Can I connect the 15A 120V AC ONLY light switch to PS_ON and GND to replicate the "digital" switch?
I don't see why not. What do you mean by a digital switch?
The soft switch the motherboard uses to turn the PSU on/off.
As you have not supplied any details about the power supply you are talking about no one can say for sure, but if the input expects a switch between it and ground I don't see any problems.
Obviously, this question does not concern the work of Arduino, but the PC.
A couple of quotes from Scott Mueller's book that I like.
The PS_ON signal can be manipulated physically by the computer’s power switch or electronically by the motherboard under software control. PS_ON is an active low signal, meaning the power supply voltage outputs are disabled (the system is off) when the PS_ON is high (greater than or equal to 2.0V).
The power supply maintains the PS_ON signal at either 3.3V or +5V. This signal is then routed through the motherboard to the remote switch on the front of the case. When the switch is pressed, the PS_ON signal is grounded. When the power supply sees the PS_ON signal drop to 0.8V or less, the power supply (and system) is turned on.
The actual power switch used in ATX systems is normally a tiny momentary contact push button switch, which is connected to the motherboard front panel header via a tiny two-pin connector.
Yes, you can connect, but I think it should be a button and not a switch.
I don't see how that is obvious, there is nothing in the question to say the that a PC power supply was being used, although you obviously inferred that from some of the details. Someone who does not know those details would not know. Also, this is an Arduino forum, not a PC forum, so it's reasonably to suppose that where a power supply is mentioned it is one intended to be used for an Arduino unless stated otherwise.
I just know that PS_ON concerns the operation of the computer's power supply.
What do you advise, it is better not to answer such questions?
The forum category is general electronics, which I definitely think fits.
As long as the switch is rated for the voltage and current needed you can use whatever switch you want.
No, sorry, I didn't mean don't answer them, by all means answer and be as helpful as you can be. My objection was the suggestion that it was obvious that the question referred to a PC power supply rather than, as I thought, some generic power supply. Answers are only as good as the questions, questions with incomplete information get incomplete answers.
I mean the PS_ON signal has to be grounded and then opened like a momentary button does. The light switch remains closed, I do not know how the power supply will behave in this case.
This is true. Questions with incomplete information can lead to even completely different answers.
Especially when the author of the question disappears for a long time.
While it's not optimal, flicking the switch on and off again will work. You do raise an interesting point. I have to admit that I'm not sure. My guess is that it will behave as wanted and that the next low pulse will turn it off again. But I suppose he'll have to try.
I was curious and tried it out. The power supply I tested was on while the PS_ON signal was grounded and off otherwise. So I would say that the lightswitch will work just fine.
Yes, that's an interesting question. Power button on a PC is normally opened.
It is known that
... press and hold down the system power button for a minimum of 4 seconds, and the system should power off.
After a few seconds, the power will be cut to your computer and it will suddenly shut down. This is normally a bad idea, as it can lead to lost data, file system corruption, and other issues ..
I have not tested it yet, but I will definitely check it.
You need to distinguish between the switch connected to the motherboard which has a behaviour defined by the motherboard electronics depending on how long you hold it down and is generally a toggle, and the actual power supply which goes on and remains on just as long as the control wire enables it.
For what it's worth, I've been using an ATX power supply as my bench test PSU for years. To switch it on, pin 16 (usually a green wire) needs to be held to ground and kept there as long as you want the PSU to be on. It will turn off as soon as you break contact between pin 16 and ground. Without a motherboard attached to the PSU, a momentary switch will not work; it would just briefly turn on power as long as the switch is being pressed.