your computer's bios setup offers... there is usually an option for the behaviour after an ac power loss, the usual options are: "off", "previous state", or "on".

now your system appears to be configured to remain in the previous state, so when it was shut down, it will remain down, if it was running (and went down tue to power loss), it will start back up.

some bioses do not have the "on" option, in that case your are stuck with building some hardware device that triggers the power on signal when power is restored.

(i read, but have not verified, that a simple capacitor over the power button terminals, parallel to the power button will suffice - it will short the button until it's charged, creating an pulse at power on)

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Use Wake on LAN. It must be supported by the system though.

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  • Sorry, I had it in mind and forgot to specify it in the question. The WOL is supported and I could use it some times (not sure about the best way to do it anyway, a scheduled task sending a magic packet every minute,maybe?) but the system could be disconnected from the network in some configurations so unless I could do some loopback or something I would need another method. – Luis Dec 20 '10 at 11:20


For the future readers: This is a tested and working real-world solution for the exact same problem.

I had the same problem so I made the following circuit that waits for a short time, "presses" power button, releases it when computer is turned on: Working circuit

This circuit is tested and working: http://youtu.be/eg2waRuW1ME

It works in the same way of: https://www.youtube.com/watch?v=aqAUmgE3WyM

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  • While you are true for most cases, it's (almost) an internal link, there is no way for this link to vanish. If its content changes, then it would possibly be for good reasons, so the referrers could benefit. Anyway, thanks for the feedback, I edited my answer accordingly. – ceremcem Sep 8 '15 at 21:30

Exactly what behaviour is it that you want?

You need to toggle the power feed off and on for that BIOS Setup option to kick in and start a properly shut down system (how else would it behave?). For this you need remote control of the PDU or power feed, obviously.

Also, you can almost always configure generic PC motherboards to start up with a press of a keyboard key, keyboard password or mouse button in BIOS Setup - apart from WoL and WoR.

An easy way is to use machines which supports a remote hardware management solution. HP has iLO, Dell has DRAC and so on. Some Intel-based desktops and laptops could possibly use vPro and AMT for this as well though don't quote me on that.

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  • Excuse me if I have been unclear. The desired behavior is that the system starts automatically after you toogle the power feed off and on.I achieve this – Luis Dec 20 '10 at 12:55
  • Excuse me if I have been unclear. The desired behavior is that the system starts always automatically after you toogle the power feed on.I achieve this without any problems with the 'restore on AC Power Loss' function if I power feed off abruptly and then on but, if I shutdown the operating system properly, when I toggle the power feed off and on it won't start. I, obviously as you said, turn the power off and on, I wouldn't expect it to wake up magically. If there is no posible solution I'll try something with the WoL or the PS2 Wakeup but I'd like to wake up just with the power feed on. – Luis Dec 20 '10 at 13:51
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    It should do that so it sounds like your particular motherboard doesn't play like the others do - and it's either a bug which may or may not be fixed with a BIOS upgrade, or it's by design and there's no way to "fix" it without switching motherboard to one that behaves like you want it to. – Oskar Duveborn Dec 21 '10 at 3:49

If you are unable to use WoL, then depending on your BIOS version, there is usually an option to switch on the system at a certain time each day. e.g. you could set this for 8am, and then if the machine had been shutdown normally, it would boot at 8am each day. If this isn't good enough, I can't think of another way of doing this without additional hardware or user intervention

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