Background

    This is an ATX-PSU 200W coversion to a laboratory bench top power supply.  There at least a few document pages on the web that can be of assistance.  A few are links to actuall pages where ATX PSU's have been converted.  At least one of the links is to a schematic, basic operation theory and problem diagnostic information.     

The mod

    First off, yes my entire conversion could essentially be exchanged out for a DPDT (double pole double throw) toggle switch, but that isn't the point, this project was meant as a proof of concept for myself.  Future revisions will involve first a move to a larger PIC with an interface to an LCD where specific voltage lines of the PSU may be independantly controlled and monitored.  The final step will be a complete reconstruction of an ATX PSU into a variable voltage, variable current PSU.

    Now, on to what I did.  I used a PIC 12F675 (8 pin DIP) to independantly control standby, power and heart beat (HB) LEDs and the PSU powerOn signal.  A momentary N.O. pushbuton is the sole user interface.  The PIC spends the majority of it's time asleep (i.e. CPU & peripheriles are off) waiting for a rising edge signal from the switch.  Upon pressing the switch the PIC debounces the button & toggles the state of the PSU, if it was on it's now off and visa versa.  If the switch is held down the HB LED will blink at a Frequency of 1.04Hz.  When the switch is released, regardless of if it has been held for an hour or released immediatley, the PIC clears the HB LED and places itself back into sleep.

Links 

PSU Mod sites:

    Basic ATX PSU mod - A nice base for everythine else 

    Adds LEDs to the basic design - this is mine toggle switch style 

    A nice howto page - Shows a better power resistor and mounting method 

ATX PSU info:

A nice site on switch mode power supplys (SMPS) - Schematics, design ideas/mods, and troubleshooting