How much voltage does a power header on motherboards generally pass?

Hi guys I wanted to turn my rasberry pi zero into a switch for my PC that could be accessed from the internet or via bluetooth on my phone. I wanted to connect it directly to the pc to the GPIO header however I do not really want to fork out for a multimeter and was wondering if anyone knew the voltage a power switch and reset switch passed through ?

Would do it for Devember but I am not a ultra software wiz and probably would have it on a closed loop :slight_smile:

Any ideas ? Else I will go the relay route!

Thanks in advance.


Even if it’s more bulky to use a relay I’d go for one anyway since, as far as I know, it’s not possible to limit the current when you’re enabling a pin on the Raspberry. The power button voltage is 5V but it’s very very low current and I don’t know how the circuit would react if you just give power to a pin on the Pi, if it would take 500mA or just the few required for the circuit to complete. With a relay you’re absolutely sure that you’ll never fry the board or the power button circuitry on it.


In case you or anyone else is looking for a better solution than a clumsy relay…
Use an opto-isolator… Tiny 4 pin chip and a resistor is all you’d need then, run straight off the Pi like any other GPIO driving LED. Because on the input side, that’s all they are - a LED.

And if you don’t want to buy one, they’re quite common in switching power supplies. Anything from those 12v 1A power packs that external 3.5" HDDs and routers come with up to high end ATX power supplies will usually have one. They’re usually easier to get out of a wall wart style pack (but not always present in them). Look for a slot cut in the board separating the mains side from the DC side. It’ll (usually) be mounted across that if there is one.

1 Like

This was a great reply thanks, not only an answer but a handy way to get one on the cheap and close by. 100% good reply :smiley: cheers.

I’ve never actually checked the headers. I assumed it was 3.3v or 5v. I’m building another pc this weekend and I’ll let you know.

You should get a DMM anyway. They’re too useful not to have one.

1 Like

This topic was automatically closed 273 days after the last reply. New replies are no longer allowed.