[SOLVED] ground on microcontroller board

[bosskardo]

I have an at90usbkey board:
http://www.atmel.com/Images/doc7627.pdf
I'm thinking of using it to drive optocouplers from io pins. The question is where on the board should I connect the ground from the optocoupler. the board is quite small, where would be the best place?

 

[embRTS]

There is a connector shown in page no.5 of the pdf
what you do basically take a wire from the Ground PIN of that 2pin Connector(Ext Power) and place it in Bread Board so you will get ample space to connect the devices and sort it to the BOARD Ground