This might be useful for someones hack.
In my attemps to make 2 atx psus turn on at the same time I made this circuit.
For testing purposes I linked it to one psu only. The 3.3V line went to the atx green sense line. The ground wire went to the same psus ground line. The 5v wire which is soldered to the transistor was left unconnected to the psu.
Anyway...i fired it up...the psu did not turn on. Which is good that is what it is suppost to do at the start! I then picked up the 5v line...and to my surprise the psu turned on! On further experimenting...i found that I could turn the psu on and off by just tapping the 5v line. One tap, on. One more tap, the psu turned off!
Its mental. For some reason the transistor is being triggered by my body. A friend suggested that my body is proving a current and has a potential difference with the psus ground. Even so...if I earth myself, the psu still turns on. If I am earthed this should not happen, as the path from me to the ground through earth is easier for electricity, than the path from me, through transistor to psu.
I then wired in a 10 megaohm resistor, in series, between me and the 5v line. Even so...it still turns on, even through the monster resistor.
I am totally baffled. On the plus side, if you wired this to a metal case...one tap and the computer would turn on. I think this effect would get better if you use a darlington pair...
Now to another off bit. This transistor is acting like a latching relay. One tap its on...one tap off. If my body is really suppling charge, then the psu should turn off when I release the line, yet it does not...only if I tap it again.
I would be greatful if you have any ideas??
The transistor is a spare n-channel power mosfet I had lieing around. The psu is a 300w atx powersupply. The 1000ohm resistor is really a 10000ohm variable resistor.