Arduino - PC isolation communication

[singera]

hey

I need to build isolator between the arduino and th CP2102 (USB to TTL) transiver, I bought on ebay 10*pc817
and I want to build this:

http://softsolder.files.wordpress.com/2009/12/schematic.png

what Is  the VCC voltage on the arduino and the CP2102 that I need to connect to this (5V or 3.3V tha I have both in the arduino and the cp2102)?

the arduino will operate with battery or plug pack and the cp2102 will operate with usb power.

[Harvs]

On the Arduino side it's pretty easy, just use the 5V from the Arduino itself.

On the cp2102 side, assuming you're powering it off USB power, then the cp2102 has an internal voltage regulator capable of 100mA.  Given the cp2102 needs about 26mA of power, that leaves you with around 70mA at 3V. 

Or alternatively it looks like the IO pins are 5V tolerant, so you could power it off the USB supply directly.  But double check that on the datasheet before you go ahead, I've only had a quick look.

https://www.silabs.com/Support%20Documents/TechnicalDocs/cp2102.pdf