How can I turn on PC motherboard with Arduino/Teensy? (measurements inside)

I'm trying to connect a Teensy 3.2 to a PC motherboard to turn the PC on/off. The motherboard header is 2-pin (PWRBTN# and GND), like all PC motherboards.

I'd also like to use a 2-pin Y-splitter to enable both my Teensy and the physical PC power button to turn the PC on/off.

The voltage between the PWRBTN# and GND is 3.458v. If I short PWRBTN# and GND (turns the PC on), the current is 0.83 mA.

  1. Can I use a simple Y-splitter to connect my Teensy and physical PC power button together?
  2. How can I wire the motherboard to my Teensy and then use it to turn on/off the PC?

A simple way is with a small relay. Control the relay with the Teensy. The relay will need a driver. Connect the PWRBTN# pin to the NO terminal of the relay and the common terminal to ground. When the relay is closed, the PWRBTN# pin will short to ground.

Is it not a momentary switch ?

Close the relay and a moment later open it. Boom, momentary switch.

How about a solid state relay?:


The TLP175A might be a better choice, 'cuz it's not obsolete :wink:

If a solid state relay works, a (much cheaper, much smaller) optocoupler will work just fine as well. An SSR is for power switching, and total overkill for this.

As this is a computer it's probably a low voltage DC signal, so an optocoupler should do the job.

If you are powering the Teensy from the computer’s standby supply - which makes the most sense - then opto-isolation is not necessary given that the wiring is short - a few inches inside the PC case - and run together. Just use a common NPN transistor at your “Y” connector, emitter to ground, collector to the switch and base via a 470 Ohm resistor to the Teensy.

wvmarle:
If a solid state relay works, a (much cheaper, much smaller) optocoupler will work just fine as well. An SSR is for power switching, and total overkill for this.

As this is a computer it's probably a low voltage DC signal, so an optocoupler should do the job.

Dang, you're right -- I saw 0.83mA and read .83A (i.e. 830mA). Post updated.

Paul__B:
If you are powering the Teensy from the computer's standby supply - which makes the most sense - then opto-isolation is not necessary given that the wiring is short - a few inches inside the PC case - and run together. Just use a common NPN transistor at your "Y" connector, emitter to ground, collector to the switch and base via a 470 Ohm resistor to the Teensy.

wvmarle:
If a solid state relay works, a (much cheaper, much smaller) optocoupler will work just fine as well. An SSR is for power switching, and total overkill for this.

Except, can we know for sure how that power switch is wired. The opto can be used High-Side, Low-Side, sideways, and on it's ear. It's just a more forgiving solution, in an arena of newbie obfuscation -- is all I'm saying :wink:

The TLP175A costs a buck thirty, and is for switching currents below 100mA, with a mere tenth of that current on the input. So, seems like an excellent solution to me.

ReverseEMF:
Except, can we know for sure how that power switch is wired. The opto can be used High-Side, Low-Side, sideways, and on it's ear. It's just a more forgiving solution, in an arena of newbie obfuscation -- is all I'm saying :wink:

The TLP175A costs a buck thirty, and is for switching currents below 100mA, with a mere tenth of that current. So, seems like an excellent solution to me.

Absolutely right, the opto also realize a "galvanic isolation", so if you have a short-circuit in your "Teensy" that will not impact the PC or motherboard.

If you program the on/off of a computer remember: The most motherboard switch the PC completely off by hold it pressed by 4 seconds, for switching on is 1 second more than enough.
Note besides that in programs the time is given in milliseconds (ms), so 1 second are 1000 ms & 4 s are 4000 ms.

Enjoy!

ReverseEMF:
Except, can we know for sure how that power switch is wired. The opto can be used High-Side, Low-Side, sideways, and on it's ear.

That's funny. The OP said:

sofakng:
The motherboard header is 2-pin (PWRBTN# and GND), like all PC motherboards.

Paul__B:
That's funny. The OP said:
"The motherboard header is 2-pin (PWRBTN# and GND), like all PC motherboards."

Yeah, right -- that's real specific. And you're going to believe the OP really knows the nature of "all PC Motherboards", or that "GND" is actually ground, or that GND is the negative side of the supply, or that there isn't some other unrevealed mystery, or that the OP even has enough skill to get their MCU based system properly connected to the PC's ground [no offense to the OP]. They very well might know what the heck they're talking about. But, so often the gotcha, is a confident sounding OP who [inadvertently, we hope] fools all the fools.