ATX boards and restart after power failure

[Axel Simon]

On Wed, May 14, 2003 at 07:17:12AM +0200, Ivo Hazmuk wrote:
> > I have an Asus P5A r1.04 mainboard that I want to use for a server but
> > it does not reboot after a power failure.
> > r1.06 of the P5A does but that doesn't help me.
> 
> Now I have 5 or 6 pieces of this card. If you want I can send it to you.
> But I don't know the cost. It was about 60 US$.

Indeed, I think you need to generate a pulse after the power comes up and
that pulse has to stop within a specific time. But the most luxury version
of doing this is a NE555 ($0.12) used as a mono-flop (I know it sounds
funny, but that's what it's called when you only want to generate a single
pulse.).

http://www.national.com/ds.cgi/LM/LM555.pdf (page 7 top left)

Connect an RC combination to pin 2 (C to +5V and the R to ground). 
Calculate this to fall down to 2/3 of +5V which starts the timer. The 
other RC combination can be choosen so that it gives a 1s pulse according 
to the diagram on the right. You might need to invert the output, 
depending if you power switch connects to ground or to +5V.

Hope this helps,
Axel.