Mini-Itx

I believe that's a CMOS setup option.

on -

The BIOS has an 'AC Loss Auto Restart' option. This will make the system auto-start in an event of power loss while it was on, but if someone shuts down the system properly, a power cycle will not start the system.

Rob

Ah. In that case, there's no direct way to do it, because I can tell you from (silly) experience that jumpering the power button connector doesn't make the board start up automatically. Actually, it's weird-sometimes it will, sometimes it won't. I found this out because I wired an Epia board into a custom housing with an external power button, and didn't realize that some SOB had put a NC button in the drawer where the NO buttons go. Took a LOT of head-scratching before I worked out what was going on.

I would suggest making a simple active-low one-shot with a 555 powered from the 5V standby line, to ping the power button for maybe 1s when power is applied.

We solved this problem with our Thin Client

by putting a PIC processor in the power supply. The PIC sequences the voltages, provides a watchdog function and provides a positive power on boot (depending on jumper settings).

There is of course no such thing as "The BIOS" in PCs any more. There's lots of variance, and one of the little details that varies is what options you have on "AC power loss restart". Quite some BIOSes offer a three-way selection: "never", "last state" and "always start".

Wire an ATX power header to an AT power supply.

This remind me of the big boys ways of solving problems.

1. Microsoft gives annoying pop-ups on internet explorer. It solves the problem with another annoying MSN adv. bar to block the pop-ups. I would prefer a configuration option to stop pop-ups.
2. Intel gives ATX power switch. You solves the problem with another micro to power sequence it. I would prefer to go back to AT power and declare that ATX power was a big mistake.

But there are definitely preferential relationships between specific mobo or chipset vendors and specific BIOS vendors, and the context of the discussion implies that we are talking very specifically about Via's Epia series of motherboards (see

Sigh. I was happy with AT power supplies, and I don't particularly enjoy sticking processors in power supplies. The reality is that you can't outsmart anything with a couple diodes and a resistor any more so we're stuck with somewhat inelegant but cost-effective solutions.

I thought that a "Power Good" signal was output by *all* ATX and AT PSUs. Can't this be used to turn the Mobo on? I expect it would require a jumper or maybe even an inverter, but that is a lot simpler than an MCU.

Argh! No! Not an RC power strobe! :)

You missed the top part of the thread. The original issue was making sure that the machine would always power up when input power came up, whether or not the user did a shutdown.

I *do* understand that. But the power good signal can be used to control the power on button. There is a standby supply that can provide voltage to control a simple circuit that will use the power good signal to activate the power on button. As long as power good is not asserted, the power on button should be asserted. When power good comes up, the power on button can be released.

If the Power Good signal is high true, this circuit would be two transistors. If the Power Good signal is low true, this circuit can be

You can use cheap external modem powered from the same mains as headless computer. As soon as power comes up, the DTR signal gets active indicating that external power is present and modem is ready (which might or might not be of value in the case).

Vadim

I should have know better than to bother a reply to you. I don't recall all the details, but I do know that what you propose didn't work reliably. That plus the fact that we needed a watchdog forced the MCU issue.

"rickman" wrote

provide

signal

asserted,

Ain't gonna work, at least not reliably. There are allot of power supplies out there that just have the PwrGd connected directly to the 5V sources in the supply. I'm not saying that's a good thing, just saying that's the way it is.

be

Really.....no passives needed? It's clear that you don't even know whether PwrGd is active high or low, I hope the OP sees the big red flag on that.

If that is true, then the supply is not in spec.

Why does it matter if I know the polarity of Power Good. Or are just trying to be insulting? I do know that the power on button is pulled high with a resistor so that you can parallel the switch with another switch of any sort. I expect the power good signal to be high true, but I don't recall what the spec says and I don't assume *anything* when it comes to the PC.

It might be better to combine ATX 5VSTBY and a 5V source from the mobo that's only on when in power-up state. Like the 5V that's available on the extra USB headers on many ITX boards. Or the +5V that powers the keyboard. When +5VSTBY is present and the USB header +5V is not, then after 500ms trigger the power button.

Rob

yes

LOL no !

Bios "power on after power fail"

Pozdrawiam.