This project explains the workings of a recent design to enable starting up and shutting down of a vintage PC's ATX power supply using a single push button instead of a toggle switch.  This circuit features a micro-controller at its heart and also a simple network featuring a few resistors, a diode (D1) and a transistor (Q1) which assist in deciding the on/off state of the PSU. 
I have designed this circuit so I can send AT type strings into the MCU's UART port for status updates e.g. if current/temp/voltage sensing and a bluetooth module is attached. 
This is a snippet from a circuit I have running to power a HP desktop PSU (HP part no. 702307-001) and the MCU (which is a PIC18F26K80 , shown here is the PIC18F1220 ) also manages the HP PSU's internal fan speed by monitoring its temperature fed back to it by a remote NTC resistor attached just above its heatsink.

 

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