The ATX power supply has several voltages on its motherboard connector.
One of them is 5VSB which is a 5V present when the power supply is under mains voltage.
This 5VSB is used to power the microcontroler.
The role of the microcontroller is :
- to switch on and off the power supply when a push button is pressed.
- to switch off the power supply when the Raspberry Pi goes to power down mode (using a GPIO).
- to monitor the temperature of the RPI's microcontroler and activate a 12V Fan.
The RPI is powered by a µUSB cord and the board gives the opportunity to power an external 2.5" USB drive directly from USB (check my previous article "A Cloud in the Shape of a Raspberry").
This board is built around an ATTINY85.
The code is developped using Arduino libraries but under Eclipse IDE.
For doing this I have written a small utility which creates for you script files to compile the code under Eclipse but this is another subject...