Control Arduino through UART txd rxd

[ironman]

Looking for some confirmation of some working examples without USB.

If you don't care about isolation you can simply tie the Pi's TxD output to the arduino's RxD, and tie the arduino's TxD to the pi's Rxd with a simple voltage divider. Remember the pi i/o is 3.3 Volts and the arduino's i/o is 5 volts based. I have this and it works - so far.