Arduino & Firmata
Firmata Protocol Documentation
...and many more
The simplest way to talk to any Microcontroller Board from vvvv is by using the FirmataBoard (Devices) node via the Firmata protocol. Check the dedicated Firmata page on how to use it.
A bit more advanced and direct way to talk to a microcontroller is by using the RS232 (Devices).
Examples in your vvvv\ directory