Originally Posted by Hark
The diode just prevents 12 volts from going into the uSDC and damaging it if you can only use the 12 volt line. If you are connecting it up to 5 volts, you don't need the diode.
What happens, is when the Computer Power supply is off, the 5 volts that is connected to onsense, is pulled to ground by the power supply being off. (No voltage on the 5 volt rail) The diode just lets you use the 12 volt rail too. But because people will try everything under the sun, I just allways reccomend the diode.
Any diode will work. Signal, schottky, 4148, etc..