In article . com,
(known to some as ee_design) scribed...

Can any one tell me how to effect a simple on/off control of a standard
ATX type power supply to use it on bench or for other projects? How
does motherboard control this function?

It's usually a 'soft' logic switch. A momentary contact closure
toggles a flip-flop in the supply which turns it on. A continuous
closure of more than ten or so seconds usually turns it off.

With that said: Using a PC supply for any type of serious bench
work is a poor idea, IMO. They are often very (electrically) noisy, in
terms of RF emissions, their outputs are rarely variable, and most of
them need a minimum load on the +5V line to even regulate properly.

There are plenty of very decent and affordable 'lab' type variable
power supplies that show up at ham radio swap meets and electronic
surplus places, to say nothing of Greed-bay. If you're serious about
clean experiment power for your bench, or something noise-critical like
servicing radio equipment, you should seriously consider investing in
such.

Happy hunting.


--
Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
http://www.bluefeathertech.com -- kyrrin a/t bluefeathertech d-o=t calm
"Salvadore Dali's computer has surreal ports..."